Datasheet

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• JP3-SW EN: Switcher converter enable jumper. To enable the SWITCHER output, leave this jumper
unconnected (there is an internal pull up on this pin). To disable, install a shorting jumper. This will
short the enable pin to ground.
• TP1-PWRGD: Power Good connector test point. It is power good open collector flag for the switcher
converter. Tie this pin through a 10k resistor to a regulated supply <5.5V to monitor the status of the
switcher converter output.
• TP2-SENSE: The SW sense (feedback) pin test point.
• TP3-SW OUT: This is the positive switcher output test point. In addition to J7, this test point can also
be used to measure the output voltage of the switcher.
• TP4-LDO IN: The LDO input voltage test point.
• TP5-LDO OUT: The LDO output test point. In addition to J1, this test point can also be used to
measure the output voltage of the LDO.
2.2 Modifications
These evaluation modules are designed to provide access to the features of the TPS54120. However,
some modifications can be made to this module.
2.2.1 SW Output Voltage Set Point
The output voltage of the switcher is set by the resistor divider network of R5 and R6. R6 is fixed at
10kohm. To change the switcher output voltage of the EVM, it is necessary to change the value of resistor
R5. The value of R5 for a specific output voltage can be calculated using Equation 1. Note that the SW
output should be 0.8V above the LDO output for best PSR and noise performance.
R5 = 10 kΩ (SW Vout–0.8V)/ (0.8V) (1)
Table 2 lists the R5 values for some common output voltages. The values given in Table 2 are standard
values, not the exact value calculated using Equation 1.
Table 2. Sample 1% Resistor Values for Common SW Output Voltages
SW Output Voltage (V) R5 Value (kΩ)
1.8 12.4
2.5 21.5
3.3 31.6
4.1 41.2
5 52.3
6 64.9
2.2.2 LDO Output Voltage Set Point
The output voltage of the LDO also can be set by an external resistor divider network (R1 and R2). R2 is
fixed at 10kohm. To change the LDO output voltage of the EVM, it is necessary to change the value of
resistor R1. Changing the value of R1 can change the output voltage from 0.8 V to 6V. The value of R1 for
a specific output voltage can be calculated using Equation 2. Note that the LDO output should be 0.8V
below the SW output for best PSR and noise performance.
R1 = 10 kΩ (LDO Vout–0.8V)/ (0.8V) (2)
Table 3 lists the R1 values for some common output voltages. Note that the minimum VIN equals VOUT +
VDO or 2.2V, whichever is greater. The values given in Table 3 are standard values, not the exact value
calculated using Equation 2.
Table 3. Sample 1% Resistor Values for Common LDO Output Voltages
LDO Output Voltage (V) R1 Value (kΩ)
0.8 0 (Short)
1 2.49
3
SLVU641– January 2012 TPS54120EVM, Low Noise 1A Power Supply Evaluation Module
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