AAT4295 Datasheet, PDF (11/16 Pages) Advanced Analogic Technologies – Single/Dual RGB Controller

AAT4295/97
Single/Dual RGB Controller
Sn
EN/SET
T_H T_L
T_LAT ^T_ON
T_O T _OFF
Figure 3: EN/SET Timing Diagram.
Application Information
External Component Selection
The AAT4295 and AAT4297 have been designed
so that no external parts are required for the device
to function as a general purpose three- or six-posi-
tion low-side switch. For some applications, the
addition of bypass capacitors or pull-up or pull-
down resistors may be desired to improve overall
system performance.
For lighting applications, such as controlling RGB
LEDs, keypad or display backlight LEDs, or photo
flash LEDs, no bypass capacitors are necessary.
For other general purpose load switching applica-
tions which may use some or all of the outputs to
switch light load current levels to application cir-
cuits, good engineering practice would dictate the
use of small bypass capacitors placed on the V_CC
input and each switch connection that is used to
conduct current from the load to ground. The use
of small ceramic capacitors between the input and
output nodes will aid in reducing line and load tran-
sient response effects when the load switch on a
given output is turned on or off.
Input Capacitor
Typically, a 0.1µF capacitor is recommended for
C_IN in most applications to provide input line tran-
sient response immunity to small changes in the
input supply. A C_IN capacitor is not required for
basic operation. If used, 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
recommended for C_IN due to their inherent capabil-
ity over tantalum or aluminum electrolytic capaci-
tors to withstand input current surges from low
impedance sources, such as batteries in portable
devices.
Output Capacitor
For typical applications where the AAT4295/97 is
used for LED lighting control, no output capacitors
are required because the end load is not sensitive
to device turn-on or turn-off transient effects.
For improved load transient response in systems
using the AAT4295/97 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.
The output capacitor has no specific capacitor type
or ESR requirement. If desired, C_OUT may be
increased to a value greater than 0.1µF without
limit to accommodate any load transient condition
without adversely affecting the device turn-on slew
rate time.
Thermal Considerations
The AAT4295 and AAT4297 are designed to sink a
continuous load current to ground when a respec-
tive switch is enabled via the S²Cwire control. The
limiting characteristic for maximum safe operating
load current through a given switch or set of switch-
es is package power dissipation. In order to obtain
high operating currents, careful device layout and
circuit operating conditions must be taken into
account. At any given ambient temperature (T_A),
the maximum package power dissipation can be
determined by the following equation:
P_D(MAX)
=
T_J(MAX) - T_A
θ_JA
Constants for the AAT4295 are maximum junction
temperature, T_J(MAX) = 125°C, and package thermal
resistance, θ_JA = 225°C/W. Worst case conditions
are calculated at the maximum operating tempera-
4295.2006.03.1.3
11