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Microchip Technology MCP79400T-I/ST
- Part No.:
- MCP79400T-I/ST
- Manufacturer:
- Microchip Technology
- Category:
- Real Time Clocks
- Package:
- 8-TSSOP (0.173", 4.40mm Width)
- Datasheet:
-
MCP79400T-I/ST.pdf
- Description:
- IC RTC CLK/CALENDAR I2C 8TSSOP
- Quantity:
- Payment:
- Shipping:
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Product details
Overview
MCP79400T-I/ST from Microchip Technology is a battery-backed I²C Real-Time Clock/Calendar (RTCC) IC with integrated 64-byte SRAM and unprogrammed protected EEPROM. It maintains time across hours, minutes, seconds, day of week, date, month, and year with leap-year compensation to 2399, operates from 1.8V–5.5V main supply and 1.3V–5.5V backup, and draws only 1.2 µA at 3.3V for timekeeping - used in industrial metering, embedded controllers, and power-loss-resilient instrumentation.
For engineers reviewing the MCP79400T-I/ST datasheet, MCP79400T-I/ST pinout, MCP79400T-I/ST application, or MCP79400T-I/ST equivalent, this page delivers verified timing accuracy (±1 ppm digital trim), dual alarm capability, power-fail timestamp logging, I²C interface compliance up to 400 kHz, and TSSOP-8 package mapping - all confirmed for the exact MCP79400T-I/ST variant.
Technical Context
The MCP79400T-I/ST implements a fully autonomous RTCC subsystem using an internal 32.768 kHz oscillator circuit optimized for 6–9 pF crystals, with on-chip digital trimming providing ±1 ppm resolution over ±129 ppm range. Its I²C slave interface uses fixed 7-bit addresses: 0x6F (1101111X) for RTCC/SRAM access and 0x57 (1010111X) for EEPROM operations.
Power management includes automatic switchover between VCC and VBAT at 1.3–1.7 V (typ. 1.5 V), with separate timestamp registers capturing both power-down and power-up events. The multifunction pin (MFP) supports configurable alarm assertion, selectable square-wave output (32.768 kHz, 1024 Hz, 32 Hz, 1 Hz), or general-purpose output - all open-drain with external pull-up required.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Oscillator Frequency | 32.768 kHz nominal - directly drives RTC counters; requires external crystal with 6–9 pF load capacitance |
| Timekeeping Current (VCC) | 1.2 µA at 3.3V - enables multi-year operation from coin-cell backup when main supply fails |
| I²C Clock Rate | Up to 400 kHz - supports fast register read/write in high-throughput embedded systems |
| Digital Trim Resolution | ±1 ppm - allows precise calibration against reference clocks without external components |
| Backup Supply Range | 1.3V to 5.5V - ensures reliable timekeeping down to low-voltage lithium or supercapacitor sources |
| SRAM Capacity | 64 bytes battery-backed - retains user data across power cycles without software intervention |
| EEPROM Size | 8 bytes protected - write-locked via unlock sequence; unprogrammed in MCP79400T-I/ST (vs EUI-48/EUI-64 in MCP79401/79402) |
Pinout & Package
Package: 8-pin TSSOP (lead pitch 0.65 mm, body width 3.0 mm, JEDEC MO-153). Pinout validated per DS20005009G, Table 3-1 and Figure 1-1.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| X1 | Crystal input / External clock input | Accepts 32.768 kHz crystal or external oscillator signal; enables EXTOSC mode when configured |
| X2 | Crystal output | Drives crystal resonator; must be left floating if external clock is used on X1 |
| VBAT | Battery backup supply input | Provides continuous power to RTC and SRAM during VCC loss; switchover threshold 1.3–1.7 V |
| VSS | Ground reference | Common return path for all analog/digital circuits; must be low-impedance for oscillator stability |
| SDA | I²C bidirectional data line | Open-drain interface requiring external pull-up; supports standard/fast-mode I²C up to 400 kHz |
| SCL | I²C clock input | Master-generated clock synchronizing all register transfers; rise/fall times specified per VCC level |
| MFP | Multifunction output pin | Configurable as alarm flag, programmable frequency square wave, or GPIO - all open-drain |
| VCC | Main power supply | 1.8–5.5V operating range; powers I²C logic, SRAM, EEPROM, and digital trimming circuitry |
Key Features
| Feature | Design Value |
|---|---|
| Dual programmable alarms | Independent alarm registers (ALM0/ALM1) support match on seconds through months - enabling wake-up or event-triggered interrupts |
| Power-fail timestamp | Separate registers log exact time of VCC-to-VBAT switchover and VBAT-to-VCC restoration - critical for failure analysis in industrial systems |
| On-chip digital trimming | ±129 ppm adjustment range with ±1 ppm resolution - eliminates need for external trim capacitors or manual calibration |
| 12/24-hour format support | Runtime-selectable time display mode via RTCHOUR register bit - simplifies UI integration across global markets |
