LED Backlight Driver IC CXA3834AM Description The CXA3834AM is an LED driver IC with boost DC-DC converter. It enables luminance control using the peak current and PWM signal, and blinking control using the BLINK signal. This IC has an optimum configuration for realizing a simple and compact power supply circuit for an LCD TV equipped with a LED backlight. (Applications: Power supply circuit, etc.) Features Shared UVLO function Overheat protection function Error detection output function (xBL_ERR) Detection timer latch function when abnormalities occur LED driver control block On-chip LED lighting FET gate driver Luminance adjustment function using peak current control Luminance adjustment function using the PWM signal Blinking control using the BLINK signal LED overcurrent detection function DC-DC converter control block On-chip boost type DC-DC converter Output overvoltage detection function Continuous overcurrent detection function Slope compensation function Structure BiCMOS silicon monolithic IC Package 16P-SOP Sony reserves the right to change products and specifications without prior notice. This information does not convey any license by any implication or otherwise under any patents or other right. Application circuits shown, if any, are typical examples illustrating the operation of the devices. Sony cannot assume responsibility for any problems arising out of the use of these circuits. -1- E11711C22 CXA3834AM Absolute Maximum Ratings Item Symbol Rating Unit Maximum supply voltage VCC_MAX +24.0 V VCC xBL_ERR pin voltage VxBL_ERR -0.3 to +24.0 V xBL_ERR I/O pin voltage 1 VIO1 -0.3 to VCC + 0.3 V DRV, DIM_SW, PWM_DIM, BLINK, DC_DIM, EN VREF pin voltage VREF -0.3 to + 7.0 V VREF I/O pin voltage 2 VIO2 -0.3 to VREF + 0.3 V ISENSE, OCP, COMP, FB, PROTECT, OVP_DD Allowable power dissipation PD *1 mW Allowable power dissipation reduction characteristics Operating ambient temperature Ta -30 to +85 C Junction temperature Tj_max +150 C Storage temperature range Tstg -55 to +150 C Allowable power dissipation reduction characteristics Allowable power dissipation [mW] *1 Remarks 1000 When mounted on a 4-layer board 800 When mounted on a single layer board 600 400 321 mW 200 193 mW -20 0 20.7 C 20 40 72.1 C 60 80 125 C 100 120 140 160 Operating ambient temperature Ta [C] Glass fabric base epoxy board 76 mm x 114 mm t = 1.6 mm Recommended Operating Conditions Item Supply voltage range DC_DIM pin input voltage Symbol VCC VDC_DIM PWM_DIM pin input frequency FPWM_DIM PWM_DIM pin minimum pulse width TPWM_DIM BLINK pin input frequency BLINK pin input minimum pulse width Rating 10.0 to 18.0 0.3 to 3.3 Unit V V Remarks 20 k to 40 k Hz Rated input frequency > 1 kHz 48 to 1 k Hz When PWM_DIM and BLINK pin are short circuited. 1.0 s 48 to 240 Hz 48 to 1 k Hz 2.0 ms 1.0 s FBLINK TBLINK -2- When PWM_DIM and BLINK pin are short circuited. When PWM_DIM and BLINK pin are short circuited. CXA3834AM Pin Assignment Block Diagram 13 VCC VREF clk 5.0 V 11 VREF UVLO Oscillator slope Thermal Shutdown clk slope V/I Slope Compensator VREF 1.0 V OCP PWM L/S Error Amplifier COMP 10 S Q R Q 1 DRV 2 ISENSE 3 OCP 1.2 V DC_DIM 8 23R 10R 15 DIM_SW 14 FB VREF 12 GND PROTECT 9 Latch 3.0 V Control Logic comp_ovp latch ocp dd_en pwm_out xBL_ERR 5 bl_err PWM_DIM 7 pwm_in BLINK 6 blink_in fb_ocp 16 OVP_DD dd_ovp EN 4 2.0 V/ 1.0 V en -3- 2.0 V 3.2 V CXA3834AM Pin Assignment DRV 1 16 OVP_DD ISENSE 2 15 DIM_SW OCP 3 14 FB EN 4 13 VCC Top View xBL_ERR 5 12 GND BLINK 6 11 VREF PWM_DIM 7 10 COMP DC_DIM 8 9 PROTECT Pin Table Pin No. Symbol Description Protective element connection destination 1 DRV MOSFET driver output for boost converter -- 2 ISENSE Current detection input for boost converter VREF, GND 3 OCP Overcurrent detection input for boost converter VREF, GND 4 EN Enable signal input VCC, GND 5 xBL_ERR Error signal output -- 6 BLINK Blinking signal input VCC, GND 7 PWM_DIM PWM dimming signal