BD9488F-GE2

Datasheet Boost 1channel white LED driver For large LCDs BD9488F ●General Description BD9488F is a high efficiency driver for white LEDs and designed for large LCDs. This IC is built-in a boost DCDC converters that employ an array of LEDs as the light source. BD9488F has some protect function against fault conditions, such as the over-voltage protection (OVP), the over current limit protection of DCDC (OCP), LED over current protection (LEDOCP), the open detection of LED string. Therefore BD9488F is available for the fail-safe design over a wide range output voltage. ●Key Specifications  Input voltage range: 9.0V to 18.0V  DCDC oscillation frequency: 150kHz (RT=100kΩ)  Active current consumption: 1.2mA(Typ.)  Operating temperature range: -40℃ to +85℃ ●Package(s) SOP18 ●Features  Current mode DCDC converter  Vout discharge circuit as shutdown  LED protection circuit (OPEN protection, LED OCP protection)  LED protect detection as small PWM dimming signal  Over-voltage protection (OVP) for the output voltage.  Adjustable soft start time constant  The wide range of analog dimming 0.2V-3.5V  The built-in transformation circuit from pulse to DC  2 PWM dimming signal  The UVLO detection for the input voltage of the power stage  FAIL logic output Figure 1. W(Typ.) x D(Typ.) x H(Max.) 11.20mm x 7.80mm x 2.01mm Pin pitch 1.27mm SOP18 ●Applications  TV, PC display and other LCD backlight system. ●Typical Application Circuit(s) VCC VIN VCC UVLO OVP TC54 STB GATE RT CS Css SS FAILB DIMOUT PWM1 PWM2 ISENSE ADIM_P FB ADIM GND Figure 2. Typical application circuit ○Product structure：Silicon monolithic integrated circuit .www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・14・001 ○This product is not designed protection against radioactive rays 1/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F ●Absolute Maximum Ratings (Ta=25℃) Symbol Ratings Unit Vccmax 20 V STB VCC V OVP, UVLO, SS, RT, ISENSE, FB, CS, TC54 7 V Parameter Input voltage STB pin voltage OVP, UVLO, SS, RT, ISENSE, FB, CS, TC54 pin voltage PWM1, PWM2, FAILB, ADIM, ADIM_P pin voltage DIMOUT, GATE pin voltage PWM1, PWM2, FAILB, ADIM, ADIM_P DIMOUT, GATE 20 V VCC V Pd 687 (*1) mW Topr -40 to +85 ℃ Tjmax 150 ℃ Tstg -55 to +150 ℃ Symbol Range Unit VCC 9.0 to 18.0 V Power Dissipation Operating Temperature Range Junction Temperature Storage Temperature Range *1 Pd derated at 5.5 mW/℃ for temperature above Ta=25℃, mounted on 70mm×70mm×1.6mm 1 layer glass-epoxy PCB. ●Operation range Parameter VCC Power source voltage DC/DC oscillation frequency fsw 50 to 800 kHz The effective range of ADIM signal VADIM 0.2 to 3.5 V PWM input frequency range FPWM 90 to 100k Hz ●Pin Configuration ●Package dimension, marking diagram OVP 1 18 TC54 UVLO 2 17 CS SS 3 16 FB RT 4 15 ISENSE PWM1 5 14 VCC PWM2 6 13 STB FAILB 7 12 GATE ADIM 8 11 DIMOUT ADIM_P 9 10 GND BD9488F Lot No. Figure 3-1. Pin configuration www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 Figure 3-2. Package dimension 2/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F ●1.1 Electrical character (Unless otherwise specified Ta=25℃，VCC=12V) Limit Parameter Symbol 【Total current consumption】 Min. Typ. Max. Unit Condition Circuit current Icc － 1.2 1.8 mA VSTB=3V, PWM1=PWM2=0V Standby current IST － 0 3 μA VSTB=0V VCC=SWEEP UP 【UVLO block】 Operation voltage（VCC） VUVLO_VCC 6.5 7.5 8.5 V Hysteresis Voltage（VCC） VUHYS_VCC 150 300 600 mV UVLO release voltage VUVLO 2.88 3.00 3.12 V UVLO hysteresis voltage VUHYS 250 300 350 mV VUVLO=SWEEP DOWN UVLO_LK -2 0 2 μA VUVLO=4V ISENSE threshold voltage 1 VLED1 1.47 1.50 1.53 V VADIM=1.5V ISENSE threshold voltage 2 VLED2 3.33 3.50 3.67 V VADIM=5.0V (as mask analog dimming) ISENSE threshold voltage 3 VLED3 -2 - +2 % VADIM=0.7V Oscillation frequency GATE pin MAX DUTY output GATE pin ON resistance (as source) GATE pin ON resistance (as sink) FCT 142.5 150 157. 