AAT4290/91
I/O Expander Load Switches with Serial Control
Functional Block Diagram
OUT1
OUT2
OUT3
OUT4*
IN
OUT5*
UVLO
Control Logic
and Level Shift
ROM
S2Cwire Interface
EN/SET
GND
*AAT4290 only
and monitoring of the MOSFET gate voltage.
When the device is switched ON, the gate voltage
is quickly increased to the threshold level of the
MOSFET. Once at this level, the current begins to
slew as the gate voltage is slowly increased until
the MOSFET becomes fully enhanced. Once it
has reached this point, the gate is quickly
increased to the full input voltage and RDS(ON) is
minimized.
Functional Description
The AAT4290 consists of five P-channel MOSFET
power switches designed for I/O expansion appli-
cations. The AAT4291 has all of the features
offered in the AAT4290, but integrates three
switches instead of five. It operates with input volt-
ages ranging from 1.8V to 5.5V which, along with
its extremely low operating current, makes it ideal
for battery-powered applications. In cases where
the input voltage drops below 1.8V, the AAT4290
MOSFETs are protected from entering the linear
region of operation by automatically shutting down.
In addition, the TTL-compatible EN/SET pin makes
the AAT4290 an ideal level-shifted load switch. An
optional slew rate controlling feature eliminates in-
rush current when a MOSFET is turned on, allow-
ing the AAT4290 to be implemented with a small
input capacitor or no capacitor at all, while main-
taining isolation between channels. During slew-
ing, the current ramps linearly until it reaches the
level required for the output load condition. The
proprietary control method works by careful control
The ON/OFF state of the five MOSFET switches
are controlled by the EN/SET serial data input. An
internal control counter is clocked on the rising
edge of the EN/SET pin and is decoded into the 32
possible states of the MOSFET (see Table 1). The
counter rolls over after 32 clocks and the table
repeats. The counter can be clocked at speeds up
to 1MHz, but the count value is not latched until
clocking has stopped and the EN/SET pin has
remained high for approximately 2.6µs. The first
rising edge of EN/SET enables the AAT4290 and is
counted as the first clock. To change states, addi-
tional low going clock pulses may be asserted on
the EN/SET pin with the resulting change taking
8
4290.2006.03.1.2
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
