Vishay Siliconix
SiC413DB
Document Number: 65172
S09-1350-Rev. A, 20-Jul-09
www.vishay.com
3
SET UP LOAD STEP
The hardware to test transient response is included in the
board, which allows users to see how the transient response
performs. The setup steps are:
1. Decide what load step is wanted, then based on the
output voltage calculate the external voltage V
EXT
that
will be connected between V
CTRL
and GND. For
example, a load step of 2 A between 0.5 A (I
1
) and 2.5 A
(I
2
) is required and the output voltage is 3.3 V. V
EXT
=
V
O
- (I
2
- I
1
) * 3.01
Ω
= V
O
- (2.5 A - 0.5 A) * 3.01
Ω
=
- 2.72 V. Preset a DC source voltage to V
EXT
= 2.72 V
(current capability around 1 A) and connect it to the
board with positive side to GND and negative side to
V
CTRL
(if V
EXT
is a positive value, then connect the DC
source positive to V
CTRL
and negative to GND).
2. Preset a waveform from a function generator using the
following parameters and set its output to OFF (refer to
the specific function generator manual for its setup):
Shape:
square
Freqency:
50 Hz or whatever is required
Duty cycle:
1 % to 2 % or whatever is required
Amplitude:
-12 V low level and + 10 V high level
Rising time
and
falling time:
1 µs or whatever is
required.
3. Connect the function generator output positive to
LDTRG and negative to GND.
4. Preset the current of an electronic load to I
1
and turn it
on.
5. Set up an oscilloscope using the following parameters.
Channel 1 for probing output voltage:
AC coupled,
20 mV/div to 50 mV/div, 100 mV offset, or whatever is
required .
Channel 2 for probling the current
on the 3.01
Ω
resistor (R2) (needs to be an isolated probe): DC
coupled, 3 V/div (corresponds to 1 A/div) for I
O
< 2.5 A or
5 V/div (corresponds to 1.661 A/div) for I
O
> 2.5 A.
Time base:
100 µs/div
Bandwidth:
20 MHz
6. Connect oscilloscope channel 1 probe positive to V
OUT
(J11) and negative to GND (J14), and channel 2 probe
positive to V
OUT
(J11) and negative to Q1 DRAIN.
7. Turn on the system power. Output voltage should be
shown on the electronic load with current of I
1
.
8. Turn on the power source for V
EXT
.
9. Set the function generator output to be ON. The transient
response waveforms should be seen on the oscilloscope.
10. If needed, re-adjust the trigger waveform’s rising and
falling time on the function generator so that the current
slew rate is satisfied (the current slew rate can be seen
on oscilloscope channel 2 waveform by setting the time
base to 1 µs or 500 ns).
11. To change load step, decrease or increase the value of
V
EXT
.
12. To cease transient response test, simply set the function
generator output to off, turn off the power source for
V
EXT
, and then shut down the system power.
CHANGE OUTPUT VOLTAGE
If, at any time, different output voltage is needed, then
simply change the value of R9 based on the following
formula:
R9 = R7/(V
O
/V
REF
- 1) = 10K/(V
O
/0.6 - 1)
Figure 5. An Example of Load Step Waveforms
COMP
Output Voltage
Inductor Current I
L