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M48T35 M48T35Y
5 V, 256 Kbit (32 Kb x 8) TIMEKEEPER(R) SRAM
Features

Integrated, ultra low power SRAM, real-time clock, power-fail control circuit and battery BYTEWIDETM RAM-like clock access BCD coded year, month, day, date, hours, minutes, and seconds Frequency test output for real-time clock Automatic power-fail chip deselect and WRITE protection WRITE protect voltages VPFD = Power-fail deselect voltage): - M48T35: VCC = 4.75 to 5.5 V 4.5 V VPFD 4.75 V - M48T35Y: VCC = 4.5 to 5.5 V 4.2 V VPFD 4.5 V Self-contained battery and crystal in the CAPHATTM DIP package SOIC package provides direct connection for a SNAPHAT(R) housing containing the battery and crystal SNAPHAT(R) housing (battery and crystal) is replaceable Pin and function compatible with JEDEC standard 32 Kb x 8 SRAMs RoHS compliant - Lead-free second level interconnect
28 1 28 1
PCDIP28 (PC) Battery/crystal CAPHATTM
SNAPHAT(R) (SH) Battery/crystal

SOH28 (MH)
September 2010
Doc ID 2611 Rev 9
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www.st.com 1
Contents
M48T35, M48T35Y
Contents
1 2 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Operation modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1 2.2 2.3 READ mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 WRITE mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Data retention mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3
Clock operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.1 3.2 3.3 3.4 3.5 3.6 Reading the clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Setting the clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Stopping and starting the oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Calibrating the clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Century bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 VCC noise and negative going transients . . . . . . . . . . . . . . . . . . . . . . . . . 16
4 5 6 7 8 9
Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 DC and AC parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Part numbering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Environmental information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
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M48T35, M48T35Y
List of tables
List of tables
Table 1. Table 2. Table 3. Table 4. Table 5. Table 6. Table 7. Table 8. Table 9. Table 10. Table 11. Table 12. Table 13. Table 14. Table 15. Table 16. Table 17. Table 18. Signal names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Operating modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 READ mode AC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 WRITE mode AC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Operating and AC measurement conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 DC characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Power down/up AC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Power down/up trip points DC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 PCDIP28 - 28-pin plastic DIP, battery CAPHATTM, package mech. data . . . . . . . . . . . . . 21 SOH28 - 28-lead plastic SO, 4-socket battery SNAPHAT(R), package mechanical data . . 22 SH - 4-pin SNAPHAT(R) housing for 48 mAh battery & crystal, package mechanical data . 23 SH - 4-pin SNAPHAT(R) housing for 120 mAh battery & crystal, package mechanical data 24 Ordering information scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 SNAPHAT(R) battery table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
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List of figures
M48T35, M48T35Y
List of figures
Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. Figure 16. Figure 17. Logic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 DIP connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 SOIC connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 READ mode AC waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 WRITE enable controlled, WRITE AC waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Chip enable controlled, WRITE AC waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Crystal accuracy across temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Clock calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Supply voltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 AC measurement load circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Power down/up mode AC waveforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 PCDIP28 - 28-pin plastic DIP, battery CAPHATTM, package outline . . . . . . . . . . . . . . . . . 21 SOH28 - 28-lead plastic small outline, 4-socket battery SNAPHAT(R), package outline . . . 22 SH - 4-pin SNAPHAT(R) housing for 48 mAh battery & crystal, package outline. . . . . . . . . 23 SH - 4-pin SNAPHAT(R) housing for 120 mAh battery & crystal, package outline. . . . . . . . 24 Recycling symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
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M48T35, M48T35Y
Description
1
Description
The M48T35/Y TIMEKEEPER(R) RAM is a 32 Kb x 8 non-volatile static RAM and real-time clock. The monolithic chip is available in two special packages to provide a highly integrated battery-backed memory and real-time clock solution. The M48T35/Y is a non-volatile pin and function equivalent to any JEDEC standard 32 Kb x 8 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. The 28-pin, 600 mil DIP CAPHATTM houses the M48T35/Y silicon with a quartz crystal and a long life lithium button cell in a single package. The 28-pin, 330 mil SOIC provides sockets with gold plated contacts at both ends for direct connection to a separate SNAPHAT(R) 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 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 surface-mounting. 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 (e.g., SNAPHAT) part number is "M4T28BR12SH". Figure 1. Logic diagram
VCC
15 A0-A14
8 DQ0-DQ7
W E G
M48T35 M48T35Y
VSS
AI01620B
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Description Table 1.
