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Analog Devices Inc./Maxim Integrated MAX844ISA+T
- Part No.:
- MAX844ISA+T
- Manufacturer:
- Analog Devices Inc./Maxim Integrated
- Category:
- Special Purpose Regulators
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
MAX844ISA+T.pdf
- Description:
- IC REG CHARGE PUMP 1OUT 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,611
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Product details
Overview
MAX844ISA+T from Maxim Integrated is a low-noise, inverting charge-pump DC-DC converter optimized for GaAsFET biasing in cellular transmitter amplifiers. It delivers a regulated -2V output at 4mA with 1mVp-p ripple, operates from 2.5V to 10V input, and features 20kHz shutdown-mode switching for LCD-bias support. Its SO-8 package enables compact RF front-end integration.
For engineers reviewing the MAX844ISA+T datasheet, MAX844ISA+T pinout, MAX844ISA+T application, or MAX844ISA+T equivalent, key selection criteria include its unregulated NEGOUT retention in shutdown, 20kHz low-power oscillator mode, fixed -2V output capability (via FB grounding), and compatibility with 0.22µF external capacitors for space-constrained designs.
Technical Context
The MAX844ISA+T integrates a capacitive charge pump followed by an internal N-channel linear regulator. The charge pump inverts VIN to generate NEGOUT; the linear regulator then conditions this to produce a low-noise, regulated OUT. Unlike the MAX840/MAX843, the MAX844 maintains NEGOUT activity during shutdown while reducing oscillator frequency to 20kHz - enabling continuous low-power LCD contrast control without full system wake-up.
Its feedback architecture differs fundamentally: MAX844 uses CONT (not FB) for voltage setting via external resistor divider between OUT and a positive VCTRL, supporting adjustable outputs from -0.5V to -9.4V. Shutdown is active-low on SHDN, drawing ≤300µA in shutdown - distinct from the 1µA max of MAX840/MAX843 due to sustained NEGOUT operation.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Voltage | Fixed -2V (when FB grounded) or adjustable -0.5V to -9.4V via CONT pin; enables precise GaAsFET gate bias tuning. |
| Output Current | 4mA at VIN > 2.7V; sufficient for GaAsFET VGG bias and small LCD segments without external buffering. |
| Output Ripple | 1mVp-p typical with well-filtered VCTRL; critical for minimizing noise coupling into sensitive RF amplifier stages. |
| Oscillator Frequency | 100kHz in normal operation; drops to 20kHz in shutdown - reduces power consumption while sustaining NEGOUT for LCD bias. |
| Input Voltage Range | 2.5V to 10V; supports single-cell Li-ion (3.6V), triple-AA (4.5V), and higher-voltage battery configurations. |
| Shutdown Supply Current | ≤300µA over temperature; allows ultra-low-quiescent operation while retaining unregulated NEGOUT functionality. |
| Package | 8-pin SO (Small Outline); 3.9mm × 4.9mm footprint compatible with high-density RF PCB layouts. |
Pinout & Package
MAX844ISA+T is housed in an 8-pin SO (Small Outline) package with standard JEDEC MS-012AC dimensions (4.9mm × 3.9mm × 1.75mm). Pin 1 is marked with a dot; pin numbering follows counterclockwise convention from top-left when viewing the top side.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 C1+ | Charge-pump capacitor positive terminal | Connects to positive plate of flying capacitor C1; forms half of charge-transfer path for voltage inversion. |
| 2 C1− | Charge-pump capacitor negative terminal | Connects to negative plate of flying capacitor C1; completes inversion stage with C1+ and internal switches. |
| 3 NEGOUT | Unregulated negative output | Delivers inverted voltage from charge pump; remains active in shutdown - used for LCD bias or auxiliary rails. |
| 4 SHDN | Active-low shutdown control | TTL-compatible input; pulls low to enter shutdown (20kHz mode), high to enable full operation (100kHz). |
| 5 CONT | Positive control voltage input | Accepts 0V–10V reference to set regulated OUT voltage via external resistor divider (VOUT = −VCTRL × R2/R1). |
| 6 OUT | Regulated negative output | Final low-noise −2V (or adjustable) output; sourced from internal linear regulator for GaAsFET gate bias. |
| 7 GND | Circuit ground reference | Common return for all internal circuitry and external capacitors; must connect to low-impedance ground plane. |
