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x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s april 2012 rev. 1.2. 2 exar corporation www.exar.com 48720 kato road, fremont ca 94538, usa tel. +1 510 668 - 70 00 C fax. +1 510 668 - 70 01 general description the XRP7708 and xrp7740 are quad - output pulse - width modulated (pwm) step - down dc - dc controller s with a built - in ldo for standby power and gpios. the device s provide a complete power mana gement solution in one ic and are fully programmab le via an i 2 c serial interface. independent digital pulse width modulator (dpwm) channels regulate output voltages and provide all required protection functions such as current limiti ng and over - voltage protection. each output voltage can be programmed fro m 0.9v to 5.1v without the need of an external voltage divider. the wide range of the programmable dpwm switching frequency (from 300 khz to 1.5 mhz) enables the user to optimize between efficiency and component size. input voltage range is from 6.5v to 20 v. an i 2 c bus interface is provided to program the ic as well as to communicate with the host for fault reporting and handling, power rail parameters monitoring, etc. the device offers a complete solution for soft - start and soft - stop. the start - up delay a nd ramp of each pwm regulator can be independently controlled. the device can start up a pre - biased pwm channel without causing large negative inductor current . applications ? multi channel programmable power supplies ? audio - video equipment ? industrial & tel ecom equipment ? processors & dsps based equipment features ? 4 channel step down controller ? 3ohm/1.8ohm driver C xrp7740 ? 5ohm/1.8ohm driver C XRP7708 ? programmable output voltage 0.9v - 5.1v ? programmable 1.5mhz dpwm frequency ? 6.5v - 20v single input voltage range ? up to 6 reconfigurable gpio pins ? fully programmable via i2c interface ? independent digital pulse width modulator (dpwm) channels ? complete monitoring and reporting ? complete power up/down sequencing ? full on board protection otp, uvlo, ocp and ovp ? built - in 3 .3v/5v ldo ? powerarchitect? design software ? green/halogen free 40 - pin tqfn typical application diagram fig. 1 : XRP7708 or xrp7740 application diagram XRP7708 xrp7740 ex posed pad: agnd
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 2 / 28 rev. 1.2. 2 absolute maximum rat ings these are stress ratings only and fu nctional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. exposure to absolute maximum rating conditions for extended periods of time may affect reliability. v cca, vccd, ldoout, glx, voutx ............................ 6v avdd, dvdd ........................................................ 2.0v vin1, vin2 ............................................................ 22v lxx .............................................................. - 1v to 22v logic inputs ............................................................. 6v bstx, ghx .................................................... v lxx + 5v storage temperature .............................. - 65c to 150c lead temperature (soldering, 10 sec) ................... 300c operating ratings operating input voltage vin x ........................ 6.5v to 20v jun ction temperature range .................... - 40c to 1 25c thermal resistance ja .................................... 24.3 c/w electrical specifica tions specifications with standard type are for an operating junction temperature of t j = 25c only; limits applying over the full operating junction temperature r ange are denoted by a ? . minimum and maximum limits are guaranteed through test, design, or statistical correlation. typical values represent the most likely parametric norm at t j = 25c, and are provided for reference purposes only. unless otherwise ind icated, v in 1 = 6.5 v to 20 v, v in 2 = 6.5 v to 20 v, enable=high, c gl = c gh = 1 n f. quiescent current parameter min. typ. max. units conditions vin supply current in standby 9 ma ldoout enabled (no load) no switching converter channels enabled i 2 c communica tion active switching frequency = 400khz vin supply current in shutdown 180 a en=0v, vin1=vin2=12v vin supply current 28 ma 4 channels running, gh and gh = 1nf load each vin=12v, switching frequency = 300khz vin supply current 50 ma 4 channels running, gh and gh = 1nf load each vin=12v, switching frequency = 1mhz step down controllers parameter min. typ. max. units conditions vout regulation accuracy - 20 20 mv ? 0.9 v vout 2.5v - 40 40 mv ? 2.6v vout 5.1v vout regulation range 0.9 5.1 ? programmable range of each channel 1 vout set point resolution 50 0.9 v vout 2.5v vout set point resolution 100 2.6 v vout 5.1v vout input current 1 u a ? 0.9 v < vout <= 2.5v vout input resistance 120 k ? 2.6 v vout 5.1v note 1: voltages above 5.1v can be obtained by using an external voltage divider.
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 3 / 28 rev. 1.2. 2 low drop - out regulator parameter min. typ. max. units conditions ldoout output voltage ldo=l ow 3.15 3.3 3.45 v ? 6.5v vin120v 0ma x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 4 / 28 rev. 1.2. 2 i 2 c specification parameter min. typ. max. units conditions i 2 c speed 400 khz based upon i 2 c master clock input pin low level, v il 1.0 v input pin high level, v i h 2.97 v hysteresis of schmitt trigger inputs, v hys 0.165 v output pin low level (open drain or collector) v ol 0.4 v i sink =3ma input leakage current - 10 10 a input is betw een 0.33v and 2.97v output fall time from v ihmin to v ilmax 20+0.1c b 2 250 ns with a bus capacitance from 10pf to 400pf capacitance for each i/o pin 10 pf note 2: c b is the capacitance one one bus in pf gate drivers parameter min. typ. max. units c onditions gh, gl rise and fall time 30 ns at 10% to 90% of full scale pulse. 1nf c load gh, gl pull - up on - state output resistance 5 ? XRP7708 gh, gl pull - up on - state output resistance 3 ? xrp7740 gh, gl pull - down on - state output resistance 1.8 ? both XRP7708 and xrp7740 gh, gl pull - down off - state output resistance 50 k ? vin=vccd=0v
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 5 / 28 rev. 1.2. 2 block diagram bst1 gpio 0-3 channel 1 C 6 gh1 vin1 gl1 lx1 pgnd1 vin2 vcc vdd ldoout hybrid dpwm digital pid feedback adc vtar dac prescaler ss & pd current adc 1 delay gate driver vout1 bst2 channel 2 gh2 gl2 lx2 pgnd2 hybrid dpwm digital pid feedback adc vtar dac prescaler ss & pd dead time gate driver vccd vout2 2-ch mux channel 3 channel 4 current adc 2 2-ch mux ldo 7-ch mux aux adc vout1 vout2 vout3 vout4 vtj stby lr gpio i2c sda,scl otp vref osc clock pwr good configuration registers vout3 vout4 uvlo fault handling fig. 2 : XRP7708 and xrp7740 block diagram
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 6 / 28 rev. 1.2. 2 pin assignment 30 29 28 27 26 25 24 23 21 22 19 18 16 17 15 14 12 13 11 10 1 2 3 4 5 6 7 8 9 32 33 35 34 36 37 39 38 40 20 31 avdd dvdd gpio0 gpio1 gpio2 gpio3 gpio4_sda gpio5_scl enable gl2 lx2 gh2 bst2 vccd bst4 gh4 lx4 gl4 pgnd4 agnd vout1 vout2 vout3 vout4 pgnd3 gl3 lx3 gh3 bst3 ldoout vin1 vin2 vcca pgnd1 gl1 lx1 gh1 bst1 pgnd2 dgnd exposed pad: agnd XRP7708 xrp7740 tqfn 6mm x 6mm fig. 3 : XRP7708 /40 pin assignment p in description name pin numbe r description vin1 39 power source for the internal linear regulators to generate vcca, vdd and the standby ldo (ldoout). place a decoupling capacitor close to the controller ic. also used in uvlo1 fault generation C if vin1 falls below the user programm ed limit, all channels are shut down. the vin1 pin needs to be tied to vin2 on the board with a short trace. vin2 38 if the vin2 pin voltage falls below the user programmed uvlo vin2 level all channels are shut down. the vin2 pin needs to be tied to vin1 on the board with a short trace . vcca 37 output of the internal 5v ldo. this voltage is internally used to power analog blocks. this pin should be bypassed with a minimum of 4.7uf to agnd vccd 26 gate drive input voltage. this is not an output voltage. this pin can be connected to vcca to provide power for the gate drive. vccd should be connected to vcca with the shortest possible trace and decouple with a minimum 1 f capacitor . alternatively, vccd could be connected to an external supply (not greater th an 5v). pgnd1 - pgnd4 36,31,16,21 gl return connection . ground connection for the low side gate driver. connect at low side fet source. connecting to the ground plane at the chip will inject noise into the local ground resulting in potential i 2 c communic ations problems and pwm jitter. avdd 1 output of the internal 1.8v ldo. a decoupling capacitor should be placed between avdd and agnd close to the chip (with short traces). dvdd 2 input for powering the internal digital logic. this pin should be connecte d to avdd.
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 7 / 28 rev. 1.2. 2 name pin numbe r description dgnd 10 digital ground. this pin should be connected to the ground plane at the exposed pad with a separate trace. agnd 11 analog ground. this pin should be connected to the ground plane at the exposed pad with a separate trace gl1 - gl4 35 ,30 ,17,22 output pin of the low side gate driver. connect directly to the respective gate of an external n - channel mosfet. gh1 - gh4 33 ,28,19,24 output pin of the high side gate driver. connect directly to the respective gate of an external n - channel mosfet. lx1 - lx4 34,29, 18, 23 lower supply rail for the high - side gate driver (ghx) . connect this pin to the switching node at the junction between the two external power mosfets and the inductor. these pins are also used to measure voltage drop across bottom mosfet s in order to provide output current information to the control engine. bst1 - bst4 32,27,20,25 high side driver supply pin (s) . connect bst to an external boost diode and a capacitor as shown in the front page diagram. the high side driver is connected betw een the bst pin and lx pin . gpio0 - gpio3 3,4,5,6 these pins can be configured as inputs or outputs to implement custom flags, power good signals and enable/disable controls. a gpio pin can also be programmed as an input clock synchronizing ic to external clock. refer to the gpio pins section and the external clock synchronization section for more information. gpio4_sda, gpio5_scl 7,8 i 2 c serial interface communication pins. these pin s can be re - progr ammed to perform gpio functions in applications when i 2 c bus is not used. vout1 - vout4 12,13,14,15 voltage sense. connect to the output of the corresponding power stage. ldoout 40 output of the s tandby ldo. it can be configured as a 5v or 3.3v output . a compensation capacitor should be used on this pin [ see application note]. enable 9 if enable is pulled high, the chip power s up (logic reset, registers configuration loaded, etc.). if pulled low for longer than 100us , the xrp 7708 /40 is placed into shutdown. see applications section for proper sequencing of this pin. agnd exposed pad analog ground. connect to analog ground (as noted above for pin 11). ordering information part number junction temp range marking package packing quantity note 1 default i 2 c address XRP7708ilb - f - 40c t j + 12 5c XRP7708ilb yyww x 40- pin t qfn bulk halogen free XRP7708ilbtr - f - 40c t j + 12 5c XRP7708ilb yyww x 40- pin t qfn 3 k/tape & reel halogen free xrp7740ilb - f - 40c t j +125c xrp77 40 ilb yyww x 40- pin tqfn bulk halogen free xrp7740ilbtr - f - 40 c t j +125c xrp7740 ilb yyww x 40- pin tqfn 3k/tape & reel halogen free xrp7740ilb - 0x180 - f - 40c t j +125c xrp7740 ilb yyww x 0x18 40- pin tqfn bulk halogen free 0x18 xrp7740ilbtr - 0x18 - f - 40c t j +125c xrp7740 ilb yyww x 0x18 40- pin tqfn 3k/tape & reel halo gen free 0x18 XRP7708evb XRP7708 evaluation board xrp7740evb xrp7740 evaluation board yy = year C ww = work week C x = lot number
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 8 / 28 rev. 1.2. 2 typical performance characteristics all data taken at t j = t a = 25c, unless otherwise specified - schematic and bom from application information section of this datasheet. fig. 4 : 12vin efficiency: single channel 300khz - channels not in use are disabled fet: si4944; inductor: 744314xxx 7x7x5mm fig. 5 : 12vin combined ef ficiency, 5v & 3v3 @ 5a, 1v8 & 1v @ 8a, 5v & 3v3 - fet: fds8984; inductor: 744314490 7x7x5mm 1v8 & 1v - fets: sir466 upper, sir464 lower; inductor: 7443551130 13x13x6.5mm fig. 6 : 12vin efficiency: single channel 300khz - channels not in use are disabled fet: fds8984; inductor:744310200 7x7x3mm fig. 7 : 12vin efficiency: single channel 1mhz - channels not in use are disabled fet: fds8984; inductor:744310200 7x7x3mm fig. 8 : simul taneous start - up configuration ch1:3.3v ch2:5v ch3:1v ch4:1.8v fig. 9 : simultaneous soft - stop ch1:3.3v ch2:5v ch3:1v ch4:1.8v
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 9 / 28 rev. 1.2. 2 fig. 10: sequential start - up configuration ch1:3.3v ch2:5v ch3:1v ch4:1.8v fig. 11: sequential soft - stop configuration ch1:5v ch2:3.3v ch3:1.8v ch4:1.2v vout shutdown = 0.8v, 3a load fig. 12 : startup into 3v prebias C 5v output ch1: vout(5v) fig. 13 : sequ ential soft - stop configuration vout shutdown = 0.8v, no load ch1:3.3v ch2:5v ch3:1v ch4:1.8v fig. 14 : load transient response ch1:iout (1a/div) ch2: vout (3.3v)
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 10/ 28 rev. 1.2. 2 fig. 15: XRP7708 temperature regulatio n 1.8v out (+/ - 1% vo window) fig. 16: XRP7708 temperature regulation 1.0v out (+/ - 1% vo window) fig. 17 7 : xrp7740 temperature regulation 1.8v out (+/ - 1% vo window) fig. 18 8 :xrp7740 temperature regulation 1.0v out (+/ - 1% vo window)
