Dear Power by Linear,

I have several questions about LTC4020.
My conditions of use 1: Vin = 12V, Vout = 16.8V, Vbattery = 16.58V (4S 3300mAh Li-Ion Battery). Use CC / CV Mode to charge. Use 220nF Timer capacitor, charge termination time is set to 3.2 hours. Use Control the RNG / SS Pin for charging current control. When the output system power is off, charge the battery with 1.7A. When the output system power is on, charge the battery with 0.1A.
Question 1. What value should I use for RNG / SS resistor?
Question 2. When the output system is powered on and charged with low current, is the Charge termination time only 3.2 hours?

My conditions of use 2: Vin = 24V, Vout = 30.9V, Vbattery = 28.4V (12-cell lead-acid Battery). Use Lead-Acid Mode to charge. Use 350nF Timer capacitor, Charge termination time is set to 5.1 hours.
Question 3. When the battery is fully charged, is Vout powered by the LTC4020 or battery?

[edited by: lallison at 11:56 AM (GMT -4) on 27 Aug 2020]

## Top Replies

• The spreadsheet you included in your post is proprietary and should not have been shared in the public forum. The spreadsheet has been removed.

Dear members,

• Apology if we cannot share the excel file to you. Please connect to a local FAE who has access to the file and who can help better…

1. The behaviour of RNG/SS is described in the datasheet, p.9-10 and 28-29. For your application, you might choose the battery-charging current-sense resistor, RCS=30mΩ. Then, with RNG/SS resistor ≥ 20kΩ (which means the RNG/SS is effectively disabled) the charge rate will be 1.67A.  For 0.1A charging, change RCS=(0.1A/1.67A)*20kΩ  = 1.2kΩ.  You could connect RNG/SS to a 1.2kΩ resistor in series with an NFET which would go to SGND.  When the NFET is off you will get full charge current (1.67A with RCS=30mΩ).  When the NFET is on you will get 1.2kΩ/20kΩ=0.1A/16.7A=0.06 (6%) of full charge current.
2. The safety timer operation is not affected by any changes to the RNG/SS resistor or charge current.
3. If input power is present Vout will be powered by the input, not the battery.
• Dear WATaylor,

If I set the Timer to 5 hours. No matter the charging current is high or low, will be charging stop after 5 hours, right?

Thanks.

• You are correct.  The only event that will pause the timer is an NTC fault.  See NTC pin description, datasheet, p. 16.

• Hi, I am interested on that image you attached. Did you create that "calculator" or that is downloadable?

Thanks

• Hi WATaylor,

Is there a downloadable calculator/sheet for LTC4020 same as the image Andy attached in his original post? Some IC's at times have their own excel sheet calculator. Hoping there is one for LTC4020 available.

Thanks