CAT3636_07 Datasheet, PDF (8/16 Pages) Catalyst Semiconductor – 6-Channel Quad-ModeTM Fractional LED Driver in TQFN3x3

CAT3636
BLOCK DIAGRAM
C_1-
C₁₊
C_2- C₂₊
V_IN
1x mode (LDO)
1.33x, 1.5x, 2x Charge Pump
V_OUT
EN/SET
0.8, 1.1MHz
Oscillator
Mode Control
100kΩ
Serial
Interface
Referece
Voltage
Registers
Current
Setting DAC
LEDA1
LEDA2
LEDB1
LEDB2
LEDC1
LEDC2
6 Current
Sink Regulators
GND
Figure 2. CAT3636 Functional Block Diagram
BASIC OPERATION
At power-up, the CAT3636 starts operating in 1x
mode where the output will be approximately equal to
the input supply voltage (less any internal voltage
losses). If the output voltage is sufficient to regulate all
LED currents, the device remains in 1x operating
mode.
If the input voltage is insufficient or falls to a level
wher e the regulated currents cannot be maintained,
the device automatically switches into 1.33x mode
(after a fixed delay time of about 400μs). In 1.33x
mode, the output voltage is approximately equal to
1.33 times the input supply voltage (less any internal
voltage losses).
If the input voltage is insufficient again or falls to a
level where the regulated currents cannot be
maintained, the device will automatically switch to the
1.5x boost mode (after a fixed delay time of about
400μs). In 1.5x mode, the output is approximately
equal to 1.5 times the input supply voltage (less any
internal voltage losses).
If the input voltage fails more or is still insufficient to
drive the LEDs, it will automatically switch again into
2x mode where the output is approximately equal to 2
times the input supply voltage (less any internal
voltage losses).
If the device detects a sufficient input voltage is
present to drive all LED currents in 1x mode, it will
change automatically back to 1x mode. This only
applies for changing back to the 1x mode
Doc. No. 5020 Rev. C
8
© 2007 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice