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600mA, 1.2MHz, Micropower Synchronous Step-Up Converter General Description Features
AAT1217
SwitchRegTM
The AAT1217 a high efficiency, synchronous, fixed frequency, step-up converter designed for singlecell or dual-cell alkaline, NiMH, or NiCd batterypowered applications. The high 1.2MHz switching frequency and completely integrated control circuitry minimize the total solution footprint area while maintaining excellent regulation, ripple, and transient response throughout the full load range.
* * * * * * *
The AAT1217 is available in a Pb-free, space-saving low profile (1mm) 6-pin TSOT23 package and is rated over the -40C to +85C ambient temperature range.
Pulse skipping mode operation and low quiescent current allow the AAT1217 to maintain high efficiency performance for light load and sleep mode conditions. With a 1.2A peak switch current limit, the AAT1217 is capable of delivering 100mA to the load from a single AA cell or up to 400mA from dual AA cells. The AAT1217 has a 0.85V start-up voltage with operation down to 0.5V.
* * * * * * * * * *
VIN Operation Range: 0.5V to VOUT VOUT Range: 2.5V to 5.5V 100mA Output from a Single AA Cell Input 400mA Output from a Dual AA Cell Input High Efficiency: Up to 93% Efficiency Low Start-Up Voltage: 0.85V Typical Internal Synchronous Rectifier -- VOUT 4.5V: No External Schottky Diode Fixed Frequency Pulse Width Modulation (PWM) Current-Mode Control Scheme with Internal Compensation 1.2MHz Fixed Switching Frequency 1.2A Current Limit Light Load Pulse Skipping Mode Operation Low 80A No Load Input Current Over-Current Protection EMI Reduction Anti-Ringing Control Circuitry Low Shutdown Current: <1.0A -40C to +85C Ambient Temperature Range Low Profile (1mm) TSOT23-6 Package
Applications
* * * * * *
Cellular and Smart Phones Digital Still and Video Cameras Microprocessors and DSP Core Supplies MP3 Player Portable Instruments Wireless and DSL Modems
Typical Application
L1 4.7H SW
L1 4.7H SW
VIN: 0.85V C IN 4.7F
R3 1M
VIN
SHDN
AAT1217-1.2
GND
VOUT FB
VOUT: 3.3V,100 mA R1 1.02M R2 604k C OUT 4.7F
VIN: 0.85V C IN 4.7F
R3 1M
VIN
SHDN
AAT1217-3.3
GND
VOUT FB
VOUT: 3.3V,100 mA C OUT 4.7F
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600mA, 1.2MHz, Micropower Synchronous Step-Up Converter Pin Descriptions
Pin #
1 2 3 4 5 6 SW
AAT1217
Symbol
GND FB SHDN VOUT VIN
Power Switch Pin. Ties to the drains of the PMOS synchronous rectifier and the NMOS switch. Ground Pin Feedback Input Pin. Connect FB to the center point of the external resistor divider. The feedback threshold voltage is 1.23V. Shutdown Signal Input. Logic high enables the IC. Logic low disables the IC. Shutdown current is <1A. Power Output Pin. Tied to the source of the PMOS synchronous rectifier. Power Supply Input. Must be closely decoupled to GND, Pin 2, with a 4.7F or greater ceramic capacitor.
Function
Pin Configuration
SW FB
TSOT23-6 (Top View)
1 2 3 6 5 4
GND
VIN
VOUT
SHDN
2
1217.2007.07.1.0
600mA, 1.2MHz, Micropower Synchronous Step-Up Converter Absolute Maximum Ratings1
VIN VSW VFB, VSHDN VOUT TA TSTORAGE TLEAD TJ
AAT1217
Symbol
Input Supply Voltage SW Voltage FB, SHDN Voltages VOUT Voltage Operating Ambient Temperature Range2 Storage Temperature Range Lead Temperature (Soldering, 10s) Operating Junction Temperature Range2
Description
-0.3 to 6 -0.3 to 6 -0.3 to 6 -0.3 to 6 -40 to 85 -65 to 150 300 -40 to 150
Value
Units
V V V V C C C C
Thermal Information3
Symbol
JA PD Maximum Thermal Resistance Maximum Power Dissipation
Description
Value
190 526
Units
C/W mW
1. Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. 2. TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: TJ = TA + PD x JA. 3. Mounted on an FR4 board. 1217.2007.07.1.0
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600mA, 1.2MHz, Micropower Synchronous Step-Up Converter Electrical Characteristics1
Symbol
VIN VOUT VFB VOUT/VOUT/ VIN VOUT/VOUT/ IOUT IQ ILNMOS ILPMOS
AAT1217
VIN = 1.2V, VOUT = 3.3V, TA = 25C, unless otherwise noted.
