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5/15/2017 1:26 AM
 

Hello,

 

I need to feed GPRS modem with 4.2V from 15V DC IN. The modem takes up to 2.5A high slew rate pulses for short periods of time so i want to improve the load transient response by adding bulk capacitance to the output…

 

So i need to know what is the maximum allowable load capacitance for the MPM3630 DC/DC module and what are the limitations?

I can connect these bulk capacitors via small value serial resistor if it helps....

 

Thanx,

Eli. 

 
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5/16/2017 1:03 PM
 

Hi Eli,

 

The characteristics of the output capacitor affect the stability of the regulation system. MPM3630 can be optimized for a wide range of capacitance (ceramic caps, tantalum, etc.) and ESR values. In the datasheet, from 1.5A to 3A, Vin = 12V, and Vout = 3.3V, the pk-pk transient ripple is about 200mV using 2 x 22uF ceramic caps at the output. 

 

For a slew rate of 2.5A from 0A to almost full load, if you'd want a pk-pk transient ripple of about 200mV or less as in the datasheet, for best results, you could use 2 x 47uF in a 1206 package because 0805 package would be a bit marginal in terms of achieving that transient spec. Hope this helps!

 

Regards,

Christian  

 
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5/16/2017 2:15 PM
 

Hi, Christian.

Actually i was thinking not just about the ripple but also about large capacitance which provide low ESR and smooths the load transient which is high slew rate 0 to 2.5A step...

Thanx,

Eli.

 
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5/16/2017 6:20 PM
 

Hi Eli,

 

The maximum capacitance you can put on MPM3630 is around 1000uF. Adding too much output cap may cause some difficulties for the regulator to start up. 

 

Thanks,

Kevin

 
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