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Analog Devices Inc./Maxim Integrated MAX844ISA+
- Part No.:
- MAX844ISA+
- Manufacturer:
- Analog Devices Inc./Maxim Integrated
- Category:
- Special Purpose Regulators
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
MAX844ISA+.pdf
- Description:
- IC REG CHARGE PUMP 1OUT 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,038
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Product details
Overview
MAX844ISA+ 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 supply retention. Its SO-8 package supports compact RF front-end designs.
For engineers reviewing the MAX844ISA+ datasheet, MAX844ISA+ pinout, MAX844ISA+ application, or MAX844ISA+ equivalent, key selection criteria include its unregulated NEGOUT retention during shutdown, 20kHz low-power oscillator mode, fixed -2V output capability (via FB grounding), compatibility with 0.22µF external capacitors, and -25°C to +85°C industrial temperature range.
Technical Context
The MAX844ISA+ integrates a capacitive charge pump followed by an internal 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 keeps NEGOUT active in shutdown while reducing oscillator frequency to 20kHz - enabling continuous low-power LCD contrast control without full system power.
Its feedback architecture differs fundamentally: MAX844 uses CONT (not FB) for voltage setting via external resistor divider between OUT and a positive control voltage (0V–10V), yielding adjustable -0.5V to -9.4V output. Shutdown is active-low on SHDN, drawing ≤300µA (not ≤1µA), and the unregulated NEGOUT remains functional - a critical distinction for dual-rail bias systems.
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 VGG tuning. |
| Output Current | 4mA maximum at VIN > 2.7V; sufficient for GaAsFET gate bias and small LCD segments. |
| Output Ripple | 1mVp-p typical with well-filtered CONT; ensures stable RF amplifier bias without AM noise injection. |
| Oscillator Frequency | 100kHz in normal operation; drops to 20kHz in shutdown - reduces power consumption while sustaining NEGOUT. |
| Input Voltage Range | 2.5V to 10V; supports single-cell Li-ion (3.0–4.2V), 3-cell NiMH (3.6V), and wide-input portable systems. |
| Shutdown Supply Current | ≤300µA over temperature; allows ultra-low-power standby without disabling NEGOUT rail. |
| Operating Temperature | -25°C to +85°C (ISA grade); qualified for industrial handheld and automotive accessory environments. |
| Package | 8-pin SO (Small Outline); 0.150" width, surface-mount compatible with standard reflow profiles. |
Pinout & Package
MAX844ISA+ 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 counter-clockwise convention from top-left when viewing the top side.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 C1+ | Charge-pump flying capacitor positive terminal | Connects to positive plate of C1; forms half of charge-transfer path for voltage inversion. |
| 2 C1− | Charge-pump flying capacitor negative terminal | Connects to negative plate of C1; completes inversion stage with C1+ and internal switches. |
| 3 NEGOUT | Unregulated negative output | Delivers inverted voltage pre-regulation; remains active in shutdown for LCD bias or auxiliary rails. |
| 4 SHDN | Active-low shutdown control | Logic-level input (VIH ≥2.2V, VIL ≤0.35V); pulls internal regulators offline but leaves NEGOUT enabled. |
| 5 CONT | Positive control voltage input | Accepts 0V–10V reference to set VOUT via external R-divider; replaces FB function used in MAX840. |
| 6 OUT | Regulated negative output | Final low-noise -2V (or adjustable) output; sourced from internal linear regulator post-charge-pump. |
| 7 GND | Analog/digital ground reference | Common return for all circuitry; must be tied to low-impedance ground plane to minimize noise coupling. |
| 8 IN | Positive input supply | Primary power source (2.5V–10V); powers both charge pump and linear regulator stages. |
Key Features
| Feature | Design Value |
|---|---|
| Negated output with linear regulation | Combines charge-pump inversion and low-noise linear post-regulation to achieve 1mVp-p ripple - essential for RF amplifier stability. |
| Shutdown-mode NEGOUT retention | Unlike MAX840/MAX843, MAX844 maintains NEGOUT during shutdown at 20kHz switching - enables always-on LCD contrast control. |
| Minimal external components | Operates with 0.22µF ceramic or tantalum flying/output capacitors; reduces BOM count and PCB area in space-constrained handsets. |
| Wide input voltage support | 2.5V minimum start-up allows use with partially discharged batteries; 10V max rating accommodates 3-cell alkaline or backup supplies. |
| Industrial temperature grade | ISA suffix denotes -25°C to +85°C operation - validated for extended life in consumer handhelds and industrial telemetry devices. |
| CONT-based voltage programming | Uses positive control voltage (0V–10V) and resistor divider to set negative output - simplifies system-level DAC or MCU interface vs. negative-feedback schemes. |
Applications
| Cellular Phone Transmitter Amplifiers | GaAsFET Power Amplifier Modules |
|---|---|
|
Use Scenario: Biasing gate voltage (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 in RF output; 20kHz shutdown mode sustains bias during receive intervals. |
Use Scenario: Setting precise negative gate voltage across discrete GaAsFET arrays in multi-band front-end modules. IC Role / Device Role / Timing Role: Delivers adjustable -0.5V to -9.4V output via CONT pin to match varying FET threshold requirements. Use Value: Eliminates need for external op-amps or DACs; resistor-divider programming enables factory calibration without firmware changes. |
| LCD Contrast Control | Portable Wireless Data Loggers |
|
Use Scenario: Generating negative bias for STN or FSTN LCD segments in battery-powered meters and PDAs. IC Role / Device Role / Timing Role: Supplies unregulated NEGOUT during system sleep to maintain display contrast without waking main processor. Use Value: 20kHz shutdown oscillator draws minimal current while preserving display state - extends battery life by >30% vs. full-power operation. |
Use Scenario: Providing regulated negative supply for analog front-end sensors (e.g., precision ADC references, op-amp rails) in field-deployed loggers. IC Role / Device Role / Timing Role: Acts as compact, low-quiescent DC-DC source replacing bulky inductor-based solutions. Use Value: SO-8 footprint and 0.22µF capacitor support conformal coating and vibration-resistant layouts required in industrial enclosures. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar charge-pump bias 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) with ≤1µA IQ; no CONT pin. | Used where complete power removal is required; unsuitable for LCD bias retention. | Select MAX840ESA+ only if full shutdown (no NEGOUT) and lowest possible quiescent current are mandatory. |
| MAX843ISA+ | Same CONT-based adjustment as MAX844ISA+, but fully disables NEGOUT in shutdown (≤1µA IQ). | Preferred for GaAsFET bias where no auxiliary rail is needed during sleep; lacks LCD support. | Choose MAX843ISA+ when adjustable output is needed but NEGOUT retention is unnecessary - avoids MAX844's higher shutdown current. |
Compared with MAX840ESA+ and MAX843ISA+, the MAX844ISA+ uniquely retains NEGOUT during shutdown at 20kHz - making it the only option among the three for simultaneous GaAsFET bias and LCD contrast control in a single IC, albeit with higher shutdown current.
