TPS51216
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SLUSAB9 –NOVEMBER 2010
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 mA typically at
room temperature, and has 4700ppm/°C temperature coefficient to compensate the temperature dependency of
the low-side MOSFET RDS(on)
.
V
= R ´I
TRIP
TRIP TRIP
(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
æ
ç
ö
÷
æ
ç
ö
÷
I
IND ripple
(
V
IN - VOUT
VOUT
VTRIP
VTRIP
)
1
2
IOCL
=
+
=
+
´
´
ç
è
÷
ø
ç
è
÷
ø
8´RDS on
2
8´RDS on
LX
fSW ´ V
IN
( )
( )
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).
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