IN1 (see Table 4). The DO0 and DO1 outputs are three-
stated when WEND = 1. When programmed as direct
inputs (WEND = 0), any input changes on IN0 and IN1
are not reflected by the status register.
Bits 9 and 8: Switch Configuration for IN7–IN4 (M1, M0)
The M1 and M0 bits set the switch configuration in
groups of two for IN7 through IN4 (see Table 5). Set M1
to configure IN7 and IN6 for battery-connected switches
and clear M1 for ground-connected switches. Set M0 to
configure IN5 and IN4 for battery-connected switches
and clear M0 for ground-connected switches.
Bits 7–0: Interrupt Enable for IN7–IN0 (P7–P0)
The P7 through P0 bits allow independent control of
whether inputs IN7 through IN0 generate an interrupt
(INT). Set any bit to disable interrupts on the corre-
sponding input and clear the bit to enable interrupts on
the corresponding channel. An interrupt is asserted
when any input configured for interrupts changes state.
IN0 and IN1 do not generate an interrupt when confi-
gured as direct inputs (WEND = 0).
Operating Modes
The MAX13037/MAX13038 feature three modes of oper-
ation: normal mode, scan mode, and shutdown mode.
Normal mode is entered when the scanning period bits
in the command register are configured for continuous
scanning ([SC2:SC1:SC0] = [1:1:1] or [1:1:0]). Scan
mode is entered when the scanning period bits are set
for a periodic scanning time as shown in Table 3.
Shutdown mode is entered by driving the shutdown
input (SD) low. The default mode after power-up is scan
mode (when SD = high) with a scan period of 64ms.
Normal Mode (Continuous Scanning)
In normal mode, the input sense resistors are always
connected to the switch inputs to detect any input status
change (except IN0 and IN1 when WEND = [0]). Wetting
currents are enabled according to the WEN, WEND, and
WTOFF bits in the command register. If adjustable hys-
teresis is not required, this feature can be disabled to
reduce power consumption (see the
Typical Operating
Characteristics
) by setting the scanning period bits in the
command register to ([SC2:SC1:SC0] = [1:1:0]). The
hysteresis is set to 0.166 x V
BATREF
when adjustable
hysteresis is disabled.
Scan Mode
In scan mode, each sense resistor is connected for a
finite duration of 250µs (typ) and is repeated at a period
according to the scanning period bits SC2, SC1, and SC0
(see Table 3). All input resistors are connected simultane-
ously and the inputs are polled at the same time. When all
external switches are open and the scanning period is set
to 64ms the scanning mode reduces current consump-
tion to typically 28µA (LDO on) and 17µA (LDO off).
Wetting currents (if enabled) are applied to closed
switches during the polling time of 250µs (typ) and are
pulsed at the programmed 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. Inputs
IN0 and IN1 cannot be used as direct inputs (WEND = 0)
in scan mode. When configured as direct inputs in scan
mode, the outputs DO0 and DO1 are high impedance.
The quiescent current for a given scan mode can be cal-
culated by the following formula (LDO off):
Where V
BAT
= SD = +14V, I
BAT
is the BAT current
expressed in microamps and t
SCAN_P
is the scanning
period expressed in milliseconds.
Shutdown Mode
In shutdown mode, the LDO is disabled, all switch
inputs are high impedance and the external switches
are no longer monitored, reducing current consumption
on BAT to 2.85µA (typ). The MAX13037/MAX13038
reset upon entering shutdown mode and the contents
of the command register are lost. Exit shutdown mode
by bringing the voltage on SD above +2.4V. The SD
input is compatible with voltages up to V
BAT
. The
MAX13037/MAX13038 take 200µs (typ) to exit shutdown
