CAT3614_08 Datasheet, PDF (10/13 Pages) Catalyst Semiconductor – 4-Channel 1-Wire LED Driver in 3 x 3mm Package

CAT3614
LED Current Setting
Figure 1 shows the timing diagram necessary at the
EN/DIM input for setting the LED currents.
The EN/DIM set up time requires the signal to be held
high for 10µs or longer to ensure the initialization of
the driver at power-up. Each subsequent pulse on the
EN/DIM (300ns to 200µs pulse duration) steps down
the LED current from full scale of 31mA to zero with a
1mA resolution. Consecutive pulses should be
separated by 300ns or longer. Pulsing beyond the
0mA level restores the current level back to full scale
and the cycle repeats. Pulsing frequencies from 5kHz
up to 1MHz can be supported during dimming
operations. When the EN/DIM is held low for 1.5ms or
more, the CAT3614 enters the shutdown mode and
draws “zero” current.
For applications with three LEDs or less, any unused
LED pins should be tied to VOUT, as shown on Figure 3.
Protection Mode
If an LED becomes open-circuit, the output voltage
VOUT is internally limited to about 5.5V. This is to
prevent the output pin from exceeding its absolute
maximum rating.
The driver enters a thermal shutdown mode as soon
as the die temperature exceeds about +165ºC. When
the device temperature drops down by about 20ºC,
the device resumes normal operation.
External Components
The driver requires a total of four external 1µF
ceramic capacitors: two for decoupling input and
output, and two for the charge pump. Both capacitor
types X5R and X7R are recommended for the LED
driver application. In the 1.5x charge pump mode, the
input current ripple is kept very low by design, and an
input bypass capacitor of 1µF is sufficient. In 1x mode,
the device operating in linear mode does not introduce
switching noise back onto the supply.
Recommended Layout
In 1.5x charge pump mode, the driver switches
internally at a high frequency of 1MHz. 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 Cin and
Cout can be implemented with the use of multiple
vias. A copper area matching the TDFN exposed pad
(GND) must be connected to the ground plane
underneath. The use of multiple vias improves the
package heat dissipation.
1µF
1µF
V_IN
3V to ^CIN
5.5V
1µF
ENABLE/
DIMMING
C1+
VIN
C1- C2+ C2-
VOUT
CAT3614
EN/DIM
GND
LED1
LED2
LED3
LED4
Figure 3. Three LED Application
1µF
1µF
V_IN
C_OUT
1µF
3V to ^CIN
5.5V
1µF
ENABLE/
DIMMING
C1+
VIN
C1- C2+ C2-
VOUT
CAT3614
EN/DIM
GND
LED1
LED2
LED3
LED4
C_OUT
1µF
Flash
LED
120mA
Figure 4. Single Flash LED Application
Doc. No. MD-5035, Rev.B
10
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice