STMICROELECTRONICS M48T35AV

M48T35AV
3.3V, 256Kbit (32Kbit x 8) TIMEKEEPER® SRAM
Features
■
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):
– M48T35AY: VCC = 4.5 to 5.5V
4.2V ≤ VPFD ≤ 4.5V
– M48T35AV: VCC = 3.0 to 3.6V
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
28
1
PCDIP28 (PC)
battery/crystal
CAPHAT
SNAPHAT (SH)
battery/crystal
28
®
■
SNAPHAT housing (battery and crystal) is
replaceable
■
Pin and function compatible with JEDEC
standard 32Kbit x 8 SRAMs
■
RoHS compliant
– Lead-free second level interconnect
November 2007
1
SOH28 (MH)
Rev 6
1/28
www.st.com
1
Contents
M48T35AV
Contents
1
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2
Operation modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3
2.1
Read mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2
Write mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3
Data retention mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Clock operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.1
Reading the clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2
Setting the clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.3
Stopping and starting the oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.4
Calibrating the clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.5
Century bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.6
VCC noise and negative going transients . . . . . . . . . . . . . . . . . . . . . . . . . 17
4
Maximum rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5
DC and AC parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
6
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7
Part numbering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
8
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2/28
M48T35AV
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Operating and AC measurement conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
DC characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Power down/up AC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Power down/up trip points DC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
PCDIP28 – 28-pin plastic DIP, battery CAPHAT™, pack. mech. data . . . . . . . . . . . . . . . . 22
SOH28 – 28-lead plastic small outline, 4-socket battery SNAPHAT, pack. mech. data . . . 23
SH – 4-pin SNAPHAT housing for 48mAh battery & crystal, pack. mech. data . . . . . . . . . 24
SH – 4-pin SNAPHAT housing for 120mAh battery & crystal, pack. mech. data . . . . . . . . 25
Ordering information scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
SNAPHAT battery table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3/28
List of figures
M48T35AV
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.
4/28
Logic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
DIP connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
SOIC connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Read mode AC waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Write enable controlled, write mode AC waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Chip enable controlled, write mode AC waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Checking the BOK flag status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Crystal accuracy across temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Clock calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Supply voltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
AC measurement load circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Power down/up mode AC waveforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
PCDIP28 – 28-pin plastic DIP, battery CAPHAT™, package outline . . . . . . . . . . . . . . . . . 22
SOH28 – 28-lead plastic small outline, 4-socket battery SNAPHAT, package outline . . . . 23
SH – 4-pin SNAPHAT housing for 48mAh battery & crystal, package outline . . . . . . . . . . 24
SH – 4-pin SNAPHAT housing for 120mAh battery & crystal, pack. outline. . . . . . . . . . . . 25
M48T35AV
1
Description
Description
The M48T35AV TIMEKEEPER® RAM is a 32Kbit 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-up memory and real-time clock solution.
The M48T35AV is a non-volatile pin and function equivalent to any JEDEC standard 32Kb 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, 600mil DIP CAPHAT™ houses the M48T35AV 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 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 numbers are listed
in Table 17 on page 26.
Figure 1.
Logic diagram
VCC
15
8
A0-A14
DQ0-DQ7
W
M48T35AV
E
G
VSS
AI02797B
5/28
Description
M48T35AV
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
Figure 2.
DIP connections
A14
A12
A7
A6
A5
A4
A3
A2
A1
A0
DQ0
DQ1
DQ2
VSS
1
2
3
4
5
6
7
M48T35AV
8
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
AI02798B
Figure 3.
SOIC connections
A14
A12
A7
A6
A5
A4
A3
A2
A1
A0
DQ0
DQ1
DQ2
VSS
1
2
3
4
5
6
7
M48T35AV
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
AI02799
6/28
VCC
W
A13
A8
A9
A11
G
A10
E
DQ7
DQ6
DQ5
DQ4
DQ3
M48T35AV
Figure 4.
