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DETAILED DESCRIPTION

POWER SWITCH

CHARGE PUMP

DRIVER

ENABLE (EN)

OVERCURRENT (OC)

CURRENT SENSE

THERMAL SENSE

UNDERVOLTAGE LOCKOUT

TPS2020

,, TPS2021

TPS2022, TPS2023, TPS2024

SLVS175C – DECEMBER 1998 – REVISED SEPTEMBER 2007

The power switch is an N-channel MOSFET with a maximum on-state resistance of 50 m

Configured as a high-side switch, the power switch prevents current flow from OUT to IN and IN to OUT when

disabled.

An internal charge pump supplies power to the driver circuit and provides the necessary voltage to pull the gate

of the MOSFET above the source. The charge pump operates from input voltages as low as 2.7 V and requires

very little supply current.

The driver controls the gate voltage of the power switch. To limit large current surges and reduce the associated

electromagnetic interference (EMI) produced, the driver incorporates circuitry that controls the rise times and fall

times of the output voltage. The rise and fall times are typically in the 2-ms to 9-ms range.

The logic enable disables the power switch, the bias for the charge pump, driver, and other circuitry to reduce the

supply current to less than 10

μA when a logic-high is present on EN. A logic-zero input on EN restores bias to

the drive and control circuits and turns the power on. The enable input is compatible with both TTL and CMOS

logic levels.

The OC open drain output is asserted (active low) when an overcurrent or overtemperature condition is

encountered. The output remains asserted until the overcurrent or overtemperature condition is removed.

A sense FET monitors the current supplied to the load. The sense FET measures current more efficiently than

conventional resistance methods. When an overload or short circuit is encountered, the current-sense circuitry

sends a control signal to the driver. The driver, in turn, reduces the gate voltage and drives the power FET into

its saturation region, which switches the output into a constant-current mode and holds the current constant while

varying the voltage on the load.

An internal thermal-sense circuit shuts off the power switch when the junction temperature rises to approximately

140

°C. Hysteresis is built into the thermal sense circuit. After the device has cooled approximately 20°C, the

switch turns back on. The switch continues to cycle off and on until the fault is removed.

A voltage sense circuit monitors the input voltage. When the input voltage is below approximately 2 V, a control

signal turns off the power switch.

Copyright © 1998–2007, Texas Instruments Incorporated

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