10" Tablet Car Charger Circuit

[zejulios]

Hello,

I'm developing a system with a Tablet.
The system will run on a car (12V), and I need to charge the tablet from my circuit.

I think I'll need about 2A for a 10" tablet charger, does anyone have a small/cheap design so I can convert 10-18V of the car to 5V 2A?
I've found out a cheap NCP3170ADR2G, is it worth it? Do you have a better solution?

Also, how do I tell the tablet that my circuit is capable of charging at 2A, since the PC only should supply 500mA?

Thanks for any tip,

ZJ

 

[ZASto]

LM2576-5, 4 additional components required: 10uF/25V Low ESR, 1000uF/10V Low ESR, 100uH/3A choke and 1N5822 diode.

 

[ard]

Hello,

Also, how do I tell the tablet that my circuit is capable of charging at 2A, since the PC only should supply 500mA?
ZJ

This is slightly tricky, different manufacturers use different ways to tell the tablet whether the charger is capable of heavy currents.

Generically, I'd suggest you start by using a spliced USB cable where you short the 2 USB signal pins together at the tablet end. Measure the current your tablet is charging at; if its still drawing 500ma or less, use a potential divider of 2 resistors to give about 2 volts, and connect this point to the 2 shorted d+ and d- pins.

Regards,

Anand

 

[zejulios]

@ZASto
Thanks for the tip.

@ard
My project connects to the tablet, using a micro controller so I need D+ and D- free.
I'll use microchip accessory firmware.

 

[zejulios]

Hello,

What is the main difference from LM2576 and LM2596, besides the frequency...
Which is the best?

Thanks.

 

[ZASto]

Compare the datasheets to figure out the differences.
Two days ago just made one stepdown converter to use in car or with my LiIo 12V/4400mAh battery pack.