LM4702 pin questions

[panson_hk]

What is the purpose of pin Comp1,2? Has any one measured the DC level of source1,2 and sink1,2? I am planning to build an LM4702 amp with ON's ThermalTrak BJTs.

[glennb]

Originally posted by panson_hk
What is the purpose of pin Comp1,2? Has any one measured the DC level of source1,2 and sink1,2? I am planning to build an LM4702 amp with ON's ThermalTrak BJTs.

The Comp1 and Comp2 pins appear to be for a pair of miller compensation capacitors to connect to the Sink1 and Sink2 pins respectively. They would set a high frequency dominant-pole to limit the bandwidth and hence assist with stability of the amplifier. They are like the capacitor connected between the Base and Collector of a typical VAS in a SS power amplifier. Use the recommended range of 30 - 40 pF. Polystyrene or Silver Mica are best. Ceramic is barely acceptable.

source1,2 and sink1,2 are the outputs of the operation amplifiers in the LM4702. Their DC level represents a very high gain of the difference between the - and + inputs. The voltage between source and sink should be no more than a few volts, as constrained by the output stage deivces as shown in the in the data sheet and application note. The can only provide a few milliamps of current to drive the output stage.

The ON ThermalTrack BJTs would be connected in a similar manner to the SAP16N/P design at http://www.tech-diy.com/Amplifiers/LM4702_Sanken.htm

See my LM4702 page at http://home.pacific.net.au/~gnb/audio/lm4702.html for more info and links.

HTH

[panson_hk]

Thanks Glenn!