input VCC, GND 8 DC_DIM Control voltage input VCC, GND 9 PROTECT Protection stop timer time adjustment VREF, GND 10 COMP Error amplifier output for boost converter control VREF, GND 11 VREF Reference voltage output 12 GND GND 13 VCC Power supply input 14 FB LED current detection input 15 DIM_SW PWM dimming MOSFET driver output 16 OVP_DD Boost converter output voltage detection input VCC, GND -- GND -4- VREF, GND -- VREF, GND CXA3834AM Pin Description Pin No. Symbol I/O Typical pin voltage Equivalent circuit Description VCC 1 DRV O Pch Pch Nch Nch DRV 1 VCC to GND MOSFET driver output for boost converter (Connect to the boost converter NMOS gate.) GND VREF Pch 2 ISENSE I/O 1.0 V to GND Pch ISENSE 2 Pch Current detection input for boost converter (Connect to a slope compensation resistor.) GND VREF Pch 3 OCP I 1.0 V to GND OCP 3 Pch Overcurrent detection input for boost converter (Connect to a current detection resistor.) GND VCC 4 EN I VCC to GND EN Enable signal input 4 Pch GND VCC xBL_ERR 5 xBL_ERR I/O VCC to GND Error signal output (Connect to a pull-up resistor.) Pch 5 Nch Nch GND -5- CXA3834AM Pin No. Symbol I/O Typical pin voltage Equivalent circuit Description VCC Pch 6 BLINK I 3.3 V to GND BLINK Blinking signal input 6 Nch GND VCC Pch 7 PWM_DIM I 3.3 V to GND PWM_DIM PWM dimming signal input 7 Nch GND VCC Pch Control voltage input (Connect to the R-C filter output side.) DC_DIM 8 DC_DIM I 3.3 V to GND 8 Pch GND VREF 9 PROTECT I/O 3.0 V to GND Pch PROTECT Nch 9 Nch Protection stop timer time adjustment (Connect to the timer adjusting capacitor.) GND VREF Pch 10 COMP I/O 3.8 V to GND COMP 10 Pch Nch GND -6- Error amplifier output for boost converter control (Connect the phase compensation circuit between COMP and GND.) CXA3834AM Pin No. Symbol I/O Typical pin voltage Equivalent circuit Description VCC Nch 11 VREF O 5.0 V VREF 11 Pch Internal supply voltage output (Connect a stabilizing capacitor.) Nch GND 12 GND GND 13 VCC Power supply input (Connect a stabilizing capacitor.) VREF Pch Pch 14 FB I 1.0 V to GND Pch FB 14 LED current detection input (Connect to a current detection resistor.) GND VCC MOSFET driver output for PWM dimming (Connect to the dimming NMOS gate.) Pch 15 DIM_SW O VCC to GND DIM_SW 15 Nch GND VREF Pch 16 OVP_DD I 3.2 V to GND OVP_DD 16 Pch GND -7- Output voltage detection input for boost converter (Connect to an output voltage detection resistor.) CXA3834AM Electrical Characteristics Shared Blocks (Unless otherwise specified, Ta = 25 C, VCC = 12 V, EN = 3.3 V, PWM_DIM = 3.3 V, BLINK = 3.3 V, DC_DIM = 3.3 V) Power Supply Block (VCC pin) Item Symbol Measurement conditions Min. Typ. Max. Unit Operation start voltage VCC_ON 9.0 9.5 10.0 V Operation stop voltage VCC_OFF 8.5 9.0 9.5 V Hysteresis width VCC VCC_ON - VCC_OFF 0.3 0.5 0.7 V Operating current consumption ICC1 FB = 1.5 V * Non switching -- 1.15 1.65 mA Current consumption when stopped ICC2 EN = 0 V PWM_DIM = 0 V -- 0.85 1.10 mA Min. Typ. Max. Unit 4.85 5.00 5.15 V Reference Voltage Block (VREF pin) Item Symbol Measurement conditions Output voltage VREF Input stability VREF_LINE VCC = 10.0 V to 18.0 V, No load -- 10 50 mV Load stability VREF_LOAD Iout = 0.1 m to 5.0 mA -- 20 50 mV Min. Typ. Max. Unit Enable Signal Input Block (EN pin) Item Symbol Measurement conditions High level detection voltage VEN_H 1.9 2.0 2.1 V Low level detection voltage VEN_L 0.9 1.0 1.1 V Hysteresis width VEN VEN_H - VEN_L 0.9 1.0 1.1 V Pin input resistance REN EN = 1.0 V 200 300 400 k Measurement conditions Min. Typ. Max. Unit Error Output Block (xBL_ERR pin) Item Symbol Output Low voltage VxBL_ERR_L EN = 0 V, Iout = -3 mA -- 0.15 0.3 V Output off leak current IxBL_ERR_OFF xBL_ERR = 18 V -- -- 1.0 A Min. Typ. Max. Unit 2.9 3.0 3.1 V Protective Detection Pin (PROTECT pin) Item Symbol Measurement conditions Latch stop detection voltage VPROTECT Charge current IPROTECT_CHG PROTECT = 1.0 V, PWM_DIM = 