a8732 Allegro MicroSystems, Inc., a8732 Datasheet

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a8732

Manufacturer Part Number
a8732
Description
Ultra Small Mobile Phone Xenon Photoflash Capacitor Charger With Igbt Driver
Manufacturer
Allegro MicroSystems, Inc.
Datasheet
Features and Benefits
▪ Ultra small 2 × 2 DFN/MLP-8 package
▪ Low quiescent current draw (0.5 μA max. in shutdown mode)
▪ Primary-side output voltage sensing; no resistor divider required
▪ Adjustable switch peak current limit up to 1.5 A with
▪ 1V logic (V
▪ Integrated IGBT driver with internal gate resistors
▪ Optimized for mobile phone, 1-cell Li+ battery applications
▪ Zero-voltage switching for lower loss
▪ >75% efficiency
▪ Charge complete indication
▪ Integrated 50 V DMOS switch with self-clamping
Package: 8-pin DFN/MLP (suffix EE)
Not to scale
8732-DS
single-wire programming through the CHARGE pin
protection
Figure 1. Typical applications: (A) with single battery supply and (B) with separate bias supply
VIN_VDRV
C2
CHARGE
TRIG
HI
(min)) compatibility
2 mm × 2 mm, 0.60 mm height
V IN_VDRV
VBAT
Battery Input
2.3 to 5.5 V
Control
IGBT Driver
Block
GND
(A)
DONE
VOUT Detect
+
I
SW
Ultra Small Mobile Phone Xenon Photoflash
sense
C1
SW
DONE
GATE
IGBT Gate
C
100F
315 V
Typical Applications
VPULLUP
OUT
100 kΩ
Capacitor Charger with IGBT Driver
The Allegro
Description
to meet the needs of ultra low power, small form factor cameras,
particularly camera phones. By using primary-side voltage
sensing, the need for a secondary-side resistive voltage divider
is eliminated. This has the additional benefit of reducing leakage
currents on the secondary side of the transformer. To extend
battery life, the A8732 features very low supply current draw
(0.5 μA max in shutdown mode). The switch current limit can
be programmed from 0.45 to 1.5 A, in 16 steps with single wire
interface, through the CHARGE pin.
The IGBT driver also has internal gate resistors for minimum
external component count. The charge and trigger voltage
logic thresholds are set at 1 V
implementing low-voltage control logic.
The A8732 is available in an 8-contact 2 mm × 2 mm
DFN/MLP package with a 0.60 maximum overall package
height, and an exposed pad for enhanced thermal performance.
It is lead (Pb) free with 100% matte tin leadframe plating.
VIN_VDRV
C2
CHARGE
TRIG
®
A8732 is a Xenon photoflash charger IC designed
V IN_VDRV
VBAT
Battery Input
1.5 to 5.5 V
Control
IGBT Driver
Block
GND
DONE
(B)
VOUT Detect
HI
+
(min) to support applications
I
SW
sense
C1
GATE
SW
DONE
IGBT Gate
A8732
100F
C
315 V
VPULLUP
OUT
100 kΩ

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a8732 Summary of contents

Page 1

... The charge and trigger voltage logic thresholds are set implementing low-voltage control logic. The A8732 is available in an 8-contact 2 mm × DFN/MLP package with a 0.60 maximum overall package height, and an exposed pad for enhanced thermal performance lead (Pb) free with 100% matte tin leadframe plating. ...

Page 2

... A8732 Selection Guide Part Number Packing A8732EEETR-T 3000 pieces per reel Absolute Maximum Ratings Characteristic Symbol V SW Pin VIN_DRV, VBAT Pins CHARGE, TRIG, ¯ D ¯ ¯ O ¯ ¯ N ¯ ¯ E ¯ Pins Remaining Pins Operating Ambient Temperature Maximum Junction T J Storage Temperature ...

Page 3

... A8732 VBAT V – BAT ILIM Reference V ref DS VIN_DRV Decoder CHARGE TRIG Pin-out Diagram DONE 1 8 CHARGE TRIG 2 7 VIN_DRV PAD GATE 3 6 VBAT GND (Top View) Ultra Small Mobile Phone Xenon Photoflash Capacitor Charger with IGBT Driver Functional Block Diagram ...

Page 4

... A8732 ELECTRICAL CHARACTERISTICS guaranteed from −40°C to 85°C ambient, unless otherwise noted Characteristics VBAT Voltage Range VIN_DRV Voltage Range UVLO Enable Threshold UVLO Hysteresis V Supply Current IN VBAT Pin Supply Current Current Limit Primary-Side Current Limit Switch Current Limit (ILIM Programming Input on CHARGE Pin) Continued on the next page… ...

Page 5

... A8732 ELECTRICAL CHARACTERISTICS specifications guaranteed from −40°C to 85°C ambient, unless otherwise noted Switch On-Resistance Switch Leakage Current CHARGE Pull-down Resistance CHARGE Input Voltage Charge Pin Programming ILIM Programming High at CHARGE Pin ILIM Programming Low at CHARGE Pin Total ILIM Setup Time at CHARGE Pin ...

Page 6

... A8732 VBAT UVLO V IN CHARGE SW Target V V OUT DONE TRIG GATE Explanation of Events A: Start charging by pulling CHARGE to high, provided that V B: Charging stops when V 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 V F: After V start the charging ...

