TLC59116-Q1: How to calculate the resistance value

Koji Hayashi92

Mastermind 7030 points

Part Number: TLC59116-Q1
Other Parts Discussed in Thread: TLC5941-Q1

Hi All

My customer is trying to use it under the following conditions.

VLED = 16 V

Iout = 40 mA/ch

Temp MAX = 80 ° C

Number of LEDs: 15 para

Number of channels = 15 ch

When calculating the maximum allowable loss, 0.9 W @ 80 ° C. (150-80)/78=0.9W

40 mA * (16 - Vf) V = 7.8 W @ Vf = 3

It will exceed the maximum allowable loss.

We are trying to add a resistor as a countermeasure.

How is it correct to calculate the resistance value?

Best Regards,
Koji Hayashi

over 7 years ago

0 Anda Zhang over 7 years ago

TI__Expert 5380 points

Hi Hayashi-san,

Leave 1V headroom on outputs will be enough for the constant current output. Based on this value to choose suitable resistor.

0 Koji Hayashi92 over 7 years ago in reply to Anda Zhang

Mastermind 7030 points

Hi Anda-san

Thank you for quick response.

I understood that Vo is 1V over.

However, the heat loss needs to be 0.9 W or less.

In the case of 0.04 A,

(16-3 - Res * 0.04) * 0.04 * 15 <0.9

Res is 287.5 Ω or more.

Output current error is ± 10%.

If it varies to 0.044 A using 287.5 Ω,

The　maximum allowable loss is (16-3-287.5 * 0.044) * 0.044 = 0.231 and there is no problem.

Vo = (16-3 - 287.5 * 0.044) = 0.35 V, but 1 V can not be satisfied.

Is the above calculation method correct?

Best Regards,
Koji Hayashi

0 Anda Zhang over 7 years ago in reply to Koji Hayashi92

TI__Expert 5380 points

Hayashi-san,

Actually from Figure 2 in TLC59116-Q1 datasheet, 0.35V can still guarantee the 40mA output current.

But if you can reduce the LED supply voltage to 5V, it will leave more margin for the design.

0 Koji Hayashi92 over 7 years ago in reply to Anda Zhang

Mastermind 7030 points

Hi Anda-san

Thank you for quick response.

In addition to variations in the output current, Vo will be much lower when considering variations in Vf and variations in VLED.

I think it impossible to add resistance under customer conditions.

Is　it correct?

Best Regards,
Koji Hayashi

0 Anda Zhang over 7 years ago in reply to Koji Hayashi92

TI__Expert 5380 points

Hi Hayashi-san,

Considering this condition, it is a big challenge.

May I know what is the application? As you know, TLC59116-Q1 thermal performance is not very good, as there is no thermal pad under the device. If customer can choose TLC5941-Q1, the situation will be much easier.

0 Koji Hayashi92 over 7 years ago in reply to Anda Zhang

Mastermind 7030 points

Hi Anda-san

Thank you for response.
I understood.

Best Regards,
Koji Hayashi

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TLC59116-Q1: How to calculate the resistance value