Datasheet

MAX7370
8 x 8 Key-Switch Controller and LED Driver/GPIOs
with I2C Interface and High Level of ESD Protection
8Maxim Integrated
Detailed Description
The MAX7370 is a microprocessor peripheral low-noise
key-switch controller that monitors up to 64 key switches
with optional autorepeat, and key events that are pre-
sented in a 16-byte FIFO. Key-switch functionality can
be traded to provide up to 16 logic inputs. The device
also features 12 push-pull GPOs configured for digital
I/O and four open-drain GPOs configurable as constant-
current outputs for LED applications up to 5V. The device
supports a second 1.62V to 3.6V power supply for level
translation. The second logic supply voltage (V
LA
) must
be set equal to or higher than V
CC
.
The device features an automatic sleep mode and auto-
matic wakeup that further reduce supply current con-
sumption. The device can be configured to enter sleep
mode after a programmable time following a key event.
The FIFO content is maintained and can be read in sleep
mode. The device does not enter autosleep when a key
is held down. The autowake feature takes the device
out of sleep mode following a keypress. Autosleep and
autowake are enabled/disabled by programming the
configuration register (0x01).
To prevent overloading the microprocessor with too
many interrupts, interrupt requests can be triggered
after a programmable number of FIFO entries have been
exceeded, and/or after a set period of time (0x05). The
key-switch status is checked by reading the key-switch
FIFO. A 1-byte read access returns both the next key
event in the FIFO (if there is one) and the FIFO status.
Up to four of the key-switch outputs function as open-
drain GPOs capable of driving additional LEDs when the
application requires fewer keys to be scanned. For each
key-switch output used as a GPO, the number of moni-
tored key switches reduces by eight.
The device meets ESD requirements for ±8kV contact dis-
charge and 15kV Air-Gap Discharge on all key-switch pins.
Initial Power-Up
On power-up, all control registers are set to power-up
values (Table 1) and the device is in sleep mode.
Table 1. Register Address Map and Power-Up Conditions
ADDRESS
CODE (hex)
READ/WRITE
POWER-UP
VALUE (hex)
REGISTER
FUNCTION
DESCRIPTION
0x00 Read only 0x3F Keys FIFO Read FIFO keyscan data out
0x01
R/W
0x0B Configuration
Power-down, key-release enable, autowake, and I
2
C
timeout enable
0x02
R/W
0xFF Debounce Key debounce time setting
0x03
R/W
0x00 Interrupt
Key-switch interrupt and INT frequency setting
0x05
R/W
0x00 Key repeat Delay and frequency for key repeat
0x06
R/W
0x07 Sleep Idle time to autosleep
0x30
R/W
0xFF Key-switch size Keyscan switch array size
0x31
R/W
0x00
LED driver
enable
LED driver enable register
0x34
R/W
0x00
GPIO
direction 1
GPIO input/output control register 1 for
ROW7–ROW0
0x35
R/W
0x00
GPIO
direction 2
GPIO input/output control register 2 for COL7–COL0
0x36
R/W
0xFF
GPO output
mode 1
GPO open-drain/push-pull output setting for
ROW7–ROW0
0x37
R/W
0x0F
GPO output
mode 2
GPO open-drain/push-pull output setting for
COL7–COL0