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 11/ 28 rev. 1.2. 2 features and benefit s general dpwm benefits: ? eliminate temperature and time variations associated with passive components in: ? output set point ? feedback compensation ? frequency set point ? under voltage loc k out ? input voltage measurement ? gate drive dead time ? tighter parameter tolerances including operating frequency set point ? easy configuration and re - configuration for different v out , iout, cout, and inductor selection by simply changing internal pid coeffic ients. no need to change external passives for a new output specification. ? higher integration: many external circuits can be handled by monitoring or modifying internal registers ? selectable dpwm frequency and controller clock frequency other benefits: ? a si ngle voltage is needed for regulation [no external ldo required]. ? i 2 c interface allows: ? communication with a system controller or other power management devices for optimized system function ? access to modify or read internal registers that control or monit or: ? output current ? input and output voltage ? soft - start/soft - stop time ? power good ? part temperature ? enable/disable outputs ? over current ? over voltage ? temperature faults ? adjusting fault limits and d isabling/enabling faults ? 6 configurable gpio pins, (4 if i 2 c is in use). pins can be configured in several ways: ? fault reporting (including ocp, ovp, temperature, soft - start in progress, power good) ? allows a logic level interface with other non - digital ics or as logic inputs to other devices ? possible to configure as traditional enable pin for all 4 outputs ? 2 gpios can be dedicate d to the i 2 c interface as required by the customers design ? frequency and synchronization capability ? selectable switching frequency between 300khz and 1.5mhz ? each output can be programmed to any one of 4 possible phases ? both internal clock and dpwm clock can be synchronized to external sources ? master, slave and stand - alone configurations are possible ? internal mosfet drivers ? internal fet drivers for each channel : iru ;53dqgiru;53 ? built - in automatic dead - time adjustment ? 30ns rise and fall times ? soft - start into a pre - biased load and soft - stop with programmable endpoint voltage ? powerarchitect? design and configuration software: ? in its simple st form only vin, vout, and iout for each channel is required. ? the software calculates configuration register content based upon customer requirements. pid coefficients for correct loop response (for automatic or customized designs) can be generated and sent to the device. ? configurations can be saved and/or recalled ? gpios can be configured easily and intuitively ? synchronization configuration can be adjusted ? interface can be used for real - time debugging and optimization ? customizing XRP7708/40 with customer parameters ? once a configuration is finalized it can be sent to exar and can reside in pre - programmed parts that customers can order with an individual part number. ? allows parts to be used without i 2 c interface system benefits: ? reliability is enhanced via communication with the system controller which can obtain real time data on an output voltage, input voltage and current. ? system proces sors can communicate with the XRP7708 /40 directly to obtain data or make adjustments to react to circuit conditions ? a sys tem process or could also be configured to log and analyze operating history, perform diagnostics and if required, take the supply off - line after m aking other system adjustments. ? if customer field service is a possibility for your end product, parameter re porting and history would provide additional capabilities for troubleshooting or aid in future system upgrades.
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 12/ 28 rev. 1.2. 2 functional descripti on and operation the XRP7708 and xrp7740 are quad - output digital pulse width modulation (dpwm) controller s with integrated gate drivers for the use in synchronous buck switching regulators. each output voltage can be programmed from 0.9v to 5.1v without the need of an external voltage divider. the wide range of the programmable dpwm switching frequency (from 300 k hz to 1.5 mh z) enables the user to optimize for efficiency or component sizes. the digital regulation loop requires no external passive components for network compensation. the loop performance does not need to be compromised due to component tolerance, aging, and op erating condition. each digital controller provides a number of safety features, such as over - current protection (ocp) and over - voltage protection (ovp). the chip also provides over - temperature protection (otp) and under - voltage lock - out (uvlo) for two in put voltage rails. the XRP7708 /40 also has up to 6 gpios and a standby linear regulator to provide standby power. an i 2 c bus interface is provided to program the ic as well as to communicate with the host for fault reporting and handling, power rail monito ring, channel enable and disable, standby low drop - out regulator voltage reconfiguration, and standby ldo enable and disable. the XRP7708 and xrp7740 offer a complete solution for soft - start and soft - stop. the delay and ramp of each pwm regulator can be in dependently controlled. when a pre - bias voltage is present, the device holds both high - side and low - side mosfets off until the reference voltage ramps up higher than the output voltage. as a result, large negative inductor current and output voltage distur bance are avoided. during soft - stop, the output voltage ramps down with a programmable slope until it reaches a pre - set stop voltage. this pre - set value can be programmed between within zero volts and the target voltage with the same set target voltage re solution (see shutdown waveforms in applications). for brevity, only the XRP7708 will be referred to unless there is a specific difference between the devices. r egister t ypes there are two types of registers in the XRP7708: read/write registers and read - on ly registers. the read/write registers are used for the control functions of the ic and can be programmed using configuration non - volatile memory (nvm) or through an i 2 c command. the read - only registers are for feedback functions such as error/warning flag s and for reading the output voltage or current. n on - v olatile c onfiguration m emory the non - volatile memory (nvm) in XRP7708 stores the configuration data for the chip and all of the power rails. this memory is normally configured during manufacturing time. once a specific bit of the nvm is programmed, that bit can never be reprogrammed again [i.e. one - time programmable]. during chip power up, the contents in the nvm are automatically transferred to the internal registers of the chip. programmed cells have b een verified to be permanent for at least 10 years and are highly reliable. p ower u p a nd s equencing r equirements the xrp77 08 can be programmed to sequence its outputs for nearly any imaginable loading requirement. however, there are some important sequenc ing requirements for the xrp 7708 itself. when power is applied to the XRP7708 , the 5v vcca and 1.8v avdd regulators must come up and stabilize to provide power for the analog and digital blocks of the ic. the e nable pin must remain below its logic level h igh threshold until the a vdd is regulating to ensure proper loading of the configuration registers. for systems that control the e nable signal through a microcontroller or other processor, this is simply a matter of providing the proper delay to the e nabl e signal after
