PCA9703 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2014. All rights reserved.
Product data sheet Rev. 4 — 5 September 2014 5 of 28
NXP Semiconductors
PCA9703
18 V tolerant SPI 16-bit GPI with maskable INT
7. Functional description
PCA9703 is a 16-bit General Purpose Input (GPI) with an open-drain interrupt output
designed to monitor switch status. By putting an external 100 k series resistor at the
input port, the device allows the input to tolerate momentary double 12 V battery, reverse
battery, 27 V jump start or 40 V load dump conditions. The interrupt output is asserted
when an input port status changes, the input is not masked and the interrupt output is
enabled. The open-drain interrupt output is enabled when INT_EN is HIGH and disabled
when INT_EN is LOW. The INT_EN also enables the GPI pins when it is HIGH. In
cyclically supplied pull-up or pull-down applications, the GPI pull-ups or pull-downs should
be active before the INT_EN is taken HIGH and the INT
output should only be sampled
after transient conditions have settled. Additionally, interrupts can be disabled in software
by using the interrupt mask feature. The input port status is accessed via the 4-wire SPI
interface.
Upon power-up, the power-up reset cell clears all the registers, resulting in all zeros in
both the input status register and the interrupt mask register. Since a zero in the interrupt
mask register masks the interrupt from that pin, there will not be any interrupts generated.
After power-up it is necessary to access the PCA9703 through the SPI pins in order to
activate the interrupt for any GPI pins. When the PCA9703 is read over the SPI wires, the
input conditions are clocked into the input status register on the CS
falling edge. Since the
inputs and the input status register now match, no interrupt is generated and any
pre-existing interrupt is cleared. The input status register data is parallel loaded into the
shift register on the first rising edge of the SCLK. The serial input data is captured on the
opposite clock edge so that there is a
1
⁄
2
clock cycle hold time. The set-up time is
diminished by the propagation time so the SCLK falling edge to rising edge must be long
enough to provide sufficient set-up time. Successive clock cycles on the SCLK pin clock
the data out of the PCA9703 and new data from the SDIN into the shift register. There is
no limit to the number of clock cycles that can be applied with the CS
LOW, however
sufficient clock cycles should be used to both shift out all of the GPI data and shift in the
new interrupt mask data to the correct position with the MSB first before the CS
rising
edge.
For cyclic switch bias applications the switch bias should be applied first, then after the
input voltage is settled the general purpose inputs are switched on by taking the INT_EN
HIGH. This also enables the interrupt output, which will only indicate an interrupt if the GPI
data does not match the input status register on a bit that is enabled by the interrupt mask
register value. If an interrupt is generated, the pull-up or pull-down source should remain
active and the INT_EN should remain active and the SPI pins are used to update the input
status register and read the data out. They are also used to store the new interrupt mask
on the rising edge of CS
. After the SPI transaction is complete the INT_EN is taken LOW
to turn the inputs off and disable the INT
output. Then the GPI pull-ups or pull-downs can
be turned off. The GPI pins are specifically designed so that any ESD/overstress current
flows to ground, not V
DD
. They are also specifically designed so that if the input voltage
returns to the same value after pull-up or pull-down bias cycling as before the input pull-up
or pull-down bias cycling, before the input is enabled it will be detected as the same state.
If the Input Status register is read when INT_EN is LOW, the input state at the INT_EN
transition will be output regardless of the actual input levels since the GPI pins are turned
off.
