Texas Instruments TLC556MD

Overview

TLC556MD from Texas Instruments is a dual CMOS timer IC designed for precision timing, pulse generation, and sequential control in industrial and military systems. It features rail-to-rail CMOS output, 2–15 V single-supply operation, 2 mW typical power at 5 V, 100 mA sink/10 mA source output drive, and functionally identical pinout to NE556.

For engineers reviewing the TLC556MD datasheet, TLC556MD pinout, TLC556MD application, or TLC556MD equivalent, this device supports monostable and astable modes up to 2.1 MHz, offers supply-voltage-independent timing intervals, and delivers low-noise switching with minimized supply-current spikes during transitions.

Technical Context

The TLC556MD implements two independent CMOS-based 555-style timers sharing a common VDD and GND. Each timer uses high-impedance comparator inputs (trigger, threshold, control) and an RS latch with active-low reset, enabling precise RC-based timing without external clocking. Its internal resistor divider sets fixed 1/3 VDD and 2/3 VDD thresholds-alterable via CONT pin-supporting voltage-controlled timing modulation.

Timing accuracy benefits from CMOS input impedance (>10¹² Ω), allowing use of smaller timing capacitors than bipolar NE556, reducing drift and improving stability across temperature. The discharge switch operates as open-collector with <0.5 V on-state voltage at 10 mA (VDD = 5 V), and output stage sustains 100 mA sink while maintaining rail-to-rail swing.

Key Specifications

Pinout & Package

Package: SOIC-14 (D package), 14-pin small-outline integrated circuit with standard JEDEC MS-012AC footprint and 1.27 mm pitch.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual timer applications.

Compared with NE556N and TLC556CDR, the TLC556MD uniquely combines military-temperature qualification, ultra-low power, rail-to-rail output, and NE556 pin compatibility - making it the only option for new high-reliability designs requiring drop-in upgrade paths and extended environmental tolerance.

Availability

TLC556MD is available at Aetrix Electronics and suitable for precision timing, pulse-width modulation, sequential control, and time-delay generation requiring stable component supply across extended temperature and long product lifecycles.

Supply support for TLC556MD includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and digital signal technologies with over 50 years of analog design heritage.

The TLC556MD belongs to TI's precision timer product line, engineered specifically for high-reliability, wide-temperature applications in defense, aerospace, and critical industrial systems where timing stability and long-term availability are mandatory.

FAQ

What is the maximum operating frequency of the TLC556MD in astable mode?

The TLC556MD achieves a maximum oscillation frequency of 2.1 MHz in astable configuration under specified conditions (VDD = 5 V, TA = 25°C, RA = 470 Ω, RB = 200 Ω, CT = 200 pF). This limit arises from internal propagation delays and discharge switch on-resistance. At higher frequencies, timing accuracy degrades due to RC constant errors and parasitic capacitance effects. For stable operation above 1 MHz, minimize PCB trace length and use low-ESR ceramic timing capacitors.

Does the TLC556MD require external pull-up resistors on its RESET pin?

Yes - the RESET pin of the TLC556MD is active-low and internally unconnected when not asserted. To prevent false triggering from noise or floating states, TI specifies that RESET must be tied to VDD via a pullup resistor (e.g., 10 kΩ) if not actively driven. Leaving RESET unconnected risks unintended resets during power-up or ESD events. The TLC556MD datasheet explicitly warns against floating RESET in Section 6.4 and Figure 6-1.

Can the TLC556MD operate from a 3.3 V supply?

Yes - the TLC556MD supports single-supply operation from 2 V to 15 V, fully including 3.3 V. At 3.3 V, trigger and threshold voltages scale to ≈1.1 V and ≈2.2 V respectively, and output swing remains rail-to-rail. Electrical characteristics such as VOL (<0.3 V at 3.2 mA), VOH (>2.8 V), and supply current (≈500 μA typ.) are validated across this range per Section 5.5 of the datasheet. No level-shifting is needed for interfacing with 3.3 V logic.

How does the CONT pin affect timing behavior in the TLC556MD?

The CONT pin on the TLC556MD directly overrides the internal 2/3 VDD reference, allowing real-time adjustment of both trigger and threshold comparator thresholds. Applying an external voltage (0.1–0.8 × VDD) to CONT linearly shifts these levels, enabling functions like pulse-width modulation (PWM) and pulse-position modulation (PPM). TI's datasheet Figure 7-1 and Section 7.2.1 confirm that CONT-driven modulation achieves 10–90% duty cycle control with predictable transfer curves - a capability absent in bipolar 556 timers.

Is the TLC556MD pin-compatible with the NE556?

Yes - the TLC556MD is explicitly designed as a functionally and pin-compatible replacement for the NE556. Section 1 of the datasheet states "Functionally interchangeable with the NE556; has same pinout", and Table 4-1 confirms identical pin numbering, names, and functions for D, J, and N packages. This allows direct substitution in legacy designs without PCB changes, provided timing capacitor values are reviewed to account for the TLC556MD's higher input impedance and lower leakage.