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.

Register Log in

[SOLVED] Help needed to select suitable components for the analog circuit

Status
Not open for further replies.
S

speedEC

Full Member level 6
Joined
Apr 1, 2011
Messages
337
Helped
23
Reputation
46
Reaction score
21
Trophy points
1,298
Activity points
4,324
Dear All,

I like to design a circuit which consists of the following components:

1. PIC16F1827 - Max - 4v (1.8V-3.6V Operation)

2. Accelerometer Sensor [3-axis] - Max - 3.6v

3. MCP 73843 - Li-Ion battery (3.7v) charger IC - Max Vin - 4.5 to 12v

4. Li-Ion Battery (3.7v)

5. 9v AC/DC 1A wall adopter

I have some doubt in the arrangement of the device in order to give correct voltage to all components.

How can I do that?

Doubts:

1. MCP 73843 - Vcc Range (V) - 4.5 to 12 - so, no problem of using 9v AC/DC adopter and no LDO required. fine

2. It charges the Li-Ion battery when connecting 9v AC/DC Adopter. Maximum battery voltage could be 4.1 or 4.2v. How can I reduce the this voltage to below 3.6v to run the PIC MCU and Sensor?

3. If I use any LDO like IL1117-3.3, its drop out voltage is 1.2v. So, when battery voltage goes low to, say for example 3v, then the output from LDO is 3 - 1.2 = 1.8v. This cannot ensure that PIC MCU and Sensor will run correctly on this voltage.

Please see the attached diagram and kindly suggests me how to achieve my goal.

Thanks
 

Attachments

  • edaboard_forum.JPG
    edaboard_forum.JPG
    33.5 KB · Views: 120
Last edited:

2951 - LDO voltage regulator. 40mV drop voltage. Can be fixed and adjusted version. I'm using 3.3 and 5.0 versions.
About 73843. If you want to use single li-ion cell, I greatly recommend to use 5V fixed voltage to supply 73843. It working like a usual linear voltage regulator. It can be overheated and burned.
If you want to use universal power adapter, the best way is to use step down converter with a wide range of supply voltage, that will produce 5.0V fixed voltage for 73843. For example:
**broken link removed**
Or this one:
http://www.datasheetcatalog.org/datasheet/lineartechnology/10765fbs.pdf
 
Last edited:
2951 - LDO voltage regulator. 40mV drop voltage. Can be fixed and adjusted version. I'm using 3.3 and 5.0 versions.
Click to expand...

Should I use LM2951 LDO in between PIC MCU and Li-Ion Battery?

About 73843. If you want to use single li-ion cell, I greatly recommend to use 5V fixed voltage to supply 73843. It working like a usual linear voltage regulator. It can be overheated and burned.
Click to expand...

Shall I use L7805 to power the MCP73843?

thanks
 

speedEC said:
Should I use LM2951 LDO in between PIC MCU and Li-Ion Battery?
Click to expand...
Sure!
speedEC said:
Shall I use L7805 to power the MCP73843?thanks
Click to expand...
Not a good idea. It depends of your charge current. In case of 500mA and 9V supply voltage from adapter, you will have a (0.5x(9-5)) 2W of heat on 7805.
 

Not a good idea. It depends of your charge current. In case of 500mA and 9V supply voltage from adapter, you will have a (0.5x(9-5)) 2W of heat on 7805.
Click to expand...

If so, which IC should I use to supply fixed 5v to MCP73843 IC? We can supply up to 1A (fast charging) to Li-Ion using MCP73843 IC. Advice needed in this regard?

---------- Post added at 13:11 ---------- Previous post was at 13:01 ----------

Shall I use same LM2951/LM2941 IC to regulate fixed +5v to MCP73843 IC from +9v AC/DC adopter?
 

speedEC said:
If so, which IC should I use to supply fixed 5v to MCP73843 IC?
Click to expand...
I edited my first post. Watch there.
speedEC said:
We can supply up to 1A (fast charging) to Li-Ion using MCP73843 IC.
Click to expand...
The charge current depends of current sense resistor value, MOSFET open resistance, supply voltage resistance and battery resistance. What capacity of battery you planing to use? For 1Ah recommended charge current will be about 500mA and 1A for fast charge. Even 2A will be ok.
speedEC said:
Shall I use same LM2951/LM2941 IC to regulate fixed +5v to MCP73843 IC from +9v AC/DC adopter?
Click to expand...
Only if you will use it with external powerful transistor to power dissipation with very large radiator.
I think, step-down will be much better to use.
 
