A8439 Просмотр технического описания (PDF) - Allegro MicroSystems
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A8439 Datasheet PDF : 14 Pages
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A8439
Photoflash Capacitor Charger with IGBT Driver and Refresh
decoder circuit to receive ILIM inputs and set ISWLIM , and has a
minimum duration of 54 μs.
Figure 5 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 ISWIM. The ISWLIM setting
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 first start-up or an ILIM counter 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 counter, and up to 8 rising
edges will be counted to set the ISWLIM level. The first pulse
width, tILIM1(H), must be at least 20 μs long. Subsequent pulses
(up to 7 more) can be as short as 0.2 μs. The last low-to-high
edge must arrive within 54 μs from the first edge. The CHARGE
pin will stay high afterwards. The four panels of figure 6 show
examples of the pulse streams and the resulting current levels.
Clock input at
CHARGE pin
t ILIM(L) 0.2 μs
t ILIM1(H) = min.
first pulse width
t ILIM(H) 0.2 μs
t ILIM(SU) = maximum
ILIM setup time
First rising
edge
Subsequent rising
edges (0 to 7)
Switching
starts
0 μs
20 μs
54 μs
Figure 4. ILIM Clock Timing Definition
(A) 1.4 A
(B) 1.2 A
(C) 1.0 A
Start ILIM counter
Reset ILIM counter
CHARGE
Four rising edges
within tILIM(SU)
ISWLIM4 = 0.86 A
ISW
0 μs 20 μs
Switching
starts
54 μs
Switching
stops
(D) 0.86 A
Figure 5. Current Limit Programming Example (ISWLIM4 selected).
Figure 6. ILIM programming waveforms for ISWLIM = 1.4 A, 1.2 A, 1.0 A,
and 0.86 A.
Allegro MicroSystems, Inc.
10
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
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