a8739 Allegro MicroSystems, Inc., a8739 Datasheet - Page 15

• Manufacturer Part Number: a8739
• Description: Ultra-small Mobile Adjustable Xenon Photoflash Capacitor Charger With Igbt Driver
• Manufacturer: Allegro MicroSystems, Inc.

A8739
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 A8739 at required current
limits. The battery life can be effectively extended by setting a
lower current limit at low battery voltages. Figure 6 shows the
ILIM clock timing scheme protocol. The total ILIM setup time,
t
receive ILIM inputs and set I
200 μs.
Figure 7 shows the timing definition of the primary current
Figure 6. ILIM programming timing definition
ILIM(SU)
, denotes the time needed for the decoder circuit to
SWLIM
(0 to 15)
Ultra-Small Mobile Adjustable Xenon Photoflash
, and has a typical duration of
Capacitor Charger with IGBT Driver
limiting circuit. At the end of the setup period, t
current starts to ramp up to the set I
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, t
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.
Figure 7. Current limit timing example (I
ILIM1(H)
, must be at least 15 μs long. Subsequent
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Worcester, Massachusetts 01615-0036 U.S.A.
SWLIM4
SWLIM
selected)
. The I
ILIM(SU)
SWLIM
setting
, primary
15