12.0 V 8.0 10.0 12.0 A Discharge current IPROTECT_RST PROTECT = 1.0 V 0.8 1.0 1.2 A -8- CXA3834AM LED Driver Control Block (Unless otherwise specified, Ta = 25 C, VCC = 12 V, EN = 3.3 V, PWM_DIM = 3.3 V, BLINK = 3.3 V, DC_DIM = 3.3 V) MOSFET Driver Output Block (DIM_SW pin) Item Symbol Measurement conditions Min. Typ. Max. Unit Output rise time *1 TR_DIM_SW CLOAD = 1000 pF -- 30 60 ns Output fall time *1 TF_DIM_SW CLOAD = 1000 pF -- 30 60 ns Output High voltage VDIM_SW_H Iout = 10 mA 11.90 11.95 -- V Output Low voltage VDIM_SW_L PWM_DIM = 0 V, Iout = -10 mA -- 0.05 0.1 V *1 Rise time and fall time use VCC 0.1 to VCC 0.9 as the judgment voltages. Error Amplifier Input Circuit Block (FB pin, DC_DIM pin) Item Symbol Measurement conditions Min. Typ. Max. Unit Feedback control voltage 1 VFB_REF1 DC_DIM = 3.3 V 0.98 1.00 1.02 V Feedback control voltage 2 VFB_REF2 DC_DIM = 1.65 V 0.495 0.500 0.505 V FB pin pull-up current IFB FB = 0.1 V 0.05 0.1 0.2 A Overcurrent detection voltage VFB_OCP 1.9 2.0 2.1 V DC_DIM pin input resistance RDC_DIM 700 990 1300 k Min. Typ. Max. Unit DC_DIM = 1.0 V PWM Dimming Signal Input Block (PWM_DIM pin) Item Symbol Measurement conditions High level input voltage VPWM_DIM_H 2.0 -- VCC - 2.0 V Low level input voltage VPWM_DIM_L -- -- 1.0 V Pin input resistance RPWM_DIM PWM_DIM = 1.0 V 200 300 400 k Measurement conditions Min. Typ. Max. Unit BLINK Signal Input Block (BLINK pin) Item Symbol High level input voltage VBLINK_H 2.0 -- VCC - 2.0 V Low level input voltage VBLINK_L -- -- 1.0 V Pin input resistance RBLINK 200 300 400 k BLINK = 1.0 V -9- CXA3834AM DC-DC Converter Control Block (Unless otherwise specified, Ta = 25 C, VCC = 12 V, EN = 3.3 V, PWM_DIM = 3.3 V, BLINK = 3.3 V, DC_DIM = 3.3 V) MOSFET Driver Output Block (DRV pin) Item Symbol Output rise time *1 Measurement conditions Min. Typ. Max. Unit TR_DRV CLOAD = 1000 pF -- 35 70 ns TF_DRV CLOAD = 1000 pF -- 25 50 ns Output High voltage VDRV_H Iout = 10 mA (Design guarantee) 11.85 11.90 -- V Output Low voltage VDRV_L EN = 0 V, Iout = -10 mA -- 0.03 0.1 V Oscillation frequency FOSC ISENSE = 0 V, OCP = 0 V, FB = 0 V 95 100 105 kHz Maximum On duty DMAX ISENSE = 0 V, OCP = 0 V, FB = 0 V 85 90 95 % Output fall time *1 *1 Rise time and fall time use VCC 0.1 to VCC 0.9 as the judgment voltages. Error Amplifier Output Block (COMP pin) Min. Typ. Max. Unit Transconductance Item gm Symbol (Design guarantee) Measurement conditions -- 520 -- A/V Output source current ICOMP_H FB = 0 V, COMP = 3.0 V 60 80 100 A Output sink current ICOMP_L FB = 1.5 V, COMP = 0.5 V 60 80 100 A Min. Typ. Max. Unit -- 50 -- A Min. Typ. Max. Unit Current Detection Circuit Block (ISENSE pin) Item Slope compensation output current Symbol ISLOPE Measurement conditions FB = 0 V, OPC = 0 V (Peak current value during maximum ON duty operation) (Design guarantee) Overcurrent Detection Block (OCP pin) Item Symbol Measurement conditions Overcurrent limit detection voltage VOCP FB = 0 V, ISENSE = 0 V 0.9 1.0 1.1 V DD blanking pulse width TDD_BLK OCP = 1.5 V, FB = 0 V 350 500 650 ns OCP pin pull-up current IOCP OCP = 0.1 V 0.05 0.1 0.2 A Min. Typ. Max. Unit 3.1 3.2 3.3 V 0.05 0.1 0.2 A Output Voltage Detection Block (OVP_DD pin) Item Symbol Output overvoltage detection voltage VOVP OVP_DD pin pull-up current IOVP Measurement conditions OVP_DD = 0.1 V Note) Shipping inspection is performed at room temperature. (The design is guaranteed with respect to temperature fluctuation.) - 10 - CXA3834AM Detailed Description of Blocks Start-up/Stop CXA3834AM operation starts when voltage of 9.5 V (typ.) or more is applied to the VCC pin. When this voltage is applied to the VCC pin, the internally generated reference voltage (VREF pin) is generated and the reset state (POR) is canceled. In addition, VCC has a built-in UVLO function, and when the VCC pin voltage falls to 9.0 V (typ.) or less, the IC enters the reset state, the DC-DC converter stops operation and the DIM_SW output goes to Low output regardless of the input signals of other pins. When the VCC pin voltage rises to 9.5 V or more again, the reset is canceled and stopped functions can be operated. 