IS32BL3556 WIDE INPUT VOLTAGE RANGE, HIGH EFFICIENCY FAULT TOLERANT LED DRIVER Advanced Information March 2014 GENERAL DESCRIPTION FEATURES The IS32BL3556 is a multi-output white LED driver for small-size LCD backlighting. It integrates a current-mode boost converter with internal power switch and four current sinks. The boost converter can drive up to 48 LEDs, 12 LEDs per string, at 100mA. The LED sinks can be paralleled together to achieve even higher LED currents, up to 320mA. The IS32BL3556 can operate with a single power supply, from 4.75 to 40V, which allows the part to withstand load dump conditions encountered in automotive systems. The IS32BL3556 can drive an external P-FET to disconnect the input supply from the system in the event of a fault. The IS32BL3556 provides protection against output short and overvoltage, open or shorted diode, open or shorted LED pin, shorted boost switch or inductor, shorted FSET or ISET resistor, and IC overtemperature. A dual level cycle-by-cycle current limit function provides soft start and protects the internal current switch against high current overloads. The IS32BL3556 has a synchronization pin that allows PWM switching frequencies to be synchronized in the range of 580kHz to 2.3MHz. The high switching frequency allows the IS32BL3556 to operate above the AM radio band. The IS32BL3556 is provided in a TSSOP-20 package (suffix LP) with an exposed pad for enhanced thermal dissipation. It is lead (Pb) free, with 100% matte tin lead frame plating. APPLICATIONS Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 AEC-Q100 qualified Wide input voltage range of 4.75 to 40V for start/stop, cold crank and load dump requirements Fully integrated LED current sinks and boost converter with 60V DMOS Sync function to synchronize boost converter switching frequency up to 2.3MHz, allowing operation above the AM band Excellent input voltage transient response Single resistor primary OVP minimizes VOUT leakage Internal secondary OVP for redundant protection LED current of 100mA per channel Drives up to 12 series LEDs in 4 parallel strings 0.7% to 0.8% LED to LED matching accuracy PWM and analog dimming inputs 5000:1 PWM dimming at 200Hz Provides driver for external PMOS input disconnect switch Extensive protection against: -Shorted boost switch or inductor -Shorted FSET or ISET resistor -Shorted output -Open or shorted LED pin -Open boost Schottky -Overtemperature (OTP) LCD Monitor LCD Display Module LCD TV 1 IS32BL3556 TYPICAL APPLICATION CIRCUIT SENSE VCC IS32BL3556 FAULTB EN/PWM FR/SYNC 10 Figure 1 Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 Typical Application Circuit 2 IS32BL3556 PIN CONFIGURATION Package TSSOP-20 Pin Configuration (Top View) GATE 1 20 SW SENSE 2 19 OVP VIN 3 18 PGND FAULTB 4 17 PGND COMP 5 16 PGND APWM 6 15 VCC EN/PWM 7 14 LED1 FR/SYNC 8 13 LED2 ISET 9 12 LED3 AGND 10 11 LED4 Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 3 IS32BL3556 PIN DESCRIPTION No. Pin Description 1 GATE Output gate driver pin for external P-channel FET control. 2 SENSE Connect this pin to the negative sense side of the current sense resistor RSC. The threshold voltage is measured as VIN VSENSE. There is also a fixed current sink to allow for trip threshold adjustment. 3 VIN Input power to the IS32BL3556 as well as the positive input used for current sense resistor. 4 FAULTB Indicates a fault condition. Connect a 100kΩ resistor between this pin and the required logic level voltage. The pin is an open drain type configuration that will be pulled low when a fault occurs. 5 COMP Output of the error amplifier and compensation node. Connect a series RZ-CZ network from this pin to ground for control loop compensation. 6 APWM Analog trimming option for dimming. Applying a digital PWM signal to this pin adjusts the internal ISET current. 7 EN/PWM PWM dimming pin, used to control the LED intensity by using pulse width modulation. Also used to enable the IS32BL3556. 8,12 FR/SYNC Frequency and synchronization pin. A resistor RFR from this pin to ground sets the switching frequency. This pin can also be used to synchronize two or more IS32BL3556s in the system. The maximum synchronization frequency is 2.3MHz. 9 ISET Connect the RSET resistor between this pin and ground to set the 100% LED current. 10 AGND LED signal ground. 11~14 LED4~LED1 Connect the cathodes of the LED strings to these pins. All unused pins should be connected with a 1.54kΩ resistor to ground 15 VCC Output of internal LDO; connect a 0.1μF decoupling capacitor between this pin and ground. 16~18 PGND Power ground for internal DMOS device. 19 OVP Overvoltage condition (OVP) sense; connect the ROVP resistor from VOUT to this pin to adjust the overvoltage protection. 20 SW The drain of the external NMOS switch of the boost converter. Thermal Pad Connect to GND. Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 4 IS32BL3556 ORDERING INFORMATION Automotive Range: -40°C to +125°C Order Part No. Package QTY IS32BL3556-ZLA3-TR IS32BL3556-ZLA3 TSSOP-20, Lead-free TSSOP-20, Lead-free 2500/Reel TBD Copyright © 2014 Integrated Silicon Solution, Inc. All rights reserved. ISSI reserves the right to make changes to this specification and its products at any time without notice. ISSI assumes no liability arising out of the application or use of any information, products or services described herein. Customers are advised to obtain the latest version of this device specification before relying on any published information and before placing orders for products. Integrated Silicon Solution, Inc. does not recommend the use of any of its products in life support applications where the failure or malfunction of the 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 Integrated Silicon Solution, Inc. receives written assurance to its satisfaction, that: a.) the risk of injury or damage has been minimized; b.) the user assume all such risks; and c.) potential liability of Integrated Silicon Solution, Inc is adequately protected under the circumstances Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 5 IS32BL3556 ABSOLUTE MAXIMUM RATINGS Voltage in LEDx pins Voltage in OVP pin Voltage in VIN, SENSE, GATE, FAULTB pins Voltage in ISET, FR, APWM, COMP pins Voltage in SW pin, continuous Voltage in SW pin, t<50ns All other pins Package thermal resistance, RθJA, on 2-layer PCB, 3 in on 4-layer PCB based on JEDEC standard Operating junction temperature, TJ Storage temperature range, TSTG Operating ambient temperature range, TA -0.3V ~ +55V -0.3V ~ +60V -0.3V ~ +40V -0.3V ~ +5.5V -0.6V ~ 65V -1.0V -0.3V ~ +7.0V 48.5°C/W 34°C/W 150°C -55°C ~ +150°C -40°C ~ +125°C Note: Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only and functional operation of the device at these or any other condition beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (NOTE 1, 2) (TBD) TA =-40°C ~ +125°C, VIN =12V. Typical value is TA = 25°C, unless otherwise specified. Symbol Parameter Condition Min. Typ. Max. Unit 40 V Input Supply VIN Input voltage (Note 3,4) VUVLO_R UVLO start threshold VIN rising (Note 3) 4.35 V VUVLO_F UVLO stop threshold VIN falling (Note 3) 3.90 V 450 600 mV VUVLO_HY UVLO hysteresis (Note 2) 4.75 300 ICC Quiescent current VEN = VIH ; fSW = 2MHz, no load (Note 3) 5.5 10 mA ISD Shutdown current VIN = 12V, VEN = VFR/SYNC = 0V (Note 3) 5.0 10 μA 0.4 V Input Logic Levels (EN and APWM) VIL Input logic level-low VIN throughout operating input voltage range (Note 3) VIH Input logic level-high VIN throughout operating input voltage range (Note 3) REN EN pin open drain pull-down resistor VEN = 5V 60 100 140 kΩ APWM pull-down resistor VEN = VIH 60 100 140 kΩ APWM frequency VIH = 1.5V, VIL = 0.4V (Note 2,3) 20 1000 kHz 52 dB RAPWM 1.5 V APWM fAPWM Error Amplifier AVOL Open loop voltage gain gm Transconductance ∆ICOMP = ±10μA ISC Source current VCOMP = 1.5V -350 μA Sink current VCOMP = 1.5V 350 μA COMP pin pull-down resistance VFAULTB = 0 2 kΩ ISINK RCOMP Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 44 48 750 990 1220 μA/V 6 IS32BL3556 ELECTRICAL CHARACTERISTICS (CONTINUED) TA =-40°C ~ +125°C, VIN =12V. Typical value is TA = 25°C, unless otherwise specified. Symbol Parameter Condition Min. Typ. Max. Unit Overvoltage Protection VOVP1 OVP threshold OVP connected to VOUT (Note 3) 7.7 8.1 8.5 V IOVPS OVP sense current (Note 3) 188 199 210 µA IOVPL OVP leakage current (Note 3) 0.1 1 µA VOVP2 Secondary over voltage protection (Note 3) 62 65 68 V Switch on-resistance ISW = 0.750A, VIN = 16V(Note 3) 75 300 600 mΩ ISW_LKG Switch leakage current VSW = 16V, VPWM/EN = VIL(Note 3) 0.1 1 µA ISW_LIM1 Switch current limit (Note 3) 3.5 4.2 A ISW_LIM2 Secondary switch current limit Higher than maximum ISW_LIM1 for all conditions, device latches when detected (Note 2) 7.0 A ISW_BL Soft start boost current limit Initial soft start current for boost switch 700 mA tSW_ON Minimum switch on-time (Note 3) 60 85 111 ns tSW_OFF Minimum switch off-time (Note 3) 30 47 68 ns RFR = 10kΩ (Note 3) 1.8 2 2.2 MHz RFR = 20kΩ (Note 3) 0.9 1.0 1.1 MHz RFR = 35.6kΩ 520 580 640 kHz Boost Switch RSW 3.0 Oscillator Frequency fSW VFR/SYNC fFR Oscillator frequency FR/SYNC pin voltage RFR = 10kΩ FR frequency range 1.0 V 580 2500 kHz 2300 kHz Synchronization fSY Synchronized PWM frequency (Note 3) 580 tSY_OFF Synchronization input minimum off-time (Note 3) 150 ns tSY_ON Synchronization input minimum on-time (Note 3) 150 ns VSY_H VSY_L SYNC input logic voltage FR/SYNC pin, high level (Note 3) FR/SYNC pin, low level (Note 3) 0.4 2.0 V V Thermal Protection (TSD) TSD_TH Thermal shutdown threshold Temperature rising (Note 2) 165 °C TSD_HY Thermal shutdown hysteresis (Note 2) 20 °C Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 7 IS32BL3556 ELECTRICAL CHARACTERISTICS (CONTINUED) TA =-40°C ~ +125°C, VIN =12V. Typical value is TA = 25°C, unless otherwise specified. Symbol Parameter Condition Min. Typ. Max. Unit 0.5 V FAULTB Pin VFAULT_PD IFAULT_L FAULTB pull-down voltage IFAULTB = 1mA (Note 3) FAULTB pin leakage current VFAULTB = 5V 1 μA LED Current Sinks ErrLED LEDx accuracy ISET = 100μA (Note 3) 2 % ∆ILED LEDx matching 1 % VLED LEDx regulation voltage AISET ISET to ILEDx current gain ISET = 100μA (Note 3) VLED1 = VLED2= VLED3 = VLED4, ISET = 100μA (Note 3) ISET = 100μA (Note 3) VSET ISET pin voltage ISET Allowable ISET current (Note 3) 20 VLED_S VLED short detect While LED sinks are in regulation, sensed from LEDx pin to ground (Note 3) 4.6 ILED_SS Soft start LEDx current Current through each enabled LEDx pin during soft start tPWM_OFF 620 720 820 mV 960 980 1000 A/A 0.988 1.003 1.018 V 120 μA 5.6 V 5.1 2.0 mA Maximum PWM dimming until off-time (Note 2) Measured while VEN = low, during dimming control and internal references are powered-on (exceeding tPWM_OFF results in shutdown) 32,75 0 fSW cycles tPWM_ON Minimum PWM on-time First cycle when