SC5826

© 2000 SEMTECH CORP.

HotSwitch™

USB Power Distribution Switch

PRELIMINARY - February 18, 2000

652 MITCHELL ROAD NEWBURY PARK CA 91320

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DETAILED DESCRIPTION

The SC5826 HotSwitch™ is a dual port, high-side

switch optimized for power control & distribution in Uni-

versal Serial Bus (USB) applications. It features an n-

channel power MOSFET with a low on-state resistance

for meeting USB voltage regulation requirements. It

available with active high (SC5826-1) or active low

(SC5826-2) inputs.

In/Out

The input is the supply voltage connection to the drain

of the power switch MOSFET. The output is con-

nected to the source of the MOSFET. Under normal

operating conditions when the power switch is enabled,

current flows from the input to the output towards the

load. The power switch is designed to sustain a mini-

mum load current of 500mA in accordance with USB

specifications.

Charge Pump

An internal charge pump powers the MOSFET gate

drive circuit and provides the necessary voltage to pull

the gate above the source.

Control Logic

The gate drive circuit controls the gate voltage of the

MOSFET power switch. The gate drive circuit also

controls the rise & fall times of the power switch output

voltage. The typical “soft start” or output voltage rise

time is 1ms.

Enable Input

A logic signal at the enable (EN) pin activates the

power MOSFET switch. A logic 1 (SC5826-1) or logic

0 (SC5826-2) will bias the charge pump, gate drive,

and control circuitry turning on the power switch. A

logic signal of opposite polarity turns off the switch. If

both outputs are off, the device powers down. The en-

able input is compatible with 3V & 5V logic levels.

Error Flag

The error flag (FLG) output is an n-channel, open drain

MOSFET. The FLG pin is an active low during short

circuit, undervoltage, or thermal shutdown conditions.

The output remains low until the fault condition is re-

moved.

Thermal Sense

An internal thermal shutdown circuit turns off the power

switch output MOSFET when the die junction tempera-

ture exceeds 160°C. The output FLG pin is asserted

to a logic low signaling a fault condition. A built in hys-

teresis prevents the switch from turning on until the die

temperature has cooled approximately 10°C. The

switch will continue to cycle on and off until the fault

condition is removed. The thermal sense circuit func-

tions only when the switch is enabled.

Undervoltage Lockout

An undervoltage lockout circuit monitors the input volt-

age and prevents the power switch MOSFET from

turning on until the input voltage (IN) exceeds 2.5V

(typical). If the input voltage falls 90mV (typical) below

that point after the switch has been turned on, the un-

dervoltage lockout turns off the power switch output

MOSFET and asserts the FLG output to logic low. The

undervoltage lockout functions only when the switch is

enabled.