Datasheet

TLV2322, TLV2322Y, TLV2324, TLV2324Y
LinCMOS LOW-VOLTAGE LOW-POWER
OPERATIONAL AMPLIFIERS
SLOS187 – FEBRUARY 1997
25
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
single-supply operation (continued)
The TLV232x works well in conjunction with digital logic; however, when powering both linear devices and digital
logic from the same power supply, the following precautions are recommended:
• Power the linear devices from separate bypassed supply lines (see Figure 41); otherwise, the linear
device supply rails can fluctuate due to voltage drops caused by high switching currents in the digital
logic.
• Use proper bypass techniques to reduce the probability of noise-induced errors. Single capacitive
decoupling is often adequate; however, RC decoupling may be necessary in high-frequency
applications.
–
+
Logic Logic Logic
Power
Supply
–
+
Logic Logic Logic
Power
Supply
(a) COMMON-SUPPLY RAILS
(b) SEPARATE-BYPASSED SUPPLY RAILS (preferred)
Figure 41. Common Versus Separate Supply Rails
input characteristics
The TLV232x is specified with a minimum and a maximum input voltage that, if exceeded at either input, could
cause the device to malfunction. Exceeding this specified range is a common problem, especially in
single-supply operation. The lower the range limit includes the negative rail, while the upper range limit is
specified at V
DD
– 1 V at T
A
= 25°C and at V
DD
– 1.2 V at all other temperatures.
The use of the polysilicon-gate process and the careful input circuit design gives the TLV232x very good input
offset voltage drift characteristics relative to conventional metal-gate processes. Offset voltage drift in CMOS
devices is highly influenced by threshold voltage shifts caused by polarization of the phosphorus dopant
implanted in the oxide. Placing the phosphorus dopant in a conductor (such as a polysilicon gate) alleviates the
polarization problem, thus reducing threshold voltage shifts by more than an order of magnitude. The offset
voltage drift with time has been calculated to be typically 0.1 µV/month, including the first month of operation.
Because of the extremely high input impedance and resulting low bias-current requirements, the TLV232x is
well suited for low-level signal processing; however, leakage currents on printed-circuit boards and sockets can
easily exceed bias-current requirements and cause a degradation in device performance. It is good practice
to include guard rings around inputs (similar to those of Figure 38 in the Parameter Measurement Information
section). These guards should be driven from a low-impedance source at the same voltage level as the
common-mode input (see Figure 42).
The inputs of any unused amplifiers should be tied to ground to avoid possible oscillation.