UCC27201A-Q1: Problem in High side Gate Output of UCC27201A-Q1

Rabi Narayan Rath

Part Number: UCC27201A-Q1

Tool/software:

Hi All,

WE are using UCC27201A-Q1 for high side gate drive purpose. Our Operating frequency is 2kHz with maximum duty of 25%. We have used Boot-cap of 470nF/100V (X7R).

Vdd supply voltage is 12V. The HI pin gets input pulse amplitude of 5V. The 1.8V_out is available. But the HO pin doesn't give any output pulse and it remains at 0V during the input pulse high too.

It is not changing its pulse.

Kindly suggest If any mistake or improvement can be done.

Thank you

4 months ago

0 Rubas Khalid 4 months ago

TI__Expert 8420 points

Hello,

Our half bridge drivers do not internally generate the bias for the high side channel. The high side channel relies on the switching of the high side and low side FETs in order to charge the bootstrap capacitor to keep the high side biased. However, you can use the low-side output as an external charge-pump to bias the high-side, which you can read about (and more methods) in this FAQ: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1330910/faq-how-to-bias-the-high-side-of-a-half-bridge-gate-driver-and-why

You can also use a low-side driver as a high-side drive, which you can read about in this FAQ: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1082920/faq-ucc27624-can-i-use-a-low-side-driver-as-a-high-side-driver

Thanks,
Rubas

0 Rabi Narayan Rath 3 months ago in reply to Rubas Khalid

Prodigy 20 points

Hi.

Thank you for your reply. The bootstrap capacitor gets charged with Internal boot diode and R91 & R92 (Effective value: 25Ohm).

When input pulse is Zero (HI=0), The HS pin is grounded through R91 & R92 and Bootstrap capacitor gets charged. HO pin = 0V.

When Input pulse is High (HI=5V); The HO Pin should be at around 11.3V (Vdd-Vdiode = 12-0.7 = 11.3V). This turns on the high side MOSFET, HS pin should have shifted to 1.8V and HO pin should have sifted to 11.3 + 1.8V = 13.1V.

But the HO pin remains at Zero irrespective of input pulse although the HS in grounded.

Also, in the functional mode, its clearly mentioned that The high side switching is independent from the Low side input.

Its just the HS pin should come zero before switching of HI, which is here done by R91 & R92.

Thank you

Rubas Khalid said:
generate

0 Rubas Khalid 3 months ago in reply to Rabi Narayan Rath

TI__Expert 8420 points

Hello,

If the voltage at the HO pin is 0V, then please check if HB-HS voltage is switching and above UVLO.

Your circuit should theoretically work, but try testing it with a more simplified HS-VSS impedance path (try having only 25Ω resistor), and see if HO works. It's possible the other components in parallel with R91 and R92 are affecting the bootstrap capacitor from charging properly.

Can you also resend the schematic with component values (specifically R86) and explain what C110 and R88 is used for? Have you tried running the system without C110, R88, and R86?

Also, we recommend tying unused inputs (LI) to GND to prevent noise coupling.

Thanks,
Rubas

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UCC27201A-Q1: Problem in High side Gate Output of UCC27201A-Q1