Datasheet

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IND(ripple)
OCTRIP OCTRIP IN OUT OUT
OCL
X SW IN
DS on DS on
I
V V V V V
1
I
R 2 R 2 L f V
= ´
TRIP
OCTRIP TRIP
I
V R
8
TPS51916
www.ti.com SLUSAE1D –DECEMBER 2010–REVISED JUNE 2012
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 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.
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 R
DS(on)
, and the controller maintains the off-state when the inductor current
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,
V
OCTRIP
, is determined by Equation 5, where R
TRIP
is the value of the resistor connected between the TRIP pin
and GND, and I
TRIP
is the current sourced from the TRIP pin. I
TRIP
is 10 μA typically at room temperature, and
has 4700ppm/°C temperature coefficient to compensate the temperature dependency of the low-side MOSFET
R
DS(on)
.
(5)
Because the comparison is done during the off-state, V
OCTRIP
sets the valley level of the inductor current. The
load current OCL level, I
OCL
, can be calculated by considering the inductor ripple current as shown in Equation 6.
where
• I
IND(ripple)
is inductor ripple current (6)
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
The TPS51916 has a 5-V supply undervoltage lockout protection (UVLO) threshold. When the V5IN voltage is
lower than UVLO threshold voltage, typically 3.9 V, VDDQ, VTT and VTTREF are shut off. This is a non-latch
protection.
Thermal Shutdown
The TPS51916 includes an internal temperature monitor. If the temperature exceeds the threshold value, 140°C
(typ), VDDQ, VTT and VTTREF are shut off. The state of VDDQ is open, and that of VTT and VTTREF are high
impedance (high-Z) at thermal shutdown. The discharge functions of all outputs 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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