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january 2008 rev 2 1/43 PM6600 6-rows 30 ma leds driver with boost regulator for lcd panels backlight features boost section ? 4.7 v to 28 v input voltage range ? internal power mosfet ? internal +5 v ldo for device supply ? up to 36 v output voltage ? constant frequency peak current-mode control ? 200 khz to 1 mhz adjustable switching frequency ? external synchronization for multi-device application ? pulse-skip power saving mode at light load ? programmable soft-start ? programmable ovp protection ? stable with ceramic output capacitors ? thermal shutdown backlight driver section ? six rows with 30 ma maximum current capability (adjustable) ? up to 10 wleds per row ? unused rows detection ? 500 ns minimum dimming time (1 % minimum dimming duty-cycle at 20 khz) ? 2.1 % current accuracy ? 2 % current matching between rows ? led failure (open and short circuit) detection applications notebook monitors backlight umpc backlight description the PM6600 consists of a high efficiency monolithic boost converter and six controlled current generators (rows), specifically designed to supply leds arrays used in the backlight of lcd panels. the device can manage a nominal output voltage up to 36 v (i.e. 10 white-leds per row). the generators can be externally programmed to sink up to 30 ma and they can be dimmed via a pwm signal (1% dimming duty- cycle at 20 khz can be managed). the device allows to detect and manage the open and shorted led faults and to let unused rows floating. basic protections (output over-voltage, internal mosfet over-current and thermal shutdown) are provided. vfqfpn-24 4x4 table 1. device summary part number package packaging PM6600 vfqfpn-24 4x4 (exposed pad) tu b e PM6600tr tape and reel www.st.com
contents PM6600 2/43 contents 1 typical application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2 pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1 connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2 pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3 electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1 maximum rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2 thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.3 recommended operating conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4 electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 5 typical operating char acteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 7 operation description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 7.1 boost section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 7.1.1 functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 7.2 over voltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 7.3 switching frequency selection and synchronization . . . . . . . . . . . . . . . . . 25 7.4 system stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 7.4.1 loop compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 7.4.2 slope compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 7.5 soft-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 7.6 boost current limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 7.7 enable function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 7.8 thermal protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
PM6600 contents 3/43 8 backlight driver section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 8.1 current generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 8.2 pwm dimming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 9 fault management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 9.1 fault pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 9.2 mode pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 9.3 open led fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 9.4 shorted led fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 9.5 intermittent connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 10 package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 11 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
typical application circuit PM6600 4/43 1 typical application circuit figure 1. application circuit dim en fault avcc PM6600 comp 1 mod e 5 avcc 6 ldo5 7 vin 8 slope 9 row1 11 row2 12 row3 13 row4 14 row5 15 row6 16 pgnd 17 ovsel 18 lx 19 dim 20 en 21 fault 22 sync 23 ss 24 fsw 4 rilim 2 bilim 3 sgnd 10 th pd 25 cout r1 l vin+ c10 cav cc cldo5 css cin ccomp rf ilt rslope vboost vin- sw2 fsw rf sw r2 c13 rcomp sw3 mod e d rbilim avcc rrilim avcc
PM6600 pin settings 5/43 2 pin settings 2.1 connections 2.2 pin description figure 2. pin connection (through top view) table 2. pin functions n pin function 1comp error amplifier output. a simple rc series between this pin and ground is needed to compensate the loop of the boost regulator. 2 rilim output generators current limit setting. th e output current of the rows can be programmed connecting a resistor to sgnd. 3 bilim boost converter current limit setting. the internal mosfet current limit can be programmed connecting a resistor to sgnd. 4fsw switching frequency selection and exte rnal sync input. a resistor to sgnd is used to set the desired switching frequency. the pin can also be used as external synchronization input. see section 1.3 for details. 5mode current generators fault management selector. it allows to detect and manage leds failures. see section 3.2 for details. 6 avcc +5 v analog supply. connect to ldo5 through a simple rc filter. 7ldo5 internal +5 v ldo output and power section supply. bypass to sgnd with a 1 f ceramic capacitor. 8 vin input voltage. connect to the main supply rail.
