LT3420EMS-1#TRPBF Linear Technology, LT3420EMS-1#TRPBF Datasheet - Page 14

• Manufacturer Part Number: LT3420EMS-1#TRPBF
• Description: IC PHOTOFLASH CAP CHARGER 10MSOP
• Manufacturer: Linear Technology

Specifications of LT3420EMS-1#TRPBF

• Applications: Photoflash Capacitor Charger
• Current - Supply: 90µA
• Voltage - Supply: 2.2 V ~ 16 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LT3420/LT3420-1
APPLICATIO S I FOR ATIO
risk of drawing too much current from the battery. The
input current to the LT3420/LT3420-1 circuit can be
adjusted by driving the CHARGE pin with a PWM (pulse
width modulation) signal. The microprocessor can adjust
the duty cycle of the PWM signal to achieve the desired
level of input current. Many schemes exist to achieve this
function. Once the target output voltage is reached, the
PWM signal should be halted to avoid overcharging the
photoflash capacitor, since the signal at the CHARGE pin
overrides the refresh timer.
A simple method to achieve adjustable input current is
shown in Figure 9. The PWM signal has a frequency of
14
U
U
W
Figure 9. Simple Logic for Adjustable Input Current
Figure 10. Input Current as Duty Cycle is Varied
1kHz PWM
SIGNAL
800
600
400
200
0
10
ON
U
30
LT3420
DUTY CYCLE (%)
A2
50
LT3420-1
1kHz. When ON is logic high, the circuit is enabled and the
CHARGE pin is driven by the PWM signal. When the target
output voltage is reached, DONE goes high while CHARGE
is also high. The output of A1 goes high, which forces
CHARGE high regardless of the PWM signal. The part is
now in the Refresh mode. Once the refresh period is over,
the DONE pin goes low, allowing the PWM signal to drive
the CHARGE pin once again. This function can be easily
implemented in a microcontroller. Figure 10 shows the
input current for the LT3420 and LT3420-1 as the duty
cycle of the PWM signal is varied.
A3
A1
70
3420 F10
90
DONE
CHARGE
TO
LT3420
CIRCUIT
3420 F09
3420fb