Keypad I/O Expander
ADP5588
FUNCTIONAL BLOCK DIAGRAM
FEATURES
18-GPIO port expander or 10 × 8 keypad matrix
GPIOs configurable to GPIs, GPOs, and keypad rows or
columns
Dual light sensor inputs (C8 and C9)
I2C interface
I2C register read autoincrement
1.8 V to 3.0 V operation
REF
ADP5588
VOLTAGE
GND
19
21
23
22
20
24
C9
18
V
CC
C9
C8
C9
C8
SCL
SDA
RST
INT
REF
VOLTAGE
CONTROL
REGISTERS INTERFACE
CONTROL
C8
17
Keypad lock capability
Open-drain interrupt output
Key press and key release interrupts
GPI interrupt with level programmability
Programmable pull-ups
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16
Key event counter with overflow interrupt
50 μs debounce on the reset line and GPIs
1 μA typical idle current, 55 μA typical polling current drain
for one key press
Figure 1.
Small 4 mm × 4 mm LFCSP package
APPLICATIONS
Keypad and I/O expander designed for QWERTY type phones
that require a large keypad matrix
When used for smaller keypad matrices, unused row and
GENERAL DESCRIPTION
column pins can be reconfigured to act as general-purpose
inputs, outputs, or light sensor inputs. R0, R1, R2, R3, R4, R5,
R6, and R7 denote the row pins of the matrix, while C0, C1, C2,
C3, C4, C5, C6, C7, C8, and C9 denote the column pins. At
power-up, all rows and columns default as GPIs and must be
programmed to function as part of the keypad matrix, GPOs, or
light sensor inputs. In addition to keypad and GPIO functionalities,
C8 and C9 can also be configured as light sensor inputs.
The ADP5588 is an I/O port expander and keypad matrix
designed for QWERTY type phones that require a large keypad
matrix and expanded I/O lines. I/O expander ICs are used in
mobile platforms as a solution to the limited number of GPIOs
available in the main processor.
In its small 4 mm × 4 mm package, the ADP5588 contains
enough power to handle all key scanning and decoding and flag
the processor of key presses and releases via the I2C® interface
and interrupt. It frees the main microprocessor from having to
monitor the keypad, thereby minimizing current drain and
increasing processor bandwidth. It is also equipped with a
buffer/FIFO and key event counter to handle and keep track of
up to 10 unprocessed key or GPI events with overflow wrap and
interrupt capability.
When configured as keypad lines, the function of the C8 and
C9 lines is straightforward: the control interface disconnects
these lines from the comparator inputs, disables the light sensor
comparator, and connects them to the keypad columns of the
keypad matrix. When used as light sensor comparator inputs,
the control interface disconnects these pins from the keypad,
enables the comparators, and connects these lines to the com-
parator inputs. Two external capacitors (0.1 μF) are required
when these pins are configured as light sensor inputs. When
used as GPIOs, these pins are removed from the keypad and the
light sensor interface, and the light sensor comparators are
disabled, along with the logic for the sensors.
The ADP5588 has a keylock capability with an option to trigger
or not trigger an interrupt at key presses and releases. All com-
munication to the main processor is done using one interrupt line
and two I2C-compatible interface lines. The ADP5588 can be
configured to have a keypad matrix of up to 8 rows × 10 columns
(a maximum of 80 keys).
Rev. A
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registeredtrademarks arethe property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.461.3113
www.analog.com
©2008 Analog Devices, Inc. All rights reserved.
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