ISOUSB211DPR datasheet(20/44 Pages) TI

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UD+

FSM

PU/PD

LDO

SERXD-

SERXD+

LSFSRX

LSFSTX

FSM

PU/PD

LDO

SERXD-

SERXD+

LSFSRX

LSFSTX

FSM

UD-

BUS1

3P3V1

DD+

DD-

BUS2

3P3V2

LDO

CC1

1P8V1

CC2

1P8V2

HSRX

HSTX

HSRX

HSTX

Figure 8-1. ISOUSB211 Simplified Functional Block Diagram

8.3 Feature Description

8.3.1 Power Supply Options

The ISOUSB211 can be powered by connecting a 4.25 V to 5.5 V supply on VBUSx pins, in which case an

internal LDO generates V3P3Vx voltage. This option is suitable for the side facing the USB connector, where a

5-V VBUS supply is available. Alternatively, VBUSx and V3P3Vx pins can be shorted together and an external 3.3-

V power supply can be connected to both. This second option is suitable for the side facing the microcontroller,

where a 5-V supply may not be available.

The ISOUSB211 also needs a 1.8-V supply for operation. A 2.4 V to 5.5 V supply can be connected on VCCx

pins, in which case internal LDOs generate the V1P8Vx supplies. In the simplest implementation, VCCx can be

connected to the USB VBUS on the side facing the connector, and to the 3.3-V local supply on the side facing

the microcontroller. In this implementation, there is power dissipation on the internal LDOs of ISOUSB, which

limits the maximum ambient temperature supported by ISOUSB211.

To reduce power dissipation inside the ISOUSB211, an external 1.8-V supply can be connected to both VCCx

and V1P8Vx pins shorted together, in which case the internal 1.8-V LDOs of ISOUSB211 are bypassed. In this

implementation, some of the power dissipation is transferred to the external 1.8-V supply, and overall higher

ambient temperature operation is achieved for the ISOUSB211. If the external 1.8-V supply is an LDO, the effect

is to reduce power dissipation inside ISOUSB211, but overall no reduction in system current or power dissipation

is achieved. Alternatively, if the external 1.8-V supply is a DC-DC (buck) converter, both system power and

ISOUSB211 power dissipation can be reduced.

A third option is to include external resistors between VCCx pins and VBUS and 3.3-V local supplies. These

resistors can be accomodated since VCCx pins operate down to 2.4 V. The resistors drop voltage and dissipate

ISOUSB211

SLLSFC5B – NOVEMBER 2021 – REVISED SEPTEMBER 2022

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