pin settings PM6600 6/43 9slope slope compensation setting. a resist or between the output of the boost converter and this pin is needed to avoid sub-harmonic instability. refer to section 1.4 for details. 10 sgnd signal ground. supply return for t he analog circuitry and the current generators. 11 row1 row driver output #1. 12 row2 row driver output #2. 13 row3 row driver output #3. 14 row4 row driver output #4. 15 row5 row driver output #5. 16 row6 row driver output #6. 17 pgnd power ground. source of the internal power-mosfet. 18 ovsel over-voltage selection. used to set the desired ov threshold by an external divider. see section 1.2 for details. 19 lx switching node. drain of the internal power-mosfet. 20 dim dimming input. used to externally set the brightness of the leds by using a pwm signal. 21 en enable input. when low, the device is turned off. if tied high or left floating, the device is turned on and a soft-start sequence takes place. 22 fault fault signal output. open drain output. the pin goes low when a fault condition is detected (see section 3.1 for details). 23 sync synchronization output. used as external synchronization output. 24 ss soft start. connect a capacitor to sgnd to set the desired soft-start duration. table 2. pin functions (continued) n pin function
PM6600 electrical data 7/43 3 electrical data 3.1 maximum rating 3.2 thermal data table 3. absolute maximum ratings (1) 1. stresses beyond those listed under "absolute ma ximum ratings" may cause permanent damage to the device. exposure to absolute maximu m rated conditions for extended periods may affect device reliability. symbol parameter value unit v avcc avcc to sgnd -0.3 to 6 v v ldo5 ldo5 to sgnd -0.3 to 6 pgnd to sgnd -0.3 to 0.3 v in vin to pgnd -0.3 to 40 v lx lx to sgnd -0.3 to 40 lx to pgnd -0.3 to 40 rilim, bilim, sync, ovsel, ss to sgnd -0.3 to v avcc + 0.3 en, dim, fsw, mode, fault to sgnd -0.3 to 6 rowx to pgnd/ sgnd -0.3 to 40 slope to vin v in - 0.3 to v in + 6 slope to sgnd -0.3 to 40 maximum lx rms current 2.0 a p tot power dissipation @=25c 2.3 w maximum withstanding voltage range test condition: cdf-aec-q100-002- ?human body model? acceptance criteria: ?normal performance? 1000 v table 4. thermal data symbol parameter value unit r thja thermal resistance junction to ambient 42 c/w t stg storage temperature range -50 to 150 c t j junction operating temperature range -40 to 125 c t a operating ambient temperature range -40 to 85 c
electrical data PM6600 8/43 3.3 recommended operating conditions table 5. recommended operating conditions symbol parameter values unit min typ max supply section v in input voltage range 4.7 28 v boost section v bst output voltage range 36 v f sw adjustable switching frequency fsw connected to r fsw 200 1000 khz fsw sync input duty-cycle 40 % rows output maximum current 30 ma
PM6600 electrical characteristics 9/43 4 electrical characteristics v in = 12 v; t a = 0 c to 85 c and mode connected to avcc unless specified (1) . table 6. electrical characteristics symbol parameter test condition values unit min typ max supply section v ldo5, v avcc ldo output and ic supply voltage en high, i ldo5 = 0 ma 4.6 5 5.5 v i in,q operating quiescent current r rilim = 51 k ? , r bilim = 220 k ? , r slope = 680 k ? dim tied to sgnd. 1ma i in,shdn operating current in shutdown en low 20 30 a v uvlo,on ldo5 under voltage lockout upper threshold 4.6 4.75 v v uvlo,off ldo5 under voltage lockout lower threshold 3.8 4.0 ldo linear regulator line regulation 6 v = v in = 28 v, i ldo5 = 30 ma 25 mv ldo dropout voltage v in = 4.3 v, i ldo5 = 10 ma 80 120 ldo maximum output current limit v ldo5 > v uvlo,on 25 40 60 ma v ldo5 < v uvlo,off 30 1. t a = t j . all parameters at operating temperature extremes are guaranteed by desi gn and statistical analysis (not production tested)
electrical characteristics PM6600 10/43 symbol parameter test condition values unit min typ max boost section t on,min minimum switching on time 200 ns default switching frequency fsw connected to avcc 570 660 750 khz minimum fsw sync frequency 210 fsw sync input low level threshold 240 mv fsw sync input hysteresis 60 fsw sync min on time 270 ns sync output duty-cycle fsw connected to avcc (internal oscillator selected) 34 40 % sync output high level i sync = 10 ua v avcc -20 mv sync output low level i sync = -10 ua 20 power switch k b lx current coefficient r bilim = 300 k ? 5.7e5 6.7e5 7.7e5 v internal mosfet rdson 280 500 m ? ov protections v th,ovp over-voltage protection reference (ovsel) threshold 1.190 1.235 1.280 v v th,frd floating rows detection (ovsel) threshold 1.100 1.145 1.190 ? v ovp,frd voltage gap between the ovp and frd thresholds 90 mv table 6. electrical characteristics (continued)
