Advanced Monolithic Systems, Inc.

6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140

AMS2026

PIN FUNCTIONS

Pin Name

Pin No.

I / O

Description

Enable

/EN (A/B)

1/4

I

Enable Input, Logic turns power switch on.

Ground

GND

6

I

Ground.

Input

IN

7

I

Power switch input, also supplies IC’s internal circuitry.

Error Flag

ERROR (A/B)

2/3

O

Overcurrent, Over temperature, Logic output.

Output

OUT(A/B)

6-8

O

Power switch output.

BLOCK DIAGRAM

THERMAL

SENSE

IN

1.2V

REFERENCE

CHARGE

PUMP

UVLO

*

CS

GATE

DRIVER

CURRENT

LIMIT

POWER SWITCH

OUT A

ERROR

FLAG

CHARGE

PUMP

UVLO

*

CS

GATE

DRIVER

CURRENT

LIMIT

POWER SWITCH

OUT B

ERROR

FLAG

ENABLE A

ENABLE B

ERROR A

GND

ERROR B

*Current Sense

FUNCTIONAL DESCRIPTION

Power Switch

The power switch is an N-channel MOSFET with a maximum on-

state resistance of 140m

Ω (V

side switch.

Charge Pump

An internal 100kHz charge pump supplies the power to the driver

circuit and provides the required voltage to pull the gate of the

MOSFET above the source. The charge pump requires very little

supply current and operates from input voltages as low as 3.0V.

Gate Driver

The driver controls the gate voltage of the power switch. The

driver incorporates circuitry that controls the rise and fall times of

the output voltage, as a result it limits large current surges and

reduces

the

associated

electromagnetic

interference

(EMI)

produced. The rise and fall times of the output voltage are

typically in the 2ms to 4ms range instead of the microsecond or

nanosecond range for a standard FET.

Enable

A logic high on the /EN input turns off the power switch and the

bias for the charge pump, driver, and other circuitry to reduce the

supply current to less than 10

µA. A logic zero input restore bias

to the drive and control circuits and turns the power on. The

enable input is compatible with both TTL and CMOS logic

levels.

Error Flag

The error flag output, is an open drain logic output that is active

low when output current exceeds current limit. Until the fault

condition is removed the output will remain active low.

Current Limit

A sense FET monitors the current supplied to the load. In case of

an overload or short circuit, the current limit circuitry sends a

signal to the driver. The driver will then reduce the gate voltage

and drive the power FET into its linear region, which switches

the output into a constant current mode and holds the current

constant while varying the voltage on the load.

Thermal Shutdown

The internal thermal shutdown circuit will shut the power switch

off when the junction temperature rises to approx. 180°C.

Hysteresis is build into the thermal sense circuitry, and after the

junction temperature has dropped about 20°C, the switch turns

back on. Until the fault is removed the switch will continue to

cycle off and on.

Undervoltage Lock-out

An internal voltage sense monitors the input voltage. When the

input voltage is below 3.2V nominal, the switch is turned off by a

control signal. The typical fall time range due to the sense of a

low voltage is 250

µs to 750µs.