Datasheet

www.ti.com
4 General Configuration and Description
4.1 Adjusting Output Voltage (R7)
V =V
VOUT VREF
´
R +R
R
8 7
7
(1)
4.2 Adjusting Short-Circuit Protection (R9)
General Configuration and Description
This section reviews the general configurations for using the TPS40193EVM-001.
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 shown in Equation 1 :
where:
• V
VREF
= 0.591V and
• R
8
= 20k Ω
Table 2 contains common values for R7 to generate popular output voltages. The TPS40193EVM-001 is
stable through these output voltages, but efficiency may suffer because the power stage is optimized for
1.8V output.
Table 2. Adjusting V
OUT
with R7
V
OUT
R7 (k Ω )
3.3V 4.32
2.5V 6.19
2.25V 7.15
2.0V 8.25
1.8V 9.76
1.5V 13.0
1.2V 19.1
1.0V 28.7
0.9V 38.3
The values in Table 2 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.
The TPS40193 uses a selectable current limit for short-circuit protection. The current limit is selected from
three predefined levels by placing a resistor at R9. The TPS40193 compares the voltage drop across the
high-side FET (VDD to SW) to an internal reference voltage selected during start-up. Table 3 shows the
voltage levels.
Table 3. Adjusting V
SCP
with R9
V
SCP
(min) R7 (k Ω )
88mV 3.9
160mV Open
228mV 12
The current before declaring short-circuit protection can be determined by dividing the V
SCP
by the R
DS(ON)
of the high-side FET (Q2)
SLUU274 – May 2007 Using the TPS40193EVM-001 5
Submit Documentation Feedback