2.1 Input and Output Connections and Jumper Descriptions
J1-LDO OUT and J2-GND: The output of the
LDO and the ground connector. The default setting is 3.3 V. This is the low
noise output from the TPS54120.
J3-VIN and J4-GND: Input power supply
voltage and the ground connector. The positive input lead and ground return lead
from the input power supply should be twisted and kept as short as possible to
minimize EMI transmission. Additional bulk capacitance should be added across J3
and J4 if the supply leads are greater than six inches. For example, an
additional 47-μF electrolytic capacitor across J3 and J4 can improve the
transient response of the TPS54120 while eliminating unwanted ringing on the
input due to long wire connections.
J5: The SMA connector for the output
voltage of the LDO. The connector for J5 is not populated on the TPS54120EVM
(PWR103). This footprint allows the mounting of an SMA-style connector for more
accurate PSRR measurements.
J7-SW OUT and J6-GND: The output of the SW
and the ground connector. This is the output voltage from the switcher converter
and the input voltage to the LDO. The default setting is 4.1 V.
J8: The SMA connector for the output
voltage of the SW. The connector for J8 is not populated on the TPS54120EVM
(PWR103). This footprint allows the mounting of an SMA-style connector for more
accurate PSRR measurements.
JP1-LDOEN: LDO enable. To enable the
output of the LDO, connect this jumper from the center pin to the “on” pin. This
will connect the enable pin to the LDO input supply. To disable, connect this
jumper from the center pin to the “off” pin. This will short the LDO enable pin
to ground.
JP2: The jumper connection between the output of the switcher converter to the LDO input. A shorting jumper is required for normal operation. If you want to disconnect the LDO from the SW, remove the shorting jumper wire.
JP3-SW EN: Switcher converter enable
jumper. To enable the SWITCHER output, leave this jumper unconnected (there is
an internal pullup on this pin). To disable, install a shorting jumper. This
will short the enable pin to ground.
TP1-PWRGD: The power-good connector test
point. It is power-good open-collector flag for the switcher converter. Tie this
pin through a 10-k resistor to a regulated supply < 5.5 V 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.