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 13/ 28 rev. 1.2. 2 power up. however, most users will want the part to automatically power up when power is applied to the system. to that end there are a number of recommended solutions. the most ideal sequencing method is to provide an rc time constant del ay from dvdd to the e nable pin. a 10 kohm resistor and a 0.1uf are all that is required. if the system needs to externally control the e nable pin as well, it is recommended that the e nable pin be pulled to ground using an open drain i/o. using 3.3v activ e logic would back feed dvdd and exceed the maximum rated voltage of the pin. for those using active 3.3v or 5v logic on the e nable pin an rc delay from vcca to the e nable pin may be used. when using an rc delay from vcca, attention must be paid to the am ount of bypass capacitance loading avdd since it will delay the time it takes for avdd to power up and regulate. the avdd and dvdd pins do not require more than 2.2uf for proper bypassing. see figure 21 for the recommended components for sequencing the e nable pin through an rc delay from vcca. if more capacitance is added to avdd and dvdd, the time constant must be increased. once enable is asserted, an internal chip_ready flag goes high and enables the i 2 c to acknowledge the hosts serial commands. chan nels that are configured as always - on channels are enabled. channels that are configured to be enabled by gpios are also enabled if the respective gpio is asserted. enable pin vcca 10k .1uf fig. 19 : rc delay for enable taken from vcca in almost all c ases, a simple check will ensure proper sequencing has been achieved . vcca regulate s a t approximately 4.6v when the enable pin is logic level low and at 5.1v when e nable is asserted. vcca will typically power up and regulate before avdd and because the in ternal logic is not yet powered up there is no internal shutdown signal, it will regulate at 5.1v. once avdd has reached sufficient voltage (and e nable is low) it will assert the internal shutdown signal and vcca will reduce its regulated voltage to 4.6v. when the e nable is asserted, the chip will power up and vcca will regulate at 5.1v. if our device is sequenced properly, vcca will achieve 5.1v then drop down to 4.6v and toggle back to 5.1v. see figure 22 for an example.
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 14/ 28 rev. 1.2. 2 fig. 19 0 : vcca (green) startup waveform s tandby l ow d rop - out r egulator this 100ma low drop - out regulator can be programmed as 3.3v or 5v in set_stbldo_en_config r egister. its output is seen on the ldoout pin. this ldo is fully controllable via the enable pin (co nfigured to turn on as soon as power is applied), a gpio, and/or i 2 c communication. the standby ldo should be bypassed with a minimum of 2.2uf ceramic capacitor. e nabling , d isabling and r eset the xrp 7708 is enabled via raising the enable pin high. the chi p can then be disabled by lowering the same enable pin. there is also the capability for resetting the chip via an i 2 c softreset command. for enabling a specific channel, there are several ways that this can be achieved. the chip can be configured to ena ble a channel at start - up as the default configuration residing in the non - volatile configuration memory of the ic. the channels can also be enabled using gpio pins and/or an i 2 c bus serial command. the registers that control the channel enable functions a re the set_en_config and set_ch_en_i 2 c. i nternal g ate d rivers the XRP7708 integrates internal gate drivers for all 4 pwm channels. these drivers are optimized to drive both high - side and low side n - mosfets for synchronous operation. both high side and low side drivers have the capability of driving 1 nf load with 30 ns rise and fall time. the drivers have built - in non - overlapping circuitry to prevent simultaneous conduction of the two mosfets. f ault h andling while the chip is operating there are four differ ent types of fault handling: ? under voltage lockout (uvlo) monitors the input voltage to the chip, and the chip will shutdown all channels if the voltage drops to critical levels. ? over temperature protection (otp) monitors the temperature of the chip, and t he chip will shutdown all channels if the temperature rises to critical levels. ? over voltage protection (ovp) monitors the voltage of channel and will shutdown the channel if it surpasses its voltage threshold.
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 15/ 28 rev. 1.2. 2 ? over current protection (ocp) monitors the cu rrent of a channel, and will shutdown the channel if it surpasses its current threshold. the channel will be automatically restarted after a 200ms delay. under voltage lockout (uvlo) there are two locations where the under voltage can be sensed: vin1 and vin2. the set_uvlo_warn_vinx register that sets the under voltage warning set point condition at 100mv increments . when the warning threshold is reached, the host is informed via a gpio or by reading the read_warn_flag register. the set_uvlo_targ_vinx regi ster that controls the under voltage fault set point condition at 100mv increments . this fault condition will be indicated in the read_fault_warn register. when an under voltage fault condition occurs (either on vin1 or vin2), the fault flag register is s et and all of the XRP7708 outputs are shut down. the measured input voltages can be read back using the read_vin1 or read_vin2 register , and both registers have a resolution of 100mv per lsb. when the uvlo condition clears (voltage rises above the uvlo wa rning threshold), the chip can be configured to automatically restart. vin 1 this is a multi - function pin that provides power to both the s tandby linear regulator and internal linear regulators to generate v cca, vdd, and the standby ldo (ldout). it is also used as a uvlo detect ion pin. if vin1 falls below its user programmed limit, all channels are shut down. vin 2 vin2 is required to be tied to vin1 pin. it can be used as a uvlo detect ion pin. if vin2 falls below its user programmed limit, all channels are shut down. temperature monitoring and over temperature protection (otp) ? r eading the junction temperature this register allows the user to read back the temperature of the ic. the temperature is expressed in kelvin with a maximum range of 520k , a minimum o f 200k , and an lsb of 5 degrees k . the temperature can be accessed by reading the read_ v t j register. ? over temperature warning there are also warning and fault flags that get set in the read_ovv_uvlo_ovt_flag register. the warning threshold is configurable to 5 or 10 degrees c below the fault threshold . when the junction temperature reaches 5 or 10 degrees c below the user defined set point , the over - temperature warning bit [ ot p w ] gets set in the read_ovv_uvlo_ovt_flag register to warn the user that the ic might go into an over temperature condition (and shutdown all of the regulators) . ? over temperature fault if the over temperature condition occurs both the otp and ot p w bits will be set in the read_ovv_uvlo_ovt_flag register and the ic will shut down all ch annels (but i 2 c will remain operational) . the actual over temperature threshold can be set by the user by using a 7bit set_thermal_shdn register with an lsb of 5k. if the over temperature fault condition clears, then the ic can be set to restart the chip a utomatically. the restart temperature threshold can be set by the set_thermal_restart register.
