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Mobile Phone Xenon Photoflash Capacitor Charger With IGBT Driver A8731 2Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Selection Guide Part Number Package Packing A8731EEJTR-T 10-contact DFN Tape and reel, 1500 pieces per reel *Contact Allegro for additional ordering information. Thermal Characteristics Characteristic Symbol Test Conditions* Value Units Package Thermal Resistance R θJA On 2-layer PCB with 0.88 in.2 area of 2 oz. copper each side, based on JEDEC standard 65 ºC/W On 4-layer PCB based on JEDEC standard 45 ºC/W *Additional thermal information available on Allegro website. Absolute Maximum Ratings Characteristic Symbol Notes Rating Units SW Pin V SW DC voltage. (VSW is self-clamped by internal active clamp and is allowed to exceed 40 V during flyback spike durations. Maximum repetitive energy during flyback spike: 0.5 μJ at frequency ≤ 400 kHz.) –0.3 to 40 V VIN Pin V IN –0.3 to 6.0 V CHARGE, TRIGGERx, ¯D¯ ¯O¯ ¯N¯ ¯E¯ Pins Care should be taken to limit the current when –0.6 V is applied to these pins. –0.6 to VIN + 0.3 V V Remaining Pins –0.3 to VIN + 0.3 V V Operating Ambient Temperature T A Range E –40 to 85 ºC Maximum Junction T J(max) 150 ºC Storage Temperature T stg –55 to 150 ºC
Mobile Phone Xenon Photoflash Capacitor Charger With IGBT Driver A8731 3Allegro MicroSystems, Inc. Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Functional Block Diagram VIN SW GND OCP ISET CHARGE VDSref ton(max) toff(max) DONE GATE TRIGGER1 TRIGGER2 DMOS VSW – VBAT Q QS R Q QS R DCM Detector ISET Buffer H m L Triggered Timer Control Logic 18 μs 18 μs Enable One Shot VIN IGBT Driver
Mobile Phone Xenon Photoflash Capacitor Charger With IGBT Driver A8731 4Allegro MicroSystems, Inc. Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com (Contacts Down View) NC DONE TRIGGER1 SW TRIGGER2 ISET GATE VIN GND CHARGE PAD Pin-out Diagram Terminal List Table Number Name Function
1 ISET Sets the maximum switch current; connect an external resistor to GND to
set the desired peak current
2 GATE IGBT gate drive – sink/source
3 VIN Input voltage; connect to a 2.3 to 5.5 V battery supply
4 GND Ground connection
5 CHARGE Pull high to initiate charging; pull low to enter low-power standby mode
6 TRIGGER2 IGBT input trigger 2
7 SW Drain connection of internal power MOSFET switch; connect to
transformer primary winding
8 TRIGGER1 IGBT input trigger 1
9 ¯D¯ ¯O¯ ¯N¯ ¯E¯ Pulls low when output reaches target value and CHARGE pin is high; goes high during charging or whenever CHARGE pin is low
10 NC No connection , electrically floating pin
– PAD Exposed pad for enhanced thermal dissipation; connect to ground plane
Mobile Phone Xenon Photoflash Capacitor Charger With IGBT Driver A8731 5Allegro MicroSystems, Inc. Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com ELECTRICAL CHARACTERISTICS typical values valid at VIN = 3.6 V, RSET = 33 kΩ, ISWlim = 1.0 A, and TA=25°C, unless otherwise noted Characteristics Symbol Test Conditions Min. Typ. Max. Unit VIN Voltage Range V IN 2.3 – 5.5 V UVLO Enable Threshold V INUV VIN rising – 2.05 2.2 V UVLO Hysteresis V INUVhys – 150 – mV VIN Supply Current I IN Shutdown (CHARGE = 0 V, TRIGGER1 and TRIGGER2 = 0 V) – 0.01 0.5 μA Charging complete – 10 50 μA Charging (CHARGE = VIN, TRIGGER1 and TRIGGER2 = 0 V) –2 – m A Current Limits Switch Current Limit1 ISWlimMAX RSET = 26.7 kΩ 1.08 1.2 1.32 A ISWlimMIN RSET = 85 kΩ – 0.4 – A SW / ISET Current Ratio I SW/ISET CHARGE = high – 28 – kA/A ISET Pin Voltage While Charging V SET CHARGE = high – 1.2 – V ISET Pin Internal Resistance R SET(INT) – 1000 – Ω Switch On-Resistance R SWDS(on) VIN = 3.6 V, ID = 800 mA, TA = 25°C – 0.25 – Ω Switch Leakage Current2 ISWlk VSW = VIN(max), over temperature range – – 2 μA Combined VIN and SW leakage current at TA=25°C VIN= 5.5 V in Shutdown – – 0.5 μA CHARGE Input Current I CHARGE VCHARGE = VIN – 36 – μA CHARGE Input Voltage2 VCHARGE High, over input supply range 1.1 – – V Low, over input supply range – – 0.4 V CHARGE Pull-Down Resistor Value R CHPD – 100 – k Ω CHARGE ON/OFF Delay t CH Time between CHARGE = 1 and charging enabled – 20 – us Maximum Switch-Off Timeout t offMAX – 18 – μs Maximum Switch-On Timeout t onMAX – 18 – μs ¯D¯ ¯O¯ ¯N¯ ¯E¯ Output Leakage Current2 IDONElk ––1 μA Output Comparator Trip Voltage2 VOUTTRIP Measured as VSW – VIN 31 31.5 32 V Output Comparator Overdrive V OUTOV Pulse width = 200 ns (90% to 90%) – 200 400 mV dV/dt Threshold of ZVS Comparator dV/dt Measured at SW pin – 20 – V/ μs IGBT Driver TRIGGER, TRIGGER2 Input Voltage2 VTRIG(H) Input = logic high, over input supply range 1.1 – – V VTRIG(L) Input = logic low, over input supply range – – 0.4 V TRIGGER, TRIGGER2 Pull-Down Resistor R TRIGPD – 100 – k Ω GATE Resistance to VIN R SrcDS(on) VIN = 3.6 V, VGATE =1.8 V – 23 – Ω GATE Resistance to GND R SnkDS(on) VIN = 3.6 V, VGATE = 1.8 V – 30 – Ω Propagation Delay (Rising) t Dr Measurement taken at pin, CL= 6500 pF, VIN = 3.6 V – 110 – ns Propagation Delay (Falling) t Df – 140 – ns Output Rise Time t r – 290 – ns Output Fall Time t f – 360 – ns 1Current limit guaranteed by design and correlation to static test. Refer to application section for peak current in actual circuits. 2Specifications over the range TA= –40°C to 85°C; guaranteed by design and characterization.
Mobile Phone Xenon Photoflash Capacitor Charger With IGBT Driver A8731 6Allegro MicroSystems, Inc. Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com IGBT Drive Timing Definition GATE TRIGGER tDr tr tDf tf 50% 10% 90% 50% 10% 90% IGBT Drive Timing Characteristic Performance CGATE = 6200 pF. VIN = 3.6 V, Time = 200 ns/div; CH1 = TRIGGER input, 2 V/div, CH2 = Gate driver output, 1 V/div
Mobile Phone Xenon Photoflash Capacitor Charger With IGBT Driver A8731 7Allegro MicroSystems, Inc. Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com high transition at the CHARGE pin. VOUT CHARGE DONE VIN TRIGGER1 and TRIGGER2 IGBTDRV SW AB A8731 Operation Timing Diagram Explanation of Events A: Start charging by pulling CHARGE to high, provided that V IN is above UVLO level. B: Charging stops when VOUT reaches the target voltage. C: Start a new charging process with a low-to- D: Pull CHARGE to low to put the controller in low-power standby mode. E: Charging does not start, because VIN is below UVLO level when CHARGE goes high. F: After VIN goes above UVLO, another low-to-high transition at the CHARGE pin is required to start the charging. T1, T2, T3(Trigger instances): IGBT driver output pulled high whenever both TRIGGER pins are logic high. It is recommended to avoid applying any trigger pulses during charging. UVLO Target VOUT CD E F T3T1 T2
