PCA9507_1 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 01 — 7 February 2008 4 of 20
NXP Semiconductors
PCA9507
2-wire serial bus extender for HDMI DDC I
2
C-bus and SMBus
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 pull-down pulls port B down to
about 0.5 V. Port B falls below 0.4 V because it is not possible to know who is driving the
port A LOW, so the PCA9507 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
PCA9507 is on and holds port A down 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 crosses the port A threshold ~0.3V
CC(A)
the port B driver is turned off and the rising edge accelerator is turned on, which causes a
faster rising edge until it reaches the turn-off point for the rising edge accelerator
~0.7V
CC(A)
. Then it continues to rise at the slower rate determined by the RC of port A.
When the port B driver turns off, port B rises with the RC of port B.
V
CC(A)
powers the port A I/Os and the 0.3V
CC(A)
reference for port A as well as the port A
power good detect circuit. V
CC(B)
powers the rest of the chip including the port B I/Os and
the support functions. Figure 4 illustrates the threshold and I/O levels for port A and
port B.
6.1 Enable
The EN pin is active HIGH with an internal ~100 kΩ pull-up to V
CC(B)
and allows the user
to select when the buffer is active. This can be used to isolate the line when the HDMI
DDC transmitter or receiver is not ready, or from a badly behaved slave on power-up until
after the system power-up reset. It should never change state during an I
2
C-bus operation
because disabling during a bus operation will hang the bus and enabling part way through
a bus cycle could confuse the I
2
C-bus parts being enabled. The enable pin should only
change state when the global bus and the buffer port are in an idle state to prevent system
failures.
6.2 Rise time accelerators
PCA9507 has rise time accelerators on port A only. During port A positive bus transitions
a current source is switched on to quickly slew the SDAA and SCLA lines HIGH once the
input level of 0.3V
CC(A)
is exceeded for the PCA9507 and turns off as the 0.7V
CC(A)
voltage is approached.
Fig 4. 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