Minimum Start-Up Voltage Minimum Operating Voltage Output Voltage Range Output Voltage Accuracy3 Reference Voltage Reference Voltage Line Regulation Reference Voltage Load Regulation Quiescent Current (Shutdown) Quiescent Current (Active) Quiescent Current (Active) NMOS Switch Leakage PMOS Switch Leakage
Description
IOUT = 1mA VSHDN = VIN
Conditions
Min
2.5 -4 1.192
0.85 0.5 1.230 0.2 0.4 0.003 0.004 0.01 115
Typ
RDS(ON)L RDS(ON)H ICL t(ICL) DMAX FOSC VSHDN ISHDN TSD
NMOS Switch ON Resistance PMOS Switch ON Resistance NMOS Current Limit Current Limit Delay to Output Maximum Duty Cycle Switching Frequency SHDN Input Low SHDN Input High SHDN Input Current Thermal Shutdown
IOUT = 10mA; TA = -40C to +85C TA = -40C to +85C VIN = 1.2V to 2.4V, IOUT = 10mA, VOUT = 3.3V VIN = 2.4V to 4.2V, IOUT = 10mA, VOUT = 5.0V VIN = 1.2V, IOUT = 10mA to 100mA VOUT = 3.3V VIN = 3.6V, IOUT = 10mA to 400mA VOUT = 5.0V VSHDN = 0 VIN = 1.8V, Current from input voltage source. VSHDN = VIN Measured on VOUT, VSHDN = VIN VSW = 5V VSW = 0V VOUT = 3.3V VOUT = 5V VOUT = 3.3V VOUT = 5V VFB = 1.15V, TA = -40C to +85C TA = -40C to +85C VSHDN = 5.5V Hysteresis
1 0.65 5.5 +4 1.268
Max
Units
V % V %/V V
%/mA 1 500 5 5
750 80 0.9 1.00
300 0.1 0.1 0.35 0.30 0.60 0.55 1200 40 85 1.2 0.01 160 20
A A A
1.5 0.35 1
mA ns % MHz A C V
1. Specifications over the temperature range are guaranteed by design, characterization, and correlation with statistical process controls. 2. Not including the current into internal resistance divider. 3. For fixed 3.3V and 5.0V output voltage version. The adjustable output voltage is guaranteed by reference voltage accuracy.
4
1217.2007.07.1.0
600mA, 1.2MHz, Micropower Synchronous Step-Up Converter Typical Characteristics
Efficiency vs. Output Current
(VOUT = 3.3V; TA = 25C)
100 90 80 100
AAT1217
Efficiency vs. Output Current
(VOUT = 5V; TA = 25C)
90 80
VIN = 2.4V
VIN = 2.4V VIN = 3.6V VIN = 1.2V VIN = 1.5V
Efficiency (%)
Efficiency (%)
70 60 50 40 30 20 10 0 0.1 1 10 100 1000
70 60 50 40 30 20 10 0 0.1 1 10 100 1000
VIN = 1.5V VIN = 1.2V
Output Current (mA)
Output Current (mA)
Output Voltage vs. Output Current
(VOUT = 3.3V; TA = 25C)
3.5 5.2
Output Voltage vs. Output Current
(VOUT = 5V; TA = 25C)
Output Voltage (V)
3.4
Output Voltage (V)
5.1
VIN = 1.2V
3.3
VIN = 1.5V
VIN = 2.4V
VIN = 1.2V
5
VIN = 1.5V
VIN = 2.4V
VIN = 3.6V
4.9
3.2
3.1 0 100 200 300 400 500 600
4.8 0 100 200 300 400 500 600
Output Current (mA)
Output Current (mA)
Minimum Start-Up Voltage vs. Output Current
(VOUT = 3.3V; TA = 25C)
1.5
Maximum Output Current vs. Input Voltage
(L = 4.7H; TA = 25C)
1000
Start-Up Voltage (V)
Maximum Output Current (mA)
1.35 1.2 1.05 0.9 0.75 0.6 0 20 40 60 80 100 120 140 160 180 200
800
VOUT = 3.3V
600
400
VOUT = 5V
200
0 0.5
1
1.5
2
2.5
3
3.5
4
4.5
Output Current (mA)
Input Voltage (V)
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600mA, 1.2MHz, Micropower Synchronous Step-Up Converter Typical Characteristics
No Load Input Current vs. Input Voltage
(VOUT = 3.3V; TA = 25C; No Load)
150 140 130 120 110 100 90 80 70 60 50 1.5 1.8 2.1 2.4 2.7 3 3.35 3.34
AAT1217
Output Voltage vs. Temperature
Output Voltage (V)
Input Current (A)
3.33 3.32 3.31 3.3 3.29 3.28 3.27 3.26 3.25 -50 -25 0 25 50 75 100
Input Voltage (V)
Temperature (C)
Pulse Skipping Mode Operation
(VIN = 1.8V; VOUT = 3.3V; IOUT = 5mA) VSW 2V/div
Anti-Ringing Operation at SW
(VIN = 2.4V; VOUT = 5V; IOUT = 20mA)
VSW 2V/div
0V
0V
VOUT 50mV/div (AC)
Time (1ms/div)
Time (400ns/div)
Load Transient Response
(VIN = 1.5V; VOUT = 3.3V; CFF = 100pF)
IOUT 50mA/div
0A
100mA 40mA
VOUT 100mV/div (AC)
Time (100s/div)
6
1217.2007.07.1.0
600mA, 1.2MHz, Micropower Synchronous Step-Up Converter Functional Block Diagram
VIN VIN Slope Compensation Start-Up Oscillator MUX VOUT GOOD 2.3V -
AAT1217
+
L1
SW
