TPS54331-Q1
www.ti.com
SLVSAB5 –NOVEMBER 2010
TYPICAL CHARACTERISTICS (continued)
SUPPLEMENTAL APPLICATION CURVES
TYPICAL MINIMUM OUTPUT
VOLTAGE
TYPICAL MAXIMUM OUTPUT
VOLTAGE
MAXIMUM POWER DISSIPATION
vs
vs
vs
INPUT VOLTAGE
INPUT VOLTAGE
JUNCTION TEMPERATURE
1.25
1.15
1.05
30
25
20
15
150
125
IO = 2 A
IO = 2 A
100
75
0.95
0.85
0.75
10
5
IO = 3 A
50
IO = 3 A
0
25
3
8
13
18
23
28
3
8
13
18
23
28
0
0.2
0.4
PD
0.6
0.8
1
1.2
VI - Input Volatage - V
VI - Input Voltage - V
-
Power Dissipation - W
Figure 9.
Figure 10.
Figure 11.
OVERVIEW
The TPS54331 is a 28-V, 3-A, step-down (buck) converter with an integrated high-side n-channel MOSFET. To
improve performance during line and load transients, the device implements a constant frequency, current mode
control which reduces output capacitance and simplifies external frequency compensation design. The
TPS54331 has a pre-set switching frequency of 570kHz.
The TPS54331 needs a minimum input voltage of 3.5V to operate normally. The EN pin has an internal pull-up
current source that can be used to adjust the input voltage under-voltage lockout (UVLO) with two external
resistors. In addition, the pull-up current provides a default condition when the EN pin is floating for the device to
operate. The operating current is 110 mA typically when not switching and under no load. When the device is
disabled, the supply current is 1mA typically.
The integrated 80 mΩ high-side MOSFET allows for high efficiency power supply designs with continuous output
currents up to 3A.
The TPS54331 reduces the external component count by integrating the boot recharge diode. The bias voltage
for the integrated high-side MOSFET is supplied by an external capacitor on the BOOT to PH pin. The boot
capacitor voltage is monitored by an UVLO circuit and will turn the high-side MOSFET off when the voltage falls
below a preset threshold of 2.1V typically. The output voltage can be stepped down to as low as the reference
voltage.
By adding an external capacitor, the slow start time of the TPS54331 can be adjustable which enables flexible
output filter selection.
To improve the efficiency at light load conditions, the TPS54331 enters a special pulse skipping Eco-modeTM
when the peak inductor current drops below 160mA typically.
The frequency foldback reduces the switching frequency during startup and over current conditions to help
control the inductor current. The thermal shut down gives the additional protection under fault conditions.
DETAILED DESCRIPTION
FIXED FREQUENCY PWM CONTROL
The TPS54331 uses a fixed frequency, peak current mode control. The internal switching frequency of the
TPS54331 is fixed at 570kHz.
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