LP8556: use at low frequency operation

user021864

Intellectual 2145 points

Part Number: LP8556
Other Parts Discussed in Thread: LP8555, TPS61199

Hi,

My customer is having below questions:

PWM pin is used for dimming mode control, so frequency is from 100Hz to 22K.

In our application, we use direct PWM as LED one/off control, so IC might work as low as 60Hz.

Can you help to check if using directly PWM mode, can we use 60~120Hz 5% duty for this IC?

Please let us know if there are further information needed.

Thanks a lot.

over 5 years ago

0 Sean Zhou over 5 years ago

TI__Mastermind 22745 points

Hi Sir,

Some VR projects has used LP8556 with direct PWM mode, it can support 60-120Hz, but for such kind of low frequency, the output voltage ripple will be large, so pay attention for such kind of application, it better to add more output capacitor to aviode such kind of ripple issue.

Regards

Sean

0 user4134045 over 5 years ago in reply to Sean Zhou

Intellectual 320 points

Sean

Thanks for advise, How about LP8555, Same design concept with this?

Yihung

0 Sean Zhou over 5 years ago in reply to user4134045

TI__Mastermind 22745 points

Hi Yihuang,

LP8555 can't support direct PWM mode, it is a little different from LP8556.

Regards

Sean

0 user4134045 over 5 years ago in reply to Sean Zhou

Intellectual 320 points

Sean

Try to find a BL driver with below requirement, please advise IC for us

1. VIn typical voltage is 12V

2. LED current is 70mA

3. Direct PWM control LED

4. PWM frequency is 60~120Hz

5. Vout is around 21V

6. Channel# is around 6 channel ( if you didn't have 6 channel for 70mA, you can advise 12ch with 40mA)

0 Sean Zhou over 5 years ago in reply to user4134045

TI__Mastermind 22745 points

Hi Sir,

LP8555 and TPS61199 maybe a good solution, what's the detail application?

Regards

Sean

0 user4134045 over 5 years ago in reply to Sean Zhou

Intellectual 320 points

Sean

But seem LP8555 and TPS61199 didn't support direct PWM mode.

We use pulse mode current for LCM in VR product.

Yihung

0 Sean Zhou over 5 years ago in reply to Sean Zhou

TI__Mastermind 22745 points

Hi Sir,

TPS61199 can support direct PWM dimming.

Regards

Sean

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LP8556: use at low frequency operation