Can the LM4651 be used to drive discrete output FETs for higher output current and lower impedance loads for higher output power?
As question number 1 helps explain there can be some difficulty with driving discrete FETs with the LM4651. The major problem is that the bootstrap capacitors (CBT) charge to 6 Volts. Some discrete FETs specify a minimum of 10 Volts for Vgs to have the minimal RDS(on). Since the Vgs will be only 6 Volts the FETs may not turn fully on and RDS(on) will not be minimize. This will result in lower efficiency. If the discrete FETs use a slightly lower supply voltage than the LM4651 then Vgs can be increased. For example, if the LM4651 has a +/-22 Volt supply and the discrete output FETs have a +/-18V supply then Vgs will be 10 Volts. There are two other possible problems with using discrete FETs instead of the LM4652. One is that Thermal Shut Down (TSD) will have to be implemented separately. The LM4652 has a TSD output flag that goes back to the LM4651. This flag transitions to 6V when the die temperature exceeds approximately 150° C. The LM4651 needs a 5V signal to shut down the output sta
