TC7652 Просмотр технического описания (PDF) - TelCom Semiconductor Inc => Microchip
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TC7652 Datasheet PDF : 6 Pages
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LOW NOISE, CHOPPER-STABILIZED
OPERATIONAL AMPLIFIER
TC7652
CONNECTION OF INPUT GUARDS
INPUT
Inverting Amplifier
R1
R2
–
+
OUTPUT
TC7652
INPUT
Noninverting Amplifier
R2
Follower
–
OUTPUT
+
TC7652
–
+
R1
INPUT
OUTPUT
TC7652
a 6dB/octave response from 0.1Hz to 2MHz, with phase
shifts of less than 2 degrees in the transition region, where
the main amplifier takes over from the null amplifier.
Thermoelectric Effects
The thermoelectric (Seebeck) effects in thermocouple
junctions of dissimilar metals, alloys, silicon, etc. limit ultra-
high-precision DC amplifiers. Unless all junctions are at the
same temperature, thermoelectric voltages around 0.1µV/
°C (up to tens of µV/°C for some materials) are generated.
To realize the low offset voltages of the chopper, avoid
temperature gradients. Enclose components to eliminate air
movement, especially from power-dissipating elements in
the system. Where possible, use low thermoelectric-coeffi-
cient connections. Keep power supply voltages and power
dissipation to a minimum. Use high-impedance loads and
seek maximum separation from surrounding heat-dissipat-
ing elements.
Guarding
To benefit from TC7652 low-input currents, take care
assembling printed circuit boards. Clean boards with alco-
hol or TCE, and blow dry with compressed air. To prevent
contamination, coat boards with epoxy or silicone rubber.
Even if boards are cleaned and coated, leakage cur-
rents may occur because input pins are next to pins at supply
potentials. To reduce this leakage, use guarding to lower the
3-284
voltage difference between the inputs and adjacent metal
runs. The guard (a conductive ring surrounding inputs) is
connected to a low-impedance point at about the same
voltage as inputs. The guard absorbs leakage currents from
high-voltage pins.
The 14-pin dual-in-line arrangement simplifies guard-
ing. Like the LM108 pin configuration (but unlike the 101A
and 741), pins next to inputs are not used.
Pin Compatibility
Where possible, the 8-pin device pinout conforms to
such industry standards as the LM101 and LM741. Null-
storing external capacitors connect to pins 1 and 8, which
are usually for offset-null or compensation capacitors. Output
clamp (pin 5) is similarly used. For OP05 and OP07 devices,
replacement of the offset-null potentiometer (connected
between pins 1 and 8 and VDD by two capacitors from
those pins to VSS) provides compatibility. Replacing the
compensation capacitor between pins 1 and 8 by two
capacitors to VSS is required. The same operation (with the
removal of any connection to pin 5) works for LM101,
µA748, and similar parts.
Because NC pins provide guarding between input and
other pins, the 14-pin device pinout conforms closely to the
LM108. Because this device does not use any extra pins and
does not provide offset-nulling (but requires a compensation
capacitor), some layout changes are necessary to convert to
the TC7652.
TELCOM SEMICONDUCTOR, INC.
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