PM6600 electrical characteristics 11/43 note: the current mismatch is the maximum current difference among the rows of one device. symbol parameter test condition values unit min typ max soft start and power management en, turn-on level threshold 1.6 v en, turn-off level threshold 0.8 dim, high level threshold 1.3 dim, low level threshold 0.8 en, pull-up current 2.5 a ss, charge current 4 5 6 ss, end-of-startup threshold 2 2.4 2.8 v ss, reduced switching frequency release threshold 0.8 current generators section t dim-on,min minimum dimming on-time r rilim = 51 k ? 500 ns k r rows current coefficient accuracy r rilim = 51 k ? 998 21 v ? i rowx rows current mismatch (1) r rilim = 51 k ? 2 % v ifb feedback regulation voltage no leds mismatch 400 mv v th,fault shorted led fault detection threshold 8.2 v v fault,low fault pin low-level voltage i fault,sink = 4 ma 350 mv thermal shutdown t shdn thermal shutdown turn-off temperature 150 c table 6. electrical characteristics (continued)
typical operating characteristics PM6600 12/43 5 typical operating characteristics all the measures are done with a standard PM6600eval demoboard and a standard wled6021nb demoboard, with the components listed in the eval_kit document. the measures are done with this working conditions, unless specified: vin = 12 v vout = 6 rows x 10 wleds = 34 v (typ) iout = 20 ma each row fsw = 660 khz (nominal switching frequency, with fsw .. avcc) vrow1 to vrow6 = {0.697, 0.75, 0.818, 0.696, 0.822, 0.363} v figure 3. efficiency vs dim duty cycle @ f dim = 200 hz figure 4. efficiency vs dim duty cycle @ f dim = 500 hz figure 5. efficiency vs dim duty cycle @ f dim = 1 khz figure 6. efficiency vs dim duty cycle @ f dim = 5 khz 0 10 20 30 40 50 60 70 80 90 100 0 20406080100 dim duty cycle [%] efficiency [%] vin = 6v vin = 12v vin = 18v vin = 24v 0 10 20 30 40 50 60 70 80 90 100 020406080100 dim duty cycle [%] efficiency [%] vin = 6v vin = 12v vin = 18v vin = 24v 0 10 20 30 40 50 60 70 80 90 100 0 20406080100 dim duty cycle [%] efficiency [%] vin = 6v vin = 12v vin = 18v vin = 24v 0 10 20 30 40 50 60 70 80 90 100 0 20406080100 dim duty cycle [%] efficiency [%] vin = 6v vin = 12v vin = 18v vin = 24v
PM6600 typical operating characteristics 13/43 figure 7. efficiency vs dim duty cycle @ f dim = 10 khz figure 8. efficiency vs dim duty cycle @ f dim = 20 khz 0 10 20 30 40 50 60 70 80 90 100 0 20406080100 dim duty cycle [%] efficiency [%] vin = 6v vin = 12v vin = 18v vin = 24v 0 10 20 30 40 50 60 70 80 90 100 0 20 40 60 80 100 dim duty cycle [%] efficiency [%] vin = 6v vin = 12v vin = 18v vin = 24v figure 9. efficiency vs dim duty cycle @ vin = 8 v figure 10. efficiency vs dim duty cycle @ vin = 12 v figure 11. efficiency vs dim duty cycle @ vin = 18 v figure 12. efficiency vs dim duty cycle @ vin = 24 v 0 10 20 30 40 50 60 70 80 90 100 0 20406080100 dim duty cycle [%] efficiency [%] fdim = 200hz fdim = 500hz fdim = 1khz fdim = 5khz fdim = 10khz fdim = 20khz 0 10 20 30 40 50 60 70 80 90 100 020406080100 dim duty cycle [%] efficiency [%] fdim = 200hz fdim = 500hz fdim = 1khz fdim = 5khz fdim = 10khz fdim = 20khz 0 10 20 30 40 50 60 70 80 90 100 020406080100 dim duty cycle [%] efficiency [%] fdim = 200hz fdim = 500hz fdim = 1khz fdim = 5khz fdim = 10khz fdim = 20khz 0 10 20 30 40 50 60 70 80 90 100 0 20406080100 dim duty cycle [%] efficiency [%] fdim = 200hz fdim = 500hz fdim = 1khz fdim = 5khz fdim = 10khz fdim = 20khz
typical operating characteristics PM6600 14/43 figure 13. efficiency vs vin @ dim duty cycles = 10 % figure 14. efficiency vs vin @ dim duty cycles = 50 % figure 15. efficiency vs vin @ dim duty cycles = 75 % figure 16. efficiency vs vin @ dim duty cycles = 100 % 0 10 20 30 40 50 60 70 80 90 100 6121824 vin [v] efficiency [%] fdim = 200hz fdim = 500hz fdim = 1khz fdim = 5khz fdim = 10khz fdim = 20khz 0 10 20 30 40 50 60 70 80 90 100 6 121824 vin [v] efficiency [%] fdim = 200hz fdim = 500hz fdim = 1khz fdim = 5khz fdim = 10khz fdim = 20khz 82 84 86 88 90 92 94 96 6121824 vin [v] efficiency [%] fdim = 200hz fdim = 500hz fdim = 1khz fdim = 5khz fdim = 10khz fdim = 20khz 87 88 89 90 91 92 93 94 95 6 121824 vin [v] efficiency [%] fdim = 200hz fdim = 500hz fdim = 1khz fdim = 5khz fdim = 10khz fdim = 20khz
PM6600 typical operating characteristics 15/43 figure 17. working waveforms @ f dim = 100 hz, d = 1 % figure 18. working waveforms @ f dim = 100 hz, d = 10 % figure 19. working waveforms @ f dim = 100 hz, d = 50 % figure 20. working waveforms @ f dim = 100 hz, d = 80 %
typical operating characteristics PM6600 16/43 figure 21. working waveforms @ f dim = 200 hz, d = 1 % figure 22. working waveforms @ f dim = 200 hz, d = 20 % figure 23. working waveforms @ f dim = 200 hz, d = 50 % figure 24. working waveforms @ f dim = 200 hz, d = 80 %
PM6600 typical operating characteristics 17/43 figure 25. working waveforms @ f dim = 500 hz, d = 1 % figure 26. working waveforms @ f dim = 500 hz, d = 50 % figure 27. working waveforms @ f dim = 1 khz, d = 1% figure 28. working waveforms @ f dim = 1 khz, d = 50 %
typical operating characteristics PM6600 18/43 figure 29. working waveforms @ f dim = 10 khz, d = 1 % figure 30. working waveforms @ f dim = 10 khz, d = 50 % figure 31. working waveforms @ f dim = 20 khz, d = 1 % figure 32. working waveforms @ f dim = 20 hz, d = 50 %
PM6600 typical operating characteristics 19/43 figure 33. output voltage ripple @ f dim = 200 hz, d = 1 % figure 34. output voltage ripple @ f dim = 200 hz, d = 20 % figure 35. output voltage ripple @ f dim = 200 hz, d = 50 % figure 36. output voltage ripple @ f dim = 200 hz, d = 80 %
