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Analog Devices Inc./Maxim Integrated MAX851ISA
- Part No.:
- MAX851ISA
- Manufacturer:
- Analog Devices Inc./Maxim Integrated
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
MAX851ISA.pdf
- Description:
- IC REG CHG PUMP ADJ/-1.28V 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,638
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Product details
Overview
MAX851ISA from Maxim Integrated is a low-noise, inverting, regulated charge-pump DC/DC converter optimized for GaAsFET biasing in cellular transmitter amplifiers. It delivers a fixed -4.1V output at up to 5mA, operates from 4.5V to 10V input, features 2mVp-p output ripple, and includes active-high TTL-level shutdown with ≤5µA max shutdown current over temperature.
For engineers reviewing the MAX851ISA datasheet, MAX851ISA pinout, MAX851ISA application, or MAX851ISA equivalent, this device is selected for precision negative bias generation where ultra-low noise, stable regulation under load variation, and minimal PCB footprint in an 8-pin SO package are critical design requirements.
Technical Context
The MAX851ISA uses a two-stage architecture: a capacitive charge pump inverts the input voltage to generate an unregulated negative rail at NEGOUT, followed by an internal N-channel linear regulator that stabilizes and filters the output at OUT. Its feedback node (FB) is internally tied to a -1.28V reference, enabling fixed -4.1V output when grounded.
Unlike the MAX850 (active-low SHDN) or MAX852 (external OSC), the MAX851ISA implements active-high shutdown logic on Pin 4, and shares the same 100kHz internal oscillator frequency and 8-pin SO package as the MAX850/MAX852 variants - but excludes external clock synchronization capability.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Voltage | Fixed -4.1V (±2%) - set by grounding FB pin; enables direct GaAsFET VGG bias without external resistors. |
| Output Current | 5mA continuous - sufficient for biasing multiple GaAsFETs or low-power RF front-end stages. |
| Input Voltage Range | 4.5V to 10V - compatible with 4-cell NiCd/NiMH or single Li-ion battery systems. |
| Output Ripple | 2mVp-p - achieved via integrated linear post-regulator; critical for minimizing phase noise in RF power amplifiers. |
| Shutdown Current | ≤5µA max over temperature - ensures ultra-low quiescent drain during standby in battery-powered handsets. |
| Switching Frequency | 100kHz - balances EMI control, capacitor size, and efficiency; not user-adjustable on MAX851ISA. |
| Operating Temp | -25°C to +85°C - qualified for industrial and extended commercial handset environments. |
Pinout & Package
MAX851ISA is housed in an 8-pin plastic small-outline (SO) package, 3.9mm × 4.9mm body, 1.27mm pitch, with exposed pad not connected. Pin 1 is marked by a beveled corner or dot.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 IN | Positive supply input | Accepts 4.5V–10V DC; must be decoupled with ≥1µF low-ESR capacitor near the pin. |
| 2 GND | Ground reference | System ground return for charge pump, regulator, and logic; requires low-impedance connection to PCB ground plane. |
| 3 OUT | Regulated negative output | Delivers -4.1V at up to 5mA; connects directly to GaAsFET gate (VGG) with local 10µF low-ESR capacitor. |
| 4 SHDN | Active-high shutdown control | Drives internal circuitry into low-power state when pulled ≥2.0V; ≤0.5V disables regulation and reduces IQ to ≤5µA. |
| 5 NEGOUT | Unregulated negative charge-pump output | Provides inverted voltage (≈ -VIN) to linear regulator; connects to C1- and C2+; not intended for external loading. |
| 6 C1- | Negative terminal of flying capacitor C1 | Completes charge-pump switching loop; requires 1µF low-ESR ceramic/tantalum capacitor between C1+ and C1-. |
| 7 C1+ | Positive terminal of flying capacitor C1 | Switches between IN and NEGOUT; forms core inversion stage with C1- and internal switches. |
| 8 FB | Feedback input | Internally referenced to -1.28V; grounding sets VOUT = -4.1V; floating or resistor-divider enables adjustable outputs (not default mode). |
Key Features
| Feature | Design Value |
