June 2011 Doc ID 2411 Rev 11 1/31
1
M48T08
M48T08Y, M48T18
5 V, 64 Kbit (8 Kb 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
■Typical clock accuracy of ±1 minute a month, at
25 °C
■Automatic power-fail chip deselect and WRITE
protection
■WRITE protect
VPFD = power-fail deselect voltage):
–M48T08: V
CC = 4.75 to 5.5 V;
4.5 V ≤ VPFD ≤ 4.75 V
– M48T18/T08Y: VCC = 4.5 to 5.5 V;
4.2 V ≤ VPFD ≤ 4.5 V
■Software controlled clock calibration for high
accuracy applications
■Self-contained battery and crystal in the
CAPHAT™ DIP package
■Packaging includes a 28-lead SOIC and
SNAPHAT® top (to be ordered separately)
■SOIC package provides direct connection for a
snaphat top which contains the battery and
crystal
■Pin and function compatible with DS1643 and
JEDEC standard 8 K x 8 SRAMs
■RoHS compliant
– Lead-free second level interconnect
28
1
28
1
PCDIP28
battery/crystal
CAPHAT™
SNAPHAT®
battery/crystal
SOH28
www.st.com
Contents M48T08, M48T08Y, M48T18
2/31 Doc ID 2411 Rev 11
Contents
1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2 Operation modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1 READ mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 WRITE mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3 Data retention mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.4 Power-fail interrupt pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3 Clock operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.1 Reading the clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.2 Setting the clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.3 Stopping and starting the oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.4 Calibrating the clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.5 VCC noise and negative going transients . . . . . . . . . . . . . . . . . . . . . . . . . 18
4 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5 DC and AC parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
6 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
7 Part numbering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
8 Environmental information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
9 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
M48T08, M48T08Y, M48T18 List of tables
Doc ID 2411 Rev 11 3/31
List of tables
Table 1. Signal names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Table 2. Operating modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Table 3. READ mode AC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Table 4. WRITE mode AC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Table 5. Register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Table 6. Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Table 7. Operating and AC measurement conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Table 8. Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Table 9. DC characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Table 10. Power down/up AC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Table 11. Power down/up trip points DC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Table 12. PCDIP28 – 28-pin plastic DIP, battery CAPHAT™, package mech. data . . . . . . . . . . . . . 23
Table 13. SOH28 – 28-lead plastic SO, 4-socket battery SNAPHAT®, package mech. data. . . . . . . 24
Table 14. SH – 4-pin SNAPHAT® housing for 48 mAh battery & crystal, package mech. data . . . . . 25
Table 15. SH – 4-pin SNAPHAT® housing for 120 mAh battery & crystal, package mech. data . . . . 26
Table 16. Ordering information scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Table 17. SNAPHAT® battery table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Table 18. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
List of figures M48T08, M48T08Y, M48T18
4/31 Doc ID 2411 Rev 11
List of figures
Figure 1. Logic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Figure 2. DIP connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Figure 3. SOIC connections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Figure 4. Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Figure 5. READ mode AC waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Figure 6. WRITE enable controlled, WRITE AC waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 7. Chip enable controlled, WRITE AC waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 8. Crystal accuracy across temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 9. Clock calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 10. Supply voltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Figure 11. AC testing load circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Figure 12. Power down/up mode AC waveforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 13. PCDIP28 – 28-pin plastic DIP, battery CAPHAT™, package outline . . . . . . . . . . . . . . . . . 23
Figure 14. SOH28 – 28-lead plastic small outline, 4-socket battery SNAPHAT®, package outline . . . 24
Figure 15. SH – 4-pin SNAPHAT® housing for 48 mAh battery & crystal, package outline. . . . . . . . . 25
Figure 16. SH – 4-pin SNAPHAT® housing for 120 mAh battery & crystal, package outline. . . . . . . . 26
Figure 17. Recycling symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
M48T08, M48T08Y, M48T18 Description
Doc ID 2411 Rev 11 5/31
1 Description
The M48T08/18/08Y TIMEKEEPER® RAM is an 8 K x 8 non-volatile static RAM and real-
time clock which is pin and function compatible with the DS1643. The monolithic chip is
available in two special packages to provide a highly integrated battery-backed memory and
real-time clock solution.
