pca9511a NXP Semiconductors, pca9511a Datasheet - Page 7

• Manufacturer Part Number: pca9511a
• Description: Hot Swappable I2c-bus And Smbus Bus Buffer
• Manufacturer: NXP Semiconductors

Philips Semiconductors
9397 750 13269
Product data sheet
8.5 Rise time accelerators
8.6 READY digital output
8.7 ENABLE low current disable
8.8 Resistor pull-up value selection
turn-on delay and the falling edge slew rate. The output falling edge slew rate is a function
of the internal maximum slew rate which is a function of temperature, V
well as the load current and the load capacitance.
During positive bus transitions a 2 mA current source is switched on to quickly slew the
SDA and SCL lines HIGH once the input level of 0.6 V for the PCA9511A is exceeded.
The rising edge rate should be at least 1.25 V/ s to guarantee turn on of the accelerators.
This pin provides a digital flag which is LOW when either ENABLE is LOW or the start-up
sequence described earlier in this section has not been completed. READY goes HIGH
when ENABLE is HIGH and start-up is complete. The pin is driven by an open-drain
pull-down capable of sinking 3 mA while holding 0.4 V on the pin. Connect a resistor of
10 k to V
Grounding the ENABLE pin disconnects the backplane side from the card side, disables
the rise-time accelerators, drives READY LOW, disables the bus precharge circuitry, and
puts the part in a low current state. When the pin voltage is driven all the way to V
part waits for data transactions on both the backplane and card sides to be complete
before reconnecting the two sides.
The system pull-up resistors must be strong enough to provide a positive slew rate of
1.25 V/ s on the SDA and SCL pins, in order to activate the boost pull-up currents during
rising edges. Choose maximum resistor value using the formula:
where R is the pull-up resistor value in , V
and C is the equivalent bus capacitance in picofarads (pF).
In addition, regardless of the bus capacitance, always choose R
maximum, R
voltages on SDAOUT and SCLOUT to connect the backplane to the card, and these
pull-up values are needed to overcome the precharge voltage. See the curves in
and
R 800 10
Figure 6
CC
3
for guidance in resistor pull-up selection.
to provide the pull-up.
V
---------------------------------- -
24 k for V
CC min
C
Rev. 01 — 15 August 2005
–
0.6
CC
= 3.6 V maximum. The start-up circuitry requires logic HIGH
Hot swappable I
CC(min)
is the minimum V
2
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
C-bus and SMBus bus buffer
16 k for V
PCA9511A
CC
CC
voltage in volts,
and process, as
CC
Figure 5
= 5.5 V
CC
7 of 23
, the