PCA9600DP datasheet(4/30 Pages) NXP

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PCA9600_4

Product data sheet

Rev. 04 — 11 November 2009

4 of 30

NXP Semiconductors

PCA9600

Dual bidirectional bus buffer

The logic threshold voltage levels at SX on this I2C-bus are independent of the IC supply

voltage VCC. The maximum I2C-bus supply voltage is 15 V.

When interfacing with Fast-mode systems, the SX pin is guaranteed to sink the normal

3 mA with a VOL of 0.74 V maximum. That guarantees compliance with the Fast-mode

I2C-bus speciﬁcation for all I2C-bus voltages greater than 3 V, as well as compliance with

SMBus or other systems that use TTL switching levels.

SX is guaranteed to sink an external 3 mA in addition to its internally sourced pull-up of

typically 300

µA (maximum 1 mA at −40 °C). When selecting the pull-up for the bus at SX,

the sink capability of other connected drivers should be taken into account. Most TTL

devices are speciﬁed to sink at least 4 mA so then the pull-up is limited to 3 mA by the

requirement to ensure the 0.8 V TTL LOW.

For Fast-mode I2C-bus operation, the other connected I2C-bus parts may have the

minimum sink capability of 3 mA. SX sources typically 300

µA (maximum 1 mA at

−40 °C), which forms part of the external driver loading. When selecting the pull-up it is

necessary to subtract the SX pin pull-up current, so, worst-case at

−40 °C, the allowed

pull-up can be limited (by external drivers) to 2 mA.

When the interface at SX is an Fm+ bus with a voltage greater than 4 V, its higher

speciﬁed sink capability may be used. PCA9600 has a guaranteed sink capability of 7 mA

at VOL = 1 V maximum. That 1 V complies with the bus LOW requirement (0.25Vbus) of

any Fm+ bus operating at 4 V or greater. Since the other connected Fm+ devices have a

drive capability greater than 20 mA, the pull-up may be selected for 7 mA sink current at

VOL = 1 V. For a nominal 5 V bus (5.5 V maximum) the allowed pull-up is

(5.5 V

− 1V)/7mA=643 Ω. With 680 Ω pull-up, the Fm+ rise time of 120 ns maximum

can be met with total bus loading up to 200 pF.

The logic level on RX is determined from the power supply voltage VCC of the chip. Logic

LOW is below 40 % of VCC, and logic HIGH is above 55 % of VCC (with a typical switching

threshold just slightly below half VCC).

TX is an open-collector output without ESD protection diodes to VCC. It may be connected

via a pull-up resistor to a supply voltage in excess of VCC, as long as the 15 V rating is not

exceeded. It has a larger current sinking capability than a normal I2C-bus device, being

able to sink a static current of greater than 30 mA, and typical 100 mA dynamic pull-down

capability as well.

A logic LOW is transmitted to TX when the voltage at I2C-bus pin SX is below 0.425 V. A

logic LOW at RX will cause I2C-bus pin SX to be pulled to a logic LOW level in accordance

with I2C-bus requirements (maximum 1.5 V in 5 V applications) but not low enough to be

looped back to the TX output and cause the buffer to latch LOW.

The LOW level this chip can achieve on the I2C-bus by a LOW at RX is typically 0.64 V

when sinking 1 mA.

If the supply voltage VCC fails, then neither the I2C-bus nor the TX output will be held

LOW. Their open-collector conﬁguration allows them to be pulled up to the rated maximum

of 15 V even without VCC present. The input conﬁguration on SX and RX also presents no

loading of external signals when VCC is not present.

The effective input capacitance of any signal pin, measured by its effect on bus rise times,

is less than 10 pF for all bus voltages and supply voltages including VCC =0V.

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