LTC4020 - Buck/Boost Converter and Battery Charger Controller

Hi,

I have designed and implemented the hardware of a DC/DC buck boost converter and charger with the IC LTC4020. However, I am not getting the output as desired 12 V DC, instead getting the output as 0 V. Apparently, the system does not work.

On checking the PWM signals from the pins of the LTC4020, I found that the chip is unable to generate the signals and the voltages at these PWM signal pins remains at nearly 0 V. So it looks like that the problem is with the chip. May be, it have got malfunctioned due to the heat during soldering. I am planning to replace this chip with a new one.

Could you please let me know if there is anything which I am missing or anything else which would help me in troubleshooting and debugging the system?

I need to make this circuit work as soon as possible, and struggling a lot with the deadlines. Your help will be greatlhy appreciated. Thank you.

P.S. I have done the simulation using LTC4020 model in LTSpice and the simulation results are fine.

The output of a buckboost is negative, and cannot be directly compared with any reference voltage inside the supply rails. You may need to devise some kind of level-shifting network, or resistive divider, etc.

You might have success by driving your converter from a common op amp, or logic gate, or darlington transistor, or sziklai pair. Any of these can give you the 'snap action' needed to switch the inductor on and off. The control signal is a small change in voltage tapped from somewhere in your converter.

Or you might try driving your converter with a pulse generator made from a 555 timer IC.

- - - Updated - - -

If you can get the converter to work with a simple On-Off driver, then this verifies you built it properly. Then it might be an easier job getting your LTC4020 to work.

Hi,

* show your schematic (not one from the datasheet)
* show us your PCB layout

If the 4020 does not work: measure all the voltages pin by pin and show us the DC values (if DC) or show us scope pictures.
...measured directly at the IC pin....

Klaus

So it looks like that the problem is with the chip. May be, it have got malfunctioned due to the heat during soldering.

Click to expand...

Possible but not necessary. More likely you didn't solder every pin correctly (e.g. missed the exposed ground pin) or have a circuit fault not obvious at first sight.

Hi,

Please check the attachments for my 4-layer design. Note that there is a rectifier circuit before the converter and the rectifier works fine producing DC voltage above 4.5 V. And now I am trying to test the converter individually by isolating it from the rectifier.

I will try to measue the DC voltages at various pins.
View attachment layout.pdf
View attachment schematic.pdf

Hi,

Please check the attachments

Click to expand...

How do you think we can check your design if you don´t give the part values?

Klaus

Please check the list.

View attachment Online Ordering _ Digi-Key_Updated_05.14.2018.pdf

Hi,

are you serious?

Klaus

Hi,

Please check the schematic with the component values.View attachment Schematic1.pdf

- - - Updated - - -

Hi,

I have replaced the old IC LTC4020 chip with a new one. Again, it is not working. Also, when the new chip was tested separately, it worked fine and generated four PWM signals at four pins TG1, BG1, TG2, and BG2. However, the same chip when soldered on the board does not actually work. Only TG1 pin has some voltage available at it, around 7 V. All other PWM pins have no voltages at them.

youo have a lot of connections in there...and probably one of them is wrong.....what you shoudl do is maybe you start again, and just connect the chip to operate as a simple boost converter, and just have the sync fets with VGS at 0V so that the fets just act as diodes (disconnect the series gate resistor)....then you can check it through.

What is the chips Vdd pin voltage?
What is the chjips vref pin voltage (i'm assuming it has one)
What is the feedback pin voltage
WHhat is the comp pin voltage.
What is the shutdown pin's voltage.

I think you need to diconnect stuff, strip it back, take the fets off, and just see if you can get switching pulses coming out of the chip gate drive.......or at least, some of them........you may have to ground the feedback pin to get this.

Thanks for the reply. I found that some of the pins which were not supposed to be connected to the ground, were falsely connected to the ground. With the previous experience, I have found that the chip works fine when not soldered on the board, that is, the chip generates some voltages at the pwm pins when Vin is supplied. However, when the chip is soldered to the board, some of its pins are shorted to the ground.

So, I have ordered new chips and will solder the chip again. Accordingly, I will check the voltages at various pins of the chip.

Hi,

I wonder why it took almost three weeks to measure the pin voltages....

And then you come with only vage informations... I can't imagine how these informations can help you or others:
* "some if the pins"
* "the chip generates some voltages"
* "some of its pins are shorted"
* "I will check the voltages at various pins"
...

Klaus