RT9715CA

8

DS9715CA-00 April 2015

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Copyright 2015 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

Applications Information

The RT9715CA is a single N-MOSFET high-side power

switches with enable input, optimized for self-powered and

bus-powered Universal Serial Bus (USB) applications. The

RT9715CA is equipped with a charge pump circuitry to

drive the internal N-MOSFET switch; the switch's low

Ω, meets USB voltage drop requirements;

and a flag output is available to indicate fault conditions

to the local USB controller.

Input and Output

the source of the MOSFET. In a typical application, current

Unlike a normal MOSFET, there is no parasitic body diode

between drain and source of the MOSFET, the RT9715CA

Chip Enable Input

The switch will be disabled when the EN pin is in a logic

low condition. During this condition, the internal circuitry

and MOSFET will be turned off, reducing the supply current

to 0.1

μA typical. Floating the EN may cause unpredictable

operation. EN should not be allowed to go negative with

(GND) to keep the part on.

Soft-Start for Hot Plug-In Applications

In order to eliminate the upstream voltage droop caused

by the large inrush current during hot-plug events, the

“soft-start” feature effectively isolates the power source

from extremely large capacitive loads, satisfying the USB

voltage droop requirements.

D

G

S

D

G

S

Normal MOSFET

RT9715CA

Fault Flag

The RT9715CA series provides a FLG signal pin which is

an N-Channel open drain MOSFET output. This open drain

output goes low when current limit or the die temperature

exceeds 120

°C approximately. The FLG output is capable

of sinking a 10mA load to typically 200mV above ground.

The FLG pin requires a pull-up resistor, this resistor should

be large in value to reduce energy drain. A 100k

Ω pull-up

resistor works well for most applications. In the case of

an over-current condition, FLG will be asserted only after

that FLG is asserted only upon valid over-current conditions

and that erroneous error reporting is eliminated.

For example, false over-current conditions may occur

during hot-plug events when extremely large capacitive

loads are connected and causes a high transient inrush

current that exceeds the current limit threshold. The FLG

Under-Voltage Lockout

Under-voltage lockout (UVLO) prevents the MOSFET

switch from turning on until input the voltage exceeds

approximately 1.7V. If input voltage drops below

approximately 1.3V, UVLO turns off the MOSFET switch.

Under-voltage detection functions only when the switch

is enabled.

Current Limiting and Short-Circuit Protection

The current limit circuitry prevents damage to the MOSFET

switch and the hub downstream port but can deliver load

current up to the current limit threshold of typically 1.5A

through the switch for RT9715CA. When a heavy load or

short circuit is applied to an enabled switch, a large

transient current may flow until the current limit circuitry

responds. Once this current limit threshold is exceeded,

the device enters constant current mode until the thermal

shutdown occurs or the fault is removed.