View LTC3456_5851742.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

1 LTC3456 3456fa 2-cell, multi-output dc/dc converter with usb power manager seamless transition between 2-cell battery, usb and ac wall adapter input power sources main output: fixed 3.3v output core output: adjustable from 0.8v to v batt(min) hot swap tm output for memory cards all outputs discharged to ground during shutdown power supply sequencing: main and hot swap outputs come up after core output accurate usb current limiting high frequency operation: 1mhz high efficiency: up to 92% small (4mm 4mm 0.75mm) 24-pin qfn package gps portable navigators mp3 players digital cameras handheld computers descriptio u features applicatio s u typical applicatio u the ltc 3456 is a complete power management system ic optimized for a variety of portable applications. the device generates two separate power rails: a 3.3v (fixed) main supply and a 1.8v (adjustable) core supply. in addition, the LTC3456 contains a usb power manager, a hot swap output, a low-battery indicator and an always- alive v max output. the LTC3456 takes power from one of three sources: a wall adapter, a usb port or a 2-cell alkaline/nicd/nimh battery, in that order of priority. cur- rent drawn from the usb port is accurately limited to 100ma or 500ma based on the state of the usbhp pin. the main and core switchers are all high efficiency, 1mhz fixed frequency pwm converters. availability in a small (4mm 4mm 0.75mm) 24-pin qfn package makes the LTC3456 ideal for space-sensitive portable devices. + wallfb pwrkey v max v ext 10 f 4.7 f 4.7 f 1k 11.3k on/off 1 ? 4.7 f 1 ? ac wall adapter (5v 10%) usb power (4.35v to 5.5v) usb controller 4.32k 80.6k 100k l2 4.7 h 2 aa cells l3 10 h ext_pwr usb suspend usbhp ao ain v main v batt v int sw2_bst LTC3456 sw2_bk pbstat reset mode p pwron pgnd agnd 22 f v int 3.3v main output 3.3v 150ma 1 f hso hot swap output 3.3v 50ma 1 f 1 f 3456 ta01 sw1 fb1 l1 10 h core output 1.8v 200ma v max (powers real-time clock) 10 f 220pf 100k 80.6k load current (ma) 1 40 efficiency (%) power loss (mw) 50 60 70 80 10 100 1000 3456 ta01b 30 20 10 0 90 100 100 150 200 50 0 250 v batt = 2.4v mode = 0v efficiency power loss 1.8v output 1.8v output 3.3v output 3.3v output efficiency and power loss vs load current (battery powered) , ltc and lt are registered trademarks of linear technology corporation. hot swap is a trademark of linear technology corporation. all other trademarks are the property of their respective owners. protected by u.s. patents including 5481178, 6580258, 6304066.
2 LTC3456 3456fa (note 1) v batt , v max voltages ................................. 0.3v to 6v v int , v main , v ext , hso voltages ................ 0.3v to 6v sw1, sw2_bk, sw2_bst voltages ........... 0.3v to 6v usb, usbhp, suspend voltages .............. 0.3v to 6v pwrkey, pbstat, pwron voltages ........ 0.3v to 6v mode, ao, ext_pwr, reset voltages ..... 0.3v to 6v fb1, ain, wallfb voltages ....................... 0.3v to 2v junction temperature .......................................... 125 c operating temperature range (note 2) .. 40 c to 85 c storage temperature range ................. 65 c to 125 c absolute axi u rati gs w ww u electrical characteristics the denotes specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v batt = 2.4v, v int = 3.3v, v pwron = 2v, pwrkey is open, v usb = 0v, v wallfb = 0v, unless otherwise specified. order part number LTC3456euf t jmax = 125 c, ja = 37 c/ w, jc = 2 c/ w exposed pad (pin 25) is pgnd must be soldered to pcb package/order i for atio uu w uf part marking consult ltc marketing for parts specified with wider operating temperature ranges. 3456 24 23 22 21 20 19 7 8 9 top view 25 uf package 24-lead (4mm 4mm) plastic qfn 10 11 12 6 5 4 3 2 1 13 14 15 16 17 18 ain ao agnd v batt sw1 pgnd suspend hso v main v int sw2_bst sw2_bk fb1 reset mode pwron pbstat pwrkey wallfb ext_pwr v ext usb v max usbhp parameter conditions min typ max units battery voltage range 1.8 3.2 v quiescent current (battery powered) (note 3) burst mode operation v mode = 2v, v fb1 = 1v, v int = 3.4v 180 250 a pwm operation v mode = 0v, v fb1 = 1v, v int = 3.4v 380 450 a shutdown v pwron = 0v, v int = 0v 0.1 1 a v batt pin current (wall powered) v wallfb = 1.5v, v ext = 5v (note 4) 1 2 a v batt pin current (usb powered) v usb = 5v, v ext = 5v (note 4) 1 2 a switching frequency battery powered v batt = 2.4v 0.8 1 1.2 mhz usb or wall powered v ext = 5v, v wallfb = 1.5v 0.8 1 1.2 mhz main output v int voltage regulation 3.22 3.3 3.38 v v int voltage line regulation v batt = 1.8v to 3.2v 0.1 0.5 %/v max duty cycle 80 87 % switch leakage (battery powered) v pwron = 0v sw2_bst pmos switch v sw2_bst = 0v 0.1 1 a sw2_bst nmos switch v sw2_bst = 3.3v 0.1 1 a switch on-resistance (battery powered) sw2_bst pmos switch i sw2_bst = 150ma 0.8 ? sw2_bst nmos switch i sw2_bst = ?50ma 0.5 ? burst mode is a registered trademark of linear technology order options tape and reel: add #tr lead free: add #pbf lead free tape and reel: add #trpbf lead free part marking: http://www.linear.com/leadfree/
3 LTC3456 3456fa electrical characteristics the denotes specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v batt = 2.4v, v int = 3.3v, v pwron = 2v, pwrkey is open, v usb = 0v, v wallfb = 0v, unless otherwise specified. parameter conditions min typ max units switch leakage (usb/wall powered) v ext = 5v, v wallfb = 1.5v, v pwron = 0v sw2_bk pmos switch v sw2_bk = 0v 0.1 1 a sw2_bk nmos switch v sw2_bk = 5v 0.1 1 a switch on-resistance (usb/wall powered) v ext = 5v, v wallfb = 1.5v sw2_bk pmos switch i sw2_bk = 150ma 0.9 ? sw2_bk nmos switch i sw2_bk = ?50ma 0.4 ? switch current limit battery powered (sw2_bst nmos current) v batt = 2.4v 700 900 ma wall/usb powered (sw2_bk pmos current) v ext = 5v, v wallfb = 1.5v 400 500 ma v main pmos switch on-resistance measured between v int and v main pins 0.4 ? v main turn-on delay after fb1 and v int in regulation battery powered v batt = 2.4v 0.8 2 ms usb or wall powered v ext = 5v, v wallfb = 1.5v 1.5 2 ms hot swap output hso pmos switch on-resistance measured between v int and hso pins 0.8 ? hso pmos switch current limit v int = 3.3v, v hso = 2.5v 90 120 ma hso turn-on delay after fb1 and v int in regulation battery powered v batt = 2.4v 0.5 1 ms usb or wall powered v ext = 5v, v wallfb = 1.5v 0.5 1 ms v max output v max output voltage v max output unloaded shutdown v pwron = 0v v batt v battery powered v pwron = 2v, v batt = 2.4v 3.3 v usb/wall powered v pwron = 2v, v ext = 5v, v wallfb = 1.5v 5 v maximum v max output current v max output < 12.5% below nominal value 1ma core output fb1 voltage 0.784 0.800 0.816 v fb1 voltage line regulation v batt = 1.8v to 3.2v 0.1 0.5 %/v fb1 pin input bias current v fb1 = 0.8v 2 20 na duty cycle range buck switchers 0 100 % sw1 pmos switch current limit battery powered v batt = 2.4v 400 550 ma wall/usb powered v ext = 5v 350 450 ma sw1 leakage current v sw1 = 0v, v ext = 5v or v batt = 5v 0.1 1 a sw1 pmos switch on-resistance i sw1 = 150ma battery powered v batt = 2.4v 0.5 ? wall/usb powered v ext = 5v, v wallfb = 1.5v 0.5 ? sw1 nmos switch on-resistance i sw1 = ?50ma battery powered v batt = 2.4v 0.4 ? wall/usb powered v ext = 5v, v wallfb = 1.5v 0.4 ?
