Analog Devices Inc./Maxim Integrated MAX1621EEE

Summary of MAX1621EEE Capabilities

The MAX1621EEE, developed by Analog Devices Inc./Maxim Integrated, is a compact power management IC designed specifically for digitally adjustable LCD bias supplies. Housed in a space-saving 16-pin QSOP package, the device serves to convert battery voltages ranging from 1.8V to 20V into precisely controlled positive or negative bias voltages for LCD backplanes. Its minimal footprint and ability to use small, low-profile external components make it an ideal choice for portable and space-constrained devices.

Key Functions of the MAX1621EEE

The distinguishing features of the MAX1621EEE include a wide battery input voltage range (1.8V to 20V), automatic disable on display logic shutdown, and a digitally adjustable output voltage. Central to its operation is a 32-level internal digital-to-analog converter (DAC), allowing bias voltage control via SMBus™ serial interface. The IC can generate both positive and negative output voltages, supporting versatile LCD panel requirements. The typical operating current is just 150μA, making it optimal for battery-powered applications.

Use Cases of MAX1621EEE

This device is tailored for portable electronics where display bias needs to be adjustable and highly reliable. Typical uses include notebook computers, palmtop computers, personal digital assistants (PDAs), and portable data-collection terminals. In these devices, the MAX1621EEE helps prolong battery life while providing accurate and safe biasing to LCD panels, ensuring display clarity and protecting the panel in shutdown scenarios.

Working Mechanism of MAX1621EEE

The MAX1621EEE operates as a step-up power controller using an external N-channel MOSFET or NPN transistor, configured for either positive or negative outputs. Its discontinuous-conduction mode eschews the need for a current-sense resistor, improving efficiency and simplifying design. Switch on-time is managed by a k-factor (microsecond-volt time constant), ensuring output current scales with input voltage and peak inductor current. The controller detects when inductor energy has fully transferred and only issues switching pulses as needed to maintain regulation.

Setting Output Voltage on the MAX1621EEE

The output voltage can be set for either positive or negative polarity, selectable by the polarity pin. In positive mode, a standard boost topology is employed, with feedback regulation at 1.5V. For negative outputs, an inverting charge-pump configuration adds minimal additional components, with feedback at 0V. Designers can select the minimum and maximum output voltages via resistor dividers; the range is then further programmable with the internal DAC or via a potentiometer for manual adjustments. The negative output configuration also offers an alternative topology for higher voltages, subject to output ripple and voltage constraints.

Digital Management and Communication of MAX1621EEE

A central advantage of the MAX1621EEE lies in its digital control. The onboard 5-bit DAC allows for output voltage adjustment in 32 discrete steps. The device communicates using the industry-standard SMBus serial interface—responding only to its assigned address—for seamless integration with system management controllers. Configuration registers control the shutdown state and LCD panel connectivity, all accessible via single-byte writes and reads on SMBus. The DAC state is preserved through shutdown events and supply toggling, ensuring reliable operation in dynamic battery environments.

Design Guidelines for the MAX1621EEE

Several key engineering considerations must be accounted for when implementing the MAX1621EEE:

Output adjustment: The minimum voltage is set with a resistor divider, and the maximum via the DAC. Calculations for resistor values depend on feedback thresholds and desired output swing.

Shutdown and reset: The device can be shut down either via SMBus or hardware, with the reference circuitry powering down to save energy. On reset, the DAC sets to mid-scale, providing a predictable startup bias.

LCD bias switching: The LCDON output allows the positive bias to be switched via an external transistor, providing protection and system-level control.

Inductor selection: Choose inductance values based on desired output current and available input voltage, with ferrite-core components preferred for efficiency.

Diode and switching transistor selection: High-speed Schottky diodes are recommended for rectification, and logic-level N-channel MOSFETs for switching, ensuring robust performance even at the device’s peak 300kHz switching frequency.

Output and input capacitors: Use low-ESR tantalum or ceramic capacitors sized for load and ripple requirements, bypassing both IC and battery inputs for optimal noise filtering.

Compensation capacitors: Parasitic effects on the feedback pin are managed with parallel capacitors; a reference compensation capacitor ensures stable operation of the internal reference.

Standard Part Selection for MAX1621EEE Circuits

Engineers designing with the MAX1621EEE should bear in mind:

Inductors: Typical values range from 33μH to 1mH, with 100μH as a standard choice. The peak inductor current must be matched to output current requirements.

Diodes: Components like the MBRS0540 Schottky diode, with reverse voltage ratings above the output maximum, are recommended for high efficiency.

External FETs: Devices such as the MMFT3055VL provide the necessary speed and breakdown voltage for switching.

Output capacitors: 22μF, 35V low-ESR tantalum types (e.g., AVX TPS, Sprague 593D/595D series) are preferred; alternatives from Matsuo/Nichicon can be used for lower current.

Feedback and compensation: Voltage divider resistors (e.g., 300kΩ), compensation capacitors (33pF–220pF), and reference compensation (0.1μF ceramic) all contribute to stable loop dynamics and reliable output regulation.

PCB Layout and Grounding Advice for MAX1621EEE

Fast switching and significant current transients necessitate careful board layout for the MAX1621EEE:

Keep all high-current and sensitive traces (inductor, MOSFET, feedback components) as short as possible.

Place feedback resistors close to the feedback pin to minimize parasitic effects.

Use a star grounding strategy, connecting the grounds of all power capacitors and switching transistors at the IC's PGND pin.

Ensure AGND and PGND are tied together at the device for optimal noise performance.

MAX1621EEE Packaging Details

The MAX1621EEE is supplied in a 16-pin QSOP package, defined by industry standard mechanical tolerances. This package offers a compact footprint for high-density designs and supports robust thermal performance in power management applications. Full mechanical details are provided in the manufacturer’s documentation.

Alternative Models or Direct Replacements for MAX1621EEE

For designers seeking alternatives to the MAX1621EEE, the following models may provide similar functionality and can be evaluated as substitutes depending on the program requirements and the specific interface needs:

MAX1620EEE (Analog Devices Inc./Maxim Integrated): Nearly identical except that output adjustment is via hardware pins (UP/DN) rather than SMBus serial interface.

Other digitally controlled LCD bias supplies from Maxim Integrated, Analog Devices, or Texas Instruments may also be considered, provided they offer comparable input voltage ranges, DAC control resolution, and package options.

Conclusion

The MAX1621EEE stands out as a versatile, compact, and digitally controllable LCD bias supply, tailored for modern portable electronics. Its flexible bias selection, robust digital interface, and low quiescent current allow designers to maximize LCD performance while minimizing power consumption and footprint. With comprehensive application support and straightforward circuit design principles, the MAX1621EEE fits seamlessly into demanding engineering scenarios, serving both selection engineers and procurement specialists seeking high-reliability LCD power management solutions.