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rt2810a/b ? ds2810a/b-06 november 2016 www.richtek.com 1 copyright 2016 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. ? 10a, 18v, 500khz, acot tm synchronous step-down converter general description the rt2810a/b is a synchronous step-down converter with advanced constant on-time (acot tm ) mode control. the acot tm provides a very fast transient response with few external components. the low impedance internal mosfet supports high efficiency operation with wide input voltage range from 4.5v to 18v. the proprietary circuit of the rt2810a/b enables to support all ceramic capacitors. the output voltage can be adjustable between 0.7v and 8v. the soft-start is adjustable by an external capacitor. ordering information note : richtek products are : ? rohs compliant and compatible with the current require- ments of ipc/jedec j-std-020. ? suitable for use in snpb or pb-free soldering processes. features ? ? ? ? ? 4.5v to 18v input voltage range ? ? ? ? ? 10a output current ? ? ? ? ? 12m internal high-side n-mosfet and 5.4m internal low-side n-mosfet ? ? ? ? ? advanced constant on-time control ? ? ? ? ? fast transient response ? ? ? ? ? support all ceramic capacitors ? ? ? ? ? up to 95% efficiency ? ? ? ? ? adjustable switching frequency from 300khz to 700khz ? ? ? ? ? adjustable output voltage from 0.7v to 8v ? ? ? ? ? adjustable soft-start ? ? ? ? ? pre-bias start up ? ? ? ? ? adjustable current limit from 6a to 16a ? ? ? ? ? cycle-by-cycle overcurrent protection ? ? ? ? ? power good output ? ? ? ? ? input under-voltage lockout ? ? ? ? ? hiccup/latched mode under-voltage selection applications ? industrial and commercial low power systems ? computer peripherals ? lcd monitors and tvs ? green electronics/appliances ? point of load regulation for high-performance dsps, fpgas, and asics simplified application circuit rt2810a/b package type quf : uqfn-16jl 3x3 (u-type) (fc) lead plating system g : green (halogen free and pb free) uvp option h : hiccup mode uvp l : latched ovp & uvp a : psm b : pwm pgood rt2810a/b rlim fb v in boot sw ss vin en gnd v out pvcc en signal power good rt
rt2810a/b 2 ds2810a/b-06 november 2016 www.richtek.com ? copyright 2016 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. functional pin description pin configurations (top view) uqfn-16jl 3x3 (fc) marking information rt pvcc agnd fb vin sw sw sw boot gnd rlim sw sw ss en pgood 6 15 12 11 10 9 1 2 3 4 13 16 7 5 14 8 7g= : product code ymdnn : date code rt2810algquf 7e= : product code ymdnn : date code rt2810blgquf 7h=ym dnn 7h= : product code ymdnn : date code RT2810AHGQUF 7f= : product code ymdnn : date code rt2810bhgquf 7g=ym dnn 7e=ym dnn 7f=ym dnn pin no. pin name pin function 1 agnd analog ground. 2 fb feedback voltage input. it is used to regulate the output of the converter to a set value via an external resistive voltage divider. the feedback reference voltage is 0.7v typically. 3 pvcc internal regulator output. connect a 1 ? f capacitor to gnd to stabilize output voltage. 4 rt an external timing resistor adjusts the switching frequency of the device. 5 ss soft-start time setting. an external capacitor should be connected between this pin and gnd. 6 vin power input. the input voltage range is from 4.5v to 18v. must bypass with a suitably large ( ? 10 ? f x 2) ceramic capacitor. 7 gnd ground. 8 pgood power good indicator open-drain output. 9 boot bootstrap. this capacitor is needed to drive the power switch's gate above the supply voltage. it is connected between sw and boot pins to form a floating supply across the power switch driver. a 0.1 ? f capacitor is recommended for use. 10 to 14 sw switch node. connect this pin to an external l-c filter. 15 en enable control input. a logic-high enables the converter; a logic-low forces the ic into shutdown mode reducing the supply current to less than 10 ? a. 16 rlim an external resistor adjusts the current limit of the device.
