TPS54202 Datasheet, PDF (11/26 Pages) Texas Instruments – 4.5-V to 28-V Input, 2-A Output, EMI Friendly Synchronous Step Down Converter

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TPS54202
SLVSD26 – APRIL 2016
Feature Description (continued)
7.3.9 Internal Soft-Start
The TPS54202 device uses the internal soft-start function. The internal soft start time is set to 5 ms typically.
7.3.10 Bootstrap Voltage (BOOT)
The TPS54202 has an integrated boot regulator and requires a 0.1-µF ceramic capacitor between the BOOT and
SW pins to provide the gate drive voltage for the high-side MOSFET. A ceramic capacitor with an X7R or X5R
grade dielectric is recommended because of the stable characteristics over temperature and voltage. To improve
drop out, the TPS54202 is designed to operate at 100% duty cycle as long as the BOOT to SW pin voltage is
greater than 2.1 V typically.
7.3.11 Overcurrent Protection
The device is protected from overcurrent conditions by cycle-by-cycle current limiting on both the high-side
MOSFET and the low-side MOSFET.
7.3.11.1 High-Side MOSFET Overcurrent Protection
The device implements current mode control which uses the internal COMP voltage to control the turn off of the
high-side MOSFET and the turn on of the low-side MOSFET on a cycle-by-cycle basis. During each cycle, the
switch current and the current reference generated by the internal COMP voltage are compared. When the peak
switch current intersects the current reference the high-side switch turns off.
7.3.11.2 Low-Side MOSFET Overcurrent Protection
While the low-side MOSFET is turned on, the conduction current is monitored by the internal circuitry. During
normal operation the low-side MOSFET sources current to the load. At the end of every clock cycle, the low-side
MOSFET sourcing current is compared to the internally set low-side sourcing current-limit. If the low-side
sourcing current-limit is exceeded, the high-side MOSFET does not turn on and the low-side MOSFET stays on
for the next cycle. The high-side MOSFET turns on again when the low-side current is below the low-side
sourcing current-limit at the start of a cycle.
Furthermore, if an output overload condition occurs for more than the hiccup wait time, which is programmed for
512 switching cycles, the device shuts down and restarts after the hiccup time of 16384 cycles. The hiccup mode
helps to reduce the device power dissipation under severe overcurrent conditions.
7.3.12 Spread Spectrum
In order to reduce EMI, TPS54202 introduces frequency spread spectrum. The jittering span is ±6% of the
switching frequency with 1/512 swing frequency.
7.3.13 Output Overvoltage Protection (OVP)
The TPS54202 incorporates an overvoltage transient protection (OVTP) circuit to minimize output voltage
overshoot when recovering from output fault conditions or strong unload transients. The OVTP circuit includes an
overvoltage comparator to compare the FB pin voltage and internal thresholds. When the FB pin voltage goes
above 108% × Vref, the high-side MOSFET will be forced off. When the FB pin voltage falls below 104% × Vref,
the high-side MOSFET will be enabled again.
7.3.14 Thermal Shutdown
The internal thermal-shutdown circuitry forces the device to stop switching if the junction temperature exceeds
155°C typically. When the junction temperature drops below 145°C typically, the internal thermal-hiccup timer
begins to count. The device reinitiates the power-up sequence after the built-in thermal-shutdown hiccup time
(32768 cycles) is over.
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