Page 7

... A8732 IGBT drive waveforms are measured at pin, with capacitive load of 6800 pF Rising Signal Symbol Parameter Units/Division TRIGGER GATE time 100 ns Conditions Parameter Value 320 6.8 nF LOAD Falling Signal Symbol Parameter Units/Division ...

Page 8

... A8732 Charge Time versus Battery Voltage at Various ILIM Transformer L = 12.8 μH, N =10.25, V PRIMARY 1.5 Efficiency versus Battery Voltage at Various ILIM Transformer L 86% 84% 82% 80% 78% 76% 74% 72% 70% 68% 66% 64% 62% 60% 58% 56% 54% 1.5 Ultra Small Mobile Phone Xenon Photoflash Capacitor Charger with IGBT Driver Characteristic Performance =3 ...

Page 9

... A8732 Final Output Voltage versus Battery Voltage at Various ILIM Transformer L 328 327 326 325 324 323 322 321 320 1.5 2.0 Note: Output voltage is sensed from the primary side winding when the switch turns off. This duration long enough (>200 ns) in order to obtain an accurate measurement. The value of t ...

Page 10

... A8732 Average Input Current versus Battery Voltage at Various ILIM Transformer L 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 1.5 Note: Peak switch current is limited by the maximum on-time and di/dt of the transformer primary current; therefore, average input current drops at very low battery voltage. Ultra Small Mobile Phone Xenon Photoflash Capacitor Charger with IGBT Driver = 12.8 μ ...

Page 11

... A8732 Output Capacitor Charging at Various Peak Current Limits Test conditions 3 3 BAT Oscilloscope settings: Ch1 = ¯ D ¯ ¯ O ¯ ¯ N ¯ ¯ E ¯ div), Ch2 = Output Voltage ( div), Ch3 = Input Current (100 mA / div), Time scale = 1 sec / div ILIM1 (1 ...

Page 12

... A8732 Output Capacitor Charging at Various Battery Voltages Test conditions 3.0 V, ILIM3 (1.36 A Oscilloscope settings: Ch1 = ¯ D ¯ ¯ O ¯ ¯ N ¯ ¯ E ¯ div), Ch2 = Battery Voltage ( div), Ch3 = Output Voltage ( div), Ch4 = Input Current (100 div), ...

Page 13

... Ultra Small Mobile Phone Xenon Photoflash Capacitor Charger with IGBT Driver Functional Description Timer Mode and Fast Charging Mode The A8732 achieves fast charging times and high efficiency by operating in discontinuous conduction mode (DCM) through level UVLO most of the charging process. The relationship of Timer mode and Fast Charging mode is shown in figure 2 ...

Page 14

... A8732 As soon as a sufficient voltage has built up at the output capaci- tor, the IC enters Fast-Charging mode. In this mode, the next switching cycle starts after the secondary side current has stopped flowing, and the switch voltage has dropped to a minimum value. A proprietary circuit is used to allow minimum-voltage switch- ing, even if the SW pin voltage does not drop ...

Page 15

... CHARGE pin. An internal digital circuit decodes the input clock signals, which sets the switch current limit. This flexible scheme allows the user to operate the A8732 at required current limits. The battery life can be effectively extended by setting a lower cur- rent limit at low battery voltages. Figure 6 shows the ILIM clock timing scheme protocol ...

Page 16

... A8732 Transformer Design 1. The transformer turns ratio, N, determines the output voltage 31.5 × N – OUT d where 31.5 is the typical value of V OUTTRIP ward drop of the output diode. 2. The primary inductance determines the on-time of PRIMARY the switch: = (– × – I ...

Page 17

... Figure 11. Input current waveforms with Li+ battery connected through . BAT 4.7 μH inductor and 4.7 μF capacitor, C Ch1 calculated as: OUT DPeak s/div / A8732 C3 C1 Figure 12. Input current waveforms with Li+ battery connected through , may IN 4.7 μH inductor and 10 μF capacitor, C Ch1: V OUT s/div Effects of Input Filters = 100 μ ...

Page 18

... A8732 Layout Guidelines Key to a good layout for the photoflash capacitor charger circuit is to keep the parasitics minimized on the power switch loop (transformer primary side) and the rectifier loop (secondary side). Use short, thick traces for connections to the transformer primary and SW pin important that the ¯ D ¯ ¯ ¯ O ¯ ¯¯ N ¯ ¯ E ¯ signal trace and other signal traces be routed away from the transformer and other switching traces, in order to minimize noise pickup ...

Page 19

... A8732 Recommended layout: C4 Schematic 0.1uF DONE CHARGE Top side Bottom side Top components Ultra Small Mobile Phone Xenon Photoflash Capacitor Charger with IGBT Driver VBAT C2 10uF R10 6 5 A8732 2k VBAT VIN_DRV GATE 1 2 DONE TRIG 8 4 CHARGE GND C5 1nF U1 TRIGGER ...

Page 20

... A8732 Package EE 8-Contact DFN/MLP with Exposed Thermal Pad D 9X 0.08 C 0.25 ±0.05 0.325 ±0.050 Copyright ©2008-2010, Allegro MicroSystems, Inc. The products described here are manufactured under one or more U.S. patents or U.S. patents pending. Allegro MicroSystems, Inc. reserves the right to make, from time to time, such de par tures from the detail spec tions as may be required to per- mit improvements in the per for mance, reliability, or manufacturability of its products ...

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