A8740EEETR-T Allegro Microsystems Inc, A8740EEETR-T Datasheet - Page 13

• 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
Input Capacitor Selection
Ceramic capacitors with X5R or X7R dielectrics are recom-
mended for the input capacitor, C
the device operates with 18 μs off-time. The resonant period
caused by input filter inductor and capacitor should be at least
2 times greater or smaller than the 18 μs Timer period, to reduce
input ripple current during this period. The typical input LC filter
is shown in figure 7.
The resonant period is given by:
The effects of input filter components are shown in figures 8, 9,
and 10. It is recommended to use at least 10 μF / 6.3 V to decou-
ple the battery input, VBAT , at the primary of the transformer.
Decouple the VIN pin using 0.1 μF / 6.3 V bypass
capacitor.
Output Diode Selection
Choose rectifying diodes, D1, to have small parasitic capacitance
(short reverse recovery time) while satisfying the reverse voltage
and forward current requirements. The peak reverse voltage of
the diodes, V
closed. It can be calculated as:
The peak current of the rectifying diode, I
Figure 7. Typical input section with input inductance (inductance, L
be an input filter inductor or inductance due to long wires in test setup)
+
DPeak
V BAT
, occurs when the internal MOSFET switch is
V
I
DPeak
DPeak
T
res
L IN
= 2 (L × C
= I
= V
PRIMARY_Peak
OUT
C IN
IN
+ N × V
. During initial Timer mode
IN
)
1/2
DPeak
/ N .
BAT
.
.
A8740
, is calculated as:
Ultra Small Mobile Phone Xenon Photoflash
IN
, may
Capacitor Charger with IGBT Driver
Figure 8. Input current waveforms with Li+ battery connected by
5-in. wire and decoupled by 4.7 μF capacitor, C
V
Ch3: I
Figure 9. Input current waveforms with Li+ battery connected through
4.7 μH inductor and 4.7 μF capacitor, C
Ch1: V
t = 1 s/div
Figure 10. Input current waveforms with Li+ battery connected through
4.7 μH inductor and 10 μF capacitor, C
Ch1: V
t = 1 s/div
IN
= V
C2
C3
C1
C2
C3
C1
C1
C2
C3
BAT
OUT
OUT
BAT
= 750 mA/div, t = 1 s/div
= 3.6 V, Ch1: V
= 50 V/div, Ch2: V
= 50 V/div, Ch2: V
Effects of Input Filters
OUT
BAT
BAT
= 50 V/div, Ch2: V
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
= 2 V/div, Ch3: I
= 2 V/div, Ch3: I
OUT
OUT
= 100 μF, V
= 100 μF, V
OUT
BAT
BAT
BAT
= 100 μF,
= 2 V/div,
= 300 mA/div,
= 300 mA/div,
IN
IN
= V
= V
BAT
BAT
V
V
V
V
V
V
I
I
OUT
OUT
I
OUT
BAT
BAT
BAT
BAT
BAT
BAT
= 3.6 V,
= 3.6 V,
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