The M48T08/18/08Y is a non-volatile pin and function equivalent to any JEDEC standard
8 K 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 CAPHAT™ houses the M48T08/18/08Y 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® 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 “M4T28-BR12SH” or “M4T32-BR12SH”.
Figure 1. Logic diagram
AI01020
13
A0-A12
W
DQ0-DQ7
VCC
M48T08
M48T08Y
M48T18
G
E2
VSS
8
E1 INT
Description M48T08, M48T08Y, M48T18
6/31 Doc ID 2411 Rev 11
Table 1. Signal names
Figure 2. DIP connections
Figure 3. SOIC connections
A0-A12 Address inputs
DQ0-DQ7 Data inputs / outputs
INT Power fail interrupt (open drain)
E1 Chip enable 1
E2 Chip enable 2
GOutput enable
WWRITE enable
VCC Supply voltage
VSS Ground
A1
A0
DQ0
A7
A4
A3
A2
A6
A5
E2
A10
A8
A9
DQ7
W
A11
G
E1
DQ5DQ1
DQ2
DQ3VSS
DQ4
DQ6
A12
INT VCC
AI01182
M48T08
M48T18
8
1
2
3
4
5
6
7
9
10
11
12
13
14
16
15
28
27
26
25
24
23
22
21
20
19
18
17
AI01021B
8
2
3
4
5
6
7
9
10
11
12
13
14
22
21
20
19
18
17
16
15
28
27
26
25
24
23
1
A1
A0
DQ0
A7
A4
A3
A2
A6
A5
E2
A10
A8
A9
DQ7
W
A11
G
E1
DQ5DQ1
DQ2
DQ3VSS
DQ4
DQ6
A12
INT VCC
M48T08Y
M48T08, M48T08Y, M48T18 Description
Doc ID 2411 Rev 11 7/31
Figure 4. Block diagram
AI01333
LITHIUM
CELL
OSCILLATOR AND
CLOCK CHAIN
VPFD
INTVCC VSS
32,768 Hz
CRYSTA L
VOLTAGE SENSE
AND
SWITCHING
CIRCUITRY
8 x 8 BiPORT
SRAM ARRAY
8184 x 8
SRAM ARRAY
A0-A12
DQ0-DQ7
E1
E2
W
G
POWER
Operation modes M48T08, M48T08Y, M48T18
8/31 Doc ID 2411 Rev 11
2 Operation modes
As Figure 4 on page 7 shows, the static memory array and the quartz-controlled clock
oscillator of the M48T08/18/08Y 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 1FF8h-1FFFh.
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 1FF8h 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 M48T08/18/08Y
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 M48T08/18/08Y 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. Operating modes
Note: X = VIH or VIL ; VSO = Battery backup switchover voltage.
Mode VCC E1 E2 G WDQ0-DQ7 Power
Deselect
4.75 to 5.5 V
or
4.5 to 5.5 V
VIH X X X High Z Standby
Deselect X VIL X X High Z Standby
WRITE VIL VIH XV
IL DIN Active
READ VIL VIH VIL VIH DOUT Active
READ VIL VIH VIH VIH High Z Active
Deselect VSO to
VPFD(min)(1)
1. See Table 11 on page 22 for details.
XXXXHigh ZCMOS standby
Deselect ≤ VSO(1) X X X X High Z Battery backup mode
M48T08, M48T08Y, M48T18 Operation modes
Doc ID 2411 Rev 11 9/31
2.1 READ mode
The M48T08/18/08Y is in the READ mode whenever W (WRITE enable) is high, E1 (chip
enable 1) is low, and E2 (chip enable 2) is high. The device architecture allows ripple-
through access of data from eight of 65,536 locations in the static storage array. Thus, the
unique address specified by the 13 address inputs defines which one of the 8,192 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 E1, E2, and G
access times are also satisfied. If the E1, E2 and G access times are not met, valid data will
be available after the latter of the chip enable access times (tE1LQV or tE2HQV) or output
enable access time (tGLQV).