rt2810a/b 3 ds2810a/b-06 november 2016 www.richtek.com ? copyright 2016 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. function block diagram operation the rt2810a/b is a synchronous step-down converter with advanced constant on-time control mode. using the acot tm control mode can reduce the output capacitance and fast transient response. it can minimize the component size without additional external compensation network. power good after soft-start has finished, the power good function will be activated. the pgood pin is an open-drain output. if the fb voltage is lower than 80% v ref or higher than 120% v ref , the pgood pin will be pulled low. pvcc the regulator provides 5v power to supply the internal control circuit. 1 f ceramic capacitor for decoupling and stability is required. soft-start in order to prevent the converter output voltage from overshooting during the startup period, the soft-start function is necessary. the soft-start time is adjustable by an external capacitor. current protection the inductor current is monitored via the internal switches cycle-by-cycle. once the output voltage drops under uv threshold, the rt2810a/b will enter hiccup mode or latch off mode. uvlo protection to protect the chip from operating at insufficient supply voltage, the uvlo is needed. when the input voltage of vin is lower than the uvlo falling threshold voltage, the device will be lockout. thermal shutdown when the junction temperature exceeds the otp threshold value, the ic will shut down the switching operation. once the junction temperature cools down and is lower than the otp lower threshold, the converter will autocratically resume switching. por & reg ugate lgate driver boot pvcc control vbias on-time v in fb min. off-time ripple gen. v ref zc comparator ss sw gnd en pvcc oc + - 6a pvcc uv & ov vin comparator + - fb 0.9 v ref pgood +
rt2810a/b 4 ds2810a/b-06 november 2016 www.richtek.com ? copyright 2016 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. (v in = 12v, t a = ? 40 c to 125 c, unless otherwise specified) electrical characteristics recommended operating conditions (note 4) ? supply voltage, vin ------------------------------------------------------------------------------------------------ 4.5v to 18v ? junction temperature range -------------------------------------------------------------------------------------- ? 40 c to 125 c absolute maximum ratings (note 1) ? supply voltage, vin ------------------------------------------------------------------------------------------------ ? 0.3v to 20v ? switch voltage, sw ------------------------------------------------------------------------------------------------ ? 0.3v to (v in + 0.3v) ? sw, (<10n s) ---------------------------------------------------------------------------------------------------------- ? 5v to 26.3v ? boot to sw --------------------------------------------------------------------------------------------------------- ? 0.3v to 6v ? en to gnd ------------------------------------------------------------------------------------------------------------- ? 0.3v to 6v ? other pins voltage -------------------------------------------------------------------------------------------------- ? 0.3v to 6v ? power dissipation, p d @ t a = 25 c uqfn-16jl 3x3 (fc) ----------------------------------------------------------------------------------------------- 3.623w ? package thermal resistance (note 2) uqfn-16jl 3x3 (fc), ja ------------------------------------------------------------------------------------------ 27.6 c/w uqfn-16jl 3x3 (fc), jc ----------------------------------------------------------------------------------------- 5.6 c/w ? junction temperature range -------------------------------------------------------------------------------------- 150 c ? lead temperature (soldering, 10 sec.) ------------------------------------ ------------------------------------- 260 c ? storage temperature range -------------------------------------------------------------------------------------- ? 65 c to 150 c ? esd susceptibility (note 3) hbm (human body model) ---------------------------------------------------------------------------------------- 3kv mm (ma chine model) ----------------------------------------------------------------------------------------------- 300v cdm (charged device model) ------------------------------------------------------------------------------------ 1kv parameter symbol test conditions min typ max unit supply current shutdown current i shdn v en = 0v -- 1.5 20 ? a quiescent current i q v en = 2v, v fb = 1v -- 0.8 1.2 ma logic threshold en voltage logic-high 1.1 1.2 1.3 v hysteresis -- 0.2 -- v ref voltage feedback threshold voltage v ref 4.5v ? v in ? 18v, t a = ? 40c to 125c 0.693 0.7 0.707 v feedback input current i fb v fb = 0.71v ? 0.1 -- 0.1 ? a pvcc output pvcc output voltage v pvcc 6v ? v in ? 18v, 0 < i pvcc ? 5ma -- 5 -- v line regulation 6v ? v in ? 18v, i pvcc = 5ma -- -- 20 mv load regulation 0 ? i pvcc ? 5ma -- -- 100 mv output current i pvcc v in = 6v, v pvcc = 4v -- 150 -- ma
