MAX1736EUT41+ Datasheet Comprehensive Summary

1. Overview

The MAX1736EUT41+ is a compact, low-cost single-cell lithium-ion (Li⁺) battery charger from Maxim Integrated, optimized for small hand-held devices. It works with a current-limited voltage source (e.g., wall cube adapters) to provide safe, accurate charging—including precharge, fast charge, and pulsed top-off modes—while minimizing power dissipation. This variant is preset to a 4.1V battery regulation voltage (critical for Li⁺ cell safety) and packaged in a tiny 6-pin SOT23, making it ideal for space-constrained applications like wireless handsets, digital cameras, and personal digital assistants (PDAs).

2. Key Features

2.1 Core Functional Capabilities

• Charging Modes: Three-stage charging (precharge → fast charge → pulsed top-off) to ensure safe, full-capacity charging:
• Voltage Regulation: Preset 4.1V regulation voltage with 0.5% set-point accuracy (critical for Li⁺ cell longevity; overcharging causes permanent damage).
• Control Flexibility: Stand-alone operation (no microprocessor required) or µP-controlled via the EN pin; automatic shutdown when input power is removed to minimize battery drain.

2.2 Electrical & Environmental Specifications

• Input Voltage: 4.7V (minimum, PFET off) to 22V (maximum), compatible with most wall cubes and adapters.
• Power Efficiency: Low power dissipation (no inductor required) and minimal quiescent current:
• Temperature Range:
• Package: 6-pin SOT23 (small outline transistor), dimensions: 2.80–3.00mm (length) × 2.60–3.00mm (width) × 0.90–1.45mm (height).

3. Pin Configuration & Function

The MAX1736EUT41+ features 6 pins with dedicated roles for power, control, and charging. Pin details are summarized below (top-view orientation):

4. Electrical Specifications (TA = -40°C to +85°C, VIN = 10V, VBATT = 4.1V)

4.1 Critical Charging Parameters

4.2 Control & Power Parameters

4.3 CT Capacitor-Dependent Parameters (CCT = 0.33µF)

5. Recommended External Components

The MAX1736EUT41+ requires minimal external components for operation. Key selections are:

6. Charging Operation & State Machine

The MAX1736EUT41+ follows a safety-focused state machine to charge Li⁺ cells, as outlined below:

6.1 1. Precharge Mode

• Trigger: VBATT < 2.5V (e.g., near-dead battery).
• Action: The MAX1736EUT41+ activates an internal 6mA current source to slowly charge the cell, preventing damage from high currents.
• Exit Condition: VBATT rises above 2.5V (plus 70mV hysteresis to avoid oscillation).

6.2 2. Fast Charge Mode

• Trigger: VBATT ≥ 2.5V and input power is present.
• Action: Turns on the external PFET, connecting the current-limited supply directly to the battery. Charging current is set by the supply’s current limit (not the MAX1736).
• Monitoring: Periodically turns off the PFET every 20s (CCT = 0.33µF) to check if input power is present; shuts down if power is removed.
• Exit Condition: VBATT reaches the 4.1V regulation voltage.

6.3 3. Pulsed Top-Off Mode

• Trigger: VBATT ≥ 4.1V (fast charge complete).
• Action: Uses hysteretic PWM to maintain safe charging:
• Exit Condition: VBATT no longer drops below 4.1V between pulses (battery fully charged).

6.4 Shutdown Modes

• Input Power Removed: Detected during periodic IN checks; shuts down to minimize battery drain (current ≤ 1µA).
• EN Pin Disabled: EN = GND; turns off the PFET and disables charging (current ≤ 6µA).
• Battery Removal: Detects VBATT > 5.125V (transient when battery is disconnected); immediately turns off the PFET.

7. Layout Guidelines

To ensure reliable performance and minimize noise:

1. Grounding: Use a large ground plane and wide traces for high-current paths (IN → PFET → BATT → GND) to reduce impedance and heat.
2. Component Placement:
3. Trace Sizing: Use traces rated for the supply’s current limit (e.g., 0.5mm width for 1A current).
4. Thermal Management: The SOT23 package dissipates minimal heat, but avoid placing heat-generating components (e.g., voltage regulators) nearby.

8. Ordering Information & Part Details

8.1 Soldering Requirements

• Solder Profile: Must follow IPC/JEDEC J-STD-020A (IR/VPR or convection reflow); preheating is mandatory.
• Lead Temperature: Max 300°C for 10 seconds (hand/wave soldering is not allowed).
• Thermal Derating: 6-pin SOT23 dissipates 0.65W at TA = 70°C; derate 8.1mW/°C above 70°C.

9. Typical Applications

The MAX1736EUT41+ is ideal for single-cell Li⁺ battery-powered devices, including:

• Wireless handsets and smartphones.
• Personal Digital Assistants (PDAs) and portable media players.
• Digital cameras and camcorders.
• Small hand-held equipment (e.g., Bluetooth headsets, portable scanners).
• Self-charging battery packs and cradle chargers.

10. Key Safety & Reliability Notes

• Li⁺ Cell Compatibility: Designed exclusively for single-cell Li⁺ batteries (3.6V nominal); do not use with other chemistries (e.g., NiCd, NiMH).
• Overcharge Protection: The 4.1V regulation voltage prevents overcharging (critical for Li⁺ cell safety—overcharging causes thermal runaway).
• ESD Protection: Internal ESD protection, but handle components with anti-static measures.
• Quality Assurance: 100% tested at TA = +25°C; limits over the operating temperature range are guaranteed by design.