+
-
CIN
Current Sense Antiringing Control
VOUT COUT
VOUT R1 R2
Bandgap 1.23V FB
To VIN
+
-
+
EA -
Comp
PWM Logic
GND
SHDN
Shutdown Control
Oscillator 1.2MHz
The AAT1217 is a synchronous step-up DC-DC converter. It utilizes internal MOSFET switches to achieve high efficiency over the full load current range. It operates at a fixed switching frequency of 1.2MHz, and uses the slope compensated current mode pulse width modulation (PWM) architecture. The device can operate with an input voltage below 1V; the typical start-up voltage is 0.85V. The AAT1217 integrates a synchronous rectifier to improve efficiency as well as to eliminate the need for an external Schottky diode. The synchronous rectifier is used to reduce the conduction loss contributed by the forward voltage of an external Schottky diode. The synchronous rectifier is realized by a P-channel MOSFET (PMOS) with gate
1217.2007.07.1.0
Functional Description
Synchronous Rectification
The AAT1217 can start-up with supply voltages down to 0.85V. During start-up, the internal low voltage start-up circuitry controls the internal NMOS switch. The AAT1217 leaves the start-up mode once VOUT exceeds 2.3V. An internal comparator (VOUT GOOD) monitors the output voltage and places the chip into normal operation once VOUT exceeds 2.3V. The AAT1217's control circuitry is biased by VIN during start-up and biased by VOUT once VOUT exceeds VIN. When VOUT exceeds VIN, the AAT1217's operation will be independent of VIN. 7
Low Voltage Start-Up
control circuitry that incorporates relatively complicated timing concerns. An external Schottky diode is required when the output voltage is greater than 4.5V.
600mA, 1.2MHz, Micropower Synchronous Step-Up Converter
The AAT1217 is based on a slope compensated current mode PWM control topology. It operates at a fixed frequency of 1.2MHz. At the beginning of each clock cycle, the main switch (NMOS) is turned on and the inductor current starts to ramp. After the maximum duty cycle or the sense current signal equals the error amplifier (EA) output, the main switch is turned off and the synchronous switch (PMOS) is turned on. This control topology features cycle-by-cycle current limiting which can prevent the main switch from overstress and the external inductor from saturating. At very light load, the AAT1217 automatically switches into pulse skipping mode operation to improve efficiency. During this mode, the PWM control will skip some pulses to maintain regulation. If the load increases and the output voltage drops, the device will automatically switch back to normal PWM mode and maintain regulation.
AAT1217
Current Mode Operation
Application Information
Adjustable Output Voltage
An external resistor divider is used to set the output voltage. The output voltage of the switching regulator (VOUT) is determined by the following equation:
R1 VOUT = 1.23V * 1 + R2
Table 1 lists the recommended resistor values for particular output voltage settings. VOUT
3.3V 5.0V
Pulse Skipping Mode Operation
R1()
1.02M 1.02M
R2()
604k 332k
Anti-Ringing Control
An anti-ringing circuitry is included to remove the high frequency ringing that appears on the SW pin when the inductor current goes to zero. In this case, a ringing on the SW pin is induced due to remaining energy stored in parasitic components of switch and inductor. The anti-ringing circuitry clamps the voltage internally to the battery voltage and therefore dampens this ringing. When SHDN is set logic high, the AAT1217 is put into active mode operation. If SHDN is set logic low, the device is put into shutdown mode and consumes less than 1A of current. After start-up, the internal circuitry is supplied by VOUT, however, if shutdown mode is enabled, the internal circuitry will be supplied by the input source again.
