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VOUT

+ V

VREF

R8 ) R7

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Schematic

3.1 Adjusting Output Voltage (R5)

The regulated output voltage can be adjusted within a limited range by changing the ground resistor in the

feedback resistor divider (R7). The output voltage is given by the formula

(1)

Where V

VREF

= 0.591 V and R8 = 20 kΩ

Table 1 contains common values for R7 to generate popular output voltages. TPS40192EVM-525 is stable

through these output voltages but the efficiency may suffer as the power stage is optimized for the 1.8-V

output.

Table 1. Adjusting V

OUT

with R7

OUT

(V) R7 (kΩ)

3.3 4.32

2.5 6.19

2.25 7.15

2 8.25

1.8 9.76

1.5 13

1.25 19.1

1 28.7

0.9 38.3

The values in Table 1 provide less than 1% nominal set-point error in the output voltage. If a tighter

nominal value is required, R5 can be used in parallel with R7 to obtain a wider range of resistor values

using commonly available E96 resistors.

3.2 Adjusting Short-Circuit Protection (R9)

The TPS40192 uses a selectable current limit for short-circuit protection. The current limit is selected from

three levels by placing a resistor at R9. The TPS40192 compares the voltage drop across the high-side

FET (VDD to SW) to an internal reference voltage selected during start-up. The voltage levels are shown

in Table 2.

Table 2. Adjusting V

SCP

With R9

SCP(min)

(mV) R9 (kΩ)

88 3.9

160 Open

228 12

The current before declaring short-circuit protection can be determined by dividing the V

SCP

by the R

DS(ON)

of the low-side FET (Q3).

3.3 Test Point Descriptions

Test Point Label Use Section

TP1 Vin+ Monitor input voltage to the module 3.3.1

TP2 Vin– Monitor input voltage to the module 3.3.1

TP3 Disable Vin connection for disable circuit 3.3.2

TP4 Disable Gate connection for disable circuit 3.3.2

TP5 Not Used Not present on PCB NA

TP6 COMP Monitor COMP voltage and monitor power stage frequency response 3.3.3 and 3.3.5

SLUU395–December 2009 Using the TPS40192EVM-525, A 12-V Input, 1.8-V Output, 10-A Synchronous

Buck Converter

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