LT3585EDDB-3#TRPBF Linear Technology, LT3585EDDB-3#TRPBF Datasheet - Page 18

• Manufacturer Part Number: LT3585EDDB-3#TRPBF
• Description: IC CHARGER PHOTOFLASH 10-DFN
• Manufacturer: Linear Technology

Specifications of LT3585EDDB-3#TRPBF

• Applications: Photoflash Capacitor Charger, Xenon
• Current - Supply: 5mA
• Voltage - Supply: 1.5 V ~ 16 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-DFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LT3585-0/LT3585-1
LT3585-2/LT3585-3
TYPICAL APPLICATIO S
18
The LT3585 series can be auto-refreshed using the addi-
tional circuitry shown in Figure 15 with its basic operation
shown in Figure 16. The ENABLE pin is used to enable
or disable the auto-refresh charging mode. Without an
auto-refresh circuit, the output voltage will droop due to
output capacitor and output diode leakage currents. The
circuit in Figure 15 uses the DONE and CHRG/IADJ pins
to form an open-loop control scheme. The output voltage
target is sensed through the DONE pin with the PFET of
U1, Panasonic UP04979 composite transistor. When the
CHRG/IADJ
CHRG/IADJ
100V/DIV
ENABLE < 0.3V
ENABLE
ENABLE
2V/DIV
2V/DIV
V
OUT
TO
LT3585-1
C
Figure 16. Auto Refresh Basic Operation
OUT
Figure 15. Auto Refresh Application
= 50µF
U1: PANASONIC UP04979 COMPOSITE TRANSISTORS
ENABLE > 1.1V
NORMAL OP.
6
1
R1
5k
1/10W
0402
2
R
100k
2sec/DIV
U1
REFRESH
T
AUTO
4
3
C
0.1 F
ENABLE
U
<0.3V
T
5
ENABLE
>1.1V
REFRESH
AUTO
R3
100k
1/10W
0402
ENABLE < 0.3V
3585 F16
3585 F15
V
TO
DONE
IN
DONE pin goes low during the V
PFET charges the auto-refresh timing node comprised
of R
through a NFET and disables the LT3585 series part. The
DONE pin immediately goes high in shutdown, releasing
the timing node and allowing the voltage at Pins 2 and 3
to decay. After approximately a R
CHRG/IADJ pin is released and the LT3585 series part is
enabled. This cycle is repeated to maintain a constant DC
output voltage. The open-loop control method places a
constraint on the control loop dominant time constant,
R
where I
former peak primary current, and L
primary inductance. If this condition is not met, a runaway
condition could occur. The LT3585 series part would
continue to charge the output voltage past the internal
output trip voltage. Figure 17 shows the AC ripple of a
typical auto-refresh circuit with the proper selection of
R
T
T
CHRG/IADJ
R C
• C
and C
AC RIPPLE
T
T T
2V/DIV
2V/DIV
and C
T
, given by:
V
Figure 17. V
LK
OUT
T
>
.
is the known leakage current, I
LT3585-1
C
2
OUT
T
, and in turn, pulls the CHRG/IADJ pin low
I
•
LK
= 50µF
I
PK
•
2
OUT
V
•
BAT
L
AC Ripple in Auto Refresh Mode
PRI
200ms/DIV
OUT
T
C
PRI
T
trip condition, the
time constant, the
is the transformer
PK
3585 F17
is the trans-
3585f