CAT3643_0710 Datasheet, PDF (12/17 Pages) Catalyst Semiconductor – 3-Channel Ultra High Efficiency Quad-Mode™ LED Driver

CAT3643
Unused LED Channels
For applications not requiring all the channels, it is
recommended the unused LED pins be tied directly to
V_OUT (see Figure 4).
1µF
1µF
V_IN
C_IN
1µF
ENABLE
DIMMING
R_SET
C1+
V_IN
C1- C2+
C2-
V_OUT
CAT3643
EN/DIM
RSET
GND
LED1
LED2
LED3
C_OUT
1µF
Figure 4. Application with 2 LEDs
Protection Mode
If an LED is disconnected, the driver senses that and
automatically ignores that channel. When all LEDs are
disconnected, the driver goes to 1x mode where the
output is equal to the input voltage.
As soon as the output exceeds about 6V, the driver
resets itself and reevaluate the mode.
External Components
The driver requires four external 1μF ceramic capaci–
tors for decoupling input, output, and for the charge
pump. Both capacitors type X5R and X7R are
recommended for the LED driver application. In all
charge pump modes, the input current ripple is kept
very low by design and an input bypass capacitor of
1μF is sufficient.
In 1x mode, the device operates in linear mode and
does not introduce switching noise back onto the
supply.
Recommended Layout
In charge pump mode, the driver switches internally at
a high frequency. It is recommended to minimize trace
length to all four capacitors. A ground plane should
cover the area under the driver IC as well as the
bypass capacitors. Short connection to ground on
capacitors C_IN and C_OUT can be implemented with the
use of multiple via. A copper area matching the TQFN
exposed pad (TAB) must be connected to the ground
plane underneath. The use of multiple via improves
the package heat dissipation.
Pin1
C2
If the die temperature exceeds +150°C, the driver will
RSET
enter a thermal protection shutdown mode. When the
EN/DIM
device temperature drops by about 20°C, the device
C1
will resume normal operation.
LED Selection
C_OUT
C_IN
LEDs with forward voltages (V_F) ranging from 1.3V to
GND
VIN
4.3V may be used. Selecting LEDs with lower V_F is
GND
recommended in order to improve the efficiency by
keeping the driver in 1x mode longer as the battery
VOUT
voltage decreases.
Figure 5. TDFN-12 Recommended Layout
For example, if a white LED with a V_F of 3.3V is
selected over one with V_F of 3.5V, the driver will stay
in 1x mode for lower supply voltage of 0.2V. This
helps improve the efficiency and extends battery life.
Doc. No. MD-5022 Rev. E
12
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice