MAX13362 Datasheet, PDF (9/14 Pages) Maxim Integrated Products – 24-Channel Automotive Switch Monitor

24-Channel Automotive Switch Monitor
Detailed Description
The MAX13362 is a 24-channel automotive contact
monitor designed as an interface between mechanical
switches and low-voltage microcontrollers or other logic
circuits. It features an SPI interface to monitor individual
switch inputs and to configure interrupt capability, wet-
ting current, switch configuration (battery-connected or
ground-connected), polling time and polling active
time. Any switch status change will cause an interrupt
signal if the switch is interrupt enabled. The MAX13362
has three modes of operation: continuous mode, polling
mode, and shutdown mode.
V_DD and VS
V_DD is the power-supply input for the logic input/
output circuitry. Connect V_DD to a 3V to 5.5V logic-level
supply. Bypass V_DD to GND with at least a 0.1µF
capacitor placed as close as possible to V_DD.
VS is the main power-supply input. Bypass VS to GND
with a 0.1µF ceramic capacitor placed as close as pos-
sible to VS. In addition, bypass VS with a 47µF or
greater capacitor.
Mechanical Switch Inputs (IN0–IN23)
IN0–IN23 are the inputs for remote mechanical switch-
es. The switch status is indicated by the S0–S23 bits in
the status register, and each switch input can be pro-
grammed to assert an interrupt (INT) by writing to the
IE0–IE23 bits in the command register. All switch inputs
are interrupt disabled upon power-up.
The IN4–IN22 inputs are intended for ground-connect-
ed switches. The IN0–IN3 and IN23 inputs can be pro-
grammed for either ground-connected switches or
battery-connected switches by writing to the LH0–LH3
and LH23 bits (see Table 2). The default configuration
of the IN0–IN3 and IN23 inputs after power-up is for
ground-connected switches.
Wetting Current
The MAX13362 applies a programmable wetting current
to any closed switch to clean switch contacts that are
exposed to adverse conditions. The wetting current for
each switch can be set to 0mA, 5mA, 10mA, or 15mA
by the W_.0 and W_.1 data bits in the command regis-
ters (see Table 5) by means of an SPI data transaction.
When using wetting current, special care must be
taken to avoid exceeding the maximum power dissipa-
tion of the MAX13362 (see the Applications Information
section). Disabling the wetting current or limiting the
active-wetting current time reduces power consump-
tion. The default state upon power-up is with wetting
current disabled.
Interrupt Output (INT)
INT is an active-low, open-drain output that asserts low
when any of the switch inputs change state and is
enabled for interrupts, or when the overtemperature
threshold is exceeded. An external pullup resistor to
V_DD is needed on INT. INT is cleared when CS is driven
low for a read/write operation. However, in polling mode,
any switch state change or overtemperature change
which occurs during an SPI transaction is stored and
causes an additional interrupt after the SPI transaction is
over and CS goes high (shown in Figure 2).
If V_DD is absent, the INT output is functional provided
that it is pulled up to a different supply voltage.
CS
SWITCH STATUS CHANGE
CLK
INT
Figure 2. Switch State Change During the SPI transaction
NEW INTERRUPT
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