M48T35AY M48T35AV 256 Kbit (32Kb x8) TIMEKEEPER® SRAM ■ INTEGRATED ULTRA LOW POWER SRAM, REAL TIME CLOCK, POWER-FAIL CONTROL CIRCUIT and BATTERY ■ BYTEWIDE™ RAM-LIKE CLOCK ACCESS ■ BCD CODED YEAR, MONTH, DAY, DATE, HOURS, MINUTES and SECONDS ■ BATTERY LOW FLAG (BOK) ■ FREQUENCY TEST OUTPUT for REAL TIME CLOCK ■ AUTOMATIC POWER-FAIL CHIP DESELECT and WRITE PROTECTION ■ WRITE PROTECT VOLTAGES (VPFD = Power-fail Deselect Voltage): SNAPHAT (SH) Battery/Crystal 28 1 28 PCDIP28 (PC) Battery/Crystal CAPHAT 1 SOH28 (MH) – M48T35AY: 4.2V ≤ V PFD ≤ 4.5V – M48T35AV: 2.7V ≤ VPFD ≤ 3.0V ■ SELF-CONTAINED BATTERY and CRYSTAL in the CAPHAT DIP PACKAGE ■ SOIC PACKAGE PROVIDES DIRECT CONNECTION for a SNAPHAT HOUSING CONTAINING the BATTERY and CRYSTAL ■ SNAPHAT® HOUSING (BATTERY and CRYSTAL) is REPLACEABLE ■ PIN and FUNCTION COMPATIBLE with JEDEC STANDARD 32Kb x8 SRAMs DESCRIPTION The M48T35AY/35AV TIMEKEEPER ® RAM is a 32Kb x8 non-volatile static RAM and real time clock. The monolithic chip is available in two special packages to provide a highly integrated battery backed-up memory and real time clock solution. The M48T35AY/35AV is a non-volatile pin and function equivalent to any JEDEC standard 32Kb x8 SRAM. It also easily fits into many ROM, EPROM, and EEPROM sockets, providing the non-volatility of PROMs without any requirement for special write timing or limitations on the number of writes that can be performed. May 2000 Figure 1. Logic Diagram VCC 15 8 A0-A14 W DQ0-DQ7 M48T35AY M48T35AV E G VSS AI02797B 1/19 M48T35AY, M48T35AV Figure 2A. DIP Connections A14 A12 A7 A6 A5 A4 A3 A2 A1 A0 DQ0 DQ1 DQ2 VSS 28 1 27 2 26 3 25 4 24 5 23 6 7 M48T35AY 22 8 M48T35AV 21 20 9 19 10 18 11 17 12 13 16 14 15 Figure 2B. SOIC Connections VCC W A13 A8 A9 A11 G A10 E DQ7 DQ6 DQ5 DQ4 DQ3 AI02798B Table 1. Signal Names A0-A14 Address Inputs DQ0-DQ7 Data Inputs / Outputs E Chip Enable G Output Enable W Write Enable VCC Supply Voltage VSS Ground The 28 pin 600mil DIP CAPHAT™ houses the M48T35AY/35AV silicon with a quartz crystal and a long life lithium button cell in a single package. The 28 pin 330mil SOIC provides sockets with gold plated contacts at both ends for direct connection to a separate SNAPHAT housing containing the battery and crystal. The unique design allows the SNAPHAT battery package to be mounted on top of the SOIC package after the 2/19 A14 A12 A7 A6 A5 A4 A3 A2 A1 A0 DQ0 DQ1 DQ2 VSS 1 2 3 4 5 6 7 M48T35AY 8 M48T35AV 9 10 11 12 13 14 28 27 26 25 24 23 22 21 20 19 18 17 16 15 VCC W A13 A8 A9 A11 G A10 E DQ7 DQ6 DQ5 DQ4 DQ3 AI02799 completion of the surface mount process. Insertion of the SNAPHAT housing after reflow prevents potential battery and crystal damage due to the high temperatures required for device surfacemounting. The SNAPHAT housing is keyed to prevent reverse insertion. The SOIC and battery/crystal packages are shipped separately in plastic anti-static tubes or in Tape & Reel form. For the 28 lead SOIC, the battery/crystal package (i.e. SNAPHAT) part number is "M4T28BR12SH1". As Figure 3 shows, the static memory array and the quartz controlled clock oscillator of the M48T35AY/35AV are integrated on one silicon chip. The two circuits are interconnected at the upper eight memory locations to provide user accessible BYTEWIDE™ clock information in the bytes with addresses 7FF8h-7FFFh. The clock locations contain the year, month, date, day, hour, minute, and