Description
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
DQ0-DQ7
E
VOLTAGE SENSE
AND
SWITCHING
CIRCUITRY
VCC
W
VPFD
G
VSS
AI01623
7/28
Operation modes
2
M48T35AV
Operation modes
As Figure 4 on page 7 shows, the static memory array and the quartz controlled clock
oscillator of the M48T35AV 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 BiPORT™ READ/WRITE memory cells. The M48T35AV 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 M48T35AV also has its own Power-fail Detect circuit. The control circuitry constantly
monitors the single 3V 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 Back-up Switchover Voltage (VSO), the control circuitry connects the battery which
maintains data and clock operation until valid power returns.
Table 2.
Operating modes
Mode
VCC
Deselect
WRITE
3.0 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)(1)
X
X
X
High Z
CMOS standby
Deselect
≤ VSO(1)
X
X
X
High Z
Battery back-up
mode
READ
1. See Table 11 on page 21 for details.
Note:
X = VIH or VIL; VSO = Battery back-up switchover voltage.
2.1
Read mode
The M48T35AV 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).
8/28
M48T35AV
Operation modes
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. 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
VALID
A0-A14
tAVQV
tAXQX
tELQV
tEHQZ
E
tELQX
tGLQV
tGHQZ
G
tGLQX
DQ0-DQ7
VALID
AI00925
Note:
WRITE Enable (W) = High.
Table 3.
Read mode AC characteristics
M48T35AV
Symbol
Parameter(1)
–100
Min
Unit
Max
tAVAV
READ cycle time
tAVQV
Address valid to output valid
100
ns
tELQV
Chip enable low to output valid
100
ns
tGLQV
Output enable low to output valid
50
ns
tELQX(2)
tGLQX(2)
tEHQZ(2)
tGHQZ(2)
tAXQX
100
ns
Chip enable low to output transition
10
ns
Output enable low to output transition
5
ns
Chip enable high to output Hi-Z
50
ns
Output enable high to output Hi-Z
40
ns
Address transition to output transition
10
ns
1. Valid for ambient operating temperature: TA = 0 to 70°C; VCC = 3.0 to 3.6V (except where noted).
2. CL = 5pF.
9/28
Operation modes
2.2
M48T35AV
Write mode
The M48T35AV 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; however, 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 mode AC waveform
tAVAV
A0-A14
VALID
tAVWH
tWHAX
tAVEL
E
tWLWH
tAVWL
W
tWHQX
tWLQZ
tWHDX
DATA INPUT
DQ0-DQ7
tDVWH
AI00926
Figure 7.
Chip enable controlled, write mode AC waveforms
tAVAV
VALID
A0-A14
tAVEH
tAVEL
tELEH
tEHAX
E
tAVWL
W
tEHDX
DQ0-DQ7
DATA INPUT
tDVEH
AI00927
10/28
M48T35AV
Operation modes
Table 4.
Write mode AC characteristics
M48T35AV
Parameter(1)
Symbol
Unit
Min
tAVAV
WRITE cycle time
tAVWL
Max
100
ns
Address valid to WRITE enable low
0
ns
tAVEL
Address valid to chip enable low
0
ns
tWLWH
WRITE enable pulse width
80
ns
tELEH
Chip enable low to chip enable high
80
ns
tWHAX
WRITE enable high to address transition
10
ns
tEHAX
Chip enable high to address transition
10
ns
tDVWH
Input valid to WRITE enable high
50
ns
tDVEH
Input valid to chip enable high
50
ns
tWHDX
WRITE enable high to input transition
5
ns
tEHDX
Chip enable high to input transition
5
ns
tWLQZ(2)(3)
WRITE enable low to output Hi-Z
50
ns
tAVWH
Address valid to WRITE enable high
80
ns
tAVEH
Address valid to chip enable high
80
ns
WRITE enable high to output transition
10
ns
tWHQX(2)(3)
1. Valid for ambient operating temperature: TA = 0 to 70°C; VCC = 3.0 to 3.6V (except where noted).
2. CL = 5pF.
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 M48T35AV 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 (see Figure 13,
Table 10, and Table 11 on page 21). 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 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 M48T35AV 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
M48T35AV 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).
11/28
Operation modes
M48T35AV
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. Figure 8
illustrates how a BOK check routine could be structured.
