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3.3.6 Prebias Input (TP13)
3.3.7 Output Voltage Monitoring (TP14 and TP15)
4 Test Setup
4.1 Equipment
4.1.1 Voltage Source
4.1.2 Meters
4.1.3 Loads
4.1.4 Oscilloscope
Test Setup
By moving channel A from TP9 to TP4 (COMP), the control-to-output response of the power stage (also
referred to as the power stage transfer function) can be directly measured. See Section 3.9 for a detailed
procedure of loop response measurements.
TPS40040EVM-001 contains a prebias injection circuit with 100- Ω resistor and series diode to allow
testing and evaluation of the TPS40040’s prebias support compatibility. Apply a voltage less than the
target output voltage to TP13. Monitoring the output voltage during start-up demonstrates the TPS40040’s
ability to power up without drawing current from a prebiased output. D2 prevents the output voltage from
back-driving the prebias source.
TPS40040EVM-001 provides two test points for measuring the voltage generated by the module. This
allows the user to measure the actual module output voltage without losses from output cables and
connector losses. All output voltage measurements should be made between TP14 and TP15. To use
TP14 and TP15, connect a voltmeter positive terminal to TP14 and negative terminal to TP15. For output
ripple measurements, TP14 and TP15 allow a user to limit the ground loop area by using the Tip and
Barrel measurement technique shown in Figure 3 . All output ripple measurements should be made using
the Tip and Barrel measurement.
V
IN
The input voltage source (V
IN
) should be a 0-V to 6-V variable DC source capable of 5 Adc. Connect V
IN
to J1 as shown in Figure 3 .
• A1: 0-A to 5-A dc ammeter
• V1: V
IN
, 0-V to 6-V voltmeter
• V2: V
OUT
0-V to 5-V voltmeter
LOAD1
The output load (LOAD1) should be an electronic constant-current mode load capable of 0-A to 10-A dc at
1.8 V.
OSCILLOSCOPE
A digital or analog oscilloscope can be used to measure the ripple voltage on V
OUT
. The oscilloscope
should be set for 1-M Ω impedance, 20-MHz bandwidth, ac coupling, 1- µ s/division horizontal resolution,
10-mV/division vertical resolution for taking output ripple measurements. TP15 and TP16 can be used to
measure the output ripple voltage by placing the oscilloscope probe tip through TP15 and holding the
ground barrel to TP16 as shown in Figure 3 . For a hands-free approach, the loop in TP16 can be cut and
opened to cradle the probe barrel. Using a leaded ground connection can induce additional noise due to
the large ground loop area.
SLUU266 – January 2007 Using the TPS40040EVM-001: A 12-V Input, 1.8-V Output, 10-A Synchronous Buck Converter 7
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