I came to conclusion on this circuit issue based on your suggestion.

+9v AC/DC adopter (1A) -> LM2941 (Adj LDO) -> +5v -> MCP73843 -> Li-Ion Battery 3.7v -> CLM2951 (3.0v LDO) -> PIC MCU -> Sensor

Is this sequence OK?
 

Not a big difference, where to dissipate the heat - on 2941 or on mosfet, attached to MCP73843. I prefer to use step-down converters when the current may appear more then 500-700mA. If you wish to use fast charge with current above 1A, the heat dissipation on LDO will about 4-5W. It is very high temperature. I think, if you not planing to use step-down, you may use powerful mosfet with MCP73843 and it will more then enough.
+9V adapter - diod (for safety reason) - MCP73843 with powerful mosfet - li-ion battery - PIC MCU - sensor.
If you need a very accurate supply voltage for internal ADC module of PIC, better use external reference.
 
Are you suggesting to use step-down converters than LDO? If so, can you refer some IC information to select?

Thanks
 

2951 - LDO voltage regulator. 40mV drop voltage. Can be fixed and adjusted version. I'm using 3.3 and 5.0 versions.QUOTE]

Is it mandatory to use LDO between Li-Ion battery and PIC MCU?

Suggestion needed pl?
Click to expand...
 

Step down more efficient, but produce a lot of noise. So, you'll have to use a low-pass filter with capacitors.
No, you can use Li-Ion battery directly with 5V maximum voltage supply MCU.
For example, you can't use battery with ARM because it need very stable 3.3V supply and even some times 1.8V (actual for NXP2xxx).

You can check LM2574 and 2575 for example.
 

Step down more efficient, but produce a lot of noise. So, you'll have to use a low-pass filter with capacitors.
Click to expand...

Any simple circuit design please.

For example, you can't use battery with ARM because it need very stable 3.3V supply and even some times 1.8V (actual for NXP2xxx).
Click to expand...

The PIC I am using which requires 1.8v to 3.6v. So, I must use LDO between Li-Ion and PIC MCU, as you suggested earlier. ADP121 (2.5v, 90mV drop out), I preferred. Any suggestion pl.

URL : https://www.analog.com/static/imported-files/data_sheets/ADP121.pdf

thanks
 

I think you should leavbe the LDO's alone and use switching regulator. Linear regulator is no good for battery applications, because of low efficiency. In case of regulating 4.2V down to 3.3V you lose over 20% of your battery energy as heat dissipated on regulator. Switching regulators can achieve as high as over 90% efficiency.

The noise introduced by switching regulator can be eliminated by proper shielding and filtering. All of the uber-high-end measurement equipment is powered by SMPS too. Switching regulators are very hot topic these days and almost every semiconductor company has some in its offer. There are some very integrated which need as low as 4 or 5 external components. For a good start you may try Simple Switcher family from National Semiconductor.
 
Just use any low drop regulator for 3,3v
I'm using 2951 (3.3 const) in SO8 package. The price was about 10 euro per 100 pcs.
 

Ok. This is best I think. Thank you Easyrider83, poorchava and all for providing valuable suggestion and help.

One more additional and final suggestion required. That is, should I use rectifier (for smoothing) in my circuit to supply to LDO (which is used to supply +5v to MCP73843 charger IC)? Or can we directly connect +9v/+12v the power supply to LDO?

Thanks.
 

I agree, that currently linear regulators are more cost effective than switching ones. If battery life is not critical for your design then LDO is fine. Otherwise go for switch mode regulator.

Look at Microchip's MCP1612. Input voltage up to 5.5V, output variable between 2.7 and 5.5, up to 96% efficiency, 1A current capability. Costs $1.52 at low volume. Comes in sop-8 SMD which is totally human-solderable or DFN-6 (which is not :) )
 

I can't imagine to use any types of voltage converters with long battery living devices. It just impossible because even without any load, the current consumption can't be less then few mAmps.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top