A8740EEETR-T Allegro Microsystems Inc, A8740EEETR-T Datasheet - Page 11

• Manufacturer Part Number: A8740EEETR-T
• Description: Photoflash Capacitor Charger
• Manufacturer: Allegro Microsystems Inc
• Series: -r

Specifications of A8740EEETR-T

• Constant Current: -
• Constant Voltage: -
• Topology: Flyback
• Number Of Outputs: 1
• Internal Driver: No
• Type - Primary: Flash/Torch
• Type - Secondary: -
• Frequency: -
• Voltage - Supply: 1.5 V ~ 5.5 V
• Voltage - Output: -
• Mounting Type: *
• Package / Case: *
• Operating Temperature: -40°C ~ 85°C
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

A8740
As soon as a sufficient voltage has built up at the output capaci-
tor, the IC enters Fast-Charging mode. In this mode, the next
switching cycle starts after the secondary side current has stopped
flowing, and the switch voltage has dropped to a minimum value.
A proprietary circuit is used to allow minimum-voltage switch-
ing, even if the SW pin voltage does not drop to 0 V. This enables
C2,C3
Figure 4. Minimum-voltage switching: V
Ch1: V
Ch4: I
C4
C1
SW
OUT
= 750 mA / div., t = 1 μs / div.
= 20 V / div., Ch2: V
BAT
= 5 V / div., Ch3: V
OUT
≥ 35 V, V
SW
BAT
Ultra Small Mobile Phone Xenon Photoflash
= 5 V / div.,
= 5.5 V,
V
V
V
I
SW
OUT
Capacitor Charger with IGBT Driver
SW
BAT
Fast-Charging mode to start earlier, thereby reducing the overall
charging time. Minimum-voltage switching is shown in figure 4.
During Fast-Charging mode, when V
50 V), true zero-voltage switching (ZVS) is achieved. This
further improves efficiency as well as reduces switching noise. A
ZVS interval is shown in figure 5.
Figure 5. True zero-voltage switching (ZVS): V
Ch1: V
Ch4: I
C2,C3
C4
C1
SW
OUT
= 750 mA / div., t = 0.5 μs / div.
= 20 V / div., Ch2: V
BAT
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
= 5 V / div., Ch3: V
OUT
OUT
is high enough (over
= 75 V, V
SW
= 5 V / div.,
BAT
= 5.5 V,
V
V
V
I
SW
OUT
SW
BAT
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