A0-A14 DQ0-DQ7 E G W VCC VSS
M48T35, M48T35Y Signal names
Address inputs Data inputs / outputs Chip enable Output enable WRITE enable Supply voltage Ground
Figure 2.
DIP connections
A14 A12 A7 A6 A5 A4 A3 A2 A1 A0 DQ0 DQ1 DQ2 VSS 28 1 27 2 26 3 4 25 24 5 23 6 7 M48T35 22 8 M48T35Y 21 20 9 19 10 11 18 12 17 13 16 14 15 VCC W A13 A8 A9 A11 G A10 E DQ7 DQ6 DQ5 DQ4 DQ3
AI01621B
Figure 3.
SOIC connections
A14 A12 A7 A6 A5 A4 A3 A2 A1 A0 DQ0 DQ1 DQ2 VSS 1 28 27 2 26 3 25 4 24 5 23 6 22 7 M48T35Y 21 8 20 9 19 10 18 11 17 12 16 13 15 14 VCC W A13 A8 A9 A11 G A10 E DQ7 DQ6 DQ5 DQ4 DQ3
AI01622B
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M48T35, M48T35Y Figure 4. Block diagram
Description
OSCILLATOR AND CLOCK CHAIN 32,768 Hz CRYSTAL POWER
8 x 8 BiPORT SRAM ARRAY
A0-A14
32,760 x 8 SRAM ARRAY LITHIUM CELL VOLTAGE SENSE AND SWITCHING CIRCUITRY VPFD
DQ0-DQ7
E W G
VCC
VSS
AI01623
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Operation modes
M48T35, M48T35Y
2
Operation modes
As Figure 4 on page 7 shows, the static memory array and the quartz controlled clock oscillator of the M48T35/Y 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 - valid until 2100), 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. The eight clock bytes are not the actual clock counters themselves; they are memory locations consisting of BiPORTTM READ/WRITE memory cells. The M48T35/Y 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 M48T35/Y also has its own power-fail detect circuit. The control circuitry constantly monitors the single 5 V 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 VCC. As VCC falls below the battery backup switchover voltage (VSO), the control circuitry connects the battery which maintains data and clock operation until valid power returns. Table 2.
Mode Deselect WRITE READ READ Deselect Deselect VSO to VPFD VSO (min)(1)
(1)
Operating modes
VCC 4.75 to 5.5 V or 4.5 to 5.5 V E VIH VIL VIL VIL X X G X X VIL VIH X X W X VIL VIH VIH X X DQ0-DQ7 High Z DIN DOUT High Z High Z High Z Power Standby Active Active Active CMOS standby Battery backup mode
1. See Table 11 on page 20 for details.
X = VIH or VIL; VSO = battery backup switchover voltage.
2.1
READ mode
The M48T35/Y 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 (tAVQV) 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 (tELQV) 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 tAVQV, the data lines will be driven to an indeterminate state until tAVQV.
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M48T35, M48T35Y
Operation modes
If the address inputs are changed while E and G remain active, output data will remain valid for output data hold time (tAXQX) but will go indeterminate until the next address access. Figure 5. READ mode AC waveforms
tAVAV A0-A14 tAVQV tELQV E tELQX tGLQV G tGLQX DQ0-DQ7 VALID
AI00925
VALID tAXQX tEHQZ
tGHQZ
Note: Table 3.
