SM72501 Datasheet, PDF (16/28 Pages) National Semiconductor (TI) – SolarMagic Precision, CMOS Input, RRIO, Wide Supply Range Amplifier

SM72501
SNIS157C – JANUARY 2011 – REVISED APRIL 2013
2
C_F = 0 pF
0
C_F = 1 pF
-2
C_F = 5 pF
-4
C_F = 3 pF
-6
V_S = 5V
-8 _{R1 = R2 = 100 k:}
A_V = -1
-10
1k
10k
100k
1M
10M
FREQUENCY (Hz)
Figure 44. Closed Loop Gain vs. Frequency with Compensation
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DIODES BETWEEN THE INPUTS
The SM72501 has a set of anti-parallel diodes between the input pins, as shown in Figure 45. These diodes are
present to protect the input stage of the amplifier. At the same time, they limit the amount of differential input
voltage that is allowed on the input pins. A differential signal larger than one diode voltage drop might damage
the diodes. The differential signal between the inputs needs to be limited to ±300 mV or the input current needs
to be limited to ±10 mA.
V⁺
ESD
R₁
D₁
IN⁺
ESD
D₂
V^-
V⁺
ESD
R₂
IN^-
ESD
V^-
Figure 45. Input of SM72501
PRECISION CURRENT SOURCE
The SM72501 can be used as a precision current source in many different applications. Figure 46 shows a
typical precision current source. This circuit implements a precision voltage controlled current source. Amplifier
A1 is a differential amplifier that uses the voltage drop across R_S as the feedback signal. Amplifier A2 is a buffer
that eliminates the error current from the load side of the R_S resistor that would flow in the feedback resistor if it
were connected to the load side of the R_S resistor. In general, the circuit is stable as long as the closed loop
bandwidth of amplifier A2 is greater then the closed loop bandwidth of amplifier A1. Note that if A1 and A2 are
the same type of amplifiers, then the feedback around A1 will reduce its bandwidth compared to A2.
16
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