M48T35Y-70PM1 - STMicroelectronics, Inc.

February 2009 Rev 8 1/30

M48T35

M48T35Y

5 V, 256 Kbit (32 Kb x 8) TIMEKEEPER® SRAM

Features

■Integrated, ultralow 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

■Frequency test output for real-time clock

■Automatic power-fail chip deselect and WRITE

protection

■WRITE protect voltages

(VPFD = Power-fail deselect voltage):

–M48T35: V

CC = 4.75 to 5.5 V

– 4.5 V ≤ VPFD ≤ 4.75 V

–M48T35Y: V

CC = 4.5 to 5.5 V

–4.2V ≤ VPFD ≤ 4.5 V

■Self-contained battery and crystal in the

CAPHAT™ DIP package

■SOIC package provides direct connection for a

SNAPHAT® housing containing the battery and

crystal

■SNAPHAT® housing (battery and crystal) is

replaceable

■Pin and function compatible with JEDEC

standard 32 Kb x 8 SRAMs

■RoHS compliant

– Lead-free second level interconnect

PCDIP28 (PC)

Battery/crystal

CAPHAT™

SNAPHAT® (SH)

Battery/crystal

SOH28 (MH)

www.st.com

Contents M48T35 M48T35Y
2/30   
Contents
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Operation modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1 Read mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
2 Write mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
3 Data retention mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  11
Clock operations  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1 Reading the clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  12
2 Setting the clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  12
3 Stopping and starting the oscillator  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  12
4 Calibrating the clock  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
5 Century bit  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
6 VCC noise and negative going transients  . . . . . . . . . . . . . . . . . . . . . . . . .  15
Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
DC and AC parameters  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Part numbering  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Environmental information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Revision history   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

M48T35 M48T35Y List of tables
 3/30
List of tables
Table 1. Signal names  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Table 2. Operating modes  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Table 3. Read mode AC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Table 4. Write mode AC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Table 5. Register map  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Table 6. Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Table 7. Operating and AC measurement conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Table 8. Capacitance  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Table 9. DC characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Table 10. Power down/up AC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Table 11. Power down/up trip points DC characteristics  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Table 12. PCDIP28 – 28-pin plastic DIP, battery CAPHAT™, package mech. data  . . . . . . . . . . . . . 21
Table 13. SOH28 – 28-lead plastic SO, 4-socket battery SNAPHAT®, package mechanical data  . . 22
Table 14. SH – 4-pin SNAPHAT® housing for 48 mAh battery & crystal, package mechanical data. 23
Table 15. SH – 4-pin SNAPHAT® housing for 120 mAh battery & crystal, package mechanical data 24
Table 16. PMDIP28 – 28-pin plastic DIP, hybrid, package mechanical data . . . . . . . . . . . . . . . . . . . 25
Table 17. Ordering information scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Table 18. SNAPHAT® battery table  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Table 19. Document revision history  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

List of figures M48T35 M48T35Y
4/30   
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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 7. Chip enable controlled, write AC waveforms  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 8. Crystal accuracy across temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Figure 9. Clock calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Figure 10. Supply voltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Figure 11. AC measurement load circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Figure 12. Power down/up mode AC waveforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Figure 13. PCDIP28 – 28-pin plastic DIP, battery CAPHAT™, package outline . . . . . . . . . . . . . . . . . 21
Figure 14. SOH28 – 28-lead plastic small outline, 4-socket battery SNAPHAT®, package outline . . . 22
Figure 15. SH – 4-pin SNAPHAT® housing for 48 mAh battery & crystal, package outline. . . . . . . . . 23
Figure 16. SH – 4-pin SNAPHAT® housing for 120 mAh battery & crystal, package outline. . . . . . . . 24
Figure 17. PMDIP28 – 28-pin plastic DIP, hybrid, package outline . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Figure 18. Recycling symbols  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

M48T35 M48T35Y Description

5/30

1 Description

The M48T35/Y TIMEKEEPER® 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-up 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 CAPHAT™ 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® 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” (see Table 18 on page 27).