Symbol tAVAV tAVQV tELQV tGLQV tELQX(2) tGLQX(2) tEHQZ(2) tGHQZ(2) tAXQX
WRITE enable (W) = high. READ mode AC characteristics
Parameter(1) Min READ cycle time Address valid to output valid Chip enable low to output valid Output enable low to output valid Chip enable low to output transition Output enable low to output transition Chip enable high to output Hi-Z Output enable high to output Hi-Z Address transition to output transition 10 5 5 25 25 70 70 70 35 M48T35/Y Unit Max ns ns ns ns ns ns ns ns ns
1. Valid for ambient operating temperature: TA = 0 to 70 or -40 to 85 C; VCC = 4.75 to 5.5 V or 4.5 to 5.5 V (except where noted). 2. CL = 5 pF.
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Operation modes
M48T35, M48T35Y
2.2
WRITE mode
The M48T35/Y 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.
Figure 6.
WRITE enable controlled, WRITE AC waveform
tAVAV
A0-A14
VALID tAVWH tAVEL tWHAX
E tWLWH tAVWL W tWLQZ tWHDX DQ0-DQ7 DATA INPUT tDVWH
AI00926
tWHQX
Figure 7.
Chip enable controlled, WRITE AC waveforms
tAVAV
A0-A14
VALID tAVEH tAVEL tELEH tEHAX
E tAVWL W tEHDX DQ0-DQ7 DATA INPUT tDVEH
AI00927
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Doc ID 2611 Rev 9
M48T35, M48T35Y Table 4.
Symbol tAVAV tAVWL tAVEL tWLWH tELEH tWHAX tEHAX tDVWH tDVEH tWHDX tEHDX tAVWH tAVEH
Operation modes
WRITE mode AC characteristics
Parameter(1) Min WRITE cycle time Address valid to WRITE enable low Address valid to chip enable low WRITE enable pulse width Chip enable low to chip enable high WRITE enable high to address transition Chip enable high to address transition Input valid to WRITE enable high Input valid to chip enable high WRITE enable high to input transition Chip enable high to input transition Address valid to WRITE enable high Address valid to chip enable high 70 0 0 50 55 0 0 30 30 5 5 25 60 60 5 M48T35/Y Unit Max ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns
tWLQZ(2)(3) WRITE enable low to output Hi-Z
tWHQX(2)(3) WRITE enable high to output transition
1. Valid for ambient operating temperature: TA = 0 to 70 or -40 to 85 C; VCC = 4.75 to 5.5 V or 4.5 to 5.5 V (except where noted). 2. CL = 5 pF. 3. If E goes low simultaneously with W going low, the outputs remain in the high impedance state.
2.3
Data retention mode
With valid VCC applied, the M48T35/Y operates as a conventional BYTEWIDE static RAM. Should the supply voltage decay, the RAM will automatically power-fail deselect, write protecting itself when VCC falls within the VPFD (max), VPFD (min) window. All outputs become high impedance, and all inputs are treated as "Don't care" (see Figure 12 on page 19, Table 10, and Table 11 on page 20).
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 VPFD (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 M48T35/Y may respond to transient noise spikes on VCC that reach into the deselect window during the time the device is sampling VCC. Therefore, decoupling of the power supply lines is recommended. When VCC 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 M48T35/Y for an accumulated period of at least 7 years when VCC is less than VSO. As system power returns and VCC rises above VSO, the battery is disconnected, and the power supply is switched to external VCC. Write protection continues until VCC reaches VPFD (min) plus trec (min). E should be kept high as VCC rises past VPFD (min) to prevent inadvertent WRITE cycles prior to processor stabilization. Normal RAM operation can resume trec after VCC exceeds VPFD (max). For more information on battery storage life refer to the application note AN1012.
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Clock operations
M48T35, M48T35Y
3
3.1
Clock operations
Reading the clock
Updates to the TIMEKEEPER(R) registers (see Table 5) should be halted before clock data is read to prevent reading data in transition. The BiPORTTM TIMEKEEPER cells in the RAM array are only data registers and not the actual clock counters, so 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.'
3.2
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(R) registers. The user can then load them with the correct day, date, and time data in 24-hour BCD format (see Table 5). Resetting the WRITE bit to a '0' then transfers the values of all time registers 7FF9h-7FFFh to the actual TIMEKEEPER counters and allows normal operation to resume. The FT bit and the bits marked as '0' in Table 5 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(R) Rolling Into the 21st Century" for information on century rollover.
