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TPS5402
SLVSBK4 –SEPTEMBER 2012
www.ti.com
OVERVIEW
The TPS5402 is a 28-V, 1.7-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 TPS5402’s switching frequency is adjustable with an external resistor or fixed by connecting the frequency
program pin to GND or leaving it unconnected.
The TPS5402 starts switching at V
IN
equal to 3.5 V. The operating current is 100 μA typically when not switching
and under no load. When the device is disabled, the supply current is 1 μA typically.
The integrated 120-mΩ high-side MOSFET allows for high efficiency power supply designs with continuous
output currents up to 1.7 A.
The TPS5402 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 pins. 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 2.1 V typically.
By adding an external capacitor, the slow start time of the TPS5402 can be adjustable which enables flexible
output filter selection. To improve the efficiency at light load conditions, the TPS5402 enters a special pulse
skipping mode when the peak inductor current drops below 300 mA 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
Adjustable Frequency PWM Control
The TPS5402 uses an external resistor to adjust the switching frequency. Connecting the ROSC pin to ground
fixes the switching frequency at 70 kHz, leaving it open gives 120-kHz switching frequency.
Figure 11. ROSC vs Switching Frequency
(1)
For operation at 300 kHz, an 85.5-kΩ resistor is required.
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Product Folder Links: TPS5402