TPS2047, TPS2057

TRIPLE CURRENT-LIMITED POWER-DISTRIBUTION SWITCHES

SLVS194 – APRIL 1999

4

POST OFFICE BOX 655303

detailed description

power switch

The power switch is an N-channel MOSFET with a maximum on-state resistance of 135 m

Configured as a high-side switch, the power switch prevents current flow from OUTx to INx and INx to OUTx

when disabled. The power switch can supply a minimum of 250 mA per switch.

charge pump

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.

driver

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 4-ms range.

enable (ENx or ENx)

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

the supply current to less than 20

µA when a logic high is present on ENx (TPS2047) or a logic low is present

on ENx (TPS2057). A logic zero input on ENx or logic high on ENx 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.

overcurrent (OCx)

The OCx open drain output is asserted (active low) when an overcurrent or over temperature condition is

encountered. The output will remain asserted until the overcurrent or over temperature condition is removed.

current sense

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.

thermal sense

The TPS2047 and TPS2057 implement a dual-threshold thermal trip to allow fully independent operation of the

power distribution switches. In an overcurrent or short-circuit condition the junction temperature rises. When

the die temperature rises to approximately 140

°C, the internal thermal sense circuitry checks to determine which

power switch is in an overcurrent condition and turns off that switch, thus, isolating the fault without interrupting

operation of the adjacent power switches. Hysteresis is built into the thermal sense, and after the device has

cooled approximately 20 degrees, the switch turns back on. The switch continues to cycle off and on until the

fault is removed. The (OCx) open-drain output is asserted (active low) when overtemperature or overcurrent

occurs.

undervoltage lockout

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.