|---|---|
| Fixed -4.1V Output | Eliminates external feedback resistors - simplifies layout and improves production consistency for GaAsFET bias rails. |
| 2mVp-p Output Ripple | Enables clean RF amplifier biasing without additional filtering; measured across C4 with proper probe technique. |
| Active-High Shutdown | Direct interface with microcontroller GPIOs without level-shifting; supports fast turn-on/turn-off sequencing in burst-mode transmitters. |
| 100kHz Internal Oscillator | Stable switching frequency minimizes EMI sensitivity and avoids interference with IF or RF bands in handheld radios. |
| 8-Pin SO Package | Standard footprint enables drop-in replacement among MAX850–MAX853 family; supports automated assembly and reflow. |
Applications
| Cellular Transmitter Amplifiers | LCD Contrast Control |
|---|---|
|
Use Scenario: Biasing the gate of GaAsFET power amplifier modules in GSM/EDGE handsets during transmit bursts. IC Role / Device Role / Timing Role: Provides stable, low-noise negative VGG to control FET conduction and optimize linearity/EVM. Use Value: 2mVp-p ripple prevents AM-to-PM distortion; 5mA drive supports multi-FET arrays; shutdown enables Tx/Rx power gating. |
Use Scenario: Generating adjustable negative bias for LCD segment drivers in portable PDAs and communicators. IC Role / Device Role / Timing Role: Supplies regulated negative voltage to LCD common electrode or segment backplane. Use Value: Fixed -4.1V output matches standard STN/FSTN LCD contrast ranges; low quiescent current extends battery life in always-on displays. |
| Wireless Data Loggers | Personal Communicators |
|
Use Scenario: Powering low-current analog front-ends and sensor bias circuits in battery-operated environmental monitors. IC Role / Device Role / Timing Role: Delivers clean negative rail for op-amps, ADC references, or precision current sources. Use Value: ≤5µA shutdown current enables multi-year operation on coin cells; 4.5V–10V input accommodates aging battery discharge curves. |
Use Scenario: Supplying gate bias to RF switches and low-noise amplifiers in dual-mode (cellular + Bluetooth) handheld devices. IC Role / Device Role / Timing Role: Generates isolated negative supply independent of main system rail to reduce coupling noise. Use Value: 8-pin SO package saves board space; -25°C to +85°C rating ensures reliability across indoor/outdoor operating conditions. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar negative charge-pump regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| MAX850ISA | Active-low TTL shutdown (SHDN pin low = off); identical -4.1V output, ripple, and package. | Requires inverted control signal; better suited for systems with open-drain or active-low enable logic. | Select MAX850ISA when existing MCU firmware or CPLD logic drives shutdown with active-low signals. |
| MAX852ISA | Replaces SHDN with OSC pin for external 50–250kHz clock synchronization; otherwise identical output specs. | Used where system-level clock alignment is required to avoid beat frequencies or EMI peaks. | Choose MAX852ISA only if precise frequency control or EMI coexistence with other clocks is mandatory. |
Compared with MAX850ISA and MAX852ISA, the MAX851ISA offers simplified active-high control without clock management overhead - making it optimal for cost-sensitive, space-constrained cellular front-ends where fixed-frequency operation and direct GPIO interfacing are prioritized.
Availability
MAX851ISA is available at Aetrix Electronics and suitable for cellular phone transmitter modules, LCD-bias power supplies, and wireless data loggers requiring stable component supply, consistent parametric performance, and long-term industrial temperature support.
Supply support for MAX851ISA 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 power-management ICs for high-reliability industrial, communications, and consumer applications.
The MAX850–MAX853 family was engineered specifically for low-noise, compact GaAsFET biasing in portable RF transmitters - emphasizing ripple suppression, shutdown efficiency, and integration of charge-pump and linear regulation in one SO package.