5 KHz RT=100kohm NMAX_DUTY 90 95 99 % RT=100kohm RONSO 3.0 6.0 12.0 Ω ION=-10mA RONSI 1.2 2.5 5.0 Ω ION=10mA VRT 1.0 1.5 2.0 V RT=100kohm SS pin source current ISSSO -4.20 -3.0 -2.14 μA SS pin Low output voltage VSS_L - 0.20 0.50 V VSTB=0V, Ioss=50uA VSS_END 2.7 3.0 3.3 V FB source current IFBSO -140 -100 -60 μA FB sink current IFBSI 60 100 140 μA SS=SWEEP UP VISENSE=0.2V, VFB=1.0V VISENSE=2.0V, VFB=1.0V OCP detect voltage VCS 360 400 440 mV CS=SWEEP UP UVLO pin leak current VCC=SWEEP DOWN VUVLO=SWEEP UP 【DC/DC block】 RT pin voltage Soft start ended voltage VSS=2V VADIM=1.0V, VADIM=1.0V, 【DC/DC protection block】 OVP detect voltage OVP detect hysteresis OVP pin leak current VOVP 2.88 3.00 3.12 V VOVP_HYS 50 100 150 mV VOVP SWEEP DOWN OVP_LK -2 0 2 μA VOVP=4V www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 3/38 VOVP SWEEP UP TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F ●1.2 Electrical character (Unless otherwise specified Ta=25℃，VCC=12V) Limit Parameter 【LED protection block】 Symbol Min. Typ. Max. Unit LED OCP detect voltage VLEDOCP 3.8 4.0 4.2 V VISENSE=SWEEP UP VOPEN 0.05 0.10 0.15 V VISENSE=SWEEP DOWN ADIM_PH 2.0 - 3.8 V ADIM_PL -0.3 - 0.8 V ADIM_PPU 4.2 - 18 V RADIM_P 130 200 300 kΩ VADIM_P=3.0V ADIMH 3.201 3.30 3.399 V ADIM_P=3.3V ADIM_P=0.0V LED OPEN detect voltage 【Analog dimming block】 ADIM_P pin HIGH voltage ADIM_P pin LOW voltage ADIM_P pin input mask voltage ADIM_P pin pull-down resistance ADIM pin output voltage H Condition ADIM pin output voltage L ADIM pin output resistance ADIML - 0.0 0.05 V ADIMR 6.6 10 15 kΩ ADIM pin leak current ILADIM -2 0 2 μA VADIM=4V, ADIM_P=5.0V -2 0 2 μA VISENSE=4V 6.0 12.0 24.0 Ω ION=-10mA 1.7 3.5 7.0 Ω ION=10mA IO=0mA ISENSE pin leak current IL_ISENSE 【Dimming signal output block】 DIMOUT source on-resistance RONSO DIMOUT sink on-resistance RONSI 【TC54 block】 TC54 output voltage VTC54 5.2 5.4 5.6 V TC54 available current TC54_UVLO detect voltage |ITC54| 100 - - μA TC54_TH 2.232 2.4 2.568 V VSTB=H, TC54=SWEEP DOWN TC54_UVLO hysteresis TC54_HYS 50 100 200 mV VSTB=H->L, TC54=SWEEP UP TC54 discharge current 【STB block】 TC54_DIS 5 10 15 μA VSTB=H->L, TC54=4V STB pin HIGH voltage STBH 2.2 - 19 V VSTB=SWEEP UP STB pin LOW voltage STBL -0.3 - 0.8 V VSTB=SWEEP DOWN STB pin input current 【PWM block】 ISTB 2.0 3.0 4.5 μA VSTB=3.0V PWMｘ pin HIGH Voltage PWM_H PWMｘ pin LOW Voltage PWM_L PWMｘ pin Pull Down resistance RPWM 【FAIL block (OPEN DRAIN)】 2.0 - 18 V VPWMｘ=SWEEP UP -0.3 - 0.8 V VPWMｘ=SWEEP DOWN 130 200 300 kΩ VPWMｘ=3.0V FAILB pin on-resistance RFAIL 0.75 1.5 3.0 kΩ VFAIL=1.0V FAILB pin leak current ILFAIL -2 0 2 μA VFAIL=15V www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 4/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F ●1.3 Pin number, pin name, pin function No. name IN/OUT function rating[V] 1 OVP In Over voltage protection detection pin -0.3 to 7 2 UVLO In Under voltage lock out detection pin -0.3 to 7 3 SS Out Slow start setting pin -0.3 to 7 4 RT Out For DC/DC switching frequency setting pin 5 PWM1 In External PWM dimming signal input pin1 -0.3 to 20 6 PWM2 In External PWM dimming signal input pin2 -0.3 to 20 7 FAILB Out Abnormality detection output pin -0.3 to 20 8 ADIM In/Out ADIM signal input-output pin -0.3 to 20 9 ADIM_P In ADIM pulse signal input pin -0.3 to 20 10 GND - - 11 DIMOUT Out Dimming signal pin for driving MOSFET -0.3 to VCC 12 GATE Out DC/DC switching output pin -0.3 to VCC 13 STB In IC On/OFF pin -0.3 to VCC -0.3 to 7 14 VCC - Power supply pin 15 ISENSE In Current detection input pin -0.3 to 7 16 FB In/Out Error amplifier output pin -0.3 to 7 DC/DC output current detect pin, OCP input pin -0.3 to 7 5.4V output pin, shutdown timer pin -0.3 to 7 17 CS In 18 TC54 Out www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 -0.3 to 20 5/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F ●2.1.1 Pin ESD Type OVP UVLO SS Internal vol. 50k Internal vol. OVP SS 5V RT PWM1, PWM2 FAILB ADIM ADIM_P DIMOUT GATE STB ISENSE Internal vol. 10k ISENSE 5V Figure 4-1. Internal equivalent circuit www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 6/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F ●2.1.2 Pin ESD Type FB CS TC54 Internal vol. Internal vol. 1k TC54 FB Figure 4-2. Internal equivalent circuit ●2.2 Block diagram VCC VIN VCC UVLO OVP TC54 VCC UVLO VREG STB UVLO OVP TSD REG54 UVLO VCC OSC + RT PWM COMP GATE CONTROL LOGIC CS LEB Current sense Css SS SS VCC DIMOUT SS-FB clamper LEDOCP Fail detect ERROR amp PWM1 + + - OPEN FAILB ISENSE 