The state of the eight three-state data I/O signals is controlled by E1, E2 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 E1, E2 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
Note: WRITE enable (W) = high.
AI00962
tAVAV
tAVQV tAXQX
tE1LQV
tE1LQX
tE1HQZ
tGLQV
tGLQX
tGHQZ
VALID
A0-A12
E1
G
DQ0-DQ7
tE2HQV
tE2HQX
VALID
tE2LQZ
E2
Operation modes M48T08, M48T08Y, M48T18
10/31 Doc ID 2411 Rev 11
Table 3. READ mode AC characteristics
Note: Valid for ambient operating temperature: TA = 0 to 70 °C; VCC = 4.75 to 5.5 V or 4.5 to 5.5 V
(except where noted).
2.2 WRITE mode
The M48T08/18/08Y is in the WRITE mode whenever W, E1, and E2 are active. The start of
a WRITE is referenced from the latter occurring falling edge of W or E1, or the rising edge of
E2. A WRITE is terminated by the earlier rising edge of W or E1, or the falling edge of E2.
The addresses must be held valid throughout the cycle. E1 or W must return high or E2 low
for a minimum of tE1HAX or tE2LAX 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 E1 and G
and a high on E2, a low on W will disable the outputs tWLQZ after W falls.
Symbol Parameter(1)
M48T08/M48T18/T08Y
Unit–100/–10 (T08Y) –150/–15 (T08Y)
Min Max Min Max
tAVAV READ cycle time 100 150 ns
tAVQV Address valid to output valid 100 150 ns
tE1LQV Chip enable 1 low to output valid 100 150 ns
tE2HQV Chip enable 2 high to output valid 100 150 ns
tGLQV Output enable low to output valid 50 75 ns
tE1LQX Chip enable 1 low to output transition 10 10 ns
tE2HQX Chip enable 2 high to output transition 10 10 ns
tGLQX Output enable low to output transition 5 5 ns
tE1HQZ Chip enable 1 high to output Hi-Z 50 75 ns
tE2LQZ Chip enable 2 low to output Hi-Z 50 75 ns
tGHQZ Output enable high to output Hi-Z 40 60 ns
tAXQX Address transition to output transition 5 5 ns
M48T08, M48T08Y, M48T18 Operation modes
Doc ID 2411 Rev 11 11/31
Figure 6. WRITE enable controlled, WRITE AC waveform
Figure 7. Chip enable controlled, WRITE AC waveforms
AI00963
tAVAV
tWHAX
tDVWH
DATA INPUT
A0-A12
E1
W
DQ0-DQ7
VALID
E2
tAVWH
tAVE1L
tAVE2H
tWLWH
tAVWL
tWLQZ
tWHDX
tWHQX
AI00964B
tAVAV
tE1HAX
tDVE1H
tDVE2L
A0-A12
E1
W
DQ0-DQ7
VALID
E2
tAVE1H
tAVE1L
tAVWL
tAVE2L
tE1LE1H
tE2LAX
tAVE2H tE2HE2L
tE1HDX
tE2LDX
DATA INPUT
Operation modes M48T08, M48T08Y, M48T18
12/31 Doc ID 2411 Rev 11
Table 4. WRITE mode AC characteristics
Symbol Parameter(1)
