CAT3604V

© Catalyst Semiconductor, Inc.

11

Doc. No. MD-5029 Rev. B

Characteristics subject to change without notice

PWM DIMMING

The EN pin is used to provide total Shutdown of the

device as well as High Resolution PWM dimming

control on the LED Channels.

Shutdown of the device occurs after the EN pin has

been held low for 1.5ms. During the “soft-start” power-

up sequence from the shutdown mode, the LED

current typically settles within 40µs (for 1X mode

operation). This LED current settling time becomes

400µs if 1.33X operation is needed (i.e low battery

voltage).

For High Resolution PWM dimming control (typically

frequencies at 2kHz or above), the device will remain

powered and only the LED channels output will be

switched on and off during the PWM (the rest of the

device will remain powered-up). This allows the output

channels to have “instant-on” response, where the

LED current settles within 1µs of the applied PWM

dimming signals. This “instant-on” modes makes the

device suitable for extremely high frequency PWM

dimming schemes.

Figure 5 shows the output current for PWM frequencies

up to 100kHz and with duty cycles of 30% and 70%.

Figure 5. Output current vs. PWM frequency

should meet the following timing limits:

for slow frequency

for fast frequency

10

20

30

40

50

60

70

80

90

100

0.1

1

10

100

PWM FREQUENCY [kHz]

70% DC

30% DC