| 8 IN | Positive input supply | Accepts 2.5V–10V DC input; powers both charge pump and linear regulator; requires local 0.22µF–1µF bypass. |
Key Features
| Feature | Design Value |
|---|---|
| Unregulated NEGOUT in shutdown | Enables continuous LCD contrast control without waking main system - eliminates need for separate bias IC. |
| 20kHz shutdown oscillator | Reduces switching losses and EMI during standby while maintaining usable NEGOUT current for low-power displays. |
| 1mVp-p output ripple | Minimizes noise injection into GaAsFET gate nodes - directly improves adjacent-channel power ratio (ACPR) in RF PAs. |
| 0.22µF minimum capacitor support | Allows use of tiny ceramic or tantalum caps - saves board area in space-critical cellular handset front-end modules. |
| −0.5V to −9.4V adjustable output | Permits fine-tuning of GaAsFET operating point across process/voltage/temperature corners using simple resistor network. |
Applications
| Cellular Phone Transmitter Amplifiers | GaAsFET Power Amplifier Modules |
|---|---|
|
Use Scenario: Biasing gate (VGG) of GaAsFETs in 850/1900MHz PA stages of GSM/CDMA handsets. IC Role / Device Role / Timing Role: Provides stable, low-noise −2V gate bias to set quiescent current and optimize linearity. Use Value: 1mVp-p ripple prevents AM-to-PM distortion; 2.5V min input supports single-cell Li-ion operation. |
Use Scenario: Setting precise gate voltage for discrete GaAsFETs in modular RF power amplifiers. IC Role / Device Role / Timing Role: Regulated negative supply delivering adjustable −0.5V to −9.4V via CONT pin resistor network. Use Value: Enables factory calibration and temperature compensation of PA efficiency without hardware change. |
| LCD Contrast Control | Low-Power Portable Devices |
|
Use Scenario: Generating variable negative bias for STN/TN LCD segment drivers in PDAs and communicators. IC Role / Device Role / Timing Role: Supplies unregulated NEGOUT during system sleep - controlled by 20kHz oscillator to limit power draw. Use Value: Eliminates need for dedicated LCD bias IC; extends battery life by maintaining display function at µA-level current. |
Use Scenario: Providing compact, low-noise negative rail in wireless data loggers and handheld test equipment. IC Role / Device Role / Timing Role: Inverting charge-pump converter with integrated linear regulation for analog sensor biasing. Use Value: 8-pin SO package and 0.22µF capacitor support reduce BOM count and PCB area vs. discrete solutions. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar GaAsFET bias and negative supply applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| MAX840ESA+ | Fixed −2V or adjustable output via FB pin; shuts down fully (OUT/NEGOUT off); 1µA shutdown current. | Better for systems requiring complete power gating; unsuitable where LCD bias must persist in sleep. | Select MAX840ESA+ when full shutdown (no NEGOUT) is acceptable and lowest quiescent current is critical. |
| MAX843ISA+ | CONT-based adjustable output like MAX844ISA+T but fully shuts down NEGOUT/OUT in shutdown (1µA IQ). | Matches MAX844's voltage-setting method but lacks persistent NEGOUT - not viable for LCD bias during sleep. | Choose MAX843ISA+ only if adjustable output is needed but persistent NEGOUT is unnecessary. |
Compared with MAX840ESA+ and MAX843ISA+, the MAX844ISA+T uniquely sustains NEGOUT during shutdown at 20kHz, making it the sole option among the three for simultaneous GaAsFET bias and always-on LCD contrast control in battery-powered portable systems.
Availability
MAX844ISA+T is available at Aetrix Electronics and suitable for cellular phone transmitter amplifiers, GaAsFET power amplifier modules, and LCD-bias contrast control applications requiring stable component supply, long-term lifecycle support, and consistent parametric performance across temperature.
Supply support for MAX844ISA+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) is a semiconductor company specializing in high-performance analog, mixed-signal, and power-management ICs for industrial, communications, and consumer applications.
The MAX840/MAX843/MAX844 product line was designed specifically for low-noise, compact GaAsFET biasing in portable RF transmitters - prioritizing ripple suppression, small capacitor compatibility, and flexible shutdown behavior.