3.3
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 M48T35/Y is shipped from STMicroelectronics with the STOP bit set to a '1.' When reset to a '0,' the M48T35/Y oscillator starts within 1 second.
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M48T35, M48T35Y Table 5.
Address D7 7FFFh 7FFEh 7FFDh 7FFCh 7FFBh 7FFAh 7FF9h 7FF8h 0 0 0 0 0 ST W R D6 D5 D4 D3 D2 D1 Year 10 M. Month Date 0 Day Hours Minutes Seconds Calibration D0 10 Years 0 0 FT 0 0
Clock operations Register map
Data Function/range BCD format Year Month Date Century/ day Hours Minutes Seconds Control 00-99 01-12 01-31 00-01/01-07 00-23 00-59 00-59
10 date CEB CB
10 hours 10 minutes 10 seconds S
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.
3.4
Calibrating the clock
The M48T35/Y is driven by a quartz-controlled oscillator with a nominal frequency of 32,768 Hz. 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 M48T35/Y improves to better than +1/-2 ppm at 25 C. The oscillation rate of any crystal changes with temperature (see Figure 8 on page 15). Most clock chips compensate for crystal frequency and temperature shift error with cumbersome "trim" capacitors. The M48T35/Y 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 on page 15. 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 the
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Clock operations
M48T35, M48T35Y
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 32,768 Hz, 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 M48T35/Y 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. 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 512 Hz during a READ of the seconds register. Any deviation from 512 Hz indicates the degree and direction of oscillator frequency shift at the test temperature. For example, a reading of 512.01024 Hz would indicate a +20 ppm oscillator frequency error, requiring a -10 (WR001010) to be loaded into the calibration byte for correction. Note: 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-down. For more information on calibration, see application note AN934, "TIMEKEEPER(R) Calibration."
3.5
Century bit
Bit D5 and D4 of clock register 1FFCh contain the CENTURY ENABLE bit (CEB) and the CENTURY bit (CB). Setting CEB to a '1' will cause CB to toggle, either from a '0' to '1' or from '1' to '0' at the turn of the century (depending upon its initial state). If CEB is set to a '0,' CB will not toggle.
Note:
The WRITE bit must be set in order to write to the CENTURY bit.
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M48T35, M48T35Y Figure 8.
ppm 20
Clock operations Crystal accuracy across temperature
0
-20
-40 F = -0.038 ppm (T - T )2 10% 0 F C2 T0 = 25 C -80
-60
-100 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 C
AI02124
Figure 9.
Clock calibration
NORMAL
POSITIVE CALIBRATION
NEGATIVE CALIBRATION
AI00594B
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Clock operations
M48T35, M48T35Y
3.6
VCC noise and negative going transients
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 VCC 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 0.1 F (as shown in Figure 10) 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 VCC that drive it to values below VSS 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 VCC 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 10. Supply voltage protection
VCC VCC
0.1F
DEVICE
VSS
AI02169
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Maximum ratings
4
Maximum ratings
Stressing the device above the rating listed in the absolute maximum ratings table may cause permanent damage to the device. These are stress ratings only and operation of the device at these or any other conditions above those indicated in the operating sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Table 6.
Symbol TA TSTG TSLD
(1)(2)(3)
Absolute maximum ratings
Parameter Ambient operating temperature Grade 1 Grade 6 Value 0 to 70 -40 to 85 -40 to 85 260 M48T35 M48T35Y M48T35 M48T35Y -0.3 to 7 -0.3 to 7 -0.3 to 7 -0.3 to 7 20 1 Unit C C C C V V V V mA W
Storage temperature (VCC off, oscillator off) Lead solder temperature for 10 seconds Input or output voltages Supply voltage Output current Power dissipation
VIO VCC IO PD
1. For DIP package, soldering temperature of the IC leads is to not exceed 260 C for 10 seconds. In order to protect the lithium battery, preheat temperatures must be limited such that the battery temperature does not exceed +85 C. Furthermore, the devices shall not be exposed to IR reflow. 2. For DIP packaged devices, ultrasound vibrations should not be used for post-solder cleaning to avoid damaging the crystal. 3. For SOH28 package, lead-free (Pb-free) lead finish: reflow at peak temperature of 260 C (the time above 255 C must not exceed 30 seconds).
