Can the LM4651 be used at a separate supply voltage than the output FETs (LM4652)?
Yes and No. The bootstrap capacitors (labeled CBT) are charged to 6 Volts. When the high side of the output FETs is turned on the gate voltage is 6 Volts above Vcc of the LM4651. For example if the Vcc of the LM4651 is 20 Volt, the gate voltage on the topside FETs will be 26 Volts giving a Vgs of 6 Volts. This value of 6 Volts was chosen because the LM4652 does not need a high gate voltage to turn fully on minimizing RDS(on). If the LM4651 is used at a lower supply voltage than the LM4652 the FETs may not turn fully on causing a higher RDS(on) resulting in lower efficiency. But the LM4651 can be used at a supply voltage that is HIGHER than the output FETs or the LM4652. This would result in a higher Vgs than 6 Volts. The limit for Vgs of the LM4652 is 10 Volts before damage can result. The low side FETs do not use bootstrap capacitors since the gate voltage is 6 volts above Vee (-20 Volts, Vgate = -14 Volts).
Related Questions
- Can the LM4651 be used to drive discrete output FETs for higher output current and lower impedance loads for higher output power?
- Does the output voltage fall to 0 V if a single-power supply operational amplifier is used at a common mode input voltage range?
- Can the LM4651 be used at a separate supply voltage than the output FETs (LM4652)?
