TPS2148

TPS2158

SLVS373 − AUGUST 2001

8

www.ti.com

detailed description

VIN/SWIN1

The VIN/SWIN1 serves as the input to the internal LDO and as the input to one N-channel MOSFET. The 3.3-V

LDO has a dropout voltage of 0.35 V and is rated for 200 mA of continuous current. The power switch is an

N-channel MOSFET with a maximum on-state resistance of 580 m

Ω. Configured as a high-side switch, the

power switch prevents current flow from OUT to IN and IN to OUT when disabled. The power switch is rated

at 150 mA, continuous current. VIN/SWIN1 must be connected to a voltage source for device operation.

OUTx

OUT1 and OUT2 are the outputs from the internal power-distribution switches.

LDO_OUT

LDO_OUT is the output of the internal 200-mA LDO. It is also the input to a second power switch. This power

switch in an N-channel MOSFET with a maximum on-state resistance of 580 m

Ω. Configured as a high-side

switch, the power switch prevents current flow from OUT to IN and IN to OUT when disabled. The power switch

is rated at 150 mA, continuous current.

LDO_EN

The active high input, LDO_EN, is used to enable the internal LDO and is compatible with TTL and CMOS logic.

enable (ENx, ENx)

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

both TTL and CMOS logic.

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.

toff

tpd(off)

ton

tpd(on)

50%

50%

90%

90%

10%

10%

tr

tf

90%

90%

10%

10%

VI(ENx)

VO(OUTx)

VO(OUTx)

TIMING

Figure 1. Timing and Internal Voltage Regulator Transition Waveforms