TPS65250_1 Datasheet, PDF (21/38 Pages) Texas Instruments – 4.5-V TO 18-V INPUT, HIGH CURRENT, SYNCHRONOUS STEP DOWN THREE BUCK CONVERTER WITH INTEGRATED FET AND DYING GASP STORAGE AND RELEASE CIRCUIT

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Current Limit Protection
The TPS65250 current limit trip is set by the following formulae:
I_LIM
=
180
- _RLIM
+
1.3
TPS65250
SLVSAA3 – JUNE 2010
(8)
Figure 33. Buck 1
I_LIM
=
150
- _RLIM
+
1.12
(9)
Figure 34. Buck 2 and 3
All converters operate in hiccup mode: Once an over-current lasting more than 10 ms is sensed in any of the
converters, they will shuts down for 10 ms and then the start-up sequencing will be tried again. If the overload
has been removed, the converter will ramp up and operate normally. If this is not the case the converter will see
another over-current event and shuts-down again repeating the cycle (hiccup) until the failure is cleared.
If an overload condition lasts for less than 10 ms, only the relevant converter affected will go into and out of
under-voltage and no global hiccup mode will occur. The converter will be protected by the cycle-by-cycle current
limit during that time.
Overvoltage Transient Protection
The device incorporates an overvoltage transient protection (OVP) circuit to minimize voltage overshoot. The
OVP feature minimizes the output overshoot by implementing a circuit to compare the FB pin voltage to OVTP
threshold which is 109% of the internal voltage reference. If the FB 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 FB voltage drops lower than the OVTP threshold which is 107%, the high side MOSFET is
allowed to turn on the next clock cycle.
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Product Folder Link(s): TPS65250
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