Analog Devices Inc. LTC1985ES5-1.8#TRMPBF

Overview

LTC1985ES5-1.8 from Analog Devices (formerly Linear Technology) is a micropower precision triple supply monitor IC for systems requiring simultaneous monitoring of 3V, 1.8V, and an adjustable voltage rail. It delivers ±1.5% threshold accuracy over temperature, 10µA typical supply current, and a guaranteed 200ms reset pulse width, with push-pull RST output active low at 3V. It is used in portable battery-powered equipment to ensure reliable power-on reset sequencing.

For engineers reviewing the LTC1985ES5-1.8 datasheet, LTC1985ES5-1.8 pinout, LTC1985ES5-1.8 application, or LTC1985ES5-1.8 equivalent, key selection criteria include its triple-supply glitch immunity, VCC3/VCC18 dual-supply operation down to 1V, and SOT-23-5 package compatibility with space-constrained embedded designs.

Technical Context

The LTC1985ES5-1.8 integrates three independent voltage comparators with a shared 200ms monostable timer and push-pull output stage. Its internal bandgap reference enables precise trip thresholds: 2.805V (±1.5%) for VCC3, 1.683V (±1.5%) for VCC18, and 1.000V (±1.5%) for VCCA - all specified over –40°C to 85°C.

Power is autonomously sourced from whichever of VCC3 or VCC18 is higher, ensuring RST remains valid down to 1V on either supply. The device asserts RST low whenever any monitored input falls below its threshold and holds it for 200ms after all inputs return to compliance - with <110µs undervoltage detection latency.

Key Specifications

Pinout & Package

Package: 5-lead SOT-23 (SC-74A), 2.80–3.00 mm × 1.90 mm × 1.15 mm, RoHS-compliant, tape-and-reel (TRMPBF).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar triple-supply monitoring applications.

Compared with LTC1985ES5-1.8, LTC1326 offers tighter threshold tolerance but mismatches the 1.8V rail requirement and increases board area, while LTC1728-1.8 preserves pinout and thresholds but trades push-pull drive strength for bus-sharing flexibility - making LTC1985ES5-1.8 optimal for compact, self-contained reset generation.

Availability

LTC1985ES5-1.8 is available at Aetrix Electronics and suitable for portable battery-powered equipment, notebook computers, intelligent instruments, network servers, and desktop computers requiring stable component supply and long-term lifecycle support.

Supply support for LTC1985ES5-1.8 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, Inc. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors.

The LTC1985ES5-1.8 belongs to Linear's precision power monitoring product line, designed specifically for reliable, low-power reset generation in multi-rail embedded systems where accuracy, small size, and supply robustness are critical.

FAQ

What is the function of the VCCA pin on the LTC1985ES5-1.8?

The VCCA pin on the LTC1985ES5-1.8 is a high-impedance input with a fixed 1.000V ±1.5% threshold, enabling monitoring of an adjustable supply voltage. When used with an external resistor divider, it allows customization of the trip point - for example, setting detection at 2.5V. If unused, VCCA may be tied to VCC3 or VCC18 without affecting operation, as both have higher thresholds than VCCA. This flexibility makes the LTC1985ES5-1.8 adaptable across diverse power architectures.

Does the LTC1985ES5-1.8 require an external pull-up resistor on the RST pin?

No, the LTC1985ES5-1.8 does not require an external pull-up resistor on the RST pin because it features a push-pull output stage. The RST pin actively drives high (≥0.8×VCC3) and low (≤0.4V at 2.5mA sink) without external components. This simplifies design, reduces BOM count, and improves noise immunity compared to open-drain alternatives. However, a 100kΩ pull-down resistor to GND is recommended only if RST validity must be guaranteed down to 0V during deep power-down.

How does the LTC1985ES5-1.8 handle power supply sequencing during startup?

During startup, the LTC1985ES5-1.8 asserts RST low as soon as either VCC3 or VCC18 reaches 1V and holds it until all three monitored supplies - VCC3, VCC18, and VCCA - exceed their respective thresholds for a continuous 200ms period. This ensures microprocessors and FPGAs receive a clean, extended reset pulse regardless of individual rail ramp rates. The device's autonomous dual-supply powering (from whichever of VCC3 or VCC18 is higher) guarantees consistent behavior even with asymmetric power-up sequences.

Can the LTC1985ES5-1.8 monitor only two supplies instead of three?

Yes, the LTC1985ES5-1.8 can monitor one or two supplies instead of three. VCCA may be tied to VCC3 or VCC18 to disable its independent monitoring function, effectively configuring the device as a dual-supply monitor for 3V and 1.8V rails. Similarly, tying VCC18 to VCC3 configures it as a single 3V monitor - though this is not recommended unless VCC18 is unused, as mismatched connections could cause continuous RST assertion. All configurations retain the same 200ms reset timing and ±1.5% accuracy.

What is the minimum operating voltage for the LTC1985ES5-1.8 to guarantee correct RST logic state?

The LTC1985ES5-1.8 guarantees correct RST logic state (low when any supply is out-of-spec, high when all are valid) down to 1V on either VCC3 or VCC18. Specifically, RST remains asserted low until both VCC3 and VCC18 drop below 1V, and the output voltage low (VOL) is specified at 0.05V–0.3V with 100µA sink current under those conditions. This 1V operational floor supports brownout detection in battery-powered systems where supply voltages decay gradually, ensuring deterministic reset behavior well before complete power loss.