Analog Devices Inc. LTC3704IMS#PBF

Overview

LTC3704IMS#PBF from Analog Devices (formerly Linear Technology) is a wide-input, current-mode positive-to-negative DC/DC controller driving an external N-channel MOSFET without requiring a sense resistor. It operates from 2.5V to 36V input, delivers up to 5A output current at –5V, achieves ≥90% efficiency in typical configurations, and supports programmable switching frequency from 50kHz to 1MHz. It is used in telecom SLIC power supplies and portable negative rail generation.

For engineers reviewing the LTC3704IMS#PBF datasheet, LTC3704IMS#PBF pinout, LTC3704IMS#PBF application, or LTC3704IMS#PBF equivalent, key selection considerations include its no-RSENSE operation via MOSFET R_DS(ON) sensing, Burst Mode™ for <100μA light-load efficiency, ±1% internal reference, 10μA shutdown quiescent current, and MSOP-10 package compatibility with high-density PCB layouts.

Technical Context

The LTC3704IMS#PBF implements a constant-frequency, current-mode control architecture with internal slope compensation to prevent subharmonic oscillation above 50% duty cycle. Its error amplifier drives the ITH pin (0.3V–1.4V range) to set the current comparator threshold, enabling precise peak-current regulation across load transients.

It integrates a 5.2V low-dropout regulator (INTVCC) capable of sourcing 50mA, powers internal logic and gate driver, and accepts VIN directly up to 7V. The MODE/SYNC pin enables three operating modes: Burst Mode (grounded), pulse-skip (tied to INTVCC), or external clock synchronization (up to 1.3× f_OSC).

Key Specifications

Pinout & Package

Package: 10-lead MSOP (3mm × 3mm, 0.5mm pitch), RoHS-compliant, moisture-sensitive level 1.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar positive-to-negative DC/DC controller applications.

Compared with LTC3704IMS#PBF, LTC3787IMS#PBF offers higher input voltage capability but lacks Burst Mode™ and requires redesign of gate drive and feedback networks, while TPS40057PWPR provides lower system cost at the expense of 10× higher light-load IQ and reduced duty cycle headroom.

Availability

LTC3704IMS#PBF is available at Aetrix Electronics and suitable for SLIC power supplies, telecom line cards, and portable test equipment requiring stable component supply, long-term lifecycle support, and guaranteed I-grade temperature performance.

Supply support for LTC3704IMS#PBF 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

Analog Devices acquired Linear Technology in 2017 and maintains full product support, datasheets, and application engineering for legacy Linear parts including the LTC series.

The LTC3704IMS#PBF belongs to Linear's high-efficiency DC/DC controller family, designed specifically for compact, high-reliability negative rail generation in telecom, industrial, and portable systems where sense-resistor loss and thermal density are critical constraints.

FAQ

What is the maximum input voltage supported by the LTC3704IMS#PBF?

The LTC3704IMS#PBF supports an absolute maximum input voltage of 36V on the VIN pin, with recommended continuous operation from 2.5V to 36V. Exceeding 36V risks permanent damage per Absolute Maximum Ratings. For applications requiring >36V switch node voltage (e.g., V_DS), the SENSE pin must be connected to an external shunt resistor in the MOSFET source rather than directly to the drain.

How does the LTC3704IMS#PBF achieve high efficiency without a current sense resistor?

The LTC3704IMS#PBF achieves high efficiency by sensing the voltage drop across the R_DS(ON) of the external N-channel MOSFET instead of using a discrete sense resistor. This eliminates I²R losses associated with shunt resistors, improving full-load efficiency by 3–5%. The SENSE pin includes internal leading-edge blanking to reject switching noise during MOSFET turn-on.

Can the LTC3704IMS#PBF be synchronized to an external clock, and what are the limits?

Yes, the LTC3704IMS#PBF can be synchronized to an external clock applied to the MODE/SYNC pin. The external clock must exceed 2V for ≥25ns, have ≤80% duty cycle, and operate within 100% to 130% of the internally programmed f_OSC. Attempting synchronization beyond 1.3× f_OSC reduces effective slope compensation and may cause subharmonic oscillation at duty cycles >50%.

What is the purpose of the RUN pin on the LTC3704IMS#PBF, and how is it configured?

The RUN pin on the LTC3704IMS#PBF provides micropower UVLO with 1.248V falling threshold and 100mV hysteresis. It is configured using a resistor divider from VIN to GND, where R1 and R2 set turn-on (1.348V) and turn-off (1.248V) thresholds. When pulled below 1.248V, the LTC3704IMS#PBF enters shutdown with 10μA IQ; no external pull-up is required unless "always-on" operation is needed.

Does the LTC3704IMS#PBF require external components for the INTVCC regulator?

Yes, the LTC3704IMS#PBF requires a minimum 4.7μF low-ESR tantalum or ceramic capacitor connected directly between the INTVCC and GND pins. This bypass capacitor is mandatory to supply transient gate-drive currents and prevent instability. If VIN ≤7V, INTVCC may be shorted to VIN, but doing so adds 10μA static current in shutdown mode - thus the dedicated bypass remains essential regardless of VIN routing.