12 V 9.5 V VCC 9.0 V POR (internal signal) RESET release RESET RESET Fig. 1. Start-up and Stop Operation After Power-on Enable (EN) DC-DC converter and LED driver operations are enabled by setting the EN pin to 2.0 V or more. In addition, the PWM_DIM pin and the BLINK pin must both be High for the DC-DC converter to start operation. When the EN pin falls to 1.0 V or less, the DC-DC converter stops operating instantly, but the signal input to the PWM_DIM pin is output on the DIM_SW pin. In addition, when the EN pin is Low, the signal input to the PWM_DIM pin is output as is on the DIM_SW pin even when the BLINK pin is Low. EN 2.0 V 1.0 V PWM_DIM BLINK DIM_SW DRV (DC-DC converter operation) Fig. 2. Operation During Voltage Input to the EN Pin - 11 - CXA3834AM Dimming Control Block The CXA3834AM has an on-chip constant current mode boost DC-DC converter to generate the voltage required to light the LED elements. The voltage (VOUT) boosted by the DC-DC converter is applied to the anode side of the multiple LED elements connected in series, and when a High voltage is input to the PWM_DIM pin, the DIM_SW pin also outputs a High voltage, the external FET is driven, and current flows to the LED elements. Fig. 3 shows a schematic of the operating circuit. VIN CXA3834AM VOUT DC_DIM DRV 23R 10R ISENSE DC-DC Controller ILED OCP BLINK Control Logic DIM_SW PWM_DIM FB Rfb Fig. 3. CXA3834AM Operating Circuit Diagram - 12 - CXA3834AM LED Luminance Adjustment The CXA3834AM can adjust the LED luminance using two different settings. [Luminance Adjustment by PWM Control] The pulse input to the PWM_DIM pin is output on the DIM_SW pin. The external FET gate is driven and current flows to the LED elements in accordance with the DIM_SW pin output. The average current flowing to the LED elements is proportional to the duty of the pulse input to the PWM_DIM pin, so the LED element luminance can be adjusted by controlling the duty. (See Fig. 4.) Use a CXA3834AM PWM_DIM pin input pulse with a frequency between 20 Hz and 40 kH (when PWM_DIM and BLINK pin are short circuited, use them detween 48 Hz and 1 kHz), with a minimum High pulse width of 1 s. [Luminance Adjustment by Peak Current Control] The current flowing to the LED elements is converted to a voltage by the FB resistor (Rfb), and this voltage monitored by the FB pin of the CXA3834AM. The DC-DC converter compares the FB pin voltage with the value 10/33 times the DC_DIM pin voltage (VDC_DIM), and controls the output voltage (VOUT) to hold the same potential. That is to say, the current flowing to the LED elements or the FB pin resistor can be controlled by controlling the DC_DIM pin voltage. The current flowing to the LED elements is determined by the following formula. 10 I LED = V DC_DIM ------ Rfb [A] 33 100 200 DC_DIM = 3.3 V Rfb = 10 LED current [mA] LED average current [mA] Fig. 5 shows the relationship between the DC_DIM pin voltage and FB pin resistance value and the current flowing to the LED elements. 75 50 25 Rfb = 5 PWM_DIM_Duty = 100 % 150 100 Rfb = 10 PWM_DIM_Duty = 100 % 50 1.65 3.3 DC_DIM input voltage [V] 50 100 PWM_DIM duty [%] Fig. 4. PWM_DIM_Duty - ILED Characteristics Fig. 5. DC_DIM Voltage - ILED Characteristics The DC_DIM pin is pulled down internally by resistance of 990 k (typ.). When connecting a smoothing RC filter to the DC_DIM pin, determine the constants in consideration of the IC internal impedance. - 13 - CXA3834AM LED Blinking Control (Blinking) The CXA3834AM has a BLINK pin, and the LED elements can be made to perform blinking operation by switching the signal input to the BLINK pin between High and Low. When the BLINK signal is Low, the DIM_SW pin is forcibly set to Low output (LED elements off), and at the same time the DC-DC converter output voltage ripple is suppressed, so DC-DC converter boost operation (DRV output) is also forcibly stopped. Fig. 6 shows operation relative to the signal input to the BLINK pin. BLINK PWM_DIM DIM_SW LED OFF ON OFF ON OFF ON OFF ON OFF ON OFF ON OFF ON OFF ON OFF DRV Fig. 6. Timing Chart During Blinking Operation Use a CXA3834AM BLINK pin input pulse with a maximum frequency of 240 Hz with a minimum High pulse width of 2 ms. (When PWM_DIM and BLINK pin are short circuited, use them with a maximum frequency of 1 kHz with a minimum pulse width of 1 s.) For applications that do not perform blinking operation, connect the BLINK pin to the VREF pin. - 14 - CXA3834AM LED Overcurrent Detection Circuit Block The CXA3834AM has an overcurrent detection function to detect abnormalities in the current flowing to the LED elements. Fig. 7 shows the FB pin peripheral equivalent circuit. VOUT DC_DIM 23R DRV DC-DC Controller 10R ILED DIM_SW PWM_DIM VREF FB ERR_SET PROTECT Rfb Control Logic 3.0 V Blanking Pulse 2.0 V ERR_RST Fig. 7. FB Pin Peripheral Equivalent Circuit When a FB pin voltage of 2.0 V (typ.) or more is detected (LED_OCP), charging to the PROTECT pin starts (charge current: 10 A (typ.)). LED_OCP is detected continuously, and when the PROTECT pin voltage reaches 3 V, the IC is set to stop mode (latch stop). Charging to the PROTECT pin is performed only while LED_OCP is detected. When LED_OCP is not detected, the PROTECT pin discharges at 1 A (typ.). This IC generates a blanking pulse to prevent the above-mentioned overcurrent detection from malfunctioning. This blanking pulse is approximately 500 ns (min.), and prevents false overcurrent detection due to the inrush current that occurs when DIM_SW switches from Low to High. The FB pin voltage is controlled by 10/33 times the DC_DIM pin voltage, but note that overcurrent is detected more easily when the DC_DIM pin voltage is set too high. Fig. 8 shows the timing chart during LED_OCP operation. PWM_DIM Blanking Pulse 2.0 V FB ERR_SET (OCP detection) PROTECT Fig. 8. LED_OCP Detection Timing Chart - 15 - CXA3834AM DC-DC Converter Control Block Oscillator Circuit Block The CXA3834AM DC-DC converter oscillating frequency is fixed to 100 kHz (typ.) by the internal circuit. The maximum ON duty is 90 % (typ.), and the boost converter MOSFET ON time is normally proportional to the COMP pin voltage. Fig. 9 shows the oscillator peripheral equivalent circuit. VIN VOUT clk Slope Compensator Oscillator slope V/I Rcs COMP OCP 1.0 V DC_DIM 23R Error Amplifier VREF PWM Comparator L/S 10R PWM_IN PWM S Q R Q DRV Rslope ISENSE Visense OCP Vocp FB Rfb Fig. 9. Oscillator Peripheral Equivalent Circuit [Steady-state Operation] When the CLK pulse is output from the oscillator, the DRV pin output goes High and current starts to flow to the choke coil. The current that flows to the choke coil is converted to a voltage (Vocp) by the current detection resistor (Rcs). The ISENSE pin voltage (Visense) is the sum of Vocp and the voltage generated by the internal slope compensation current flowing to the slope compensation resistor (Rslope), and is input to the PWM comparator non-inverted input pin. When Visense rises to the PWM comparator inverted input pin (PWM_IN) voltage or more, the reset signal is generated and the DRV pin output goes Low. The PWM_IN voltage (Vpwm_in) is the voltage obtained by level-shifting the COMP pin voltage (Vcomp), and is determined approximately by the following calculation formula. Here, Vt corresponds to the internal transistor threshold voltage, and is approximately 0.8 V in the CXA3834AM. Vpwm_in = (Vcomp - Vt) 3/5 When the current flowing to the choke coil is low and Visense does not reach the PWM_IN voltage during one cycle period, the DRV output automatically goes Low when the ON duty reaches 90 % (typ.). The above operation is repeated and