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TPS22918

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SLVSD76C – FEBRUARY 2016 – REVISED JULY 2017

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Copyright © 2016–2017, Texas Instruments Incorporated

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TYPICAL VALUES WITH QOD SHORTED TO VOUT

8.3 Feature Description

8.3.1 On and Off Control

The ON pin controls the state of the switch. ON is active high and has a low threshold, making it capable of

interfacing with low-voltage signals. The ON pin is compatible with standard GPIO logic threshold. It can be used

with any microcontroller with 1 V or higher GPIO voltage. This pin cannot be left floating and must be driven

either high or low for proper functionality.

8.3.2 Quick Output Discharge (QOD)

The TPS22918 includes a QOD feature. The QOD pin can be configured in one of three ways:

•

QOD pin shorted to VOUT pin. Using this method, the discharge rate after the switch becomes disabled is

controlled with the value of the internal resistance RPD. The value of this resistance is listed in the Electrical

Characteristics table.

•

QOD pin connected to VOUT pin using an external resistor REXT. After the switch becomes disabled, the

discharge rate is controlled by the value of the total resistance of the QOD. To adjust the total QOD

resistance, Equation 1 can be used:

RQOD = RPD + REXT

Where:

•

RQOD = Total output discharge resistance

•

RPD = Internal pulldown resistance

•

REXT = External resistance placed between the VOUT and QOD pin.

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•

QOD pin is unused and left floating. Using this method, there will be no quick output discharge functionality,

and the output will remain floating after the switch is disabled.

The fall times of the device depend on many factors including the total resistance of the QOD, VIN, and the

output capacitance. When QOD is shorted to VOUT, the fall time will change over VIN as the internal RPD varies

over VIN. To calculate the approximate fall time of VOUT for a given RQOD, use Equation 2 and Table 1.

VCAP = VIN × e

-t/τ

Where:

•

VCAP = Voltage across the capacitor (V)

•

t = Time since power supply removal (s)

•

τ = Time constant equal to RQOD × CL

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The fall times' dependency on VIN becomes minimal as the QOD value increases with additional external

resistance. See Table 1 for QOD fall times.

Table 1. QOD Fall Times

VIN (V)

(1)FALL TIME (μs) 90% - 10%, C

IN = 1 μF, IOUT = 0 A , VON = 0 V

TA = 25°C

TA = 85°C

CL = 1 μF

CL = 10 μF

CL = 100 μF

CL = 1 μF

CL = 10 μF

CL = 100 μF

5.5

42

190

1880

40

210

2150

5

43

200

1905

45

220

2200

3.3

47

230

2150

50

260

2515

2.5

58

300

2790

60

345

3290

1.8

75

430

4165

80

490

4950

1.2

135

955

9910

135

1035

10980

1

230

1830

19625

210

1800

19270