TLC271CDR

The TLC271CDR is a single operational amplifier from TI’s LinCMOS family, built on a silicon-gate CMOS process that provides the input characteristics of CMOS (extremely high input impedance, picoampere bias currents) with better offset voltage stability than conventional metal-gate CMOS op-amps. The LinCMOS technology achieves offset voltage drift of only 0.1 µV/month (including the first 30 days), far superior to the 10-100 µV/month typical of metal-gate CMOS.

The key differentiator of the TLC271 is the bias-select mode, controlled by the BIAS pin (pin 8). Three modes are available: High-Bias (BIAS pin to VDD+) for maximum bandwidth (1.7 MHz) and slew rate (3.6 V/µs); Low-Bias (BIAS pin to VDD-) for minimum power consumption (typical 10 µA supply current); and Medium-Bias (BIAS pin open or mid-voltage) for intermediate performance. This allows a single part to serve both high-performance and micropower applications.

In high-bias mode, the TLC271 offers 1.7-MHz GBW and 3.6-V/µs slew rate — competitive with bipolar op-amps like the LM358 — while consuming only 675 µA per channel. In low-bias mode, supply current drops to approximately 10 µA, suitable for always-on battery-powered circuits, at the expense of reduced bandwidth (~5 kHz) and slew rate.

The input common-mode voltage range extends 300 mV below the negative rail, enabling the TLC271 to sense signals at or below ground in single-supply systems. The output swings to within 30 mV of the negative rail (under light load), and within 1.2 V of the positive rail. The 60-pA maximum input bias current (0°C to 70°C) is orders of magnitude lower than bipolar op-amps, making the TLC271 suitable for high-impedance sensor interfaces (pH probes, photodiodes, piezoelectric transducers).

Three offset voltage grades are available: TLC271 (10 mV), TLC271A (5 mV), and TLC271B (2 mV). The C-suffix denotes commercial temperature range (0°C to 70°C); I-suffix covers -40°C to 85°C; M-suffix covers -55°C to 125°C. The TLC271 is in the process of being discontinued (per TI product page), so new designs should consider the TLC27L1 or TLV271 as replacements.

**LinCMOS Input Stage:** The TLC271 uses a differential input pair of P-channel MOSFETs fabricated on TI’s silicon-gate LinCMOS process. The MOSFET gates present virtually infinite DC input impedance (10^12 Ω typical), resulting in picoampere-level input bias current. The silicon-gate process provides more stable threshold voltages than metal-gate CMOS, resulting in the 0.1-µV/month offset voltage drift specification.

**Bias-Select Operation:** The BIAS pin (pin 8) controls an internal current mirror that sets the tail current for the differential pair and the bias current for subsequent stages. In high-bias mode (BIAS = VDD+), the tail current is maximized, providing maximum gm (transconductance) and therefore maximum bandwidth and slew rate. In low-bias mode (BIAS = VDD-), the tail current is minimized, reducing gm and bandwidth but cutting supply current to ~10 µA. This is a unique feature not found in most op-amps.

**CMOS Output Stage:** The output uses a CMOS push-pull (PMOS pull-up, NMOS pull-down) configuration. The NMOS pull-down provides strong sinking capability to the negative rail (within 30 mV), while the PMOS pull-up limits the positive output swing to VDD – 1.2 V. The output can drive loads as low as 600 Ω (limited by output current capability of ~10 mA).

**ESD and Latch-Up Protection:** Internal ESD protection diodes on all pins prevent damage up to 2000 V (HBM per MIL-STD-883C, Method 3015.2). The input/output structures are designed to withstand -100-mA surge currents without latch-up, a critical concern in CMOS devices.