Mobile Phone Xenon Photoflash Capacitor Charger With IGBT Driver A8731 8Allegro MicroSystems, Inc. Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Performance Characteristics Charging Time at Various Peak Current Levels Common Parameters Symbol Parameter Units/Division C1 V OUT 50 V C2 V BAT 1 V C3 I IN 100 mA t time 200 ms Conditions Parameter Value VBATT 3.6 V COUT 20 μF t Conditions Parameter Value RSET 39 kΩ ISWlim ≈0.9 A IIN VOUT VBAT t Conditions Parameter Value RSET 33.2 kΩ ISWlim ≈1.0 A IIN VOUT VBAT t IIN VOUT Conditions Parameter Value RSET 26.7 kΩ ISWlim ≈1.2 A VBAT
Mobile Phone Xenon Photoflash Capacitor Charger With IGBT Driver A8731 9Allegro MicroSystems, Inc. Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Charge Time versus Battery Voltage Transformer Lp= 8 μH, N = 10.2; COUT= 20 μF / 330 V UCC; TA=25° 0.5 1.0 1.5 2.0 2.5 3.0 3.5 VBA T (V) Time (s) 55 ≈ 0.65 45 ≈ 0.8 39 ≈ 0.9 33.2 ≈ 1.0 26.7 ≈ 1.2 RSET (kΩ) IP (A) COUT= 20 μF. For larger or smaller capacitances, charging time scales proportionally. Efficiency versus Battery Voltage V BAT (V) Efficiency (%) Transformer Lp= 8 μH, N = 10.2; COUT= 20 μF / 330 V UCC; TA=25° 55 ≈ 0.65 45 ≈ 0.8 39 ≈ 0.9 33.2 ≈ 1.0 26.7 ≈ 1.2 RSET (kΩ) IP (A) Special low-profile transformer with relatively low inductance (Lp= 8 μH) and high winding resistance (Rp = 0.37 Ω). Higher efficien- cy can be achieved by using transformers with higher Lp, which reduces switching frequency and therefore switching loses, and lower resistance, which reduces conduction losses. 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 VBAT (V) IIN (A) Average Input Current versus Battery Voltage XFM Lp= 8 μH, N = 10.2, COUT= 20 μF 330 V UCC, TA=25° 55 ≈ 0.65 RSET (kΩ) IP (A) 45 ≈ 0.8 39 ≈ 0.9 33.2 ≈ 1.0 26.7 ≈ 1.2 An increase in ISWlim with respect to VBAT actually keeps the average input current roughly constant throughout the battery voltage range. Normally, if ISWlim is kept constant, the average current will drop as VBAT goes higher.
Mobile Phone Xenon Photoflash Capacitor Charger With IGBT Driver A8731 10Allegro MicroSystems, Inc. Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com General Operation Overview The CHARGE pin enables the part and starts charging. N¯ ¯E¯ open-drain indicator is pulled low when CHARGE is high and target output voltage is reached. Pulling the CHARGE pin low stops charging and forces the chip into low-power standby mode. Selection of Switching Current Limit The A8731 features continuously adjustable peak switching current between 0.4 and 1.2A. This is done by selecting the value of an external resistor RSET, connected from the ISET pin to GND, which deter- mines the ISET bias current, and therefore the switch- ing current limit, I SWlim. To the first order approximation, ISWlim is related to ISET and RSET according to the following equations: ISWlim = ISET × K = VSET / RSET × K , (1) where K = 28000 when battery voltage is 3.6 V . In real applications, the actual switching current limit is affected by input battery voltage, and also the transformer primary inductance, Lp. If necessary, the following expressions can be used to determine ISWlim more accurately: ISET = VSET / (RSET + RSET(INT) – K × RGND(INT) ), (2) where: R SET(INT) is the internal resistance of the ISET pin (1 kΩ typical), R GND(INT) is the internal resistance of the bonding wire for the GND pin (27 mΩ typical), and K = (K ′ + VIN × K″), with K′ = 24350 and K″ ≈ 1040 at TA = 25°C. Then, ISWlim = ISET × K + VBAT / LP × tD , (3) where tD is the delay in SW turn-off (0.1 μs typical). Figure 3 can be used to determine the relationship between RSET and ISWlim at various battery voltages.
