A8437 View Datasheet(PDF) - Allegro MicroSystems
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Description
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A8437 Datasheet PDF : 22 Pages
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A8437
Mobile Phone Xenon Photoflash Capacitor Charger
with IGBT Driver
Charge Time versus Battery Voltage
Transformer Lp= 8 μH, N = 10.2; COUT= 20 μF / 330 V UCC; TA=25°
3.5
RSET
IP
(kΩ)
(A)
3.0
55
≈ 0.65
45
≈ 0.8
2.5
39
≈ 0.9
33.2
≈ 1.0
26.7
≈ 1.2
2.0
1.5
1.0
0.5
0
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
VBAT (V)
COUT= 20 μF. For larger or smaller capacitances, charging time
scales proportionally.
71
70
69
68
67
66
65
64
63
62
61
60
59
58
57
56
55
2.0
Efficiency versus Battery Voltage
Transformer Lp= 8 μH, N = 10.2; COUT= 20 μF / 330 V UCC; TA=25°
RSET
(kΩ)
55
45
39
33.2
26.7
IP
(A)
≈ 0.65
≈ 0.8
≈ 0.9
≈ 1.0
≈ 1.2
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
VBAT (V)
Special low-profile transformer with relatively low inductance
(Lp= 8 μH) and high winding resistance (Rp = 0.37 Ω). Higher efficien-
cy can be achieved by using transformers with higher Lp, which reduces
switching frequency and therefore switching loses, and lower resistance,
which reduces conduction losses.
Average Input Current versus Battery Voltage
0.55
XFM Lp= 8 μH, N = 10.2, COUT= 20 μF 330 V UCC, TA=25°
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
VBAT (V)
RSET
(kΩ)
26.7
33.2
39
45
55
IP
(A)
≈ 1.2
≈ 1.0
≈ 0.9
≈ 0.8
≈ 0.65
An increase in ISWlim with respect to VBAT actually keeps the average input current
roughly constant throughout the battery voltage range. Normally, if ISWlim is kept
constant, the average current will drop as VBAT goes higher.
Allegro MicroSystems, Inc.
8
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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