A8739EEETR-T Allegro Microsystems Inc, A8739EEETR-T Datasheet - Page 18

• Manufacturer Part Number: A8739EEETR-T
• Description: Photoflash Capacitor Charger
• Manufacturer: Allegro Microsystems Inc
• Type: Flash/Torchr

Specifications of A8739EEETR-T

• Number Of Outputs: *
• Internal Driver: No
• Type - Primary: Flash/Torch
• Voltage - Supply: *
• Mounting Type: Surface Mount
• Package / Case: 8-UFDFN Exposed Pad
• Operating Temperature: *
• Voltage - Output: *
• Frequency: *
• Current - Output / Channel: *
• Internal Switch(s): Yes
• Efficiency: 75%
• Topology: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 620-1365-2

A8739
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 11.
The resonant period is given by:
The effects of input filter components are shown in figures 12,
13, and 14. It is recommended to use at least 10 μF / 6.3 V to
decouple the battery input, VBAT , at the primary of the trans-
former. 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 11. 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
Ultra-Small Mobile Adjustable Xenon Photoflash
. During initial Timer mode
IN
)
1/2
DPeak
/ N .
BAT
.
.
A8739
, is calculated as:
IN
Capacitor Charger with IGBT Driver
, may
Figure 12. Input current waveforms with Li+ battery connected by
5-in. wire and decoupled by 4.7 μF capacitor, C
V
Ch3: I
Figure 13. 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 14. 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
= 500 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,
= 200 mA/div,
= 200 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,
18