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 16/ 28 rev. 1.2. 2 o utput v oltage s etting and m onitoring the output v oltage setting is controlled by the set_ vout _target_chx register. this register allows the user to set the out put voltage with a resolution of 50mv for output voltages between 0 and 2.5v and with a resolution of 100mv for output voltages between 2.6v and 5.1v. o utput voltage s higher than 5.1v can be achieved by adding an external voltage divider network. the outpu t voltage of a particular channel can be read back using the read_ vout x register. output voltage from 0.9v to 5.1v per the equation below , for values between 0.9v and 5.1v the output voltage is equal to the binary number stored in the set_ vout _target_chx r egister multiplied by 50mv. when programming an output voltage from 2.6v to 5.1v, odd binary values should be avoided . as a result, the set resolution for an output voltage higher than 2.5v is 100mv. ? ??? = ??? _ ???? _ ?????? _ ??? 50 ?? output vout higher than 5.1v to set the output voltage higher than 5.1v, the user needs to add an external voltage divider. the resistors used in the voltage divider should be below 10 k . the set_ vout _t arget_chx register should be set to 0x32 which is equivalent to an output voltage of 2.5v without the external divider network. the output voltage regulation in this case might exceed 2% due to extra error from the resistor divider. r 1 and r 2 follo ws the d efinition below . voutx pin vout5.1v r1 r2 fig. 21 : external divider network for high output voltage ? ??? = ? ? 1 ? 2 + 1? ??? _ ???? _ ?????? _ ??? 50 ?? output voltage lower than 0.9v the XRP7708 can be programmed to regulate an output voltage lower than 0.9v . however, in this case the specification of + - 2% output voltage accuracy ma y be exceeded. o ver - v oltage p rotection (ovp) the o ver - v oltage p rotection (ovp) set_ovvp_register sets the over - voltage condition in predefined steps per channel . the over - voltage protection is always active even during soft - start condition. when the over - v oltage condition is tripped , the controller will shut down th e channel. when the channel is shut down the controller will then set corresponding ovp fault bits in the read_ovv_uvlo_ovt_flag register. the vout ovp threshold is 150mv to 300mv above nominal v out for a voltage target of 2.5v or less. for the voltage target of 2.6v to 5.1v, the vout ovp threshold is 300mv to 600mv. once th e over - voltage channel is disabled, the controller will check the set_fault_resp_config_lb and set_fault_resp_config_hb to d etermine wh ether there are any following channels that need to be shut down. any following channel will be disabled when
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 17/ 28 rev. 1.2. 2 the channel with the over voltage fault is disabled. the channel(s) will remain disabled, until the host takes action to enable the c hannel(s). any of the fault and warning conditions can also be configured to be represented using the general purpose input output pins (gpio) to use as an interface with non i 2 c compatible devices. for further information on this topic see the gpio p ins section . during ovp fault shutdown of the channel, the customer has the option to choose two types of shutdown for each channel. the first shutdown is passive shutdown where the ic merely stops outputting pulses. the second shutdown is a brute force shutdown where the gl remains on as the channel reaches its discharged voltage. note that if the brute force method is chosen, then gl will permanently remain high until the channel is re - enabled. o utput c urrent s etting and m onitoring XRP7708 utilizes a low side mosfet rdson current sensing technique. the voltage drop on rdson is measured by dedicated current adc. the adc results are compared to a maximum current threshold and an over - current warning threshold to generate the fault and warning flags. maxi mum output current the maximum output current is set by the set_ v iout_max_chx register and set_isense_param_chx register . the set_ v iout_max_chx register is a n 8 bit register. bit s [ 5:0 ] set the maximum current threshold and bits [ 7:6 ] set the o ver - current warning threshold. the lsb for the current limit register is 5 mv and the allowed voltage range is between 0 and 3 15 mv. to calculate t he maximum current limit , the user needs to provide the mos fet rdson. the maximum current can be calculated as: ??????? = ?????? ????? ?? where kt is the temperature coefficient of the mosfet rdson; vsense is the voltage across rdson; ioutmax is the maximum output current. over - c urrent warning the xrp 7708 also offers an over - current warning flag. this warning flag resides in the read_ovc_flag register. the warning flag bit will be set when the output current gets to within a specified value of the output current limit threshold enabling the host to reduce power consumption. the set_viout_max_chx r egister allows the warning flag threshold to be set 10mv, 20mv, 30mv or 40mv below viout_max. the warning flag will be automatically clear ed when the current drops below the warning threshold . over - c urrent fault handling when an over - current condition occu rs, pwm drivers in the corresponding channels a re disabled. after a 200ms timeout , the controller is re - powered and soft - start is initiated. w hen the over - current condition is reached the controller will check the set_fault_resp_config_lb and set_fault_res p_config_hb to determine wh ether there are any following channels that need to be similarly restarted. the controller will also s et the fault flags in read_ ovc_f ault_warn register. typically the over - current fault threshold would be set to 130 - 140% of t he maximum desirable output current. this will help avoid any over - current conditions caused by transients that would shut down the output channel.
