Datasheet

PCA9527_1 © NXP B.V. 2009. All rights reserved.
Product data sheet Rev. 01 — 29 June 2009 4 of 22
NXP Semiconductors
PCA9527
3-channel bidirectional bus extender for HDMI, I
2
C-bus and SMBus
6. Functional description
Refer to Figure 1 “Functional diagram of PCA9527”.
The PCA9527 consists of 3 channels of bidirectional open-drain I/Os specifically designed
to support up-translation/down-translation between low voltages (as low as 2.7 V) and a
3.3 V or 5 V I
2
C-bus and SMBus. The device contains a rise time accelerator, specifically
on port A of the SCLA and SDAA that enables the device to drive a long cable or a heavier
capacitive load for DDC, I
2
C-bus and SMBus applications. With dual supply rails, the
device translates from voltage ranges 2.7 V to 5.5 V down to a voltage as low as 2.7 V
without degradation of system performance. Unlike the SDAA and SCLA, the CECA is
powered by the V
CC(B)
and does not have a rise time accelerator, but is similar in that its
port A has normal I/O and port B static level offset. All I/Os are overvoltage tolerant to
5.5 V even when the device is un-powered (V
CC(B)
and/or V
CC(A)
= 0 V).
The PCA9527 includes a power-up circuit that keeps the SDA and SCL output drivers
turned off until V
CC(A)
and V
CC(B)
rise above 2.7 V. The CECA output drivers are turned
OFF until V
CC(B)
rises above 2.7 V. V
CC(A)
and V
CC(B)
can be applied in any sequence at
power-up.
When port B falls first and goes below 0.3V
CC(B)
the port A driver is turned on and port A
pulls down to 0 V. As port A falls below 0.3V
CC(A)
the port B pulls down to about 0.5 V.
The external port B driver must drive the port B to a LOW that is ≤ 0.4 V or else it is not
possible to know who is driving the port A LOW. The PCA9527 direction control assumes
that port A is controlling the part unless port B falls below 0.4 V. When the port B voltage
is ≤ 0.4 V the port A driver of the PCA9527 is on and holds port A down to nearly 0 V. As
the port B voltage rises because the external driver turns off, the port B voltage rises up to
~0.5 V because port A is LOW; once port B rises to ~0.5 V the port A pull-down driver
turns off. Then port A rises with a rise time determined by the RC of port A when it
GND 5 supply ground (0 V)
EN 6 active HIGH buffer enable input
CECB 7 serial data with static level offset, powered by V
CC(B)
, 5 V tolerant
SDAB 8 serial data port B bus with static level offset, 5 V tolerant
SCLB 9 serial clock port B bus with static level offset, 5 V tolerant
V
CC(B)
10 port B supply voltage (2.7 V to 3.6 V)
Table 2. Pin description
…continued
Symbol Pin Description
Fig 3. Port A and port B I/O levels
002aad435
0.3V
CC(B)
0.4 V
port B
V
CC(B)
port A
V
CC(A)
0.3V
CC(A)
0.5 V
0.7V
CC(A)
0 V
0 V