RT9711A Просмотр технического описания (PDF) - Richtek Technology

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RT9711A

80mΩ, 1.5A/0.6A High-Side Power Switches with Flag

Richtek Technology 

VPCB = PCB voltage drop

The USB specification defines the maximum resistance

per contact (RCONN) of the USB connector to be 30mΩ

and the drop across the PCB and switch to be 100mV.

This basically leaves two variables in the equation: the

resistance of the switch and the resistance of the cable.

If the hub consumes the maximum current (II) of 500mA,

the maximum resistance of the cable is 90mΩ.

The resistance of the switch is defined as follows :

RSWITCH = { 4.75V − 4.4V − [ 0.5A x ( 4 x 30mΩ + 2 x

90mΩ) ] − VPCB } ÷ ( 0.1A x NPORTS )

= (200mV − VPCB ) ÷ ( 0.1A x NPORTS )

If the voltage drop across the PCB is limited to 100mV,

the maximum resistance for the switch is 250mΩ for four

ports ganged together. The RT9711A/B/C/D, with its

maximum 100mΩ on-resistance over temperature, easily

meets this requirement.

Layout Considerations

For best performance of the RT9711 series, the following

guidelines muse be strictly followed :

` Input and output capacitors should be placed close to

the IC and connected to ground plane to reduce noise

coupling.

` The GND should be connected to a strong ground plane

for heat sink.

` Keep the main current traces as possible as short and

wide.

The input and output capacitors should be

placed as close as possible to the IC.

VOUT

VIN

GND

VIN

FLG GND EN

Figure 2. PCB Layout Guide

DS9711A/B/C/D-03 April 2011

RT9711A/B/C/D

www.richtek.com

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