AAT2400 Datasheet, PDF (13/32 Pages) Skyworks Solutions Inc. – Sixteen-Channel White LED Driver Solution

DATA SHEET
AAT2400/2401
Sixteen-Channel White LED Driver Solution
with Full LED Current and Timing Control
Functional Description
The AAT2400 consists of a high efficiency DC/DC boost
controller, an integrated slew rate controlled input dis-
connect MOSFET switch, and a MOSFET power switch. A
high voltage rectifier, power inductor, output capacitor,
feedback compensation network, and OVP resistor divid-
er network are required to implement a DC/DC boost
converter.
The AAT2400’s boost controller is designed to deliver
1600mA up to 40V. It can drive a total of 16 current
regulated sinks (8 from its own and 8 from AAT2401) with
10 HB white LEDs connected in series at each channel.
The maximum LED sink current can be set by an exter-
nal resistor. Each current sink can be programmed
through the SPI interface. Each sink allows independent
control with different registers (DOT correction, Gray
Scale, Delay, On/Off control configuration).
AAT2400 and AAT2401 both provide one linear regulator
for VCCIO supply.
Control Loop
The AAT2400 provides the benefits of current mode con-
trol with a simple feedback loop. The device maintains
exceptional DC regulation, transient response, and cycle-
by-cycle current limit with additional RC compensation
components. The AAT2400 modulates the power MOSFET
switching current in response to changes in output volt-
age (LED voltage). This allows the voltage loop to directly
program the required inductor current in response to
changes in the output load. The switching cycle initiates
when the N-channel MOSFET is turned ON and current
ramps up in the inductor. The ON interval is terminated
when the feedback signal crossover the falling edge of the
saw wave from the PWM modulator. During the OFF inter-
val, the inductor discharges the energy (inductor ramps
down) until the lower threshold, or zero inductor current,
is reached. The lower current is equal to the peak current
minus a preset hysteresis threshold which determines the
inductor ripple current. The peak current is adjusted by
the controller until the output current requirement is met.
The magnitude of the feedback error signal determines
the average input current. Therefore, the AAT2400 con-
troller implements a programmed current source con-
nected to the output capacitor and load resistor. There is
no right-half plane zero, and loop stability is achieved with
simple RC compensation components.
Soft Start / Enable
The input disconnect switch is activated when a valid
supply voltage is present and the EN/SET pin is strobed
high. Slew rate control on the input disconnect switch
ensures minimal inrush current as the output voltage is
charged to the input voltage, prior to switching of the
N-channel power MOSFET. A monotonic turn-on is guar-
anteed by the built-in soft-start circuitry, which elimi-
nates output current overshoot across the full input volt-
age range and over all load conditions.
Current Limit and
Over-Temperature Protection
The switching of the N-channel MOSFET terminates when
a current limit of 6.5A (max) is exceeded. This minimizes
power dissipation and component stresses under over-
load and short-circuit conditions. Switching resumes
when the current decays below the current limit. Thermal
protection disables the AAT2400/AAT2401 when the
internal power dissipation causes the junction tempera-
ture to reach the thermal limit threshold (140°C, nomi-
nal). When the thermal threshold is reached, the control
register, CTL1 or CTL2, is reset to 00h and all current
sinks are disabled. When the AAT2400's thermal thresh-
old is reached, the boost converter is also disabled.
Over-Voltage Protection
Over-voltage protection prevents damage to the AAT2400
during open-circuit on any LED channel sinks causing
high output voltage conditions. An over-voltage event is
defined as a condition where the voltage on the OVP pin
exceeds the over-voltage threshold limit (V_OVP = 1.2V
typical). When the voltage on the OVP pin has reached
the threshold limit, the converter stops switching and
the output voltage decays. Switching resumes when the
voltage on the OVP pin drops below the lower hysteresis
limit, maintaining an average output voltage between
the upper and lower OVP thresholds multiplied by the
resistor divider scaling factor.
Under-Voltage Lockout
Internal bias of all circuits is controlled via the V_IN input.
Under-voltage lockout (UVLO) guarantees sufficient VIN
bias and proper operation of all internal circuitry prior to
soft start.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
202307A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 24, 2012
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