Analog Devices Inc. LTC3704EMS#PBF

Overview

LTC3704EMS#PBF from Analog Devices (formerly Linear Technology) is a wide-input, current-mode positive-to-negative DC/DC controller IC that drives an external N-channel MOSFET without requiring a discrete current sense resistor. It operates from 2.5V to 36V input, delivers up to 5A output current at –5V, achieves ≥90% efficiency in typical telecom power supplies, and supports programmable switching frequency from 50kHz to 1MHz.

For engineers reviewing the LTC3704EMS#PBF datasheet, LTC3704EMS#PBF pinout, LTC3704EMS#PBF application, or LTC3704EMS#PBF equivalent, key selection criteria include its no-RSENSE architecture, ±1% internal voltage reference, 10μA shutdown quiescent current, 92% max duty cycle, and MSOP-10 package compatibility with space-constrained SLIC and modem power designs.

Technical Context

The LTC3704EMS#PBF implements a constant-frequency, current-mode control loop where peak inductor current is sensed either across the MOSFET's R_DS(ON) (for V_SW ≤ 36V) or via an external source-resistor (for V_SW > 36V). Its error amplifier outputs a 0.3V–1.4V ITH voltage that sets the current comparator threshold, enabling fast transient response and stable regulation of negative output voltages.

It integrates a 5.2V low-dropout regulator (±25mV line regulation, 280mV dropout at 20mA), a programmable oscillator with external RT resistor, and MODE/SYNC logic supporting Burst Mode (for <100μA light-load efficiency) or continuous/pulse-skip mode (for fixed-frequency EMI control). Internal slope compensation prevents subharmonic oscillation above 50% duty cycle.

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 LTC3704EMS#PBF, LTC3787EMS#PBF offers higher input voltage tolerance but demands external bias and layout changes, while TPS40057PWPR simplifies design at the expense of efficiency and flexibility in low-power modes.

Availability

LTC3704EMS#PBF is available at Aetrix Electronics and suitable for SLIC power supplies, telecom power supplies, and portable electronic equipment requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for LTC3704EMS#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 its legacy precision analog and power management product lines with full datasheet, simulation model, and application support.

The LTC3704EMS#PBF belongs to Linear's high-efficiency DC/DC controller family, designed specifically for compact, high-reliability negative-output power conversion in telecom infrastructure and broadband access equipment.

FAQ

What is the maximum input voltage rating for the LTC3704EMS#PBF?

The absolute maximum input voltage (VIN) for the LTC3704EMS#PBF is 36V. Exceeding this voltage risks permanent damage. For applications requiring higher switch-node voltages (e.g., V_SW > 36V), the SENSE pin must be connected to a resistor in the MOSFET source rather than the drain - this configuration isolates the IC's SENSE pin from overvoltage while preserving current sensing functionality. Always observe the 36V limit on VIN and SENSE pins per the Absolute Maximum Ratings table.

Does the LTC3704EMS#PBF require an external current sense resistor?

No, the LTC3704EMS#PBF does not require an external current sense resistor. It achieves high-efficiency current sensing by measuring the voltage drop across the R_DS(ON) of the external N-channel MOSFET - a feature branded "No RSENSE" by Linear Technology. This method eliminates power loss and board area associated with shunt resistors. An external sense resistor is optional and only used when precise peak-current control is needed or when V_SW exceeds 36V.

How is the switching frequency programmed on the LTC3704EMS#PBF?

The switching frequency of the LTC3704EMS#PBF is programmed using a single external resistor (RT) connected between the FREQ pin (Pin 4) and ground. The nominal voltage at the FREQ pin is 0.62V, and the internal oscillator current charges/discharges a capacitor proportional to RT. Frequency ranges from 50kHz to 1MHz - for example, an 80.6kΩ resistor sets f_OSC ≈ 300kHz. A graph in the datasheet (Figure 6) provides exact RT values versus target frequency.

What is the purpose of the MODE/SYNC pin on the LTC3704EMS#PBF?

The MODE/SYNC pin (Pin 5) on the LTC3704EMS#PBF controls both operating mode and clock synchronization. When grounded, it enables Burst Mode for ultra-low IQ at light loads. When tied to INTVCC, it disables Burst Mode and enables pulse-skip operation. When driven by an external logic-level clock (≥2V, ≥25ns pulse width), it synchronizes the internal oscillator to frequencies up to 1.3×f_OSC, reducing EMI through deterministic switching edge alignment.

Can the LTC3704EMS#PBF generate output voltages more negative than –5V?

Yes, the LTC3704EMS#PBF can generate output voltages more negative than –5V. The output voltage is set by the resistor divider on the NFB pin using the formula V_OUT = –1.230V × (1 + R1/R2) – I_NFB × R1, where I_NFB ≈ –7.5μA. By selecting appropriate R1 and R2 values, outputs such as –12V, –15V, or –48V are achievable. Stability and component voltage ratings (e.g., diode, capacitor, inductor) must be verified for the target output level and load current.