rt2810a/b 5 ds2810a/b-06 november 2016 www.richtek.com ? copyright 2016 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. note 1. stresses beyond those listed ? absolute maximum ratings ? may cause permanent damage to the device. these are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions may affect device reliability. note 2. ja is measured at t a = 25 c on a high effective thermal conductivity four-layer test board. the case position of jc is on the top of the package. note 3. devices are esd sensitive. handling precaution is recommended. note 4. the device is not guaranteed to function outside its operating conditions. parameter symbol test conditions min typ max unit r ds(on) switch on-resistance high-side r ds(on)_h -- 12 -- m ? low-side r ds(on)_l -- 5.4 -- switch current limit switch current limit i lim r lim = 80k 10.8 13.3 -- a thermal shutdown thermal shutdown threshold t sd -- 150 -- ? c on-time timer control on-time t on v in = 12v, v out = 1.05v, r rt = 150k -- 200 -- ns minimum on-time t on(min) -- 60 -- ns minimum off-time t off(min) -- 230 -- ns soft-start ss charge current v ss = 0v 5 6 7 ? a uvlo uvlo threshold wake up v in 4 4.2 4.4 v hysteresis -- 0.5 -- switching frequency f sw r rt = 106k 600 700 800 khz r rt = 150k 430 500 570 r rt = 250k 250 300 350 power good pgood threshold fb rising 85 90 95 %v fb fb falling -- 80 -- pgood sink current pgood = 0.1v 10 20 -- ma ovp and uvp protection ovp threshold 115 120 125 %v fb ovp propagation delay -- 10 -- ? s uvp threshold 55 60 65 %v fb uvp hysteresis -- 17 -- %v fb uvp propagation delay -- 250 -- ? s
rt2810a/b 6 ds2810a/b-06 november 2016 www.richtek.com ? copyright 2016 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. typical application circuit pgood rt2810a/b pvcc fb v in 10f x 2 c1 0.1f c2 boot l1 1h 0.1f c6 22f x 3 c7 sw ss 10nf c5 1f c4 v out 1.4v 20k r2 c3 v pvcc vin 6 8 5 10 to 14 9 20k r1 7 en 15 gnd 2 3 enable agnd 1 rt r rt 4 rlim r lim 16 r lim = 172k, ocp typical 6a r lim = 94k, ocp typical 11.4a r lim = 80k, ocp typical 13.3a r lim = 66k, ocp typical 16a table 1. suggested component values v out (v) r1 (k ? ) r2 (k ? ) c3 (pf) l1 ( ? h) c7 ( ? f) 1 8.66 20 -- 1 66 1.4 20 20 -- 1 66 1.8 31.6 20 ? 10 1 66 2.5 51.1 20 ? 10 1.2 66 5 124 20 ? 22 2 66 ?
rt2810a/b 7 ds2810a/b-06 november 2016 www.richtek.com ? copyright 2016 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. typical operating characteristics output voltage vs. input voltage 1.10 1.12 1.14 1.16 1.18 1.20 1.22 1.24 1.26 1.28 1.30 4681012141618 input voltage (v) output voltage (v) v out = 1.2v rt2810a i out = 0a i out = 6a i out = 9a output voltage vs. input voltage 1.10 1.12 1.14 1.16 1.18 1.20 1.22 1.24 1.26 1.28 1.30 4 6 8 1012141618 input voltage (v) output voltage (v) v out = 1.2v rt2810b i out = 0a i out = 6a i out = 9a efficiency vs. output current 70 74 78 82 86 90 94 98 0246810 output current (a) efficiency (%) rt2810b : pwm, v in = 5v, f sw = 500khz v out = 1v v out = 1.1v v out = 1.2v v out = 1.5v v out = 1.8v v out = 3.3v efficiency vs. output current 70 74 78 82 86 90 94 98 0246810 output current (a) efficiency (%) rt2810a : psm, v in = 5v, f sw = 500khz v out = 1v v out = 1.1v v out = 1.2v v out = 1.5v v out = 1.8v v out = 3.3v efficiency vs. output current 70 74 78 82 86 90 94 98 0246810 output current (a) efficiency (%) rt2810a : psm, v in = 12v, f sw = 500khz v out = 1v v out = 1.1v v out = 1.2v v out = 1.5v v out = 1.8v v out = 3.3v v out = 5v efficiency vs. output current 70 74 78 82 86 90 94 98 0246810 output current (a) efficiency (%) rt2810b : pwm, v in = 12v, f sw = 500khz v out = 1v v out = 1.1v v out = 1.2v v out = 1.5v v out = 1.8v v out = 3.3v v out = 5v
