MAX13037 Datasheet, PDF (16/22 Pages) Maxim Integrated Products – Automotive Contact Monitor and Level Shifters with LDO Regulator

Automotive Contact Monitor and
Level Shifters with LDO Regulator
Notes:
Bit 15: Wetting Current Mode (WTOFF)
Set the WTOFF bit to configure the wetting currents as
continuous on closed switches. Clear the WTOFF bit to
configure the wetting current as a pulse where the wet-
ting current is turned on for a set duration of 20ms after
a switch closes (and the debounce is timed out). After
20ms elapses, the wetting current is turned off. Either
wetting current mode is only applicable to switches that
have wetting currents enabled (see WEN and WEND
bits). In scan mode, the wetting currents are on for the
polling time of 250µs (typ) and are pulsed at the pro-
grammed scanning period. When WTOFF is set, the
wetting current continuously pulses at the programmed
scanning period. When WTOFF is cleared, the wetting
current pulses at the programmed scanning period, but
turns off after 20ms elapses.
Bits 14, 13, 12: Scanning Period (SC2, SC1, SC0)
The SC2, SC1, and SC0 bits are used to program the
scanning period as depicted in Table 3. Switch inputs
are simultaneously polled for a finite duration of 250µs
(typ), and polling occurs at a period selected through
the SC2, SC1, and SC0 inputs. Figure 8 shows a timing
diagram of switch scanning and sampling. When the
inputs are not being polled, the sense resistors are dis-
connected, reducing the current consumption caused
from polling closed switches. For a continuous scanning
period ([SC2:SC1:SC0] = [1:1:1] or [1:1:0]), the switch
inputs are constantly being monitored and the sense
resistors are always connected. The state [SC2:SC1:SC0]
= [1:1:0] also disables adjustable hysteresis (normally set
by R_HYST) and fixes hysteresis at 0.166 x V_BATREF. When
adjustable hysteresis is not needed, it is recommended to
disable this feature to reduce power consumption.
Bit 11: Global Wetting Current Enable (WEN)
The WEN bit is a global enable for the wetting currents
on all the channels. Set the WEN bit to enable wetting
currents on all channels and clear the WEN bit to dis-
able wetting currents. Even with wetting currents glob-
ally enabled, the wetting currents and sense resistors
on IN0 and IN1 can still be turned off with the WEND bit
(see Table 4).
Bit 10: IN0 and IN1 Wetting Current Enable (WEND)
The WEND bit is used to turn on wetting currents and
sense resistors on inputs IN0 and IN1. Set the WEND
bit to enable wetting currents on IN0 and IN1 and clear
the WEND bit to turn off the wetting current and sense
resistors on IN0 and IN1. When the wetting currents
and sense resistors are disabled (WEND = 0), IN0 and
IN1 are configured as direct inputs with level-shifted
outputs on DO0 and D01. DO0 and DO1 can only be
used as level-shifted outputs in normal mode and are
three-stated in scan mode (see the Scan Mode sec-
tion). Note that both the WEN and WEND bits need to
be set for wetting currents to be enabled on IN0 and
Table 3. Programmable Scanning Period
SC2
SC1
SC0 SCANNING PERIOD (ms)
0
0
0
64
0
0
1
32
0
1
0
16
0
1
1
8
1
0
0
4
1
0
1
2
1
1
0
Continuous/adjustable
hysteresis off
1
1
1
Continuous
GND-CONNECTED
SWITCH INPUT
INT
t_SCAN
SWITCHES ARE
POLLED FOR 250μs
t_SCAN-P
SWITCH
DEBOUNCE
STARTS
t_DEB
SWITCH
CLOSES
Figure 8. Switch Sampling in Scan Mode
STATUS REGISTERS AND
INT ARE UPDATED
AFTER t_DEB
Table 4. Truth Table for WEN and WEND
WEN
WEND
WETTING CURRENT 16kΩ SENSE RESISTOR
(IN0, IN1)
(IN0, IN1)
0
0
Off
Off
0
1
Off
On
1
0
Off
Off
1
1
On
On
WETTING CURRENT
(IN2–IN7)
Off
Off
On
On
16kΩ SENSE RESISTOR
(IN2–IN7)
On
On
On
On
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