3
dc1859afa
DEMO MANUAL DC1859A
+
–
V
OUT
GND
C
OUT
Figure 2. Measuring Input or Output Ripple
QUICK START PROCEDURE
Changing the Output Voltage
To change the output voltage from the programmed 12V,
change the voltage divider resistors connected to LTC3124
FB pin (see the schematic on page 5).
Converter Output Current
The DC1859 output current capability depends on the
input voltage. Typical performance of DC1859A is shown
in Figure 3. As can be seen from Figure 3, the maximum
output current is 800mA with 2.6V input and 2A with 5V
input. The efficiency is high at light loads thanks to phase
shedding in BURST mode. By disabling one phase the
related switching losses are reduced and the efficiency
is maximized.
Figure 3. The Efficiency Is Maximized for Light Loads by
Shedding One Phase in Burst Mode Operation. The Efficiency Is
Over 90% at Higher Loads and It Reaches 92% at 800mA Load
Output Load Step Response
The load step response of DC1859A 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 load step transients are shown in Figure 4. Other types
of low ESR and high value capacitors can be used if space
is available to reduce load transients to desired level.
Figure 4. The LTC3124 Has Excellent Load Step Response with
Small Output Capacitors Thanks to High Switching Frequency
and Fast Feedback Loop Compensation
Start-Up and Soft-Start Function
The DC1859 features internal 10ms soft-start circuit that
prevents input current surge at start-up. The soft-start
circuit also prevents output voltage overshoot when output
voltage ramp reaches regulation.
I
OUT
(mA)
EFFICIENCY (%)
95
90
80
70
85
75
65
60
dc1859a F03
1
1000
10000
100
10
PWM MODE
Burst Mode OPERATION
V
IN
= 2.6V
V
IN
= 5V
