I

V

TRIP

R

DS(on)

)

I

RIPPLE

2

+

V

TRIP

R

DS(on)

)

1

2

L

f

V

V

OUT

V

IN

V

10 (mA)

TPS51116-EP

www.ti.com

SLUSB52A – OCTOBER 2012 – REVISED NOVEMBER 2012

VDDQ and VTT Discharge Control

TPS51116 discharges VDDQ, VTTREF and VTT outputs when S3 and S5 are both low. There are two different

discharge modes. The discharge mode can be set by connecting MODE pin as shown in Table 3.

Table 3. Discharge Selection

MODE

DISCHARGE MODE

V5IN

No discharge

VDDQ

Tracking discharge

GND

Non-tracking discharge

When in tracking-discharge mode, TPS51116 discharges outputs through the internal VTT regulator transistors

and VTT output tracks half of VDDQ voltage during this discharge. Note that VDDQ discharge current flows via

VLDOIN to LDOGND thus VLDOIN must be connected to VDDQ output in this mode. The internal LDO can

handle up to 1 A and discharge quickly. After VDDQ is discharged down to 0.2 V, the internal LDO is turned off

and the operation mode is changed to the non-tracking-discharge mode.

When in non-tracking-discharge mode, TPS51116 discharges outputs using internal MOSFETs which are

connected to VDDQSNS and VTT. The current capability of these MOSFETs are limited to discharge slowly.

Note that VDDQ discharge current flows from VDDQSNS to PGND in this mode. In no discharge mode,

TPS51116 does not discharge any output charge.

Current Protection for VDDQ

The SMPS has cycle-by-cycle overcurrent limiting control. The inductor current is monitored during the OFF state

and the controller keeps the OFF state during the inductor current is larger than the overcurrent trip level. The

trip level and current sense scheme are determined by CS pin connection (see Current Sensing Scheme

resistor.

(4)

(5)

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

the output voltage tends to be even lower. Eventually, it crosses the undervoltage protection threshold and

shutdown.

Current Protection for VTT

The LDO has an internally fixed constant overcurrent limiting of 3.8 A while operating at normal condition. This

trip point is reduced to 2.2 A before the output voltage comes within ±5% of the target voltage or goes outside of

±10% of the target voltage.

Copyright © 2012, Texas Instruments Incorporated

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