PRODUCT DATASHEET
AAT3195
ChargePump
TM
4-Channel Charge-Pump LED Driver
Functional Block Diagram
C+
C–
OUT
IN
Two-Mode
CP Control
4
D1
D2
V
F
Monitoring
D3
D4
AGND
I
REF
EN/SET
(EN/PWM)
S
2
Cwire Control
(PWM Control)
DAC
RSET
Functional Description
The AAT3195 charge-pump solution is designed to drive
up to four white LEDs. The charge pump operates from
a 2.7V to 5.5V power source and converts it to voltage
levels necessary to drive the LEDs. LED current is indi-
vidually controlled through integrated current sinks pow-
ered from the output of the charge pump. Low 1x
charge-pump output resistance and low-drop voltage
current sinks allow the charge pump to stay in 1x mode
with an input voltage as low as 3.75V and LED forward
voltages as high as 3.5V. Once in 2x mode, the charge
pump monitors the input supply voltage and automati-
cally switches back to 1x mode when there is sufficient
input voltage.
The AAT3195 requires only three external components:
one 1μF ceramic capacitor for the charge pump flying
capacitor (C
P
), one 1μF ceramic capacitor at the IN pin
(C
IN
), and one 1μF ceramic capacitor at the OUT pin
(C
OUT
). The four constant-current outputs of the AAT3195-
1 (D1 to D4) can drive four individual LEDs with a max-
imum current of 30mA each or, in the case of the
AAT3195-2, with a maximum current up to 20mA.
AnalogicTech’s single-wire S
2
Cwire serial interface
enables the AAT3195-1/-2 and changes the current sink
current in 32 steps through the EN/SET pin. The
AAT3195-3 uses an external PWM signal to enable the IC
and control the brightness of the LEDs.
S
2
Cwire Interface (AAT3195-1/-2 Only)
The LED output current of the AAT3195-1/-2 is controlled
by AnalogicTech’s S
2
Cwire serial interface. Since the LED
current is programmable, no PWM or additional control
circuitry is needed to control LED brightness. This feature
greatly reduces the burden on a microcontroller or sys-
tem IC to manage LED or display brightness, allowing
the user to “set it and forget it.” With its high-speed
serial interface (1MHz data rate), the LED current can be
changed quickly and easily. Also the non-pulsating LED
current reduces system noise and improves LED reliabil-
ity. The S
2
Cwire interface relies on the number of rising
edges to the EN/SET pin to set the register. A typical
write protocol is a burst of EN/SET rising edges, followed
by a pause with EN/SET held high for at least t
LAT
(500μs).
The programmed current is then seen at the current sink
outputs. When EN/SET is held low for an amount of time
longer than t
OFF
(500μs), the AAT3195-1/-2 enters shut-
down mode and draws less than 1μA from the input and
the internal data register is reset to zero.
The AAT3195-1/-2’s serial interface reduces the LED
current on each rising pulse of the enable input. If the
AAT3195-1/-2 is in shutdown, the first rising edge of
the EN/SET input turns on the LED driver to the maxi-
mum current. Successive rising edges decrease the
LED current as shown in Table 1 and Figure 2 for the
AAT3195-1/-2.
3195.2009.06.1.3
www.analogictech.com
9
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