PCA9701_PCA9702_3

© NXP B.V. 2008. All rights reserved.

Product data sheet

Rev. 03 — 3 December 2008

8 of 28

NXP Semiconductors

PCA9701; PCA9702

18 V tolerant SPI 16-bit/8-bit GPI with INT

[1]

Input status register is the value or content of the D flip-flops.

[2]

Logic states shown for INT pin assumes 10 k

Ω pull-up resistor.

7.3 General Purpose Inputs

The General Purpose Inputs (GPI) are designed to behave like a typical input in the 0 V to

5.5 V range, but are also designed to have low leakage currents at elevated voltages. The

input structure allows for elevated voltages to be applied through a series resistor. The

series resistor is required when the input voltage is above 5.5 V. The series resistor is

required for two reasons: first, to prevent damage to the input avalanche diode, and

second, to prevent the ESD protection circuitry from creating an excessive current flow.

The ESD protection circuitry includes a latch-back style device, which provides excellent

ESD protection during assembly or typical 5.5 V applications. The series resistor limits the

current flowing into the part and provides additional ESD protection. The limited current

prevents the ESD latch-back device from latching back to a low voltage, which would

cause excessive current flow and damage the part.

The minimum required series resistance for applications with input voltages above 5.5 V is

100 k

Ω. For applications requiring an applied voltage above 27 V, Equation 1 is

recommended to determine the series resistor. Failure to include the appropriate input

series resistor may result in product failure and will void the warranty.

(1)

The series resistor should be placed physically as close as possible to the connected

input to reduce the effective node capacitance. The input response time is effected by the

RC time constant of the series resistor and the input node capacitance.

Table 3.

Interrupt output function truth table

H = HIGH; L = LOW; X = don’t care

INT_EN

Input port status

Input status register[1]

INT output[2]

HL

L

H

HL

H

L

HH

L

L

HH

H

H

LX

X

H

R

s

voltage applied

17 V

–

I

I

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