TPS2145, TPS2147

TPS2155, TPS2157

SLVS333 − AUGUST 2001

10

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detailed description (continued)

enable (ENx, ENx)

The logic enable disables the power switch. Both switches have independent enables and are compatible with

both TTL and CMOS logic.

overcurrent (OCx)

The OCx open-drain output is asserted (active low) when an overcurrent condition is encountered. The output

will remain asserted until the overcurrent condition is removed.

current sense

A sense FET monitors the current supplied to the load. Current is measured more efficiently by the sense FET

than by 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

A dual-threshold thermal trip is implemented 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 120

°C, the internal thermal sense circuitry determines which power switch is in an

overcurrent condition and turns off that switch, thus isolating the fault without interrupting operation of the

adjacent power switch. Because hysteresis is built into the thermal sense, the switch turns back on after the

device has cooled approximately 10 degrees. The switch continues to cycle off and on until the fault is removed.

undervoltage lockout

A voltage sense circuit monitors the input voltage. When the input voltage is below approximately 2.5 V, a control

signal turns off the power switch.

PARAMETER MEASUREMENT INFORMATION

IN

OUT

DUT

+

Current

Meter

A

Figure 1. Current Limit Test Circuit