MB96F6B5RBPMC : Max range of external divider resistors for segment LCD

[WonjinHan]

Dears.

Now our customer used MB96F6B5RBPMC to design HVAC controller.

For the segment LCD power part, this DUT is designed to use external divider resistors  as the following.

For the detail, you can find the below real implemented-schematic

Now they have a techincal issue like when this HVAC controller is operated,

the brightness of LCD gets rather darker than regular condition.

So we are taking into account to replace 10KΩ(R161 ~ R164) with 1KΩ or 4.7KΩ.

Q>
What recommended Min and Max range of each resistor value of external divider part it is ? 

It looks like that is related to the performance of internal N-ch FET such as max drain current. 

Best regards,

Kevin Han

[SungH_31]

Dear Kelvin Han,

I think R161 id different with R162,R163, R164 because it's VR for brightness and contrast depends on LCD specification as below in TRM.

And R162, R163, R164 depends on your LCD as below description in TRM.

There is no detail information about N-ch FET in TRM but CMOS level output of the P03_0/V0 pin is 4mA.

If these N-ch FET have same specification, you can use 1KΩ for external divider.

Because current to N-ch FET depends sum of RX*3+VR.

BTW, I think you would recommend investigate LCD specification to find appropriate resistor value.

Best Regards,

Sungsik Hong

[SungH_31 · Accepted solution]

Dear Kelvin Han,

I think R161 id different with R162,R163, R164 because it's VR for brightness and contrast depends on LCD specification as below in TRM.

And R162, R163, R164 depends on your LCD as below description in TRM.

There is no detail information about N-ch FET in TRM but CMOS level output of the P03_0/V0 pin is 4mA.

If these N-ch FET have same specification, you can use 1KΩ for external divider.

Because current to N-ch FET depends sum of RX*3+VR.

BTW, I think you would recommend investigate LCD specification to find appropriate resistor value.

Best Regards,

Sungsik Hong