3.5V FB PWM2 4.0V ADIM_P 1.5V + - 3.3V + 10kΩ ADIM GND Package:SOP18 Figure 5. Block diagram www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 7/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F 2.0 10000 1.5 1000 frequency [kHz] ICC[mA] ●2.3 Typical performance Curves 1.0 0.5 0.0 100 10 1 7 9 11 13 15 17 10 100 RT[kΩ] Figure 7. GATE frequency vs RT 120 0 100 -20 FB source current[uA] FB sink current [uA] VCC[V] Figure 6. Operating current (ICC) vs VCC 80 60 40 20 0 0.5 1.5 2.5 3.5 -40 -60 -80 -100 -120 4.5 0.5 FB[V] 1.5 2.5 3.5 4.5 FB[V] Figure 9. FB source current vs FB voltage Figure 8. FB sink current vs FB voltage ISENSE feedback voltage [V] 1000 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0 2 4 6 ADIM[V] Figure 10. ISENSE feedback voltage vs ADIM www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 8/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F ●2.4 Pin function description ○Pin1: OVP The OVP terminal is the input for over-voltage protection of output voltage. As OVP is more than 3.0V, the over-voltage protection (OVP) will work. At the moment of this detection, the BD9488 stops the switching of the output GATE and starts to count up the abnormal interval, but IC doesn't reach latch off state instantaneously until the detection continues up to the number of counts of GATE terminals, which depend on the kind of abnormality. (Please refer to the time chart in the section 3.5.7) The OVP pin is high impedance, because the internal resistance to a certain bias is not connected. So, the bias by the external components is required, even if OVP function is not used, because the open connection of this pin is not fixed the potential. The setting examples is separately described in the section 3.4.6, ”external components selection, how to set OVP” ○Pin2: UVLO Under voltage lock out pin for the input voltage of the power stage. More than 3.0V(typ.), IC starts the boost operation and stops lower than 2.7V(typ.). The UVLO pin is high impedance, because the internal resistance to a certain bias is not connected. So, the bias by the external components is required, even if UVLO function is not used, because the open connection of this pin is not fixed the potential. The setting examples is separately described in the section 3.4.5, ”external components selection, how to set UVLO” ○Pin3: SS The pin which sets soft start interval of DC/DC converter. It performs the constant current charge of 3.0 μA to external capacitance Css(OPEN to 4.7μF). The switching duty of GATE output will be limited during 0V to 3.0V of the SS voltage. So the equality of the soft start interval can be expressed as following 6 Css: the external capacitance of the SS pin. Tss = 1.0*10 *Css Regarding of the logic of SS=L (SS=L) = (PWM1andPWM2 have not asserted H since ResetB=L->H) or (latch off state) where ResetB = (STB=H) and (VCCUVLO=H) and (UVLO=H) and (TC54UVLO=H) As the capacitor of SS pin is smaller than about 1nF, it is necessary to notice if the inrush current I(Vin) as turning-on is too large, and if the masking interval of OPEN detection is too short. Please refer to the time chart on soft start behavior in the section 3.7.4 ○Pin4: RT DC/DC switching frequency setting pin. RT set the oscillation frequency inside IC. ○The relationship between the frequency and RT resistance value (ideal) R RT  15000 f SW [ kHz ] [ k ] The oscillation setting range from 50kHz to 800kHz. The setting examples is separately described in the section 3.4.4, ”external components selection, how to set DCDC oscillation frequency” ○Pin5, Pin6: PWM1, PWM2 The ON / OFF terminal of the LED driver. LED lights when both PWM signal are high (DIMOUT = H). The Duty signal of this pin can control the PWM dimming. The high / low level of PWM pins are following. State PWM input voltage PWM1=H or PWM2=H PWM=2.0V to 18.0V PWM1=L or PWM2=L PWM=‐0.3V to 0.8V PWM1 and PWM2 have the functional difference, and GATE pin outputs only by the logic of PWM1. This is why only boost operation continues while PWM1=H, PWM2=L. In this case, the adequate confirmation is required not to be over voltage of the output voltage Vout. www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 