1. Valid for ambient operating temperature: TA = 0 to 70 °C; VCC = 4.75 to 5.5 V or 4.5 to 5.5 V (except where noted).
M48T08/M48T18/T08Y
Unit–100/–10 (T08Y) –150/–15 (T08Y)
MinMaxMinMax
tAVAV WRITE cycle time 100 150 ns
tAVWL Address valid to WRITE enable low 0 0 ns
tAVE1L Address valid to chip enable 1 low 0 0 ns
tAVE2H Address valid to chip enable 2 high 0 0 ns
tWLWH WRITE enable pulse width 80 100 ns
tE1LE1H Chip enable 1 low to chip enable 1 high 80 130 ns
tE2HE2L Chip enable 2 high to chip enable 2 low 80 130 ns
tWHAX WRITE enable high to address transition 10 10 ns
tE1HAX Chip enable 1 high to address transition 10 10 ns
tE2LAX Chip enable 2 low to address transition 10 10 ns
tDVWH Input valid to WRITE enable high 50 70 ns
tDVE1H Input valid to chip enable 1 high 50 70 ns
tDVE2L Input valid to chip enable 2 low 50 70 ns
tWHDX WRITE enable high to input transition 5 5 ns
tE1HDX Chip enable 1 high to input transition 5 5 ns
tE2LDX Chip enable 2 low to input transition 5 5 ns
tWLQZ WRITE enable low to output Hi-Z 50 70 ns
tAVWH Address valid to WRITE enable high 80 130 ns
tAVE1H Address valid to chip enable 1 high 80 130 ns
tAVE2L Address valid to chip enable 2 low 80 130 ns
tWHQX WRITE enable high to output transition 10 10 ns
M48T08, M48T08Y, M48T18 Operation modes
Doc ID 2411 Rev 11 13/31
2.3 Data retention mode
With valid VCC applied, the M48T08/18/08Y 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.”
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 M48T08/18/08Y 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
M48T08/18/08Y for an accumulated period of at least 10 years when VCC is less than VSO.
Note: Requires use of M4T32-BR12SH SNAPHAT® top when using the SOH28 package.
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). E1 should be kept
high or E2 low as VCC rises past VPFD (min) to prevent inadvertent WRITE cycles prior to
system 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.
2.4 Power-fail interrupt pin
The M48T08/18/08Y continuously monitors VCC. When VCC falls to the power-fail detect trip
point, an interrupt is immediately generated. An internal clock provides a delay of between
10 µs and 40 µs before automatically deselecting the M48T08/18/08Y. The INT pin is an
open drain output and requires an external pull-up resistor, even if the interrupt output
function is not being used.
Clock operations M48T08, M48T08Y, M48T18
14/31 Doc ID 2411 Rev 11
3 Clock operations
3.1 Reading the clock
Updates to the TIMEKEEPER® registers 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, the seventh bit in the control
register. 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
The eighth bit of the control register 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 (on Ta bl e 5 ). Resetting the
WRITE bit to a '0' then transfers the values of all time registers (1FF9h-1FFFh) to the actual
TIMEKEEPER counters and allows normal operation to resume. The FT bit and the bits
marked as '0' in Ta b l e 5 must be written to '0' to allow for normal TIMEKEEPER and RAM
operation.
See the application note AN923, “TIMEKEEPER® rolling Into the 21st century” for
information on century rollover.
M48T08, M48T08Y, M48T18 Clock operations
Doc ID 2411 Rev 11 15/31
Keys:
S = SIGN bit
FT = FREQUENCY TEST bit (set to '0' for normal clock operation)
R = READ bit
W = WRITE bit
ST = STOP bit
0 = Must be set to '0'
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 (ST) is the MSB of the seconds register. Setting it to a '1' stops the
oscillator. The M48T08/18/08Y (in the PCDIP28 package) is shipped from
STMicroelectronics with the STOP bit set to a '1.' When reset to a '0,' the M48T08/18/08Y
oscillator starts within one second.
Note: To guarantee oscillator startup after initial power-up, first write the STOP bit (ST) to '1,' then
reset to '0.'
3.4 Calibrating the clock
The M48T08/18/08Y is driven by a quartz-controlled oscillator with a nominal frequency of
32,768 Hz. A typical M48T08/18/08Y is accurate within 1 minute per month at 25 °C without
calibration. 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 M48T08/18/08Y improves to better than
+1/–2 ppm at 25 °C.
