CAT3614 Datasheet, PDF (10/12 Pages) Catalyst Semiconductor – 4-Channel 1-Wire LED Driver in 3x3mm Package

CAT3614
LED Current Setting
Figure 2 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 10 ms or longer to ensure the initialization of the
driver at power−up. Each subsequent pulse on the EN/DIM
(300 ns to 200 ms pulse duration) steps down the LED
current from full scale of 31 mA to zero with a 1 mA
resolution. Consecutive pulses should be separated by
300 ns or longer. Pulsing beyond the 0 mA level restores the
current level back to full scale and the cycle repeats. Pulsing
frequencies from 5 kHz up to 1 MHz can be supported
during dimming operations. When the EN/DIM is held low
for 1.5 ms 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 28.
Protection Mode
If an LED becomes open−circuit, the output voltage
VOUT is internally limited to about 5.5 V. 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 +165°C. When the device
1 mF
1 mF
temperature drops down by about 20°C, the device resumes
normal operation.
External Components
The driver requires a total of four external 1 mF 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 1 mF 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 1 MHz. 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.
1 mF
1 mF
V_IN
3 V to
5.5 V
C_IN
1 mF
ENABLE/
DIMMING
C1+ C1− C2+ C2−
VIN
VOUT
CAT3614
LED1
LED2
EN/DIM
LED3
GND ^LED4
C_OUT
1 mF
V_IN
3 V to
5.5 V
C_IN
1 mF
ENABLE/
DIMMING
C1+ C1− C2+ C2−
VIN
VOUT
CAT3614
EN/DIM
GND
LED1
LED2
LED3
LED4
C_OUT
1 mF
Flash
LED
120 mA
Figure 28. Three LED Application
Figure 29. Single Flash LED Application
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