STMicroelectronics M48T35Y-70MH6E

Overview

M48T35Y-70MH6E from STMicroelectronics is a 5 V, 256 Kbit (32 Kb × 8) non-volatile TIMEKEEPER® SRAM integrating ultra-low-power static RAM, real-time clock, power-fail control circuitry, and on-board lithium battery + 32.768 kHz quartz crystal in a CAPHAT™ DIP-28 package. It delivers BCD-coded timekeeping (year/month/day/hour/minute/second), automatic leap-year correction, and BYTEWIDE™ SRAM access for embedded systems requiring persistent time-stamped data logging in industrial controllers and metering hardware.

For engineers reviewing the M48T35Y-70MH6E datasheet, M48T35Y-70MH6E pinout, M48T35Y-70MH6E application, or M48T35Y-70MH6E equivalent, this device supports JEDEC-standard 32 Kb × 8 SRAM socket replacement, battery-backed RTC operation during main power loss, and precise ±1.53 min/month accuracy at 25 °C - critical for energy metering, PLCs, and backup BIOS timekeeping.

Technical Context

The M48T35Y-70MH6E integrates a BiPORT™ SRAM array with dedicated upper-address clock registers (7FF8h–7FFFh), enabling simultaneous RAM and RTC access via standard address/data bus. Its voltage-sense circuit monitors VCC (4.5–5.5 V) and triggers automatic write protection when VPFD drops to 4.2–4.5 V, then switches to internal battery at VSO ≤ 4.2 V.

Real-time clock operation uses a 32.768 kHz crystal oscillator with programmable calibration (5-bit register, ±31 count adjustment), supporting STOP bit control, century-bit enable (CEB/CB), and frequency test output. Clock updates occur once per second and are halted via READ/WRITE bits in control register 7FF8h without affecting oscillator stability.

Key Specifications

Pinout & Package

Package: PCDIP28 CAPHAT™ - 28-pin plastic dual in-line package with integrated lithium button cell and 32.768 kHz quartz crystal housed in a hermetically sealed cap.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar non-volatile RTC+SRAM applications.

Compared with DS12887A-70IND+, M48T35Y-70MH6E offers superior long-term accuracy via calibration and full 21st-century date support; versus M48T59Y-70MH6E, it provides optimal cost/performance balance for applications needing only 256 Kbit and basic RTC functionality.

Availability

M48T35Y-70MH6E is available at Aetrix Electronics and suitable for energy metering, industrial PLCs, medical device logging, and network equipment BIOS requiring stable component supply with guaranteed 7-year battery-backed data retention.

Supply support for M48T35Y-70MH6E 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing microcontrollers, analog ICs, MEMS, and power management solutions for industrial, automotive, and consumer markets.

The TIMEKEEPER® product line delivers integrated RTC+memory devices optimized for mission-critical timekeeping in infrastructure equipment, emphasizing long-term reliability, battery longevity, and JEDEC-compatible socket replacement capability.

FAQ

What is the battery chemistry and typical lifespan under continuous backup conditions?

The M48T35Y-70MH6E uses a sealed 48 mAh lithium manganese dioxide (Li-MnO₂) button cell integrated within the CAPHAT™ package. Under continuous VCC loss at 25 °C, it guarantees ≥7 years of data and clock retention. Lifespan scales inversely with temperature: ~10 years at 0 °C, ~4 years at 60 °C. Battery replacement is not user-serviceable due to hermetic CAPHAT™ sealing.

How does the M48T35Y-70MH6E handle leap years and century rollover?

It performs automatic leap-year correction for February 29 in years divisible by 4, excluding years divisible by 100 unless also divisible by 400 - valid through year 2100. Century rollover is managed via the CENTURY ENABLE (CEB) and CENTURY (CB) bits in register 7FFCh: when CEB=1, CB toggles at 2000/2100 boundaries, ensuring unambiguous Y2K+ compliance without firmware patching.

Can the internal oscillator be calibrated in-system, and what is the resolution?

Yes - calibration is performed by writing a 5-bit value (0–31) to bits D4–D0 of control register 7FF8h. Each unit adjusts the 32.768 kHz oscillator by ±1 count at the 256-divider stage, yielding ±31 × (1/256) × (1/32768) Hz ≈ ±3.7 ppm per LSB. This enables fine-tuning to <±2 ppm at 25 °C, verified using the frequency test output (FT bit) and external counter.

Is the M48T35Y-70MH6E compatible with standard 32 Kb × 8 SRAM sockets, and what signals require special handling?

It is fully pin- and function-compatible with JEDEC-standard 32 Kb × 8 SRAMs (e.g., AS6C4008, CY62256). No signal re-routing is needed. However, VCC must remain within 4.5–5.5 V to ensure proper VPFD detection, and E should be held high during power-up until VCC exceeds VPFD(max) to prevent inadvertent writes before processor stabilization.