rt2810a/b 8 ds2810a/b-06 november 2016 www.richtek.com ? copyright 2016 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. frequency vs. r rt resistor 300 350 400 450 500 550 600 650 700 100 115 130 145 160 175 190 205 220 235 250 r rt (k ) frequency (khz) 1 v in = 12v feedback threshold vs. temperature 0.694 0.695 0.696 0.697 0.698 0.699 0.700 0.701 0.702 0.703 0.704 0.705 0.706 0.707 -50 -25 0 25 50 75 100 125 temperature (c) feedback threshold (v ) v in = 17v v in = 12v v in = 4.5v frequency vs. input voltage 300 350 400 450 500 550 600 650 700 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 input voltage (v) frequency (khz) 1 v out = 1.2v frequency vs. temperature 300 350 400 450 500 550 600 650 700 -50 -25 0 25 50 75 100 125 temperature (c) frequency (khz) 1 v in = 12v, v out = 1.2v output voltage vs. output current 1.10 1.12 1.14 1.16 1.18 1.20 1.22 1.24 1.26 1.28 1.30 012345678910 output current (a) output voltage (v) v out = 1.2v rt2810b v in = 17v v in = 12v v in = 6v output voltage vs. output current 1.10 1.12 1.14 1.16 1.18 1.20 1.22 1.24 1.26 1.28 1.30 012345678910 output current (a) output voltage (v) v out = 1.2v v in = 17v v in = 12v v in = 6v rt2810a
rt2810a/b 9 ds2810a/b-06 november 2016 www.richtek.com ? copyright 2016 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. time (40 s/div) output ripple voltage v in = 12v, v out = 1.2v, i out = 50ma rt2810a i lx (2a/div) v out (50mv/div) v lx (10v/div) time (100 s/div) load transient response v in = 12v, v out = 1.2v, i out = 5a to 10a i out (5a/div) v out (50mv/div) rt2810a time (100 s/div) load transient response v in = 12v, v out = 1.2v, i out = 5a to 10a i out (5a/div) v out (50mv/div) rt2810b time (1 s/div) output ripple voltage v in = 12v, v out = 1.2v, i out = 50ma rt2810b i lx (5a/div) v out (10mv/div) v lx (10v/div) time (100 s/div) load transient response v in = 12v, v out = 1.2v, i out = 0.1a to 10a i out (5a/div) v out (50mv/div) rt2810b time (100 s/div) load transient response v out (50mv/div) v in = 12v, v out = 1.2v, i out = 0.1a to 10a rt2810a i out (5a/div)
rt2810a/b 10 ds2810a/b-06 november 2016 www.richtek.com ? copyright 2016 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. time (2ms/div) uvp short (latch mode) i lx (10a/div) v out (1v/div) v lx (10v/div) v in = 12v, v out = 1.2v, i out = short to gnd time (4ms/div) power on from en v in = 12v, v out = 1.2v, i out = 10a rt2810b i lx (10a/div) v en (5v/div) v out (1v/div) v lx (10v/div) time (4ms/div) power off from en v in = 12v, v out = 1.2v, i out = 10a rt2810b i lx (10a/div) v en (5v/div) v out (1v/div) v lx (10v/div) time (10ms/div) uvp short (hiccup mode) v in = 12v, v out = 1.2v, i out = short to gnd i lx (10a/div) v out (500mv/div) v lx (10v/div) time (1 s/div) output ripple voltage v in = 12v, v out = 1.2v, i out = 5a rt2810a/b i lx (5a/div) v out (10mv/div) v lx (10v/div) time (1 s/div) output ripple voltage v in = 12v, v out = 1.2v, i out = 10a rt2810a/b i lx (10a/div) v out (10mv/div) v lx (10v/div)
rt2810a/b 11 ds2810a/b-06 november 2016 www.richtek.com ? copyright 2016 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. inductor saturation current should be chosen over ic's current limit. input capacitor selection the input filter capacitors are needed to smooth out the switched current drawn from the input power source and to reduce voltage ripple on the input. the actual capacitance value is less important than the rms current rating (and voltage rating, of course). the rms input ripple current (i rms ) is a function of the input voltage, output voltage, and load current : out in rms out(max) in out v v i = i 1 vv ?? ceramic capacitors are most often used because of their low cost, small size, high rms current ratings, and robust surge current capabilities. however, take care when these capacitors are used at the input of circuits supplied by a wall adapter or other supply connected through long, thin wires. current surges through the inductive wires can induce ringing at the rt2810a/b input which could potentially cause large, damaging voltage spikes at vin. if this phenomenon is observed, some bulk input capacitance may be required. ceramic capacitors (to meet the rms current requirement) can be placed in parallel with other types such as tantalum, electrolytic, or polymer (to reduce ringing and overshoot). choose capacitors rated at higher temperatures than required. several ceramic capacitors may be paralleled to meet the rms current, size, and height requirements of the application. the typical operating circuit uses two 10 f and one 0.1 f low esr ceramic capacitors on the input. output capacitor selection the rt2810a/b are optimized for ceramic output capacitors and best performance will be obtained using them. the total output capacitance value is usually determined by the desired output