MIC74 Datasheet, PDF (1/20 Pages) Micrel Semiconductor – 2-Wire Serial I/O Expander and Fan Controller Advance Information

MIC74
Micrel
MIC74
2-Wire Serial I/O Expander and Fan Controller
Advance Information
General Description
The MIC74 is a fully programmable serial-to-parallel I/O
expander compatible with the SMBus™ (system manage-
ment bus) protocol. It acts as a “slave” on the bus, providing
eight independent I/O lines.
Each I/O bit can be individually programmed as an input or
output. If programmed as an output, each I/O bit can be
programmed as an open-drain or complementary push-pull
output. If desired, the four most significant I/O bits can be
programmed to implement fan speed control. An internal
clock generator and state machine eliminate the overhead
generally associated with “bit-banging” fan speed control.
Programming the device and reading/writing the I/O bits is
accomplished using seven internal registers. All registers can
be read by the host. Output bits are capable of directly driving
high-current loads such as LEDs. A separate interrupt output
can notify the host of state changes on the input bits without
requiring the MIC74 to perform a transaction on the serial bus
or be polled by the host. Three address selection inputs are
provided, allowing up to eight devices to share the same bus
and provide a total of 64 bits of I/O.
The MIC74 is available in an ultra-small-footprint 16-lead
QSOP. Low quiescent current, small footprint, and low pack-
age height make the MIC74 ideal for portable and desktop
applications.
Features
• Provides eight bits of general purpose I/O
• Built in fan speed control logic (optional)
• 2-wire SMBus™/I²C™ compatible serial interface
plus interrupt output
• 2.7V to 3.6V operating voltage range
• 5V-tolerant I/O
• Low quiescent current: 2µA (typical)
• Bit-programmable I/O options:
input or output
push-pull or open-drain output
interrupt on input changes
• Outputs can directly drive LEDs (10mA I_OL)
• Up to 8 devices per bus
Applications
• General purpose I/O expansion via serial bus
• Personal computer system management
• Distributed sensing and control
• Microcontroller I/O expansion
• Fan Control
Ordering Information
Part Number
MIC74BQS
Temperature Range
–40°C to +85°C
Package
16-lead QSOP
Typical Application
3.0V
R9
ALERT
DATA
CLK
MIC74
VDD
P0
LED1
/ALERT P1
DATA
P2
CLK
P3
A0
P4
A1
P5
A2
P6
GND
P7 _LED8
3.0V
R1
R2
R3
R4
R5
R6
R7
R8
Serial-Bus-Controlled LED Annunciator
SMBus™ is a trademark of Intel Corporation. I²C™ is a trademark of Phillips Electronics N.V.
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 [phone] • fax + 1 [phone] • http://www.micrel.com
August 1, 2000
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MIC74