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Analog Devices Inc./Maxim Integrated MAX640CSA+T
- Part No.:
- MAX640CSA+T
- Manufacturer:
- Analog Devices Inc./Maxim Integrated
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
MAX640CSA+T.pdf
- Description:
- IC REG BUCK ADJ/1.3V 225MA 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,561
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Product details
Overview
MAX640CSA+T from Maxim Integrated is a 3.3V, 225mA step-down DC-DC switching regulator with pulse-frequency-modulated (PFM) control, 10µA quiescent current, and integrated 1A PMOS power switch-designed for high-efficiency conversion of 4V–11.5V inputs (e.g., 9V battery) to stable 3.3V supply in portable instrumentation.
For engineers reviewing the MAX640CSA+T datasheet, MAX640CSA+T pinout, MAX640CSA+T application, or MAX640CSA+T equivalent, key selection criteria include its fixed 3.3V output, low-IQ PFM operation across light-to-heavy loads, internal low-battery detection comparator (LBI/LBO), SO-8 package thermal performance, and compatibility with standard 100µH inductors and Schottky diodes like 1N5817.
Technical Context
The MAX640CSA+T implements a current-limiting PFM control scheme that dynamically adjusts on-time (tON = 50µs × VIN/(VIN − VOUT)) and off-time (tOFF ≥ 50µs × VIN/VOUT) to maintain constant peak inductor current (~600mA) while achieving >85% efficiency at 25mA–100mA loads. Its internal 1.28V bandgap reference enables both preset 3.3V regulation (via grounded VFB) and adjustable outputs using external resistive dividers.
It integrates a low-battery detector with 1.28V threshold referenced to LBI, driving open-drain LBO during undervoltage conditions-active even in shutdown mode. The PMOS switch features 0.8Ω typical on-resistance and supports inverting configurations (e.g., generating −3.3V from two AA cells), with LX rated for 1A peak current and −0.3V to (V+ + 0.3V) voltage swing.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Voltage | Fixed 3.3V ±4% (2.88V to 3.12V) - guaranteed over full temperature and load range without external components. |
| Input Voltage Range | 4.0V to 11.5V - supports common battery sources including 9V alkaline and multi-cell Li-ion stacks. |
| Max Output Current | 225mA - achievable with 100µH inductor and proper layout; limited by peak inductor current (600mA) and thermal dissipation in SO-8 package. |
| Quiescent Supply Current | 10µA typical - enables >1-year battery life in always-on portable devices with light loads. |
| Efficiency | 87% typical at 100mA, VIN = 4.3V - exceeds linear regulators by >3× at medium loads, reducing thermal stress and PCB area. |
| Low-Battery Threshold | 1.28V on LBI input - configurable via external resistor divider to trigger LBO at user-defined battery voltage (e.g., 3.0V system cutoff). |
| Shutdown Threshold | 0.80V to 1.15V on SHDN pin - ensures clean disable with TTL/CMOS logic levels; draws <0.1µA in shutdown. |
Pinout & Package
MAX640CSA+T is housed in an 8-pin SOIC (SO-8, 150-mil width) package with exposed pad not present; thermal resistance θJA = 170°C/W, derating 5.88mW/°C above +70°C. Pin functions are validated per Maxim's official datasheet (Rev 4, 7/05) and chip topography diagram.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VOUT | Regulated output sense node | Internally connected to feedback divider; must be tied directly to output capacitor for stable 3.3V regulation. |
| LBO | Open-drain low-battery indicator output | Sinks up to 10mA when LBI falls below 1.28V; requires external pull-up for logic-level signaling. |
| LBI | Low-battery detection input | High-impedance input (2nA bias) comparing against internal 1.28V reference; sets system brownout point. |
| GND | Power and signal ground reference | Common return for all currents; must be star-connected with CIN, COUT, and diode anode to minimize ground bounce. |
| LX | PMOS switch drain terminal | Drives external inductor; swings from GND to V+; requires low-ESR ceramic bypass near IC. |
| V+ | Main power input | Accepts 4V–11.5V; must be decoupled with ≥33µF low-ESR capacitor within 5mm of pin. |
| VFB | Dual-mode feedback input | Grounded for fixed 3.3V output; connected to external divider for adjustable voltages (1.3V to VIN). |