voltage ripple level and transient response requirements for sag (undershoot on positive load steps) and soar (overshoot on negative load steps). output ripple output ripple at the switching frequency is caused by the inductor current ripple and its effect on the output capacitor's esr and stored charge. these two ripple components are called esr ripple and capacitive ripple. since ceramic capacitors have extremely low esr and relatively little capacitance, both components are similar in amplitude and both should be considered if ripple is critical. application information inductor selection selecting an inductor involves specifying its inductance and also its required peak current. the exact inductor value is generally flexible and is ultimately chosen to obtain the best mix of cost, physical size, and circuit efficiency. lower inductor values benefit from reduced size and cost and they can improve the circuit's transient response, but they increase the inductor ripple current and output voltage ripple and reduce the efficiency due to the resulting higher peak currents. conversely, higher inductor values increase efficiency, but the inductor will either be physically larger or have higher resistance since more turns of wire are required and transient response will be slower since more time is required to change current (up or down) in the inductor. a good compromise between size, efficiency, and transient response is to use a ripple current ( i l ) about 15% to 40% of the desired full output load current. calculate the approximate inductor value by selecting the input and output voltages, the switching frequency (f sw ), the maximum output current (i out(max) ) and estimating a i l as some percentage of that current. ? ? ?? ??? out in out in sw l vvv l = vf i once an inductor value is chosen, the ripple current ( i l ) is calculated to determine the required peak inductor current. ? ? ?? ? ?? ? ? ? ? out in out l in sw l l(peak) out(max) l l(vally) out(max) vvv i= vf l i i = i 2 i i = i 2
rt2810a/b 12 ds2810a/b-06 november 2016 www.richtek.com ? copyright 2016 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. ? ripple ripple(esr) ripple(c) v = v v ?? ripple(esr) l esr v = ir ? ?? l ripple(c) out sw i v = 8c f feed-forward capacitor (c ff ) the rt2810a/b are optimized for ceramic output capacitors and for low duty cycle applications. however for high-output voltages, with high feedback attenuation, the circuit's response becomes over-damped and transient response can be slowed. in high-output voltage circuits (v out > 3.3v) transient response is improved by adding a small ? feed-forward ? capacitor (c ff ) across the upper fb divider resistor (figure 1), to increase the circuit's q and reduce damping to speed up the transient response without affecting the steady-state stability of the circuit. choose a suitable capacitor value that following below step. ? get the bw the quickest method to do transient response form no load to full load. confirm the damping frequency. the damping frequency is bw. figure 1. c ff capacitor setting ? c ff can be calculated base on below equation : ff 1 c 2 3.1412 r1 bw 0.8 ? ???? rt2810a/b gnd fb r1 r2 v out c ff bw soft-start (ss) the rt2810a/b soft-start uses an external capacitor at ss to adjust the soft-start timing according to the following equation : ?? ? ? ?? ss ss cnf0.7 t ms i a ? ? following below equation to get the minimum capacitance range in order to avoid uv occur. out out lim ss ref cv0.61.2 t (i load current) 0.8 t6 a c v ??? ? ?? ? ? do not leave ss unconnected. enable operation (en) for automatic start-up, the low-voltage en pin must be connected to vin with a 100k resistor. en can be externally pulled to vin by adding a resistor-capacitor delay (r en and c en in figure 2). calculate the delay time using en's internal threshold where switching operation begins (1.2v, typical). an external mosfet can be added to implement digital control of en (figure 3). in this case, a 100k pull-up resistor, r en , is connected between vin and the en pin. mosfet q1 will be under logic control to pull down the en pin. to prevent enabling circuit when vi n is smaller than the vout target value or some other desired voltage level, a resistive voltage divider can be placed between the input voltage and ground and connected to en to create an additional input under voltage lockout threshold (figure 4). figure 2. external timing control rt2810a/b en gnd v in r en c en en
