4
Rev. 0
QUICK START PROCEDURE
The DC3123A is easy to set up to evaluate the perfor-
mance of the LTC3315A. Refer to Figure 1 and Figure 2
for proper measurement equipment setup and follow the
evaluation procedure below.
NOTE: For accurate V
IN
, V
OUT
and efficiency measure-
ments, measure V
IN
at the V
IN
SNSE and GND SNSE turrets
and V
OUT
at the V
OUT
SNSE and GND SNSE turrets as illus-
trated as VM1, VM2 and VM3 in Figure 1. When measuring
the input or output voltage ripple, care must be taken to
avoid a long ground lead on the oscilloscope probe.
1. Set the JP2 and JP3 jumpers on the DC3123A board
to the HI position.
2. Set the JP1 jumper on the DC3123A board to the
desired position, BURST for best efficiency, FC/SYNC
for lowest ripple, and PS for a compromise between
the two.
3. With power off, connect 0V to 6V, 5A power supply,
PS1, between V
IN
and GND with a series ammeter and
a voltmeter as shown in Figure 1.
4. Turn on and set the PS1 input power supply to 3.3V
and observe that V
OUT1
regulates to 1.2V and V
OUT2
regulates to 1.8V.
NOTE: Make sure that the input voltage does not exceed 6V.
5. With power off, connect a 0A to 2A load to V
OUT1
and
GND with a series ammeter and a voltmeter as shown
in Figure 1.
6. Turn on LOAD1 and slowly increase from 0A to 2A
and observe the output voltage. The output ripple may
also be observed using an oscilloscope with the probe
connected as shown in Figure 2.
NOTE: Measure the output voltage ripple by touching the
probe tip directly across the output turrets or to TP1 as
shown in Figure 2. TP1 is designed for a 50Ω coax cable
to reduce any high frequency noise that might couple into
the oscilloscope probes.
7. Set LOAD1 to 500mA.
8. With power off, connect a second 0A to 2A load to
V
OUT2
and GND with a series ammeter and a voltmeter
as shown in Figure 1.
9. Turn on LOAD2 and slowly increase the from 0A to 2A
and observe the output voltage. The output ripple may
also be observed using an oscilloscope with the probe
connected as shown in Figure 2.
10. Momentarily short V
OUT1
to ground with a clip lead
and observe that the voltage on PGOOD drops to 0V.
11. To change the operating frequency of the LTC3315A,
an external clock must be used. To do this set the JP1
jumper on the DC3123A board to the FC/SYNC position.
12. Set a pulse generator to output a 0V to 3.3V pulse at
2MHz, 50% duty cycle and connect it to the MODE/
SYNC terminal and GND.
13. Change the frequency of the pulse generator from 2MHz
to 3MHz and observe how observe how the frequency
of SW1 follows the pulse generator.
14. Set LOAD1 greater than 1.0A. With an oscilloscope
probe on SW1, remove the pulse signal to the MODE/
SYNC terminal and observe how the switch frequency
settles from 3MHz back to 2MHz.
15. To test the transient response with a base load, turn
off LOADx (LOAD1 or LOAD2) and add the desired
resistor to produce a minimum load between V
OUTx
and
RSNSx turrets (RL shown on Figure 1). Note that the
total load resistance will be RL plus RSNSx (100mΩ).
16. Adjust a signal generator with a 10ms period, 10%
duty cycle and an amplitude from 1V to 2V to start.
Measure the RSNSx voltage to observe the current,
V
RSNSx
/100mΩ. Adjust the amplitude of the pulse to
provide the desired transient. Adjust the rising and
falling edge of the pulse to provide the desired ramp
rate. Refer to the following equations, the LTC3315A
DC3123A transient plots and Figure 3.
17. I
OUTx
= V
RSNSx
/100mΩ
V
RSNSx
= V
SGx
− V
GSx
Observe load transient effect on V
OUTx
18. Refer to the LTC3315A data sheet for more details on
how the LTC3315A operates.
19. When done, turn off all loads, signal generator and
power supplies.