boost operation is continued until the prescribed current flows to the LED elements. Fig. 10 shows the DC-DC converter operation timing chart during steady-state operation. CLK DRV IL PWM_IN Vocp + Visense Fig. 10. DC-DC Converter Operation Timing Chart - 16 - CXA3834AM [Overcurrent Detection] The peak current flowing to the choke coil is constantly monitored by the OCP pin, and when the OCP pin voltage reaches 1.0 V (typ.), the DRV pin output is forcibly set Low (pulse-by-pulse operation). After overcurrent detection, the PROTECT pin is charged at 10 A (typ.) until the next cycle starts. When overcurrent is detected continuously, the PROTECT pin is continuously charged, and when the PROTECT pin voltage reaches 3 V, the IC latch stops. The CXA3834AM generates a blanking pulse to prevent false OCP pin overcurrent detection. This blanking pulse is 500 ns (typ.), and prevents false overcurrent detection due to the inrush current that occurs when the DRV pin output switches from Low to High. [Slope Compensation] When the constant current mode boost converter is set so that the DRV pin ON duty is 50 % or more, sub-harmonic oscillation may occur. The CXA3834AM can operate the boost converter stably even when the ON duty is 50 % or more by inserting a series resistor (Rslope) to the ISENSE pin and applying slope compensation. For details on sub-harmonic oscillation and slope compensation, see the Application Notes. - 17 - CXA3834AM COMP Pin Hold Circuit Block The FB pin voltage temporarily goes to 0 V while a Low signal is input to the PWM_DIM pin and current is not flowing to the LED elements (DIM_SW pin output signal Low period), so the COMP pin voltage and the DC-DC converter output voltage rise temporarily. In this case, when a High signal is input to the PWM_DIM pin in the next cycle, a transient current flows to the LED elements. In the CXA3834AM, the COMP pin voltage immediately before a Low signal is input to the PWM_DIM pin is held, and DC-DC converter operation continues. By holding the COMP pin voltage, operation can be performed without a transient current flowing to the LED elements even when the PWM_DIM pin signal goes High in the next cycle. Similar operation is also performed when the BLINK pin input signal is Low, so that the COMP pin output voltage is held even when a Low signal is input to the BLINK pin and boost operation stops. Fig. 11 and Fig. 12 show the COMP pin hold function timing chart and the COMP pin peripheral equivalent circuit, respectively. BLINK PWM_DIM Hold Hold Hold Hold Hold Hold Hold Hold COMP Hold VOUT LED_Current Fig. 11. COMP Pin Hold Function Timing Chart Rcomp Ccomp1 COMP Ccomp2 DC_DIM 23R Error Amplifier PWM S Q R Q DRV L/S 10R HOLD_SW ON/OFF ISENSE BLINK Control Logic PWM_DIM DIM_SW FB Fig. 12. COMP Pin Peripheral Equivalent Circuit When the signal input to the PWM_DIM pin has a high frequency (up to approximately 40 kHz) and low duty, the effect of the hold function reduces the COMP pin response speed, and may influence the start-up time and the LED current characteristics. Make thorough evaluation before determining the phase compensation constants Rcomp, Ccomp1 and Ccomp2 connected to the COMP pin. For details, see the Application Notes. In addition, this IC detects the condition that FB pin voltage is fixed to Low when no current flows to the LED elements due to error conditions such as DRV pin open. Therefore, this IC has a function to output Low level of xBL_ERR signal when COMP voltage becomes 2.8 V (Min.) or more. - 18 - CXA3834AM Output Voltage Detection Circuit Block Fig. 13 shows the OVP_DD pin peripheral equivalent circuit. VIN VOUT DC_DIM DRV 23R DC-DC Controller 10R VREF Rovp1 Control Logic OVP_DD OVP 3.2 V ILED Rovp2 FB Rfb Fig. 13. OVP_DD Pin Peripheral Equivalent Circuit The OVP_DD pin has a protective function that detects DC-DC converter output overvoltage. When an OVP_DD pin voltage of 3.2 V (typ.) or more is detected (OVP), the IC instantly latch stops. To properly light the LED elements during normal operation, set the breeder resistance ratio (Rovp1/Rovp2) so that the voltage input to the OVP_DD pin is 3.2 V or less. In addition, pull-up current of 0.1 A (typ.) is supplied from inside the IC in consideration of the case when the OVP_DD pin is open. When the OVP_DD pin is open, the pin voltage is pulled-up to approximately the VREF pin voltage, OVP is detected, and the IC latch stops. Therefore, set the Rovp2 resistance value to a value that does not affect this 0.1 A current. - 19 - CXA3834AM Protective Detection Functions The CXA3834AM has various built-in protective functions to realize stable power supply operation. When an error is detected by a protective function, the xBL_ERR pin outputs a Low signal, and either timer latch operation is performed by charging the PROTECT pin or instant latch stop operation is performed. Table 1 lists the protective functions, error conditions, and operation after detection. When the IC latch stops after an error is detected, DC-DC converter operation stops and the DIM_SW pin outputs Low. When the IC has performed latch operation (LATCH1), the latch can be canceled by turning the power supply off and then on again, or by stopping and then restarting EN supply. When latch stop operation was performed due to overheat protective detection (TSD) (LATCH2), the latch can be canceled only by turning the power supply off and then on again. Table 1. List of Protective Functions No. Protective function Detection conditions PROTECT pin charging xBL_ERR = Low output Backlight error detection function (xBL_ERR = Low output) 1 MOS_FET open detection When the COMP pin output stays High -- 2 VREF overvoltage detection 1 VREF pin voltage > 6.0 V -- Timer latch function (PROTECT pin charging) 3 DC-DC overcurrent detection (DD_OCP) OCP pin voltage > 1.0 V -- 4 LED overcurrent detection (LED_OCP) FB pin voltage > 2.0 V -- 5 DRV pin error detection DRV pin input/output mismatch -- Backlight error detection and timer latch function 6 PWM_DIM pin protective detection PWM_DIM pin voltage > VCC - 0.5 V 7 BLINK pin protective detection BLINK pin voltage > VCC - 0.5 V 8 DC_DIM pin protective detection DC_DIM pin voltage > VCC - 0.5 V 9 VREF overvoltage detection 2 VREF pin voltage > 5.5 V Instant latch function 1 (Latch1) 10 DC-DC output overvoltage protection (OVP) OVP_DD pin voltage > 3.2 V -- 11 PROTECT latch stop detection PROTECT pin voltage > 3.0 V -- Tj > 140 C -- Instant latch function 2 (Latch2) 12 Overheat detection (TSD) [Backlight Error Detection Function] When error number 1, 2, 6, 7, 8 or 9 in Table 1 is detected, the xBL_ERR pin outputs Low, and current is pulled into the IC from an external voltage source via a pull-up resistor. When a backlight error is not detected, the xBL_ERR pin is high impedance, so the external pull-up voltage source voltage is generated on the pin. [Timer Latch Function] When error number 3, 4, 5, 6, 7, 8 or 9 in Table 1 is detected, charging to the PROTECT pin starts, and the IC latch stops when the PROTECT pin voltage reaches 3 V. The time after an error is detected until the latch stop operation can be set by connecting a capacitor to the PROTECT pin. Fig. 14 and Fig. 15 show the PROTECT pin peripheral equivalent circuit and the error detection timing chart, respectively. [Instant Latch Function] When error number 10 or 11 in Table 1 is detected, the IC instantly latch stops, and DC-DC converter and dimming operation also stop. When the IC has latch stopped, the xBL_ERR pin outputs Low. - 20 - CXA3834AM Internal reference voltage VREF 10 A ERR_SET PROTECT PROTECT Logic ERR_RST Cp rst 3.0 V 1 A Fig. 14. PROTECT Pin Equivalent Circuit When an error is detected (ERR_SET = High), stable current of 10 A flows out from the IC via the PROTECT pin. During normal operation (ERR_RST = High), stable