TCA8418 Datasheet, PDF (8/37 Pages) Texas Instruments – I2C CONTROLLED KEYPAD SCAN IC WITH INTEGRATED ESD PROTECTION

TCA8418
SCPS215 – SEPTEMBER 2009 ......................................................................................................................................................................................... www.ti.com
At power on, the GPIOs (ROW0–7 and COL0–9) are configured as inputs with internal 100-kΩ pullups enabled.
However, the system master can enable the GPIOs to function as inputs, outputs or as part of the keypad matrix.
GPIOs not used for keypad control can be used to support other control features in the application.
ROW7–ROW0 are configured as inputs in GPIO mode with a push-pull structure, at power-on. In keyscan mode,
each has an open-drain structure with a 100-kΩ pullup resistor and is used as an input.
COL9–COL0 are configured as inputs in GPIO mode with a push-pull structure, at power on. In keyscan mode,
each has an open-drain structure and is used as an output.
The system master can reset the TCA8418E in the event of a timeout or other improper operation by asserting a
low in the /RESET input, while keeping the V_CC at its operating level.
A reset can be accomplished by holding the RESET pin low for a minimum of t_W. The TCA8418E registers and
I²C/SMBus state machine are changed to their default state once RESET is low (0). When RESET is high (1),
the I/O levels at the P port can be changed externally or through the master. This input requires a pull-up resistor
to VCC, if no active connection is used.
The power-on reset puts the registers in their default state and initializes the I²C/SMBus state machine. The
RESET pin causes the same reset/initialization to occur without depowering the part. The RESET pin can also be
used as a shutdown pin, if the phone is closed.
The open-drain interrupt (INT) output is used to indicate to the system master that an input state (GPI or ROWs)
has changed. INT can be connected to the interrupt input of a microcontroller. By sending an interrupt signal on
this line, the remote input can inform the microcontroller if there is incoming data on its ports without having to
communicate via the I²C bus. Thus, the TCA8418E can remain a simple slave device.
The TCA8418E has key lock capability, which can trigger an interrupt at key presses and releases, if selected
Power-On Reset
When power (from 0 V) is applied to V_CC, an internal power-on reset holds the TCA8418E in a reset condition
until V_CC reaches V_POR. At that time, the reset condition is released, and the TCA8418E registers and I²C/SMBus
state machine initialize to their default states. After that, V_CC must be lowered below 0.2 V and back up to the
operating voltage for a power-reset cycle.
Power-On Reset Requirements
In the event of a glitch or data corruption, TCA8418E can be reset to its default conditions by using the power-on
reset feature. Power-on reset requires that the device go through a power cycle to be completely reset. This
reset also happens when the device is powered on for the first time in an application.
The two types of power-on reset are shown in Figure 1 and Figure 2.
V_CC
Ramp-Up
Ramp-Down
Re-Ramp-Up
V_{CC_TRR_GND}
V_{CC_RT}
V_{CC_FT}
Time to Re-Ramp
V_{CC_RT}
Time
Figure 1. V_CC is Lowered Below 0.2 V or 0 V and Then Ramped Up to V_CC
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