powering-up device (Note 3) 0.75 2 μs tPWMH_ON PWM high to LED-on delay Time between PWM enable and LED current reaching 90% of maximum (Note 3) 0.5 1 μs tPWML_OFF PWM low to LED-off delay Time between PWM enable going low and LED current reaching 10% of maximum (Note 3) 360 500 ns Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 8 IS32BL3556 ELECTRICAL CHARACTERISTICS (CONTINUED) TA =-40°C ~ +125°C, VIN =12V. Typical value is TA = 25°C, unless otherwise specified. Symbol Parameter Condition Min. Typ. Max. Unit GATE Pin IG_SINK GATE pin sink current VGS = VIN tG_FAULT2 Gate fault shutdown greater than 2X current (Note 2) tG_FAULT1 Gate fault shutdown greater than 1–2X current VG Gate voltage -104 μA 3 Gate to source voltage measured when gate is on μs 10,000 fSW cycles -6.7 V SENSE Pin IADJ SENSE pin sink current (Note 3) VSENSE1 SENSE trip point Measured between VIN and SENSE, RADJ = 0Ω (Note 3) VSENSE2 SENSE 2X trip 2X VSENSE trip, instantaneous shutdown, RADJ = 0Ω (Note 2) 18.8 20.3 21.8 μA 94 104 114 mV 180 mV Note 1: For input and output current specifications, negative current is defined as coming out of the node or pin (sourcing); positive current is defined as going into the node or pin (sinking). Note 2: Ensured by design and characterization, not production tested. Note 3: Indicates specifications guaranteed by design and characterization over the full operating temperature range with TA = TJ = –40°C ~ 125°C Note 4: Minimum VIN = 4.75V is only required at startup. After startup is completed, the IC is able to function down to VIN = 4V. Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 9 IS32BL3556 FUNCTIONAL BLOCK DIAGRAM VCC FR/SYNC SENSE EN/PWM FAULTB Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 10 IS32BL3556 APPLICATION INFORMATION The A8514 incorporates a current-mode boost controller with internal DMOS switch, and four LED current sinks. It can be used to drive four LED strings of up to 12 white LEDs in series, with current up to 100mA per string. For optimal efficiency, the output of the boost stage is adaptively adjusted to the minimum voltage required to power all of the LED strings. This is expressed by the following Equation (1): VOUT Max VLED 1 ,..., VLED 4 VREG The LED detect phase starts when the GATE voltage of the disconnect switch is equal to VIN – 4.5V. After the voltage threshold on the LEDx pins exceeds 120mV, a delay of between 3000 and 4000 clock cycles is used to determine the status of the pins. Thus, the LED detection duration varies with the switching frequency, as shown in the following table: Switching Frequency (MHz) Detection Time (ms) 2 1.5 ~ 2.0 1 3~4 0.800 3.75 ~ 5.0 0.600 5.0 ~ 6.7 (1) where VLEDx is the voltage drop across LED strings 1 through 4, and VREG is the regulation voltage of the LED current sinks (typically 0.7V at the maximum LED current). ENABLING THE IC The IC turns on when a logic high signal is applied on the EN/PWM pin with a minimum duration of tPWM_ON for the first clock cycle, and the input voltage present on the VIN pin is greater than the 4.35V necessary to clear the UVLO (VUVLO_R) threshold. The power-up sequence is shown in Figure 3. Before the LEDs are enabled, the IS32BL3556 driver goes through a system check to determine if there are any possible fault conditions that might prevent the system from functioning correctly. Also, if the FR/SYNC pin is pulled low, the IC will not power-up. More information on the FR/SYNC pin can be found in the synchronize section of this datasheet. The LEDx pin detection voltage thresholds are as follows: LED Pin Voltage LED Pin Status Action <70mV Short to ground Power-up is halted 150mV Not used LED removed from operation 325mV LED pin in use None VCC FR/SYNC EN/PWM Figure 3 Power-up diagram; shows VCC (C1, 2V/div.), VFR/SYNC (C2, 1V/div.), ISET (C3, 1V/div.), and EN (C4, 2V/div.) pins, t = 200μs/div. POWERING UP: LED PIN SHORT-TO-GROUND CHECK The VIN pin has a UVLO function that prevents the IS32BL3556 from powering-up until the UVLO threshold is reached. After the VIN pin goes above UVLO, and a high signal is present on the EN/PWM pin, the IC proceeds to power-up. As shown in Figure 4, at this point the IS32BL3556 enables the disconnect switch and checks if any LEDx pins are shorted to ground and/or are not used. Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 Figure 4 Power-up diagram; shows the relationship of an LEDx pin with respect to the gate voltage of the disconnect switch (if used) during the LED detect phase, as well as the duration of the LED detect phase for a switching frequency of 2MHz; shows VGATE (C1, 5V/div.), VLED (C2, 500mV/div.), ISET (C3, 1V/div.), and EN/PWM (C4, 5V/div.) pins, t = 500μs/div. All unused pins should be connected with a 1.54kΩ resistor to ground, as shown in Figure 5. The unused pin, with the pull-down resistor, will be taken out of regulation at this point and will not contribute to the boost regulation loop. 11 IS32BL3556 IS32BL3556 IS32BL3556 more than 3.5MHz. If the FR/SYNC pin is shorted to GND the part will shut down. For more details see the Fault Mode table later in this datasheet. 