STMicroelectronics ST735CD

Overview

ST735CD from STMicroelectronics is a Bi-CMOS inverting switch-mode DC-DC regulator with integrated Power MOSFETs, generating a fixed -5 V output from 4.0 V to 6.2 V input. It delivers 200 mA guaranteed output current at VIN > 4.5 V, features 160 kHz fixed-frequency current-mode PWM control, 75% typical efficiency, and 0.8 mA quiescent current-used in HDD power rails and portable equipment battery-backed circuits.

For engineers reviewing the ST735CD datasheet, ST735CD pinout, ST735CD application, or ST735CD equivalent, key selection criteria include its inverting topology, ±5% output accuracy over -40°C to +125°C, SO-8 package compatibility, shutdown current of 10 µA, and soft-start/compensation pin configuration for stable negative rail generation.

Technical Context

The ST735CD implements current-mode PWM control with a factory-trimmed 160 kHz oscillator, enabling precise duty-cycle adjustment and inherent cycle-by-cycle current limiting. Its internal high-side switch (LX) drives an external inductor-capacitor network to invert input voltage, while the VREF pin provides a stable 1.247 V reference for feedback loop compensation via the CC pin.

Undervoltage lockout activates below 3.5 V (typical), and soft-start (SS pin) controls output ramp-up to limit inrush current. The device operates with a 0.5 Ω typical LX on-resistance and supports ceramic output capacitors as low as 10 µF, minimizing board space in compact storage and portable designs.

Key Specifications

Pinout & Package

ST735CD is housed in an SO-8 surface-mount package (5.0 mm × 6.2 mm, 1.27 mm pitch), rated for -40°C to +125°C junction temperature and featuring 470 mW power dissipation at Tj = 70°C.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar inverting DC-DC regulator applications.

Compared with MAX764CSA+ and LM2662MM/NOPB, ST735CD offers higher output current (200 mA), adjustable loop compensation, and superior heavy-load efficiency-making it optimal for HDD and industrial sensor applications demanding robust negative rails.

Availability

ST735CD is available at Aetrix Electronics and suitable for HDD preamp power supplies, portable audio DAC bias rails, and industrial sensor interfaces requiring stable component supply and long-term obsolescence management.

Supply support for ST735CD 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, designing and manufacturing analog, microcontroller, power, and sensor solutions for industrial, automotive, and consumer markets.

The ST735 belongs to ST's legacy DC-DC converter product line, engineered specifically for compact, high-efficiency inverting power conversion in space- and power-constrained embedded systems.

FAQ

What is the minimum input voltage required for ST735CD to regulate -5 V output?

The ST735CD requires a minimum input voltage of 4.0 V to maintain regulation at full load (200 mA). Below 4.0 V, undervoltage lockout engages at 3.5 V (typical), disabling switching and forcing the device into shutdown. Operation at 4.0–4.4 V yields reduced output current (175 mA max) but retains ±5% output accuracy across temperature.

Can ST735CD drive a 22 µH inductor instead of the recommended 10 µH?

Yes-ST735CD supports inductors from 10 µH to 47 µH. Using 22 µH lowers peak switch current and reduces EMI, but increases output voltage ripple and slows transient response. Ensure the inductor's saturation current exceeds 1.5 A and DC resistance stays below 0.1 Ω to maintain efficiency and thermal performance.

Is the VREF pin intended for external feedback or only for monitoring?

VREF is a buffered 1.247 V reference output used exclusively for external feedback network biasing-not for direct monitoring. It sources up to 1 mA and connects to the top of the resistor divider between VOUT and GND; the bottom leg ties to the FB node (internal to the IC), enabling precise -5 V regulation via standard resistive scaling.

Does ST735CD require a heatsink in SO-8 package at 200 mA load?

No heatsink is required. At 200 mA output and 5 V input, power dissipation is ~180 mW (calculated from 72% efficiency). With SO-8 R_thj-amb ≈ 125°C/W, junction temperature rise is ~22.5°C above ambient-well within the -40°C to +125°C operating range. PCB copper pour under the exposed pad further enhances thermal performance.