For more information on Battery Storage Life refer to the Application Note AN1012.
Figure 8.
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
12/28
M48T35AV
Clock operations
3
Clock operations
3.1
Reading the clock
Updates to the TIMEKEEPER® registers (see Table 5) should be halted before clock data is
read to prevent reading data in transition. The BiPORT™ 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® registers. The user can then load them with
the correct day, date, and time data in 24 hour BCD format (seeTable 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® 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 M48T35AV is shipped from STMicroelectronics with the STOP Bit set to a '1.'
When reset to a '0,' the M48T35AV oscillator starts within 1 second.
13/28
Clock operations
Table 5.
M48T35AV
Register map
Data
Address
D7
D6
7FFEh
0
0
7FFDh
0
0
7FFCh
0
FT
7FFBh
0
0
7FFAh
0
10 minutes
7FF9h
ST
10 seconds
Seconds
7FF8h
W
7FFFh
D5
D4
D3
10 Years
0
10 M.
10 Date
CEB
D1
S
D0
Year
Year
00-99
Month
Month
01-12
Date
CB
10 Hours
R
D2
Function/range
BCD format
Date
01-31
Century/day
00-01/01-07
Hours
Hours
00-23
Minutes
Minutes
00-59
Seconds
00-59
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.
3.4
Calibrating the clock
The M48T35AV 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 M48T35AV improves to better than +1/–2
ppm at 25°C.
The oscillation rate of any crystal changes with temperature (see Figure 9 on page 16).
Most clock chips compensate for crystal frequency and temperature shift error with
cumbersome “trim” capacitors. The M48T35AV 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 10 on page 16. 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 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
14/28
M48T35AV
Clock operations
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 M48T35AV 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.
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®
Calibration.”
3.5
Century bit
Bit D5 and D4 of Clock Register 7FFCh 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.
15/28
Clock operations
Figure 9.
M48T35AV
Crystal accuracy across temperature
ppm
20
0
-20
-40
ΔF = -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
70
°C
AI02124
Figure 10. Clock calibration
NORMAL
POSITIVE
CALIBRATION
NEGATIVE
CALIBRATION
AI00594B
16/28
M48T35AV
3.6
Clock operations
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 0.1µF (as shown in
Figure 11) 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 11. Supply voltage protection
VCC
VCC
0.1μF
DEVICE
VSS
AI02169
17/28
Maximum rating
4
M48T35AV
Maximum rating
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. Refer also to the STMicroelectronics SURE
Program and other relevant quality documents.
Table 6.
Absolute maximum ratings
Symbol
TA
TSTG
TSLD(1)(2)
Parameter
Ambient operating temperature
Storage temperature (VCC off, oscillator off)
Lead solder temperature for 10 seconds
Value
Unit
0 to 70
°C
–40 to 85
°C
260
°C
VIO
Input or output voltages
–0.3 to 4.6
V
VCC
Supply voltage
–0.3 to 4.6
V
IO
Output current
20
mA
PD
Power dissipation
1
W
1. For DIP package: Soldering temperature not to exceed 260°C for 10 seconds (total thermal budget not to
exceed 150°C for longer than 30 seconds).
2. For SO package, Lead-free (Pb-free) lead finish: Reflow at peak temperature of 260°C (total thermal
budget not to exceed 245°C for greater than 30 seconds).
Caution:
Negative undershoots below –0.3V are not allowed on any pin while in the Battery Back-up
mode.
Caution:
Do NOT wave solder SOIC to avoid damaging SNAPHAT sockets.
18/28
M48T35AV
5
DC and AC parameters
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
M48T35AV
Unit
3.0 to 3.6
V
0 to 70
°C
Load capacitance (CL)
50
pF
Input rise and fall times
≤5
ns
0 to 3
V
1.5
V
Supply voltage (VCC)
Ambient operating temperature (TA)
Input pulse voltages
Input and output timing ref. voltages
Note:
Output Hi-Z is defined as the point where data is no longer driven.
Figure 12. AC measurement load circuit
DEVICE
UNDER
TEST
CL = 50pF
(or 5pF)
CL includes JIG capacitance
Table 8.
