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LTC7001 charge pump Voltage drop

Category: Software
Product Number: LTC7001

I am trying to use LTC7001 to switch 4 mosfets in parallel as a static switch. I am facing several issues reagarding the Vgs charge pump voltage of LTC7001.

                                                                                                                                                Fig 1

                                                                                                               Fig 2

Fig 1 and Fig 2 show the schematic of the LTC7001 used with 4 mosfets in parallel to use it as a static switch.

The design decision is explained in the schematic

1. The Vccuv is configured to be 3.5V as the Vccuv pin is grounded. But what I am observing is, unless the Vcc is 7V, it does not boost the voltage. The Vccuv is set to 3.5V but it is behaving as the Vccuv is set to 7V.

2. When Vcc = 7V is applied the voltage between gate and source pin is about 4V when there is no load voltage.

3. When Vcc = 11V is applied the voltage between gate and source pin is about 7V when there is no load voltage. When I start applying load voltage (>2V), the Vgs voltage starts dropping very quickly and at a load voltage of 10V, the Vgs voltage again collapses to 4V as before with Vcc = 7V.

In a Forum post related to LTC7001 it was mentioned that the Si diode between Vcc and BST pin was creating problem. So I removed the Si diode, but still same problem persists.

Only one notable change that took place as compared to before was that when I used to apply load voltage of about 28V with Si diode, the Vgs voltage used to collapse to 0. But now with diode removed this condition is eliminated. But still Vgs voltage is only 4V which barely turns on the mosfets.

Mosfet PN: NTBLS1D7N08H

Si diode PN: MMBD1501A (suggested in datasheet)

1) How can I solve this issue so that the Vccuv is 3.5V and not 7V?

2) How do I increase the Vgs voltage to 10V with load voltage applied?

Edited question regarding Vccuv and removed question whose answer was mentioned in datasheet.
[edited by: Srishtik at 4:43 AM (GMT -4) on 13 Jun 2022]
  • 1) The problem No 2 is solved. The 100k pull down resistor was the problem (Fig 2). It was drawing around 100uA from the LTC7001 and it is clearly mentioned in data sheet that a current above 40uA, the Vgs voltage will collapse to 5V which was in my case above 40uA. Now I have replaced the 100k pull down resistor with 4.7M resistor and the Vgs voltage is now boosting up to 12V with load voltage of about 66V.

    2) The Vccuv is still 7V while I have configured it to be 3.5V by grounding the Vccuv pin. How do I configure the Vccuv to 3.5v?

  • Hi Srishtik,

    Have you checked the voltage seen by the VCCUV pin? Make sure it is connected properly to GND. Please also check for manufacturing issues such as cold solders. You may also try replacing the LTC7001 IC just to check if you have a damaged one.

  • Thank you for your reply. I have soldered a new board with new LTC7001 and now it works with Vccuv of 3.5V.

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