4 LTC3456 3456fa electrical characteristics the denotes specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v batt = 2.4v, v int = 3.3v, v pwron = 2v, pwrkey is open, v usb = 0v, v wallfb = 0v, unless otherwise specified. note 1: absolute maximum ratings are those values beyond which the life of the device may be impaired. note 2: the LTC3456 is guaranteed to meet performance specifications from 0 c to 70 c. specifications over the 40 c to 85 c operating temperature range are assured by design, characterization and correlation with statistical process controls. note 3: quiescent current is pulled from the v int pin when neither usb nor wall power is present. multiply this value by v int /v batt to get the equivalent input (battery) current. note 4: quiescent current is pulled from the v ext pin when either usb or wall power is present. note 5: specification is guaranteed by design and not 100% tested in production. parameter conditions min typ max units usb usb turn-on voltage threshold rising edge 3.9 4 4.1 v usb turn-on voltage hysteresis 75 mv usb pmos switch on-resistance v usb = 5v 0.5 ? usb current limit v usbhp = 2v (500ma mode), v usb = 5v 420 500 ma v usbhp = 0v (100ma mode), v usb = 5v 85 100 ma suspend pin threshold v usb = 5v 0.3 0.8 1.2 v usbhp pin threshold v usb = 5v 0.3 0.8 1.2 v suspend pin pull-down current v usb = 5v, v suspend = 2v 2.5 a usbhp pin pull-down current v usb = 5v, v usbhp = 2v 2.5 a usb pin bias current (suspend mode) v usb = 5v, v suspend = 2v 100 150 a ac adapter wallfb pin threshold rising edge 1.2 1.25 1.3 v wallfb pin hysteresis 20 mv wallfb pin input bias current v wallfb = 1.25v, v ext = 5v 2 20 na v ext uvlo voltage rising edge 3.9 4 4.1 v v ext uvlo hysteresis 150 mv ext_pwr pin low voltage v usb > 4v and v suspend = 0v or 0.25 0.5 v wallfb > 1.25v, i ext_pwr = 1ma gain block ain pin reference voltage 0.76 0.800 0.84 v ain pin input bias current v ain = 0.8v 2 20 na ao pin low voltage v ain = 0v, i ao = 1ma 0.25 0.5 v logic inputs pwrkey pin input high voltage 0.7v max v pwrkey pin input low voltage 0.3v max v pwrkey pin pull-up resistor to v max 400 k ? pbstat pin low voltage v pwrkey = 0v, i pbstat = 100 a 0.05 0.1 v pwron pin threshold 0.3 0.8 1.2 v pwron pin pull-down current v pwron = 2v 1 a mode pin threshold 0.3 0.8 1.2 v mode pin pull-down current v mode = 2v 1 a reset pin low voltage i reset = 100 a 0.05 0.1 v reset pulse duration after v fb1 and v int in regulation 262 ms
5 LTC3456 3456fa typical perfor a ce characteristics uw core converter efficiency (battery powered) main converter efficiency (battery powered) efficiency (usb powered) oscillator frequency vs battery voltage oscillator frequency vs v ext voltage oscillator frequency vs temperature no load battery supply current vs battery voltage no load battery supply currrent vs temperature shutdown current vs temperature load current (ma) 1 60 efficiency (%) 80 100 10 100 1000 3456 g01 40 30 50 70 90 20 0 10 v batt = 2.4v v core = 1.8v pwm mode burst mode operation v batt (v) 1.6 frequency (khz) 1000 1100 3.2 3456 g04 900 800 2.0 2.4 2.8 1.8 2.2 2.6 3.0 1200 950 1050 850 1150 v ext (v) 4 frequency (khz) 1000 1100 5.5 3456 g05 900 800 4.5 5 4.25 4.75 5.25 1200 950 1050 850 1150 temperature ( c) ?0 frequency (khz) 1000 1100 125 3456 g06 900 800 0 50 ?5 25 100 75 1200 950 1050 850 1150 v batt = 2.4v v batt (v) 1.6 battery supply current (ma) 4 5 6 2.8 3456 g07 3 2 2 2.4 1.8 3 2.2 2.6 3.2 1 0 7 pwm mode burst mode operation fb1 = 1v (core converter not switching) temperature ( c) ?0 battery supply current (ma) 3.5 25 3456 g08 2.0 1.0 ?5 0 50 0.5 0 4.0 3.0 2.5 1.5 75 100 125 pwm mode burst mode operation fb1 = 1v (core converter not switching) temperature ( c) 50 ?5 0 shutdown current ( a) 2 5 0 50 75 3456 g09 1 4 3 25 100 125 v batt = 2.4v load current (ma) 1 60 efficiency (%) 80 100 10 100 1000 3456 g02 40 30 50 70 90 20 0 10 v batt = 2.4v v main = 3.3v pwm mode burst mode operation load current (ma) 1 60 efficiency (%) 80 100 10 100 1000 3456 g02 40 30 50 70 90 20 0 10 v usb = 5v v usbhp = 2v 1.8v output 3.3v output t a = 25 c unless otherwise specified.
6 LTC3456 3456fa v batt pin current when usb or wall powered no load v ext suppy current when usb or wall powered sw1 current limit sw2_bst current limit sw2_bk current limit hot swap (hso) current limit v int load current vs start-up battery voltage maximum v main load current capability (output 4% below regulation) maximum v core load current capability (output 4% below regulation) temperature ( c) ?0 0 v batt pin current ( a) 1 2 3 4 ?5 0 25 50 3456 g10 75 100 125 v ext = 5v v ext (v) 4 0 v ext supply current (ma) 0.4 0.8 1.2 1.6 2.0 4.25 4.5 4.75 5 3456 g11 5.25 5.5 fb1 = 1v core converter not switching temperature ( c) ?0 sw1 current limit (ma) 600 700 800 25 75 3456 g12 500 400 ?5 0 50 100 125 300 200 v ext = 5v v batt = 2.4v temperature ( c) ?0 sw2_bst current limit (ma) 925 25 3456 g13 850 800 ?5 0 50 775 750 950 900 875 825 75 100 125 v batt = 2.4v temperature ( c) ?0 sw2_bk current limit (ma) 575 25 3456 g14 500 450 ?5 0 50 425 400 600 550 525 475 75 100 125 v ext = 5v temperature ( c) ?0 hso current limit (ma) 175 25 3456 g15 100 50 ?5 0 50 25 0 200 150 125 75 75 100 125 v batt = 2.4v v batt (v) 1.8 v main load current (ma) 500 600 700 2.4 2.8 3456 g17 400 300 2 2.2 2.6 3 3.2 200 100 l = 4.7 h (battery powered) v batt (v) 1.8 v core load current (ma) 400 500 600 2.4 2.8 3456 g18 300 200 2 2.2 2.6 3 3.2 100 0 l = 10 h (battery powered) v core = 1.5v v core = 1.8v typical perfor a ce characteristics uw t a = 25 c unless otherwise specified. v batt (v) 1.80 v int load current (ma) 200 250 300 2.40 2.80 150 100 2.00 2.20 2.60 3.00 3.20 50 0 resistor load
7 LTC3456 3456fa maximum v core load current capability (output 4% below regulation) maximum v main load current capability (output 4% below regulation) usb undervoltage lockout usb current limit a in pin reference voltage wallfb trip point v ext undervoltage lockout v max output voltage (battery powered) v max output voltage (usb/wall powered) v ext (v) 4 200 v core load current (ma) 300 400 500 600 4.25 4.5 4.75 5 3456 g19 5.25 5.5 l = 10 h (usb/wall powered) v ext (v) 4 100 v main load current (ma) 200 300 400 500 4.25 4.5 4.75 5 3456 g20 5.25 5.5 l = 10 h (usb/wall powered) temperature ( c) ?0 usb votlage (v) 4.00 4.05 4.10 25 75 3456 g21 3.95 3.90 ?5 0 50 100 125 3.85 3.80 rising falling temperature ( c) ?0 0 usb current limit (ma) 50 150 200 250 500 350 0 50 75 3456 g22 100 400 450 300 ?5 25 100 125 v usb = 5v usbhp = 2v usbhp = 0v temperature ( c) ?0 1.20 wallfb voltage (v) 1.22 1.24 1.26 1.28 ?5 0 25 50 3456 g24 75 100 125 rising falling temperature ( c) ?0 3.50 v ext (v) 3.75 4.00 4.25 4.50 ?5 0 25 50 3456 g25 75 100 125 rising falling v batt (v) 1.6 v max (v) 2.0 2.5 3.0 2.8 3456 g26 1.5 1.0 2 2.4 1.8 3 2.2 2.6 3.2 0.5 0 3.5 pwron = 2v v max output current = 0.5ma pwron = 0v v ext (v) 4 0 v max (v) 1 2 3 4 6 4.25 4.5 4.75 5 3456 g27 5.25 5.5 5 pwron = 0v, 2v v max output current = 0.5ma temperature ( c) ?0 a in (v) 0.815 25 3456 g23 0.800 0.790 ?5 0 50 0.785 0.780 0.820 0.810 0.805 0.795 75 100 125 v ext = 5v v batt = 2.4v typical perfor a ce characteristics uw t a = 25 c unless otherwise specified.