AAT1217 has two fixed output voltage options: 3.3V and 5V. An internal resistor divider is connected to the FB pin inside the package which eliminates the need for external feedback resistors. When designing with the fixed output voltage option, remember to leave the FB pin open; otherwise the output voltage will be affected. However, a feed-forward capacitor can still be added between the FB and VOUT pins to enhance the control loop performance. The high switching frequency of 1.2MHz allows for small surface mount inductors. For most applications, the AAT1217 operates with inductors from 2.2H to 10H. Use the following equations to select the proper inductor value for a particular application condition:
Fixed Output Voltage
Table 1: Resistor Selection for Output Voltage Setting.
Device Shutdown
Inductor Selection
8
1217.2007.07.1.0
600mA, 1.2MHz, Micropower Synchronous Step-Up Converter
IL IPEAK = IDC + 2
AAT1217
IDC =
IL = IL =
IOUT * VOUT * VIN
VIN * D VOUT - VIN ; D= L * FSW VOUT VIN * (VOUT - VIN) L * FSW * VOUT
IPEAK =
VIN * (VOUT - VIN) IOUT * VOUT * VIN + 2L * FSW * VOUT
IPEAK Peak Inductor Current IDC DC Component (Average) of the Inductor Current IL Peak-Peak Inductor Ripple Current IOUT Output (Load) Current VOUT Output Voltage VIN Input Voltage AAT1217 Efficiency (consult the performance graphs in the "Typical Characteristics" section of the data sheet) D Steady-State Duty Cycle FSW Switching Frequency L Inductor Value
For a given chosen inductor value and application conditions make sure the peak inductor current does not exceed the maximum current rating of the selected vendor's inductor. For optimum load transient and efficiency, low DCR inductors should be selected. Table 2 lists some typical surface mount inductors that are suitable for typical AAT1217 applications.
A laboratory test set-up typically consists of two long wires running from the bench power supply to the evaluation board input voltage pins. The inductance of these wires, along with the low-ESR ceramic input capacitor, can create a high Q network that may affect converter performance. This problem often becomes apparent in the form of excessive ringing in the output voltage during load transients which can produce errors in loop phase and gain measurements. Since the inductance of a short printed circuit board (PCB) trace feeding the input voltage is significantly lower than the power leads from the bench power supply, most actual applications do not exhibit this problem. In applications where the input power source lead inductance cannot be reduced to a level that does not affect the converter performance, a high ESR tantalum or aluminum electrolytic capacitor should be placed in parallel with the low ESR, ESL bypass input ceramic capacitor. The introduction of the high ESR capacitor dampens the high Q network and stabilizes the AAT1217.
A surface mount 4.7F or greater, X5R or X7R, ceramic capacitor is suggested for the input capacitor. The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the AAT1217. Low ESR/ESL X7R and X5R ceramic capacitors are ideal for this function. To minimize stray inductance, the capacitor should be placed as close as possible to the IC. This keeps the high frequency content of the input current localized, minimizing EMI and input voltage ripple. Always examine the ceramic capacitor DC voltage coefficient characteristics to get the proper value. For example, the capacitance of a 10F, 6.3V, X5R ceramic capacitor with 5.0V DC applied is actually about 6F.
Input Capacitor
1217.2007.07.1.0
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600mA, 1.2MHz, Micropower Synchronous Step-Up Converter
Part Number
Sumida CDH28D11/S Coiltronics SD3112 TDK VLF3012A Sumida CR43 Sumida CDRH4D28 Toko D53LC
AAT1217
L (H)
2.2 4.7 10 2.2 4.7 10 2.2 4.7 10 2.2 4.7 10 2.2 4.7 10 4.7 10
Max DCR (m)
123 238 431 140 (typ) 246 (typ) 446 (typ) 100 190 410 71.2 108.7 182 31.3 72 128 45 90
Rated DC Current (A)
1.15 0.75 0.53 1.12 0.8 0.55 1 0.74 0.49 1.75 1.15 1.04 2.04 1.32 1 1.87 1.33
Size WxLxH (mm)
3x3.3x1.2 3.1x3.1x1.2 2.8x2.6x1.2 4.3x4.8x3.5 5.0x5.0x3.0 5.0x5.0x3.0
The output capacitor limits the output ripple and provides holdup during large load transitions. A 4.7F to 10F, X5R or X7R, ceramic capacitor is suggested for the output capacitor. Typically the recommended capacitor range provides sufficient bulk capacitance to stabilize the output voltage during large load transitions and has the ESR and ESL characteristics necessary for low output voltage ripple. In addition, the output voltage droop during load transient is dominated by the capacitance of the ceramic output capacitor. During a step increase in load current, the ceramic output capacitor alone supplies the load current until the loop responds. Within several switching cycles, the loop responds and the inductor current increases to match the load current demand. Larger output capacitor values help to reduce the voltage droop during large load current transients.
