PCA9508D,112 Datasheet PCA9508DP,118, PCA9508D,118, PCA9508D,112 | P4-P6

Product data sheet Rev. 01 — 28 April 2008 4 of 21

NXP Semiconductors

PCA9508

Hot swappable level translating I

C-bus repeater

5. Pinning information

5.1 Pinning

5.2 Pin description

6. Functional description

Refer to Figure 1 “Functional diagram of PCA9508”.

The PCA9508 enables I

C-bus or SMBus translation down to V

CC(A)

as low as 0.9 V

without degradation of system performance. The PCA9508 contains two bidirectional

open-drain buffers speciﬁcally designed to provide superior hot-swap and/or support

up-translation/down-translation between the low voltage (as low as 0.9 V) and a 3.3 V or

5VI

C-bus or SMBus. All inputs and I/Os are overvoltage tolerant to 5.5 V even when the

device is unpowered (V

CC(B)

and/or V

CC(A)

= 0 V). The PCA9508 includes a power-up

circuit that keeps the output drivers turned off until V

CC(B)

is above 2.5 V and the V

CC(A)

above 0.8 V. V

CC(B)

and V

CC(A)

can be applied in any sequence at power-up. V

CC(A)

is only

used to provide the 0.5V

CC(A)

reference to the A side input comparators and for the power

good detect circuit. The PCA9508 logic and all I/Os are powered by the V

CC(B)

pin.

An undervoltage/initialization circuit holds the PCA9508 in a disconnected state which

presents high-impedance to all SDA and SCL pins during power-up. A LOW on the enable

pin (EN) also forces the parts into the disconnected state. As the power supply is brought

up and EN is HIGH or the part is powered and EN is taken from LOW to HIGH it enters an

initialization state where the internal references are stabilized. At the end of the

initialization state the ‘STOP bit and bus idle’ detect circuit is enabled. With the EN pin

Fig 2. Pin conﬁguration for SO8 Fig 3. Pin conﬁguration for TSSOP8

PCA9508D

CC(A)

CC(B)

SCLA SCLB

SDAA SDAB

GND EN

002aac652

PCA9508DP

CC(A)

CC(B)

SCLA SCLB

SDAA SDAB

GND EN

002aac653

Table 3. Pin description

Symbol Pin Description

CC(A)

1 A side supply voltage (0.9 V to 5.5 V)

SCLA 2 open-drain input/output serial clock A side bus

SDAA 3 open-drain input/output serial data A side bus

GND 4 supply ground (0 V)

EN 5 active HIGH repeater enable input with an internal pull-up (100 kΩ)

SDAB 6 open-drain input/output serial data B side bus

SCLB 7 open-drain input/output serial clock B side bus

CC(B)

8 B side supply voltage (2.7 V to 5.5 V)

Product data sheet Rev. 01 — 28 April 2008 5 of 21

NXP Semiconductors

PCA9508

Hot swappable level translating I

C-bus repeater

HIGH long enough to complete the initialization state (t

) and remaining HIGH when all

the SDA and SCL pins have been HIGH for the bus idle time or when all pins are HIGH

and a STOP condition is seen on the SDAA and SCLA pins, SDAA is connected to SDAB

and SCLA is connected to SCLB.

6.1 A side to B side

Once connected, when the PCA9508 senses a LOW level on the A side (below

0.5V

CC(A)

), it turns on the corresponding B side driver (either SDA or SCL) and drives the

B side down to about 0.5 V. When the external driver turns off, the A side will begin to rise

as it is pulled HIGH by the bus pull-up resistor. When the A side reaches 0.5V

CC(A)

, the

B side driver turns off and both A and B will continue to rise. The result is two smooth

exponential rising edges on both buses with a propagation delay between them which is a

function of the RC time constant on the A side bus.

6.2 B side to A side

When a LOW level is sensed on the B side (below 0.4 V), the corresponding A side driver

is turned on to drive the A side to nearly 0 V. When the external driver turns off, the B side

will begin to rise as it is pulled HIGH by the bus pull-up resistor. When the B side reaches

0.5 V, the A side driver will turn off. The B side driver will remain at about 0.5 V until the

A side rises above 0.5V

CC(A)

, then the B side will continue to rise. The result is a plateau

on the B side rising edge. See Figure 11.

