21-Aug-14
DCDC
+
-
+
-
+Vout
- Vout
C2 C3
C1
L1
LDU
Input Filter to meet Class B Conducted Emissions
+
Vout
- Vout
C
ontrol
LDU
-
Vin
LDU
+Vout
- Vout
-Vin
GND
PWM
0V
1.25V
Control
LDU0848
By connecting a variable resistor between control
and GND, simple dimming can be achieved.
C
apacitor is optional for HF noise rejection.
R
ecommended value is 0.22 µF.
The output current can be determined using the equation:
W
here the value of R is between 0 and 2 MΩ, the
maximum adjustment range of output current is 25% to 90%
(For Vin-Vout, LDU08 & 24: <20 VDC, LDU48: <30 VDC )
Output Current Adjustment by Variable Resistor
Output Current Adjustment by DC Voltage
Output Current Adjustment by PWM
Directly driving control input
A Pulse Width Modulated (
PWM) signal with duty cycle
D
PWM can be applied to the control pin, as shown:
Application Notes
LDU
Control
+Vout
-Vout
+
-
Vin
The output current is given by:
Control Voltage Range: 0.3 V to 1.25 VDC
Iout = Iout nom x Control
Iout = Iout nom x Dpwm (Dpwm = PWM duty cycle)
LDU08 LDU24 LDU48
C1
10 µF 10 µF 4.7 µF
C2
Not Fitted Not Fitted 4.7 µF
C3
47 µF 47 µF Not Fitted
L1
68 µH 68 µH 47 µH
I
out =
Iout nom x R
(R + 200 k)
I
out =
F
or LDU48For LDU08-24
Iout nom x R
(R + 50 k)
1.25
