3
dc2569af
DEMO MANUAL DC2569A
QUICK START PROCEDURE
CHANGING THE OUTPUT VOLTAGE
To change the output voltage from the programmed
12V, change the voltage setting resistors connected to
LTM4661 FB pin (see the schematic on page 5).
CONVERTER OUTPUT CURRENT
The DC2569 output current capability depends on the
input voltage and programmed input current limit. Typi-
cal performance of DC2569A is shown in Figure 3. As can
be seen from Figure 3, the maximum output current is 1A
with 5V input. Switching the mode of operation to BURST
mode can increase the efficiency at light loads.
Figure 3. The 5V Input Efficiency is 90% at 0.6A Load
Figure 4. Thermal Image, 3.3V Input to 12V Output
at 0.8A, 200LFM Air Flow, No Heat Sink
LOAD CURRENT (A)
0
EFFICIENCY (%)
93
75
91
87
83
79
89
85
81
77
73
1
0.6
4661 G02
0.8
0.4
1.2
0.2
V
OUT
= 12V, 1A DC
OUTPUT LOAD STEP RESPONSE
The load step response of DC2569A is dependent on the
amount and type of output caps used. If higher load steps
need to be handled more output capacitance can be added
in order to keep the voltage transients at the desired level.
The 200mA to 400mA load step transients with 3.3V input
are shown in Figure 5. Other types of low ESR and high
value capacitors can be used if space is available to reduce
load transients to desired level.
Figure 5. The LTM4661 Has Good Load Step Response
with Small Output Capacitors (2
×
22µF)
500µs/DIV
V
OUT
(AC)
200mV/DIV
LOAD STEP
200mA
TO 400mA
4661 G05
V
IN
= 3.3V, V
OUT
= 12V
f
S
= 1MHz (DEFAULT)
200mA TO 400mA LOAD STEP
C
OUT
= 2×22µF CERAMIC
START-UP AND SOFT-START FUNCTION
The DC2569 features internal soft-start circuit that ramps
the output voltage up in monotonic fashion. The soft-start
circuit also prevents output voltage overshoot when out-
put voltage ramp reaches regulation.
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