The oscillation rate of any crystal changes with temperature. Figure 8 on page 17 shows the
frequency error that can be expected at various temperatures. Most clock chips compensate
for crystal frequency and temperature shift error with cumbersome “trim” capacitors. The
Table 5. Register map
Address
Data Function/range
BCD format
D7 D6 D5 D4 D3 D2 D1 D0
1FFFh 10 years Year Year 00-99
1FFEh 0 0 0 10 M Month Month 01-12
1FFDh 0 0 10 date Date Date 01-31
1FFCh 0 FT 0 0 0 Day Day 01-07
1FFBh 0 0 10 hours Hours Hours 00-23
1FFAh 0 10 minutes Minutes Minutes 00-59
1FF9h ST 10 seconds Seconds Seconds 00-59
1FF8h W R S Calibration Control
Clock operations M48T08, M48T08Y, M48T18
16/31 Doc ID 2411 Rev 11
M48T08/18/08Y 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 17. The number of times pulses are blanked (subtracted,
negative calibration) or split (added, positive calibration) depends upon the value loaded into
the five-bit calibration byte 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 in the control register. This byte can
be set to represent any value between 0 and 31 in binary form. The sixth bit 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 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 M48T08/18/08Y
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 standard test equipment. When the frequency test (FT) bit, the seventh-most significant
bit in the day register, is set to a '1,' and the oscillator is running at 32,768 Hz, the LSB
(DQ0) of the seconds register will toggle at 512 Hz. 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 device must be selected and addresses must be stable at address 1FF9h when reading
the 512 Hz on DQ0.
The LSB of the seconds register is monitored by holding the M48T08/18/08Y in an extended
READ of the seconds register, but without having the READ bit set. The FT bit MUST be
reset to '0' for normal clock operations to resume.
For more information on calibration, see the application note AN934, “TIMEKEEPER®
calibration.”
M48T08, M48T08Y, M48T18 Clock operations
Doc ID 2411 Rev 11 17/31
Figure 8. Crystal accuracy across temperature
Figure 9. Clock calibration
AI02124
-80
-60
-100
-40
-20
0
20
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70
ΔF= -0.038 (T - T0)2 ± 10%
F
ppm
C2
T0 = 25 °C
ppm
°C
AI00594B
NORMAL
POSITIVE
CALIBRATION
NEGATIVE
CALIBRATION
Clock operations M48T08, M48T08Y, M48T18
18/31 Doc ID 2411 Rev 11
3.5 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 ceramic bypass capacitor value of 0.1 µF (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
AI02169
VCC
0.1µF DEVICE
VCC
VSS
M48T08, M48T08Y, M48T18 Maximum ratings
Doc ID 2411 Rev 11 19/31
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. Absolute maximum ratings
Caution: Negative undershoots below –0.3 V are not allowed on any pin while in the battery backup
mode.
Caution: Do NOT wave solder SOIC to avoid damaging SNAPHAT® sockets.
Symbol Parameter Value Unit
TAAmbient operating temperature 0 to 70 °C
TSTG Storage temperature (VCC off, oscillator off) –40 to 85 °C
TSLD(1)(2)(3)
1. For DIP package, soldering temperature of the IC leads is to not exceed 260 °C for 10 seconds.
Furthermore, the devices shall not be exposed to IR reflow nor preheat cycles (as performed as part of
wave soldering). ST recommends the devices be hand-soldered or placed in sockets to avoid heat damage
to the batteries.
2. For DIP packaged devices, ultrasound vibrations should not be used for post-solder cleaning to avoid
damaging the crystal.
3. For SO package, lead-free (Pb-free) lead finish: reflow at peak temperature of 260 °C (the time above
255 °C must not exceed 30 seconds).