FAQ
What is the output voltage tolerance of the MAX851ISA?
The MAX851ISA delivers a nominal -4.1V output with ±2% tolerance over temperature and load. This specification is guaranteed across the full -25°C to +85°C operating range and at output currents from 0 to 5mA, as verified in the MAX850–MAX853 datasheet Figure 2a and Electrical Characteristics table. The MAX851ISA achieves this stability using an internal -1.28V reference and precision resistor network within the feedback path.
Can the MAX851ISA be used with a 3.3V input supply?
No - the MAX851ISA requires a minimum 4.5V input to maintain regulation at -4.1V output. At VIN < 4.5V, the internal charge pump cannot generate sufficient headroom for the linear post-regulator, causing output voltage collapse and loss of regulation. The datasheet explicitly specifies 4.5V to 10V as the valid input range, and Figure 2a shows VIN = 6V as the typical test condition for VOUT = -4.1V.
How does the MAX851ISA achieve 2mVp-p output ripple?
The MAX851ISA achieves 2mVp-p output ripple through cascaded noise reduction: first, the charge-pump stage generates a coarse negative rail at NEGOUT; then, an internal N-channel linear regulator filters and stabilizes that rail before delivering it to OUT. This two-stage architecture - confirmed in the "Detailed Description" section and Figure 1a - attenuates switching artifacts far more effectively than standalone charge pumps, enabling RF-grade biasing without external LDOs.
Is the MAX851ISA pin-compatible with the MAX850ISA?
Yes - the MAX851ISA and MAX850ISA share identical 8-pin SO packaging, pin numbering, and functional pin assignments (IN, GND, OUT, SHDN, NEGOUT, C1-, C1+, FB). The only difference is SHDN logic polarity: MAX851ISA uses active-high, while MAX850ISA uses active-low. No PCB layout change is needed, but control signal polarity must be verified in system firmware or hardware interface design.
What external capacitors are required for stable operation of the MAX851ISA?
The MAX851ISA requires four external capacitors: C1 (1µF, low-ESR ceramic/tantalum) between C1+ and C1-; C2 (1µF, same spec) between C1+ and NEGOUT; C3 (1µF) from IN to GND; and C4 (10µF, 0.2Ω ESR) from OUT to GND. These values are specified in Figures 2a and 2b of the datasheet and validated in Typical Operating Characteristics - deviating significantly impacts ripple, start-up time, and load regulation.
MAX851ISA 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
- Function:
- Step-Down
- Output Configuration:
- Negative
- Topology:
- Charge Pump
- Output Type:
- Adjustable (Fixed)
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 4.5V
- Voltage - Input (Max):
- 10V
- Voltage - Output (Min/Fixed):
- -1.28V (-4.1V)
- Voltage - Output (Max):
- -9V
- Current - Output:
- 5mA
- Frequency - Switching:
- 100kHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- -25°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SOIC
MAX851ISA FAQ
1.How can I place an order for MAX851ISA through Aetrix?
Please submit a Request for Quotation (RFQ) for MAX851ISA 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 MAX851ISA reliable?
The price and inventory of MAX851ISA are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for MAX851ISA is usually 5 days.
3.What payment methods are accepted for MAX851ISA?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for MAX851ISA transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for MAX851ISA?
MAX851ISA orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your MAX851ISA 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 MAX851ISA?
For technical support, including MAX851ISA datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your MAX851ISA requirements.
6.How does Aetrix verify that MAX851ISA is sourced from the original manufacturer or authorized distributors?
All MAX851ISA 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 MAX851ISA meets industry standards.
7.What is the process for return or replacement of MAX851ISA?
All MAX851ISA units undergo pre-shipment inspection (PSI). If there is an issue with MAX851ISA, 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 MAX851ISA part is unused and in its original packaging.
Return procedure for MAX851ISA:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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