A8732 Просмотр технического описания (PDF) - Allegro MicroSystems

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A8732

Ultra Small Mobile Phone Xenon Photoflash Capacitor Charger with IGBT Driver

Allegro MicroSystems 

A8732

Ultra Small Mobile Phone Xenon Photoflash

Capacitor Charger with IGBT Driver

ILIM Programming

The peak current limit can be programmed to sixteen differ-

ent levels, from 100% to 29%, with programming through the

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. The total ILIM setup time, tILIM(SU) ,

denotes the time needed for the decoder circuit to receive ILIM

inputs and set ISWLIM , and has a typical duration of 200 μs.

Figure 7 shows the timing definition of the primary current

limiting circuit. At the end of the setup period, tILIM(SU) , primary

current starts to ramp up to the set ISWLIM . The ISWLIM setting

remains in effect as long as the CHARGE pin is high. To reset the

ILIM decoder, pull the CHARGE pin low before clocking-in the

new setting.

After the first start-up or an ILIM decoder reset, each new current

limit can be set by sending a burst of pulses to the CHARGE

pin. The first rising edge starts the ILIM decoder, and up to 16

rising edges will be counted to set the ISWLIM level. The first

pulse width, tILIM1(H), must be at least 15 μs long. Subsequent

pulses (up to 15 more) can be as short as 0.2 μs. The last low-

to-high edge must arrive within 200 μs from the first edge. The

CHARGE pin will stay high afterwards.

(0 to 15)

Figure 6. ILIM programming timing definition

Figure 7. Current limit timing example (ISWLIM4 selected)

Allegro MicroSystems, Inc.

15

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

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