BQ24040 Vin=10...30V ?

Hello Zoltan,

The BQ24040 is a linear charger so it would not be recommended to run the device all the way up to 30V on the input. This is evident by looking at Fig 5 on Pg. 11 of the datasheet only showing output regulation for input voltages up to 6.5V

A switching topology would be better suited for the input voltage range you are expecting for a single cell application. With that in mind all of the chargers that can operate over this input range of up to 30 volts  are higher current and are typically host controlled. I would recommend looking at a two stage approach of regulating down to an intermediate voltage of 5V or so and then using a simple charger such as the BQ24040 to manage the charging

What sort of charging currents are you hoping to accomplish?

Is 30V max a steady state max or a transient voltage max?

Hello Ryan,

My stable input voltages are 12V and some cases (trucks) 24V. The max current is somewhat 800...1000mA. The transients (ignition and charging) covering the 10....30V range. 

In this case I feel that the TI product matrix table contains a mistake, so instead of +30V it should show +6.5V during the parametric search.

I was looking at the switching mode regulators, however I'm a bit afraid of the switching noise as my circuitry is noise sensitive RF application. 

What is your best guess, which is the most "silent" switching mode regulator? It's used to said that down converters are not so bad guys then up converters in term of noise generation...

Which architecture / chip would fit my goals, what do you think?

Thanks,

Zoltan

Hello Zoltan,

I understand your concerns about introducing switching noise into your system. There are a number of ways to reduce the noise that is produced by a SMPS.

The fact that you will be using an the battery charger as an additional linear stage in your system will help filter out some of the noise that is produced by the switching regulator.

A large component of switching regulator noise comes from the selection of the passive components and how the board is laid out. A combination of bulk and decoupling capacitors on the output, a shielded inductor, and a tight layout will substantially reduce the noise. You could also add a PI filter to the output to reduce the noise even further.

I would look at either one of TI's step-down buck regulators or one of the LMZ modules. The modules will simplify your design and they higher switching frequency and shielding will help to reduce noise. There are also a number of step down converters that could fit this application.

Will these parts need to be auto qualitifed?

Hi Ryan,

To give you a better explanation about my noise issues, I'm not afraid of failing EMC tests, but to disturb the -150dBm sensitivity receiver stage of the radio next inch on the same PCB :)

Under automotive application I'm not meaning super serious and critical in-car electronics, but kind of optional accessories what you can buy.

Thanks,

Zoltan 

Hello Zoltan,

Off hand I do not know of what would be classified as TI's "quietest" converter.

It would be interested to hear your thoughts on the modules particularly the LMZ35003 and LMZ14202.

The benefit of these modules is that by bring the inductor into the package along with the FETs the parasitics are cut drastically and moving the switch node off the board will improve the noise characteristics.

All of this onto of the fact that by using a module the design is greatly simplified.

Otherwise I would recommend looking into the WEBENCH tool that TI has for selecting and modeling power supply solutions.

http://www.ti.com/lsds/ti/analog/webench/power.page