| Leap-year compensation | Automatically adjusts February length through year 2399 - removes firmware burden for calendar correctness |
Applications
| Smart Energy Metering | Industrial PLC HMI |
|---|---|
|
Use Scenario: Utility-grade electricity meters requiring tamper-proof time-stamped consumption logs across power outages. IC Role / Device Role / Timing Role: Primary timekeeping engine with battery-backed SRAM storing interval data and power-fail timestamps. Use Value: Maintains sub-second time accuracy for billing intervals and records outage duration with no firmware dependency. |
Use Scenario: Human-machine interface panels in factory automation where local time sync is needed for alarm logging and audit trails. IC Role / Device Role / Timing Role: Standalone RTC providing real-time stamps for operator actions and system events. Use Value: Eliminates host MCU timekeeping overhead and ensures consistent timestamping even during controller resets. |
| Medical Diagnostic Equipment | Network Infrastructure Devices |
|
Use Scenario: Portable diagnostic tools that must retain calibrated timestamps for test results despite intermittent battery use. IC Role / Device Role / Timing Role: Time source for result metadata with guaranteed continuity during battery swaps or charging cycles. Use Value: Enables regulatory-compliant audit trails by preserving time integrity across all power states. |
Use Scenario: Routers and switches requiring accurate time for SNMP logging, NTP synchronization fallback, and firmware update scheduling. IC Role / Device Role / Timing Role: Local time anchor independent of network connectivity or GPS availability. Use Value: Provides deterministic timekeeping during network outages - critical for security event correlation and diagnostics. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar real-time clock/calendar applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| MCP79401T-I/ST | Preprogrammed with EUI-48™ MAC address in protected EEPROM; otherwise identical pinout, timing, and register map | Required when device-level network identity is needed for Ethernet/Wi-Fi stack initialization | Select MCP79401T-I/ST only if EUI-48 is mandatory; MCP79400T-I/ST offers same RTC functionality at lower cost |
| DS3231SN#T&R | Integrated temperature-compensated crystal oscillator (TCXO); ±2 ppm accuracy over -40°C to +85°C vs ±129 ppm max for MCP79400 after trim | Used in high-precision timing applications where crystal aging or thermal drift cannot be tolerated | Choose DS3231SN#T&R when absolute accuracy > ±5 ppm is required; MCP79400T-I/ST suits cost-sensitive designs with calibration capability |
Compared with MCP79401T-I/ST, the MCP79400T-I/ST omits factory-programmed MAC addressing but retains full RTC, SRAM, alarm, and timestamp functionality - making it optimal for non-networked devices. Against DS3231SN#T&R, it trades higher initial accuracy for lower BOM cost and digital trim flexibility, requiring external crystal but supporting wider voltage and simpler layout.
Availability
MCP79400T-I/ST is available at Aetrix Electronics and suitable for smart metering, industrial HMI, medical diagnostics, and network infrastructure requiring stable component supply with long-term lifecycle assurance.
Supply support for MCP79400T-I/ST 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
Microchip Technology Inc. is a U.S.-based semiconductor company specializing in microcontrollers, analog devices, and timing solutions, with broad industrial and automotive qualification coverage.
The MCP7940X product line was designed specifically for battery-backed, low-power real-time clock/calendar applications in resource-constrained embedded systems - emphasizing precision, data retention, and seamless power switchover.
FAQ
What is the primary function of the MCP79400T-I/ST?
The MCP79400T-I/ST is a standalone I²C Real-Time Clock/Calendar IC that maintains accurate time and date (hours, minutes, seconds, day, date, month, year) with leap-year compensation to 2399. It integrates 64-byte battery-backed SRAM, unprogrammed protected EEPROM, dual alarms, and power-fail timestamping - all in a TSSOP-8 package. The MCP79400T-I/ST operates across 1.8–5.5V and draws just 1.2 µA at 3.3V for timekeeping.
Does the MCP79400T-I/ST include factory-programmed identifiers?
No, the MCP79400T-I/ST contains unprogrammed protected EEPROM. Unlike the MCP79401T-I/ST (EUI-48™) or MCP79402T-I/ST (EUI-64™), the MCP79400T-I/ST ships with blank 8-byte EEPROM space that can be custom-programmed via the unlock sequence defined in DS20005009G. This makes the MCP79400T-I/ST ideal for applications requiring unique IDs not tied to IEEE standards.
