3
dc1877af
DEMO MANUAL DC1877A
Quick start proceDure
Figure 2. Measuring Input or Output Voltage Ripple
Circuit Options
Detailed information is contained in the data sheet.
Optional Output Voltage:
Additional output voltages can
be programmed by selecting proper resistors for the R6
and R7 feedback network. C5 is a feedforward capacitor
to optimize transient response and increase stability. Both
JP1 and JP2 must be in A position if R6 and R7 are used.
The 10V rated output capacitors should be replaced with
suitable voltage ratings.
ISET Components:
C3, R3 and R4 are used to provide a
number of features and circuit enhancements such as,
output current limit, input current limit, optimizing output
ripple voltage reduction and efficiency improvement. R4
sets maximum output current, see Figure 2 in LTC3630A
data sheet, leave open for maximum load current. R3 and
R4 can be used to set input current limit. C3 is used to
reduce output voltage ripple and optimize efficiency. See
data sheet for details.
RUN Pin Components:
The converter is enabled when
the RUN pin voltage exceeds 1.21V and is disabled when
dropping below 1.1V. Pulling the RUN pin below 700mV
forces a low quiescent current shutdown. Moving JP3
to the ON position allows an internal current to pull the
RUN pin up to 5V. R1 and R2 are used to program input
undervoltage lockout. Select suitable resistors to divide
the input voltage down to the precision threshold voltage
levels that enable and disable the converter. Note that
the maximum voltage on the RUN pin is 6V, therefore a
nominal 5V zener diode (D1) is required to limit the RUN
pin voltage when high input voltages are used.
Figure 3. Efficiency Curves
LOAD CURRENT (A)
EFFICIENCY (%)
DC1788a F03a
100
95
90
85
80
75
70
50
55
60
65
35
40
45
30
0.001
0.1
1
0.01
12V
IN
36V
IN
76V
IN
1.8V
OUT
LOAD CURRENT (A)
EFFICIENCY (%)
DC1788a F03b
100
95
90
85
80
75
70
50
55
60
65
35
40
45
30
0.001
0.1
1
0.01
12V
IN
36V
IN
76V
IN
3.3V
OUT
LOAD CURRENT (A)
EFFICIENCY (%)
DC1788a F03c
100
95
90
85
80
75
70
50
55
60
65
35
40
45
30
0.001
0.1
1
0.01
12V
IN
36V
IN
76V
IN
5V
OUT
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