L6924D MOS Max Current

[TIENHUA]

What's the max current of the mosfet in the L6924D?

We want to use AC adaptor to charge the battery and supply the system loading at the same time. 

So, we want to know the max current of power mosfet.

Thank you.

 

[Peter BENSCH]

Well, the L6924D is a battery charger which, according to the data sheet, is capable of 0.67W at 70°C. If you take this value and the minimum Rdson of 280mohms of the MOSFET, you get a current of I = sqrt(0.67W/280mohms) = 1.547A. Alternatively, you can use the thermal resistance 75K/W, the Rdson, the maximum junction temperature TJ  (125DEGC) and your expected ambient temperature and you will probably get similar values.

However, the problem could be that the fast charge current is programmed according to Rprg and is only available once the pre-charge voltage has been reached.

Hope that helps?

Regards
/Peter

[TIENHUA]

Hi Peter,

Thank you for your reply.

I have one more question.  Does Rdson change with Ichg?  

In the datasheet, the Ichg is 500mA. Is the maximum Rdson the same as 380mohm if now Ichg is 1.3A?  

 

[Peter BENSCH]

The Rdson will increase approximately linearly with the current, but there is no specification for this in the data sheet. However, you can estimate this on the basis of comparable discrete MOSFETs, where the Rdson increases by approx. 3...4% when the current is increased to 260%.

Hope thas helps?

Regards
/Peter