Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic 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.

Register Log in

Can you build an on-chip LDO ?

Status
Not open for further replies.

jayateertha.r

Newbie level 1
Joined
Aug 7, 2007
Messages
1
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,295
Hi,

I am designing a LDO which has load onchip.

Although I have a big off chip capacitor(4.7uF), the bond pad inductance coming in series is affecting the load regulation transient. I am getting big spikes.

How to get rid of this problem? This must be a common problem as many chips will have a onchip LDO for a onchip load.

Is it possible to eleminate the offchip cap and build a LDO totally onchip?

thanks in advance.

regards,
jay.
 

rfzheng

Member level 5
Joined
May 17, 2006
Messages
86
Helped
3
Reputation
6
Reaction score
0
Trophy points
1,286
Activity points
1,670
onchip ldo

yes , of course, TI has a LDO without offchip CAP , the datasheet NO. is TPS73101,which is a capless LDO
 

jt_rf

Member level 2
Joined
Oct 19, 2006
Messages
43
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,286
Activity points
1,546
on-chip ldo

rfzheng

Thanks for the reply. I went thru the TPS part no. It uses a nmos pass element in LINEAR.

I was just thinking, if there is an even simpler solution with PMOS pass element with some sort of compensation technique with small onchip (300pF) cap.

regards,
jay.
 

sunilreddybvs

Newbie level 1
Joined
Sep 26, 2007
Messages
1
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,284
replica bias using nmos driver

better to go for replica based architecture for bigger cap loads to avoid stability problems but it needs a bigger driver
 

dhasmana

Member level 5
Joined
Jan 19, 2005
Messages
88
Helped
8
Reputation
16
Reaction score
0
Trophy points
1,286
Location
Bangalore , India.
Activity points
578
site:edaboard.com capless ldo

Replica bias using NMOS driver has no stability problems but the dropout voltage will be more than a Vt if you are not using a cargepump to boost the regulator OTA supply voltage.

Regards,
Jitendra Dhasmana.
 

hung_wai_ming@hotmail.com

Full Member level 6
Joined
Jan 5, 2004
Messages
383
Helped
52
Reputation
104
Reaction score
11
Trophy points
1,298
Activity points
2,464
data sheet ldo load capless

jayateertha.r

Did u resolve the problem having bonding inductance? I am having the same issue as well, but it looks like we can't solve it.
However, the reality is I didn't see that spike in real silicon and I am still scratching head now
 

niezimei

Junior Member level 3
Joined
Dec 1, 2006
Messages
28
Helped
2
Reputation
4
Reaction score
0
Trophy points
1,281
Activity points
1,390
capless ldo

It's easy to fix. Use Kelvin Connect
 

mists

Full Member level 5
Joined
May 14, 2002
Messages
277
Helped
22
Reputation
44
Reaction score
9
Trophy points
1,298
Location
China
Activity points
1,281
Onchip LDO

may you explain detailly about "Kelvin Connect ", thanks!
 

arghpok

Member level 3
Joined
Feb 13, 2007
Messages
55
Helped
5
Reputation
10
Reaction score
4
Trophy points
1,288
Activity points
1,739
Re: Onchip LDO

How big is your series inductance ? Maybe 3 nH ? How heavy is your load ? You can reduce your overall inductance making thinner pads in parallel to the pin and/or with the multihole pad technique explained in detail in "Tha art of analog layout" from Alan Hastings. Can you upload your floorplan ? I might help you making a better one.

If you wanna make a capless LDO, you can make it using both the Active Miller capacitor multiplier techique developed by Rincon-Mora and the Compensation technique from Milliken. These techniques would lead you to an onchip cap of 100 pF or less.

PAZ PARA COLOMBIA !
 

Status
Not open for further replies.
Toggle Sidebar

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top