rt2810a/b 13 ds2810a/b-06 november 2016 www.richtek.com ? copyright 2016 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. figure 4. resistor divider for lockout threshold setting figure 3. digital enable control circuit rt2810a/b en gnd 100k v in r en q1 enable rt2810a/b en gnd v in r en1 r en2 figure 5. output voltage setting place the fb resistors within 5mm of the fb pin. choose r2 between 10k and 100k to minimize power consumption without excessive noise pick-up and calculate r1 as follows : out r2 (v 0.7) r1 0.7 ?? ? output voltage setting set the desired output voltage using a resistive divider from the output to ground with the midpoint connected to fb. the output voltage is set according to the following equation : v out = 0.7 x (1 + r1 / r2) rt2810a/b gnd fb r1 r2 v out for output voltage accuracy, use divider resistors with 1% or better tolerance. figure 6. external bootstrap diode sw boot 5v 0.1f rt2810a/b external boot bootstrap diode when the input voltage is lower than 5.5v it is recommended to add an external bootstrap diode between vin (or vinr) and the boot pin to improve enhancement of the internal mosfet switch and improve efficiency. the bootstrap diode can be a low cost one such as 1n4148 or bat54. external boot capacitor series resistance the internal power mosfet switch gate driver is optimized to turn the switch on fast enough for low power loss and good efficiency, but also slow enough to reduce emi. switch turn-on is when most emi occurs since v sw rises rapidly. during switch turn-off, sw is discharged relatively slowly by the inductor current during the dead time between high-side and low-side switch on-times. in some cases it is desirable to reduce emi further, at the expense of some additional power dissipation. the switch turn-on can be slowed by placing a small (<47 ) resistance between boot and the external bootstrap capacitor. this will slow the high-side switch turn-on and v sw 's rise. to remove the resistor from the capacitor charging path (avoiding poor enhancement due to undercharging the boot capacitor), use the external diode shown in figure 6 to charge the boot capacitor and place the resistance between boot and the capacitor/diode connection. pvcc capacitor selection decouple pvcc to gnd with a 1 f ceramic capacitor. high grade dielectric (x7r, or x5r) ceramic capacitors are recommended for their stable temperature and bias voltage characteristics.
rt2810a/b 14 ds2810a/b-06 november 2016 www.richtek.com ? copyright 2016 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. output under-voltage protection hiccup mode the rt2810ah/rt2810bh provides hiccup mode under- voltage protection (uvp). when the fb voltage drops below 70% of the feedback reference voltage, the output voltage drops below the uvp trip threshold for longer than 250 s (typical) then ic's uvp is triggered. uvp function will be triggered to shut down switching operation. if the uvp condition remains for a period, the rt2810 will retry automatically. when the uvp condition is removed, the converter will resume operation. the uvp is disabled during soft-start period. latch mode for the rt2810al/rt2810bl, it provides latch-off mode under voltage protection (uvp). when the fb voltage drops below 70% of the feedback reference voltage, the output voltage drops below the uvp trip threshold for longer than 250 s (typical) then ic's uvp is triggered. uvp function will be triggered to shut down switching operation. in shutdown condition, the rt2810 can be reset by en pin or power input vin. current limit the rt2810 current limit is a cycle-by-cycle ? valley ? type, measuring the inductor current through the synchronous rectifier during the off-time while the inductor current ramps down. the current is determined by measuring the voltage between source and drain of the synchronous rectifier. if the inductor current exceeds the current limit, the on- time one-shot is inhibited (mask high side signal) until the inductor current ramps down below the current limit. thus, only when the inductor current is well below the current limit is another on time permitted. this arrangement prevents the average output current from greatly exceeding the guaranteed current limit value, as typically occurs with other valley-type current limits. if the output current exceeds the available inductor current (controlled by the current limit mechanism), the output voltage will drop. if it drops below the output under-voltage protection level, the ic will enter uvp protection. the current limit of low side mosfet is adjustable by an external resistor connected