second in 24 hour BCD format. Corrections for 28, 29 (leap year), 30, and 31 day months are made automatically. Byte 7FF8h is the clock control register. This byte controls user access to the clock information and also stores the clock calibration setting. M48T35AY, M48T35AV Table 2. Absolute Maximum Ratings (1) Symbol TA TSTG TSLD (2) VIO Parameter Value Unit Grade 1 0 to 70 °C Grade 6 –40 to 85 °C –40 to 85 °C 260 °C M48T35AY –0.3 to 7 V M48T35AV –0.3 to 4.6 V M48T35AY –0.3 to 7 V M48T35AV –0.3 to 4.6 V Ambient Operating Temperature Storage Temperature (VCC Off, Oscillator Off) Lead Solder Temperature for 10 seconds Input or Output Voltages VCC Supply Voltage IO Output Current 20 mA PD Power Dissipation 1 W Note: 1. Stresses greater than those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to the absolute maximum rating conditions for extended periods of time may affect reliability. 2. Soldering temperature not to exceed 260°C for 10 seconds (total thermal budget not to exceed 150°C for longer than 30 seconds). CAUTION: Negative undershoots below –0.3V are not allowed on any pin while in the Battery Back-up mode. Table 3. Operating Modes (1) Mode VCC Deselect Write Read 4.5V to 5.5V or 3.0V to 3.6V Read E G W DQ0-DQ7 Power VIH X X High Z Standby VIL X VIL DIN Active VIL VIL VIH DOUT Active VIL VIH VIH High Z Active Deselect VSO to VPFD (min) (2) X X X High Z CMOS Standby Deselect ≤ VSO X X X High Z Battery Back-up Mode Note: 1. X = VIH or VIL; VSO = Battery Back-up Switchover Voltage. 2. See Table 7 for details. The eight clock bytes are not the actual clock counters themselves; they are memory locations consisting of BiPORT™ read/write memory cells. The M48T35AY/35AV includes a clock control circuit which updates the clock bytes with current information once per second. The information can be accessed by the user in the same manner as any other location in the static memory array. The M48T35AY/35AV also has its own Power-fail Detect circuit. The control circuitry constantly mon- itors the single 5V supply for an out of tolerance condition. When VCC is out of tolerance, the circuit write protects the SRAM, providing a high degree of data security in the midst of unpredictable system operation brought on by low V CC. As VCC falls below approximately 3V, the control circuitry connects the battery which maintains data and clock operation until valid power returns. 3/19 M48T35AY, M48T35AV Figure 3. Block Diagram OSCILLATOR AND CLOCK CHAIN 8 x 8 BiPORT SRAM ARRAY 32,768 Hz CRYSTAL A0-A14 POWER 32,760 x 8 SRAM ARRAY LITHIUM CELL E VOLTAGE SENSE AND SWITCHING CIRCUITRY VCC READ MODE The M48T35AY/35AV is in the Read Mode whenever W (Write Enable) is high and E (Chip Enable) is low. The unique address specified by the 15 Address Inputs defines which one of the 32,768 bytes of data is to be accessed. Valid data will be available at the Data I/O pins within Address Access time (t AVQV) after the last address input signal is stable, providing that the E and G access times are also satisfied. If the E and G access times are not met, valid data will be available after the latter of the Chip Enable Access time (t ELQV) or Output Enable Access time (tGLQV). The state of the eight three-state Data I/O signals is controlled by E and G. If the outputs are activated before t AVQV, the data lines will be driven to an indeterminate state until tAVQV. If the Address