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Analog Devices Inc./Maxim Integrated MAX639CSA
- Part No.:
- MAX639CSA
- Manufacturer:
- Analog Devices Inc./Maxim Integrated
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
MAX639CSA.pdf
- Description:
- IC REG BUCK ADJ/1.3V 225MA 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,405
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Product details
Overview
The MAX639CSA from Maxim Integrated is a 5V fixed-output, high-efficiency step-down DC-DC switching regulator with internal 1A PMOS power switch, 10µA quiescent current, and 225mA output capability over 4V–11.5V input range. It integrates low-battery detection (LBI/LBO), shutdown control, and adjustable feedback for use in portable instrumentation and battery-powered 9V-to-5V conversion.
For engineers reviewing the MAX639CSA datasheet, MAX639CSA pinout, MAX639CSA application, or MAX639CSA equivalent, key selection criteria include its PFM control scheme enabling high efficiency across light-to-heavy loads, SO-8 package compatibility with space-constrained PCB layouts, and verified 5V/225mA operation without external FETs.
Technical Context
The MAX639CSA employs a current-limiting pulse-frequency-modulated (PFM) control architecture that dynamically adjusts switching frequency and duty cycle to maintain constant peak inductor current (IPEAK = 50µs × V / L), ensuring stable regulation across wide input voltage (4V–11.5V) and load (0–225mA) ranges. Its internal 1A PMOS switch eliminates need for external drive circuitry.
It features dual-mode feedback (VFB grounded for 5V fixed output or externally divided for adjustable output), an always-active low-battery comparator (1.28V threshold on LBI, open-drain LBO output), and active-low shutdown (SHDN < 0.8V disables LX). All functions operate within 0°C to +70°C ambient temperature range in SO-8 package.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Voltage | Fixed 5.00V ±2% (guaranteed by correlation to switch timing and feedback thresholds) |
| Input Voltage Range | 4.0V to 11.5V - supports standard 9V batteries and industrial 5V–12V rails |
| Max Output Current | 225mA - achievable with ≥100µH inductor and proper layout per Figure 5 |
| Quiescent Supply Current | 10µA typical - enables multi-year battery life in standby mode |
| Efficiency | Up to 91% at 100mA (V+ = 9V, L = 100µH) - exceeds linear regulators under medium load |
| Low-Battery Threshold | 1.28V on LBI pin - sets precise undervoltage lockout independent of V+ |
| Shutdown Threshold | SHDN < 0.8V disables regulator; >2.0V enables - compatible with TTL/CMOS logic levels |
Pinout & Package
MAX639CSA is housed in an 8-pin SO (Small Outline) package per JEDEC MS-012, 150-mil body width, with exposed pad not present. Pin 1 is bottom-left corner when notch or mark faces up.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VOUT (Pin 1) | Regulated output sense node | Internally connected to voltage divider; must be tied directly to output capacitor for stable 5V regulation |
| LBO (Pin 2) | Open-drain low-battery indicator output | Sinks up to 10mA when LBI < 1.28V; requires external pull-up for logic-level signaling |
| LBI (Pin 3) | Low-battery detection input | Compares external voltage (e.g., via R1/R2 divider from V+) to 1.28V reference |
| GND (Pin 4) | Power and signal ground reference | Must be star-connected with CIN, COUT, and diode anode to minimize ground bounce |
| LX (Pin 5) | PMOS switch drain terminal | Drives external inductor; peak current limited to 600mA; requires Schottky catch diode |
| V+ (Pin 6) | Main power input | Accepts 4V–11.5V; absolute max 12V; decoupled with ≥33µF electrolytic capacitor |
| VFB (Pin 7) | Dual-mode feedback input | Grounded for 5V fixed output; connected to resistor divider for adjustable outputs (1.3V–V+) |
| SHDN (Pin 8) | Active-low enable/disable control | Pulled high internally; driven low (<0.8V) to halt switching and reduce IQ to 1µA |
Key Features
| Feature | Design Value |
|---|---|