8 LTC3456 3456fa switching waveforms (battery powered) switching waveforms (wall/usb powered) usb ? battery switchover (main converter transient waveforms) usb ? battery switchover (core converter transient waveforms) power up/power down sequencing (battery powered) power supply sequencing (battery powered) i l1 50ma/div v sw1 5v/div i l2 200ma/div v sw2_bst 5v/div 0.5 s/div v batt = 2.4v v pwron = 2v i core = 100ma i main = 100ma 3456 g28 i l1 200ma/div v sw1 5v/div i l3 100ma/div v sw2_bk 5v/div 0.5 s/div v ext = 5v v pwron = 2v i core = 100ma i main = 100ma 3456 g29 v main 100mv/div (ac coupled) i l2 200ma/div i l3 100ma/div suspend 5v/div 200 s/div v usb = 5v v usbhp = 5v v batt = 2.4v i core = 100ma i main = 100ma 3456 g30 v core 100mv/div (ac coupled) i l1 100ma/div suspend 5v/div 200 s/div v usb = 5v v usbhp = 5v v batt = 2.4v i core = 100ma i main = 100ma 3456 g31 v pwron 5v/div v main 5v/div v core 2v/div reset 5v/div 100ms/div v batt = 2.4v i core = 10ma i main = 10ma 3456 g32 v pwron 5v/div v int 5v/div v core 2v/div v main 5v/div 200 s/div v batt = 2.4v i core = 5ma 3456 g33 typical perfor a ce characteristics uw t a = 25 c unless otherwise specified.
9 LTC3456 3456fa uu u pi fu ctio s ain (pin 1): low-battery detector input pin. the detector compares the voltage on this pin to an 800mv reference. connect the resistor divider tap to this pin to set the low- battery trip point. ao (pin 2): open-drain digital output. this open-drain logic output is pulled to gnd whenever the ain pin voltage falls lower than 0.8v. agnd (pin 3): analog ground. all resistor dividers should be connected to this pin. v batt (pin 4): battery input supply. the input voltage at this pin can range from 1.8v to 3.2v. must be locally bypassed with a 1 f (or greater) x5r or x7r type ceramic capacitor. sw1 (pin 5): switch pin for core regulator. connect the inductor between sw1 and the output capacitor. keep these pcb trace lengths as short and wide as possible to reduce emi. pgnd (pin 6): power ground. this is the ground pin for all internal drivers and switches. provide a short pcb path between pgnd and pcb system ground. wallfb (pin 7): wall feedback pin. this pin receives the feedback voltage from an external resistor divider across the ac wall adapter input. when the pin voltage is higher than 1.25v, the chip is powered from the v ext pin and the usb switch is turned off. ensure that the resistor ratio is set so that the wall adapter voltage (min) is still high enough to make v ext > 4v. connect to ground if not used. ext_pwr (pin 8): external power good pin. this open- drain logic output is pulled to gnd whenever the wallfb pin is pulled higher than 1.25v or the usb pin voltage is greater than 4v and suspend is low. essentially this pin is pulled low whenever the ac adapter or the usb power is present. when pulled low, this pin is capable of sinking 5ma suitable for driving an external led. v ext (pin 9): external power pin. this pin is connected to the usb pin via an internal 0.5 ? (typ) pmos switch. the ac wall adapter can be connected to this pin through a schottky diode. an onboard voltage detector prevents the ic from drawing power from this pin until the pin voltage rises above 4v. the voltage detector for v ext has built-in 150mv hysteresis. connect a 10 f x5r or x7r type ceramic capacitor from this pin to ground. usb (pin 10): usb input supply. input current into this pin is limited to either 100ma or 500ma based on the state of the usbhp pin. when the usb pin voltage is greater than 4v and suspend is low, and wallfb is less than 1.25v, usb is connected to the v ext pin via an internal 0.5 ? current limited pmos switch. connect a 4.7 f (x5r or x7r type) ceramic capacitor in series with a 1 ? resistor from this pin to ground. v max (pin 11): maximum supply voltage pin. a special internal powerpath tm controller monitors the v batt , v int , v ext and usb voltages and passes the highest available supply voltage to the v max pin. this pin is used to power some of the internal circuitry of the ic. connect a 1 f bypass capacitor from this pin to ground. it can be used to supply a maximum of 1ma output load. the v max output voltage stays alive even when the ic is in shutdown. usbhp (pin 12): usb high power select pin. this pin is used to set the usb current limit. pull high to select 500ma current limit (high power mode); low to select 100ma current limit (low power mode). this pin has a weak pull- down current source to ensure that low power mode is in effect during start-up. sw2_bk (pin 13): switch pin for main regulator (usb or wall powered). connect the inductor between sw2_bk and the output voltage. keep these pcb trace lengths as short and wide as possible to reduce emi. sw2_bst (pin 14): switch pin for main regulator (bat- tery powered). connect the inductor between sw2_bst and v batt . keep these pcb trace lengths as short and wide as possible to reduce emi. v int (pin 15): internal supply voltage pin. the v int voltage is regulated to 3.3v. this pin is used to power most of the internal circuitry of the ic. do not load this output. connect an output capacitor from this pin to ground. v main (pin 16): main regulator output voltage. an inter- nal 0.4 ? pmos switch connects this pin to the v int pin 0.8ms (typ) after the core voltage comes into regulation. this ensures that v main will always power up after core output during start-up. connect an output capacitor from this pin to ground. powerpath is a trademark of linear technology corporation.