Lead solder temperature for 10 seconds 260 °C
VIO Input or output voltages –0.3 to 7 V
VCC Supply voltage –0.3 to 7 V
IOOutput current 20 mA
PDPower dissipation 1 W
DC and AC parameters M48T08, M48T08Y, M48T18
20/31 Doc ID 2411 Rev 11
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
Note: Output Hi-Z is defined as the point where data is no longer driven.
Figure 11. AC testing load circuit
Table 8. Capacitance
Parameter M48T08 M48T18/T08Y Unit
Supply voltage (VCC) 4.75 to 5.5 4.5 to 5.5 V
Ambient operating temperature (TA) 0 to 70 0 to 70 °C
Load capacitance (CL) 100 100 pF
Input rise and fall times ≤ 5 ≤ 5ns
Input pulse voltages 0 to 3 0 to 3 V
Input and output timing ref. voltages 1.5 1.5 V
Symbol Parameter(1)(2)
1. Effective capacitance measured with power supply at 5 V; sampled only, not 100% tested.
2. At 25 °C, f = 1 MHz.
Min Max Unit
CIN Input capacitance - 10 pF
CIO(3)
3. Outputs deselected.
Input / output capacitance - 10 pF
AI01019
5V
OUT
CL = 100pF
CL includes JIG capacitance
1.8kΩ
DEVICE
UNDER
TEST
1kΩ
M48T08, M48T08Y, M48T18 DC and AC parameters
Doc ID 2411 Rev 11 21/31
Table 9. DC characteristics
Figure 12. Power down/up mode AC waveforms
Note: Inputs may or may not be recognized at this time. Caution should be taken to keep E1 high
or E2 low as VCC rises past VPFD (min). Some systems may perform inadvertent WRITE
cycles after VCC rises above VPFD (min) but before normal system operations begin. Even
though a power on reset is being applied to the processor, a reset condition may not occur
until after the system clock is running.
Symbol Parameter Test condition(1)
1. Valid for ambient operating temperature: TA = 0 to 70 °C; VCC = 4.75 to 5.5 V or 4.5 to 5.5 V (except where noted).
M48T08/M48T18/T08Y
Unit
Min Max
ILI Input leakage current 0V ≤ VIN ≤ VCC ±1 µA
ILO(2)
2. Outputs deselected.
Output leakage current 0V ≤ VOUT ≤ VCC ±1 µA
ICC Supply current Outputs open 80 mA
ICC1(3)
3. Measured with control bits set as follows: R = '1'; W, ST, FT = '0.'
Supply current (standby) TTL E1 = VIH, E2 = VIL 3mA
ICC2(3) Supply current (standby) CMOS E1 = VCC – 0.2V,
E2 = VSS + 0.2V 3mA
VIL Input low voltage –0.3 0.8 V
VIH Input high voltage 2.2 VCC + 0.3 V
VOL
Output low voltage IOL = 2.1 mA 0.4 V
Output low voltage (INT)(4)
4. The INT pin is open drain.
IOL = 0.5 mA 0.4 V
VOH Output high voltage IOH = –1 mA 2.4 V
AI00566
VCC
INPUTS
INT
(PER CONTROL INPUT)
OUTPUTS
DON'T CARE
HIGH-Z
tF
tFB
tPFX
tR
tPFH
trec
tPD tRB
tDR
VALID VALID
NOTE
(PER CONTROL INPUT)
RECOGNIZEDRECOGNIZED
VPFD (max)
VPFD (min)
VSO
DC and AC parameters M48T08, M48T08Y, M48T18
22/31 Doc ID 2411 Rev 11
Table 10. Power down/up AC characteristics
Table 11. Power down/up trip points DC characteristics
Symbol Parameter(1)
1. Valid for ambient operating temperature: TA = 0 to 70 °C; VCC = 4.75 to 5.5 V or 4.5 to 5.5 V (except where
noted).
Min Max Unit
tPD E1 or W at VIH or E2 at VIL before power-down 0 µs
tF(2)
2. VPFD (max) to VPFD (min) fall time of less than tF may result in deselection/write protection not occurring
until 200 µs after VCC passes VPFD (min).
