TPS65140-Q1 Vo3 drop

The max positive charge pump voltage is descibed in the datasheet for doubler and trippler.

Voltage doubler: Vo3max = 2 ´ Vo1 - (2 VD + 2 ´ Io ´ (2 ´ rDS(on)Q5 + rDS(on)Q3 + rDS(on)Q4 + XC1))

Voltage tripler: Vo3max = 3 ´ Vo1 - (3 ´ VD + 2 ´ Io ´ (3 ´ rDS(on)Q5 + rDS(on)Q3 + rDS(on)Q4 + XC1 + XC2)

The voltage drop caused by load current is due to Rds/on of transistors Q3, Q4, Q5, capacitor impedance at 1.6Mhz and the higher diodes forward voltage. If C1 is 0.22uF the typical drop will be 89mV at 2mA and additional drop caused by forward diodes.

400mV drop in doubler mode is possible becasue the output is pushed to max but in trippler mode the charge pump output have enough room for load regulation. It should not drop 500mV. can you send schematic? I suggest to increase the Vo3 output to 20V and try again. 

Thank you so much. Please try again.

Is schematic all right at the attached contents?

Will you be able to send schematic so I can review it?

7840.TPS65140 schematic.xls

I have attached the schematic.

Please confirm it.

Hello Harmouch-san,

When can you review it?

Thanks and Best Regards,

Sato-san,

I will review it and post my answer today

Sato-san, here are my inputs after reviewing the schematic:

1- BOOST output V01 looks OK

2- Positive charge pump V03 looks OK

3- Negative charge pump is not OK to me because C14 supposed to be a fly capacitor can not be charged. I follow the diodes D2, D3, D4, D5 and internal switches logic and can not find how the cap is charging. One way to make doubler charge pump is to disconnect C14 one side from D2, D3 and connect it to SW device pin. In this case the C14 is charge up to 2xSUP and V02 can be doubled

This configuration may affect the device functionality because of internal protection circuit. I suggest first to to remove D4, D5 and C14, change R3 to make V02 = -5V. Make sure the V03 load is 2mA. Try the measurment again. V03 should not drop with 2mA load.

If negative charge pump doubler is necessary connect everything back but capacitor C14 should be connected to SW and not D2, D3 node.

Please try this and let me know 

Harmouch-san,

Thank you for reviewing the schematic.

> Please try this and let me know

Yes it is.

> This configuration may affect the device functionality because of internal protection circuit.

What kind of influence is thought about?

Do you not recommend negative charge pump doubler?

Sato-san,

what do you mean by "Yes it is" do you still have the drop issue at 2mA? Or it is fixed?

Device has internal protection against over current and any rail below regulation.

If negative charge pump V02 needs to be higher than SUP, it can be done following my previous instructions 

1488.TPS65140 schematic and waveform.xls

Harmouch-san,

sorry. I rewrite it again.

> I suggest first to to remove D4, D5 and C14, change R3 to make V02 = -5V. Make sure the V03 load is 2mA.

> Try the measurment again. V03 should not drop with 2mA load.

I tried it. It is just what you say.

but I am necessary to make a doubler mode at Vo2.

Because Vo2 is -10V necessity.

> If negative charge pump doubler is necessary connect everything back but capacitor C14 should be connected to SW and

> not D2, D3 node.

I also tried it .

When I had 2mA from no load, the output of Vo3 drop  approximately 1V.

Why will Vo3 drop 1V?

Can you please let me know when can I get the answer?

Thanks and Best Regards,

Sato-san, It could be the negative charge pump when used as doubler causes coupling noise and corrupts the internal circuit. Can you please try these steps:

Step1- Lower the feedback resistors on V03 to less than 200K

Step2- Change the capacitor C6, C11, C14 and C15 from 0.22uF to 1uF

Is this circuit built on PCB with optimized layout or breadboard?

Can you check the signals on SUP and REF?