TLC251 Datasheet, PDF (17/18 Pages) Texas Instruments – LinCMOSE PROGRAMMABLE LOW-POWER OPERATIONAL AMPLIFIERS

TLC251, TLC251A, TLC251B, TLC251Y
LinCMOS™ PROGRAMMABLE
LOW-POWER OPERATIONAL AMPLIFIERS
SLOS001E – JULY 1983 – REVISED AUGUST 1994
APPLICATION INFORMATION
using BIAS SELECT
The TLC251 has a terminal called BIAS SELECT that allows the selection of one of three I_DD conditions (10,
150, and 1000 µA typical). This allows the user to trade-off power and ac performance. As shown in the typical
supply current (I_DD) versus supply voltage (V_DD) curves (Figure 4), the I_DD varies only slightly from 4 V to 16
V. Below 4 V, the I_DD varies more significantly. Note that the I_DD values in the medium- and low-bias modes at
V_DD = 1.4 V are typically 2 µA, and in the high mode are typically 12 µA. The following table shows the
recommended BIAS SELECT connections at V_DD = 10 V.
BIAS MODE
AC PERFORMANCE
BIAS SELECT
CONNECTION†
TYPICAL IDD‡
Low
Medium
High
Low
Medium
High
VDD
0.8 V to 9.2 V
Ground pin
10 µA
150 µA
1000 µA
† _{Bias selection may also be controlled by external circuitry to conserve power, etc.}
For information regarding BIAS SELECT, see Figure 3 in the typical
characteristics curves.
‡ _{For IDD characteristics at voltages other than 10 V, see Figure 4 in the typical}
characteristics curves.
output stage considerations
The amplifier’s output stage consists of a source-follower-connected pullup transistor and an open-drain
pulldown transistor. The high-level output voltage (V_OH) is virtually independent of the I_DD selection and
increases with higher values of V_DD and reduced output loading. The low-level output voltage (V_OL) decreases
with reduced output current and higher input common-mode voltage. With no load, V_OL is essentially equal to
the potential of V_{DD –} /GND.
input offset nulling
The TLC251C series offers external offset null control. Nulling may be achieved by adjusting a 25-kΩ
potentiometer connected between the offset null terminals with the wiper connected to the device V_{DD –} /GND
pin as shown in Figure 2. The amount of nulling range varies with the bias selection. At an I_DD setting of
1000 µA (high bias), the nulling range allows the maximum offset specified to be trimmed to zero. In low or
medium bias or when the amplifier is used below 4 V, total nulling may not be possible for all units.
supply configurations
Even though the TLC251C series is characterized for single-supply operation, it can be used effectively in a
split-supply configuration when the input common-mode voltage (V_ICR), output swing (V_OL and V_OH), and
supply voltage limits are not exceeded.
circuit layout precautions
The user is cautioned that whenever extremely high circuit impedances are used, care must be exercised in
layout, construction, board cleanliness, and supply filtering to avoid hum and noise pickup, as well as excessive
dc leakages.
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