8.3.3 Flexible Gain Setting

The THP210 offers considerable flexibility in the configuration and selection of resistor values. Low input bias

current and bias current noise allows for larger gain resistor values with minimal impact to noise or offset, see

Section 9.1.3 for more details.

The design starts with the selection of the feedback resistor value. The 2-kΩ feedback resistor value used for the

characterization curves is a good compromise among power, noise, and phase margin considerations. With the

feedback resistor values selected (and set equal on each side), the input resistors are set to obtain the desired

gain, with input impedance also set with these input resistors. Differential I/O designs provide an input

impedance that is the sum of the two input resistors. Single-ended input to differential output designs present a

more complicated input impedance. Most characteristic curves implement the single-ended to differential design

as the more challenging requirement over differential-to-differential I/O designs.

8.3.4 Amplifier Overload Power Limit

During overload or fault conditions, many bipolar-based amplifiers draw significant (three to five times) quiescent

current if the output voltage is clipped (meaning the output voltage becomes limited by the negative or positive

supply rail).

The primary cause for this condition is that common-emitter output stages can consume excessive base current

(up to 100x) when overdriven into saturation. In addition, the overload condition causes the feedback to be

broken, which causes the slew boost to be permanently on. Depending on the slew boost circuit, this increases

the tail current up to 4x.

The THP210 has an intelligent overload detection scheme that eliminates this problem, meaning that there is

virtually no additional current consumption in the case of an overload event, represented in Figure 8-1. The

protection circuit continuously monitors both the input and output stages of the amplifier. Figure 8-1 shows a

If the output is not changing because the output is clipped at supply rail, the protection circuit disables the slew-

boost circuit and limit the base current of the predriver to prevent output saturation. After the overload condition

is removed, the amplifier rapidly recovers to normal operating condition. Figure 8-1 indicates that in case of an

limitations, and quickly recovers as soon as the overload condition has been removed.

Time (s)

0.06

0.075

0.09

0.105

0.12

0.135

-2

-2

-1

-1.5

0

-1

1

-0.5

2

0

3

0.5

4

1

5

1.5

6

2

Figure 8-1. Supply Current Change With Overloaded Outputs

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THP210

SBOS932B – FEBRUARY 2020 – REVISED OCTOBER 2020

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