9/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F Figure 11. PWM pin function ○Pin7: FAILB FAIL signal output pin (open drain). As abnormal, the internal NMOS turn on. Status FAILB output Normal OPEN Abnormal GND Level ○Pin8: ADIM ADIM_P input level -0.3VTrise_min. www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 16/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F ●3.4.2 how to shutdown and set TC54 capacitance This IC is equipped the discharge function when shutdown is operated. Figure 23. the shutdown waveform and circuit ○Explanation of shutdown sequence ①When STB=L, DC/DC and TC54 are stop. ②When STB=L, TC54UVLO=H, the DIMOUT logic asserts the PWM logic. The voltage of TC54 (5.4V) will decrease by the constant current -10uA and is discharged to 2.4V. ③VOUT will be discharged and ILED decresing. ④When the voltage of TC54 pin is under 2.4V(typ.), the IC will shutdown. ○The setting method of TC54 external capacitance Please use below formula to calculate the shutdown time TOFF. TOFF  CREG[ F ]  3.0 [V ] [　 Sec] 10 [A] As shown the above, the PWM signal is required even after STB=L. The discharge interval of VOUT is the longest in the minimum PWM duty. Please set the Creg value with a enough timing margin from the end of the VOUT discharge to shutdown. ●3.4.3 The LED current setting LED current can be adjusted by setting the resistance RISENSE which connects to ISENSE pin. ○the relationship between RISET and ILED current RISENSE  ADIM [V ] [ ] I LED [ A] RISENSE  3.5[V ] [ ] I LED [ A] Without DC dimming Error AMP [setting example] If ILED current is 400mA as ADIM is 1.5V, we can calculate RISENSE as below. RISENSE DIMOUT + + - With DC dimming Vout ISENSE 3.5V ADIM RISENSE FB ADIM [V ] 1.5[V ]    3.75[] 　 I LED [ A] 0.4[ A] Figure 24. the example of LED current setting www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 17/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F ●3.4.4. how to set DCDC oscillation frequency RRT which connects to RT pin set the oscillation frequency of DCDC. ○ the relationship between OSC and RRT (ideal) R RT  15000 f SW [ kHz ] [ k ] where fsw is the oscillation frequency of DCDC [kHz] Frequency (fsw) Ideal GATE RT CS Rcs RRT GND Figure 25. RT pin setting example This equation is an ideal equation in which correction factors are not applied. The adequate verification with an actual set needs to be performed to set frequency precisely. [setting example] If DCDC oscillation frequency is 200kHz, we can calculate the RRT as below. RRT  15000 15000   75 [ k] 　 f sw [ kHz ] 200[ kHz ] www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 18/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F ●3.4.5. how to set UVLO Under voltage lock out pin for the input voltage of the power stage. More than 3.0V(typ.), IC starts boost operation and stops lower than 2.7V(typ.). The UVLO pin is high impedance, because the internal resistance to a certain bias is not connected. So, the bias by the external components is required, even if UVLO function is not used, because the open connection of this pin is not fixed the potential. The resistor value can be calculated by the below formula, if the VIN voltage is monitored, and that is divided by the resistor R1, R2 like the below diagram. ○UVLO detection equality If VIN decreases, R1, R2 value is expressed the following formula by the VINdet, the detect voltage of UVLO. R1  R 2[k]  (VINDET [V ]  2.7[V ]) 2.7[V ] [k] ○UVLO release equality By using the R1, R2 in the above equality, the release voltage of UVLO can be expressed as following. VINCAN  3.0V  ON/ OFF UVLO + - 2.7V/3.0V R1 R2 CUVLO ( R1[k]  R2[k]) [V ] R2[k] [setting example] If the normal input voltage, VIN is 24V, the detect voltage of UVLO is 18V, R2 is 30k ohm, R1 is calculated as following. R1  R 2[k]  VIN Figure 26. UVLO setting example (VINDET [V ]  2.7[V ]) (18[V ]  2.7[V ])  170.0 [k]  30[k]  2.7[V ] 2.7[V ] By using these R1, R2, the release voltage of UVLO, VINcan can be calculated as following. VINCAN  3.0[V ]  (R1[k]  R 2[k]) 170.0[k]  30[k]  3.0[V ]  [V ]　  20.0 [V ] R 2[k] 30[k] www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 