typical operating characteristics PM6600 20/43 figure 37. shorted led protection @ f dim = 200 hz all wleds connected figure 38. shorted led protection @ f dim = 200 hz 1 wled shorted figure 39. shorted led protection @ f dim = 200 hz 2 wleds shorted figure 40. shorted led protection @ f dim = 200 hz 3 wleds shorted - row disabled
PM6600 typical operating characteristics 21/43 figure 41. open row detection @ f dim = 200 hz
block diagram PM6600 22/43 6 block diagram figure 42. simplified block diagram _ + ldo5 bilim co mp s yn c fsw rilim en fa u lt row4 p g nd lx r o w 6 dim vin r o w1 s l o pe av cc r o w 3 control logic r o w2 + _ thermal shutdown r o w 5 o v s el + _ sg nd ext sync detector osc ovp boost_en 1.2v 8.2v boost_en 0.4v min voltage selector uvlo uvlo detector +5v ld o ramp generator current sense 1.143v 1.235v soft start frd ovp frd ctrl1 ctrl6 v row1 v row2 v row5 v row4 v row3 v row6 ctrl2 v th,flt ctrl5 ctrl3 ctrl4 ctrl2 uvlo ctrl3 ctrl4 ctrl5 ctrl6 current generator 2 current generator 3 current generator 4 current generator 5 current generator 6 current generator 1 current limit + + logic boost control logic zcd + _ g m + _ i to v i to v ss m o de 2 prot_en prot_en
PM6600 operation description 23/43 7 operation description 7.1 boost section 7.1.1 functional description the PM6600 is a monolithic leds driver for the backlight of lcd panels and it consists of a boost converter and six pwm-dimmable current generators. the input voltage range is from 4.7 v up to 28 v. the boost section is based on a constant switching frequency, peak current-mode architecture. the boost output voltage is controlled such that the lowest rows' voltage, referred to sgnd, is equal to an internal reference voltage (400 mv typ.). in addition, the PM6600 has an internal ldo that supplies the internal circuitry of the device and is capable to deliver up to 40 ma. the inpu t of the ldo is the vin pin. the ldo5 pin is the ldo output and the supply for the power-mosfet driver at the same time. the avcc pin is the supply for the analog circuitry and should be connected to the ldo output through a simple rc filter, in order to improve the noise rejection. figure 43. avcc filtering two loops are involved in regulating the current sunk by the generators. the main loop is related to the boost regulato r and uses a constant frequency peak current- mode architecture (see figure 10), while an internal current loop regulates the same current at each row according to the set value (rilim pin). a dedicated circuit automatically selects the lowest voltage drop among all the rows and provides this voltage the main loop that, in turn, regulates the output voltage. in fact, once the reference generator has been detected, the error amplifier compares its voltage drop to the internal reference voltage and varies the comp output. the voltage at the comp pin determines the inductor peak current at each switching cycle. the output voltage of the boost regulator is thus determined by the total forward voltage of the leds strings: equation 1 vin ldo5 avcc sgnd PM6600 cavcc 100n rfilt 4r7 ldo mv 400 ) v ( max v j , f m 1 j n 1 i out leds rows + = = =
operation description PM6600 24/43 where the first term represents the highest total forward voltage drop over active rows and the second is the voltage drop across the leading generator (400 mv typ.). the device continues to monitor the voltage drop across all the rows and automatically switches to the current generator having the lowest voltage drop. 7.2 over voltage protection an adjustable over-voltage prot ection is available. it can be set feeding the ovsel pin with a partition of the output voltage. the voltage of the central tap of the divider is thus compared to a fixed 1.235 v threshold. when the voltage on the ovsel pin exceeds the ov threshold, the fault pin is tied low (see se ction 3) and the device is turned off; this condition is latched and the PM6600 is restarted by toggling the en pin or by performing a power-on reset (the por occurs when the ldo output falls below the lower uvlo threshold and subsequently crosses the upper uvlo threshold during the rising phase of the input voltage). normally, the value of the high-side resistors of the divider is in the order of 100k ? to reduce the output capacitor dischar ge when the boost converter is off (during the off phase of the dimming cycle). the ovsel divider should be a compensated one, with the capacitors c10 (typically in the 100 pf-330 pf r ange) that improves nois e rejection at the ovsel pin (see figure 5) and c13 (typically 22 pf) that avoids ovp fault detection when a row is open. the following formula permits to properly select the ovp threshold, according to the vout value and considering the worst case: equation 2 where equation 3 v ovp is the over-voltage protection threshold v rowx,fault is the shorted led threshold v row_max is the maximum voltage drop across the current generators, measured in the rowx pin with the leds' series with minimum v f_wled : forward voltage of the single led. ) v v ( v v v max _ row fault , rowx out ovp out ? + < < v 4 . 0 v n v wled _ f series _ wled out + ? =
