HELP: BATTERY CHARGER USING MC33340 IC

[charudatt]

I am working on a design of a Ni-MH battery charger using ON- SEMI's IC MC33340.

I am a bit confused in determining the values of R2/R1 the voltage divider circuit on Pin#1.

I am interested in charging 4 (1.2V) @2500mAH Ni-MH cells in series with the proposed charger.

Could anyone help me derive the values of these resistors using the formula mentioned in the DS.

Has anyone successfully built a Smart Charger using this chip ?

regards

[titi]

Hi charudatt,

Effectively datasheet explications are not realy clear.

I have understand that Vsen (pin 1) can't exceed 2v, so they say : In order to obtain maximum sensing accuracy, the
R2/R1 voltage divider must be adjusted so that the Vsen input
voltage is slightly less than 2.0 V when the battery pack is
fully charged.

So, if you have 4 elements, as you can see in datasheet Figure 9, the max voltage in 1.55v for full charge so VBatt is 1.55*4.
use 1.8v for Vsen (too have goot sensitivity)
You need to fixe R1
And use formula R2=R1*((VBatt/Vsen)-1)

I have found a application schematic for MC33340 with 4 elements (they used R1=560K and R2=1M) page 2

May be this help you.

Best regards.

[charudatt]

Thank you Titi. I shall try it and post my finding.

regards