Inputs are changed while E and G remain active, 4/19 DQ0-DQ7 W VPFD G VSS AI01623 output data will remain valid for Output Data Hold time (tAXQX) but will go indeterminate until the next Address Access. WRITE MODE The M48T35AY/35AV is in the Write Mode whenever W and E are low. The start of a write is referenced from the latter occurring falling edge of W or E. A write is terminated by the earlier rising edge of W or E. The addresses must be held valid throughout the cycle. E or W must return high for a minimum of tEHAX from Chip Enable or tWHAX from Write Enable prior to the initiation of another read or write cycle. Data-in must be valid tDVWH prior to the end of write and remain valid for tWHDX afterward. G should be kept high during write cycles to avoid bus contention; although, if the output bus has been activated by a low on E and G, a low on W will disable the outputs tWLQZ after W falls. M48T35AY, M48T35AV Figure 4. AC Testing Load Circuit Table 4. AC Measurement Conditions Input Rise and Fall Times Input Pulse Voltages Input and Output Timing Ref. Voltages ≤ 5ns 0 to 3V 1.5V Note that Output Hi-Z is defined as the point where data is no longer driven. DATA RETENTION MODE With valid VCC applied, the M48T35AY/35AV operates as a conventional BYTEWIDE static RAM. Should the supply voltage decay, the RAM will automatically power-fail deselect, write protecting itself when V CC falls within the VPFD (max), VPFD (min) window. All outputs become high impedance, and all inputs are treated as "don’t care." Note: A power failure during a write cycle may corrupt data at the currently addressed location, but does not jeopardize the rest of the RAM’s content. At voltages below V PFD (min), the user can be assured the memory will be in a write protected state, provided the VCC fall time is not less than tF. The M48T35AY/35AV may respond to transient noise spikes on VCC that reach into the deselect window during the time the device is sampling V CC. Therefore, decoupling of the power supply lines is recommended. When V CC drops below VSO, the control circuit switches power to the internal battery which preserves data and powers the clock. The internal button cell will maintain data in the M48T35AY/ 35AV for an accumulated period of at least 7 years when VCC is less than V SO. As system power returns and V CC rises above VSO , the battery is disconnected, and the power supply is switched to external V CC. Write protection continues until VCC reaches V PFD (min) plus tREC (min). E should be kept high as V CC rises past VPFD (min) to prevent inadvertent write cycles prior to processor stabilization. Normal RAM operation can resume tREC after VCC exceeds VPFD (max). Also, as VCC rises, the battery voltage is checked. If the voltage is less than approximately 2.5V, an internal Battery Not OK (BOK) flag will be set. The BOK flag can be checked after power up. If the BOK flag is set, the first write attempted will be blocked. The flag is automatically cleared after the first write, and normal RAM operation resumes. 