TPS54521 Datasheet, PDF (18/33 Pages) Texas Instruments – 4.5V to 17V Input, 5A Synchronous Step Down SWIFT™ Converter

TPS54521
SLVS981 – JUNE 2010
EN = 2 V / div
Vout1 = 1 V / div
Vout2 = 1 V / div
Time = 2 msec / div
Figure 28. Ratio-metric Startup with Vout2 Leading Vout1
EN = 2 V / div
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Vout1 = 1 V / div
Vout2 = 1 V / div
Time = 2 msec / div
Figure 29. Simultaneous Startup
Output Overvoltage Protection (OVP)
The device incorporates an output overvoltage protection (OVP) circuit to minimize output voltage overshoot. For
example, when the power supply output is overloaded, the error amplifier compares the actual output voltage to
the internal reference voltage. If the VSENSE pin voltage is lower than the internal reference voltage for a
considerable time, the output of the error amplifier demands maximum output current. Once the condition is
removed, the regulator output rises and the error amplifier output transitions to the steady state voltage. In some
applications with small output capacitance, the power supply output voltage can respond faster than the error
amplifier. This leads to the possibility of an output overshoot. The OVP feature minimizes the overshoot by
comparing the VSENSE pin voltage to the OVP threshold. If the VSENSE pin voltage is greater than the OVP
threshold the high-side MOSFET is turned off preventing current from flowing to the output and minimizing output
overshoot. When the VSENSE voltage drops lower than the OVP threshold, the high-side MOSFET is allowed to
turn on at the next clock cycle.
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.
High-side MOSFET overcurrent protection
High-side MOSFET overcurrent protection is achieved by an internal current comparator that monitors the current
in the high-side MOSFET on a cycle-by-cycle basis. If this current exceeds the current limit threshold, the
high-side MOSFET is turned off for the remainder of that switching cycle.
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