10 LTC3456 3456fa hso (pin 17): hot swap output. an internal 0.8 ? current limited pmos switch connects this pin to the v int pin 0.5ms after the core voltage comes into regulation. the nominal voltage at this pin is 3.3v. it is short-circuit protected and the current out of this pin is limited to 120ma (typ). suspend (pin 18): usb suspend pin. pull this pin high to disable all usb functionality. the usb switch connected between usb and v ext behaves like a back-to-back diode whenever suspend is pulled high. in suspend mode the device limits the current drawn from the usb port to 100 a (typ). pwrkey (pin 19): power on/off key. connecting this pin to gnd will turn on the ic. this pin is typically used with a momentary-on pushbutton switch to turn on the LTC3456. this pin must be held low until the pwron pin is pulled high (usually from a microprocessor) in order to keep the ic turned on. this pin has a 400k pull-up resistor to v max . pbstat (pin 20): power on/off key status pin. this open-drain output pin indicates the state of the pwrkey pin to the microcontroller. the pin output follows the state of the pwrkey pin (pbstat goes low when pwrkey is pulled low). pwron (pin 21): power on pin. when pulled high this microprocessor controlled pin turns on the ic. this pin has a weak 1 a pull-down current source. uu u pi fu ctio s mode (pin 22): burst mode select pin. tie this pin high to allow automatic burst mode operation. burst mode opera- tion will provide superior efficiency when any of the outputs are operating with very low output currents. tie this pin low to force pwm operation under all load current conditions. the device operates in forced pwm mode when powered from usb or wall input (irrespective of the state of the mode pin). furthermore, at initial power-up, the device operates in forced pwm mode during the 262ms internal delay timeout. this pin has a weak 1 a pull-down current source. reset (pin 23): fault indicator output pin. this open- drain output is active both at power-up and power-down. reset is held low at initial power up. when both the core and main outputs come into regulation, an internal reset delay timer is activated. reset is released at the end of the 262ms timeout. if either main or core outputs fall out of regulation during normal operation, reset is pulled low. also, reset is pulled low at power-off to prevent spurious turn-on of the microprocessor. fb1 (pin 24): feedback pin for the core regulator. the regulator drives the voltage at this pin to 0.8v. connect the resistor divider tap to this pin. the output voltage of the core regulator can be adjusted from 0.8v to v batt(min) . exposed pad (pin 25): the exposed pad must be soldered to the pcb system ground.
11 LTC3456 3456fa block diagra w hso 18 12 + + + r 4v 1.25v 0.8v v ext v os en 4v v ext_rdy usb_rdy usb suspend 10 usb 11 v max powerpath controller usb ac adapter v ext ao v batt v core 4.7 f 1 ? usbhp wallfb control usb controller logic 10 f 4.7 f 10 f 4.32k 100k 100k 220pf 80.6k 80.6k l1 10 h d2 d1 11.3k 7 ext_pwr 8 v ext 9 1k ao 2 ain 1 + + + v batt 4 fb1 5 sw1 0.8v + 0.8v 24 1 f 19 pwrkey 20 pbstat microcontroller turn-on switchers pwron usb v ext v int v batt mode 21 22 reset 23 hso pswitch 625k 200k 17 v main 16 start-up logic 262ms timer 1 f v main v int 15 sw2_bst 14 sw2_bk 13 agnd 3 pgnd 6 v int v batt 4.7 f l2 4.7 h 1 f 22 f l3 10 h 3456 f01 drv + v os r drv figure 1. LTC3456 block diagram
12 LTC3456 3456fa operatio u introduction the LTC3456 is a complete system-level power supply ic used to power gps portable navigators and other portable systems. it takes power from one of three sources: battery, usb or wall adapter. the device provides an integrated standard solution resulting in a reduced parts count and higher efficiency. the LTC3456 generates two separate power supplies: a core supply for the processor and a main supply for the peripheral circuitry. the main supply is a fixed 3.3v output and the core supply voltage can be adjusted from 0.8v to v batt(min) . in addition, the LTC3456 provides a hot swap output which can be used for powering flash memory cards. both regulators utilize a 1mhz constant frequency current mode architecture. the device also incorporates a low-battery detector (configurable as a low dropout regulator), usb power manager and several protection features in a single pack- age. the LTC3456? control scheme allows 100% duty cycle operation for the core output. it provides low dropout operation when the core output is powered from the battery, thereby extending battery life. operating modes the LTC3456 is powered from an ac wall adapter, usb or battery, in that order of priority. it has onboard voltage detectors to monitor the status of the wall adapter and usb voltages. the unique control scheme of the LTC3456 allows seamless transition between battery, usb and wall adapter input power sources. battery powered the LTC3456 is designed to accept an input battery voltage range from 1.8v to 3.2v. this range is ideal for 2-cell alkaline, nicd or nimh designs. figure 2 shows an LTC3456 being powered from two aa cells. when enabled, the internal supply voltage v int (3.3v) is generated via the boost regulator. v int is used to power the bandgap reference, drivers and other internal circuitry. core output (1.8v) comes up next via the buck regulator. main output and the hot swap output are powered up with a delay after the core output is in regulation. figure 2. battery-powered LTC3456 17 + + hso v os r v main hot swap output 3.3v 50ma 1 f 3456 f02 16 main output 3.3v 150ma v int 3.3v 1 f v int sw2_bst 15 14 22 f 10 f boost LTC3456 core output 1.8v 200ma sw1 v batt v batt 2 aa cells 1.8v to 3.2v 5 4 buck l2 4.7 h l1 10 h
13 LTC3456 3456fa ac wall adapter powered the LTC3456 can be powered off the ac wall adapter as shown in figure 3. the wall adapter is connected to the v ext pin via the diode d1. the status of the ac wall adapter power is monitored through the wallfb pin. the nominal voltage at this pin is 1.25v. when the pin voltage is higher than 1.25v, the ic operatio u 17 + hso r 1.25v v os wall_rdy v main hot swap output 3.3v 50ma 1 f 3456 f03 16 main output 3.3v 150ma v int 3.3v 1 f sw2_bk 13 v int 15 wallfb 22 f 10 f 10 f d1 4.32k buck 2 LTC3456 core output 1.8v 200ma sw1 v ext 4v en v ext 5 9 buck 1 l1 10 h l3 10 h + 7 11.3k ac adapter 5v 5% + figure 3. ac adapter-powered LTC3456 will draw all its power from the ac adapter via the v ext pin. the wallfb voltage should always be kept below 2v. when enabled, the onboard voltage detector checks the status of the v ext voltage. if the v ext pin voltage is greater than 4v, the v int , core output, main output and hot swap outputs power-up in that sequence.
