Accel Instruments TS200 User Manual - page 15
15
Line Transient Measurement
LDO/SMPS
TS200
Mod
Input
Output
DUT
Load
Function
Generator
Or AWG
Oscilloscope
CH1
CH2
Figure 8. Line transient measurement setup.
Most LDOs and switch-mode power supply (MSPS) specified their line
transient specifications. Line transient response specifies its output voltage
change after an input voltage step change. For example, an LDO specified its
output voltage deviates less than 5mV for a 200mV input voltage step from
3.6V to 3.8V in 10 microseconds. This is also called line step response.
Figure 8 shows how to measure line transient response. A function generator
generates a square pulse with a specific rise and fall time (i.e. 10us). The
function generator is connected to the Mod input of TS200 and the TS200
output is connected to the device under test. Typically the TS200 is set to DC-
couple. Set the function generator’s pulse high and low voltages generate the
transient step. For example, to generate a 3.6V to 3.8V voltage step, set the
function generator output voltage low to 3.6V and output high voltage to 3.8V.
If B-version is used, set the output voltage low to 0.36V and output high
voltage to 0.38V, since the TS200 gain is 20dB.
It is recommended to keep the DUT input capacitor to minimum (0.1uF or less)
to allow faster rise and fall time. Use as short cables as possible (Less than 12
inches) connecting TS200 output and the DUT. Twist the cables to together to
minimize inductance.
To measure the line transient step, connect an oscilloscope probe (CH1) to the
DUT input and another probe (CH2) to the DUT output as shown in Figure 8.
The transient response is measured at CH2. Figure 9 shows an example of line
transient measurement.