A8837EEJTR-T Allegro Microsystems Inc, A8837EEJTR-T Datasheet

A8837EEJTR-T

Manufacturer Part Number

A8837EEJTR-T

Description

IC IGBT DRIVER PHOTOFLASH 10-MLP

Manufacturer

Allegro Microsystems Inc

Datasheet

1.A8837EEJTR-T.pdf (11 pages)

Specifications of A8837EEJTR-T

Applications

Photoflash Capacitor Charger

Current - Supply

1.5mA

Voltage - Supply

3 V ~ 5.5 V

Operating Temperature

-40°C ~ 85°C

Mounting Type

Surface Mount

Package / Case

10-WFDFN Exposed Pad

Lead Free Status / RoHS Status

Lead free / RoHS Compliant

Other names

620-1248-2

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Features and Benefits

▪ Power with 1 Li+ or 2 Alkaline/NiMH/NiCAD batteries

▪ Eight-level, digitally-programmable current limits from

▪ Voltage sensing feedback before output diode for low

▪ Adjustable output voltage

▪ No primary-side Schottky diode needed

▪ Integrated IGBT driver with trigger

▪ Charge complete indication

▪ >75% efficiency

▪ Low-profile (0.75 mm high) 3 mm × 3 mm MLP/TDFN

Package: 10-contact TDFN/MLP (suffix EJ)

Figure 1. Typical circuit with separate power supply to transformer

A8837-DS

BIAS

700 mA to 2 A

leakage

10-contact package

100 k

3.0 to 5.5 V

Approximate Scale

10 k

CHARGE

DONE

TRIGGER

VIN

Photoflash Capacitor Charger with IGBT Driver

A8837

GND

0.1 μF

BATT

IGBTDRV

1.5 to 5.5 V

To IGBT Gate

N =10.2

150 k

1.20 k

C1, C2:

X5R or X7R, 10 V

Typical Applications

COUT

100 μF

330 V

OUT

Description

The A8837 is a highly integrated IC that charges photoflash

capacitors for digital and film cameras. An integrated MOSFET

switch drives the transformer in a flyback topology. It also

features an integrated IGBT driver that facilitates the flash

discharge function and saves board space.

The CHARGE pin enables the A8837 and starts the charging

of the output capacitor. When the designated output voltage is

reached, the A8837 stops the charging until the CHARGE pin

is toggled again. The ¯ D ¯ ¯ ¯ O ¯ ¯¯ N ¯ ¯ E ¯ pin is an open-drain indicator of

when the designated output voltage is reached.

The peak current limit can be adjusted to eight different levels

between 700 mA and 2 A, by clocking the CHARGE pin.

This allows the user to operate the flash even at low battery

voltages.

The A8837 can be used with two Alkaline/NiMH/NiCAD or one

single-cell Li+ battery connected to the transformer primary.

Connect the VIN pin to a 3.0 to 5.5 V supply, which can be

either the system rail or the Li+ battery, if used.

The A8837 is available in a very low profile (0.75 mm)

10-contact 3 mm × 3 mm MLP/TDFN package, making it

ideal for space-constrained applications. It is lead (Pb) free,

with 100% matte-tin leadframe plating.

Applications include the following:

Figure 2. Typical circuit with single power supply

▪ Digital camera flash

▪ Film camera flash

BIAS

100 k

3.0 to 5.5 V

10 k

CHARGE

TRIGGER

DONE

VIN

A8837

GND

0.1 μF

IGBTDRV

▪ Cell phone flash

▪ Emergency strobe light

4.7 μF

To IGBT Gate

A8837

150 k

1.20 k

COUT

OUT

Related parts for A8837EEJTR-T

A8837EEJTR-T Summary of contents

Page 1

Photoflash Capacitor Charger with IGBT Driver Features and Benefits ▪ Power with 1 Li Alkaline/NiMH/NiCAD batteries ▪ Eight-level, digitally-programmable current limits from 700 ▪ Voltage sensing feedback before output diode for low leakage ▪ ...

Page 2

... A8837 Selection Guide Part Number A8837EEJTR-T *Contact Allegro for additional packing options Absolute Maximum Ratings Characteristic SW pin IGBTDRV pin FB pin All other pins Operating Ambient Temperature Maximum Junction Temperature Storage Temperature Package Thermal Characteristics Characteristic Package Thermal Resistance *Additional information is available on the Allegro website. ...

Page 3

A8837 VIN CHARGE I Decoder LIM DONE V IN TRIGGER IGBTDRV Device Pin-out Diagram IGBTDRV DONE VIN 3 GND 4 7 TRIGGER CHARGE Photoflash Capacitor Charger with IGBT Driver ...

Page 4

A8837 ELECTRICAL CHARACTERISTICS Characteristics Supply Voltage* Supply Current Primary Side Current Limit (ILIM clock input at CHARGE pin Resistance SW Leakage Current* SW Maximum Off-Time SW Maximum On-Time CHARGE Input Current CHARGE Input Voltage* ILIM Clock High Time ...

Page 5

A8837 V UVLO VIN CHARGE SW Target V OUT V OUT DONE TRIGGER IGBTDRV A Explanation of Events: A. Start charging by pulling CHARGE to high, provided that V B. Charging stops when V completion of the charging process. C. ...

Page 6

A8837 IGBT Drive waveforms are measured with R-C load (12 Ω, 6800 pF) Rising Signal Symbol Parameter Units/Division C2 V IGBTDRV C3 V TRIGGER t time 50 ns Conditions Parameter Value t 22.881 63.125 ...

Page 7

A8837 Overview The A8837 is a photoflash capacitor charger control IC with adjustable input current limiting. It also integrates an IGBT driver for strobe operation of the flash tube, dramatically saving board space in comparison to discrete solutions for strobe ...

Page 8

A8837 current starts to ramp up to the set I SWLIM remains in effect as long as the CHARGE pin is high. To reset the ILIM counter, pull the CHARGE pin low before clocking in the new setting. After the ...

Page 9

A8837 Transformer Design The minimum transformer turns ratio, N, (Second- Turns Ratio. ary : Primary) should be chosen based on the following formula Drop OUT BATT where: (V) is the required output voltage ...

Page 10

A8837 Leakage Inductance and Secondary Capacitance. former design should minimize the leakage inductance to ensure the turn-off voltage spike at the SW node does not exceed the 40 V limit. An achievable minimum leakage inductance for this applica- tion, however, ...

Page 11

A8837 3.00 ±0. 11X 0.08 C +0.05 0.25 –0. 0.40 ±0.10 10 Copyright ©2008, Allegro MicroSystems, Inc. The products described here are manufactured under one or more U.S. patents or U.S. patents pending. ...

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