Datasheet

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3.1 Adjusting Output Voltage (R3 & R13)
3.2 Disable (J3)
3.3 Test Set Up
3.3.1 Equipment
3.3.1.1 Voltage Source
3.3.1.2 Meters
3.3.1.3 Loads
3.3.1.4 Oscilloscope
Schematic
The regulated output voltage can be adjusted within a limited range by changing the ground resistors in
the feedback resistor-divider (R3, R13).
Table 2 contains common values for R3 and R13 to generate popular output voltages.
TPS40077EVM-001 is stable through these output voltages but the efficiency may suffer as the power
stage is optimized for the 1.8 V output.
Table 2. Adjusting V
OUT
With R3
V
OUT
R3 R13
1.2 V 9.53 k 62.0 k
1.5 V 5.36 k 140 k
1.8 V 4.42 k 24.9 k
2.5 V 2.37 k 71.5 k
3.3 V 1.60 k 220 k
The TPS40077EVM-001 provides a Disable input (J3) that allows the user to evaluate the TPS40077’s
Enable/Disable Function. When a short is applied across the pins of J3 the TPS40077 controller is
disabled and the EVM shuts down. When the TPS40077 is disabled, both FET Drivers are off.
V
12V_IN
The input voltage source (V
12V_IN
) should be a 0–16 V variable-DC source capable of 5 A DC. Connect
V
12V_IN
to J1 as shown in Figure 3 .
A1: 0-5 A DC, ammeter
V1: V
12V_IN
, 0-16 V voltmeter
V2: V
1V5_OUT
0-5 V voltmeter
LOAD1
The Output Load (LOAD1) should be a constant-current mode electronic load capable of 0-15 A DC at
1.8 V.
A digital or analog oscilloscope can be used to measure the ripple voltage on V
OUT
. The oscilloscope
should be set for 1-M impedance, 20-MHz bandwidth, AC coupling, 1- µ s/division horizontal resolution,
20-mV/division vertical resolution for measuring output ripple. TP9 and TP10 can be used to measure the
output ripple voltage by placing the oscilloscope probe tip through TP9 and holding the ground barrel to
TP10 as shown in Figure 2 . For a hands free approach, the loop in TP10 can be cut and opened to cradle
the probe barrel. Using a leaded ground connection should be avoided because it induces additional noise
due to its large ground-loop area.
SLVU192A February 2007 Revised March 2008 Using the TPS40077EVM-001 12-V Input, 1.8-V Output, 5
10-A Synchronous Buck Converter
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