Diodes Incorporated ZSCT1555D8

Overview

ZSCT1555D8 from Zetex Semiconductors is a precision single-cell timer IC compatible with the classic 555 architecture, operating down to 0.9 V supply voltage. It functions as a monostable or astable multivibrator for accurate time delays and oscillation generation in ultra-low-power systems, featuring 74 µA quiescent current, independent duty-cycle control via two external resistors, and programmable threshold/trigger levels via the CONTROL pin. Used in battery-powered boost converters and portable instrumentation.

For engineers reviewing the ZSCT1555D8 datasheet, ZSCT1555D8 pinout, ZSCT1555D8 application, or ZSCT1555D8 equivalent, key selection criteria include sub-1V operation capability, temperature-stable timing accuracy (±1.6% monostable initial error), discharge transistor on-state voltage (≤225 mV at 0.3 mA), and SO8 package compatibility with legacy 555 footprints.

Technical Context

The ZSCT1555D8 implements a bipolar-based flip-flop and comparator architecture with internal resistor-divider networks setting trigger (≈0.2×V_CC) and threshold (≈0.8×V_CC) thresholds-both adjustable via the CONTROL pin. Its reset-dominant logic ensures deterministic state initialization independent of trigger/threshold timing.

Monostable timing relies on a single RC network (t = 1.63R_AC_T), while astable mode uses two resistors and one capacitor to independently set frequency (f = 0.62/(R_A + 2R_B)C_T) and duty cycle (d = R_B/(R_A + 2R_B)). Discharge transistor saturation voltage and low I_CC enable stable operation across –20°C to +100°C.

Key Specifications

Pinout & Package

Package: SO8 (Small Outline Integrated Circuit, 150 mil width, gull-wing leads).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LMC555IMX/NOPB and NE555DR, ZSCT1555D8 uniquely delivers sub-1V operation with 74 µA I_CC and 100 mA output drive-enabling true single-cell timing without trade-offs in drive capability or temperature range.

Availability

ZSCT1555D8 is available at Aetrix Electronics and suitable for portable medical sensors, single-cell boost converters, and low-power data loggers requiring stable component supply across extended product lifecycles.

Supply support for ZSCT1555D8 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

Zetex Semiconductors (now part of Diodes Incorporated) specialized in high-performance analog and mixed-signal ICs for power management, timing, and interface applications.

The ZSCT1555 series was designed specifically for ultra-low-voltage timing in battery-constrained systems, extending the utility of the 555 architecture into energy-harvesting and single-cell domains.

FAQ

What is the minimum supply voltage required for reliable operation of ZSCT1555D8?

The ZSCT1555D8 is guaranteed to operate down to 0.9 V at 25°C, with full functionality-including trigger response, output drive, and timing accuracy-maintained across its –20°C to +100°C operating range. This specification is validated per the Absolute Maximum Ratings table and confirmed in Typical Characteristics plots showing normalized pulse duration vs. supply voltage.

Can ZSCT1555D8 replace standard NE555 in existing PCB layouts?

Yes-the ZSCT1555D8 uses the same SO8 pinout as industry-standard 555 timers, including identical GND, TRIGGER, OUTPUT, RESET, CONTROL, THRESHOLD, DISCHARGE, and V_CC assignments. No layout changes are needed, though external RC values may require adjustment due to differences in internal threshold ratios and propagation delay.

How does the CONTROL pin affect timing behavior in monostable mode?

The CONTROL pin overrides the internal 5-resistor divider, allowing direct setting of trigger and threshold reference voltages. In monostable mode, this enables custom pulse widths independent of V_CC, supports PWM generation via analog modulation, and permits operation with asymmetric thresholds for noise-immune triggering in noisy environments.

What is the maximum recommended load capacitance on the OUTPUT pin?

The OUTPUT pin is rated for 100 mA sink and 150 µA source. For capacitive loads, rise/fall times increase with C_L; the datasheet specifies t_R = 1.2 µs and t_F = 240 ns at C_L = 10 pF. Loads exceeding 100 pF require external buffering to maintain timing integrity and avoid excessive current spikes during transitions.