1.54kΩ Figure 5 Channel select setup: (left) using only LED1, LED2, and LED3, and (right) using all four channels. If a LEDx pin is shorted to ground the IS32BL3556 will not proceed with soft start until the short is removed from the LEDx pin. This prevents the IS32BL3556 from powering-up and putting an uncontrolled amount of current through the LEDs. SOFT START FUNCTION During soft start the LEDx pins are set to sink (ILED_SS) and the boost switch current is reduced to the ISW_SS level to limit the inrush current generated by charging the output capacitors. When the converter senses that there is enough voltage on the LEDx pins the converter proceeds to increase the LED current to the preset regulation current and the boost switch current limit is switched to the ISW_LIM1 level to allow the IS32BL3556 to deliver the necessary output power to the LEDs. This is shown in Figure 6. Figure 7 Typical switching frequency versus value of RSET resistor SYNCHRONIZE The IS32BL3556 can also be synchronized using an external clock on the FR/SYNC pin. Figure 8 shows the correspondence of a sync signal and the FR/SYNC pin, and Figure 9 shows the result when a sync signal is detected: the LED current does not show any variation while the frequency changeover occurs. At power-up if the FR/SYNC pin is held low, the IC will not power-up. Only when the FR/SYNC pin is tri-stated to allow the pin to rise, to about 1V, or when a synchronization clock is detected, will the IS32BL3556 try to power-up. FR/SYNC EN/PWM Figure 8 Diagram showing a synchronized FR/SYNC pin and switch node; shows VOUT (C1, 20V/div.), IOUT (C2, 200mA/div.), FR/SYNC (C3, 2V/div.), and SW node (C4, 20V/div.), t = 2μs/div. Figure 6 Startup diagram showing the input current, output voltage, and output current; shows IOUT (C1, 200mA/div.), IIN (C2, 1A/div.), VOUT (C3, 20V/div.), and EN/PWM (C4, 5V/div.), time = 1ms/div. FREQUENCY SELECTION The switching frequency on the boost regulator is set by the resistor connected to the FR/SYNC pin. The switching frequency can be anywhere from 580kHz to 2.3MHz. Figure 7 shows the typical switching frequencies, in MHz, for given resistor values, in kΩ. FR/SYNC In case during operation a fault occurs that will increase the switching frequency, the FR/SYNC pin is clamped to a maximum switching frequency of no Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 12 IS32BL3556 Figure 9 Transition of the SW waveform when the SYNC pulse is detected. The IS32BL3556 switching at 2MHz, applied SYNC pulse at 1MHz; shows VOUT (C1, 20V/div.), IOUT (C2, 200mA/div.), FR/SYNC (C3, 2V/div.), and SW node (C4, 20V/div.), t = 5μs/div. The basic requirement of the sync signal is 150ns minimum on time and 150ns minimum off time, as indicated by the specifications for tSY_ON and tSY_OFF. Figure 10 shows the timing for a synchronization clock into the IS32BL3556 at 2.2MHz. Thus any pulse with a duty cycle of 33% to 66% at 2.2MHz can be used to synchronize the IC. RSET 1.003 1000 / I LED (2) Where ILED is in A and RSET is in Ω. This sets the maximum current through the LEDs, referred to as the 100% current. Standard RSET values, at gain equals 1000, are as follows: Standard Closest Resistor, RSET (kΩ) LED Current, ILED (mA) 8.3 120 10.0 100 25.1 40 33.4 30 PWM DIMMING Figure 10 SYNC pulse on and off time requirements The SYNC pulse duty cycle ranges for selected switching frequencies are: The LED current can be reduced from the 100% current level by PWM dimming using the EN/PWM pin. When the EN/PWM pin is pulled high, the IS32BL3556 turns on and all enabled LEDs sink 100% current. When EN is pulled low, the boost converter and LED sinks are turned off. The compensation (COMP) pin is floated, and critical internal circuits are kept active. The typical PWM dimming frequencies fall between 200Hz and 1kHz. Figures 11A to 11D provide examples of PWM switching behavior. SYNC Pulse Frequency(MHz) Duty Cycle Range(%) 2.2 33 ~ 66 2 30 ~ 70 1 15 ~ 85 0.800 12 ~ 88 0.600 9 ~ 91 If during operation a sync clock is lost, the IC will revert to the preset switching frequency that is set by the resistor RFQ. During this period the IC will stop switching for a maximum period of about 7μs to allow the sync detection circuitry to switch over to the externally preset switching frequency. If the clock is held low for more than 7μs, the IS32BL3556 will shut down. In this shutdown mode the IC will stop switching, the input disconnect switch is open, and the LEDs will stop sinking current. To shutdown the IC into low power mode, the user must disable the IC using the EN pin, by keeping the pin low for a period of 32,750 clock cycles. If the FR/SYNC pin is released at any time after 7μs, the IS32BL3556 will proceed to soft start. Figure 11A Typical PWM diagram showing VOUT, ILED, and COMP pin as well as the PWM signal. PWM dimming frequency is 500Hz at 50% duty cycle; shows VOUT (C1, 10V/div.), COMP (C2, 2V/div.), PWM (C3, 5V/div.), and ILED (C4, 50mA/div.), t = 500μs/div. LED CURRENT SETTING AND LED DIMMING The maximum LED current can be up to 100mA per channel, and is set through the ISET pin. To set the ILED current, connect a resistor, RSET, between this pin and ground, according to the following Formula (2): Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 13 IS32BL3556 Figure 11B Typical PWM diagram showing VOUT, ILED, and COMP pin as well as the PWM signal. PWM dimming frequency is 500Hz at 1% duty cycle; shows VOUT (ch1, 10 V/div.), COMP (ch2, 2 V/div.), PWM (ch3, 5 V/div.), and ILED (ch4, 50mA/div.), time = 500μs/div adjusts the ISET current. When this pin is not used it should be tied to ground. RSET Figure 13 Simplified block diagram of the APWM and ISET circuit The typical input