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Document Number: MC33978
Rev. 7.0, 8/2017
NXP Semiconductors
Advance Information
* This document contains certain information on a new product.
Specifications and information herein are subject to change without notice.
© NXP B.V. 2017.
22 channel multiple switch detection
interface with programmable wetting
current
The 33978 is designed to detect the closing and opening of up to 22 switch
contacts. The switch status, either open or closed, is transferred to the
microprocessor unit (MCU) through a serial peripheral interface (SPI). This
SMARTMOS device also features a 24-to-1 analog multiplexer for reading the
input channels as analog inputs. The analog selected input signal is buffered and
provided on the AMUX output pin for the MCU to read.
Independent programmable wetting currents are available as needed for the
application. A battery and temperature monitor are included in the IC and
available via the AMUX pin.
The 33978 device has two modes of operation, Normal and Low-power mode
(LPM). Normal mode allows programming of the device and supplies switch
contacts with pull-up or pull-down current as it monitors the change of state on
the switches. The LPM provides low quiescent current, which makes the 33978
ideal for automotive and industrial products requiring low sleep-state currents.
Features
• Fully functional operation 4.5 V ≤ V
BATP
≤ 36 V
• Full parametric operation 6.0 V ≤ V
BATP
≤ 28 V
• Operating switch input voltage range from -1.0 V to 36 V
• Eight programmable inputs (switches to battery or ground)
• 14 switch-to-ground inputs
• Selectable wetting current (2, 6, 8, 10, 12, 14, 16, or 20 mA)
• Interfaces directly to an MCU using 3.3 V / 5.0 V SPI protocol
• Selectable wake-up on change of state
• Typical standby current I
BATP
= 30 μA and I
DDQ
= 10 μA
• Active interrupt (INT_B) on change-of-switch state
• Integrated battery and temperature sensing
Figure 1. 33978 simplified application diagram
Notes
1. The IC is functional from 4.5 V < V
BATP
< 6.0 V, but with degraded parametric values. The parameters may not meet the minimum and maximum
specifications when VBATP drops below 6.0 V.
MULTIPLE SWITCH DETECTION INTERFACE
33978
34978
Applications
• Automotive
• Heating ventilation and air conditioning (HVAC)
• Lighting
• Central gateway/in-vehicle networking
• Gasoline engine management
• Industrial
• Programmable logic control (PLC)
• Process control, temperature control
• Input-output control (I/O Control)
• Single board computer
• Ethernet switch
EK SUFFIX (PB-FREE)
98ASA10556D
32-PIN SOICW-EP
ES SUFFIX (PB-FREE)
98ASA00656D
32-PIN QFN (WF-TYPE)
SP0
SG12
SG13
SG0
SP7
SP1
Battery
VBATP
VDDQ
MISO
MOSI
SCLK
AMUX
EP
GND
WAKE_B
Battery
Power
Supply
Power
Supply
V
DDQ
MCU
MISO
MOSI
SCLK
AN0
INT_B
CS_B
CSB
INTB
SG1
33978
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