14 LTC3456 3456fa usb powered the LTC3456 is designed to be powered from the usb as shown in figure 4. the LTC3456 has an internal current- limited 0.5 ? (typ) pmos switch with preset 0.1a and 0.5a current limits. the LTC3456 interfaces with the usb controller bus via logic pins usbhp and suspend. the usbhp pin is used to set the usb current limit to either 100ma or 500ma. this pin has a weak 2.5 a pull-down current source to ensure that low power mode is in effect during start-up. if the usbhp pin is held low, it limits the input power drawn from the usb port. the usb port can supply the core output (1.8v at 200ma) effortlessly in low power mode (usbhp = 0v). however, the loading on the 3.3v output must be held below 100ma (typ) when the usb is in low power mode. if the loading on 3.3v output is increased beyond 100ma (typ), the usb port is unable to supply the load current and the LTC3456 will switch between the battery and the usb port. this results in undesirable switching noise and increased voltage ripple at the 3.3v output. pulling the suspend pin logic high disables all usb functionality. the usb switch connected between usb and v ext behaves like a back-to-back diode whenever suspend is pulled high. in suspend mode the device limits the current drawn from the usb pin to 100 a (typ). the minimum voltage to a usb-powered device may drop as low as 4.35v due to cable and connector drops. the LTC3456 has an internal voltage monitor that checks the usb supply voltage and cuts off the usb power if the usb voltage falls below 4v. there is 75mv of hysteresis built- in the usb voltage monitor. when the ic is enabled, the usb pin is connected to the v ext pin via the pmos switch. the v ext pin gets charged by the preset 0.1a or 0.5a current limit determined by the state of the usbhp pin. as the v ext pin voltage rises above 4v, the v int , core output, main output and hot swap outputs power-up in that sequence. operatio u 17 + hso r v main hot swap output 3.3v 50ma 1 f 3456 f04 16 main output 3.3v 150ma v int 3.3v 1 f sw2_bk 13 v int 15 usb usb_rdy 22 f 10 f 10 f 4.7 f 1 ? buck 2 v os LTC3456 core output 1.8v 200ma sw1 v ext 4v en v ext 5 9 buck 1 l1 10 h l3 10 h 10 suspend suspend 4v usb 4.35v to 5.5v 18 usbhp usbhp 100ma 500ma 12 + + figure 4. usb-powered LTC3456
15 LTC3456 3456fa main regulator v int output the main regulator produces a fixed 3.3v output from a 1.8v to 3.2v input (2-cell battery), usb port or ac adapter input supply. the main regulator output, v int , is used to power most of the internal circuitry of the ic. it is the first one to power-up. connect a 22 f or higher x5r or x7r type ceramic capacitor from this pin to ground. the loading on this output should be limited to 20ma. refer to the minimum start-up battery voltage vs v int output current graph in the typical performance characteristics. when the ic is turned off, the v int output voltage is discharged to ground. output disconnect and inrush limiting the LTC3456 allows true output disconnect when pow- ered off the battery (boost topology). it achieves this by disconnecting the body diode of the synchronous pmos switch from the output. this allows the v int to go to ground during shutdown. do not connect a schottky diode from sw2_bst to v int ; doing so will defeat the output disconnect feature. the LTC3456 also features inrush current limiting at power-up (battery powered). inrush current in boost converters is important when powering from input sources with high input impedance like alkaline cells. the LTC3456 incorporates an inrush current limiting scheme that regu- lates the inrush current to 600ma (typ) during power-up. figure 5 shows inrush current when the device is powered up from the battery. short-circuit protection the LTC3456 features short-circuit protection for the main regulator output. when the main regulator is powered from the usb or wall input, it operates in a buck topology. operatio u if the main regulator outputs (v int or v main ) are shorted to ground, the LTC3456 unique control scheme prevents inductor current runaway. when the device is powered from the battery, it operates in a boost topology. most boost converters do not allow their outputs to be shorted to ground. however, the LTC3456 allows the output of its main regulator (v int or v main ) to be short-circuited due to its unique inrush current limiting. in the event of a short-circuit, the input current is well regulated. v main output the LTC3456 is designed to supply power to the micro- processor peripheral circuitry in a controlled manner. the peripheral circuitry should be connected to the v main output. v main is connected to v int via a 0.4 ? (typ) pmos switch 0.8ms (typ) after the core output comes into regulation. this ensures that the peripheral circuitry always powers up after the microprocessor. the v main output is discharged to ground through inter- nal pull-down resistors at shutdown. this ensures that the peripheral circuitry gets turned-off completely during shutdown. connect a 1 f (x5r or x7r) bypass capacitor from this pin to ground. figure 5. inrush current at power-up (battery powered) pwron 5v/div v int 2v/div i l2 500ma/div 100 s/div v batt = 2.4v i vint = 10ma 3456 f05
16 LTC3456 3456fa operatio u hot swap output the LTC3456 is designed to supply power to flash memory cards. it has a built-in hot swap output, hso, which allows memory cards to be hot swapped into and out of the system. the hot swap output features short-circuit and reverse-voltage blocking protection. connect a 1 f (x5r or x7r) bypass capacitor from this pin to ground. after the v int and core output voltages come into regula- tion, the hso pin is connected to v int via a 0.8 ? (typ) pmos switch after a delay of 0.5ms. the pmos switch has a 120ma built-in current limit. when a flash memory card is plugged into the system, the input bypass capacitors are slowly charged up to 3.3v with the preset 120ma current limit. figure 6 shows the switching waveforms with hot swap output short-circuited. as seen in the figure, the short- circuited current out of the hso pin is well regulated. the LTC3456 also features reverse-voltage blocking capa- bility for the hso pin. in the event the hso pin voltage rises greater than 3.3v (v int pin voltage), the internal pmos switch is turned off and behaves like a back-to-back diode. during shutdown, the hot swap output is discharged to ground via internal pull-down resistors. core regulator the core regulator produces a 0.8v to 1.8v adjustable output from a 1.8v to 3.2v input (2-cell battery), usb port or ac adapter supply. the core regulator utilizes a synchro- nous n-channel mosfet, improving efficiency and elimi- nating the need for an external schottky diode. the core output voltage is measured at the fb1 pin through a resis- tive divider network. the nominal voltage at the fb1 pin is 0.8v. the divider can be adjusted to set the output voltage level. the fb1 voltage should always be kept below 2v. the LTC3456 internal soft-start circuitry limits current drawn at start-up. soft-start is essential for input sources with high input impedance like alkaline cells. soft-start is implemented by ramping up the current limit. at start-up, the current limit is set to 25% and increased by 25% every 256 s. the final inductor current limit is reached after 1ms. when the core regulator is turned off, the output voltage v core is discharged to ground. this is accomplished by pulling the switching node, sw1, to ground through the internal pull-down resistors. figure 6a. short-circuit at the hot swap output (battery powered) v int 100mv/div (ac coupled) v hso 5v/div i hso 200ma/div i l2 500ma/div 2ms/div v batt = 2.4v v pwron = 2v 3456 f06a v int 100mv/div (ac coupled) v hso 5v/div i hso 200ma/div i l3 500ma/div 2ms/div v ext = 5v v pwron = 2v 3456 f06b figure 6b. short-circuit at the hot swap output (wall/usb powered)