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 18/ 28 rev. 1.2. 2 chip operation and configuration s oft - s tart the set_ss_rise_chx register is a 16 bit register which specifie s the soft - start delay and the ramp characteristics for a specific channel . th is register allows the customer to program the channel with a 250 us step resolution and up to a maximum 16ms delay. bits [15:10] specify the delay after enabling a channel but be fore outputting pulses; where each bit represents 250us steps. bits [9:0] specify the rise time of the channel; these 10 bits define the number of microseconds for each 50mv increment to reach the target voltage . the status of the soft - start operation is indicated in the power_good_soft_start_flag register by bits [3:0] which correspond to channels 4 though 1 respectively . a value of 1 signifies that a soft start is in operation on a given channel. enable signal vout ss_rise_chx register bit [0:9] rise time delay bit [10:15] fig. 20 : channel po wer up sequence s oft - s top the set_pd_fall_chx register is a 16 bit register. this register specifies the soft - stop delay and ramp (fall - time) characteristics for when the chip receives a channel disable indication from the host to shutdown th e channel. bits [15:10] specify the delay after disabling a channel but before starting the shutdown of the channel; where each bit represents 250us steps. bits [9:0] specify the fall time of the channel; these 10 bits define the number of microseconds fo r each 50mv increment to reach the discharge threshold . delay fall time bit [10:15] bit [0:9] vout enable signal pd_delay_chx register fig. 23 : channel soft- stop sequence
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 19/ 28 rev. 1.2. 2 p ower g ood f lag the XRP7708 allows the user to set the upper and lower bound for a power good signa l per channel. the set_pwrg_targ_max _chx register sets the upper bound , the set_pwrg_targ_min_chx register sets the lower bound. each register has a 20mv lsb resolution . when the output voltage is within bounds the power good signal is asserted high. typically the upper bound should be lower than the over - voltage threshold . in addition, the power good signal can be delayed by a programmable amount set in t he set_pwrgd_dly_chx register. t he power good delay is only set after the soft - start period is finished. if the channel has a pre - charged c ondition that falls into the power good region, a power good flag is not set until the soft - start is finished. pwm s witching f requency the pwm switching frequency is set by choosing the corresponding oscillator frequency and clock divider ratio in the set_ sw_frequency register. bit s [ 6:4 ] set the oscillator frequency and bit s [2:0] set the clock divider. the tables below summarize the available main oscillator and pwm switching frequenc y settings in the XRP7708 . main oscillator frequency set_sw_frequency[6: 4] 000 001 010 011 100 101 110 111 main oscillator frequency 48mhz 44.8mhz 41.6mhz 38.4mhz 35.2mhz 32mhz 28.8mhz 25.6mhz ts 20.8ns 22.3ns 24ns 26ns 28.4ns 31.25ns 34.7ns 39ns pwm switching frequency set_sw_frequency[6:4] set_sw_frequency[2:0] 000 001 010 011 100 101 110 111 000 na na na na na na na na 001 1.5mhz 1.4mhz 1.3mhz 1.2mhz 1.1mhz 1.0mhz 900khz 800khz 010 1.0mhz 933khz 867khz 800khz 733khz 667khz 600khz 533khz 011 750khz 700khz 650khz 600khz 550khz 500khz 450khz 400khz 100 600khz 560khz 5 20khz 480khz 440khz 400khz 360khz 320khz 101 500khz 467khz 433khz 400khz 367khz 333khz 300khz na 110 429khz 400khz 370khz 343khz 314khz na na na 111 375khz 350khz 325khz 300khz na na na na there are a number of options that could result in similar pwm switching frequency as shown above . in general, the chip consumes less power at lower oscillator frequency. when synchronization to external clock is needed, the user can choose the oscillator frequency to be within +/ - 5% of the external clock frequency. a higher main oscillator frequency will not improve accuracy or any performance efficiency. pwm s witching f requency c onsideration s t here are several considerations when choosing the pwm switching frequency. minimum on time m inimum on time determine s the m inimum duty cycle at the specific switching frequency . the minimum on time for the xrp 7708 is 40ns. ??????? ???? ????? % = ??????? ?????? ??? ????????? 100 as an example the minimum duty cycle is 4 % for 1mhz pwm freque ncy. this is important since the minimum on time dictates the maximum conversion ratio that the pwm controller can achieve .
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 20/ 28 rev. 1.2. 2 ??????? ???? ????? % > ???? ?????? maximum duty cycle the maximum duty cycle is dictated by the minimum req uired time to sample the current when the low side mosfet is on. for the XRP7708, the minimum required sampling time is about 16 clock cycles at the main oscillator frequency. when calculating maximum duty cycle, the sampling time needs to be subtracted us ing the below equation. for example, if operating at 1mhz using the 32mhz main oscillator frequency, the maximum duty cycle would be: ??????? ???? ????? % = ?1 ? ( 16 ????? ????????? ??? ????????? ? 0. 03 ) ? 100 47 % on the other hand, if the 48mhz main oscillator frequency was chosen for the 1mhz pwm frequency, the maximum duty cycle would be: ????? ?? ???? ????? % = ?1 ? ( 16 ????? ????????? ??? ????????? ? 0. 03 ) ? 100 64 % therefore, it is best to choose the highest main oscillator frequency for a particular pwm frequency if duty cycle limit might be encountered. the max imum duty cycle for any pwm frequency can easily be determined using the following table: main oscillator frequency maximum duty cycle 48mhz 44.8mhz 41.6mhz 38.4mhz 35.2mhz 32mhz 28.8mhz 25.6mhz 47% 1.5mhz 1.4mhz 1.3mhz 1.2mhz 1.1mhz 1.0mhz 900khz 800kh z 64% 1.0mhz 933khz 867khz 800khz 733khz 667khz 600khz 533khz 72% 750khz 700khz 650khz 600khz 550khz 500khz 450khz 400khz 77% 600khz 560khz 520khz 480khz 440khz 400khz 360khz 320khz 80% 500khz 467khz 433khz 400khz 367khz 333khz 300khz na 83% 429khz 40 0khz 370khz 343khz 314khz na na na 85% 375khz 350khz 325khz 300khz na na na na fig. 21 : pwm frequency it is highly recommended that the maximum duty cycle obtained from the table above be programmed into each of the channels using the set_duty_limiter_chx register. this ensures that under all conditions (including faults), there will always be sufficient sampling time to measure the output current. when the duty cycle limit is reached, the output voltage will no longer regulate and will be clamped based on the maximum duty cycle limit setting. efficiency the pwm switching frequency plays an important role on overall power conversion efficiency. as the switching frequency increase, the switching losses also increase. please see the ap plication information, typical performance data for further examples. component selection and frequency typically the components become smaller as the frequency increases, as long as the ripple requirements remain constant. at higher frequency the inductor can be smaller in value and have a smaller footprint while still maintaining the same current rating. f requency s ync hronization f unction and e xternal c lock the user of the XRP7708 can choose to use an external source as the primary clock for the XRP7708 . this function can be configured using the set_sync_mode_config register. this register sets the operation of the XRP7708 when an external clock is required. by selecting the