645Ω DEVICE UNDER TEST CL = 100pF (or 5pF) CL includes JIG capacitance 1.75V AI02586 Figure 9 illustrates how a BOK check routine could be structured. For more information on Battery Storage Life refer to the Application Note AN1012. CLOCK OPERATIONS Reading the Clock Updates to the TIMEKEEPER registers should be halted before clock data is read to prevent reading data in transition. Because the BiPORT TIMEKEEPER cells in the RAM array are only data registers, and not the actual clock counters, updating the registers can be halted without disturbing the clock itself. Updating is halted when a ’1’ is written to the READ bit, D6 in the Control Register 7FF8h. As long as a ’1’ remains in that position, updating is halted. After a halt is issued, the registers reflect the count; that is, the day, date, and the time that were current at the moment the halt command was issued. All of the TIMEKEEPER registers are updated simultaneously. A halt will not interrupt an update in progress. Updating is within a second after the bit is reset to a ’0’. 5/19 M48T35AY, M48T35AV Table 5. Capacitance (1, 2) (TA = 25°C) Symbol CIN CIO (3) Parameter Test Condition Input Capacitance Input / Output Capacitance Min Max Unit VIN = 0V 10 pF VOUT = 0V 10 pF Note: 1. Effective capacitance measured with power supply at 5V. 2. Sampled only, not 100% tested. 3. Outputs deselected. Table 6A. DC Characteristics (TA = 0 to 70 °C or –40 to 85 °C; VCC = 4.5V to 5.5V) Symbol Parameter ILI (1) Input Leakage Current ILO (1) Output Leakage Current ICC Supply Current ICC1 Supply Current (Standby) TTL ICC2 Supply Current (Standby) CMOS Test Condition Min Max Unit 0V ≤ VIN ≤ VCC ±1 µA 0V ≤ VOUT ≤ VCC ±5 µA Outputs open 50 mA E = VIH 3 mA E = VCC – 0.2V 3 mA VIL (2) Input Low Voltage –0.3 0.8 V VIH Input High Voltage 2.2 VCC + 0.3 V VOL Output Low Voltage IOL = 2.1mA 0.4 V VOH Output High Voltage IOH = –1mA 2.4 V Note: 1. Outputs deselected. 2. Negative spikes of –1V allowed for up to 10ns once per Cycle. Table 6B. DC Characteristics (TA = 0 to 70 °C or –40 to 85 °C; VCC = 3.0V to 3.6V) Symbol Parameter ILI (1) Input Leakage Current ILO (1) Output Leakage Current ICC Supply Current ICC1 Supply Current (Standby) TTL ICC2 Supply Current (Standby) CMOS Test Condition Min Max Unit 0V ≤ VIN ≤ VCC ±1 µA 0V ≤ VOUT ≤ VCC ±5 µA Outputs open 30 mA E = VIH 2 mA E = VCC – 0.2V 2 mA VIL (2) Input Low Voltage –0.3 0.8 V VIH Input High Voltage 2.2 VCC + 0.3 V VOL Output Low Voltage IOL = 2.1mA 0.4 V VOH Output High Voltage IOH = –1mA Note: 1. Outputs deselected. 2. Negative spikes of –1V allowed for up to 10ns once per Cycle. 6/19 2.4 V M48T35AY, M48T35AV Table 7. Power Down/Up Trip Points DC Characteristics (1) (TA = 0 to 70 °C or –40 to 85 °C) Symbol Parameter VPFD Power-fail Deselect Voltage VSO Battery Back-up Switchover Voltage tDR Expected Data Retention Time (at 25°C) Min Typ Max Unit M48T35AY 4.2 4.35 4.5 V M48T35AV 2.7 2.9 3.0 V M48T35AY 3.0 V M48T35AV VPFD –100mV V Grade 1 10 (2) YEARS Grade 6 10 (3) YEARS Note: 1. All voltages referenced to VSS. 2. CAPHAT and M4T32-BR12SH1 SNAPHAT only, M4T28-BR12SH1 SNAPHAT top tDR = 7 years (typ). 3. Using larger M4T32-BR12SH6 SNAPHAT top (recommended for Industrial Temperature Range - grade 6 device). Table 8. Power Down/Up AC Characteristics (TA = 0 to 70 °C or –40 to 85 °C) Symbol Parameter Min E or W at VIH before Power Down tPD tF (1) VPFD (max) to VPFD (min) VCC Fall Time tFB (2) VPFD (min) to VSS VCC Fall Time Max Unit 0 µs 300 µs M48T35AY 10 µs M48T35AV 150 µs tR VPFD (min) to VPFD (max) VCC Rise Time 10 µs tRB VSS to VPFD (min) VCC Rise Time 1 µs tREC (3) VPFD (max) to Inputs Recognized 40 200 ms Note: 1. VPFD (max) to VPFD (min) fall time of less than tF may result in deselection/write protection not occurring until 200µs after VCC passes V PFD (min). 