Availability
MAX844ISA+ is available at Aetrix Electronics and suitable for cellular phone transmitter amplifiers, GaAsFET power amplifier modules, and portable wireless data loggers requiring stable component supply, long-term lifecycle support, and industrial-grade temperature performance.
Supply support for MAX844ISA+ 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 fabless semiconductor company specializing in high-performance analog, mixed-signal, and power-management ICs for industrial, communications, and consumer applications.
The MAX840/MAX843/MAX844 family was designed specifically for low-noise, compact GaAsFET bias generation in battery-powered RF transmitters - prioritizing ripple suppression, capacitor minimization, and flexible voltage programming.
FAQ
What is the primary function of the MAX844ISA+ in RF power amplifier circuits?
The MAX844ISA+ provides a low-noise, regulated -2V gate bias voltage (VGG) for GaAsFETs in cellular transmitter amplifiers. Its 1mVp-p output ripple prevents AM-to-PM distortion, while its ability to retain NEGOUT during shutdown enables seamless transition between transmit and receive modes without disrupting bias stability in the MAX844ISA+ design.
How does the MAX844ISA+ differ from the MAX840ISA+ in shutdown behavior?
Unlike the MAX840ISA+, which disables both OUT and NEGOUT in shutdown, the MAX844ISA+ keeps NEGOUT active while reducing oscillator frequency to 20kHz. This allows the MAX844ISA+ to sustain LCD contrast control or auxiliary bias rails during system sleep - a key differentiator confirmed in the device's functional block diagram and electrical characteristics table.
Can the MAX844ISA+ generate output voltages other than -2V?
Yes - the MAX844ISA+ supports adjustable output from -0.5V to -9.4V using the CONT pin. A resistor divider between OUT and a positive control voltage (0V–10V) sets the output per VOUT = -VCTRL(R2/R1). This flexibility is intrinsic to the MAX844ISA+ architecture and distinct from the MAX840ISA+'s FB-based adjustment.
What capacitor values are recommended for optimal noise performance in the MAX844ISA+?
For lowest noise, use C1/C2/C3 = 1µF (ESR < 0.8Ω) and C4 = 10µF (ESR < 0.2Ω), all ceramic or chip tantalum. The MAX844ISA+ also supports smaller 0.22µF/4.7µF values with only moderate ripple increase - verified in Figures 2d and 4 of the official datasheet - enabling size- and cost-sensitive designs.
Is the MAX844ISA+ pin-compatible with other members of the MAX84x family?
No - the MAX844ISA+ is not pin-compatible with MAX840ISA+ or MAX843ISA+. While all share the same SO-8 package, pin 5 is FB on MAX840ISA+ but CONT on MAX844ISA+, and pin 4 is SHDN on all, but functional behavior differs (e.g., NEGOUT retention). Swapping requires PCB redesign and firmware updates to accommodate the CONT interface in the MAX844ISA+.
MAX844ISA+ Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc./Maxim Integrated
- Series:
- -
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tube
- 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+ FAQ
1.How can I place an order for MAX844ISA+ through Aetrix?
Please submit a Request for Quotation (RFQ) for MAX844ISA+ 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+ reliable?
The price and inventory of MAX844ISA+ are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for MAX844ISA+ is usually 5 days.
3.What payment methods are accepted for MAX844ISA+?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for MAX844ISA+ transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for MAX844ISA+?
MAX844ISA+ orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your MAX844ISA+ 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+?
For technical support, including MAX844ISA+ datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your MAX844ISA+ requirements.
6.How does Aetrix verify that MAX844ISA+ is sourced from the original manufacturer or authorized distributors?
All MAX844ISA+ 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+ meets industry standards.
7.What is the process for return or replacement of MAX844ISA+?
All MAX844ISA+ units undergo pre-shipment inspection (PSI). If there is an issue with MAX844ISA+, 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+ part is unused and in its original packaging.
Return procedure for MAX844ISA+:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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