V ,

IN

V

OUT

PG

t

softstart

V

IN

Step Down Operation

100%

Mode

100%

Mode

V

TH_100+

V

TH_100-

V

UVLO+

V

UVLO-

V

TH_PG+

V

PG_Hys

V

tracks V

OUT

IN

V

tracks V

OUT

IN

High

Low

Low

V

discharge

OUT

TPS62740, TPS62742

SLVSB02B – NOVEMBER 2013 – REVISED JULY 2014

www.ti.com

Feature Description (continued)

9.3.7 Undervoltage Lockout UVLO

The device includes an under-voltage lockout (UVLO) comparator which prevents the device from misoperation

at too low input voltages. The UVLO comparator becomes active once the device is enabled with EN set to high.

releases the device for start up and operation. With a falling input voltage, the device operates down to the

load switch at pin LOAD is disabled and both rails, VOUT and LOAD are discharged. The converter starts

9.4 Device Functional Modes

9.4.1 VOUT And LOAD Output Discharge

Both the VOUT pin and the LOAD pin feature a discharge circuit to connect each rail to GND, once they are

disabled. This feature prevents residual charge voltages on capacitors connected to these pins, which may

impact proper power up of the main- and sub-system. With CTRL pin pulled to low, the discharge circuit at the

LOAD pin becomes active. With the EN pin pulled to low, the discharge circuits at both pins VOUT and Load are

active. The discharge circuits of both rails VOUT and LOAD are associated with the UVLO comparator as well.

9.4.2 Automatic Transition Into 100% Mode

Once the input voltage comes close to the output voltage, the DC/DC converter stops switching and enters 100%

duty cycle operation. It connects the output VOUT via the inductor and the internal high side MOSFET switch to

regulator is turned off, not switching and therefore it generates no output ripple voltage. Because the output is

connected to the input, the output voltage tracks the input voltage minus the voltage drop across the internal high

side switch and the inductor caused by the output current. Once the input voltage increases and trips the 100%

Figure 49, Figure 50, Figure 51.

Figure 6. Automatic 100% Mode Transition

10

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