TPS54319_1 Datasheet, PDF (16/35 Pages) Texas Instruments – 2.95-V to 6-V Input, 3-A Output, 2-MHz, Synchronous Step-Down Switcher With Integrated FETs ( SWIFT™)

TPS54319
SLVSA83 – JUNE 2010
www.ti.com
REVERSE OVERCURRENT PROTECTION
The TPS54319 implements low side current protection by detecting the voltage across the low side MOSFET.
When the converter sinks current through its low side FET, the control circuit turns off the low side MOSFET if
the reverse current is typically more than 2 A. By implementing this additional protection scheme, the converter is
able to protect itself from excessive current during power cycling and start-up into pre-biased outputs.
SYNCHRONIZE USING THE RT/CLK PIN
The RT/CLK pin is used to synchronize the converter to an external system clock. See Figure 30. To implement
the synchronization feature in a system, connect a square wave to the RT/CLK pin with an on time of at least
75ns. If the pin is pulled above the PLL upper threshold, a mode change occurs and the pin becomes a
synchronization input. The internal amplifier is disabled and the pin is a high impedance clock input to the
internal PLL. If clocking edges stop, the internal amplifier is re-enabled and the mode returns to the frequency set
by the resistor. The square wave amplitude at this pin must transition lower than 0.6 V and higher than 1.6 V
typically. The synchronization frequency range is 300 kHz to 2000 kHz. The rising edge of the PH is
synchronized to the falling edge of RT/CLK pin.
TPS54319
SYNC Clock = 2 V / div
Clock
Source
R_T
PLL
RT/CLK
PH = 2 V / div
Figure 30. Synchronizing to a System Clock
Time = 500 nsec / div
Figure 31. Plot of Synchronizing to System Clock
POWER GOOD (PWRGD PIN)
The PWRGD pin output is an open drain MOSFET. The output is pulled low when the VSENSE voltage enters
the fault condition by falling below 91% or rising above 107% of the nominal internal reference voltage. There is
a 2% hysteresis on the threshold voltage, so when the VSENSE voltage rises to the good condition above 93%
or falls below 105% of the internal voltage reference the PWRGD output MOSFET is turned off. It is
recommended to use a pull-up resistor between the values of 1kΩ and 100kΩ to a voltage source that is 6 V or
less. The PWRGD is in a valid state once the VIN input voltage is greater than 1.2 V.
OVERVOLTAGE TRANSIENT PROTECTION
The TPS54319 incorporates an overvoltage transient protection (OVTP) circuit to minimize voltage overshoot
when recovering from output fault conditions or strong unload transients. The OVTP feature minimizes the output
overshoot by implementing a circuit to compare the VSENSE pin voltage to the OVTP threshold which is 107%
of the internal voltage reference. If the VSENSE pin voltage is greater than the OVTP threshold, the high side
MOSFET is disabled preventing current from flowing to the output and minimizing output overshoot. When the
VSENSE voltage drops lower than the OVTP threshold the high side MOSFET is allowed to turn on the next
clock cycle.
THERMAL SHUTDOWN
The device implements an internal thermal shutdown to protect itself if the junction temperature exceeds 165°C.
The thermal shutdown forces the device to stop switching when the junction temperature exceeds the thermal
trip threshold. Once the die temperature decreases below 150°C, the device reinitiates the power up sequence
by discharging the SS pin to below 40 mV. The thermal shutdown hysteresis is 15°C.
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