VPFD (max) to VPFD (min) VCC fall time 300 µs
tFB(3)
3. VPFD (min) to VSS fall time of less than tFB may cause corruption of RAM data.
VPFD (min) to VSS VCC fall time 10 µs
tRVPFD (min) to VPFD (max) VCC rise time 0 µs
tRB VSS to VPFD (min) VCC rise time 1 µs
trec E1 or W at VIH or E2 at VIL before power-up 1 ms
tPFX INT low to auto deselect 10 40 µs
tPFH VPFD (max) to INT high 120 µs
Symbol Parameter(1)(2)
1. All voltages referenced to VSS.
2. Valid for ambient operating temperature: TA = 0 to 70 °C; VCC = 4.75 to 5.5 V or 4.5 to 5.5 V (except where
noted).
Min Typ Max Unit
VPFD Power-fail deselect voltage M48T08 4.5 4.6 4.75 V
M48T18/T08Y 4.2 4.3 4.5 V
VSO Battery backup switchover voltage 3.0 V
tDR Expected data retention time 10(3)
3. At 55 °C, VCC = 0 V; tDR = 8.5 years (typ) at 70 °C. Requires use of M4T32-BR12SH SNAPHAT® top when
using the SOH28 package.
Ye a r s
M48T08, M48T08Y, M48T18 Package mechanical data
Doc ID 2411 Rev 11 23/31
6 Package mechanical data
In order to meet environmental requirements, ST offers these devices in different grades of
ECOPACK® packages, depending on their level of environmental compliance. ECOPACK®
specifications, grade definitions and product status are available at: www.st.com.
ECOPACK® is an ST trademark.
Figure 13. PCDIP28 – 28-pin plastic DIP, battery CAPHAT™, package outline
Note: Drawing is not to scale.
Table 12. PCDIP28 – 28-pin plastic DIP, battery CAPHAT™, package mech. data
PCDIP
A2
A1
A
L
B1 B e1
D
E
N
1
C
eA
e3
Symb
mm inches
Typ 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 33.02 1.3
eA 15.24 16.00 0.600 0.630
L 3.05 3.81 0.120 0.150
N28 28
Package mechanical data M48T08, M48T08Y, M48T18
24/31 Doc ID 2411 Rev 11
Figure 14. SOH28 – 28-lead plastic small outline, 4-socket battery SNAPHAT®, package
outline
Note: Drawing is not to scale.
Table 13. SOH28 – 28-lead plastic SO, 4-socket battery SNAPHAT®, package mech.
data
SOH-A
E
N
D
C
LA1 α
1
H
A
CP
Be
A2
eB
Symb
mm inches
Typ Min Max Typ Min Max
A3.050.120
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
e1.27– –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
α0° 8° 0° 8°
N28 28
CP 0.10 0.004
M48T08, M48T08Y, M48T18 Package mechanical data
Doc ID 2411 Rev 11 25/31
Figure 15. SH – 4-pin SNAPHAT® housing for 48 mAh battery & crystal, package
outline
Note: Drawing is not to scale.
Table 14. SH – 4-pin SNAPHAT® housing for 48 mAh battery & crystal, package mech.
data
SHTK-A
A1 A
D
E
eA
eB
A2
BL
A3
Symb
mm inches
Typ Min Max Typ Min Max
A9.780.385
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
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
Package mechanical data M48T08, M48T08Y, M48T18
26/31 Doc ID 2411 Rev 11
Figure 16. SH – 4-pin SNAPHAT® housing for 120 mAh battery & crystal, package
outline
Note: Drawing is not to scale.
Table 15. SH – 4-pin SNAPHAT® housing for 120 mAh battery & crystal, package
mech. data
SHTK-A
A1 A
D
E
eA
eB
A2
BL
A3
Symb
mm inches
Typ Min Max Typ Min Max
A 10.54 0.415
A1 8.00 8.51 0.315 .0335
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 .0710
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
M48T08, M48T08Y, M48T18 Part numbering
Doc ID 2411 Rev 11 27/31
7 Part numbering
Table 16. Ordering information scheme
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.