PM6600 operation description 25/43 figure 44. ovp threshold setting 7.3 switching frequency selection and synchronization the switching frequency of the boost converte r can be set in the 200 khz-1 mhz range by connecting the fsw pin to ground through a resistor. calculation of the setting resistor is made using equation 3 and should not exceed the 80 k ? -400 k ? range. equation 4 in addition, when the fsw pin is tied to avcc, the PM6600 uses a default 660 khz fixed switching frequency, allowing to save a resistor in minimum components-count applications. figure 45. multiple device synchronization the fsw pin can also be used as a synchronization input, allowing the PM6600 to operate both as master or slave device. if a clock signal with a 210 khz minimum frequency is applied to this pin, the device locks synchroni zed (300 mv threshold) . an internal timeout allows synchronization as long as the external clock frequency is greater than 210 khz. keeping the fsw pin voltage lower than 300 mv for more than 1/210 khz 5 s results in the device turn off. normal operation is resumed as soon as fsw rises above the mentioned threshold and the soft-start sequence is repeated. lx ovsel sgnd PM6600 v out v in r 1 r 2 c 10 c out c 13 5 . 2 f r sw fsw = sync sgnd PM6600 avcc r fsw fsw sync sgnd PM6600 slave fsw master sync out sync
operation description PM6600 26/43 the sync pin is a synchronization output and provides a 34 % (typ.) duty-cycle clock when the PM6600 is used as master or a replica of t he fsw pin when used as slave. it is used to connect multiple devices in a daisy-chain conf iguration or to synchronize other switching converters running in the system with the PM6600 (master operation). when an external synchronization clock is applie d to the fsw pin, the internal oscillator is overdriven: each switching cycle begins at the rising edge of clock, while the slope compensation ramp starts at the falling edge of the same signal. thus, the external synchronization clock is required to have a 40 % maximum duty-cycle when the boost converter is working in continuous-conduction mode (ccm). the minimum pulse width which allows the synchronizing pulses to be detected is 270 ns. figure 46. external sync waveforms slave sync pin voltage 300mv threshold fsw pin voltage (ext. sync) slave lx pin voltage 270ns minimum
PM6600 operation description 27/43 7.4 system stability the boost section of the PM6600 is a fixed frequency, peak current-mode converter. during normal operation, a minimum voltage se lection circuit compares all the voltage drops across the active current generators and provides the minimum one to the error amplifier. the output voltage of the error amplifier determines the inductor peak current in order to keep its inverting input equal to the reference voltage (400 mv typ). the compensation network consists of a simple rc series (r comp - c comp ) between the comp pin and ground. the calculation of r comp and c comp is fundamental to achieve optimal loop stability and dynamic performance of the boost converter and is strictly relate d to the operating conditions. 7.4.1 loop compensation the compensation network can be quickly calc ulated using equations 4 through 9. once both r comp and c comp have been determined, a fine-tuning phase may be required in order to get the optimal dynamic performance from the application. the first parameter to be fixed is the swit ching frequency. normally, a high switching frequency allows reducing the size of the in ductor but increases the switching losses and negatively affects the dynamic response of the converter. for most of applications, the fixed value (660 khz) represents a good trade-off between power dissipation and dynamic response, allowing to save an e xternal resistor at th e same time. in low- profile applications, the inductor value is often kept low to reduce the number of turns; an inductor value in the 4.7 h-15 h range is a good starting choice. even if the loop bandwidth of the boost conver ter should be chosen as large as possible, it should be set to 20 % of the switching frequ ency, taking care not to exceed the ccm-mode right half-plane zero (rhpz). equation 5 equation 6 where v in,min is the minimum input voltage, i out is the overall output current, note that, the lower the inductor value (or the lower the switching frequency) the higher the bandwidth can be achieved. the ou tput capacitor is directly involved in the loop of the boost converter and must be large enough to avoid excessive output voltage drop in case of a sudden line transition from the maximum to the minimum input voltages ( ? v out should not exceed 50-100 mv): sw u f 2 . 0 f ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? = ? ? out min , in v v m = out out i v r =