signal frequency is between 20kHz and 1MHz. The duty cycle of this signal is inversely proportional to the percentage of current that is delivered to the LEDs (Figure 14). Figure 11C Delay from rising edge of PWM signal to LED current; shows PWM (C1, 2V/div.), and ILED (C2, 50mA/div.), t = 200ns/div Figure 14 Figure 11D Delay from falling edge of PWM signal to LED current turn off; shows PWM (C1, 2V/div.), and ILED (C2, 50mA/div.), t = 200ns/div Another important feature of the IS32BL3556 is the PWM signal to LED current delay. This delay is typically less than 500ns, which allows greater accuracy at low PWM dimming duty cycles, as shown in Figure 12. Output current versus duty cycle; 200kHz APWM signal. To use this pin for a trim function, the user should set the maximum output current to a value higher than the required current by at least 5%. The LED ISET current is then trimmed down to the appropriate value. Another consideration that also is important is the limitation of the user APWM signal duty cycle. In some cases it might be preferable to set the maximum ISET current to be 25% to 50% higher, thus allowing the APWM signal to have duty cycles that are between 25% and 50%. Figure 12 Percentage error of the LED current versus PWM duty cycle (at 200Hz PWM frequency) APWM PIN The APWM pin is used in conjunction with the ISET pin (Figure 13). This is a digital signal pin that internally Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 Figure 15 Percentage error of the LED current versus PWM duty cycle; 200kHz APWM signal. As an example, a system that delivers a full LED current of 80mA per LED would deliver 60mA of 14 IS32BL3556 current per LED when an APWM signal is applied with a duty cycle of 25% (Figures 16 and 17). EN/PWM Figure 16 Diagram showing the transition of LED current from 60mA ~ 80mA, when a 25% duty cycle signal is removed from the APWM pin. PWM = 1; shows ILED (C1, 50mA/div.), APWM (C2, 10V/div.), and EN (C3, 5V/div.), t = 500μs/div. Figure 18 Diagram showing power-up sequencing LED current of 5mA per channel with a 10% duty cycle PWM signal and a 95% duty cycle APWM signal; shows APWM (ch1, 5V/div.), ILED (ch2, 50mA/div.), PWM/EN (ch3, 5V/div.), and VOUT (ch4, 10V/div.), time = 500μs/div. Although the APWM dimming function has a wide frequency range, if this function is used strictly as an analog dimming function it is recommended to use frequency ranges between 50 and 500kHz for best accuracy. The frequency range must be considered only if the user is not using this function as a closed loop trim function. Another limitation is that the propagation delay between this APWM signal and IOUT takes several milliseconds to change the actual LED current. This effect is shown in Figures 16, 17, and 19. EN/PWM Figure 17 Diagram showing the transition of LED current from 80mA ~ 60mA, when a 25% duty cycle signal is applied to the APWM pin; PWM = 1; shows ILED (C1, 50mA/div.), APWM (C2, 10V/div.), and EN/PWM (C3, 5V/div.), t = 500μs/div. Although the order in which APWM and the PWM signal are enabled does not matter, when enabling the IS32BL3556 into low current output while PWM and APWM dimming, the APWM signal should be enable before or at the same time as the PWM signal. This sequence will prevent the light output intensity from changing during power up of the IC. Figure 18 shows the sequencing of the APWM and PWM signal during power-up to prevent inadvertent light intensity changes. The full intensity light output with no APWM or PWM dimming is 80mA per channel. Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 EN/PWM Figure 19 Transition of output current level when a 50% duty cycle signal is applied to the APWM pin, in conjunction with a 50% duty cycle PWM dimming being applied to the PWM pin; shows IOUT (C1, 50mA/div.), APWM (C2, 10V/div.), and EN/PWM (C3, 5V/div.), t = 500μs/div. ANALOG DIMMING The IS32BL3556 can also be dimmed by using an external DAC or another voltage source applied either directly to the ground side of the RSET resistor or through an external resistor to the ISET pin (Figure 19). The limit of this type of dimming depends on the range of the ISET pin. In the case of the IS32BL3556 the limit is 20μA ~ 125μA. 15 IS32BL3556 RSET IS32BL3556 LED1 IS32BL3556 EN/PWM RSET Figure 20 Simplified diagrams of voltage control of ILED: typical applications using a DAC to control ILED using a single resistor (upper), and dual resistors (lower). Figure 21 Example of the disabling of an LED string when the LED pin voltage is increased above 4.6V; shows IOUT (C1, 200mA/div.), CH1 (C2, 5V/div.), and EN (C3, 5V/div.), t = 10μs/div. • For a single resistor (Panel A of Figure 20), the ISET current is controlled by the following Formula (3): While the IC is being PWM-dimmed, the IC rechecks the disabled LED every time the PWM signal goes high, to prevent false tripping of an LED short event. This also allows some self-correction if an intermittent LED pin short to VOUT is present. I SET VSET VDAC RSET (3) Where VSET is the ISET pin voltage and VDAC is the DAC output voltage. When the DAC voltage is 0V the LED current will be at its maximum. To keep the internal gain amplifier stable, the user should not decrease the current through the RSET resistor to less than 20μA • For a dual-resistor configuration (Panel B of Figure 20), the ISET current is controlled by the following Formula (4): I SET VSET VDAC VSET RSET R1 