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IND ripple

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TPS51216

SLUSAB9A – NOVEMBER 2010 – REVISED APRIL 2013

www.ti.com

VDDQ Overvoltage and Undervoltage Protection

TPS51216 sets the overvoltage protection (OVP) when the VDDQSNS voltage reaches a level 20% (typ) higher

than the REFIN voltage. When an OV event is detected, the controller latches DRVH low and DRVL high.

VTTREF and VTT are turned off and discharged using the non-tracking discharge MOSFETs regardless of the

tracking mode.

The undervoltage protection (UVP) latch is set when the VDDQSNS 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

discharges the VDDQ, VTT and VTTREF outputs. UVP detection function is enabled after 1.2 ms of SMPS

operation to ensure startup.

To release the OVP and UVP latches, toggle S5 or adjust the V5IN voltage down and up beyond the

undervoltage lockout threshold.

VDDQ Overcurrent Protection

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

off-state using the low-side MOSFET RDS(on) and the controller maintains the off-state while the voltage across

the low-side MOSFET is larger than the overcurrent trip level. The current monitor circuit inputs are PGND and

SW pins so that those should be properly connected to the source and drain terminals of low-side MOSFET. The

overcurrent trip level, VTRIP, is determined by Equation 4, where RTRIP is the value of the resistor connected

between the TRIP pin and GND, and ITRIP is the current sourced from the TRIP pin. ITRIP is 10 μA typically at

room temperature, and has 4700ppm/°C temperature coefficient to compensate the temperature dependency of

the low-side MOSFET RDS(on).

(4)

Because the comparison is done during the off-state, VTRIP sets the valley level of the inductor current. The load

current OCL level, IOCL, can be calculated by considering the inductor ripple current as shown in Equation 5

where

•

IIND(ripple) is inductor ripple current

(5)

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.

VTT Overcurrent Protection

The LDO has an internally fixed constant overcurrent limiting of 3-A (typ) for both sink and source operation.

V5IN Undervoltage Lockout Protection

TPS51216 has a 5-V supply undervoltage lockout protection (UVLO) threshold. When the V5IN voltage is lower

than UVLO threshold voltage, typically 3.93 V, VDDQ, VTT and VTTREF are shut off. This is a non-latch

protection.

Thermal Shutdown

TPS51216 includes an internal temperature monitor. If the temperature exceeds the threshold value, 140°C (typ),

VDDQ, VTT and VTTREF are shut off. The thermal shutdown state of VDDQ is open, VTT and VTTREF are high

impedance (high-Z) respectively, and the discharge functions are disabled. This is a non-latch protection and the

operation is restarted with soft-start sequence when the device temperature is reduced by 10°C (typ).

20

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