Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

[SOLVED] Input decoupling capacitance change vs bias voltage

Status
Not open for further replies.

ridgemao1983

Junior Member level 1
Joined
Dec 3, 2009
Messages
18
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,445
The LM27342(buck convertor) datasheet says:
"The recommended input capacitance is 10µF, Make sure to verify if there is any significant change in capacitance at the operating input voltage"

My input voltage is 24v, so I chose an input capacitor rated 10uF/50V. But the capacitor's dc-bias graph shows that its capacitance will reduce 37%(reduce to 6v) at 24v dc bias. Much less than the 10uF input capacitance.

Does it mean I have to choose another capacitor to make sure its capacitance is 10uF at 24v dc-bias(24v input voltage)?

The 10uF/50v capacitor is TDK C5750X7R1H106K(230KB), its capacitance-voltage graph is shown below
 

Attachments

  • C5750X7R1H106K(230KB).jpg
    C5750X7R1H106K(230KB).jpg
    52.8 KB · Views: 82

Yes, the maximum input voltage is 20V.
The 10uF capacitor will work as 4.7uF is still ok according to the datasheet.

I would put in parallel aluminum
electrolytic capacitor.
The datasheet strongly recommends MLCC capacitors, aluminum electrolytic may not be approppriate for this high frequency buck due to its high ESL.
 

Yeah, sure, I understand that. Therefore, in parallel with MLCC.

- - - Updated - - -

What output current and voltage you want. Would you be satisfied SD45215 dc/dc converter.
https://www.datasheetarchive.com/SD45215-datasheet.html
VIN Supply Voltage +32 V
Up to 1.5A output current
No need for external pulse generator
as a variant 2 * C5750X7R1H685K250KA 5.7x5.0 C=6.8uF
graph.asp.png
 
Last edited:

Thank you all. My input voltage is 10v, I mistyped the 24v.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top