OVERVOLTAGE PROTECTION The IS32BL3556 has overvoltage protection (OVP) and open Schottky diode (D1 in figure 1) protection. The OVP protection has a default level of 8.1V and can be increased up to 53V by connecting resistor ROVP between the OVP pin and VOUT. When the current into the OVP pin exceeds 199μA (typical), the OVP comparator goes low and the boost stops switching. The following Equation (5) can be used to determine the resistance for setting the OVP level: (4) The advantage of this circuit is that the DAC voltage can be higher or lower, thus adjusting the LED current to a higher or lower value of the preset LED current set by the RSET resistor: ▫ VDAC = 1.003V; the output is strictly controlled by RSET ▫ VDAC > 1.003V; the LED current is reduced ▫ VDAC < 1.003V; the LED current is increased LED SHORT DETECT Both LEDx pins are capable of handling the maximum VOUT that the converter can deliver, thus providing protection from the LEDx pin to VOUT in the event of a connector short. ROVP VOVP _ OUT VOVP I OVPH (5) where: VOUT_OVP is the target overvoltage level, ROVP is the value of the external resistor, in Ω, VOVP is the pin OVP trip point found in the Electrical Characteristics Table, and IOVPH is the current into the OVP pin. There are several possibilities for why an OVP condition would be encountered during operation, the two most common being: a disconnected output, and an open LED string. Examples of these are provided in Figures 22 and 23. An LEDx pin that has a voltage exceeding VLED_S will be removed from operation (Figure 21). This is to prevent the IC from dissipating too much power by having a large voltage present on a LEDx pin. Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 16 IS32BL3556 as well as there being no load present, the switch node voltage will rise above the trip point voltage. Figure 22 OVP protection in an output disconnect event; shows VOUT (C1, 10V/div.), SW node (C2, 50V/div.), PWM (C3, 5V/div.), and ILED (C4, 200mA/div.), t = 1ms/div. Figure 24 OVP protection in an open schottky diode event, while the IC is in normal operation; shows PWM (C1, 5V/div.), SW node (C2, 50V/div.), VOUT (C3, 20V/div.), and IOUT (C4, 200mA/div.), t = 1μs/div. Figure 25 illustrates when the IS32BL3556 is being enabled during an open diode condition. The IC goes through all of its initial LED detection and then tries to enable the boost, at which point the open diode is detected. Figure 23 OVP protection in an open LED string event; shows VOUT (C1, 10V/div.), SW node (C2, 50V/div.), PWM (C3, 5V/div.), and ILED (C4, 200mA/div.), t = 500μs/div. Figure 22 illustrates when the output of the IS32BL3556 is disconnected from load during normal operation. The output voltage instantly increases up to OVP voltage level and then the boost stops switching to prevent damage to the IC. If the output is drained off, eventually the boost might start switching for a short duration until the OVP threshold is hit again. Figure 23 displays a typical OVP event caused by an open LED string. After the OVP condition is detected, the boost stops switching, and the open LED string is removed from operation. Afterwards VOUT is allowed to fall, and eventually the boost will resume switching and the IS32BL3556 will resume normal operation. IS32BL3556 also has built-in secondary overvoltage protection to protect the internal switch in the event of an open diode condition. Open schottky diode detection is implemented by detecting overvoltage on the SW pin of the device. If voltage on the SW pin exceeds the device safe operating voltage rating, the IS32BL3556 disables and remains latched. To clear this fault, the IC must be shut down either by using the EN/PWM signal or by going below the UVLO threshold on the VIN pin. Figure 24 illustrates this. As soon as the switch node voltage (VSW) exceeds 60V, the IC shuts down. Due to small delays in the detection circuit, Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 Figure 25 OVP protection when the IC is enabled during an open diode condition; shows PWM (C1, 5V/div.), SW node (C2, 50V/div.), VOUT (C3, 10V/div.), and IOUT (C4, 200mA/div.), t = 500μs/div. BOOST SWITCH OVERCURRENT PROTECTION The boost switch is protected with cycle-by-cycle current limiting set at a minimum of 3.0A. There is also a secondary current limit that is sensed on the boost switch. When detected this current limit immediately shuts down the IS32BL3556. The level of this current limit is set above the cycle-by-cycle current limit to protect the switch from destructive currents when the boost inductor is shorted. Various boost switches over current conditions are shown in Figures 26 through 28. 