3.1 Adjusting Output Voltage (R5 and R6)
The regulated output voltage can be adjusted within a limited range by changing the ground resistor in the
feedback resistor divider (R6 and R5). The output voltage is given by
.
V
VOUT
+
V
VREF
R5
)
R65
)
R3
R5
)
R6
(1)
where
• V
VREF
= 0.700 V
• R3 = 10.0 kΩ
contains common values for R6 to generate popular output voltages with R5 open R5 can be used to
increase the accuracy that can be obtained without using more expensive resistors. The TPS40074EVM-001 is
stable through these output voltages but the efficiency can suffer as the power stage is optimized for the 1.5-V
output.
Table 3-1. Adjusting V
1V5_OUT
With R14
VOUT
R16
2.67 K
3.83 K
4.64 K
8.36 K
1.8 V
6.34 K
1.5 V
8.66 K
1.2 V
14.0 K
(1)
Due to higher duty cycles associated with higher output voltages or lower input voltages, output
current should be limited to 10 A when operating with output voltages greater than 2.0 V or input
voltages below 6 V to reduce conduction losses in the main switching FET (Q1). Under these
conditions, a lower R
dsON
FET would normally be selected.
3.2 Using Remote Sense (J3)
The TPS40074EVM-001 provides the user with remote sense capabilities through the connector J3. When
remote sense is used, J3 should be connected at the load to provide more accurate load regulation by
compensating for losses over the terminal connections and load wire connections. When remote sense
is connected the output voltage measured between TP15 and TP16 can show a positive load regulation
characteristic (increasing output voltage with increasing load). This is the result of the compensation of the
controller of resistive losses between the local sense voltage (TP15 and TP16) and the remote sense connection
(J3). TP17 and TP18 are connected to the remote sense lines and thus will show the voltage at the load when
remote sense is connected.
Excessive phase shift from inductive components in the load or remote sense connections can cause instability
if care is not taken to minimize these parasitic effects in the remote sense line. A twisted pair of insulated cables
from the load connection to J3 is preferred to minimize noise injection and inductance in the remote sense line.
In a device layout, care should be taken to shield the remote sense line from high-noise, high-current, or digital
signals to limit noise injection into the feedback path and provide the most accurate regulation possible.
3.3 5V Input Operation (R10 and R15)
To operate with a 5-V input, two resistors need to be changed. R10 (RKFF) sets the voltage ramp amplitude and
needs to be reduced to 53.6 kΩ to lower the UVLO to 3.9 V for 5-V operation. In addition, a 330-kΩ resistor
should be added at R15 to prevent an internal race condition during soft start.
1
Due to higher duty cycles associated with higher output voltages or lower input voltages, output current should be limited to 10 A when
operating with output voltages greater than 2.0 V or input voltages below 6 V to reduce conduction losses in the main switching FET
(Q1). Under these conditions, a lower RdsON FET would normally be selected.
Schematic
SLUU231A – JUNE 2006 – REVISED JANUARY 2022
TPS40074 Buck Controller Evaluation Module User's Guide
5
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