A8739EEETR-T Allegro Microsystems Inc, A8739EEETR-T Datasheet - Page 16

• 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
Output Voltage Adjustment
The target output voltage of the A8739 is primarily determined
by the transformer turns ratio, N:
Typically N = 10, so the output voltage is approximately 315 V.
This output voltage can be further programmed in 5 V decre-
ments down to 295 V, by using an external resistor at the VBAT
pin. This enables fine-tuning to achieve better accuracy, and pro-
vides greater flexibility in the selection of transformers. Refer to
Figure 8. Adjustment of V
(V
OUT
2.3 to 5.5 V
Bias Input
= 30.5 × N).
VIN_VDRV
C2
CHARGE
100 pF
TRIG
C3
A8739
V
P
= Power Supply
2.0 to 5.5 V
V
OUT
VBAT
R
2.32 kΩ
V IN_VDRV
OUT
BAT
Control
Block
IGBT Driver
GND
using a series resistor at the VBAT pin
V
= 31.5 (V) × N
SW
DONE
I
SW
Ultra-Small Mobile Adjustable Xenon Photoflash
C1
sense
SW
DONE
GATE
(N = 9 -11)
IGBT Gate
1 : N
VPULLUP
100 kΩ
COUT
100F
330 V
Capacitor Charger with IGBT Driver
figure 8 for example: An external resistor R
to set the target output voltage at two steps lower, or 305 V when
the transformer turns ratio = 10. Capacitor C3 is needed in case
excessive switching noises is coupled into the VBAT pin, which
may affect accuracy of target voltage.
The relationship of output voltage and VBAT resistance is shown
in figure 9. To ensure proper voltage selection, use only
1% resistors. If C3 is used, make sure the RC filter time constant
(R
BAT
Figure 9. Relationship of V
Resistance,
0.65 to 1.03
2.15 to 2.49
4.58 to 5.08
8.68 to 9.76
× C3) is less than 1 μs approximately.
320
315
310
305
300
295
290
0 to 0.10
R
(kΩ)
BAT
0
1
Output Voltage versus VBAT Resistance
Output Voltage,
2
31.5 × N
31.0 × N
30.5 × N
30.0 × N
29.5 × N
Transformer turns ratio N = 10
V
(V)
OUT
3
OUT
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
Resistance (kΩ)
and a series resistor at the VBAT pin
4
Recommended 1%
5
Resistor Values
0.
0.845
2.32
4.87
9.09
(kΩ)
6
BAT
7
= 2.32 kΩ is used
8
C3 capacitance
Recommended
Optional
9
(pF)
100
100
100
47
10
16