AAT4296 Datasheet, PDF (12/17 Pages) Advanced Analogic Technologies – Five/Six Channel Push/Pull I/O Expander

AAT4296/98
Five/Six Channel Push/Pull I/O Expander
The S²Cwire interface relies on the number of ris-
ing edges of the EN/SET pin to address and load
the registers. S²Cwire latches data or address
after the EN/SET pin has been held high for time
T_LAT. The interface records rising edges of the
EN/SET pin and decodes them into 32 (for
AAT4296) or 64 (for AAT4298) different states, as
indicated in Table 1. There are 32 (for AAT4296)/
64 (for AAT4298) different sequences for control-
ling individual turn-on/turn-off of each switch. The
counter can be clocked at speeds up to 1MHz,
such that intermediate states are not visible.
Alternatively, the EN/SET clock pulses may be
entered one at a time for desired setting. The first
rising edge of EN/SET enables the IC and turns all
the switches ON. Once the final clock cycle is
received, the EN/SET pin is held high to maintain
the device setting. The device is disabled 500µs
(T_OFF) after the EN/SET pin transitions to a logic
low state.
OUTn
EN/SET
T_H T_L
T_LAT
T_ON
Figure 3: Timing Diagram.
T_O T_OFF
Applications Information
The AAT4296 and AAT4298 have been designed
so that no external parts are required for the device
to function as a general purpose I/O expander.
Such external parts could include bypass capaci-
tors, or pull-up or pull-down resistors.
For applications which may use some or all of the
output to switch light load current levels to applica-
tion circuits, good engineering practice would dic-
tate the use of small bypass capacitors place on
the V_CC input and each output which is being used
to conduct current to a load. The use of small
ceramic capacitors between the input and output
nodes to ground will aid in reducing line and load
transient response effects. Refer to the application
schematic of Figure 4 for an example for placing
bypass capacitors.
Input Capacitor
Typically a 0.1µF to 1µF capacitor is recommend-
ed for C_IN in most applications. A C_IN capacitor is
not required for basic operation; however, C_IN is
useful in preventing load transient effects from
affecting upstream circuits when internal switches
are enabled to their respective output load circuits.
12
C_IN should be located as close to the device V_IN pin
as practically possible.
There is no specific capacitor equivalent series
resistance (ESR) requirement for C_IN; however, for
higher current operation, ceramic capacitors are rec-
ommended for CIN due to their inherent capability
over tantalum or aluminum electrolytic capacitors to
withstand input current surges from low impedance
sources, such as batteries in portable devices.
Output Capacitor
For typical applications where the AAT4696/98 is
used for I/O expansion, no output capacitors are
required. Many other common applications such
as controlling LED indicator lamps in portable prod-
ucts do not require an output capacitor because
the end load is not sensitive to device turn-on tran-
sient effects.
For improved load transient response in systems
using the AAT4296/98 for load switching, the addi-
tion of a small output capacitor placed between the
output pins and ground can have a beneficial
effect. A 0.1µF ceramic capacitor is suggested as
a reasonable value for an output capacitor. Please
refer to Figure 4.
4296.2006.02.1.1