17 LTC3456 3456fa operatio u the LTC3456 incorporates additional features like output short-circuit protection and thermal regulation. when the core regulator output (v core ) is shorted to ground, the LTC3456? unique control scheme prevents inductor cur- rent runaway. dropout operation the LTC3456 is capable of operating at 100% duty cycle when powered from the battery. if the input supply voltage decreases to a value close to the output voltage, the core regulator will run at 100% duty cycle. the output voltage is then determined by the input voltage minus the voltage drop across the pmos switch and the inductor. when running off the usb or the ac adapter, this situation never arises (there is plenty of voltage headroom). when the LTC3456 operates with low input supply volt- age, say 1.8v (fully discharged two aa cells) the maximum allowable output current gets reduced. figure 7 shows the reduction in the maximum output current as a function of input voltage for various output voltages. to power some of the internal circuitry of the ic. connect a 1 f bypass capacitor from this pin to ground. it can be used to supply a maximum of 1ma output load. the v max output voltage stays alive even when the ic is in shutdown. during shutdown, the v max output will be the highest of v batt , v ext and usb voltages. v max output can be used to supply power to a critical block like the real-time clock, which needs to stay alive even during shutdown. power sequencing power on/off the LTC3456 can turned on in two different ways: pulling the pwrkey pin low pulling the pwron pin high pulling the pwrkey pin low is usually the first step in turning on the LTC3456. when pwrkey is pulled low, it powers on the bandgap reference. onboard voltage moni- tors check the status of the ac adapter and usb supply. the ic is powered from either the ac adapter, usb or the battery, in that order of preference. the v int voltage powers up, followed by the core, main and hot swap outputs. at initial power up, the reset pin is held low. when the core output comes into regulation, the reset timer is started. after a 262ms timeout, the reset pin is released. this allows the microprocessor to turn on. the micropro- cessor in turn pulls pwron high. after the pwron pin is pulled high, the pwrkey pin can be released. there is a 400k ? pull-up resistor on the pwrkey pin. the pwrkey pin serves the dual purpose of turning on and off the ic. during regular operation, if pwrkey is pressed low, the microprocessor detects this by monitor- ing the status of pbstat pin. the pbstat pin goes low whenever the pwrkey pin is pulled low. the micropro- cessor then goes into shutdown mode and pulls the pwron pin low. this results in powering off the LTC3456. figure 8 shows the device power-on/power-off sequence. figure 7. maximum output current vs battery voltage v batt (v) 1.8 v core load current (ma) 400 500 600 2.4 2.8 3456 g18 300 200 2 2.2 2.6 3 3.2 100 0 l = 10 h (battery powered) v core = 1.5v v core = 1.8v v max output a special internal powerpath controller monitors the v batt , v int , v ext and usb voltages and passes the highest available supply voltage to the v max pin. this pin is used
18 LTC3456 3456fa reset the LTC3456 contains a reset circuitry that is active during both power-up and shutdown. the reset pin is held low during initial power-up. when both the v int and core outputs come into regulation, a reset delay timer gets activated. there is a full 262ms timeout before reset is released. during power-off mode reset is pulled low. this prevents the microprocessor from entering into any spurious operating mode. mode the LTC3456 has a user selectable mode pin. when the mode pin is pulled logic high and the LTC3456 is battery powered, the device will automatically enter into burst mode operation under light load current situations. if the load current in either of the regulators falls below a predetermined value, the regulator will enter into burst mode operation independent of the other regulator. when the mode pin is connected to ground, continuous pwm operation is selected. it provides the lowest output voltage ripple and current ripple, albeit at the cost of lower efficiency under light load conditions. operatio u the burst mode operation is disabled when the device is usb or wall powered. the device operates in forced pwm mode when powered from usb or wall input (irrespective of the state of the mode pin). also, at initial power up, the device operates in forced pwm mode during the 262ms initial delay timeout. figure 9 shows the main and core converters in burst mode operation. pwrkey v core pwrkey pulled low pwrkey released reset 262ms timeout power-on sequence power-off sequence pwron pbstat 3456 f08 figure 8. power-on/power-off sequence figure 9. the LTC3456 in burst mode operation v main 100mv/div (ac coupled) v core 100mv/div (ac coupled) i l1 100ma/div i l2 500ma/div 20 s/div v batt = 2.4v i main = 37.5ma i core = 6.2ma 3456 f09
19 LTC3456 3456fa voltage monitors low-battery detection the LTC3456 has an on-chip gain block that can be used for low-battery detection. the low-battery trip point can be set by two resistors (figure 10). the nominal voltage at ain is 0.8v. if the voltage at ain falls below 0.8v, ao sinks current to ground. the battery minimum voltage can be set according to the formula: vv r r batt min () . =+ ? ? ? ? ? ? 08 1 2 1 the ain input bias current is quite low, on the order of 2na (typ). large resistor values (r2 ~ 100k) can be used in the divider network. this helps in minimizing the loading on the battery. ao is an open-drain logic output. the voltage at ain must always be kept less than 2v. if the gain block is not used then connect ain to ground. there is no built-in hysteresis in the gain block. hysteresis can be added by connecting resistor r4 from ain to ao as shown in figure 10. ensure that r4 ? 10r3 for correct operation. with the values shown in figure 10b, the circuit has 180mv of hysteresis. figure 10. low-battery detector (10a) and low-battery detector with hysteresis (10b) figure 11. generating auxiliary voltage supply (10b) v core r4 1m r3 100k 3456 f10 r2 100k r1 80.6k v batt LTC3456 ain ao (10a) v core r3 100k r2 100k r1 80.6k v batt 1.8v to 3.2v LTC3456 ain ao 100k 2.2 f v main 3.3v 20.5k 43.2k 3456 f11 v aux 2.5v 20ma q1 philips mmbt3906 LTC3456 ain ao the gain block can be configured to drive an external pnp transistor and generate an auxiliary voltage as shown in figure 11. an auxiliary output voltage 2.5v/20ma is gen- erated from the v main (3.3v) power supply. external power detection the LTC3456 has an ext_pwr output pin to indicate the presence of usb or wall power. whenever the wallfb pin is pulled higher than 1.25v (ac adapter present), or the usb input is greater than 4v and the suspend pin is low (usb power available), the ext_pwr pin is pulled to ground. when pulled low, this pin is capable of sinking 5ma suitable for driving an external led. otherwise, this pin is in a high impedance state. overtemperature protection the maximum allowable junction temperature for LTC3456 is 125 c. in normal operation, the ic does not dissipate much heat and its junction temperature stays well below 125 c at an ambient temperature of 85 c or less. if the junction temperature exceeds 150 c, the core, main and hot swap outputs are turned off and reset is pulled low. the v int output stays alive in this state. the core and main outputs will remain off until the die temperature falls below 150 c, regardless of the state of the pwrkey and pwron inputs. operatio u