6.3 Weak drive on B side

The following condition should be avoided as it causes the PCA9508 to create a glitch on

the bus. As long as I

C-bus devices connected to the B side can pull the bus lines lower

than 0.4 V, this problem will never occur. When the B side falls ﬁrst and goes below

0.3V

CC(B)

, the A side driver is turned on and the A side is pulled down to 0 V. The B side

pull-down is switched on and unless the B side is pulled below 0.4 V by an external driver,

the A side pull-down will switch off and the A side will be pulled up by the pull-up resistor.

When the A side rises above 0.5V

CC(A)

, the B side pull-down will turn off. To prevent this

glitch, it is necessary to make certain that the B side LOW level driven by an external

driver is below 0.4 V.

6.4 Enable pin (EN)

The EN pin is active HIGH with an internal pull-up to V

CC(B)

and allows the user to select

when the repeater is active. This can be used to isolate a badly behaved slave on

power-up until after the system power-up reset. It should never change state during an

C-bus operation because disabling during a bus operation will hang the bus.

The EN pin should only change state when the global bus and the repeater port are in an

idle state to prevent system failures.

If the PCA9508 is enabled while the bus is active, the PCA9508 will connect at the ﬁrst

STOP signal or at the ﬁrst gap in activity that satisﬁes the internal idle bus time after the

enable sequence is complete.

Product data sheet Rev. 01 — 28 April 2008 6 of 21

NXP Semiconductors

PCA9508

Hot swappable level translating I

C-bus repeater

6.5 I

C-bus systems

As with the standard I

C-bus system, pull-up resistors are required to provide the logic

HIGH levels on the buffered bus (standard open-collector conﬁguration of the I

C-bus).

The size of these pull-up resistors depends on the system, but each side of the repeater

must have a pull-up resistor. This part designed to work with Standard-mode and

Fast-mode I

C-bus devices in addition to SMBus devices. Standard-mode I

C-bus devices

only specify 3 mA output drive; this limits the termination current to 3 mA in a generic

C-bus system where Standard-mode devices and multiple masters are possible. Under

certain conditions higher termination currents can be used.

Please see application note

AN255, I

C/SMBus Repeaters, Hubs and Expanders

for

additional information on sizing resistors and precautions when using more than one

PCA9508 in a system or using the PCA9508 in conjunction with other bus buffers.

7. Application design-in information

A typical application is shown in Figure 4. In this example, the system master is running

on a 3.3 V I

C-bus while the slave is connected to a 1.2 V bus. Both buses run at 400 kHz.

Master devices can be placed on either bus.

The PCA9508 is 5 V tolerant, so it does not require any additional circuitry to translate

between 0.9 V to 5.5 V bus voltages and 2.7 V to 5.5 V bus voltages.

When the A side of the PCA9508 is pulled LOW by a driver on the I

C-bus, a comparator

detects the falling edge when it goes below 0.5V

CC(A)

and causes the internal driver on the

B side to turn on, causing the B side to pull down to about 0.5 V. When the B side of the

PCA9508 falls, ﬁrst a CMOS hysteresis type input detects the falling edge and causes the

internal driver on the A side to turn on and pull the A side pin down to ground. In order to

illustrate what would be seen in a typical application, refer to Figure 7 and Figure 8. If the

bus master in Figure 4 were to write to the slave through the PCA9508, waveforms shown

in Figure 7 would be observed on the A bus. This looks like a normal I

C-bus transmission

except that the HIGH level may be as low as 0.9 V, and the turn on and turn off of the

acknowledge signals are slightly delayed.

Fig 4. Typical application

002aac654

CC(A)

CC(B)

PCA9508

SDAB SDAA

SCLB SCLA

10 kΩ 10 kΩ

SDA

SCL

BUS

MASTER

400 kHz

SLAVE

400 kHz

SDA

SCL

bus B bus A

1.2 V

3.3 V

10 kΩ 10 kΩ

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21

PCA9508D,112

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Manufacturer:

NXP Semiconductors

Description:

Interface - Signal Buffers, Repeaters HOTSWAP LVTTL

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PCA9508D,112

PCA9508D,112

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