Output Capacitor
Table 2. Typical Surface Mount Inductors.
Load Disconnect in Shutdown
In conventional synchronous step-up converters, a conduction path exists from input to output through the backgate (body diode) of the P-channel MOSFET during shutdown. Special application circuitry can disconnect the load from the battery during shutdown (see Figure 1). The AAT1217 typically operates at 1.2MHz. This is a considerably high frequency for DC-DC converters. PCB layout is important to guarantee satisfactory performance. It is recommended to make traces of the power loop, especially where the switching node is involved, as short and wide as possible. First of all, the inductor, input and output capacitor should be as close as possible to the device. Feedback and shutdown circuits should avoid the proximity of large AC signals involving the power inductor and switching node. The optional rectifier diode (D1 in Figure 1) can improve efficiency and alleviate the stress on the integrated MOSFETs. The diode should also be close to the inductor and the chip to form the shortest possible switching loop. While the two-layer PCB shown in Figures 2 and 3 is enough for most applications, large and integral multi-layer ground planes
1217.2007.07.1.0
PCB Layout Guidance
An external Schottky diode is required when the output voltage is above 4.5V. The Schottky diode is optional for output voltages 4.5V, but can improve efficiency by about 2% to 3%. 10
External Diode Selection
600mA, 1.2MHz, Micropower Synchronous Step-Up Converter
are ideal for high power applications. Large areas of copper have lower resistance and help to dissipate heat. The converter's ground should join the system ground to which it supplies power at one point only.
L1 4.7H 1 VIN 0.85V CIN 4.7F 6 VIN SW VOUT FB
AAT1217
Figure 1 is the schematic for a highly efficient load disconnect application circuit for the AAT1217. An example PCB layout for the AAT1217 is shown in Figures 2 and 3.
D1 MBR0520 Q1 Si2305 DS R4 510k R1 1.02M R2 604k VOUT 3.3V,100mA COUT 4.7F
4
AAT1217
GND 2
5 3
SHDN
ON/OFF Control
R3 510k
Q2 2N3904
Figure 1. AAT1217 High Efficiency Load Disconnect Application Circuit
Figure 2. AAT1217 Evaluation Board Layout Example Top Layer
Figure 3. AAT1217 Evaluation Board Layout Example Bottom Layer
1217.2007.07.1.0
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600mA, 1.2MHz, Micropower Synchronous Step-Up Converter Ordering Information
Output Voltage1
Adj. Fixed 3.3V Fixed 5.0V
AAT1217
TSOT23-6 TSOT23-6 TSOT23-6
Package
Marking2
VZMYY WAMYY WBMYY
Part Number (Tape and Reel)3
AAT1217ICA-1.2-T1 AAT1217ICA-3.3-T1 AAT1217ICA-5.0-T1
Package Information
Part Dimensions
All AnalogicTech products are offered in Pb-free packaging. The term "Pb-free" means semiconductor products that are in compliance with current RoHS standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more information, please visit our website at http://www.analogictech.com/pbfree.
TSOT23-6
0.40 0.10
0.95 BSC
Detail "A"
2.80 BSC
1.60 BSC
Top View
End View
2.90 BSC
0.25 BSC
0.127 BSC
1.00 +10 -0 0.45 0.15
1.00 0.10
0.000
+ 0.100 - 0.000
All dimensions in millimeters.
Side View
Detail "A"
1. Please contact sales for other voltage options. 2. YY = Manufacturing Date Code. 3. Sample stock is generally held on part numbers listed in BOLD.
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1217.2007.07.1.0
600mA, 1.2MHz, Micropower Synchronous Step-Up Converter
AAT1217
AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Except as provided in AnalogicTech's terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer's applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
(c) Advanced Analogic Technologies, Inc.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737- 4600 Fax (408) 737- 4611
1217.2007.07.1.0
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