20 LTC3456 3456fa applicatio s i for atio wu uu component selection inductor selection the high frequency operation of LTC3456 allows the use of small surface mount inductors. for most applications, the inductance value will be between 2.2 h and 10 h. the desired value of inductance is determined by the amount of ripple current, ? i l , in the converter. the inductor current ripple, ? i l , for boost mode operation neglecting the voltage drop across the switches is given by: ? = () i vv v vfl l in out in out the inductor current ripple, ? i l , for buck mode operation neglecting the voltage drop across the switches is given by: ? = () i vvv vfl l out in out in 1 where l = inductor f = operating frequency v in = input voltage v out = output voltage the ? i l is typically set to 20% to 40% of the maximum inductor current. the inductor should have a saturation current rating greater than the peak inductor current required for the application. also, ensure that the inductor has a low dcr (copper wire resistance) to minimize i 2 r power losses. several inductors that work well with the lt3456 are listed in table 1. consult each manufacturer for more detailed information and for their entire selection of related parts. output capacitor selection low esr (equivalent series resistance) capacitors should be used at the output to minimize the output ripple voltage. multilayer ceramic capacitors are an excellent choice, as they have an extremely low esr and are available in very small packages. use only x7r or x5r dielectrics, as these materials retain their capacitance over wider voltage and temperature ranges than other dielectrics. a 1 f to 22 f output capacitor is sufficient for most applications. solid tantalum or os-con capacitors can be used, but they will occupy more board area than a ceramic and will have a higher esr for the same device footprint. always use a capacitor with a sufficient voltage rating. table 2 shows a list of several ceramic capacitor manufac- turers. consult the manufacturers for detailed information on their entire selection of ceramic parts. table 1. recommended inductors max current l dcr rating part ( h) ( ? ) (ma) vendor elt5kt-4r7 4.7 0.2 950 panasonic elt5kt-100 10 0.36 680 (714) 373-7939 www.panasonic.com cdrh4d18-4r7 4.7 0.16 840 sumida cdrh4d18-100 10 0.2 610 (847) 956-0666 www.sumida.com lqh32cn4r7 4.7 0.15 650 murata lqh32cn100 10 0.3 450 (814) 237-1431 www.murata.com 1002as-4r7m 4.7 0.19 910 toko 1002as-100m 10 0.32 620 (800) 745-8656 www.toko.com table 2. ceramic capacitor manufacturers taiyo yuden (408) 573-4150 www.t-yuden.com avx (803) 448-9411 www.avxcorp.com murata (714) 852-2001 www.murata.com tdk (847) 803-6100 www.component.tdk.com
21 LTC3456 3456fa input capacitor selection the LTC3456 can be powered from three different power sources: battery, usb or the ac wall adapter. choose a 4.7 f or higher x5r or x7r type ceramic capacitor for bypassing the input of LTC3456. however, special care must be taken when bypassing the usb and ac wall adapter inputs with ceramic capacitors. ceramic capacitors with their low esr can form a resonant tank circuit with the stray wiring inductance of the power leads. this can cause large voltage transients at the input of the device when the power is applied quickly (for example, plugging the ac adapter output into the portable device). this voltage spike can be large enough to damage the LTC3456. a possible solution is to clamp the input voltage or insert a small resistor in series with the ceramic capacitor as shown in figure 12. please refer to linear technology application note an88 for more details. applicatio s i for atio wu uu figure 12. bypassing usb and ac wall adapter inputs ac adapter usb input 1 ? 4.7 f 1 ? 4.7 f 10 f 3456 f12 usb LTC3456 v ext figure 13(a) shows the voltage waveforms at the usb and v ext pins resulting from hot-plugging a 5.5v input supply. as seen in the figure, there is a large voltage transient (in excess of 8v) at the usb input pin. this voltage spike exceeds the 6v absolute maximum voltage rating of the pin, and can cause serious performance degradation or, even complete failure of the part. the spike can be greatly reduced by adding a 1 ? series resisitor with the 4.7 f ceramic capacitor, as seen in figure 13(b). the voltage ringing at the usb pin is completely removed and the maximum voltage spike at the usb pin is less than the maximum voltage rating of 6v. figure 13(a). hot-plugging the usb power (5.5v input) with a 4.7 f ceramic capacitor used for bypassing. figure 13(b). hot-plugging the usb power (5.5v input) with a 4.7 f ceramic capacitor and 1 ? series resistor used for bypassing output voltage programming the output of the core converter can be set by a resistor divider according to the formula: vv r r core =+ ? ? ? ? ? ? 08 1 2 1 . the external resistor divider is connected at the output as shown in figure 14. choose 1% resistors for better accuracy. r1 should be 80.6k or smaller for better noise immunity. figure 14. setting the core output voltage r1 r2 0.8v v core v batt(min) 3456 f13 fb1 LTC3456 agnd v usb (2v/div) v ext (2v/div) 0.1ms/div v usb (2v/div) v ext (2v/div) 0.1ms/div
22 LTC3456 3456fa when the device is powered from the usb input (ac adapter is not present), the v ext pin is charged close to the usb voltage. the reverse leakage current of the diode d1 flows through r1 and r2 as shown in figure 16. if the leakage current is large enough to pull the wallfb pin above 1.25v, then the usb power is switched off. the LTC3456 will then enter into a hiccup mode with usb power being turned on and off in a periodic fashion. applicatio s i for atio wu uu a 4.32k or smaller resistor should be chosen for r1 to prevent this behavior. when the power is being delivered from the wall adapter, efficiency is not a big concern and choosing small value r1 and r2 resistors should be acceptable. connect the wallfb pin to ground if the wall adapter is not used. rectifier diode selection the diode, d1, shown in figures 15 and 16 is used to connect the v ext pin to the ac adapter input. the ic is powered through the diode d1 when running off the ac adapter. a schottky diode is recommended to minimize the voltage drop from the ac adapter to the v ext pin. v ext(min) = v adapter(min) ?v diode(max) always ensure that v ext > 4v during regular operation. choose a diode with a current rating high enough to handle the input current. choose a schottky diode with low reverse leakage current (as explained in previous section). on semiconductor mbrm120e (20v/1a) is a good choice for a low leakage schottky rectifier. the zetex zlls400 (40v/0.5a) schottky diode is available in a small surface mount package and is also a good fit for this application. ac adapter uvlo voltage programming the ac wall adapter uvlo voltage can be set by a resistor divider connected across the ac wall adapter as shown in figure 15. the ac wall adapter uvlo voltage can be set by a resistor divider according to the formula: vv r r adapter min () . =+ ? ? ? ? ? ? 125 1 2 1 choose 1% resistors for better accuracy. when the wallfb pin voltage is higher than 1.25v, the LTC3456 will be powered from the v ext pin. the internal usb power switch is turned off and the power is derived from the ac adapter through the diode d1. ensure that the ac adapter uvlo voltage is set high enough to make v ext > 4v during regular operation. figure 15. setting the wall adapter uvlo voltage ac adapter usb power r2 1 ? d1 r1 4.7 f 10 f 3456 f14 usb wallfb en LTC3456 v ext figure 16. diode d1 leakage current flow in usb powered mode usb power ac adapter not present r2 1 ? i lkg d1 r1 4.7 f 10 f 3456 f15 usb wallfb en LTC3456 v ext
23 LTC3456 3456fa applicatio s i for atio wu uu board layout consideration as with all switching regulators, careful attention must be paid to the pcb board layout and component placement. to prevent electromagnetic interference (emi) problems, proper layout of high frequency switching paths is essen- tial. minimize the length and area of all traces connected to the switching node pins (sw1, sw2_bk, sw2_bst). keep the feedback pins fb1 and ain away from the switching nodes. the power traces shown as bold lines in figure 17 should be kept short, direct and wide. the qfn package has an exposed paddle and it must be connected to the system ground. the ground connection for the feedback resistors should be tied directly to the ground plane and not shared with any other component, ensuring a clean, noise-free connection. design example as a design example, we target a 2 aa cell powered gps navigator application. figure 18 shows LTC3456 being used to provide power to the core and i/o peripherals. the flash memory card is powered from the hot swap output. core output needs to be 1.8v and the maximum load current is 200ma. the inductor current ripple, ? i l , for buck mode of operation is given by: ? = () i vvv vfl l out in out in 1 1 ? ) the maximum inductor current in l1 is set by the core converter current limit; i.e., 400ma (minimum). choosing ? i l = 100ma (~25% of peak inductor current) is a reason- able starting value. substituting v out = 1.8v, v in(max) = 3.2v, ? i l1 = 100ma, f = 1mhz in above equation gives: l vvv v ma mhz h 1 18 32 18 3 2 100 1 78 = () = ... . . + wallfb pwrkey v max v ext 10 f 4.7 f 4.7 f 1k 11.3k 1 ? 4.7 f 1 ? ac adapter (5v 10%) usb power (4.35v to 5.5v) usb controller 4.32k 80.6k 100k l2 4.7 h 2 aa cells l3 10 h ext_pwr usb suspend usbhp ao ain v main v batt v int sw2_bst LTC3456 bold lines indicate high current paths sw2_bk pbstat reset mode p pwron pgnd agnd 22 f v int 3.3v main output 3.3v 150ma 1 f hso hot swap output 3.3v 50ma 1 f 1 f 3456 ta01 sw1 fb1 l1 10 h core output 1.8v 200ma v max (powers real-time clock) 10 f 220pf 100k 80.6k figure 17. layout diagram
