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IND(ripple)

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DS on

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TPS51518

SLUSAO8

– DECEMBER 2011

www.ti.com

Out-of-Bound Operation

When the output voltage rises to 8% above the target value, the out-of-bound operation starts. During the

out-of-bound condition, the controller operates in forced PWM-only mode. Turning on the low-side MOSFET

beyond the zero inductor current quickly discharges the output capacitor. During this operation, the

cycle-by-cycle negative overcurrent limit is also valid. Once the output voltage returns to within regulation range,

the controller resumes to auto-skip mode.

Current Sensing

current sensing node so that GND should be connected to the sense resistor or the source terminal of the

low-side MOSFET.

Overcurrent Protection

TPS51518 has cycle-by-cycle overcurrent limiting protection. The inductor current is monitored during the

off-state and the controller maintains the off-state when the inductor current is larger than the overcurrent trip

(8)

where

•

(9)

In an overcurrent condition, the current to the load exceeds the current to the output capacitor, thus the output

voltage tends to fall down. Eventually, it crosses the undervoltage protection threshold and shuts down.

Overvoltage and Undervoltage Protection

The TPS51518 sets the overvoltage protection (OVP) when VSNS voltage reaches a level 20% (typ) higher than

the target voltage. When an OV event is detected, the controller changes the output target voltage to 0 V. This

usually turns off DRVH and forces DRVL to be on. When the inductor current begins to flow through the low-side

MOSFET and reaches the negative OCL, DRVL is turned off and DRVH is turned on, for a minimum on-time.

After the minimum on-time expires, DRVH is turned off and DRVL is turned on again. This action minimizes the

output node undershoot due to LC resonance. When the VSNS reaches 0 V, the driver output is latched as

DRVH off, DRVL on.

The undervoltage protection (UVP) latch is set when the VSNS voltage remains lower than 68% (typ) of the

REFIN voltage for 1 ms or longer. In this fault condition, the controller latches DRVH low and DRVL low and

To release the OVP and UVP latches, toggle EN or adjust the V5IN voltage down and up beyond the

undervoltage lockout threshold.

V5IN Undervoltage Lockout Protection

TPS51518 has a 5-V supply undervoltage lockout protection (UVLO) threshold. When the V5IN voltage is lower

18

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