How to design CS function and resistance

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Mugi
Level 1
Level 1
First like received 5 sign-ins First question asked

How to design CS function and resistance for TDA38812

1 Solution
Vishnu_Pulik
Moderator
Moderator
Moderator
50 sign-ins 25 replies posted 10 solutions authored

Hi @Mugi ,

During the ON time of the Synchronous MOSFET, the inductor current is sensed and mirrored to CS pin with the ratio of GCS. By using an external resistor (RCS) from CS to AGND, the voltage on CS pin (VCS) is proportional to the SW current cycle-by-cycle. The Control MOSFET is only allowed to turn on when VCS is below the internal OCP voltage threshold of 1.2V (during the ON state of Synchronous MOSFET) to limit the SW valley current cycle-by cycle.

The resistor  RCS can be calculated as below.

Vishnu_Pulik_0-1704709022612.png

Where, VCS =1.2 V, GCS = 20 µA/A, VIN - Input voltage, VOUT-Output voltage, L-Output inductance, FSW- Switching frequency and ILIM is the desired DC current limit.

Kindly refer the TDA38812 datasheet for detailed information.

Regards,

Vishnu P

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Jerry102662
Level 1
Level 1
First like received First solution authored First reply posted

The inductor current is sensed and mirrored to CS pin with the ratio of G CS . By using an external resistor (R CS ) from CS to AGND, the voltage on CS pin (V CS ) is proportional to the SW current cycle-by-cycle. The Control MOSFET is only allowed tto turn on when V CS  is below the internal OCP voltage threshold of 1.2V (during the ON state of Synchronous MOSFET) to limit the SW valley current cycle-by-

cycle. The resistor R CS  can be calculated as below.

Jerry102662_0-1704562168615.png

 

 

Vishnu_Pulik
Moderator
Moderator
Moderator
50 sign-ins 25 replies posted 10 solutions authored

Hi @Mugi ,

During the ON time of the Synchronous MOSFET, the inductor current is sensed and mirrored to CS pin with the ratio of GCS. By using an external resistor (RCS) from CS to AGND, the voltage on CS pin (VCS) is proportional to the SW current cycle-by-cycle. The Control MOSFET is only allowed to turn on when VCS is below the internal OCP voltage threshold of 1.2V (during the ON state of Synchronous MOSFET) to limit the SW valley current cycle-by cycle.

The resistor  RCS can be calculated as below.

Vishnu_Pulik_0-1704709022612.png

Where, VCS =1.2 V, GCS = 20 µA/A, VIN - Input voltage, VOUT-Output voltage, L-Output inductance, FSW- Switching frequency and ILIM is the desired DC current limit.

Kindly refer the TDA38812 datasheet for detailed information.

Regards,

Vishnu P

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