SC2041 datasheet(9/14 Pages) SEMTECH

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SC2041

HotSwitch™ USB Power Distribution

Switch With Shutdown

July 18, 2000

652 MITCHELL ROAD NEWBURY PARK CA 91320

TYPICAL CHARACTERISTICS (Cont.)

Figure 10: Inrush Current, Device Enabled Into

470µF and 10

Ω

Top Trace: V

SHDN, 5V/div.

Bottom Trace: I

OUT, 0.2A/div.

Timebase: 2.5ms/div.

IN = 5V, ROUT = 10Ω, COUT = 470µF

APPLICATIONS INFORMATION

Theory Of Operation

The SC2041 is a current limited 80m

Ω power switch

with error reporting and enable features. The power

switch is an N-channel MOSFET with its gate driven by

an internal charge pump. The switch has been de-

signed to turn on slowly (1.7ms typical) to minimize

inrush currents at turn-on.

The Shutdown pin (SHDN) is compatible with 3V or 5V

logic, and when pulled high, shuts off the power switch,

causing the device to enter a very low power shutdown

mode, where it will draw less than 1µA from the supply.

While enabled, the SC2041 draws only 100µA from the

supply.

The power switch has current limit detection circuitry

which will limit the current through the switch to 0.85A

(typical) and reduce the output voltage accordingly.

When current limit is entered, the open drain Flag pin

(FLG) is asserted low, indicating a fault condition. If an

overcurrent or short condition is continuous, the power

dissipation in the switch will cause the junction temper-

ature to rise, triggering the thermal protection circuitry

to shut the switch down (at T

J = 150°C typical). This will

shut off the output current altogether, and also cause

the Flag pin to be asserted low. Once the junction

temperature has dropped by 20°C (typical), the device

will start up once more in a controlled manner.

The SC2041 will operate from supply voltages as low

as 2.8V, and internal undervoltage lockout circuitry

ensures that the power switch will be turned off at

power-up, even if the device is enabled. Once the

UVLO threshold voltage (2.7V typical) is reached, the

switch will turn on (if enabled) and slowly ramp up the

output.

The SC2041 has been designed for use in USB appli-

cations such as:

1) hosts or self-powered hubs that need to current limit

downstream ports and report overcurrent conditions;

2) bus-powered hubs that need to be able to switch

power to downstream ports, limit inrush currents at

power-up (to less than a 44

Ω resistor in parallel with a

10µF capacitor) and power-up and draw less than

100mA;

3) bus-powered functions that need to limit inrush

currents at power-up (to less than a 44

Ω resistor in

parallel with a 10µF capacitor) and power-up and draw

less than 100mA.

Figure 9: Inrush Current, Device Enabled Into

100µF and 10

Ω

Top Trace: V

SHDN, 5V/div.

Bottom Trace: I

OUT, 0.2A/div.

Timebase: 2.5ms/div.

IN = 5V, ROUT = 10Ω, COUT = 100µF

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