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 21/ 28 rev. 1.2. 2 appropriate bit combination the user can configure the ic to function as a master or a slave when two or more XRP7708s are used to convert power in a system. automatic clock selection is also provided to allow operation even if the external clock fails by switching the ic back to an in ternal clock. external clock synchronization even w hen configured to use an external clock , the chip initially powers up with its internal clock. the user can set the percent target that the frequency detector will use when comparing the internal clock with the clock frequency input on the gpio pin. if the external clock frequency is detected to be within th e window specified by the user, then a switchover will occur to the external clock. if the ic does not find a clock in the specified frequency target range then the external clock will not be used an d the ic will run on the internal clock that was specified by the user. if the external clock fails the user can chose to have the internal clock take over , using the automatic switch back mode in the set_sync_mode_config register. XRP7708 configured for external clock use clk_in gpio1 fig. 22: XRP7708 configured for external clock use synchronized operation as a master and slave unit two XRP7708s can be synchronized together. this master - slave configuration is described below. ? master when the XRP7708 powers up as a master unit after the internal configuration memory is loaded the unit will sen d clk_out and sync_out signals to the slave on the preconfigured gpio pins . ? slave when powering in sync mode the slave unit will initially power up with its internal clo ck to transfer the configuration memory . once this transfer occurs , then the unit is set to function as a slave unit. in turn the unit will take the external clock provided by the master to run as its main internal clock. gpio2 gpio2 XRP7708 configured as a master XRP7708 configured as a slave clk_out sync_out sync_in clk_in gpio1 gpio1 fig. 23 : master/slave configuration of the XRP7708
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 22/ 28 rev. 1.2. 2 external c lock s ynchronization master slave combination when an external clock is used, the user will need to setup the master to also have an external clock in function. all of the same rules apply as in the external clock synchronization, synchronized operation as a slave unit section of this document. there are two ways of synchronizing this, either the external clock going to both master/slave clk_in, or clk_in can go to the master, a nd the master can synchronize sync_out and clk_out to the slave. gpio2 gpio2 XRP7708 configured as a master with external clock sync XRP7708 configured as slave sync_out sync_in clk_in clk_in gpio1 gpio1 fig. 24 : external clock synchronization master slave combination gpio2 gpio2 XRP7708 configured as a master with external clock sync XRP7708 configured as slave sync_out sync_in clk_in clk_in gpio1 gpio3 clk_out gpio1 fig. 25 8 : alternative e xternal clock synchronization master slave combination p hase s hift each switching channel can be programmed to a phase shift of the multiples of 90 degrees [for a 4 phase configuration] or 120 degrees [for a 3 phase configuration]. two or more of the chann els can use the same phase shift, however, it is preferable to run each channel at separate phases. gpio p ins the g eneral p urpose i nput o utput (gpio) p ins are the basic interface between the XRP7708 and the system. although all of the stored data within t he ic can be read back using the i 2 c bus it is sometimes convenient to have some of those internal register to be displayed and or controlled by a single data p in . besides simple input output functions the gpio pins can be configured to serve as external c lock inputs. these pins can be programmed using otp bits or can be programmed using the i 2 c bus. this gpio_config register a llows the user close to 100 different configuration functions that the gpio can be programmed to do. note: the gpio pins (and all i/ os) should not be driven without a 10k resistor when vin is not being applied to the ic.
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 23/ 28 rev. 1.2. 2 gpio pins polarity the polarity of the gpio pin can be set by using the gpio_act_pol register. this register allo ws any gpio pin whether configured as an input or ou tput to change polarity. bits [ 5:0 ] are used to set the polarity of gpio 0 though 5 . if the ic operates in i 2 c mode , then the commands for bits [5: 4 ] are ignored. supply rail enable each gpio can be configured to enable a specific power rail for the system . the gpiox_cfg register allows a gpio to enable/disable any of the following rails controlled by the chip: ? a single buck power controller ? the standby ldo ? any mix of the standby ldo and power controller(s) when the configured gpio is asserted externally, the corresponding rails will be enabled, and they will be similarly disabled when the gpio is de - asserted. this supply enabling/disabling can also be controlled through the i 2 c interface. power g ood i ndicator the gpio pins can be configured as power g ood indicators for one or more rails. the gpio pin is asserted when all rails configured for this specific io are within specified limits for regulation. this information can also be found in the read_pwrgd_ss_flag status register. fault and warning indicat ion the gpios can be configured to signal fault or warning conditions when they occur in the chip. each gpio can be configured to signal one of the following: ? ocp fault on channel 1 - 4 ? ocp warning on channel 1 - 4 ? ovp fault on channel 1 - 4 ? uvlo fault on vin1 or vin2 ? uvlo warning on vin1 or vin2 ? over temperature fault or warning i 2 c c ommunication the i 2 c communication is standard 2 - wire communication available between the host and the ic. this interface allows for the full control, monitoring, and reconfi guration of the semiconductor. each device in an i 2 c - bus system is activated by sending a valid address to the device. the address always has to be sent as the first byte after the start condition in the i 2 c - bus protocol msb 6 5 4 3 2 1 0 r/w lsb fig. 29 : alignment of i2c address in 8 bit byte there is one address byte required since 7 - bit addresses are used. the last bit of the address byte is the read/write - bit and should always be set according to the required operation. this 7 - bit i 2 c address is sto red in the nvm. one can program a blank device with the 7 - bit slave address or select one of the preprogrammed options. the 7 - bit address plus the r/w bit create an 8 - bit data value that is sent on the bus.
