i.MX Processors中的主题 Re: MC34708 on START-R Board

MC34708 on START-R Board

Filippo — Mon, 12 Mar 2012 10:56:26 GMT

Hi all,

I'm designing a board starting from START-R reference schematic. I'm planning to use the MC34708 PMIC, but I have two questions:

1) In my understanding, the ITRIC pin ( ball E8 on page 15 ) seems to me an output, but on the schematics I see this pin connected to VCC_BP. The VCC_BP is generated by U28 on page 3. Is this correct ?

2) The GBAT pin ( ball B6 on page 15 ) is tied to ground, but on the datasheet I see this is an output that drives the external mosfet for the battery charging section. Is this correct ?

There are also some warnings detected by OrCad drc, but I think they are pin defines issues on the MC34708 symbol.

Thank you for your help

Filippo

Re: MC34708 on START-R Board

TheAdmiral — Mon, 12 Mar 2012 16:03:29 GMT

Hi Filippo,

I think the first thing you need to know is that the MC34708 PMIC was primarily designed to work in portable devices with a Li-ION battery. The Quick Start board, as a software development board, is designed primarily to run from a DC wall power source. The PMIC must be connected to either use an always conencted battery, or to operate without a battery. Since Freescale does not ship Li-ION batteries for liability reasons, we could not guarantee that customers would have a Li-ION battery, and therefore, the PMIC power structure on the Quick Start board is designed for only 5V wall power operations.

This means that U28 was required to simulate battery power, and is conencted to the PMIC like it was a battery. But since charging functions are disabled, there cannot be a 5V connection to either VBUSVIN or VAUXVIN.

So to answer your questions:

1) ITRIC is a trickle charge pin used to provide an initial conditioning current to a dead battery. Because there is no real battery in this case, it is simple connected to the battery bus VCC_BP and left that way for this design.

2) GBAT is a pin that controls a battery charging FET. Again, since there is no actual battery, there is no charging. Per the datasheet, this pin must be connected to ground.

I hope this clears things up,

Mark

Re: MC34708 on START-R Board

Filippo — Mon, 12 Mar 2012 16:22:35 GMT

Hi Mark,

thanks a lot for your fast reply.

In my application I have no battery.

I will leave that pins connected as per the Quick Start board schematics.

Regards,

Filippo

Mark Middleton said:

Hi Filippo,

I think the first thing you need to know is that the MC34708 PMIC was primarily designed to work in portable devices with a Li-ION battery. The Quick Start board, as a software development board, is designed primarily to run from a DC wall power source. The PMIC must be connected to either use an always conencted battery, or to operate without a battery. Since Freescale does not ship Li-ION batteries for liability reasons, we could not guarantee that customers would have a Li-ION battery, and therefore, the PMIC power structure on the Quick Start board is designed for only 5V wall power operations.

This means that U28 was required to simulate battery power, and is conencted to the PMIC like it was a battery. But since charging functions are disabled, there cannot be a 5V connection to either VBUSVIN or VAUXVIN.

So to answer your questions:

1) ITRIC is a trickle charge pin used to provide an initial conditioning current to a dead battery. Because there is no real battery in this case, it is simple connected to the battery bus VCC_BP and left that way for this design.

2) GBAT is a pin that controls a battery charging FET. Again, since there is no actual battery, there is no charging. Per the datasheet, this pin must be connected to ground.

I hope this clears things up,

Mark