Caution: Caution:
Negative undershoots below -0.3 V are not allowed on any pin while in the battery backup mode. Do NOT wave solder SOIC to avoid damaging SNAPHAT(R) sockets.
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DC and AC parameters
M48T35, M48T35Y
5
DC and AC parameters
This section summarizes the operating and measurement conditions, as well as the DC and AC characteristics of the device. The parameters in the following DC and AC characteristic tables are derived from tests performed under the measurement conditions listed in the relevant tables. Designers should check that the operating conditions in their projects match the measurement conditions when using the quoted parameters. Table 7. Operating and AC measurement conditions
Parameter Supply voltage (VCC) Ambient operating temperature (TA) Load capacitance (CL) Input rise and fall times Input pulse voltages Input and output timing ref. voltages M48T35 4.75 to 5.5 0 to 70 100 5 0 to 3 1.5 M48T35Y 4.5 to 5.5 -40 to 85 100 5 0 to 3 1.5 Unit V C pF ns V V
Note:
Output Hi-Z is defined as the point where data is no longer driven. Figure 11. AC measurement load circuit
5V
1.9k DEVICE UNDER TEST 1k
OUT
CL = 100pF or 5pF
CL includes JIG capacitance
AI01030
Table 8.
Symbol CIN COUT(3)
Capacitance
Parameter(1)(2) Input capacitance Output capacitance Min Max 10 10 Unit pF pF
1. Effective capacitance measured with power supply at 5 V; sampled only, not 100% tested. 2. At 25 C, f = 1 MHz. 3. Outputs deselected.
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Symbol ILI ILO(2) ICC ICC1 ICC2 VIL VIH VOL VOH
DC and AC parameters
DC characteristics
Parameter Input leakage current Output leakage current Supply current Supply current (standby) TTL Supply current (standby) CMOS Input low voltage Input high voltage Output low voltage Output high voltage IOL = 2.1 mA IOH = -1 mA 2.4 Test condition(1) 0 V VIN VCC 0 V VOUT VCC Outputs open E = VIH E = VCC - 0.2 V -0.3 2.2 M48T35 Min Max 1 1 50 3 2 0.8 VCC + 0.3 0.4 2.4 -0.3 2.2 M48T35Y Unit Min Max 1 1 30 3 2 0.8 VCC + 0.3 0.4 A A mA mA mA V V V V
1. Valid for ambient operating temperature: TA = 0 to 70 or -40 to 85 C; VCC = 4.75 to 5.5 V or 4.5 to 5.5 V (except where noted). 2. Outputs deselected.
Figure 12. Power down/up mode AC waveforms
VCC VPFD (max) VPFD (min) VSO tF tFB tPD INPUTS
RECOGNIZED
tR tRB tDR DON'T CARE trec
RECOGNIZED
HIGH-Z OUTPUTS VALID
(PER CONTROL INPUT)
VALID
(PER CONTROL INPUT)
AI01168C
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DC and AC parameters Table 10.
Symbol tPD tF
(2)
M48T35, M48T35Y
Power down/up AC characteristics
Parameter(1) E or W at VIH before power down VPFD (max) to VPFD (min) VCC fall time VPFD (min) to VSS VCC fall time VPFD (min) to VPFD (max) VCC rise time VSS to VPFD (min) VCC rise time VPFD (max) to inputs recognized M48T35 M48T35Y Min 0 300 10 10 10 1 40 200 Max Unit s s s s s s ms
tFB(3) tR tRB trec(4)
1. Valid for ambient operating temperature: TA = 0 to 70 or -40 to 85 C; VCC = 4.75 to 5.5 V or 4.5 to 5.5 V (except where noted). 2. VPFD (max) to VPFD (min) fall time of less than tF may result in deselection/write protection not occurring until 200 s after VCC passes VPFD (min). 3. VPFD (min) to VSS fall time of less than tFB may cause corruption of RAM data. 4. trec (min) = 20 ms for industrial temperature grade 6 device.
Table 11.