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 24/ 28 rev. 1.2. 2 the xrp7740ilb - 0x18 - f has an i 2 c address of 0x18. the internal registers are written by sending a data value of 0x 30 and read by sending a data value of 0x 31 . this reflects the address being shifted one bit to the left and the least significant bit being set to reflect a read or write operation in order to stuff the byte correctly. the second byte sent to the device is the location of a specific register. using gpio3 to select i 2 c address gpio3 may be used to change the lsb of the 7 - bit address. this option can be enabled within the powerarchitect tm sof tware by checking the use gpio3 to control lsb of i2c address box at the top right of the digital design tab. more about the use of this option and other methods of changing the default i2c address of the part are available in anp - 31 power xr configur ation and programming . e xternal c omponent s election inductor selection select the inductor for inductance l and saturation current isat. select an inductor with isat higher than the programmed over current limit. calculate inductance from: ? = ( ??? ? ???? ) ???? ??? 1 ?? 1 ???? where: vin is the converter input voltage vout is the converter output voltage fs is the switching frequency irip is the inductor peak - to - peak current ripple (nominally set to 30% of iout) keep in mind that a higher irip results in a smaller inductance value which has the advantages of smaller size, lower dc equivalent resistance (dcr), and allows the use of a lower output capacitance to meet a given step load transient. a higher irip, however, i ncreases the output voltage ripple, requires higher saturation current limit, and increases critical conduction. notice that this critical conduction current is half of irip. capacitor selection x output capacitor selection select the output capacitor for vo ltage rating, capacitance and equivalent series resistance (esr). nominally the voltage rating is selected to be at least twice as large as the output voltage. select the capacitance to satisfy the specification for output voltage overshoot/undershoot caus ed by the current step load. a sudden decrease in the load current forces the energy surplus in the inductor to be absorbed by cout. this causes an overshoot in output voltage that is corrected by power switch reduced duty cycle. use the follow ing equation to calculate cout: ? = ? ( ? 2 ? ? 1 ) 2 ? ?? 2 ? ? ??? 2 where: l is the output inductance i2 is the step load high current
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 25/ 28 rev. 1.2. 2 i1 is the step load low current vos is output voltage including the overshoot vout is the steady state output v oltage or it can be expressed approximately by ? = ? ( ? 2 ? ? 1 ) 2 2 ???? ? ? ? here, out os v v v is the overshoot voltage deviation. select esr such that output voltage ripple ( vrip ) specification is met. there are two components in vr ip . first component arises from the charge transferred to and from cout during each cycle. the second component of vrip is due to the inductor ripple current flowing through the output capacitors esr. it can be calculated for vrip: ???? = ???? ? ? ?? 2 + ? 1 8 ???? ?? ? where: irip is the inductor ripple current fs is the switching frequency cout is the output capacitance note that a smaller inductor results in a higher irip, therefore requiring a larger cout and/or lower esr in order to mee t vrip. x input capacitor selection select the input capacitor for voltage, capacitance, ripple current, esr and esl. voltage rating is nominally selected to be at least twice the input voltage. the rms value of input capacitor current, assuming a low induct or ripple current, can be approximated as: ??? = ???? ? ? ( 1 ? ? ) where: iin is the rms input current iout is the dc output current d is the duty cycle in general, the total input voltage ripple should be kept below 1.5% of vin . the input voltage ripple also has two major components: the volt age drop on the main capacitor cin v and the voltage drop due to esr - esr v . the contribution to input voltage ripple by each term can be calculated from: 2 ) ( in in s out in out out cin v c f v v v i v ) 5 . 0 ( rip out esr i i esr v
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 26/ 28 rev. 1.2. 2 total input voltag e ripple is the sum of the above: esr cin tot v v v ? + ? = ? power mosfets selection selecting mosfets with lower rdson reduces conduction losses at the expense of increased switching losses. a simplified expression for conduction losses is given by : in out dson out cond v v r i p ? ? = mosfets junction temperature can be estimated from: ambient thja cond j t r p t + = this assumes that the switching loss is the same as the conduction loss. thja r is the total mosfet thermal resistance from junction to ambient. l ayout g uidelines refer to application note anp - 32 practical layout guidelines for power xr designs and anp - 35 xrp77xx: extending th e mosfet gate drive conductors . r egister m ap see anp - 31 powerxr configuration and programming for details of the register map and other programming information.
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 27/ 28 rev. 1.2. 2 package specificatio n 40 - pin 6mmx6mm tqfn
x x r r p p 7 7 7 7 0 0 8 8 a a n n d d x x r r p p 7 7 7 7 4 4 0 0 q q u u a a d d c c h h a a n n n n e e l l d d i i g g i i t t a a l l p p w w m m s s t t e e p p d d o o w w n n c c o o n n t t r r o o l l l l e e r r s s ? 201 2 exar corporation 28/ 28 rev. 1.2. 2 revision history revision date description 1.0 . 2 02/01/2010 approved and first release of data sheet 1.0.3 02/02/2010 minor edits 1.2.0 04/ 14 /2010 combined XRP7708 rev 1.0.3 and xrp7740 rev 1.1.0 into one document. added i2c information. added enable pin sequencing information. updated gate drive resistance information. corrected package thermal resistance. added part to order information table 1.2.1 12/5/2011 added information on soft - start flag. added new anp - 35 reference and anp - 31 reference. changed logo color. more emphasis on the connection of pgnd pins. 1.2.2 04/20/2012 corrected typographical errors. first page, change exposed pad designation from dgnd to agnd. pin description table; gl1 corrected from pin 34 to 35, lx3 and lx4 corrected from pins 23,18 to 18,23 for further assistan ce email: powerxr @exar.com exar technical documentation: http://powerxr.exar.com http://www.exar.com/techdoc/default.aspx? e xar c orporation h eadquarters and s ales o ffices 48720 kato road fremont, ca 94538 C usa tel.: +1 (510) 66 8 - 7000 fax: +1 (510) 668 - 7030 www.exar.com notice exar corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. exar corporation assumes no responsibility for the use of any circuits described herein, conveys no li cense under any patent or other right, and makes no representation that the circuits are free of patent infringement. charts and schedules contained here in are only for illustration purposes and may vary depending upon a users specific application. while the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies. exar corporation does not recommend the use of any of its products in life support applications where the failure or malfunction of th e product can reasonably be expected to cause failure of the life support system or to significantly affect its safety or effectiveness. products are not authorized for use in such applications unless exar corporation receives, in writing, assurances to it s satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; (c) potential liability of exar corporation is adequately protected under the circumstances. reproduction, in part or whole, without the prior wr itten consent of exar corporation is prohibited.

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