Analog Devices LTC3308A Demo Manual page 4

DEMO MANUAL DC2991A
QUICK START PROCEDURE
Demonstration circuit 2991A is easy to set up and use
to evaluate the performance of the LTC3308A. Refer to
Figure 1 for proper measurement equipment setup and
follow the procedure below.
NOTE: For accurate V
IN
ments, measure V at the V
IN
turrets and V at the V
OUT
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.
1. Set the JP1 jumper to the SKIP position and JP2 to the
HI position.
2. With power off, connect the input power supply to V
and GND. If the input EMI filter is desired, connect the
input power supply to V
3. Slowly increase PS1 to 1.0V. If AM1 reads less than
20mA, increase PS1 to 3.3V. Verify that VM1 reads
3.3V and VM2 reads 1.2V.
4. Connect an oscilloscope voltage probe as shown in
Figure 2 in parallel with VM2. Set channel to AC cou-
pled, voltage scale to 20mV and time base to 10μs.
Observe the V ripple voltage.
OUT
NOTE: Measure the output voltage ripple by touching
the probe tip directly across the output turrets or to
TP1 as shown in . TP1 is designed for a 50Ω coax
cable to reduce any high frequency noise that might
couple into the oscilloscope probes.
5. Verify that PGOOD turret is high.
6. Increasing the load by 1A intervals up to 4A and record
VM1, VM2, AM1 and AM2 for each interval.
7. Repeat Step 6 for PS1 set to 2.5V and again for PS1
set to 5.0V.
8. Set the load to a constant 2A. Remove the oscilloscope
voltage probe from V
OUT
terminal and set the voltage scale to 1V and the time
scale to 500ns/Division. Trigger on the rising edge of the
voltage probe. Using a tip on the voltage probe, contact
the SW node on the pad of L1. Observe the duty cycle
and the period of the switching waveform (~500ns).
4
, V and efficiency measure-
OUT
SNSE and GND SNSE
IN
SNSE and GND SNSE
OUT
.
IN
. Place a ground clip on PGND
9. Set the load current to 0.3A and repeat Step 8. Observe
that the switching waveform is now operating in pulse-
skipping mode.
10. Move the jumper on JP2 to LO. Verify that V
0V and verify that PGOOD is low. Return jumper on
JP2 to HI and verify VM2 is 1.2V and verify PGOOD2
is high.
11. If forced continuous or Burst Mode operation is
desired, set PS1 to 0V. Move JP1 to FC/SYNC or
BURST. Repeat Steps 3 through 9. In Step 9 observe
that the switching waveform is now operating in
forced continuous or Burst Mode operation.
12. To change the frequency, remove R9 if installed.
Install the desired R
IN
the inductor and output capacitors to provide the
desired inductor ripple and a stable output. Refer to
the LTC3308A data sheet and
information on choosing the required components.
13. To test the transient response with a base load, add the
desired resistor to produce a minimum load between
V and RSNS turrets (RL shown on Figure 1). Note
OUT
that the total load resistance will be RL plus R11
(100mΩ).
14. Adjust a signal generator with a 10ms period, 10%
duty cycle and an amplitude from 1V to 2V to start.
15. Measure the RSNS voltage to observe the current,
RSNS/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 and the optional
transient response circuit.
I = V /100mΩ
OUT RSNS
Where:
V = V
SG_INPUT SG_INPUT
16. When done, turn off PS1 and load. Remove all
connections to the demo board.
OUT
resistor in the R4 location. Size
T
LTpowerCAD for more
− V
GS
reads
Rev. 0