2. VPFD (min) to VSS fall time of less than tFB may cause corruption of RAM data. 3. tREC (min) = 20ms for industrial temperature grade 6 device. Figure 5. Power Down/Up Mode AC Waveforms VCC VPFD (max) VPFD (min) VSO tF tR tFB tDR tPD INPUTS tRB RECOGNIZED tREC DON'T CARE RECOGNIZED HIGH-Z OUTPUTS VALID (PER CONTROL INPUT) VALID (PER CONTROL INPUT) AI01168C 7/19 M48T35AY, M48T35AV Table 9. Read Mode AC Characteristics (TA = 0 to 70 °C or –40 to 85 °C; VCC = 4.5V to 5.5V or 3.0V to 3.6V) Symbol M48T35AY M48T35AV -70 -100 Parameter Min tAVAV Read Cycle Time Max 70 Min Unit Max 100 ns tAVQV (1) Address Valid to Output Valid 70 100 ns tELQV (1) Chip Enable Low to Output Valid 70 100 ns tGLQV (1) Output Enable Low to Output Valid 35 50 ns tELQX (2) Chip Enable Low to Output Transition 5 10 ns tGLQX (2) Output Enable Low to Output Transition 5 5 ns tEHQZ (2) Chip Enable High to Output Hi-Z 25 50 ns tGHQZ (2) Output Enable High to Output Hi-Z 25 40 ns tAXQX (1) Address Transition to Output Transition 10 10 ns Note: 1. CL = 100pF. 2. CL = 5pF. Figure 6. Read Mode AC Waveforms. tAVAV VALID A0-A14 tAVQV tAXQX tELQV tEHQZ E tELQX tGLQV tGHQZ G tGLQX DQ0-DQ7 VALID AI00925 Note: Write Enable (W) = High. 8/19 M48T35AY, M48T35AV Table 10. Write Mode AC Characteristics (TA = 0 to 70 °C or –40 to 85 °C; VCC = 4.5V to 5.5V or 3.0V to 3.6V) Symbol M48T35AY M48T35AV -70 -100 Parameter Min Max Min Unit Max tAVAV Write Cycle Time 70 100 ns tAVWL Address Valid to Write Enable Low 0 0 ns tAVEL Address Valid to Chip Enable Low 0 0 ns tWLWH Write Enable Pulse Width 50 80 ns tELEH Chip Enable Low to Chip Enable High 55 80 ns tWHAX Write Enable High to Address Transition 0 10 ns tEHAX Chip Enable High to Address Transition 0 10 ns tDVWH Input Valid to Write Enable High 30 50 ns tDVEH Input Valid to Chip Enable High 30 50 ns tWHDX Write Enable High to Input Transition 5 5 ns tEHDX Chip Enable High to Input Transition 5 5 ns tWLQZ (1, 2) Write Enable Low to Output Hi-Z 25 50 ns tAVWH Address Valid to Write Enable High 60 80 ns tAVEH Address Valid to Chip Enable High 60 80 ns Write Enable High to Output Transition 5 10 ns tWHQX (1, 2) Note: 1. CL = 5pF. 2. If E goes low simultaneously with W going low, the outputs remain in the high impedance state. Setting the Clock Bit D7 of the Control Register 7FF8h is the WRITE bit. Setting the WRITE bit to a '1', like the READ bit, halts updates to the TIMEKEEPER registers. The user can then load them with the correct day, date, and time data in 24 hour BCD format (see Table 11). Resetting the WRITE bit to a '0' then transfers the values of all time registers 7FF9h7FFFh to the actual TIMEKEEPER counters and allows normal operation to resume. The FT bit and the bits marked as '0' in Table 11 must be written to '0' to allow for normal TIMEKEEPER and RAM operation. After the WRITE bit is reset, the next clock update will occur within one second. See the Application Note AN923 "TIMEKEEPER rolling into the 21st century" on the for information on Century Rollover. Stopping and Starting the Oscillator The oscillator may be stopped at any time. If the device is going to spend a significant amount of time on the shelf, the oscillator can be turned off to minimize current drain on the battery. The STOP bit is the MSB of the seconds register. Setting it to a '1' stops the oscillator. The M48T35AY/35AV is shipped from STMicroelectronics with the STOP bit set to a '1'. When reset to a '0', the M48T35AY/ 35AV oscillator starts within 1 second. 