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 2003 Semtech Corp.

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POWER MANAGEMENT

SC2615

desirable.

A MOSFET in series with the top pass MOSFET (See typical

application circuit) must block this reverse current during

S3. This MOSFET can be driven from the inverted BF_CUT

signal. By removing the gate drive for this series MOSFET,

the current path from the VDDQ supply back into the

input power source is removed. This MOSFET is enhanced

during S0 state.

Short Circuit Protection

Short Circuit Protection is implemented by sensing the

VDDQ voltage. If the SS/EN pin has risen above 1.25V

(i.e. the controller has completed the startup cycle), and

the output falls to 60% of its nominal voltage, as sensed

by the FB pin, the TG pin is latched off and the linear

controllers shut down. To recover from this condition,

either the power rails have to be recycled, or the SS/EN

pin must be pulled low and released to restart controller

operation. The short circuit protection function is disabled

when any of the input rails are below their respective

UVLO thresholds.

Thermal Shutdown

There are three independent Thermal Shutdown

protection circuits in the SC2615, the VDDQ linear

regulator the VTT source regulator, and the VTT sink

regulator. If any of the three regulators’ temperature

rises above the threshold, that regulator will turn off

independently, until the temperature falls below the

thermal shutdown limit.

Power Good

An open collector output provides indication that the

VDDQ is regulating. This is accomplished by monitoring

the SS/EN pin. When the voltage on this pin has risen

above 1.0V, the PGOOD goes high (open). When BF_CUT

goes high (standby), the 5V and 12V rails go low, and the

SS/EN also goes low. Subsequently, PWRGD will also go

low, and stays low until the 3.3V and/or 12V rails are

recycled and rise above their respective UVLO thresh-

olds.

Applications Information (Cont.)