operation description PM6600 28/43 equation 7 once the output capacitor has been chosen, the r comp can be calculated as: equation 8 where g m = 2.7 s and g ea = 375 s. the c comp capacitor is determined to place the frequency of the compensation zero 5 times lower than the loop bandwidth: equation 9 where f z = f u / 5. the close loop gain function (g loop ) is thus given by equation 10: equation 10 a simple technique to optimize different applications is to replace r comp with a 20k ? trimmer and adjust its value to properly damp the output transient response. insufficient damping will result in excessive ringing at the output and poor phase margin. figures 5a and 5b give an example of compensation adjustment for a typical application. ? ? ? ? ? ? ? ? ? ? ? = ? max _ in min _ in u out out v v 1 c f 2 i v m g g c f 2 r ea m u comp ? ? ? ? = comp z comp r f 2 1 c ? ? = src 1 r m l s 1 rm sc 1 r g g g 2 comp comp ea m loop + ? ? ? ? ? ? ? ? ? ? + ? ? = figure 47. poor phase margin (a) and properly damped (b) load transient responses
PM6600 operation description 29/43 figure 48. load transient re sponse measurement set-up 7.4.2 slope compensation the constant frequency, peak current-mode topol ogy has the advantage of very easy loop compensation with output ceramic capacitors (r educed cost and size of the application) and fast transient response. in addition, the intrinsic peak-current measurement simplifies the current limit protection, avoiding undesired saturation of the inductor. on the other side, this topology has a drawback: there is inherent op en loop in stability when operating with a duty-ratio greater than 0.5. this phenomenon is known as "sub-harmonic instability" and can be avoided by adding an external ramp to the one coming from the sensed current. this compensating techniqu e, based on the additional ramp, is called "slope compensation". in figure 11, where the sw itching duty-cycle is higher than 0.5, the small perturbation ? il dies away in subsequent cycles thanks to the slope compensation and the system reverts to a stable situation. figure 49. main loop and current loop diagram row1 row2 row3 row4 row5 row6 ldo5 bilim rilim ss sgnd slope vin lx ovsel fsw avcc fault en sync mode pgnd dim v in = 6v v bst=3036v in c comp +5v up to 10 wleds per row PM6600 6.8 h 4.7 f mlcc 50ma 500hz r l = v bst v in 0.4v pwm minimum voltage drop selector comp lx rowx sgnd rilim g m
operation description PM6600 30/43 the slope pin allows to properly set the amount of slope compensation connecting a simple resistor r slope between the slope pin and the output. the compensation ramp starts at 35 % (typ.) of each switching period and its slope is given by the following equation: equation 11 where k slope , v be = 2 v (typ.) and se is the slope ramp in [a/s]. to avoid sub-harmonic instabilit y, the compensating slope shoul d be at least half the slope of the inductor current during the off-phase for a duty-cycle greater than 50 % (i.e. at the lowest input voltage). the value of r slope can be calculated according to equation 9. equation 12 figure 50. effect of slope compensation on small inductor current perturbation (d > 0.5) ? ? ? ? ? ? ? ? ? ? = slope be in out slope e r v v v k s ) v v ( ) v v v ( l k 2 r in out be in out slope slope ? ? ? ? ? ? t sw programmed inductor peak current with slope compensation (s e ) inductor current (ccm) t i trip 0.35 t sw ? i l inductor current perturbation
PM6600 operation description 31/43 7.5 soft-start the soft-start function is required to perform a correct start-up of the system, controlling the inrush current required to charge the output capa citor and to avoid output voltage overshoot. the soft-start duration is set connecting an external capacitor between the ss pin and ground. this capacitor is charged with a 5 a constant current, forcing the voltage on the ss pin to ramp up. when this voltage increases from zero to nearly 1.2 v, the current limit of the power-mosfet is proportionally released to its final value. in addition, during the initial part of the soft-start, the switching frequency of th e boost converter is reduced to half of the nominal value to permit to use inductors with lower saturation current value; the nominal switching frequency is restored after the ss pin voltage has crossed 0.8 v. in this mode, the current runaway is avoided. figure 51. soft-start sequence waveforms in case of floating rows during the soft-start phase it is also perfor med the floating rows detection. in presence of one or more floating rows, the error amplifier is unbalanced and the output voltage increases; when it reaches t he floating row detection (frd) threshold (93 % of the ovp threshold), the floating rows are managed according to table 3 (see section 3). after the ss voltage reaches a 2.4 v threshold, the start-up finishes and all the protections turn active. the soft-start capacitor css can be calculated according to equations 12. equation 13 where i ss = 5 a and t ss is the desired soft-start duration. avcc t ss ss pin voltage t protections turn active 1.2v 0.8v current limit en pin voltage 100% output voltage ovp 93% of ovp floating rows detection 2.4v nominal switching frequency release ) v v ( c 10 12 c 5 . 2 t i c min , in max , out out 6 ss ss ss ss ? ? ? ? ? ? ?