9/19 M48T35AY, M48T35AV Figure 7. Write Enable Controlled, Write AC Waveform tAVAV VALID A0-A14 tAVWH tWHAX tAVEL E tWLWH tAVWL W tWHQX tWLQZ tWHDX DQ0-DQ7 DATA INPUT tDVWH AI00926 Figure 8. Chip Enable Controlled, Write AC Waveforms tAVAV A0-A14 VALID tAVEH tAVEL tELEH tEHAX E tAVWL W tEHDX DQ0-DQ7 DATA INPUT tDVEH AI00927 10/19 M48T35AY, M48T35AV Calibrating the Clock The M48T35AY/35AV is driven by a quartz controlled oscillator with a nominal frequency of 32,768Hz. The devices are tested not to exceed 35 ppm (parts per million) oscillator frequency error at 25°C, which equates to about ±1.53 minutes per month. With the calibration bits properly set, the accuracy of each M48T35AY/35AV improves to better than ±4 ppm at 25°C. The oscillation rate of any crystal changes with temperature (see Figure 11). Most clock chips compensate for crystal frequency and temperature shift error with cumbersome trim capacitors. The M48T35AY/35AV design, however, employs periodic counter correction. The calibration circuit adds or subtracts counts from the oscillator divider circuit at the divide by 256 stage, as shown in Figure 9. The number of times pulses are blanked (subtracted, negative calibration) or split (added, positive calibration) depends upon the value loaded into the five Calibration bits found in the Control Register. Adding counts speeds the clock up, subtracting counts slows the clock down. The Calibration byte occupies the five lower order bits (D4-D0) in the Control Register 7FF8h. These bits can be set to represent any value between 0 and 31 in binary form. Bit D5 is a Sign bit; '1' indicates positive calibration, '0' indicates negative calibration. Calibration occurs within a 64 minute cycle. The first 62 minutes in the cycle may, once per minute, have one second either shortened by 128 or lengthened by 256 oscillator cycles. If a binary '1' is loaded into the register, only the first 2 minutes in the 64 minute cycle will be modified; if a binary 6 is loaded, the first 12 will be affected, and so on. Therefore, each calibration step has the effect of adding 512 or subtracting 256 oscillator cycles for every 125,829,120 actual oscillator cycles, that is +4.068 or –2.034 ppm of adjustment per calibration step in the calibration register. Assuming that the oscillator is in fact running at exactly 32,768Hz, each of the 31 increments in the Calibration byte would represent +10.7 or –5.35 seconds per month which corresponds to a total range of +5.5 or –2.75 minutes per month. Two methods are available for ascertaining how much calibration a given M48T35AY/35AV may require. The first involves simply setting the clock, letting it run for a month and comparing it to a known accurate reference (like WWV broadcasts). While that may seem crude, it allows the designer to give the end user the ability to calibrate his clock as his environment may require, even after the final product is packaged in a non-user serviceable enclosure. All the designer has to do is provide a simple utility that accesses the Calibration byte. Figure 9. Checking the BOK Flag Status POWER-UP READ DATA AT ANY ADDRESS WRITE DATA COMPLEMENT BACK TO SAME ADDRESS READ DATA AT SAME ADDRESS AGAIN IS DATA COMPLEMENT OF FIRST READ? (BATTERY OK) YES NO (BATTERY LOW) NOTIFY SYSTEM OF LOW BATTERY (DATA MAY BE CORRUPTED) WRITE ORIGINAL DATA BACK TO SAME ADDRESS CONTINUE AI00607 The second approach is better suited to a manufacturing environment, and involves the use of some test equipment. When the Frequency Test (FT) bit, the seventh-most significant bit in the Day Register is set to a '1', and D7 of the Seconds Register is a '0' (Oscillator Running), DQ0 will toggle at 512Hz during a read of the Seconds Register. Any deviation from 512Hz indicates the degree and direction of oscillator frequency shift at the test temperature. For example, a reading of 512.01024Hz would indicate a +20 ppm oscillator frequency error, requiring a –10 (WR001010) to be loaded into the Calibration Byte for correction. Note that setting or changing the Calibration Byte does not affect the Frequency test output frequency. The FT bit MUST be reset to '0' for normal clock operations to resume. The FT bit is automatically Reset on power-up. For more information on calibration, see the Application Note AN934 "TIMEKEEPER Calibration". 11/19 M48T35AY, M48T35AV Table 11. Register Map Data Address D7 7FFFh D6 D5 D4 D3 10 Years 0 10 M. D2 D1 D0 Function/Range BCD Format Year Year 00-99 Month Month 01-12 Date Date 01-31 Century/Day 00-01/01-07 Hours Hour 00-23 7FFEh 0 0 7FFDh 0 0 7FFCh 0 FT 7FFBh 0 0 7FFAh 0 10 Minutes Minutes Minutes 00-59 7FF9h ST 10 Seconds Seconds Seconds 00-59 7FF8h W 10 Date CEB CB 10 Hours R S 0 Day Calibration Control Keys: S = SIGN Bit FT = FREQUENCY TEST Bit (Must be set to ‘0’ upon power for normal operation) R = READ Bit W = WRITE Bit ST = STOP Bit 0 = Must be set to ‘0’ CEB = Century Enable Bit CB = Century Bit Note: When CEB is set to ‘1’, CB will toggle from ‘0’ to ‘1’ or from ‘1’ to ‘0’ at the turn of the century (dependent upon the initial value set). When CEB is set to ‘0’, CB will not toggle. The WRITE Bit does not need to be set to write to CEB and CB. Figure 10. Clock Calibration NORMAL POSITIVE CALIBRATION NEGATIVE CALIBRATION AI00594B 12/19 M48T35AY, M48T35AV Figure 11. Crystal Accuracy Across Temperature ppm 20 0 -20 -40 ∆F = -0.038 ppm (T - T )2 ± 10% 0 F C2 -60 T0 = 25 °C -80 -100 0 5 10 15 20 25 30 35 40 45 50 55 60 65 °C 70 AI02124 POWER SUPPLY DECOUPLING and UNDERSHOOT PROTECTION ICC transients, including those produced by output switching, can produce voltage fluctuations, resulting in spikes on the VCC bus. These transients can be reduced if capacitors are used to store energy, which stabilizes the V CC bus. The energy stored in the bypass capacitors will be released as low going spikes are generated or energy will be absorbed when overshoots occur. A bypass capacitor value of 0.1µF (as shown in Figure 12) is recommended in order to provide the needed filtering. In addition to transients that are caused by normal SRAM operation, power cycling can generate negative voltage spikes on V CC that drive it to values below V SS by as much as one Volt. These negative spikes can cause data corruption in the SRAM while in battery backup mode. To protect from these voltage spikes, it is recommended to connect a schottky diode from V CC to VSS (cathode connected to VCC, anode to VSS). Schottky diode 1N5817 is recommended for through hole and MBRS120T3 is recommended for surface mount. Figure 12. Supply Voltage Protection VCC VCC 0.1µF DEVICE VSS AI02169 13/19 M48T35AY, M48T35AV Table 12. Ordering