19/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F ●3.4.6. how to set OVP The OVP terminal is the input for over-voltage protection of output voltage. The OVP pin is high impedance, because the internal resistance to a certain bias is not connected. So, the bias by the external components is required, even if OVP function is not used, because the open connection of this pin is not fixed the potential. The resistor value can be calculated by the below formula, if the OVP VOUT voltage is monitored, and that is divided by the resistor R1, OVP + R2 like the below diagram. - 2.9V/3.0V ○OVP detection equality If the VOUT is boosted abnormally, VOVPdet is the detect voltage of OVP, R1, R2 can be expressed by the following formula. R1  R2[k]  VOUT R1 R2 COVP (VOVPDET [V ]  3.0[V ]) [k] 3.0[V ] ○OVP release equality By using the R1, R2 in the above equality, the release voltage of OVP, VOVPcan can be expressed as following. VOVPCAN  2.9V  Figure 27. OVP setting example ( R1[k]  R2[k]) [V ] R2[k] [setting example] If the normal output voltage, VOUT is 40V, the detect voltage of OVP is 48V, R2 is 10k ohm, R1 is calculated as following. R1  R2[k]  (VOVPDET [V ]  3.0[V ]) (48[V ]  3[V ])  10[k]   150 [k] 3.0[V ] 3[V ] By using these R1, R2, the release voltage of OVP, VOVPcan can be calculated as following. VOVPCAN  2.9[V ]  10[k]  150[k] ( R1[k]  R2[k])  2.9[V ]  [V ]　  46.4 [V ] 10[k] R2[k] www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 20/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F ●3.4.7. how to set the interval until latch off BD9488 built in the counter by latch off time, that is performed by counting the oscillation clock which is set by the RT pin. Since the common oscillation circuit is used for counting, the interval until latch off is corresponding to the 130k clock, which the GATE pulse output continuously. Please refer the time chart of the operation from the detect abnormality to the latch off in the section 3.7. ○latch off time BD9488 starts the counting up from the detection of each abnormal state, falls to the latch off state when the following interval has passed. Only PWM=L input does not reset the timer counter, if the abnormal state continues. LATCHTIME  217  RRT [] R [k]  130k  RT 7 [sec] 10 1.5  10 1.5  10 Where LATCHTIME is the interval until latch off state RRT is the connected resistor of RT pin. [setting example] If the resistor of RT pin is 100k ohm, the timer latch interval is as following. LATCHTIME  130k  www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 RRT [k] 100[k]  130 k   866[m sec]　 1.5 107 1.5 107 21/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F ●3.5. DCDC parts selection 3.5.1. how to set OCP / the calculation method for the current rating of DCDC parts BD9488 stops the switching by the OCP detect, when the CS pin voltage is more than 0.4V. The resistor value of CS pin, RCS need to be considered by the coil L current. And the current rating of DCDC external parts is required more than the peak current of the coil. It is shown below that the calculation method of the coil peak current, the selection method of Rcs (the resistor value of CS pin) and the current rating of the external DCDC parts. I IN  L VIN VOUT IL IOUT (the calculation method of the coil peak current, Ipeak) At first, since the ripple voltage at CS pin depend on the application condition of DCDC, those put onto the equality to calculate as following. The output voltage = VOUT [V] LED total current = IOUT [A] The DCDC input voltage of the power stage = VIN [V] The efficiency of DCDC =η[%] And then, the averaged input current IIN is calculated by the following equality fsw VOUT [V ]  I OUT [ A] [ A] VIN [V ] [%] GATE CS Rcs And the ripple current of the inductor L (ΔIL[A]) can be calculated by using DCDC the switching frequency, fsw, as following. Δ IL  GND (VOUT [V ]  V IN [V ])  V IN [V ] [ A] L[ H ]  VOUT [V ]  f SW [ Hz ] (V) Ipeak  I IN [ A]  IL[ A] 2 [ A] … (1) N[V] On the other hand, the peak current of the inductor Ipeak can be expressed as the following equality. Therefore, the bottom of the ripple current Imin is （A) (t) or 0 Ipeak As Imin>0, that operation mode is CCM (Continuous Current Mode), otherwise another mode is DCM (Discontinuous Current Mode). VCS peak  Rcs  Ipeak Imin (t) （V) 0.4V VCS[V] (the selection method of Rcs) Ipeak flows into Rcs and that cause the voltage signal to CS pin. (Please refer the right timing chart) That peak voltage VCSpeak is as following. ΔIL IIN IL[A] IL[ A] Im in  I IN [ A]  　 2 [V ] VCSpeak As this VCSpeak reaches to 0.4V, the DCDC output stops the switching. Therefore, Rcs value is necessary to meet the under condition. (t) Rcs  Ipeak [V ]  0.4[V ] Figure 28. Coil current waveform (the current rating of the external DCDC parts) The peak current as the CS voltage reaches to OCP level (0.4V) is defined as Ipeak_det. I peak _ det  0.4[V ] [ A] Rcs[ ] … (2) The relation among Ipeak (equality (1)), Ipeak_det (equality (2)) and the current rating of parts is required to meet the following I peak  I peak _ det  The current rating of parts Please make the selection of the external parts to meet the above condition such as FET, Inductor, diode. [setting example] The output voltage = VOUT [V] = 40V LED total current = IOUT [A] = 0.48V The DCDC input voltage of the power stage = VIN [V] = 24V www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 22/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F The efficiency of DCDC =η[%] = 90% The averaged input current IIN is calculated as the following. I IN [ A]  VOUT [V ]  I OUT [ A] 40[V ]  0.48[ A]   0.89 [ A] 　 24[V ]  90[%] VIN [V ] [%] And the ripple current of the inductor L (ΔIL[A]) can be calculated if the switching frequency, fsw = 200kHz, the inductor, L=100μH. Δ IL  (VOUT [V ]  V IN [V ])  V IN [V ] ( 40[V ]  24[V ])  24[V ] 　  0.48 [ A]  L[ H ]  VOUT [V ]  f SW [ Hz ] 100  10  6 [ H ]  40[V ]  200  10 3 [ Hz ] Therefore the inductor peak current, Ipeak is Ipeak  I IN [ A]  IL[ A] 0.48[ A] [　 A]  0.89[ A]   1.13 [ A] 2 2 The calculation result of the peak current If Rcs is assume to be 0.3 ohm VCS peak  Rcs  Ipeak  0.3[  ]  1.13[ A]  0.339 [V ]  0.4V The Rcs value confirmation The above condition is met. And Ipeak_det, the current OCP works is I peak _ det  0.4[V ]  1.33 [ A] 0.3[ ] If the current rating of the used parts is 2A, I peak  I peak _ det  The current rating  1.13[ A]  1.33[ A]  2.0[ A] The current rating confirmation of DCDC parts This inequality meets the above relationship. The parts selection is proper. And Imin, the bottom of the IL ripple current can be calculated as following. I MIN  I IN [ A]  IL[ A] [ A]  1.13[ A]  0.48[ A]  0.65[ A]  0 　 2 This inequality implies the operation is the continuous current mode. www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 23/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F 3.5.2. Inductor selection The inductor value affects the input ripple current. The equality in the section 3.5.1 is as following. Δ IL  ΔIL I IN  VIN (VOUT [V ]  V IN [V ])  V IN [V ] [ A] L[ H ]  VOUT [V ]  f SW [ Hz ] VOUT [V ]  I OUT [ A] [ A] VIN [V ] [%] Ipeak  I IN [ A]  IL L VOUT IL[ A] 2 [ A] Where L: the coil inductance [H] Vout: the DCDC output voltage [V] Vin: the input voltage [V] Iout: the output load current (the summation of LED current) [A] Iin: the input current [A] Fsw: the oscillation frequency [Hz] If in the continuous current mode, Please set ⊿IL to 30% - 50% of the output load current. RCS COUT Figure 29. the waveform and the circuit of inductor current * The current exceeding the rated current value of inductor flown through the coil causes magnetic saturation, results in decreasing in efficiency. Inductor needs to be selected to have such adequate margin that peak current does not exceed the rated current value of the inductor. * To reduce inductor loss and improve efficiency, inductor with low resistance components (DCR, ACR) needs to be selected 3.5.3. Output capacitance Cout selection Output capacitor needs to be selected in consideration of equivalent series VIN resistance required to even the stable area of output voltage or ripple voltage. Be aware that set LED current may not be flown due to decrease in LED IL terminal voltage if output ripple componet is high. Output ripple voltage ⊿VOUT is determined by Equation (4): L VOUT