TPS923653: About Analog Dimming

Hi Steven,

Thanks for the reply.
The minimum ON time for this device is 100ns, so I was wondering if I could follow that.
If the period is 50 kHz, then it is 2000ns, so I think 200 steps of dimming is possible.
If only 64 steps of dimming is possible, then I feel it is fixed at 6 or 8 bits.

Best Regards,
Ryu.

Hi Ryu,

Ryu Yamashita said:

The minimum ON time for this device is 100ns, so I was wondering if I could follow that.

I am wondering if you misinterpret the "switching FET minimum on time" (t_min_ON in Section 7.5 Electrical Characteristics from the datasheet) here as the minimum the pulse for the AIDM/HD.

Ryu Yamashita said:

If only 64 steps of dimming is possible, then I feel it is fixed at 6 or 8 bits.

This device only has 8-bit resolution (256 steps) for analog dimming. You cannot have more steps than this value.

Best Regards,

Steven

Hi Steven,

Steven Li said:

I am wondering if you misinterpret the "switching FET minimum on time" (t_min_ON in Section 7.5 Electrical Characteristics from the datasheet) here as the minimum the pulse for the AIDM/HD.

What is the minimum pulse for AIDM?

Steven Li said:

This device only has 8-bit resolution (256 steps) for analog dimming. You cannot have more steps than this value.

What does 8 bits only mean?
I believe that frequencies above 39khz will be 6bit dimming.
My understanding is that there is a minimum ON time and the cycle/minimum ON time can be the resolution.

Best Regards,
Ryu.

Hi Ryu,

Ryu Yamashita said:

What is the minimum pulse for AIDM?

The minimum on-time of the PWM pulse after the first is 100 ns for the digital circuits to detect the duty cycle. Please refer to Section 8.3.5.2 Analog Dimming from the datasheet.

Ryu Yamashita said:

What does 8 bits only mean?
I believe that frequencies above 39khz will be 6bit dimming.
My understanding is that there is a minimum ON time and the cycle/minimum ON time can be the resolution.

The reference voltage for current sensing is generated by an internal DAC, which has a resolution of 8 bits. This sets the higher limit for the steps of analog dimming that this device can achieve.

Best Regards,

Steven

Hi Steven,

I understand that the maximum is 8 bits, but I am not sure why it is limited to 6 bits.
If the minimum pulse is 150ns, wouldn't the resolution be the period divided by 150ns?

Best Regards,
Ryu.

Hi Ryu,

Steven is OoO, please expect some delay on the response. Thanks for your patience.

BR, Jared

Hi Ryu,

Sorry for the late response.

This is due to the internal ADIM/HD recognition mechanism of the device.

Best Regards,

Steven

Hi Steven,

In other words, regardless of the frequency, if the data sheet is in the 6-bit range, would it be adjusted to 6 bits or less, and if it is in the 8-bit range, would it be adjusted to 8 bits or less?

Best Regards,
Ryu.

Hi Ryu,

Steven is OoO, please expect some delay on the response. Thanks for your patience.

BR, Jared

Hi Ryu,

Sorry for the late response.

Sorry but I may not clearly get you meaning. Let me clarify.

If the ADIM dimming input frequency is within the range of first line below (0.1kHz to 156kHz) shown in the below figure, then you can use 6-bit or less ADIM resolution.

If the ADIM dimming input frequency is within the range of second line (0.1kHz to 39kHz) shown in the below figure, then you can use 8-bit or less ADIM resolution.

You can refer to these parameters in Section 7.5 Electrical Characteristics from the datasheet.

Best Regards,

Steven

Hi Steven,

My point was whether the resolution of dimming is frequency independent.
For example, if the ADIM signal is 40 kHz or 156 kHz, can it be dimmed down to only 6 bits?

Best Regards,
Ryu.

Hi Ryu,

Ryu Yamashita said:

For example, if the ADIM signal is 40 kHz or 156 kHz, can it be dimmed down to only 6 bits?

Yes, it can.

Best Regards,

Steven

Hi Steven,

My apologies.
I guess I didn't get what I wanted to ask.
For example, if you input a 40kHz signal, the period is 25μs.
If the minimum pulse is 150ns, the minimum duty is 150ns/25μs, and the light can be dimmed in 166 steps.
For 156 kHz, the period is 6.4 µs, the minimum duty is 150 ns/6.4 µs, and the dimming can be done in 42 steps.
We would like to know the significance of this being fixed at 6 bits.
Am I wrong in my understanding of analog dimming to begin with?

Best Regards,
Ryu.

Hi Steven,

Let me confirm one point just to be sure.
In the data sheet “8.3.5.2 Analog Dimming” it says that the minimum pulse for the ADIM/HD pin is 100ns.
But you tell me it is 150ns.
Which is correct?

Best Regards,
Ryu.

Hi Ryu,

Our expert will give you reply later.

BR

Patrick