2
Rev. 0
QUICK START PROCEDURE
Demonstration circuit 3018A is easy to set up and evalu-
ate the performance of the LTC3311S. Refer to Figure 1
for proper measurement equipment setup and follow the
procedure below:
NOTE: For accurate V
IN
, V
OUT
and efficiency measure-
ments, measure V
IN
at the VIN SNSE and GND SNSE tur-
rets and V
OUT
at the VOUT SNSE and GND SNSE turrets as
illustrated as VM1 and VM2 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.
Measure the output voltage ripple by touching the probe
tip directly across the output turrets or to TP1 as shown
1. Set the JP1 Jumper to the HI position.
2. With power off, connect the input power supply to VIN
and GND. If the input EMI filter is desired, connect the
input power supply to VIN EMI and GND.
3. Slowly increase PS1 to 1V. If AM1 reads less than
20mA, increase PS1 to 3.3V. Verify that VM1 reads 3.3V
and VM2 reads 1.2V. Record VM1, VM2, VM3 AM1
and AM2. Connect an oscilloscope voltage probe as
shown in Figure 2. Set Channel to AC-coupled, voltage
scale to 20mV and time base to 10μs. Record V
OUT
ripple voltage. Verify that PGOOD voltage is above 3V.
Calculate die temperature using formula below:
T
J
(
°
C)
=
V
SSTT
4mV
– 273
4. Increase the load by 1A intervals up to 12A and observe
the voltage output regulation, ripple voltage, and the
voltage on the SSTT turret. Observe the switching
waveform by contacting a second voltage probe, set
to 1V scale, to the SW node of UI pins 6, 7, 8 and 9
as shown in Figure 1.
5. If pulse skip mode is desired, set PS1 to 0V. Install a
100k resistor in the R3 location and remove R6 or short
the MODE/SYNC turret to VIN. Repeat steps 1 through
4. In step 4 observe that the switching waveform is
now operating in pulse skip mode at low currents.
6. To change the frequency, remove R4 and R6 if installed.
Install the desired RT resistor in the R7 location.
Note, the MODE/SYNC pin is an output when R4 is
installed and the MODE/SYNC pin should have high
impedance to GND and VIN. Size the inductor, output
capacitors and compensation components to provide
the desired inductor ripple and a stable output. Refer
to the LTC3311S data sheet and LTPowerCAD for more
information on choosing the required components.
7. To test the transient response with a base load, add the
desired resistor to produce a minimum load between
VOUT and I_STEP turrets (RL shown on Figure 1).
Note that the total load resistance will be RL plus
R14 (50mΩ). Adjust a signal generator with a 10ms
period, 10% duty cycle and an amplitude from 1V to
2V to start.
8. Measure the I_STEP voltage to observe the current,
VI_STEP/50mΩ. 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. Figure 3 shows a load step from 2.5A (RL =
0.43Ω) to 8A. Refer to the following equations:
I
OUT
=
V
I_STEP
50m
Ω
V
GS
= V
SG_INPUT
– V
I_STEP
9. Turn off PS1 and Load. Remove all connections to
demo board.