COUT(3)
AI02586
Capacitance
Parameter(1)(2)
Symbol
CIN
1.75V
Min
Max
Unit
Input capacitance
10
pF
Output capacitance
10
pF
1. Effective capacitance measured with power supply at 5V; sampled only, not 100% tested.
2. At 25°C, f = 1MHz.
3. Outputs deselected.
19/28
DC and AC parameters
Table 9.
M48T35AV
DC characteristics
Symbol
M48T35AV
Test condition(1)
Parameter
Unit
Min
Input leakage current
ILI
ILO(2)
Output leakage current
ICC
Supply current
ICC1
Supply current (standby) TTL
ICC2
Supply current (standby) CMOS
VIL
(3)
Max
0V ≤ VIN ≤ VCC
±1
µA
0V ≤ VOUT ≤ VCC
±1
µA
Outputs open
30
mA
E = VIH
2
mA
E = VCC – 0.2V
2
mA
–0.3
0.8
V
2.2
VCC + 0.3
V
0.4
V
Input low voltage
VIH
Input high voltage
VOL
Output low voltage
IOL = 2.1mA
VOH
Output high voltage
IOH = –1mA
2.4
V
1. Valid for ambient operating temperature: TA = 0 to 70°C; VCC = 3.0 to 3.6V (except where noted).
2. Outputs deselected.
3. Negative spikes of –1V allowed for up to 10ns once per cycle.
Figure 13. 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
20/28
M48T35AV
Table 10.
DC and AC parameters
Power down/up AC characteristics
Parameter(1)
Symbol
tPD
E or W at VIH before power down
tF(2)
tFB(3)
Min
Max
Unit
0
µs
VPFD (max) to VPFD (min) VCC fall time
300
µs
VPFD (min) to VSS VCC fall time
150
µs
tR
VPFD (min) to VPFD (max) VCC rise time
10
µs
tRB
VSS to VPFD (min) VCC Rise Time
1
trec
VPFD (max) to inputs recognized
40
µs
200
ms
1. Valid for ambient operating temperature: TA = 0 to 70°C or –40 to 85°C; VCC = 4.5 to 5.5V or 3.0 to 3.6V (except where
noted).
2. VPFD (max) to VPFD (min) fall time of less than tF may result in deselection/write protection not occurring until 200µs after
VCC passes VPFD (min).
3. VPFD (min) to VSS fall time of less than tFB may cause corruption of RAM data.
Table 11.
Power down/up trip points DC characteristics
Parameter(1)(2)
Symbol
VPFD
Power-fail deselect voltage
VSO
Battery back-up switchover voltage
tDR(3)
Expected data retention time
Min
Typ
Max
Unit
2.7
2.9
3.0
V
VPFD –100mV
10(4)
V
YEARS
1. Valid for ambient operating temperature: TA = 0 to 70°C or –40 to 85°C; VCC = 4.5 to 5.5V or 3.0 to 3.6V (except where
noted).
2. All voltages referenced to VSS.
3. At 25°C, VCC = 0V.
4. CAPHAT and M4T32-BR12SH1 SNAPHAT only, M4T28-BR12SH1 SNAPHAT top tDR = 7 years (typ).
21/28
Package mechanical data
6
M48T35AV
Package mechanical data
In order to meet environmental requirements, ST offers these devices in ECOPACK®
packages. These packages have a lead-free second level interconnect. The category of
second Level Interconnect is marked on the package and on the inner box label, in
compliance with JEDEC Standard JESD97. The maximum ratings related to soldering
conditions are also marked on the inner box label. ECOPACK is an ST trademark.
ECOPACK specifications are available at: www.st.com.
Figure 14. PCDIP28 – 28-pin plastic DIP, battery CAPHAT™, package outline
A2
A
A1
B1
B
L
C
e1
eA
e3
D
N
E
1
Note:
PCDIP
Drawing is not to scale.
Table 12.