Information Scheme Example: M48T35AY -70 MH 1 TR Device Type M48T Supply Voltage and Write Protect Voltage 35AY = VCC = 4.5V to 5.5V; VPFD = 4.2V to 4.5V 35AV = VCC = 3.0V to 3.6V; VPFD = 2.7V to 3.0V Speed -70 = 70ns (35AY) -10 = 100ns (35AV) Package PC = PCDIP28 MH (1) = SOH28 Temperature Range 1 = 0 to 70 °C 6 (2) = –40 to 85 °C Shipping Method for SOIC blank = Tubes TR = Tape & Reel Note: 1. The SOIC package (SOH28) requires the battery package (SNAPHAT) which is ordered separately under the part number "M4TXX-BR00SH1" in plastic tube or "M4TXX-BR00SH1TR" in Tape & Reel form. 2. Available in SOIC package only. Caution: Do not place the SNAPHAT battery package "M4TXX-BR00SH1" in conductive foam since will drain the lithium button-cell battery. For a list of available options (Speed, Package, etc...) or for further information on any aspect of this device, please contact the ST Sales Office nearest to you. Table 13. Revision History Date Revision Details November 1999 First Issue 04/21/00 From Preliminary Data to Data Sheet 05/29/00 tFB change (Table 8) 14/19 M48T35AY, M48T35AV Table 14. PCDIP28 - 28 pin Plastic DIP, battery CAPHAT, Package Mechanical Data mm inches Symb Typ Min Max A 8.89 A1 Typ Min Max 9.65 0.350 0.380 0.38 0.76 0.015 0.030 A2 8.38 8.89 0.330 0.350 B 0.38 0.53 0.015 0.021 B1 1.14 1.78 0.045 0.070 C 0.20 0.31 0.008 0.012 D 39.37 39.88 1.550 1.570 E 17.83 18.34 0.702 0.722 e1 2.29 2.79 0.090 0.110 e3 29.72 36.32 1.170 1.430 eA 15.24 16.00 0.600 0.630 L 3.05 3.81 0.120 0.150 N 28 28 Figure 13. PCDIP28 - 28 pin Plastic DIP, battery CAPHAT, Package Outline A2 A1 B1 B e1 A L C eA e3 D N E 1 PCDIP Drawing is not to scale. 15/19 M48T35AY, M48T35AV Table 15. SOH28 - 28 lead Plastic Small Outline, 4-socket battery SNAPHAT, Package Mechanical Data mm inches Symb Typ Min Max A Typ Min 3.05 Max 0.120 A1 0.05 0.36 0.002 0.014 A2 2.34 2.69 0.092 0.106 B 0.36 0.51 0.014 0.020 C 0.15 0.32 0.006 0.012 D 17.71 18.49 0.697 0.728 E 8.23 8.89 0.324 0.350 – – – – eB 3.20 3.61 0.126 0.142 H 11.51 12.70 0.453 0.500 L 0.41 1.27 0.016 0.050 α 0° 8° 0° 8° N 28 e 1.27 0.050 28 CP 0.10 0.004 Figure 14. SOH28 - 28 lead Plastic Small Outline, 4-socket battery SNAPHAT, Package Outline A2 A C B eB e CP D N E H A1 1 SOH-A Drawing is not to scale. 16/19 α L M48T35AY, M48T35AV Table 16. M4T28-BR12SH SNAPHAT Housing for 48 mAh Battery & Crystal, Package Mechanical Data mm inches Symb Typ Min A Max Typ Min Max 9.78 0.385 A1 6.73 7.24 0.265 0.285 A2 6.48 6.99 0.255 0.275 A3 0.38 0.015 B 0.46 0.56 0.018 0.022 D 21.21 21.84 0.835 0.860 E 14.22 14.99 0.560 0.590 eB 3.20 3.61 0.126 0.142 L 2.03 2.29 0.080 0.090 Figure 15. M4T28-BR12SH SNAPHAT Housing for 48 mAh Battery & Crystal, Package Outline A1 eA A2 A A3 B L eB D E SHTK-A Drawing is not to scale. 17/19 M48T35AY, M48T35AV Table 17. M4T32-BR12SH SNAPHAT Housing for 120 mAh Battery & Crystal, Package Mechanical Data mm inches Symb Typ Min A Max Typ Min Max 10.54 0.415 A1 8.00 8.51 0.315 0.335 A2 7.24 8.00 0.285 0.315 A3 0.38 0.015 B 0.46 0.56 0.018 0.022 D 21.21 21.84 0.835 0.860 E 17.27 18.03 0.680 0.710 eB 3.20 3.61 0.126 0.142 L 2.03 2.29 0.080 0.090 Figure 16. M4T32-BR12SH SNAPHAT Housing for 120 mAh Battery & Crystal, Package Outline A1 eA A2 A A3 B L eB D E SHTK-A Drawing is not to scale. 18/19 M48T35AY, M48T35AV Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. 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