17 IS32BL3556 INPUT OVER CURRENT PROTECTION AND DISCONNECT SWITCH The primary function of the input disconnect switch is to protect the system and the device from catastrophic input currents during a fault condition. The external circuit implementing the disconnect is shown in Figure 29. If the input disconnect switch is not used, the SENSE pin must be tied to VIN and the GATE pin must be left open. EN/PWM Figure 26 Normal operation of the switch node (SW); inductor current (IL) and output voltage (VOUT) for 9 series LEDs in each of 4 strings configuration; shows SW node (C1, 20V/div.), inductor current, IL (C2, 1A/div.), VOUT (C3, 10V/div.), and EN (C4, 5V/div.), t = 2μs/div. Figure 29 Typical circuit showing the implementation of the input disconnect feature. When selecting the external PMOS, check for the following parameters: • Drain-source breakdown voltage VDS_BD > -40V • Gate threshold voltage (make sure it is fully conducting at VGS = -4V, and cut off at -1V) EN/PWM • RDS_ON: Make sure the on-resistance is rated at VGS = -4.5V or similar, not at -10V; derate it for higher temperature Figure 27 Cycle-by-cycle current limiting; inductor current (yellow trace, IL), note reduction in output voltage as compared to normal operation with the same configuration (Figure 26); shows SW node (C1, 20V/div.), inductor current, IL (C2, 1A/div.), VOUT (C3, 10V/div.), and EN (C4, 5V/div.), t = 2μs/div. EN/PWM FAULTB The input disconnect switch has two modes of operation: • 1X Mode When the input current is between one and two times the preset current limit value, the disconnect switch enters a constant- current mode for a maximum duration of 10,000 cycles or 5ms at 2MHz. During this time, the fault flag is set immediately and the disconnect switch goes into a linear mode of operation, in which the input current will be limited to a value approximate to the 1X current trip point level (Figure 30). If the fault corrects itself before the expiration of the timer, the fault flag will be removed and normal operation will resume. Figure 28 Secondary boost switch current limit; when this limit is hit, the IS32BL3556 immediately shuts down; shows EN/PWM (C1, 5V/div.), FAULTB (C2, 5V/div.), SW node (C3, 50V/div.), and inductor current, IL (C4, 2A/div.), t = 100ns/div. Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 18 IS32BL3556 FAULTB SETTING THE CURRENT SENSE RESISTOR The typical threshold for the current sense circuit is 104mV, when RADJ is 0Ω. This voltage can be trimmed by the RADJ resistor. The typical 1X trip point should be set at about 3A, which coincides with the cycle-by-cycle current limit minimum threshold. For example, given 3A of input current, and the calculated maximum value of the sense resistor, RSC = 0.033Ω. The RSC chosen is 0.03Ω, a standard. Also: R ADJ Figure 30 Showing typical wave forms for a 3-A, 1X current limit under a fault condition; shows fSW = 800kHz, FAULTB (C1, 5V/div.), IIN (C2, 2A/div.), GATE (C3, 5V/div.), and EN/PMW (C4, 5V/div.), t = 5ms/div. The user can also during this time decide whether to shut down the IS32BL3556. To immediately shut down the device, pull the FR/SYNC pin low for more than 7μs. After the FR/SYNC pin has been low for a period longer than 7μs, the IC will stop switching, the input disconnect switch will open, and the LEDx pins will stop sinking current. The IS32BL3556 can be powered-down into low power mode. To do so, disable the IC by keeping the EN pin low for a period of 32,750 clock cycles. To keep the discon-nect switch stable while the disconnect switch is in 1X mode, use a 22nF capacitor for CC and a 20Ω resistor for RC. VSENSE V ADJ I ADJ (6) The trip point voltage is calculated as: VADJ = 3.0A × 0.03Ω = 0.090V RADJ = (0.104 – 0.09V)/(20.3μA) = 731Ω INPUT UVLO When VIN and VSENSE rise above the VUVLO_R threshold, the IS32BL3556 is enabled. IS32BL3556 is disabled when VIN falls below the VUVLO_F threshold for more than 50μs. This small delay is used to avoid shutting down because of momentary glitches in the input power supply. When VIN falls below 4.35V, the IC will shut down (see Figure 32). • 2X Current Limit If the input current level goes above 2X of the preset current limit threshold, the IS32BL3556 will shut down in less than 3μs regardless of user input (Figure 30). This is a latched condition. The fault flag is also set to indicate a fault. This feature is meant to prevent catastrophic failure in the system due to inductor short to ground, switch pin short to ground, or output short to ground. VCC FAULTB EN/PWM Figure 32 Shutdown showing a falling input voltage (VIN); shows VIN (C1, 2V/div.), IOUT (C2, 200mA/div.), VCC (C3, 5V/div.), and EN/PWM (C4, 2V/div.), t = 5ms/div. VCC EN/PWM Figure 30 2X mode, secondary over current fault condition. IIN is the input current through the switch. The fault flag is set at the 1X current limit, and when the 2X current limit is reached the IS32BL3556 disables the gate of the disconnect switch (GATE); shows FAULTB (C1, 5V/div.), GATE (C2, 10V/div.), IIN (C3, 2A/div.), and EN (C4, 5V/div.), t = 5μs/div. Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 The VCC pin provides regulated bias supply for internal circuits. Connect the capacitor CVCC with a value of 0.1μF or greater to this pin. The internal LDO can deliver no more than 2mA of current with a typical VCC of about 3.5V, enabling this pin to serve as the pull-up voltage for the FAULTB pin. SHUTDOWN If the EN/PWM pin is pulled low for more than tPWM_OFF (32,750 clock cycles), the device enters shutdown mode and clears all internal fault registers. As an example, at a 2MHz clock frequency, it will take 19 IS32BL3556 approximately 16.3ms to shut down the IC into the low power mode (Figure 33). When the IS32BL3556 is shut down, the IC will disable all current sources and wait until the EN signal goes high to re-enable the IC. If faster shut down is required, the FR/SYNC pin can be used. FAULT PROTECTION DURING OPERATION The IS32BL3556 constantly monitors the state of the system to determine if any fault conditions occur during normal operation. The response to a triggered fault condition is summarized in the Fault Mode Table 1. The possible fault conditions that the device can detect are: Open LED pin, LED pin shorted to ground, shorted inductor, VOUT short to ground, SW pin shorted to ground, ISET pin shorted to ground, and input disconnect switch source shorted to ground. Note the following: VCC EN/PWM Figure 33 Shutdown using the enable function, showing the 16ms delay between the EN signal and when the VCC and GATE of the disconnect switch turns off; shows GATE (C1, 10V/div.), IOUT (C2, 200mA/div.), VCC (C3, 5V/div.), and EN (C4, 2V/div.), t = 5ms/div. Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 • Some of the protection features might not be active during startup, to prevent false triggering of fault conditions. • Some of these faults will not be protected if the input disconnect switch is not being used. An example of this is VOUT short to ground. 20 IS32BL3556 TABLE 1 FAULT MODE Fault Name Type Active Flag Primary switch overcurrent protection Auto-restart Always (Cycle-by-cycle current limit) No Secondary switch current limit Latched Always Yes Input disconnect current limit Latched Always Yes Secondary OVP Latched Always Yes Auto-restart Startup No LED pin short protection LED pin open Auto-restart Normal Operation No ISET short protection Auto-restart Always No FSET/SYNC short Auto-restart Always protection Yes Overvoltage protection Auto-restart Always LED short protection Auto-restart Always No No Overtemperature protection Auto-restart Always No VIN UVLO Auto-restart Always No Description This fault condition is triggered by the cycle-by-cycle current limit, ISW(LIM) Boost Off for a single cycle On On Off Off Off Off Off Off On Off On Off for open pins. On for all others. On Off Off Off On On On On Off for shorted pins. On for all others. Off Off Off Off Off Off When the current through the boost switch exceeds secondary current SW limit, ISW(LIM2), the device immediately shuts down the disconnect Off switch, LED drivers and boost. The fault flag is set. To re-enable the device, the PWM/EN pin must be pulled low for 32,750 clock cycles. The device is immediately shut off if the voltage across the input sense resistor is 2X the preset current value. The fault flag is set. If the input current limit is between 1X and 2X, the fault flag is Off set but the IC will continue to operate normally for tGFAULT1 or until it is shut down. To re-enable the device the PWM/EN pin must be pulled low for 32,750 clock cycles. Secondary overvoltage protection is used for open diode detection. When diode D1 opens, the SW pin voltage will increase until VOVP(SEC) is reached. This fault latches the IC. The input disconnect Off switch is disabled as well as the LED drivers, and the fault flag is set. To re-enable the part the PWM/EN pin must be pulled low for 32,750 clock cycles. This fault prevents the device from starting-up if either of the LEDx pins are shorted. The device stops soft-start from starting while either of the Off LEDx pins are determined to be shorted. After the short is removed, soft-start is allowed to start. When a LEDx pin is open the device will determine which LED pin is open by increasing the output voltage until OVP is reached. Any LED string not in regulation will be turned off. The On device will then go back to normal operation by reducing the output voltage to the appropriate voltage level. This fault occurs when the ISET current goes above 150% of the maximum current. The boost will stop switching, the disconnect switch will turn Off off, and the IC will disable the LED sinks until the fault is removed. When the fault is removed the IC will try to regulate to the preset LED current. Fault occurs when the FSET/SYNC current goes above 150% of maximum current, about 180µA. The boost will stop switching, the disconnect Off switch will turn off, and the IC will disable the LED sinks until the fault is removed. When the fault is removed the IC will try to restart with soft-start. Fault occurs when OVP pin exceeds VOVP(TH) threshold. The IC will immediately stop switching Stop to try to reduce the output voltage. If the output during voltage decreases then the IC will restart OVP event switching to regulate the output voltage. Fault occurs when the LED pin voltage exceeds VLEDSC. When the LED short protection is detected the LED string that is above the threshold will be removed from operation. Fault occurs when the die temperature exceeds the overtemperature threshold, 165°C. Fault occurs when VIN drops below VUVLO, 3.9V maximum. This fault resets all latched faults. Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 Disconnect Sink Switch Driver 21 IS32BL3556 CLASSIFICATION REFLOW PROFILES Profile Feature Pb-Free Assembly Preheat & Soak Temperature min (Tsmin) Temperature max (Tsmax) Time (Tsmin to Tsmax) (ts) 150°C 200°C 60-120 seconds Average ramp-up rate (Tsmax to Tp) 3°C/second max. Liquidous temperature (TL) Time at liquidous (tL) 217°C 60-150 seconds Peak package body temperature (Tp)* Max 260°C Time (tp)** within 5°C of the specified classification temperature (Tc) Max 30 seconds Average ramp-down rate (Tp to Tsmax) 6°C/second max. Time 25°C to peak temperature Figure 33 8 minutes max. Classification Profile Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 22 IS32BL3556 PACKAGE INFORMATION TSSOP-20 Note: All dimensions in mm unless otherwise stated. Integrated Silicon Solution, Inc. – www.issi.com Rev. 00E, 02/26/2014 23