CAT3604A
http://onsemi.com
5
Basic Operation
At power-up, the CAT3604A starts operation in 1x mode.
If it is able to drive the programmed LED current, it
continues in 1x mode. If the battery voltage drops to a level
where the LED current cannot be met, the driver
automatically switches into 1.5x mode. The 1.5x charge
pump will boost the output voltage accordingly to achieve
the nominal LED current.
The operating mode is reinitialized each and every time
the chip is powered up or is taken out of shutdown mode (via
EN pin). The use of the control pins (CTR0, CTR1, CTR2)
does not reconfigure the mode of operation.
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.
The digital control lines CTR0, CTR1 and CTR2 allow to
turn On or Off a combition of LEDs as shown in Table 6.
Table 5. RSET Resistor Selection
LED Current (mA)
R
SET
(kW)
1 649
2 287
5 102
10 49.9
15 32.4
20 23.7
30 15.4
Table 6. LED Selection
Control Lines LED Outputs
CTR2 CTR1 CTR0 LED4 LED3 LED2 LED1
0 0 0 – – – ON
0 0 1 – – ON –
0 1 0 – ON – –
0 1 1 ON − – –
1 0 0 – – ON ON
1 0 1 – ON ON ON
1 1 0 ON ON ON ON
1 1 1 – – – –
NOTE: 1 = logic high (or VIN)
0 = logic low (or GND)
– = LED output OFF