Application Information
0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 25 30 35 40 45 50 55 60 65 70 75 80 85 90 RSET (kΩ) ISWlim (A) VIN = 5.5 V VIN = 4.5 V VIN = 3.6 V VIN = 3.0 V VIN = 2.3 V Figure 3. Peak Current Limit versus ISET Resistance. VIN = VBAT, transformer LP = 8 μH, TA = 25°C.
11Allegro MicroSystems, Inc. output capacitor, the IC enters Fast-Charging Mode. Figure 5. Timer Mode and Fast Charging Mode. t =200 ms/div, Figure 6. Timer Mode expanded view. VOUT ≤ 14 V, t = 2 μs / div., Figure 4. Smart Current Limit reference circuit
12Allegro MicroSystems, Inc. together inside the IC to control the IGBT gate driver. pins together and use as a single input. ing through the phototransistor is in less than 1 μA. gate driver (and thereby fire the flash). Figure 7. Minimum voltage switching. VOUT ≥ 15 V; t =1 μs/div.,
13Allegro MicroSystems, Inc. would be a small leakage current even when the camera is turned off. Figure 9. ALS typical application Figure 10. Adaptive timing of photoflash. (A) Subject near to camera, and (B) subject far from camera.
14Allegro MicroSystems, Inc.
- The transformer turns ratio, N, determines the out-
the forward drop of the output diode.
- The primary inductance, LP , determines the on-time
- The secondary inductance, LS, determines the off-
Figure 11. Pulse width relationship definitions.
Mobile Phone Xenon Photoflash Capacitor Charger With IGBT Driver A8731 15Allegro MicroSystems, Inc. Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Package EJ, 3 mm x 3 mm 10-Contact DFN with Exposed Thermal Pad 2.38 A A Terminal #1 mark area B Exposed thermal pad (reference only, terminal #1 identifier appearance at supplier discretion) For Reference Only (reference JEDEC MO-229WEED) Dimensions in millimeters Exact case and lead configuration at supplier discretion within limits shown C Reference land pattern layout (reference IPC7351 SON50P300X300X80-11WEED3M); All pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary to meet application process requirements and PCB layout tolerances; when mounting on a multilayer PCB, thermal vias at the exposed thermal pad land can improve thermal dissipation (reference EIA/JEDEC Standard JESD51-5) B PCB Layout Reference View 1.64 2.38 0.30 10 0.500.85 3.10 C 1.64 C0.08 11X CSEATING PLANE D 0.25 +0.05 –0.07 0.50 0.75 ±0.05 3.00 ±0.15 3.00 ±0.15 0.40 ±0.10
Mobile Phone Xenon Photoflash Capacitor Charger With IGBT Driver A8731 16Allegro MicroSystems, Inc. Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com Copyright ©2008-2012, Allegro MicroSystems, Inc. Allegro MicroSystems, Inc. reserves the right to make, from time to time, such de par tures from the detail spec i fi ca tions as may be required to per- mit improvements in the per for mance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the information being relied upon is current. Allegro’s products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the failure of that life support device or system, or to affect the safety or effectiveness of that device or system. The in for ma tion in clud ed herein is believed to be ac cu rate and reliable. How ev er, Allegro MicroSystems, Inc. assumes no re spon si bil i ty for its use; nor for any in fringe ment of patents or other rights of third parties which may result from its use. For the latest version of this document, visit our website: www.allegromicro.com
Revision History
Revision Revision Date Description of Revision Rev. 1 April 19, 2012 Miscellaneous format changes