3
dc2328af
DEMO MANUAL DC2328A
Quick start proceDure
Figure 3. Efficiency vs Load Current (V
OUT
= –24V)
Figure 4. Efficiency vs Load Current (V
OUT
= –12V)
LOAD CURRENT (A)
EFFICIENCY (%)
DC2328A F03
55.0
60.0
65.0
70.0
75.0
80.0
85.0
90.0
95.0
0.0
2.5
2.0
1.5
1.0
0.5
12V
IN
24V
IN
34V
IN
LOAD CURRENT (A)
0
0.5
1
1.5
2
2.5
3
3.5
70
75
80
85
90
95
EFFICIENCY (%)
DC2328 F04
5V
IN
, 475kHz
12V
IN
, 825kHz
24V
IN
, 1.1MHz
36V
IN
, 1.2MHz
Optional –12V
OUT
Besides the default –24V output voltage which shows the
full capacity of LTM4651, it is very easy to customize
the DC2328A demo board to make other negative output
voltages available. As an example, to implement –12V
OUT
with 5V – 36V V
IN
,
1. Change R4 from 14k to 39k. This sets the minimum
operation input voltage, 5V for this case.
2. Change R1 and R8 from 240k to 121k. This sets the
output voltage, –12V for this case.
Check the input and output capacitor voltage rating.
And then it is done.
However, to maximize the efficiency of the regulator for
different input voltage, the switching frequency can be
adjusted by changing R13. For the recommended switch-
ing frequency for given input voltage and given output
voltage, please refer to the LTM4651 data sheet.
The results for the –12V
OUT
are listed below.
For 5V
IN
, change R13 from 124k to 1.3MΩ. The switching
frequency will be 475kHz. For 12V
IN
, change R13 from
124k to 237k. The switching frequency will be 825kHz.
For 24V
IN
, change R13 from 124k to 143k. The switch-
ing frequency will be 1.1MHz. For 36V
IN
, keep the default
R13. The switching frequency will be 1.2MHz.
The optimized efficiency for –12V
OUT
is as shown in