to the rlim pin. the current limit range is from 6a to 16a. output over-voltage protection if the output voltage v out rises above the regulation level and lower 1.2 times regulation level, the high-side switch naturally remains off and the synchronous rectifier turns on. for rt2810bl, if the output voltage remains high, the synchronous rectifier remains on until the inductor current reaches the low side current limit. if the output voltage still remains high, then ic's switches remain that the synchronous rectifier turns on and high-side mos keeps off to operate at typical 500khz switching protection, again if inductor current reaches low side current limit, the synchronous rectifier will turn off until next protection clock. if the output voltage exceeds the ovp trip threshold (1.2 times regulation level) for longer than 5 s (typical), then ic's output over-voltage protection (ovp) is triggered. rt2810bl chip enters latch mode. for rt2810al, if the output voltage v out rises above the regulation level and lower 1.2 times regulation level, the high-side switch naturally remains off and the synchronous rectifier turns on until the inductor current reaches zero current. if the output voltage remains high, then ic's switches remain off. if the output voltage exceeds the ovp 67 lim lim 1 r = i105.58810 ?? ?? ? figure 7. current limit vs. r lim through extra resister r lim connect to rlim pin to setting the current limit value as figure 7, below offer approximate formula equation for design reference : current limit vs. r lim 6 7 8 9 10 11 12 13 14 15 16 65 75 85 95 105 115 125 135 145 155 165 175 185 r lim (k ) current limit (a)
rt2810a/b 15 ds2810a/b-06 november 2016 www.richtek.com ? copyright 2016 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. figure 9. derating curve of maximum power dissipation 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 25 50 75 100 125 ambient temperature (c) maximum power dissipation (w) 1 four-layer pcb thermal considerations for continuous operation, do not exceed absolute maximum junction temperature. the maximum power dissipation depends on the thermal resistance of the ic package, pcb layout, rate of surrounding airflow, and difference between junction and ambient temperature. the maximum power dissipation can be calculated by the following formula : p d(max) = (t j(max) ? t a ) / ja where t j(max) is the maximum junction temperature, t a is the ambient temperature, and ja is the junction to ambient thermal resistance. for recommended operating condition specifications, the maximum junction temperature is 125 c. the junction to ambient thermal resistance, ja , is layout dependent. for uqfn-16jl 3x3 (fc) package, the thermal resistance, ja , is 27.6 c/w on a standard four-layer thermal test board. the maximum power dissipation at t a = 25 c can be calculated by the following formula : p d(max) = (125 c ? 25 c) / (27.6 c/w) = 3.623w for uqfn-16jl 3x3 (fc) package the maximum power dissipation depends on the operating ambient temperature for fixed t j(max) and thermal resistance, ja . the derating curve in figure 9 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. trip threshold (1.2 times regulation level) for longer than 5 s (typical), the ic's ovp is triggered. rt2810al chip enters latch mode. for rt2810bh, if the output voltage remains high, the synchronous rectifier remains on until the inductor current reaches the low side current limit. if the output voltage still remains high, the synchronous rectifier turns on and high-side mosfet keeps off to operate at typical 500khz switching protection, again if inductor current reaches low side current limit, the synchronous rectifier will turn off until next protection clock. rt2810bh is without ovp latch function and recover when ov condition release. for rt2810ah, if the output voltage remains high, the synchronous rectifier remains on until the inductor current reaches zero current. if the output voltage still remains high, then ic's switches remain off. rt2810ah is without ovp latch function and recover when ov condition release. switching frequency setting the switching frequency can be set by using extra resister r rt . switching frequency range is from 300khz to 700khz. through extra resister r rt connect to rt pin to setting the switching frequency f sw as figure 8, below offer approximate formula equation : setting frequency = f sw (khz) figure 8. frequency vs. r rt resistor ?? 6 54 rt sw 10 r = f 1.374 10 1.541 10 ?? ???? frequency vs. r rt resistor 300 350 400 450 500 550 600 650 700 100 115 130 145 160 175 190 205 220 235 250 r rt (k ) frequency (khz) 1