| SHDN | Active-low enable/disable control | Pulled high internally; <0.8V disables regulator and reduces IQ to <0.1µA; remains functional during LBI monitoring. |
Key Features
| Feature | Design Value |
|---|---|
| PFM Control Architecture | Maintains >85% efficiency from 10µA to 225mA load by varying switching frequency instead of duty cycle-eliminates light-load inefficiency of PWM. |
| Integrated 1A PMOS Switch | Reduces BOM count to only inductor, diode, and two capacitors; eliminates gate-drive complexity and external FET selection. |
| Low-Battery Detection | Dedicated LBI/LBO circuit with 25µs response time and 1.28V precision threshold-enables autonomous battery management without MCU intervention. |
| Adjustable or Fixed Output | Zero-component 3.3V operation (VFB = GND); flexible 1.3V–VIN adjustment via external resistors-supports diverse rail requirements. |
| Inverting Configuration Support | Enables generation of regulated negative outputs (e.g., −3.3V) from positive supplies-uses same component set as buck mode. |
Applications
| 9V Battery to 3.3V Conversion | High-Efficiency Linear Regulator Replacement |
|---|---|
Use Scenario: Powering 3.3V microcontrollers and sensors from a single 9V alkaline battery in handheld test equipment. IC Role / Device Role / Timing Role: Primary DC-DC converter providing regulated 3.3V rail with dynamic load response and battery monitoring. Use Value: Extends battery life >3× versus LM1117-3.3 due to 10µA quiescent current and PFM efficiency at partial loads. |
Use Scenario: Replacing inefficient 78L33 linear regulators in industrial sensor nodes requiring 3.3V at up to 150mA. IC Role / Device Role / Timing Role: Efficient step-down regulator eliminating heat-sink requirement and enabling compact enclosure design. Use Value: Reduces thermal rise from >25°C to <5°C at 100mA, enabling conformal coating and sealed housing without derating. |
| Portable Instruments and Handy-Terminals | 5V-to-3.3V Converters |
Use Scenario: Supplying 3.3V logic rails in battery-powered multimeters and barcode scanners with intermittent high-current bursts. IC Role / Device Role / Timing Role: Load-adaptive regulator delivering fast transient response (<1ms recovery) and low-noise output via optimized LC filter. Use Value: Maintains 3.3V ±2% during 0–200mA load steps, preventing digital glitches in ARM Cortex-M0+ processors. |
Use Scenario: Generating clean 3.3V auxiliary rail from existing 5V system bus in embedded controllers and FPGA carrier boards. IC Role / Device Role / Timing Role: Point-of-load converter with independent shutdown control and LBO signaling for upstream power sequencing. Use Value: Enables coordinated power-down of 3.3V peripherals when main 5V rail drops, improving system reliability during brownouts. |
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 |
|---|---|---|---|
| TPS62231DRYR | 3MHz fixed-frequency PWM, 2.05V–6.5V input, 3.3V output, 300mA max, 17µA IQ | Better EMI control via fixed frequency; higher IQ reduces ultra-low-power runtime | Prefer for noise-sensitive analog circuits where PFM ripple is unacceptable; requires different inductor (2.2µH vs. 100µH) |
| RT8059GJ6 | Hysteretic PFM controller, 2.5V–5.5V input, 3.3V output, 300mA max, 22µA IQ, no LBI/LBO | No integrated low-battery monitor; simpler feedback but less system-level integration | Choose when battery monitoring is handled externally; offers smaller solution size with 4.7µH inductor |
Compared with TPS62231DRYR and RT8059GJ6, the MAX640CSA+T delivers superior light-load efficiency and built-in battery monitoring in a legacy-compatible SO-8 footprint-making it optimal for cost-sensitive, long-life portable designs where PFM noise is manageable and system-level fault detection is required.
Availability
MAX640CSA+T is available at Aetrix Electronics and suitable for portable instrumentation, battery-powered hand terminals, and industrial sensor nodes requiring stable component supply with extended lifecycle support and traceable sourcing.
Supply support for MAX640CSA+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 U.S.-based semiconductor company specializing in high-performance analog and mixed-signal ICs for power management, sensing, and interface applications.
