Analog Devices Inc./Maxim Integrated MAX6845UKD3+T

Overview

MAX6845UKD3+T from Maxim Integrated is an ultra-low-voltage microprocessor supervisory circuit with adjustable reset threshold, active-low open-drain RESET output, 210ms typical reset timeout, ±2.5% threshold accuracy over temperature, and 5.7µA typical supply current - designed for reliable power monitoring in portable 0.9V–1.5V digital systems.

For engineers reviewing the MAX6845UKD3+T datasheet, MAX6845UKD3+T pinout, MAX6845UKD3+T application, or MAX6845UKD3+T equivalent, key selection criteria include its RESET IN–based threshold adjustability, guaranteed reset validity down to VCC = 0.55V, immunity to sub-150ns VCC transients, and compatibility with bidirectional µP reset pins via open-drain configuration.

Technical Context

The MAX6845UKD3+T implements a precision voltage comparator referenced to a 187.4mV internal bandgap (relative to VCC) at the RESET IN pin, enabling externally adjustable reset thresholds via resistive divider networks. Its reset assertion logic responds to either falling RESET IN voltage or active-low MR input.

It features a fixed 210ms (D3 option) timeout period after VCC or RESET IN recovery, debounced manual reset with 20kΩ internal pullup, and hysteresis of 0.75% of VTH to prevent oscillation near threshold. The open-drain RESET output sinks up to 80µA at VCC ≥ 0.83V while requiring an external pullup to any voltage between 0 and 6V.

Key Specifications

Pinout & Package

MAX6845UKD3+T is housed in a space-saving 5-pin SOT23-5 package (JEDEC MO-178AA), with gull-wing leads, 0.95mm pitch, and thermal pad omitted. Pin 1 is marked by a beveled corner.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar microprocessor supervisory applications.

Compared with MAX6844UKD3+T and TPS3808G33DBVR, the MAX6845UKD3+T uniquely combines adjustable threshold, open-drain output, and sub-1V operation - making it the only option among the three suitable for battery-powered 0.9V–1.2V systems requiring bidirectional reset interoperability.

Availability

MAX6845UKD3+T is available at Aetrix Electronics and suitable for portable/battery-powered equipment, industrial sensor nodes, telecom line cards, and embedded edge AI modules requiring stable component supply, long-term lifecycle support, and lead-free compliance.

Supply support for MAX6845UKD3+T 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

Maxim Integrated (now part of Analog Devices) designs precision analog, mixed-signal, and high-reliability semiconductor solutions for industrial, communications, and computing markets.

The MAX6841–MAX6845 family was engineered specifically for ultra-low-voltage microprocessor supervision in portable and energy-constrained systems - delivering accurate, low-power reset functionality in minimal SOT23-5 footprint.

FAQ

What is the exact reset timeout period of the MAX6845UKD3+T?

The MAX6845UKD3+T has a typical reset active timeout period of 210ms, corresponding to the D3 suffix in its part number. This value is guaranteed within a range of 140ms (min) to 280ms (max) over temperature and process variation. The timeout begins after VCC or RESET IN rises above the threshold and MR is released, ensuring consistent µP initialization timing across operating conditions.

How do I set the reset threshold for MAX6845UKD3+T?

To set the reset threshold for MAX6845UKD3+T, connect a resistive divider between VCC and GND, with the midpoint tied to the RESET IN pin. The internal reference is 187.4mV relative to VCC, so V_TH = V_CC × (R2 / (R1 + R2)) = 187.4mV. For example, to monitor a 0.9V rail, use R2 = 100kΩ and R1 ≈ 26.3kΩ. The MAX6845UKD3+T's low RESET IN leakage (<±25nA) ensures minimal divider error.

Does MAX6845UKD3+T support operation below 1.0V?

Yes, MAX6845UKD3+T supports full operation from VCC = 0.55V to 1.8V. Its reset comparator remains functional down to 0.55V, and the open-drain RESET output can sink 80µA at VCC ≥ 0.83V. This makes MAX6845UKD3+T suitable for emerging ultra-low-voltage systems using 0.8V–0.9V core supplies, unlike many competitors limited to ≥1.2V minimum VCC.

Can MAX6845UKD3+T interface with a microprocessor that has a bidirectional reset pin?

Yes, MAX6845UKD3+T is explicitly designed for this use case. Its active-low open-drain RESET output connects directly to a bidirectional µP reset pin using a single pullup resistor - allowing either the MAX6845UKD3+T or the µP to assert reset. This eliminates contention and avoids the need for external logic or level shifters, as confirmed in Maxim's Application Note and Figure 4 of the MAX6845UKD3+T datasheet.

What is the purpose of the MR pin on MAX6845UKD3+T?

The MR (Manual Reset) pin on MAX6845UKD3+T is an active-low input with internal 20kΩ pullup to VCC. Pulling MR low forces an immediate reset regardless of VCC or RESET IN status, and reset remains asserted for the full 210ms timeout after MR is released. It supports CMOS-logic or open-drain driving, requires no external debounce, and tolerates glitches shorter than 150ns - making it ideal for pushbutton reset, test-mode entry, or system-level fault recovery.