PCA9522

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© NXP B.V. 2011. All rights reserved.

Product data sheet

Rev. 1 — 28 September 2011

5 of 20

NXP Semiconductors

PCA9522

Fast dual bidirectional bus buffer with hot insertion logic

7.4 Ready (RDY) — buffer connected indicator

The ready output (RDY) indicates that the buffer has met its enable conditions, and that

communication will now occur. This is an open-collector transistor which is switched off

when ready, allowing the voltage at the pin to be pulled HIGH by a pull-up resistor.

7.5 Start-up

During power-up or live insertion into backplanes, the PCA9522 will start-up in an

UnderVoltage LockOut (UVLO) state where any activity on the input/output ports will be

ignored. This is to ensure that the PCA9522 does not try to operate when there is not

enough voltage on the supply.

During this time, the precharge circuit will charge all SCLB/SDAB backplane ports to

typically 0.92 V. This will minimize any voltage difference between the ports and hence

minimizes disruptions to the bus during hot insertion into backplanes.

When the supply increases above the UVLO state the PCA9522 will then monitor the bus

for either stop bit or bus idle condition. When a stop bit condition is detected and

SCLC/SDAC are both idle or when all SCL/SDA ports idle for a time period of typically

95

s, then the PCA9522 will activate the input-output connection circuitry. The precharge

circuitry is switched off. The voltage at the RDY pin is pulled HIGH by an external pull-up

resistor to indicate the input/output connection has been made.

8.

Limiting values

[1]

Voltages are specified with respect to pin 4 (GND).

Table 3.

Limiting values

In accordance with the Absolute Maximum Rating System (IEC 60134).

Symbol

Parameter

Conditions

Min

Max

Unit

supply voltage

[1]

0.3

+7

V

voltage on any other pin

SCLB, SCLC,

SDAB, SDAC

[1]

0.3

+12

V

input voltage on pin EN

[1]

0.3

+12

V

input/output current

DC; any pin

-

20

mA

total power dissipation

-

300

mW

storage temperature

55

+125

C

ambient temperature

operating

40

+85

C