ΔVOUT  ILMAX  R ESR  1 C OUT  I OUT   1 f SW 　 [V ]　・・・・・　　 (4) where, RESR is the equivalent series resistance of Cout. RESR RCS COUT Figure 30. the circuit of the output capacitor * Rating of capacitor needs to be selected to have adequate margin against output voltage. * To use an electrolytic capacitor, adequate margin against allowable current is also necessary. Be aware that the LED current is larger than the set value transitionally in case that LED is provided with PWM dimming especially. www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 24/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F 3.5.4. MOSFET selection Though there is no problem if the absolute maximum rating is larger than the rated current of the inductor L, or is larger than the sum of the tolerance voltage of COUT and the rectifying diode VF. The product with small gate capacitance (injected charge) needs to be selected to achieve high-speed switching. * One with over current protection setting or higher is recommended. * The selection of one with small on resistance results in high efficiency. 3.5.5. Rectifying diode selection A schottky barrier diode which has current ability higher than the rated current of L, the reverse voltage larger than the tolerance voltage of COUT, and the low forward voltage VF especially needs to be selected. www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 25/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F ●3.6. Loop compensation A current mode DCDC converter has each one pole (phase lag) fp due to CR filter composed of the output capacitor and the output resistance (= LED current) and zero (phase lead) fZ by the output capacitor and the ESR of the capacitor. Moreover, a step-up DCDC converter has RHP zero (right-half plane zero point) fZRHP which is unique with the boost converter. This zero may cause the unstable feedback. To avoid this by RHP zero, the loop compensation that the cross-over frequency fc set as following, is suggested. fc = fZRHP /5 (fZRHP: RHP zero frequency) Considering the response speed, the below calculated constant is not always optimized completely. It needs to be adequately verified with an actual device. VOUT VIN ILED L VOUT - FB gm RESR + RCS RFB1 COUT CFB2 CFB1 Figure 31. the circuit of output stage and the error amplifier i. Calculate the pole frequency fp and the RHP zero frequency fZRHP of DC/DC converter fp  I LED [　 Hz ] 　 2  VOUT  COUT Where ILED = the summation of LED current, ii. Where VOUT  (1  D) 2 [　 Hz ]　　 2  L  I LED (Continuous Current Mode) VOUT  VIN 　 output (fc = fZRHP/5) VOUT D Calculate the phase compensation of the error amp f RHZP  RCS  I LED [　 ] 　 5  f p  gm  VOUT  (1  D) R FB1  iii. f ZRHP  C FB1  1 [　 F ]　　 2  RFB1  f p gm  4.0  10 4 [ S ] Calculate zero to compensate ESR (RESR) of COUT (electrolytic capacitor) C FB 2  RESR  C OUT [　 F] 　 RFB1 *When a ceramic capacitor (with RESR of the order of milliohm) is used to COUT, the operation is stabilized by insertion of CFB2. To improve the transient response, RFB1 need to be increase, CFB1 need to be decrease. It needs to be adequately verified with an actual device in consideration of vary from parts to parts since phase margin is decreased. www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 26/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F ●3.7. Timing chart 3.7.1 starting up 1 (STB inputs and PWM signal succeeds) 7.5V VCC STB PWM1 andPWM2 2.4V 2.5V 2.5V TC54 V5UVLO 3.0V 1.1V SS 1.1V GATE FAILB OFF SS STANDBY Normal OFF SS (Reset) (*1) (*2) (*3) (*4) STANDBY (*5) (*1)…TC54 starts up if STB turns from L to H. The pin SS is not charged in the state that the PWM signal is not input, the boost is not started. (*2)…The charge of the pin SS starts by the positive edge of PWM=L to H, and the soft start starts. The GATE pulse outputs only during PWM=H. And as the SS is less than 1.1V, the pulse does not output. The pin SS continues charging in spite of the assertion of PWM and OVP. (*3)…The soft start interval will end if the voltage of the pin SS, Vss reaches to 3.0V. By this time, BD9488 boost Vout where the set LED current flows. It is started to monitor the abnormal detection