The first four inputs (IN0–IN3) are intended for ground-

connected switches. The remaining four inputs (IN4–IN7)

can be programmed in sets of two for either ground-con-

nected or battery-connected switches by writing to the

M0 and M1 bits (see Table 5). The default state after

power-up is IN2–IN7 configured for ground-connected

switches, and IN0/IN1 configured for direct inputs.

All switch inputs have internal 16k

Ω sense resistors to

detect switch transitions. Inputs configured for ground-

connected switches are pulled up to BAT and inputs

configured for battery-connected switches are pulled

down to GND. Figure 3 shows the switch input structure

for IN0 and IN1. IN0 and IN1 can be programmed as

direct inputs with level-shifted outputs (DO0 and DO1)

by clearing the WEND bit in the command register (nor-

mal mode only). When programmed as direct inputs,

IN0 and IN1 can be used for PWM or other signaling.

Clearing the WEND bit disables the sense resistors and

wetting currents on IN0 and IN1. When programmed as

direct inputs, the status of IN0 and IN1 is not reflected

in the status register, and interrupts are not allowed on

these inputs.

Switch Threshold Levels and

Hysteresis (BATREF, HYST)

Input thresholds for the remote switches are 50% of the

voltage applied to BATREF. The BATREF input is typi-

cally connected to the battery voltage before the

reverse-battery protection diode. The MAX13036 fea-

tures adjustable hysteresis on the switch inputs by con-

necting an external 0 to 900kΩ resistor from HYST to

ground (normal mode only). Short HYST to ground to

approximate formula for hysteresis is given below:

To reduce power consumption, the adjustable hystere-

sis can be disabled by setting [SC2:SC1:SC0 = 1:1:0]

in the command register. When the adjustable hystere-

Switch Debounce and Deglitch

The switch inputs IN0–IN7 share a common program-

mable debounce timer to increase the noise immunity

of the system in normal and scan mode. The switch

debounce time is set by connecting a capacitor

value of this capacitor is 500pF and the maximum value

is 10nF, corresponding to a debounce time of 5ms to

100ms respectively. To calculate other debounce times

the following formula should be used:

All switch input glitches of less than 20µs in duration

are automatically rejected by the MAX13036.

Debounce in Normal Mode

When a change of state occurs at the switch input the

debounce timer starts. If the new state is stable for at

rupt is generated (if enabled). If the input returns to its

previous state before the debounce time has elapsed,

an interrupt is not generated and the status register is

not updated.

Debounce in Scan Mode

A change of state at the switch input causes the device

to automatically enter normal mode and the debounce

timing to start. The device remains in normal mode as

long as the input state differs from the previous state.

As soon as the debounce time ends, the status register

is updated, an interrupt is generated, and the device

re-enters scan mode.

If the input returns to its previous state before the end

of the debounce time, the device re-enters scan mode,

an interrupt is not generated, and the status register is

not updated.

V

R

V

HYST

HYST(k )

BATREF

=+

+

⎡

⎣

⎢

⎢

⎤

⎦

⎥

⎥

Ω

0 166

43

123

.

((

)

()

Automotive Contact Monitor

and Level Shifter

10

______________________________________________________________________________________

MAX13036

16k

Ω*

NOTES:

* WETTING CURRENT AND PULLUP/DOWN RESISTORS ARE

CONTROLLED BY THE WEN AND WEND BITS IN THE COMMAND

REGISTER (SEE TABLE 4)

WETTING*

CURRENT

IN0, IN1

CONTROL

LOGIC

Figure 3. Input Structure of IN0 and IN1