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.

[help] How can i know the circuit works

Status
Not open for further replies.

cmosbjt

Full Member level 5
Joined
Apr 25, 2004
Messages
250
Helped
10
Reputation
20
Reaction score
2
Trophy points
1,298
Location
USA
Activity points
2,293
how would i konw if my circuit is working


I have a supply voltage ramp from 0V to 5V, my circuit (0.6um CMOS) can not work under 2V, thus I need a circuit whose output signal can tell me whether the circuit is working (high) or not (low).

You know, if the supply voltage is too low, say about 1V, the output of the circuit is uncertain, but I think there must be a way that make it certain (low), how?

Speed is not an issue, but power consumption and reliability are my concern.

Thanks.
 

This circuit is named under voltage lockout.
It consists of a bandgap, comparator and resistor divider (for example).
 

gevy said:
This circuit is named under voltage lockout.
It consists of a bandgap, comparator and resistor divider (for example).

Hei, thans a lot for giving me this information. I've hear undervoltage lockout before but have no idea what it is. Could you provide more info about it? or where can I get the reading material about it? Thanks.
 

Maybe you mean that you need a power on reset circuit. it can give you a info whether the power is ok
 

yeewong_su said:
Maybe you mean that you need a power on reset circuit. it can give you a info whether the power is ok

Hi, do you mean a circuit like voltage detector (like LMS33460)? what if the supply voltage drops to a level (less than 2V in my case) that both bandgap and comparator are not able to work, at this moment, the output signal is uncertain, it will be 0.5v or something like that, so how to make sure when VDD drops, the circuit can give a reliable 0V output? Thanks.
 

using two amps to test the high voltage &low voltage.
 

    cmosbjt

    Points: 2
    Helpful Answer Positive Rating
Under voltage lockout circuit is applied in swiched mode converters.
Make search in this forum and Internet.
 

cetc1525 said:
using two amps to test the high voltage &low voltage.

Can you tell me more detail. And what if at the low voltage that both amps can not work?
 

cmosbjt said:
yeewong_su said:
Maybe you mean that you need a power on reset circuit. it can give you a info whether the power is ok

Hi, do you mean a circuit like voltage detector (like LMS33460)? what if the supply voltage drops to a level (less than 2V in my case) that both bandgap and comparator are not able to work, at this moment, the output signal is uncertain, it will be 0.5v or something like that, so how to make sure when VDD drops, the circuit can give a reliable 0V output? Thanks.

You should use the por (power on reset) circuit
In a word. you should use this circuit to detect the power supply level. if the power is low more. you must power off the bandgap
 

yeewong_su said:
cmosbjt said:
yeewong_su said:
Maybe you mean that you need a power on reset circuit. it can give you a info whether the power is ok

Hi, do you mean a circuit like voltage detector (like LMS33460)? what if the supply voltage drops to a level (less than 2V in my case) that both bandgap and comparator are not able to work, at this moment, the output signal is uncertain, it will be 0.5v or something like that, so how to make sure when VDD drops, the circuit can give a reliable 0V output? Thanks.

You should use the por (power on reset) circuit
In a word. you should use this circuit to detect the power supply level. if the power is low more. you must power off the bandgap

Yes, LP3470 and LMS33460 (as I mentioned above) are power on reset or Under Voltage Detector, they both have minimum supply voltages under which their output signals are uncertain. That's my problem. I need the full range Vin (form 0v to 5v). In other word, even the circuit (opamp bandgap) can not work, ok, at least you give me a reliable 0V output from which other circuit (operating) knows you are not working. In my case, bandgap and comparator can not work under around 2V, they give out rubbish under this voltage so they perhaps give a 0.9V or 1.5v output (not sure). The problem is I need this signal to determine which one of other blocks should operate.
 

It seems what you are looking for is a method to make sure that your output will be at a known value (logic zero?, analog ground?) when supply voltage is too low to operate active devices.

Depending upon your application, active state power consumption allowed, and how close to ground the output actually has to be, you might be able to do this with passive devices.

First thought: include a pull-down resistor on your output. If the supply voltage is so low that the active devices will not turn on, the resistor will pull down the output. The (problem?) here is that the output high state will burn a lot of current (depending upon the resistor size, of course). If you can use an off-chip resistor, or if you have a lot of area, you can keep the resistor value high and not burn too much current.

Second thought: include reversed biased junction area to create leakage current to pull down the output when devices are off. The pull-down current in this condition will be VERY small (Except at high temperatures!), so will take time to pull down. If this is okay, this might be a good option for you.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top