Figure 1. Logic diagram

AI01620B

A0-A14

DQ0-DQ7

VCC

M48T35

M48T35Y

VSS

Description M48T35 M48T35Y

6/30

Table 1. Signal names

Figure 2. DIP connections

Figure 3. SOIC connections

A0-A14 Address inputs

DQ0-DQ7 Data inputs / outputs

EChip enable

GOutput enable

WWRITE enable

VCC Supply voltage

VSS Ground

DQ0

A13

A10

DQ7

A11

DQ5DQ1

DQ2

DQ3VSS

DQ4

DQ6

A12

A14 VCC

AI01621B

M48T35

M48T35Y

AI01622B

DQ0

A13

A10

DQ7

A11

DQ5DQ1

DQ2

DQ3VSS

DQ4

DQ6

A12

A14 VCC

M48T35Y

M48T35 M48T35Y Description

7/30

Figure 4. Block diagram

AI01623

LITHIUM

CELL

OSCILLATOR AND

CLOCK CHAIN

VPFD

VCC VSS

32,768 Hz

CRYSTAL

VOLTAGE SENSE

AND

SWITCHING

CIRCUITRY

8 x 8 BiPORT

SRAM ARRAY

32,760 x 8

SRAM ARRAY

A0-A14

DQ0-DQ7

POWER

Operation modes M48T35 M48T35Y

8/30

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 BiPORT™ 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. Operating modes

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.

Mode VCC E G W DQ0-DQ7 Power

Deselect

4.75 to 5.5 V

4.5 to 5.5 V

VIH X X High Z Standby

WRITE VIL XV

IL DIN Active

READ VIL VIL VIH DOUT Active

READ VIL VIH VIH High Z Active

Deselect VSO to VPFD (min)(1)

1. See Table 11 on page 20 for details.

Note: X = VIH or VIL; VSO = battery backup switchover voltage.

X X X High Z CMOS standby

Deselect ≤ VSO(1) X X X High Z Battery backup mode

M48T35 M48T35Y Operation modes

9/30

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

Note: WRITE enable (W) = high.

Table 3. Read mode AC characteristics

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

Symbol Parameter(1)

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).

M48T35/Y

Unit

Min Max

tAVAV READ cycle time 70 ns

tAVQV Address valid to output valid 70 ns

tELQV Chip enable low to output valid 70 ns

tGLQV Output enable low to output valid 35 ns

tELQX(2)

2. CL = 5 pF.

Chip enable low to output transition 5 ns

tGLQX(2) Output enable low to output transition 5 ns

tEHQZ(2) Chip enable high to output Hi-Z 25 ns

tGHQZ(2) Output enable high to output Hi-Z 25 ns

tAXQX Address transition to output transition 10 ns

AI00925

tAVAV

tAVQV tAXQX

tELQV

tELQX

tEHQZ

tGLQV

tGLQX

tGHQZ

VALID

A0-A14

DQ0-DQ7

VALID

Operation modes M48T35 M48T35Y

10/30

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

Figure 7. Chip enable controlled, write AC waveforms

AI00926

tAVAV

tWHAX

tDVWH

DATA INPUT

A0-A14

DQ0-DQ7

VALID

tAVWH

tAVEL

tWLWH

tAVWL

tWLQZ

tWHDX

tWHQX

AI00927

tAVAV

tEHAX

tDVEH

A0-A14

DQ0-DQ7

VALID

tAVEH

tAVEL

tAVWL

tELEH

tEHDX

DATA INPUT

Table 4. Write mode AC characteristics

Symbol Parameter(1) M48T35/Y

Unit

Min Max

tAVAV WRITE cycle time 70 ns

tAVWL Address valid to WRITE enable low 0 ns

tAVEL Address valid to chip enable low 0 ns

M48T35 M48T35Y Operation modes

11/30

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, Ta bl e 1 0 , 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.

tWLWH WRITE enable pulse width 50 ns

tELEH Chip enable low to chip enable high 55 ns

tWHAX WRITE enable high to address transition 0 ns

tEHAX Chip enable high to address transition 0 ns

tDVWH Input valid to WRITE enable high 30 ns

tDVEH Input valid to chip enable high 30 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 25 ns

tAVWH Address valid to WRITE enable high 60 ns

tAVEH Address valid to chip enable high 60 ns

tWHQX(2)(3) WRITE enable high to output transition 5 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.

3. If E goes low simultaneously with W going low, the outputs remain in the high impedance state.

Table 4. Write mode AC characteristics (continued)

Symbol Parameter(1) M48T35/Y

Unit

Min Max

Clock operations M48T35 M48T35Y

12/30

3 Clock operations

3.1 Reading the clock

Updates to the TIMEKEEPER® registers (see Ta b l e 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 (see Ta b l e 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 Ta b l e 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 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.

M48T35 M48T35Y Clock operations

13/30

Table 5. Register map

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

sign bit; '1' indicates positive calibration, '0' indicates negative calibration. Calibration occurs

Address

Data Function/range

BCD format

D7 D6 D5 D4 D3 D2 D1 D0

7FFFh 10 Years Year Year 00-99

7FFEh 0 0 0 10 M. Month Month 01-12

7FFDh 0 0 10 date Date Date 01-31

7FFCh 0 FT CEB CB 0 Day Century/

Day 00-01/01-07

7FFBh 0 0 10 hours Hours Hours 00-23

7FFAh 0 10 minutes Minutes Minutes 00-59

7FF9h ST 10 seconds Seconds Seconds 00-59

7FF8h W R S Calibration Control

Clock operations M48T35 M48T35Y

14/30

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®

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.

