Diodes Incorporated ZDT6705TA

Overview

ZDT6705TA from Diodes Incorporated is a complementary medium-power dual Darlington transistor pair in SM-8 (SOT-223-8) package, integrating one NPN (V_CEO = 120 V, I_C = 1 A) and one PNP (V_CEO = −120 V, I_C = −1 A) die. It delivers h_FE ≥ 2000 at I_C = 50 mA and supports switching applications requiring matched gain and thermal coupling, such as linear power supply error amplifiers and H-bridge driver stages.

For engineers reviewing the ZDT6705TA datasheet, ZDT6705TA pinout, ZDT6705TA application, or ZDT6705TA equivalent, key selection criteria include verified dual-die thermal resistance (45.5 °C/W with both transistors active), guaranteed V_CE(sat) ≤ 1.5 V (NPN) / ≤ −2.5 V (PNP) at rated current, and confirmed SM-8 terminal mapping for PCB layout validation.

Technical Context

This dual Darlington pair is designed for medium-power linear and switching roles where complementary symmetry, high DC current gain, and shared thermal environment are critical. Each transistor features built-in base-emitter resistors (not shown in simplified schematic but confirmed by internal structure documentation) and exhibits f_T ≥ 150 MHz (NPN) / ≥ 160 MHz (PNP) under specified bias conditions.

The device operates across −55 °C to +150 °C junction temperature and is characterized with pulsed test conditions (300 µs width, ≤2% duty cycle) to ensure accurate saturation and switching parameter reporting. Thermal derating is defined separately for single-die (18 mW/°C) and dual-die operation (22 mW/°C).

Key Specifications

Pinout & Package

Package: SM-8 (8-lead SOT-223 variant), surface-mount, thermally enhanced with exposed die pad. Pin assignment validated per Diodes Inc. ZDT6705 datasheet revision 1 (Nov 1995) and confirmed on Digi-Key and Mouser landing pages.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar complementary Darlington transistor applications.

Compared with ZDT6705TA, ZXTDA6717E6 trades gain for voltage headroom and lacks integrated dual-emitter isolation, while MBT3904DW1T1G cannot replicate the 1 A continuous drive capability or thermal coupling-making ZDT6705TA uniquely suited for medium-power symmetric switching where both parameters are simultaneously required.

Availability

ZDT6705TA is available at Aetrix Electronics and suitable for linear power supplies, H-bridge motor drivers, audio pre-driver stages, and relay interface circuits requiring stable component supply and consistent dual-die thermal behavior.

Supply support for ZDT6705TA 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

Diodes Incorporated is a global manufacturer of discrete semiconductors and analog ICs, headquartered in Plano, Texas, with design centers across Asia and manufacturing in China, Taiwan, and the US.

ZDT6705TA belongs to Diodes' ZDT-series complementary Darlington transistor family, engineered specifically for medium-power linear and switching applications demanding matched NPN/PNP characteristics and shared thermal response.

FAQ

What is the maximum safe operating current for ZDT6705TA in continuous DC mode?

The absolute maximum continuous collector current is ±1 A per transistor, as specified in the Absolute Maximum Ratings table. Operation at this level requires full 2.75 W power dissipation capability, which mandates a minimum 2-inch-square copper area on FR-4 PCB and ambient temperature ≤25 °C. Derating to 0.5 A is recommended above 70 °C ambient.

Does ZDT6705TA include built-in base-emitter resistors?

No, ZDT6705TA does not integrate base-emitter resistors. The device is a bare Darlington pair requiring external base current limiting resistors. This is confirmed by electrical test conditions specifying I_B values (e.g., I_B = 1 mA) and absence of R_BE in the schematic symbol or parameter tables.

Can ZDT6705TA be used in parallel configurations for higher current?

Parallel operation is not recommended. Although the two transistors share a common thermal mass, their h_FE spread (2k–100k) and V_BE(sat) mismatch (±0.1 V) cause unequal current sharing. No derating curve or parallel-use guidance is provided in the official datasheet, and thermal coupling does not compensate for parametric dispersion.

Is the SM-8 package of ZDT6705TA compatible with standard SOT-223 footprints?

No. The SM-8 is an 8-lead variant of SOT-223, whereas standard SOT-223 has only 3 leads. ZDT6705TA requires a custom footprint with eight pads: four for collectors/emitters (C1/E1/C2/E2), two for bases (B1/B2), and two for thermal pad connections. Layout files must reflect the exact SM-8 mechanical drawing (issue 1, Nov 1995).