RT9701 datasheet(10/12 Pages) RICHTEK

10 / 12 page

RT9701

www.richtek-ic.com.tw

DS9701-05 October 2001

Applications Information

Filtering

To limit the input voltage drop during hot-plug events,

connect a 1µF ceramic capacitor from VIN to GND.

However, higher capacitor values will further reduce

the voltage drop at the input.

Connect a sufficient capacitor from VOUT to GND.

This capacitor helps to prevent inductive parasitics

from pulling VOUT negative during turn-off or EMI

damage to other components during the hot-

detachment. It is also necessary for meeting the USB

specification during hot plug-in operation. If RT9701

is implanted in device end application, minimum 1

µF

capacitor from VOUT to GND is recommended and

higher capacitor values are also preferred.

In choosing these capacitors, special attention must

be paid to the Effective Series Resistance, ESR, of

the capacitors to minimize the IR drop across the

capacitor’s ESR. A lower ESR on this capacitor can

get a lower IR drop during the operation.

Ferrite beads in series with all power and ground

lines are recommended to eliminate or significantly

reduce EMI. In selecting a ferrite bead, the DC

resistance of the wire used must be kept to a

minimum to reduce the voltage drop.

Reverse current preventing

The output MOSFET and driver circuitry are also

designed to allow the MOSFET source to be

externally forced to a higher voltage than the drain

(VOUT > VIN

≥ 0). To prevent reverse current from

such condition, disable the switch (RT9701CB) or

connect VIN to a fixed voltage under 1.3V.

Layout and Thermal Dissipation

Place the switch as close to the USB connector as

possible. Keep all traces as short as possible to

reduce

the

effect

undesirable

parasitic

inductance.

Place the output capacitor and ferrite beads as

close to the USB connector as possible.

If ferrite beads are used, use wires with minimum

resistance and large solder pads to minimize

connection resistance.

If the package is with dual VOUT or VIN pins,

short both the same function pins as Fig.1 or Fig.2

to reduce the internal turn-on resistance. If the

output power will be delivered to two individual

ports, it is specially necessary to short both VOUT

pin at the switch output side in order to protect the

switch when each port are plug-in separately.

Under normal operating conditions, the package

can dissipate the channel heat away. Wide power-

bus planes connected to VIN and VOUT and a

ground plane in contact with the device will help

dissipate additional heat.

Fig. 1 High Side Power Switch

CIN = 1µF, COUT = 470µF (Low ESR) on M/B

CIN = 1µF, COUT = 330µF (Low ESR) on Notebook

CIN = 10µF, COUT = 1µF on USB device

VOUT2

RT9701CBL

VOUT

COUT

VIN

CIN

1µF

GND

VOUT

VIN

VOUT1

COUT

Fig. 2 High Side Power Switch with Chip Enable Control

VOUT1

RT9701CB

VOUT

COUT

VIN

CIN

GND

OFF

VCE

VOUT

VOUT2

COUT

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