How does the MCP79400T-I/ST handle power transitions between VCC and VBAT?
The MCP79400T-I/ST automatically switches to VBAT when VCC drops below 1.3–1.7 V (typ. 1.5 V), maintaining RTC operation and SRAM contents without interruption. It logs the exact time of both power-loss (PWRDNxx registers) and power-restoration (PWRUPxx registers) events. The MCP79400T-I/ST continues timekeeping from VBAT down to 1.3 V and draws only 925 nA at 3.0 V, ensuring multi-year backup operation.
Can the MCP79400T-I/ST generate a square-wave output, and what frequencies are supported?
Yes, the MCP79400T-I/ST's MFP pin can be configured as a square-wave output via the SQWEN and SQWFS[1:0] bits in the CONTROL register. Supported frequencies are 32.768 kHz, 1024 Hz, 32 Hz, and 1 Hz - all derived from the internal 32.768 kHz oscillator. The output is open-drain and requires an external pull-up resistor; it remains functional only when powered from VCC, not VBAT.
What crystal specifications are required for reliable operation of the MCP79400T-I/ST?
The MCP79400T-I/ST requires a 32.768 kHz tuning-fork crystal with a specified load capacitance of 6–9 pF. Crystals rated for 12.5 pF are not recommended. External load capacitors (CX1, CX2) must be selected to match the crystal's CL, accounting for pin capacitance (~3 pF) and PCB stray capacitance. Layout best practices - including grounded copper pour around X1/X2 and minimal trace length - are essential for stable oscillation.
MCP79400T-I/ST Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Microchip Technology
- Series:
- -
- Package/Case:
- 8-TSSOP (0.173", 4.40mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Programmable:
- Not Verified
- Type:
- Clock/Calendar
- Features:
- Alarm, Leap Year, Square Wave Output, SRAM, Unique ID
- Memory Size:
- 64B
- Time Format:
- HH:MM:SS (12/24 hr)
- Date Format:
- YY-MM-DD-dd
- Interface:
- I2C, 2-Wire Serial
- Voltage - Supply:
- 1.8V ~ 5.5V
- Voltage - Supply, Battery:
- 1.3V ~ 5.5V
- Current - Timekeeping (Max):
- 1.2µA (Typ) @ 3.3V
- Operating Temperature:
- -40°C ~ 85°C
- Mounting Type:
- Surface Mount
- Grade:
- -
- Qualification:
- -
- Supplier Device Package:
- 8-TSSOP
MCP79400T-I/ST FAQ
1.How can I place an order for MCP79400T-I/ST through Aetrix?
Please submit a Request for Quotation (RFQ) for MCP79400T-I/ST 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 MCP79400T-I/ST reliable?
The price and inventory of MCP79400T-I/ST are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for MCP79400T-I/ST is usually 5 days.
3.What payment methods are accepted for MCP79400T-I/ST?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for MCP79400T-I/ST transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for MCP79400T-I/ST?
MCP79400T-I/ST orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your MCP79400T-I/ST 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 MCP79400T-I/ST?
For technical support, including MCP79400T-I/ST datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your MCP79400T-I/ST requirements.
6.How does Aetrix verify that MCP79400T-I/ST is sourced from the original manufacturer or authorized distributors?
All MCP79400T-I/ST 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 MCP79400T-I/ST meets industry standards.
7.What is the process for return or replacement of MCP79400T-I/ST?
All MCP79400T-I/ST units undergo pre-shipment inspection (PSI). If there is an issue with MCP79400T-I/ST, 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 MCP79400T-I/ST part is unused and in its original packaging.
Return procedure for MCP79400T-I/ST:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
MCP79400T-I/ST Tags
-
MCP7940N-I/SN
Microchip Technology
-
MCP7940MT-I/MNY
Microchip Technology
-
PCF85063ATL/1,118
NXP USA Inc.
-
MCP7940NT-I/SN
Microchip Technology
-
MCP7940NT-I/MS
Microchip Technology
-
MCP7940N-I/MS
Microchip Technology
-
PCF85063AT/AY
NXP USA Inc.
-
PCF85063TP/1Z
NXP Semiconductors
-
PCF85063ATT/AJ
NXP USA Inc.
-
MCP7940NT-E/SN
Microchip Technology
-
MCP7940NT-I/MNY
Microchip Technology
-
MCP79400T-I/SN
Microchip Technology
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