AATIAN36 Datasheet, PDF (2/7 Pages) SiGe Semiconductor, Inc. – Step-Up DC/DC Converter

EV-130
AAT1231 EVAL: Step-Up DC/DC Converter
for White LED Backlight Applications
Getting Started
The ballast resistor (R1) is set to 30.1Ω on the evaluation board. This sets the maximum LED current to 20mA.
I_LED =
V_FB
R₁
Over-voltage protection is set to the maximum operation voltage (24V) to protect the IC from damage.
There are three (3) buttons on the evaluation board. The modes of operation are detailed in Table 1. Each
button controls a particular function. The SW1 (Up) button increments the number of EN/SET edges, and the
AAT1231 increases the FB pin voltage according to Table 2. By holding down the Up button for more than 1.5
seconds, the microcontroller enters auto-increment mode. The SW2 (Down) button decrements the number
of EN/SET edges and the AAT1231 decreases the FB pin voltage. By holding down the Down button for more
than 1.5 seconds, the microcontroller enters auto-decrement mode. The SW3 (Select) button toggles
High/Low on the SEL pin. A green LED (D8) indicates the status on the SEL pin. If the green LED turns ON,
the SEL pin is set to High. If the green LED turns off, the SEL pin is set to Low. Figure 2 details the LED nom-
inal current levels for SEL=High and SEL=Low settings with R1=30.1Ω.
25
20
SEL = HIGH
15
10
(Default)
5
SEL = LOW
0
1
4
7
10
13
16
S²Cwire Data Register
Figure 2: Programming LED Current with R_BALLAST = 30.1Ω.
Upon initial power-up and prior to S²Cwire programming, the default FB pin voltage is set at 0.1V/0.3V depend-
ing on the SEL pin logic level. The red LED (D7) should illuminate, indicating that power has been connected
to the evaluation board.
2
EV-130.2006.08.1.0