operation description PM6600 32/43 7.6 boost current limit the design of the external components, especia lly the inductor and the flywheel diode, must be optimized in terms of size relying on the programmable peak current limit. the PM6600 improves the reliability of the final application giving the way to limit the maximum current flowing into the critical comp onents. a simple resistor connected between the bilim pin and ground sets the desired value. the voltage at the bilim pin is internally fixed to 1.2 v and the current limit is proportional to the current flowing through the setting resistor, according to the following equation: equation 14 where . the maximum allowed current limit is 5 a, resulting in a minimum setting resistor r bilim > 120 k ? . the maximum guaranteed rms current in the power switch is 2 arms. the current limitation works by clamping the comp pin voltage proportionally to r bilim . peak inductor current is limited to the above th reshold decreased by the slope compensation contribution. in a boost converter the r.m.s. current through the internal mosfet depends on both the input and output voltages, according to equations 15a (dcm) and 15b (ccm). equation 15 a equation 15 b bilim b peak , boost r k i = % 15 v 10 7 . 6 k 5 b ? = 3 d l f d v i sw in rms , mos ? ? = () () () ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + ? = 3 2 sw out out 2 out rms , mos d 1 d l f i v 12 1 d 1 d i i
PM6600 operation description 33/43 7.7 enable function the PM6600 is enabled by the en pin. this pi n is active high and, when forced to sgnd, the device is turned off. this pin is connected to a permanently active 2 a current source; when sudden device turn-on at power-up is required, this pin must be left floating or connected to a delay capacitor. when turned off, the PM6600 quickly discharges the soft- start capacitor and turns off the power-mosfet, the current generators and the ldo. the power consumption is thus reduced to 20 a only. the proper startup sequence is dim ' vin ' en, or vin ' dim ' en. if the dimming signal is applied after the en pin, the devi ce will not perform the soft start again, in fact it will start switching with the maximum current limit in order to recover the output voltage. in applications where the dimming signal is us ed to turn on and off the device, the en pin can be connected to the dim pin as shown in figure 52 . figure 52. f dim enabling schematic 7.8 thermal protection in order to avoid damage due to high junction te mperature, a thermal shutdown protection is implemented. when the junction temperature rises above 150 c (typ.), the device turns off both the control logic and the boost converter and holds the fault pin low. in order to turn on the device again, it is po ssible to perform a por (power on reset) once the junction temperature has been reduced by 30 c. dim en sgnd PM6600 220k 100n bas69
backlight driver section PM6600 34/43 8 backlight driver section 8.1 current generators the PM6600 is a leds driver with six channels (rows); each row is able to drive multiple leds in series (max. 40 v) and to sink up to 30 ma maximum current, allowing to manage different kinds of leds. the leds current can be set by connecting an external resistor (r rilim ) between the rilim pin and ground. the voltage across the rilim pin is internally set to 1.2 v and the rows current is proportional to the rilim current according to the following equation: equation 16 where k r = 998 21 v ( 2.1 %). the current accuracy between the rows of more than one device is, consequently: equation 17 in the table below there are the maximum, typical and minimum i row values versus the r rilim : the maximum current mismatch between the rows of one device is 2 % @ i rowx = 20 ma, according to the formula: table 7. i row values versus r rilim r rilim i row @ kr=977 i row @ kr=998 i row @ kr=1019 47.0 k ? 20.79 ma 21.68 ma 21.68 ma 49.9 k ? 19.58 ma 20.00 ma 20.42 ma 51.0 k ? 19.16 ma 19.57 ma 19.98 ma rilim r rowx r k i = % 1 . 2 i i i i % 1 . 2 i i i i 998 k _ row 998 k _ row 977 k _ row min , row 998 k _ row 998 k _ row 1019 k _ row max , row r r r r r r ? ? = ? + ? = ? = = = = = =
PM6600 backlight driver section 35/43 equation 18 due to the spread of the leds ' forward voltage, the total dr op across the led's strings will be different. the device will manage the unc onnected rows accord ing to the mode pin setting (see ta bl e 3 ). 8.2 pwm dimming the brightness control of the leds is perfor med by a pulse-width modulation of the rows current. when a pwm signal is applied to the di m pin, the current generators are turned on and off mirroring the dim pin behavior. actually, the minimum dimming duty-cycle depends on the dimming frequency. the real limit to the pwm dimming is the minimum on-time that can be managed for the current generators; this minimum on-time is approximately 500 ns. thus, the minimum dimming duty-cycle depends on the dimming frequency according to the following formula: equation 19 for example, at a dimming frequency of 20 khz, 1% of dimming duty-cycle can be managed. during the off-phase of the pwm signal the boost converter is paused, the current generators are turned off and the output vo ltage is frozen across the output capacitor. during the start-up sequence the dimming duty-c ycle is forced to 100 % to detect floating rows regardless of the applied dimming signal. 6 i i % 2 i i i i % 2 i i i i rowi 6 1 i mean _ row mean _ row mean _ row min _ row min , rowx mean _ row mean _ row max _ row max , rowx = = ? ? = ? + ? = ? dim min , dim f ns 500 d ? =
fault management PM6600 36/43 9 fault management the main loop keeps the row having the lowest voltage drop regulated to about 400 mv. this value slightly depends on the voltage across the remainin g active rows. after the soft- start sequence, all protections turn active and the voltage across the active current generators is monitored to detect shorted leds. 9.1 fault pin the fault pin is an open-collector output, active low, which gives information regarding faulty conditions eventually detected. this pin can be used either to drive a status led (with a series resistor to not exc eed 4 ma current) or to warn the host system. the fault pin status is strictly related to the mode pin setting (see ta bl e 3 for details). 