Symbol VPFD VSO tDR(3)(5)
Power down/up trip points DC characteristics
Parameter(1)(2) Power-fail deselect voltage M48T35 M48T35Y M48T35 M48T35Y Grade 1 Grade 6 10(4) 10
(5)
Min 4.5 4.2
Typ 4.6 4.35 3.0 3.0
Max 4.75 4.5
Unit V V V V Years Years
Battery backup switchover voltage
Expected data retention time
1. Valid for ambient operating temperature: TA = 0 to 70 or -40 to 85 C; VCC = 4.75 to 5.5 V or 4.5 to 5.5 V (except where noted). 2. All voltages referenced to VSS. 3. CAPHATTM and M4T32-BR12SH1 SNAPHAT(R) only, M4T28-BR12SH1 SNAPHAT(R) top tDR = 7 years (typ). 4. Using larger M4T32-BR12SH6 SNAPHAT(R) top (recommended for industrial temperature range - grade 6 device). 5. At 25 C, VCC = 0 V.
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Package mechanical data
6
Package mechanical data
In order to meet environmental requirements, ST offers these devices in different grades of ECOPACK(R) packages, depending on their level of environmental compliance. ECOPACK(R) specifications, grade definitions and product status are available at: www.st.com. ECOPACK(R) is an ST trademark. Figure 13. PCDIP28 - 28-pin plastic DIP, battery CAPHATTM, package outline
A2
A
A1 B1 B e3 D
N
L eA
C
e1
E
1 PCDIP
Note:
Drawing is not to scale. Table 12.
Symbol Typ A A1 A2 B B1 C D E e1 e3 eA L N 33.02 15.24 3.05 28 16.00 3.81 Min 8.89 0.38 8.38 0.38 1.14 0.20 39.37 17.83 2.29 Max 9.65 0.76 8.89 0.53 1.78 0.31 39.88 18.34 2.79 1.3 0.600 0.120 28 0.630 0.150 Typ Min 0.350 0.015 0.330 0.015 0.045 0.008 1.550 0.702 0.090 Max 0.380 0.030 0.350 0.021 0.070 0.012 1.570 0.722 0.110
PCDIP28 - 28-pin plastic DIP, battery CAPHATTM, package mech. data
mm inches
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Package mechanical data
M48T35, M48T35Y
Figure 14. SOH28 - 28-lead plastic small outline, 4-socket battery SNAPHAT(R), package outline
A2 B e A C eB CP
D
N
E
H A1 L
SOH-A
1
Note:
Drawing is not to scale. Table 13. SOH28 - 28-lead plastic SO, 4-socket battery SNAPHAT(R), package mechanical data
mm Symbol Typ A A1 A2 B C D E e eB H L a N CP 1.27 0.05 2.34 0.36 0.15 17.71 8.23 - 3.20 11.51 0.41 0 28 0.10 Min Max 3.05 0.36 2.69 0.51 0.32 18.49 8.89 - 3.61 12.70 1.27 8 0.050 0.002 0.092 0.014 0.006 0.697 0.324 - 0.126 0.453 0.016 0 28 0.004 Typ Min Max 0.120 0.014 0.106 0.020 0.012 0.728 0.350 - 0.142 0.500 0.050 8 inches
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Package mechanical data
Figure 15. SH - 4-pin SNAPHAT(R) housing for 48 mAh battery & crystal, package outline
A1
A2 A A3
eA D
B eB
L
E
SHTK
Note:
Drawing is not to scale. Table 14. SH - 4-pin SNAPHAT(R) housing for 48 mAh battery & crystal, package mechanical data
mm Symbol Typ A A1 A2 A3 B D E eB L 0.46 21.21 14.22 3.20 2.03 6.73 6.48 Min Max 9.78 7.24 6.99 0.38 0.56 21.84 14.99 3.61 2.29 0.018 0.835 0.560 0.126 0.080 0.265 0.255 Typ Min Max 0.385 0.285 0.275 0.015 0.022 0.860 0.590 0.142 0.090 inches
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Package mechanical data
M48T35, M48T35Y
Figure 16. SH - 4-pin SNAPHAT(R) housing for 120 mAh battery & crystal, package outline
A1
A2 A A3
eA D
B eB
L
E
SHTK
Note:
Drawing is not to scale. Table 15. SH - 4-pin SNAPHAT(R) housing for 120 mAh battery & crystal, package mechanical data
mm Symbol Typ A A1 A2 A3 B D E eB L 0.46 21.21 17.27 3.20 2.03 8.00 7.24 Min Max 10.54 8.51 8.00 0.38 0.56 21.84 18.03 3.61 2.29 0.018 0.835 0.680 0.126 0.080 0.315 0.285 Typ Min Max 0.415 0.335 0.315 0.015 0.022 0.860 0.710 0.142 0.090 inches
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Part numbering
7
Part numbering
Table 16.
Example: Device type M48T Supply voltage and write protect voltage 35(1) = VCC = 4.75 to 5.5 V; VPFD = 4.5 to 4.75 V 35Y(2) = VCC = 4.5 to 5.5 V; VPFD = 4.2 to 4.5 V Speed -70 = 70 ns Package PC = PCDIP28 MH(3) = SOH28 Temperature range 1 = 0 to 70 C 6(4) = -40 to 85 C Shipping method For SOH28: E = ECOPACK(R) package, tubes F = ECOPACK(R) package, tape & reel For PCDIP28: blank = ECOPACK(R) package, tubes
1. The M48T35 part is offered only in the PCDIP28 (i.e. CAPHATTM) package. 2. The M48T35Y is available only in the SOH28 (i.e. SNAPHAT SOIC) package. 3. The SOIC package (SOH28) requires the SNAPHAT(R) battery package which is ordered separately under the part number "M4TXX-BR12SH" (see Table 17 on page 25). 4. Temperature grade 6 (-40 to +85 C) devices are not for new design. Contact ST sales office for availability.
Ordering information scheme
M48T 35 -70 PC 1 E
Caution:
Do not place the SNAPHAT battery package "M4TXX-BR12SH" in conductive foam as it will drain the lithium button-cell battery. For other options, or for more information on any aspect of this device, please contact the ST sales office nearest you. Table 17. SNAPHAT(R) battery table
Description Lithium battery (48 mAh) SNAPHAT(R) Lithium battery (120 mAh) SNAPHAT(R) Package SH SH
Part number M4T28-BR12SH M4T32-BR12SH
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Environmental information
M48T35, M48T35Y
8
Environmental information
Figure 17. Recycling symbols
This product contains a non-rechargeable lithium (lithium carbon monofluoride chemistry) button cell battery fully encapsulated in the final product. Recycle or dispose of batteries in accordance with the battery manufacturer's instructions and local/national disposal and recycling regulations. Please refer to the following web site address for additional information regarding compliance statements and waste recycling. Go to www.st.com/rtc, then select "Lithium Battery Recycling" from "Related Topics".
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Revision history
9
Revision history
Table 18.
Date Nov-1999 07-Feb-2000 04-Jun-2001 31-Jul-2001 06-Mar-2002 20-May-2002 26-Jun-2002 31-Mar-2003 10-Dec-2003 31-Mar-2004 05-Dec-2005 01-Aug-2007 12-Feb-2009 08-Sep-2010
Document revision history
Revision 1 1.1 2 2.1 2.2 2.3 2.4 3 4 5 6 7 8 9 First issue tDR description changed (Table 9) Reformatted; temp/voltage info. added to tables (Table 8, 9, 3, 4, 10, 11); add century bit text Formatting changes based on latest document reviews Add PMDIP packaging option, which is "Not for New Design" (NND) (Table 16) Modify reflow time and temperature footnotes (Table 6) Add footnote to table (Table 11) v2.2 template applied; data retention condition updated (Table 11) Reformatted; update DC characteristics (Table 9) Reformatted; update Pb-free package information (Table 6, 16) Updated template, lead-free text, and remove footnote (Table 9, 16) Reformatted; added lead-free second level interconnect information to cover page and Section 6: Package mechanical data. Updated Table 6; text in Section 6: Package mechanical data; added Section 8: Environmental information; minor formatting changes. Reformatted document; updated Section 4, Table 12, 16; removed PMDIP28 package. Changes
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