| PFM control architecture | Enables 10µA quiescent current while maintaining >85% efficiency at 1mA load - critical for battery longevity |
| Integrated 1A PMOS switch | Eliminates external MOSFET and gate driver, reducing BOM count and PCB area in compact designs |
| Low-battery comparator with LBO output | Provides system-level battery monitoring without additional ICs; remains active during shutdown |
| Adjustable or fixed 5V output | VFB grounding configures 5V output instantly; external resistors allow precise custom voltages (e.g., 3.3V, 2.5V) |
| SO-8 thermal performance | 471mW continuous power dissipation at +70°C (5.88mW/°C derating) - suitable for unforced-air environments |
Applications
| Portable Instrument Power | 9V Battery to 5V Conversion |
|---|---|
Use Scenario: Handheld multimeters and data loggers powered by single 9V alkaline battery requiring regulated 5V for microcontroller and analog front-end. IC Role / Device Role / Timing Role: Primary step-down regulator delivering 5V/150mA with <10µA sleep current to extend battery life beyond 500 hours. Use Value: Replaces inefficient 78L05 linear regulator, improving average efficiency from 55% to >88% across 1–100mA load range. | Use Scenario: Industrial sensor node using 9V PP3 battery to power 5V RS-232 transceiver and MCU, operating intermittently with deep sleep cycles. IC Role / Device Role / Timing Role: High-efficiency DC-DC converter with shutdown control synchronized to MCU wake-up events. Use Value: Enables >2-year field deployment on one battery due to 10µA IQ and fast start-up (<5ms to 5V at 10mA load). |
| High-Efficiency Linear Regulator Replacement | 5V-to-3.3V Point-of-Load |
Use Scenario: Legacy 5V system board needing upgrade to lower power consumption without changing input rail or footprint. IC Role / Device Role / Timing Role: Drop-in replacement for obsolete 7805-based supplies, accepting same 5V–12V input and delivering clean 5V output. Use Value: Reduces thermal load by 65% at 100mA load and eliminates heatsink requirement in enclosed enclosures. | Use Scenario: FPGA development board requiring clean 3.3V supply derived from existing 5V rail for I/O banks. IC Role / Device Role / Timing Role: Adjustable-output configuration (VFB divider) generating precise 3.3V from 5V input with <20mV ripple. Use Value: Achieves 89% efficiency at 200mA - outperforming LDOs by >30 percentage points while meeting FPGA VCCIO noise specs. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar step-down DC-DC converter applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| MAX640CSA | Fixed 3.3V output; identical SO-8 package, pinout, and control features | Designed for 3.3V systems - not interchangeable without modifying feedback network or output capacitor | Select MAX640CSA only when 3.3V (not 5V) is required; shares same layout and bill-of-materials except output voltage setting |
| TPS62231DRVR | 3MHz PWM topology; 2.05–6.0V input; 5V output; 300mA rating; 22µA IQ; WSON-6 package | Higher switching frequency allows smaller inductors/capacitors but lacks integrated LBO comparator and shutdown hysteresis | Choose TPS62231DRVR for space-constrained designs needing ultra-small passives; MAX639CSA preferred where battery monitoring and ultra-low IQ are mandatory |
Compared with MAX640CSA, the MAX639CSA delivers higher output voltage (5V vs. 3.3V) for legacy 5V logic compatibility; compared with TPS62231DRVR, it offers lower quiescent current (10µA vs. 22µA) and integrated battery monitoring, at the cost of larger external magnetics and lower switching frequency.
Availability
MAX639CSA is available at Aetrix Electronics and suitable for portable instrumentation, battery-powered terminals, and industrial sensor nodes requiring stable component supply with guaranteed long-term availability and consistent SO-8 packaging.
Supply support for MAX639CSA 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 U.S.-based semiconductor company specializing in high-performance analog and mixed-signal ICs for power management, sensing, and communications.