The MAX639/MAX640/MAX653 family was designed specifically for ultra-low-power, minimum-component DC-DC conversion in space-constrained portable systems-emphasizing PFM efficiency, integrated protection, and ease of use with standard passive components.
FAQ
What output voltage does the MAX640CSA+T provide, and how is it configured?
The MAX640CSA+T provides a fixed 3.3V output with ±4% tolerance across temperature and load. It achieves this by grounding the VFB pin, which selects the internal 3.3V feedback divider. No external resistors are needed for this configuration. For adjustable outputs between 1.3V and VIN, connect VFB to an external resistor divider per the formula R3 = R4 × ((VOUT/1.28V) − 1). The MAX640CSA+T datasheet confirms this behavior in the "Fixed or Adjustable Output" section.
Can the MAX640CSA+T operate from a 3.7V Li-ion battery?
Yes, the MAX640CSA+T supports input voltages from 4.0V to 11.5V, so a fully charged 3.7V Li-ion cell (4.2V) is within specification. However, operation below 4.0V is not guaranteed-the device may cease regulation or exhibit reduced output current capability as VIN approaches dropout. For single-cell Li-ion applications requiring full 3.0V–4.2V coverage, consider the MAX640CSA+T only if system operation is restricted to the upper 0.5V of the battery curve, or pair it with a low-VIN supervisor. The MAX640CSA+T electrical characteristics table explicitly lists VIN(min) = 4.0V.
Does the MAX640CSA+T include a low-battery detection feature, and how is it used?
Yes, the MAX640CSA+T integrates a dedicated low-battery detector with LBI (input) and LBO (open-drain output) pins. When the voltage at LBI falls below 1.28V, LBO sinks current-signaling battery depletion. This function remains active during shutdown mode. To set a custom detection threshold (e.g., 3.0V), use resistors R1 and R2 per R1 = R2 × ((VLB/1.28V) − 1). The MAX640CSA+T pin description and Applications Information sections detail this implementation with typical values.
What inductor value is recommended for the MAX640CSA+T, and why?
Maxim recommends a 100µH inductor with ≥600mA saturation current for the MAX640CSA+T. This value balances peak current limitation (per Equation 3: IPEAK = 50µs / L), efficiency (>85% at 100mA), and physical size. Smaller inductors increase ripple and risk saturation; larger ones reduce ripple but extend start-up time and may lower efficiency at light loads. Table 1 in the MAX640CSA+T datasheet lists qualified suppliers and part numbers such as Sumida CDR74-100.
Is the MAX640CSA+T pin-compatible with other devices in the MAX639/MAX640/MAX653 family?
Yes, all members of the MAX639/MAX640/MAX653 family-including MAX640CSA+T-share identical 8-pin SOIC pinouts and thermal characteristics. They differ only in preset output voltage (5.0V, 3.3V, 3.0V) and minor electrical specs (e.g., output voltage tolerance, efficiency curves). This allows direct substitution in existing layouts when changing output rails, provided the VFB connection matches the target voltage (grounded for MAX640CSA+T). The Pin Configuration diagram in the MAX640CSA+T datasheet confirms identical pin mapping.
MAX640CSA+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:
- Active
- 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 (3.3V)
- 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
MAX640CSA+T FAQ
1.How can I place an order for MAX640CSA+T through Aetrix?
Please submit a Request for Quotation (RFQ) for MAX640CSA+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 MAX640CSA+T reliable?
The price and inventory of MAX640CSA+T are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for MAX640CSA+T is usually 5 days.
3.What payment methods are accepted for MAX640CSA+T?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for MAX640CSA+T transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for MAX640CSA+T?
MAX640CSA+T orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your MAX640CSA+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 MAX640CSA+T?
For technical support, including MAX640CSA+T datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your MAX640CSA+T requirements.
6.How does Aetrix verify that MAX640CSA+T is sourced from the original manufacturer or authorized distributors?
All MAX640CSA+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 MAX640CSA+T meets industry standards.
7.What is the process for return or replacement of MAX640CSA+T?
All MAX640CSA+T units undergo pre-shipment inspection (PSI). If there is an issue with MAX640CSA+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 MAX640CSA+T part is unused and in its original packaging.
Return procedure for MAX640CSA+T:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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