Analog Devices DC2745A Demo Manual page 4

DEMO MANUAL DC2745A
QUICK START PROCEDURE
Demonstration circuit 2745A is easy to set up and use
to evaluate the performance of the LTC3309A. Refer to
Figure 1 for proper measurement equipment setup and
follow the procedure below:
NOTE: For accurate V
IN
ments, measure V at the VIN SNSE and GND SNSE tur-
IN
rets and V at the V
OUT OUT
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
coupled, 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 Figure 2. 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 6A 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 3A. Remove the oscilloscope
voltage probe from V
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
4
, V and efficiency measure-
OUT
SNSE and GND SNSE turrets as
EMI.
IN
. Place a ground clip on PGND
OUT
duty cycle and the period of the switching waveform
(~500nanoseconds).
9. Set the load current to 0.5A and repeat step 8. Observe
that the switching waveform is now operating in Pulse
Skip 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 is desired, set
PS1 to 0V. Move JP1 to FC/SYNC or BURST. Repeat
steps 3 through 9. In step 9 observe that the switch-
ing waveform is now operating in forced continuous
IN
or Burst Mode.
12. To change the frequency, remove R9 if installed.
Install the desired RT resistor in the R4 location. Size
the inductor and output capacitors to provide the
desired inductor ripple and a stable output. Refer to
the LTC3309A 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 be-
tween V and RSNS turrets (RL shown on Figure 1).
OUT
Note 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,
V /100mΩ. Adjust the amplitude of the pulse to
RSNS
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 shown in Figure 3:
I = V
OUT RSNS
where
V = V
RSNS SG_INPUT
16. When done, turn off PS1 and Load. Remove all con-
nections to demo board.
LTPowerCAD
/100mΩ (2)
− V (3)
GS
reads
OUT
for more
Rev. 0