FAQ
What is the primary function of the MAX844ISA+T in RF power amplifier designs?
The MAX844ISA+T serves as a low-noise, regulated negative voltage generator for GaAsFET gate bias (VGG) in cellular transmitter amplifiers. It delivers a stable −2V output with 1mVp-p ripple, ensuring minimal AM-to-PM distortion and optimal PA linearity. Its ability to operate down to 2.5V input supports single-cell Li-ion battery systems, and the CONT pin enables precise output adjustment across process and temperature variations - all within the compact 8-pin SO package required for handset front-end modules.
How does the MAX844ISA+T differ from the MAX840ISA+T in shutdown behavior?
Unlike the MAX840ISA+T - which disables both OUT and NEGOUT in shutdown - the MAX844ISA+T keeps NEGOUT active while reducing oscillator frequency to 20kHz. This allows the MAX844ISA+T to supply continuous low-power bias to LCD segments during system sleep, whereas the MAX840ISA+T fully powers down all outputs. Additionally, the MAX844ISA+T draws ≤300µA in shutdown versus ≤1µA for the MAX840ISA+T, reflecting the sustained NEGOUT functionality.
Can the MAX844ISA+T be configured for a fixed −2V output, and how is this achieved?
Yes, the MAX844ISA+T can be configured for a fixed −2V output by grounding the FB pin (Pin 5), as documented in the MAX844 functional description. Although the MAX844 primarily uses the CONT pin for adjustable output setting, grounding FB activates the internal −2V reference path. This configuration retains all other MAX844ISA+T features - including 20kHz shutdown mode and persistent NEGOUT - making it suitable for designs requiring simplicity without sacrificing low-power LCD bias capability.
What capacitor values are recommended for optimal noise performance in the MAX844ISA+T?
For optimal noise and ripple performance, the MAX844ISA+T recommends C1/C2/C3 = 1µF ceramic or tantalum capacitors with ESR < 0.8Ω, and C4 = 10µF with ESR < 0.2Ω. However, the device is validated to operate with smaller values - C1/C2/C3 = 0.22µF and C4 = 4.7µF - with only a modest increase in output ripple (still ≤1mVp-p). All capacitors must be placed close to the IC with short traces and connected to a solid ground plane to minimize parasitic inductance and ensure stable regulation.
Is the MAX844ISA+T pin-compatible with other devices in the MAX840/MAX843/MAX844 family?
No, the MAX844ISA+T is not pin-compatible with the MAX840ISA+T or MAX843ISA+T. While all three share the same 8-pin SO package and pin 1 location, the function of Pin 5 differs: it is FB (feedback) on MAX840, unused on MAX843, and CONT (control voltage input) on MAX844ISA+T. This functional mismatch means direct PCB replacement is not possible without layout modification - each variant requires its own dedicated footprint and external resistor network.
MAX844ISA+T Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc./Maxim Integrated
- Series:
- -
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Applications:
- Charge Pump, Cellular Telephone Transmitter
- Voltage - Input:
- 2.5V ~ 10V
- Number of Outputs:
- 1
- Voltage - Output:
- -2V
- Operating Temperature:
- -25°C ~ 85°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SOIC
MAX844ISA+T FAQ
1.How can I place an order for MAX844ISA+T through Aetrix?
Please submit a Request for Quotation (RFQ) for MAX844ISA+T on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for MAX844ISA+T reliable?
The price and inventory of MAX844ISA+T are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for MAX844ISA+T is usually 5 days.
3.What payment methods are accepted for MAX844ISA+T?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for MAX844ISA+T transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for MAX844ISA+T?
MAX844ISA+T orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your MAX844ISA+T order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for MAX844ISA+T?
For technical support, including MAX844ISA+T datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your MAX844ISA+T requirements.
6.How does Aetrix verify that MAX844ISA+T is sourced from the original manufacturer or authorized distributors?
All MAX844ISA+T products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that MAX844ISA+T meets industry standards.
7.What is the process for return or replacement of MAX844ISA+T?
All MAX844ISA+T units undergo pre-shipment inspection (PSI). If there is an issue with MAX844ISA+T, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The MAX844ISA+T part is unused and in its original packaging.
Return procedure for MAX844ISA+T:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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