QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1409
4
CHANGING THE OUTPUT VOLTAGE
To set the output voltage lower than 12V or 24V, change the bottom voltage divider resistors con-
nected to LTC3788 FB pin (see the schematic on page 6).
To get higher than 12V and 24V output voltages MOSFETs and capacitors with higher voltage rat-
ings may be required. Please contact LTC factory for details.
Note that the output voltage will start following the input voltage when input voltage is greater than
the voltage set by the voltage divider. In this mode (wire mode) the output rectifier MOSFET is
turned continuously ON. The only losses in this mode are due to the current sense resistors, induc-
tor and output MOSFET DC resistance.
CONVERTER EFFICIENCY AND OUTPUT CURRENT
The DC1409 output current capability depends on the input voltage and proper cooling. Typical per-
formance of DC1409A is shown in Figure 3. As can be seen from Figure 3, the output current ca-
pability depends on the input voltage. Also, when input voltage is equal or higher than the output
voltge setting (wire mode) the efficiency is very high (99%) since the converter is not really running
and the output MOSFET is shorting Vin to Vout (blue trace in Figure 3).
LTC3788 Efficiency 12V and 24V output
89%
91%
93%
95%
97%
99%
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Iout [A]
E
ff
ic
ie
n
c
y
5V in, 24V out
12V in, 24V out
5V in, 12V out
12V in, 12V out
Figure 3. DC1409A Efficiency
