ISL78113A AGND pin?

The ISL78113A datasheet lists pin 6 as "AGND", which is described as analog ground.  Is this is distinct from pin 1, which is labeled as PGND and described as "Power Ground".  AGND is not shown in the typical application schematic shown in Fig 1, and it is not mentioned anywhere else in the document.  The block diagram shows no connection to any functional blocks.

How should this pin be attached?  Is this simple another GND pin?

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  • Hello Ron,

    I agree the datasheet could give more details concerning this. I know the factory apps engineers for these automotive power parts assumes engineers who are designing for automotive applications understand the principles of AGND vs PGND. If you look at the Block Diagram in the datasheet you will see that all the external components such as the capacitors, resistors, battery etc. are connected to PGND (pin 1). In the Pin Description for EPAD you will find this is also connected to PGND. Notice the ground symbol for Pin 1 which is different than the ground symbol for Pin 6 AGND.

    The Power-Ground (PGND) is used as the return current path for high power components while the Analog Ground (AGND) is used as the return current path for the control/logic. The main reason why they are separated is because the PGND may see high di/dt noise spikes which can easily be in the range of 100mW. This is while the control logic signal is in the same range. Therefore, the PGND can NOT be used as the Ground for control/logic.

    Note, however, that both PGND and AGND must be connected at a single point on your board.

    You can find many resources on the open web for information on this subject. Here is just one example that I found: https://techweb.rohm.com/knowledge/dcdc/dcdc_pwm/dcdc_pwm03/4838

    Cindy

Reply
  • Hello Ron,

    I agree the datasheet could give more details concerning this. I know the factory apps engineers for these automotive power parts assumes engineers who are designing for automotive applications understand the principles of AGND vs PGND. If you look at the Block Diagram in the datasheet you will see that all the external components such as the capacitors, resistors, battery etc. are connected to PGND (pin 1). In the Pin Description for EPAD you will find this is also connected to PGND. Notice the ground symbol for Pin 1 which is different than the ground symbol for Pin 6 AGND.

    The Power-Ground (PGND) is used as the return current path for high power components while the Analog Ground (AGND) is used as the return current path for the control/logic. The main reason why they are separated is because the PGND may see high di/dt noise spikes which can easily be in the range of 100mW. This is while the control logic signal is in the same range. Therefore, the PGND can NOT be used as the Ground for control/logic.

    Note, however, that both PGND and AGND must be connected at a single point on your board.

    You can find many resources on the open web for information on this subject. Here is just one example that I found: https://techweb.rohm.com/knowledge/dcdc/dcdc_pwm/dcdc_pwm03/4838

    Cindy

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