CAT3603 Datasheet, PDF (9/11 Pages) Catalyst Semiconductor – 3-Channel LED Driver in 3x3mm Package

CAT3603
Basic Operation
At power−up, the CAT3603 starts operating in 1x mode
where the output will be approximately equal to the input
supply voltage (minus 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 falls to a level where the regulated
currents cannot be maintained, the device automatically
switches into 1.5x mode.
In 1.5x mode, the output is approximately equal to 1.5
times the input supply voltage (minus any internal voltage
losses), and high enough to achieve the nominal LED
current.
The above sequence is reinitialized every time the chip is
powered−up or is taken out of shutdown mode (via EN pin).
LED Current Setting
The LED current is set by the external resistor R_SET
connected between the RSET pin and ground. Table 5 lists
various LED currents and the associated R_SET resistor value
for standard 1% precision surface mount resistors.
Table 5. RSET Resistor Selection
LED Current [mA]
1
2
5
10
15
20
30
R_SET [kW]
649
287
102
49.9
32.4
23.7
15.4
The unused LED channels must be disabled by connecting
the respective LED pins to VOUT. A disabled channel sinks
only 0.2 mA typical. When the following equation is true on
any channel, the driver turns off the LED channel:
VOUT * V_LED v 1 V (LED channel OFF)
Note: The CAT3603 is designed to drive LEDs with forward
voltage greater than 1 V and is not compatible with resistive
loads less than 5 kW.
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
via. A copper area matching the TDFN exposed pad (GND)
must be connected to the ground plane underneath. The use
of multiple via improves the package heat dissipation.
Figure 22. Recommended Layout
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