24 LTC3456 3456fa we can choose a low resistance 7.8 h or slightly higher value inductor. we can choose a 450ma, 10 h inductor (murata lqh32cn100). we need to check the ripple current when the core output is powered from the ac adapter or the usb. l1 is used to power the output in this case too. substituting v out = 1.8v, v in(max) = 5.5v , l1 = 10 h, f = 1mhz in above equation gives: ? = () = i vvv v h mhz ma l1 18 55 18 5 5 10 1 120 ... . l1 gives a reasonable value of ripple current when pow- ered from both battery and usb or ac adapter. the main output needs to be 3.3v and the maximum load current is 200ma. hot swap current is derived from the same main converter. when powered from the 2 aa cell, the 3.3v output is generated via the l2 boost inductor. the inductor current ripple, ? i l2 , for boost mode operation is given by: ? = () i vv v vfl l in out in out 2 2 ? ) a reasonable starting value of inductor ripple current is ? i l2 = 150ma. substituting v out = 3.3v, v in(min) = 1.8v, ? i l2 = 150ma, f = 1mhz in above equation gives: l vvv v ma mhz h 2 18 33 18 3 3 150 1 54 = () = ... . . we can choose a low resistance 4.7 h, 650ma inductor (murata lqh32cn4r7m53). when powered from the ac adapter or the usb, the 3.3v output is generated via the l3 buck inductor. the inductor current ripple ( ? i l3 ) for buck mode operation is given by: ? = () i vvv vfl l out in out in 3 3 ? ) a reasonable starting value of inductor ripple current is ? i l3 = 100ma. substituting v out = 3.3v, v in(max) = 5.5v, ? i l3 = 100ma, f = 1mhz in above equation gives: l vvv v ma mhz h 3 33 55 33 5 5 100 1 13 2 = () = ... . . we can choose a 450ma, 10 h inductor (murata lqh32cn100k53). a 4.7 f to 22 f (x5r or x7r) ceramic output capacitor is sufficient for most applications. they have a low esr and result in a low output ripple. figure 18 shows the complete circuit along with the efficiency curves. applicatio s i for atio wu uu
25 LTC3456 3456fa figure 18. 2 aa cells to 1.8v/200ma and 3.3v/200ma outputs using all ceramic capacitors with lowest parts count applicatio s i for atio wu uu + wallfb pwrkey v max v ext c4 10 f c2 4.7 f c3 4.7 f c1 4.7 f 1k 11.3k 1 ? 1 ? ac adapter (5v 10%) usb power (4.35v to 5.5v) usb controller 4.32k d1 80.6k 100k l2 4.7 h 2 aa cells l3 10 h ext_pwr usb suspend usbhp ao ain v main v batt v int sw2_bst LTC3456 sw2_bk pbstat reset mode p pwron pgnd agnd c9 22 f v int 3.3v main output 3.3v 150ma c8 1 f hso hot swap output 3.3v 50ma c7 1 f c5 1 f 220pf 3456 f17 sw1 fb1 l1 10 h core output 1.8v 200ma v max (powers real-time clock) c6 10 f 100k 80.6k c2 to c5: x5r or x7r, 6.3v c1, c6 to c9: x5r or x7r, 4v d1: on semiconductor mbrm120e l1, l3: murata lqh32cn100k53 l2: murata lqh32cn4r7m53 efficiency (battery powered) load current (ma) 1 40 efficiency (%) power loss (mw) 50 60 70 80 10 100 1000 3456 ta01b 30 20 10 0 90 100 100 150 200 50 0 250 v batt = 2.4v mode = 0v efficiency power loss 1.8v output 1.8v output 3.3v output 3.3v output efficiency (wall powered) load current (ma) 1 60 efficiency (%) 80 100 10 100 1000 3456 f17d 40 30 50 70 90 20 0 10 v wall = 5v 1.8v output 3.3v output efficiency (usb powered) load current (ma) 1 60 efficiency (%) 80 100 10 100 1000 3456 g02 40 30 50 70 90 20 0 10 v usb = 5v v usbhp = 2v 1.8v output 3.3v output
26 LTC3456 3456fa + pwrkey wallfb v max v ext v ext c4 10 f c2 4.7 f 1 ? c3 4.7 f c1 4.7 f 1k d1 1 ? 11.3k 4.32k ac adapter (5v 10%) usb power (4.35v to 5.5v) usb controller l2 4.7 h 2 aa cells l3 10 h ext_pwr usb suspend usbhp v batt v main a0 ain v int sw2_bst LTC3456 sw2_bk pbstat reset mode microcontroller pwron pgnd agnd c10 22 f main output 3.3v 100ma lcd logic bias 2.8v 10ma c9 1 f 100k hso flash memory card 3.3v 50ma c7 1 f c8 2.2 f q1 49.9k 20k c5 1 f c1, c6 to c10: x5r or x7r, 4v c2 to c5: x5r or x7r, 6.3v d1: on semiconductor mbrm120e 3456 ta02a sw1 fb1 l1 10 h core output 1.8v 200ma v max (to real-time clock) c6 10 f 220pf 100k 80.6k l1, l3: murata lqh32cn100k53 l2: murata lqh32cn4r7m53 q1: philips mmbt3906 2 aa cells power complete power supply for handheld devices load transient (battery powered) load transient (usb/wall powered) v core 100mv/div (ac coupled) v main 200mv/div (ac coupled) i l2 200ma/div i l1 200ma/div 100 s/div v batt = 2.4v i main = 20ma to 100ma i core = 20ma to 150ma 3456 ta02b v core 100mv/div (ac coupled) v main 200mv/div (ac coupled) i l3 200ma/div i l1 200ma/div 200 s/div v ext = 5v i main = 20ma to 100ma i core = 5ma to 150ma 3456 ta02c typical applicatio u
27 LTC3456 3456fa u package descriptio uf package 24-lead plastic qfn (4mm 4mm) (reference ltc dwg # 05-08-1697) 4.00 0.10 (4 sides) note: 1. drawing proposed to be made a jedec package outline mo-220 variation (wggd-x)?o be approved 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side, if present 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package pin 1 top mark (note 6) 0.38 0.10 24 0.23 typ (4 sides) 23 1 2 bottom view?xposed pad 2.45 0.10 (4-sides) 0.75 0.05 r = 0.115 typ 0.25 0.05 0.50 bsc 0.200 ref 0.00 ?0.05 (uf24) qfn 1103 recommended solder pad pitch and dimensions 0.70 0.05 0.25 0.05 0.50 bsc 2.45 0.05 (4 sides) 3.10 0.05 4.50 0.05 package outline information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
28 LTC3456 3456fa ? linear technology corporation 2004 lt/lt 1005 rev a ? printed in usa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com typical applicatio u quad-output converter runs off 2 aa cells, usb or wall adapter + pwrkey wallfb v max v ext v ext c3 10 f c2 4.7 f 1 ? c4 4.7 f c1 4.7 f 1k d1 1 ? 11.3k 4.32k ac adapter (5v 10%) usb power (4.35v to 5.5v) usb controller l2 4.7 h 2 aa cells l3 10 h ext_pwr usb suspend usbhp v batt v main a0 ain v int sw2_bst LTC3456 sw2_bk pbstat reset mode microcontroller pwron pgnd agnd c10 22 f main output 3.3v 100ma lcd logic bias 2.8v 10ma c9 1 f 100k hso flash memory card 3.3v 50ma c7 1 f c8 2.2 f q2 49.9k 20k c5 1 f c1, c6 to c10: x5r or x7r, 4v c2 to c5: x5r or x7r, 6.3v d1, d2: on semiconductor mbrm120e 3456 ta03 sw1 fb1 core output 2.5v 100ma v max to real-time clock (alive or shut down) l1, l3: murata lqh32cn100k53 l2: murata lqh32cn4r7m53 q1: fairchild fdg327n q2: philips mmbt3906 43.2k 20.5k l1 10 h 10 f 330pf q1 d2 related parts part number description comments lt1616 500ma (i out ), 1.4mhz, high efficiency step-down 90% efficiency, v in : 3.6v to 25v, v out(min) = 1.25v, i q = 1.9ma, dc/dc converter i sd < 1 a, thinsot ltc1879 1.2a (i out ), 550khz, synchronous step-down 95% efficiency, v in : 2.7v to 10v, v out(min) = 0.8v, i q = 15 a, dc/dc converter i sd < 1 a, tssop16 ltc3405/ltc3405a 300ma (i out ), 1.5mhz, synchronous step-down 95% efficiency, v in : 2.7v to 6v, v out(min) = 0.8v, i q = 20 a, dc/dc converter i sd < 1 a, thinsot ltc3406/ltc3406b 600ma (i out ), 1.5mhz, synchronous step-down 96% efficiency, v in : 2.5v to 5.5v, v out(min) = 0.6v, i q = 20 a, dc/dc converter i sd < 1 a, thinsot ltc3407 dual 600ma (i out ), 1.5mhz, synchronous step-down 96% efficiency, v in : 2.5v to 5.5v, v out(min) = 0.6v, i q = 40 a, dc/dc converter i sd < 1 a, ms10e ltc3412 2.5a (i out ), 4mhz, synchronous step-down 95% efficiency, v in : 2.5v to 5.5v, v out(min) = 0.8v, i q = 60 a, dc/dc converter i sd < 1 a, tssop16e ltc3414 4a (i out ), 4mhz, synchronous step-down 95% efficiency, v in : 2.25v to 5.5v, v out(min) = 0.8v, i q = 64 a, dc/dc converter i sd < 1 a, tssop16e ltc3440/ltc3441 600ma/1a (i out ), 2mhz/1mhz, synchronous buck-boost 95% efficiency, v in : 2.5v to 5.5v, v out(min) = 2.5v, i q = 25 a/50 a, dc/dc converter i sd < 1 a, ms/dfn ltc3455 dual dc/dc converter with usb power manager 96% efficiency, seamless transition between inputs, i q = 110 a, and li-ion battery i sd < 2 a, qfn

▲Up To Search▲

Price & Availability of LTC3456

	To Download LTC3456 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .