LM5050-2: LM5050 not provide enough Volts on Gate(charge pump not work correct)

Serghei Plamadeala

Intellectual 450 points

Part Number: LM5050-2
Other Parts Discussed in Thread: LM5050-1

Schematic is look like this: Q12 is CSD19506 or CSD19505

Gate Charge Total (10 V) 120nC
Gate Charge Gate to Drain 20 nC
Drain-to-Source On Resistance VGS = 10 V 2.0 mΩ

Offset is ~4-5 V above Vin.

2 test:. I removed pool-down resistor to verify if have some changes. The same issue.

3 Test. I add a 100Ohm from gate of lm5050 to gate of Mossfet. The same result.

4. I cut line between gate of lm5050 and Gate of mossfet. Here I have 14-16V Offset.

I tried with 2 chips. Thes same results.

On monday I can provide picture from oscilloscope to confirm my investigation.

please give me any suggestion.

thanks.

over 5 years ago

0 Serghei Plamadeala over 5 years ago

Intellectual 450 points

I observe only difference between DevBoard and my board is resistence on mossfet(Rds) and capacitance

Add some Capacitor between Gate and Source of mossfet is a solution?

0 Serghei Plamadeala over 5 years ago in reply to Serghei Plamadeala

Intellectual 450 points

I place order for samples to test all of them I am very curious how all of them is work.

Maybe one of them is more friendly to my design.

LM74700QDBVRQ1

LM5050MK-2/NOPB

LM5050MK-1/NOPB

LM5051MAE/NOPB

0 Rakesh over 5 years ago in reply to Serghei Plamadeala

TI__Guru** 105611 points

Hi Serghei Plamadeala,

Can you share full schematic, test loading conditions and few waveforms to understand the issue.

Thanks, Rakesh

0 Serghei Plamadeala over 5 years ago in reply to Rakesh

Intellectual 450 points

I will provide on Monday wave forms and schematic.

Thanks

0 Serghei Plamadeala over 5 years ago in reply to Rakesh

Intellectual 450 points

How I can change status from resolve to unresolved? I press accidentally on Resolved.

0 Serghei Plamadeala over 5 years ago in reply to Rakesh

Intellectual 450 points

0 Serghei Plamadeala over 5 years ago in reply to Rakesh

Intellectual 450 points

Case with resistor 10ohm on gate

0 Serghei Plamadeala over 5 years ago in reply to Rakesh

Intellectual 450 points

Now I created separate circuit for test. Result is the same.

0 Serghei Plamadeala over 5 years ago in reply to Serghei Plamadeala

Intellectual 450 points

Yellow is current sense of Vin.

0 Serghei Plamadeala over 5 years ago in reply to Serghei Plamadeala

Intellectual 450 points

3.6V offset

0 Karikalan Selvaraj over 5 years ago in reply to Serghei Plamadeala

TI__Genius 16305 points

I am looking at this thread and will get back with comments on the early next week.

Regards,

Kari.

0 Serghei Plamadeala over 5 years ago in reply to Karikalan Selvaraj

Intellectual 450 points

can you please Give me any idea how I can do alternative solution? I command few samples of rest of devices from this type of functionality(diode) and whant to test if others device will be work.

Thanks

0 Karikalan Selvaraj over 5 years ago in reply to Serghei Plamadeala

TI__Genius 16305 points

Hello,

LM5050 is an ORing controller that implements linear ORing scheme where Vsd of external MOSFET is regulated to 22mV by controlling the gate-source voltage. At high load currents, gate will be fully enhanced (>10V) and at low currents it will be close to Vth threshold of gate.

For detailed explanation, refer to the section 6.1 in application note on "basics of ideal diodes"

LM74700 also implement linear ORing scheme.

This is normal operation of ORing controllers and if you see any concern, let us know we can help to resolve.

Regards,
Kari.

0 Serghei Plamadeala over 5 years ago in reply to Karikalan Selvaraj

Intellectual 450 points

I try with bigger load, and yes with bigger load I view enough offset on GATE of moss-fet.

1. I say now another problem: some times in a small period of time GATE go off.

This is because I don't have filter on output?

In datasheet of lm5050-2 is now say anything about tu put some filter, or I don't see maybe my mistake. To resolve this kind of situation can I use resistence and capacitor like in schematic from lm5050-1?

2. Can I connect directly to the pin of MOSS Fet without any resistor to protect Oring driver?I GATE(ON) ~32uA and I GATE(OFF) 2.8A

3. I should use external diode to prevent to broke internal diode of MOSS.

4. The Oring driver is a very small current support and Can I use pull down resistor of MOSS? In datasheet is say :I GATE(ON) ~32uA and I GATE(OFF) 2.8A. In case if I use without any resistor to command MOSS will not broke Oring driver?

I ask because you have more experience with with this kind of Oring drivers.

Thanks a lot.

0 Karikalan Selvaraj over 5 years ago in reply to Serghei Plamadeala

TI__Genius 16305 points

Hi Serghei,

1. We recommend to use small capacitor on the OUT to GND and IN to GND 0.1uF. This is to filter any noise from the system or from the load that can cause false turn off the MOSFET. Adding small 0.1uF or 1uF at the output to GND and IN to GND should help to solve this.

2. For high power MOSFET where the Qgs is large (example >20nC) it is required to add a series gate resistor of 10ohm from IC gate pin to MOSFET gate pin. This will prevent any ringing causing accidental turn on (immediately after a turn off).

3. External diode may not be required if the inrush current (initially flows through body diode of Q12) is less than the source diode current of Q12. If it exceeds MOSFET datasheet ratings then it would required to add external diode. But it would good design practise to chose mosfet capable of handling inrush current.

4. For high current support on GATE (ON), we recommend LM74700 which has 11mA turn on current.

Regards.

Kari.

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LM5050-2: LM5050 not provide enough Volts on Gate(charge pump not work correct)