current of 1 A flows into the IC via the PROTECT pin. ERR_SET (internal_signal) 3.0 V PROTECT PROTECT LATCH PROTECT pin current Latch detected dischg chg dischg chg dischg chg dischg Fig. 15. Error Detection Timing Chart The timer time when an error is continuously detected can be expressed by the following formula. T = Cp (F 3.0 V 10 A = 0.3 Cp (s) - 21 - CXA3834AM [State Transition Diagram] Fig. 16 shows the state transitions of this IC. VCC_UVLO = H Initial state xBL_ERR = L LATCH2 = H Error state 2 xBL_ERR = L RESET = H LATCH2 = H RESET = L RESET = H LATCH2 = H Normal operating state Error state 1 LATCH1 = H xBL_ERR = Hi-Z xBL_ERR = L Fig. 16. State Transition Diagram Note) RESET = High condition : VCC_UVLO = H or EN = L or VREF_UVLO = H or VREF_OVLO = H LATCH1 = High condition : PROTECT = H or OVP = H LATCH2 = High condition : TSD = H RESET = Low condition : VCC_UVLO = L and EN = H and VREF_UVLO = L and VREF_OVLO = L - 22 - CXA3834AM Application Circuit 200 H VOUT VIN 33 F 440 k 660 k 6.3 k 0.1 4.7 k 12 V 1 DRV OVP_DD 16 2 ISENSE DIM_SW 15 3 OCP FB 14 4 EN VCC 13 BL_ERR 5 xBL_ERR GND 12 BLINK 6 BLINK VREF 11 PWM_DIM 7 PWM_DIM COMP 10 8 DC_DIM PROTECT 9 10 k BL_ON 4.7 k 12 V 1V 5 2.2 k 10 k DC_DIM 2.2 k 1.0 F 1.0 F xx 0.47 F CXA3834AM 0.47 F Application circuits shown are typical examples illustrating the operation of the devices. Sony cannot assume responsibility for any problems arising out of the use of these circuits or for any infringement of third party patent and other right due to same. Fig. 17. Application Circuit (assuming Vin = 150 V, Vout = 300 V, ILED = 200 mA) - 23 - CXA3834AM Example of Representative Characteristics VCC_UVLO operation start voltage VCC_UVLO operation start voltage [V] VREF pin output voltage VREF pin output voltage [V] 5.20 5.15 5.10 5.05 5.00 4.95 4.90 4.85 4.80 -30 0 30 60 90 120 10.2 10.0 9.8 9.6 9.4 9.2 9.0 8.8 -30 0 1.1 1.0 0.9 0.8 0.7 0 30 60 120 90 120 9.4 9.2 9.0 8.8 8.6 8.4 -30 0 30 60 90 120 Temp [C] PROTECT pin latch detection voltage Operating current consumption 3.15 2.0 Latch detection voltage [V] Operating current consumption [A] 90 9.6 Temp [C] 1.5 1.0 0.5 0 -30 60 VCC_UVLO operation stop voltage Current consumption when stopped 1.2 0.6 -30 30 Temp [C] VCC_UVLO operation stop voltage [V] Current consumption when stopped [mA] Temp [C] 0 30 60 90 120 3.10 3.05 3.00 2.95 2.90 2.85 -30 0 30 60 Temp [C] Temp [C] - 24 - 90 120 CXA3834AM FB pin control voltage 2 0.506 60 0.504 Control voltage 2 [V] Rise time [ns] DIM_SW pin rise time 70 50 40 30 20 0.500 0.498 0.496 10 0 -30 0.502 0 30 60 90 0.494 -30 120 0 DIM_SW pin fall time Overcurrent detection voltage [V] Fall time [ns] 60 50 40 30 20 10 30 60 90 2.10 2.05 2.00 1.95 1.90 1.85 -30 120 0 30 60 90 120 Temp [C] FB pin control voltage 1 DRV pin oscillating frequency 1.03 108 Oscillating frequency [kHz] Control voltage 1 [V] 120 2.15 Temp [C] 1.02 1.01 1.00 0.99 0.98 0.97 -30 90 FB pin overcurrent detection voltage 70 0 60 Temp [C] Temp [C] 0 -30 30 0 30 60 90 120 Temp [C] 106 104 102 100 98 96 94 92 -30 0 30 60 Temp [C] - 25 - 90 120 CXA3834AM DRV pin maximum ON duty OCP pin overcurrent detection voltage Overcurrent detection voltage [V] Maximum ON duty [%] 96 94 92 90 88 86 84 -30 0 30 60 90 1.20 1.15 1.10 1.05 1.00 0.95 0.90 0.85 0.80 -30 120 0 Temp [C] COMP pin source current Overvoltage detection voltage [V] Source current [A] 90 80 70 60 30 60 90 120 COMP pin sink current 110 Sink current [A] 100 90 80 70 60 0 30 60 120 3.35 3.30 3.25 3.20 3.15 3.10 3.05 -30 0 30 60 Temp [C] Temp [C] 50 -30 90 OVP_DD pin overvoltage detection voltage 100 0 60 Temp [C] 110 50 -30 30 90 120 Temp [C] - 26 - 90 120 CXA3834AM Package Outline (Unit: mm) MITSUI HT: 875340660 Marking A3834M - 27 - CXA3834AM Package Outline (Unit: mm) SDT: 875339910 Marking C:CXA3834AM B: Lot No. (Max. 7) C (Control No.) B (Week manufactured) () (Year manufactured) - 28 - Sony Corporation