rt2810a/b 16 ds2810a/b-06 november 2016 www.richtek.com ? copyright 2016 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. layout consideration ? follow the pcb layout guidelines for optimal performance of the device. ? keep the traces of the main current paths as short and wide as possible. ? put the input capacitor as close as possible to vin and vin pins. ? sw node is with high frequency voltage swing and should be kept at small area. keep analog components away from the sw node to prevent stray capacitive noise pickup. ? connect feedback network behind the output capacitors. keep the loop area small. place the feedback components near the device. ? connect all analog grounds to common node and then connect the common node to the power ground behind the output capacitors. ? an example of pcb layout guide is shown in figure 10 and figure 11 for reference. rt pvcc agnd fb vin sw sw sw boot gnd rlim sw sw ss en pgood 6 15 12 11 10 9 1 2 3 4 13 16 7 5 14 8 the r en component must be connected. c boot c out v in r en c ss r pgood c in v in l v out 5v v out r1 r2 gnd r lim sw should be connected to inductor by wide and short trace. keep sensitive components away from this trace . power good indicator open-drain output. connect ic pin trace as wide as possible for thermal consideration add via for thermal consideration keep sensitive components away from this c boot . input capacitor must be placed as close to the ic as possible. the r rt resistor must be connected as close to the device as possible. keep sensitive components away. the feedback components must be connected as close to the device as possible. the r lim resistor must be connected as close to the device as possible. keep sensitive components away. internal regulator output. connect a 1f capacitor to gnd to stabilize output voltage. agnd must be connected clear ground. top layer figure 10. pcb layout guide (top layer)
rt2810a/b 17 ds2810a/b-06 november 2016 www.richtek.com ? copyright 2016 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. figure 11. pcb layout guide (bottom layer) v in gnd bottom layer add via for thermal consideration suggested inductors for typical application circuit component supplier part no. inductance ( ? h) dcr (m ? ) dimensions (mm) we 7443320100 1 1.85 12.1 x 11.4 x 9.5 we 744325120 1.2 1.8 10.2 x 10.2 x 4.7 cyntec cmmb104t-1r5ms 1.5 3.8 10.3 x 11.5 x 4 recommended component selection for typical application. component supplier part no. capacitance ( ? f) case size murata grm31cr61e106k 10 1206 tdk c3225x5r1e106k 10 1206 taiyo yuden tmk316bj106ml 10 1206 murata grm31cr60j476m 47 1206 tdk c3225x5r0j476m 47 1210 taiyo yuden emk325bj476mm 47 1210 murata grm32er71c226m 22 1210 tdk c3225x5r1c226m 22 1210
rt2810a/b 18 ds2810a/b-06 november 2016 www.richtek.com ? copyright 2016 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. outline dimension min. max. min. max. a 0.500 0.600 0.020 0.024 a1 0.000 0.050 0.000 0.002 a3 0.100 0.175 0.004 0.007 d 2.900 3.100 0.114 0.122 e 2.900 3.100 0.114 0.122 b 0.320 0.420 0.013 0.017 b1 0.458 0.558 0.018 0.022 b2 0.200 0.300 0.008 0.012 l 2.325 2.425 0.092 0.095 l1 1.300 1.400 0.051 0.055 l2 0.325 0.425 0.013 0.017 l3 1.350 1.450 0.053 0.057 l4 0.350 0.450 0.014 0.018 e k k1 k2 k3 k4 k5 k6 k7 symbol dimensions in millimeters dimensions in inches 0.500 0.020 0.325 0.013 1.224 0.048 2.175 0.086 2.675 0.105 2.675 0.105 0.785 0.031 1.675 0.066 2.175 0.086 u-type 16jl qfn 3x3 (fc) package
rt2810a/b 19 ds2810a/b-06 november 2016 www.richtek.com richtek technology corporation 14f, no. 8, tai yuen 1 st street, chupei city hsinchu, taiwan, r.o.c. tel: (8863)5526789 richtek products are sold by description only. richtek reserves the right to change the circuitry and/or specifications without notice at any time. customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a richtek product. information furnish ed by richtek is believed to be accurate and reliable. however, no responsibility is assumed by richtek or its subsidiaries for its use; nor for any infringeme nts of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of r ichtek or its subsidiaries. footprint information package number of pin footprint dimension (mm) tolerance p p1 p2 p3 ay by ax c*12 c1 c2 c3*2 d*15 d1 k k1 k2 uqfn3*3 -16j(fc) 16 0.500 0.951 0.899 0.890 3.800 2.200 3.800 0.800 2.775 1.750 1.800 0.300 0.508 0.675 0.715 0.250 0.050 ?

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