V ,

IN

V

OUT

t

softstart

V

IN

Step Down Operation

100%

Mode

100%

Mode

V

TH_100+

V

TH_100-

V

UVLO+

V

UVLO-

V

tracks V

OUT

IN

V

tracks V

OUT

IN

V

discharge

OUT

TPS62746

SLVSD27A – JUNE 2015 – REVISED AUGUST 2015

www.ti.com

9.4 Device Functional Modes

9.4.1 Enable and Shutdown

The device is turned on with EN=high. With EN=low the device enters shutdown and turns off the VIN switchand

turns off the VIN switch. This pin must be terminated.

9.4.2 Device Start-up and Softstart

The device has an internal softstart to minimize input voltage drop during start-up. This allows the operation from

high impedance battery cells. Once the device is enabled the device starts switching after a typical delay time of

10ms. Then the softstart time of typical 700 µs begins with a reduced current limit of typical 150 mA. When this

time passed by the device enters full current limit operation. This allows a smooth start-up and the device can

start into full load current. Furthermore, larger output capacitors impact the start up behaviour of the DC/DC

converter. Especially when the output voltage does not reach its nominal value after the typical sofstart time, of

700µs, passed by.

9.4.3 Automatic Transition Into No Ripple 100% Mode

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

regulator is turned off, switching stops and therefore no output voltage ripple is generated. Since the output is

connected to the input, the output voltage follows the input voltage minus the voltage drop across the internal

high side switch and the inductor. Once the input voltage increases and trips the 100% mode exit threshold,

Figure 6. Automatic Transition into 100% Mode

10

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