9.2 mode pin the mode pin is a digital input and can be connected to avcc or sgnd in order to choose the desired fault detection and management. the PM6600 can manage a faulty condition in two different ways, according to the application needs. ta b l e 3 summarizes how the device detects and handles the internal protections related to the boost section (over-current, over-temperature and over-voltage) and to the current generators section (open and shorted leds). table 8. faults management summary fault mode to gnd mode to vcc internal mosfet over current fault pin high power-mos turned off fault pin high power-mos turned off output over voltage fault pin low device turned off latched fault pin low device turned off latched thermal shutdown fault pin low device turned off latched fault pin low device turned off latched shorted leds on a single row fault pin low faulty row disabled vth,fault = 8.2 v fault pin low faulty row disabled vth,fault = 8.2 v shorted leds on more rows fault pin low device latched off vth,fault = 8.2 v fault pin low faulty rows disabled vth,fault = 8.2 v open row fault pin low faulty row disabled fault pin high faulty row disabled more than one open rows fault pin low device latched off fault pin high faulty rows disabled open rows plus shorted led (different rows) fault pin low device latched off vth,fault = 8.2 v fault pin low faulty rows disabled vth,fault = 8.2 v
PM6600 fault management 37/43 9.3 open led fault in case a row is not connected or a led fails open, the device has two different behaviors according to the mode pin status. if the mode pin is high (connected to avcc), the open row is excluded from the control loop and the device continues to work properly with the remaining rows, without asserting the fault pin. connecting the mode pin to sgnd, the PM6600 behaves in a different manner: as soon as one open row is detected, the fault pin is tied low. in case a second open row is detected, the device is turned of f. the internal logic latches this status: to restore the normal operation, the device must be restarted by t oggling the en pin or performing a power on reset (por occurs when the volt age at the ldo5 pin falls below the lower uvlo threshold and subsequently rises above the upper one). as a consequence, if less than six rows are used in the application, the mode pin must be set high. 9.4 shorted led fault when a led is shorted, the voltage across th e related current generator increases of an amount equal to the missing voltage drop of the faulty led. since the feedback voltage on each active generator is constantly compared with a fixed fault threshold v th,fault = 8.2 v, the device detects the faulty condition and acts according to th e mode pin status. in case the mode pin is connected to av cc, the PM6600 disconnects the rows whose voltage is higher than the threshold and the faul t pin is tied low. this option is also useful to avoid undesired triggering of the shorted- led protection simply due to the high voltage drop spread across the leds. if the mode pin is low, when the voltage across one row is higher than v th,fault threshold, the fault pin is set low and that row is disabled. if the voltage of a second row becomes higher than v th,fault threshold, the device is tu rned off. the internal logic latches this status until the en pi n is toggled or a por is performed. 9.5 intermitte nt connection for intermittent connection it is intended th e condition where the flat cable connector from the leds backlight driver to the leds can ha ve some issues on moving the panel of the notebook. this kind of issue is represented as an intermittent connection, that means the physical electrical connection between the ro wx pins of the PM6600 device and the white leds can be open for a while. the device will detect an open row fault. there is one possible solution to determine whether the fault is due to the intermittent connection or to a broken persistent electrical connection (open circuit). since the device disables the open rows during the intermittent connection, one possible solution is, on the customer side, to toggle the en pin and veri fy if the fault condi tion is still present. in fact, once you disconnect one row, it will resu lt as a off-row (fault -> open row, latched). when you connect it again, it is as a shorted led (vrow higher than the threshold). this is because the short l ed detection is still active.
fault management PM6600 38/43 if the fault disappears after toggling the en pin, it means that the connection is again on and the problem can be detected as a previous intermittent connection. if the fault persists also after toggling the en pi n, it means that the problem is on the leds (one or more open leds) or on the flat cable or the cable connector (broken wire). the resultant fault mana gement table will be: table 9. intermittent connecti on faults management summary fault mode to gnd mode to vcc internal mosfet over current fault pin high power-mos turned off fault pin high power-mos turned off output over voltage fault pin low device turned off latched fault pin low device turned off latched thermal shutdown fault pin low device turned off latched fault pin low device turned off latched shorted led on a single row fault pin low faulty row disabled vth,fault = 8.2 v fault pin low faulty row disabled vth,fault = 8.2 v shorted leds on more row fault pin low device latched off vth,fault = 8.2 v fault pin low faulty rows disabled vth,fault = 8.2 v open row fault pin low faulty row disabled fault pin low faulty row disabled more than one open rows fault pin low device latched off fault pin low faulty rows disabled open row plus shorted led (different rows) fault pin low device latched off vth,fault = 8.2 v fault pin low faulty rows disabled vth,fault = 8.2 v
PM6600 package mechanical data 39/43 10 package mechanical data in order to meet environmental requirements, st offers these devices in ecopack ? packages. these packages have a lead-free se cond level interconnect. the category of second level interconnect is marked on the package and on the inner box label, in compliance with jedec standard jesd97. th e maximum ratings related to soldering conditions are also marked on the inner box label. ecopack is an st trademark. ecopack specifications are available at: www.st.com . table 10. vfqfpn-24 mechanical data dim. min typ max a 0.80 0.90 1.00 a1 0.00 0.02 0.05 a3 0.20 b 0.18 0.25 0.30 d 3.85 4.00 4.15 d2 2.40 2.50 2.60 e 3.85 4.00 4.15 e2 2.40 2.50 2.60 e0.50 l 0.30 0.40 0.50 ddd 0.08
package mechanical data PM6600 40/43 figure 53. vfqfpn-24 mechanical data
PM6600 package mechanical data 41/43 figure 54. vfqfpn-24 footprint table 11. vfqfpn-24 footprint dim. min typ max x 0.28 y0.69 admax = aemax 2.78 gdmin = gemin 2.93 zdmax = zemax 4.31 d2? = e2? 2.63
revision history PM6600 42/43 11 revision history table 12. document revision history date revision changes 07-dec-2007 1 initial release 21-jan-2008 2 updated ta bl e 4 , ta b l e 5 and table 6 on page 9
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