of OPEN. (*4)…As STB=L, instantaneously the boost operation is stopped. (GATE=L, SS=L) On the other hand, the discharge circuit works in the interval “STB=L and V5UVLO=H”. Please refer to the time chart in the section 3.7.3 for details. (*5)…As STB=H again, the boost operation restarts by the next PWM=L to H. It is the same operation as the timing of (*1). Please refer to the section 3.4.1 for the setting of soft start external capacitance. www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 27/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F 3.7.2 starting up 2 (PWM signal inputs and STB succeeds) VCC 7.5V STB PWM1 andPWM2 2.4V 2.5V TC54 2.5V V5UVLO 3.0V 1.1V SS 1.1V GATE FAILB OFF SS ON OFF SS (Reset) (*1) (*2) (*3) (*4) STANDBY (*5) (*1)…TC54 starts up if STB turns from L to H. (*2)…At the moment the release of V5UVLO (the UVLO of the pin TC54), or the time of the positive edge of PWM=L to H, the soft start starts. The GATE pulse outputs only during PWM1=H. And as the SS is less than 1.1V, the pulse does not output. The pin SS continues charging in spite of the assertion of PWM and OVP. (*3)…The soft start interval will end if the voltage of the pin SS, Vss reaches to 3.0V. By this time, BD9488 boost Vout where the set LED current flows. It is started to monitor the abnormal detection of OPEN. (*4)…As STB=L, instantaneously the boost operation is stopped. (GATE=L, SS=L) On the other hand, the discharge circuit works in the interval “STB=L and V5UVLO=H”. Please refer to the time chart in the section 3.7.3 for details. (*5)…As STB=H again, it is the same operation as the timing of (*1). www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 28/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F 3.7.3 turn off STB PWM1 andPWM2 TC54 2.4V V5UVLO DIMOUT GATE Vout SS ON Dischange (*1) OFF (*2) (*1)…As STB pin turns High to Low, BD9488F stops the boost operation, starts the discharge of TC54. (*2)…During STB=L and V5UVLO=H, the DIMOUT asserts the same logic of PWM. TC54=5.4V is discharged until 2.4V by the constant current 10uA. And IC turns off. Vout need to be discharged adequately so that LED does not turns on drastically at the next start up. For detailed instructions, please refer the section 3.4.2 “how to shutdown and set TC54 capacitance” www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 29/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F 3.7.4 the soft start function (*1)…The SS pin charge does not start by just STB=H. “PWM1=H and PWM2=H” is required to start the soft start. In the low SS voltage, the GATE pin duty is depend on the SS voltage. And as the SS is less than 1.1V, the pulse does not output. (*2)…By the low STB=L, the SS pin is discharged immediately. (*3)…As the STB recovered to STB=H, The SS charge starts immediately by the logic “PWM1 and PWM2=H” in this chart. (*4)…The SS pin is discharged immediately by the UVLO=L. (*5)…The SS pin is discharged immediately by the VCCUVLO=L (*6)…The SS pin is discharged immediately by the TC54UVLO=L (*7)…The SS pin is not discharged by the abnormal detection of the latch off type such as OVP until the latch off www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 30/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F 3.7.5 the OVP detection (*1)…As OVP is detected, the output GATE=L, DIMOUT=L, and the CP counter starts (*2)…If OVP is released within 4 clock of CP counter of the GATE pin frequency, the boost operation restarts. (*3)…As the OVP is detected again, the boost operation is stopped. (*4)…As the OVP detection continues up to 4 count by the CP counter, IC will be latched off. (*5)…As the latched off, the boost operation doesn't restart even if OVP is released. (*6)…The STB=L input can make IC reset. In this chart, DIMOUT asserts high by the discharge function in the paragraph 3.7.3. (*7)…It normally starts as STB turns L to H. (*8)…The operation of the OVP detection is not related to the logic of PWM. www.rohm.com © 2012 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 31/38 TSZ02201-0F1F0C100040-1-2 27.May 2014 Rev.003 Datasheet BD9488F 3.7.6 LED OPEN detection (*1)…During starting up, even if the normality, ISENSE