LM3633: COUT

Hi Randy,

Thanks for your information.
However, 2x mode is for Low-Voltage LED control.
In my circuit, the string LEDs are connect to High-Voltage LED control bank.
How to get high voltage at C12 (in my circuit)?

Best Regards,
Alan.Lin

Hi Alan,

My apology for misreading your post, yes there is an initialization sequence required top turn on the boost output.

The initialization sequence is:

0x10 = 0x00 ; assign leds to control bank A

0x28 = 0x07 ; enable boost feedback on HVLED1,2,3

0x2D = 0x03 ; OVP = 24V, fsw=1MHz

0x2F = 0x0D ; PWM Zero Detect = Enabled, PWM Polarity = Active High, Control B PWM = Disabled, Control A PWM = Enabled

0x2B = 0x01 ; Enable Control Bank A

0x40 = (non-zero value) ; Control A Brightness LSB, range 0 to 7

0x41 = (non-zero value) ; Control A Brightness MSB, range 0 to 255

If PWM is low boost will remain off until you apply PWM pulse > 750 nsec.

Randy

Hi Randy,

Set the registers and values as below:
0x10 = 0x00
0x28 = 0x07
0x2D = 0x03
0x2F = 0x0D
0x2B = 0x01
0x40 = 0x07
0x41 = 0xFF

And, the PWM pulse = 1 usec.
The voltage at C12 was still 3.3V.
What's the problem?

BR,
Alan.Lin

Hi Alan,

What is the voltage on HVLED1,2,3 (B1,C1,D1)?
If the voltage on these pins is > 0.5V the boost will not turn on.
One other thing to try would be to disable the PWM input (reg 0x2f = 0).

Best regards,
Randy

Hi Randy,

1. The voltage on HVLED1,2,3 is 30 mV.
2. To disable (reg 0x2f = 0), the voltage on COUT is still 3.3 V.
3. To check the data sheet of LM3633, the capacitance of COUT need to be 1 uF. However, it is 47 uF on my circuit. Will it affect anything?

Best Regards,
Alan.Lin