PCDIP28 – 28-pin plastic DIP, battery CAPHAT™, pack. mech. data
mm
inches
Symb
Typ
22/28
Min
Max
Typ
Min
Max
A
8.89
9.65
0.350
0.380
A1
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
M48T35AV
Package mechanical data
Figure 15. SOH28 – 28-lead plastic small outline, 4-socket battery SNAPHAT, package outline
A2
A
C
B
eB
e
CP
D
N
E
H
A1
α
L
1
SOH-A
Note:
Drawing is not to scale.
Table 13.
SOH28 – 28-lead plastic small outline, 4-socket battery SNAPHAT, pack. mech. data
mm
inches
Symb
Typ
Min
Max
A1
Min
Max
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
–
–
–
–
A
e
Typ
3.05
1.27
0.120
0.050
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
a
0°
8°
0°
8°
N
28
CP
28
0.10
0.004
23/28
Package mechanical data
M48T35AV
Figure 16. SH – 4-pin SNAPHAT housing for 48mAh battery & crystal, package outline
A1
A2
A3
A
eA
B
L
eB
D
E
SHTK-A
Note:
Drawing is not to scale.
Table 14.
SH – 4-pin SNAPHAT housing for 48mAh battery & crystal, pack. mech. data
mm
inches
Symb
Typ
Min
A
Typ
Min
9.78
Max
0.385
A1
6.73
7.24
0.265
0.285
A2
6.48
6.99
0.255
0.275
A3
24/28
Max
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
eA
15.55
15.95
0.612
0.628
eB
3.20
3.61
0.126
0.142
L
2.03
2.29
0.080
0.090
M48T35AV
Package mechanical data
Figure 17. SH – 4-pin SNAPHAT housing for 120mAh battery & crystal, pack. outline
A1
A2
A3
A
eA
B
L
eB
D
E
SHTK-A
Note:
Drawing is not to scale.
Table 15.
SH – 4-pin SNAPHAT housing for 120mAh battery & crystal, pack. mech. data
mm
inches
Symb
Typ
Min
A
Max
Typ
Min
10.54
Max
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
eA
15.55
15.95
0.612
0.628
eB
3.20
3.61
0.126
0.142
L
2.03
2.29
0.080
0.090
25/28
Part numbering
7
M48T35AV
Part numbering
Table 16.
Ordering information scheme
Example:
M48T
35AV
–10
MH
1
E
Device type
M48T
Supply voltage and write protect voltage
35AV = VCC = 3.0 to 3.6V; VPFD = 2.7 to 3.0V
Speed
–10 = 100ns (35AV)
Package
PC = PCDIP28
MH(1) = SOH28
Temperature range
1 = 0 to 70°C
Shipping method
For SOH28:
E = Lead-free package (ECOPACK®), tubes
F = Lead-free package (ECOPACK®), tape & reel
For PCDIP28:
blank = tubes
1. The SOIC package (SOH28) requires the SNAPHAT® battery package which is ordered separately under
the part number “M4TXX-BR12SHx” in plastic tubes (see Table 17).
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.
26/28
SNAPHAT battery table
Part number
Description
Package
M4T28-BR12SH1
M4T32-BR12SH1
M4T32-BR12SH6
Lithium battery (48mAh) SNAPHAT
Lithium battery (120mAh) SNAPHAT
Lithium battery (120mAh) SNAPHAT, -40 to +85°C crystal
SH
SH
SH
M48T35AV
8
Revision history
Revision history
Table 18.
Document revision history
Date
Revision
Changes
Nov-1999
1.0
First Issue
21-Apr-2000
2.0
From Preliminary Data to Data Sheet
29-May-2000
2.1
tFB change (Table 10)
20-Jul-2001
3.0
Reformatted; temp./voltage info. added to tables (Table 8, 9, 3, 4, 10,
11); add Century Bit text
20-May-2002
3.1
Modify reflow time and temperature footnotes (Table 6)
31-Mar-2003
4.0
v2.2 template applied; data retention condition updated (Table 11)
01-Apr-2004
5.0
Reformatted; updated with lead-free package information (Table 6, 16)
21-Nov-2007
6
Reformatted document; added lead-free second level interconnect
information to cover page and Section 6: Package mechanical data,
updated Table 16, 17; removed M48T35AY and all references.
27/28
M48T35AV
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