Example: M48T 18 –100 PC 1 E
Device type
M48T
Supply voltage and write protect voltage
08(1) = VCC = 4.75 to 5.5 V; VPFD = 4.5 to 4.75 V
1. The M48T08/18 part is offered with the PCDIP28 (e.g., CAPHAT™) package only.
18/08Y = VCC = 4.5 to 5.5 V; VPFD = 4.2 to 4.5 V
Speed
–100 = 100 ns
–150 = 150 ns
–10 = 100 ns (M48T08Y)
Package
PC(1) = PCDIP28
MH(2) = SOH28
2. The SOIC package (SOH28) requires the SNAPHAT® battery/crystal package which is ordered separately
under the part number “M4TXX-BR12SH” in plastic tube or “M4TXX-BR12SHTR” in tape & reel form (see
Table 17). The M48T08Y part is offered in the SOH28 (SNAPHAT) package only.
Temperature range
1 = 0 to 70 °C
Shipping method
For SOH28:
blank = Tubes (not for new design - use E)
E = ECOPACK® package, tubes
F = ECOPACK® package, tape & reel
TR = Tape & reel (not for new design - use F)
For PCDIP28:
blank = ECOPACK® package, tubes
Part numbering M48T08, M48T08Y, M48T18
28/31 Doc ID 2411 Rev 11
Table 17. SNAPHAT® battery table
Part number Description Package
M4T28-BR12SH Lithium battery (48 mAh) SNAPHAT®SH
M4T32-BR12SH Lithium battery (120 mAh) SNAPHAT®SH
M48T08, M48T08Y, M48T18 Environmental information
Doc ID 2411 Rev 11 29/31
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.
Revision history M48T08, M48T08Y, M48T18
30/31 Doc ID 2411 Rev 11
9 Revision history
Table 18. Document revision history
Date Revision Changes
Dec-1999 1 First Issue
07-Feb-2000 2 From Preliminary Data to Datasheet; Battery Low Flag paragraph
changed; 100ns speed class identifier changed (Ta b l e 3 , 4)
11-Jul-2000 2.1 tFB changed (Ta b l e 1 0 ); Watchdog Timer paragraph changed
16-Jul-2001 3 Reformatted; SNAPHAT battery table added (Ta b l e 1 7 ); added
temp./voltage info. to tables (Ta b l e 8 , 9, 3, 4, 10, 11).
01-Aug-2001 3.1 Reference to App. Note corrected in “Calibrating the Clock” section
21-Dec-2001 3.2 Changes to text in document to reflect addition of M48T08Y option
06-Mar-2002 3.3 Fix Ordering Information table and add to footnote (Ta b l e 1 6 )
20-May-2002 3.4 Modify reflow time and temperature footnotes (Ta b l e 6 )
29-Aug-2002 3.5 tDR specification temperature updated (Ta bl e 11 )
28-Mar-2003 4 v2.2 template applied; updated test conditions (Ta bl e 1 0 )
10-Dec-2003 5 Reformatted
30-Mar-2004 6 Reformatted; Lead-free (Pb-free) information package update (Ta bl e 6 ,
16)
13-Dec-2005 7 Updated template, Lead-free information, removed footnote (Ta bl e 9 , 16)
04-Jul-2007 8 Reformatted; added lead-free second level interconnect information to
cover page and Section 6: Package mechanical data.
10-Feb-2009 9 Updated Ta b le 6 , text in Section 6: Package mechanical data; added
Section 8: Environmental information; minor formatting changes.
21-Jun-2010 10 Updated Section 4, Tabl e 12 ; reformatted document.
07-Jun-2011 11 Updated footnote 1 of Table 6: Absolute maximum ratings; updated
Section 8: Environmental information.
M48T08, M48T08Y, M48T18
Doc ID 2411 Rev 11 31/31
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