7.4 Device Functional Modes

ISO7821 functional modes are shown in Table 7-1.

Table 7-1. ISO7821 Function Table

VCCI

VCCO

INPUT

(INx)(2)

OUTPUT ENABLE

(ENx)

(DWW Package Only)

OUTPUT

(OUTx)

COMMENTS

PU

PU

H

H or open

H

Normal Operation:

A channel output assumes the logic state of the input.

L

H or open

L

Open

H or open

Default

Default mode: When INx is open, the corresponding channel output

goes to the default high logic state. Default= High for ISO7821 and

Low for ISO7821F.

X

PU

X

L

Z

A low value of Output Enable causes the outputs to be high-

impedance.

PD

PU

X

H or open

Default

Default mode: When VCCI is unpowered, a channel output assumes

the logic state based on the selected default option. Default= High for

ISO7821 and Low for ISO7821F.

When VCCI transitions from unpowered to powered-up, a channel

output assumes the logic state of the input.

When VCCI transitions from powered-up to unpowered, channel output

assumes the selected default state.

X

PD

X

X

Undetermined

When VCCO is unpowered, a channel output is undetermined (1).

When VCCO transitions from unpowered to powered-up, a channel

output assumes the logic state of the input

(1)

The outputs are in undetermined state when 1.7 V < VCCI, VCCO < 2.25 V.

(2)

A strongly driven input signal can weakly power the floating VCC using an internal protection diode and cause undetermined output.

7.4.1 Device I/O Schematics

Input (Device Without Suffix F)

Output

Enable

OUTx

VCCO

≅20W

INx

1.5MW

985W

Input (Device With Suffix F)

VCCI

VCCI

VCCI

INx

1.5MW

985W

VCCI

VCCI

VCCI VCCI

Enx

2MW

1970W

VCCO

VCCO

VCCO VCCO

Figure 7-3. Device I/O Schematics

ISO7821, ISO7821F

SLLSEM2H – NOVEMBER 2014 – REVISED NOVEMBER 2024

www.ti.com

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