The MAX639CSA belongs to Maxim's legacy high-efficiency, low-IQ DC-DC converter family designed specifically for battery-powered portable equipment where extended runtime and minimal external components are critical.
FAQ
What is the maximum input voltage the MAX639CSA can safely handle?
The MAX639CSA has an absolute maximum input voltage rating of 12V on the V+ pin. Continuous operation is specified from 4.0V to 11.5V. Exceeding 12V risks permanent damage to the internal PMOS switch and bandgap reference circuitry. For reliable 9V battery applications, the 11.5V upper limit accommodates fully charged alkaline or NiMH stacks without derating.
Does the MAX639CSA require an external Schottky diode, and why?
Yes, the MAX639CSA requires an external Schottky diode (e.g., 1N5817) connected between LX and VOUT. Because the IC integrates only a PMOS high-side switch, the diode provides the return path for inductor current during switch-off periods. Schottky type is mandatory due to its low forward voltage (~0.55V) and fast recovery - standard rectifiers like 1N4001 cause excessive losses and instability due to slow reverse recovery.
Can the MAX639CSA be used in an inverting configuration to generate -5V?
Yes, the MAX639CSA supports inverting operation per Figure 6 in its datasheet: connect VOUT to system ground, tie GND to the desired negative output node, and route the input through the inductor and diode accordingly. This yields a regulated -5V output referenced to the original system ground, provided the V+ to VOUT differential stays ≤11.5V. Efficiency remains >85% at 10mA with 470µH inductor.
What is the purpose of the VFB pin on the MAX639CSA, and how is it configured for fixed 5V output?
The VFB pin on the MAX639CSA serves as the feedback input for output voltage regulation. For fixed 5V operation, VFB must be connected directly to GND - this selects the internal 5V voltage divider ratio and disables external resistor networks. Leaving VFB floating or improperly terminated causes undefined output voltage and potential instability. The 1.28V internal reference ensures tight 5.00V ±2% tolerance across temperature and line variations.
How does the low-battery detection feature work on the MAX639CSA, and is it active during shutdown?
The MAX639CSA's low-battery detector compares the voltage on LBI to an internal 1.28V reference; when LBI falls below this threshold, LBO (open-drain) pulls low. Crucially, this comparator remains fully operational even when SHDN is asserted and the main regulator is disabled - enabling continuous battery monitoring during system sleep. LBO requires an external pull-up resistor (e.g., 10kΩ to V+) to generate a valid logic signal.
MAX639CSA 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:
- Positive
- Topology:
- Buck
- Output Type:
- Adjustable (Fixed)
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 4V
- Voltage - Input (Max):
- 11.5V
- Voltage - Output (Min/Fixed):
- 1.3V (5V)
- Voltage - Output (Max):
- 11.5V
- Current - Output:
- 225mA
- Frequency - Switching:
- -
- Synchronous Rectifier:
- No
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SOIC
MAX639CSA FAQ
1.How can I place an order for MAX639CSA through Aetrix?
Please submit a Request for Quotation (RFQ) for MAX639CSA 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 MAX639CSA reliable?
The price and inventory of MAX639CSA are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for MAX639CSA is usually 5 days.
3.What payment methods are accepted for MAX639CSA?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for MAX639CSA transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for MAX639CSA?
MAX639CSA orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your MAX639CSA 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 MAX639CSA?
For technical support, including MAX639CSA datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your MAX639CSA requirements.
6.How does Aetrix verify that MAX639CSA is sourced from the original manufacturer or authorized distributors?
All MAX639CSA 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 MAX639CSA meets industry standards.
7.What is the process for return or replacement of MAX639CSA?
All MAX639CSA units undergo pre-shipment inspection (PSI). If there is an issue with MAX639CSA, 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 MAX639CSA part is unused and in its original packaging.
Return procedure for MAX639CSA:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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