L

V

V

V

V

t

I

2

f

OUT

IN

OUT

IN

2

ON

OUT

PFM

-

´

´

´

=

TPS82084

SLVSD11A – JUNE 2015 – REVISED SEPTEMBER 2015

www.ti.com

Feature Description (continued)

(3)

In PSM, the output voltage rises slightly above the nominal output voltage in PWM mode. This effect is reduced

by increasing the output capacitance. The output voltage accuracy in PSM operation is reflected in the electrical

specification table and given for a 22-µF output capacitor.

8.3.2 Low Dropout Operation (100% Duty Cycle)

The device offers a low input to output voltage differential by entering 100% duty cycle mode. In this mode, the

high-side MOSFET switch is constantly turned on. This is particularly useful in battery powered applications to

achieve longest operation time by taking full advantage of the whole battery voltage range. The minimum input

voltage to maintain a minimum output voltage is given by:

where

•

•

(4)

8.3.3 Soft Startup

The TPS82084 has an internal soft start circuit which ramps up the output voltage to the nominal voltage during

a soft start time of typically 0.8ms. This avoids excessive inrush current and creates a smooth output voltage

slope. It also prevents excessive voltage drops of primary cells and rechargeable batteries with high internal

impedance. The device is able to monotonically start into a pre-biased output capacitor. The device starts with

the applied bias voltage and ramps the output voltage to its nominal value.

8.3.4 Switch Current Limit and Short Circuit Protection (Hiccup-Mode)

The switch current limit prevents the device from high inductor current and from drawing excessive current from

the battery or input voltage rail. Excessive current might occur with a heavy load/shorted output circuit condition.

If the inductor peak current reaches the switch current limit, the high-side FET is turned off and the low-side FET

is turned on to ramp down the inductor current. Once this switch current limits is triggered 32 times, the devices

stop switching and enables the output discharge. The devices then automatically start a new startup after a

typical delay time of 66

μs has passed. This is named HICCUP short circuit protection. The devices repeat this

mode until the high load condition disappears.

8.3.5 Undervoltage Lockout

To avoid mis-operation of the device at low input voltages, an under voltage lockout is implemented, which shuts

8.3.6 Thermal Shutdown

the device temperature falls below the threshold by 20°C, the device returns to normal operation automatically.

8

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