M48T35 M48T35Y Clock operations

15/30

Figure 8. Crystal accuracy across temperature

Figure 9. Clock calibration

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 µF (as shown in

Figure 10 on page 16) 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

AI02124

-80

-60

-100

-40

-20

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70

ΔF= -0.038 (T - T0)2 ± 10%

ppm

T0 = 25 °C

ppm

°C

AI00594B

NORMAL

POSITIVE

CALIBRATION

NEGATIVE

CALIBRATION

Clock operations M48T35 M48T35Y

16/30

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

M48T35 M48T35Y Maximum ratings

17/30

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. Refer also to the STMicroelectronics SURE

Program and other relevant quality documents.

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 Grade 1 0 to 70 °C

Grade 6 –40 to 85 °C

TSTG Storage temperature (VCC off, oscillator off) –40 to 85 °C

TSLD(1)(2)(3)

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 SOH28 package, standard (SnPb) lead finish: reflow at peak temperature of 225°C (the time above

220°C must not exceed 20 seconds).

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).

Lead solder temperature for 10 seconds 260 °C

VIO Input or output voltages M48T35 –0.3 to 7 V

M48T35Y –0.3 to 7 V

VCC Supply voltage M48T35 –0.3 to 7 V

M48T35Y –0.3 to 7 V

IOOutput current 20 mA

PDPower dissipation 1 W

DC and AC parameters M48T35 M48T35Y

18/30

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 measurement load circuit

Table 8. Capacitance

Parameter M48T35 M48T35Y Unit

Supply voltage (VCC) 4.75 to 5.5 4.5 to 5.5 V

Ambient operating temperature (TA) 0 to 70 –40 to 85 °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 5V; sampled only, not 100% tested.

2. At 25°C, f = 1 MHz.

Min Max Unit

CIN Input capacitance 10 pF

COUT(3)

3. Outputs deselected.

Output capacitance 10 pF

AI01030

OUT

CL = 100pF or 5pF

CL includes JIG capacitance

1.9kΩ

DEVICE

UNDER

TEST

1kΩ

M48T35 M48T35Y DC and AC parameters

19/30

Table 9. DC characteristics

Figure 12. Power down/up mode AC waveforms

Symbol Parameter Test condition(1)

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).

M48T35 M48T35Y

Unit

MinMaxMinMax

ILI Input leakage current 0V ≤ VIN ≤ VCC ±1 ±1 µA

ILO(2)

2. Outputs deselected.

Output leakage current 0V ≤ VOUT ≤ VCC ±1 ±1 µA

ICC Supply current Outputs open 50 30 mA

ICC1

Supply current (standby)

TTL E = VIH 33mA

ICC2

Supply current (standby)

CMOS E = VCC – 0.2 V 2 2 mA

VIL Input low voltage –0.3 0.8 –0.3 0.8 V

VIH Input high voltage 2.2 VCC + 0.3 2.2 VCC + 0.3 V

VOL Output low voltage IOL = 2.1 mA 0.4 0.4 V

VOH Output high voltage IOH = –1 mA 2.4 2.4 V

AI01168C

VCC

INPUTS

(PER CONTROL INPUT)

OUTPUTS

DON'T CARE

HIGH-Z

tFB

tPD

tRB

tDR

VALID VALID

(PER CONTROL INPUT)

RECOGNIZEDRECOGNIZED

VPFD (max)

VPFD (min)

VSO

trec

DC and AC parameters M48T35 M48T35Y

20/30

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 or –40 to 85°C; VCC = 4.75 to 5.5 V or 4.5 to 5.5 V (except where

noted).

Min Max Unit

tPD E or W at VIH 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 M48T35 10 µs

M48T35Y 10 µs

tRVPFD (min) to VPFD (max) VCC rise time 10 µs

tRB VSS to VPFD (min) VCC rise time 1 µs

trec(4)

4. trec (min) = 20 ms for industrial temperature grade 6 device.

VPFD (max) to inputs recognized 40 200 ms

Symbol Parameter(1)(2)

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.

Min Typ Max Unit

VPFD Power-fail deselect voltage M48T35 4.5 4.6 4.75 V

M48T35Y 4.2 4.35 4.5 V

VSO Battery backup switchover voltage M48T35 3.0 V

M48T35Y 3.0 V

tDR(3)(5)

3. CAPHAT™ and M4T32-BR12SH1 SNAPHAT® only, M4T28-BR12SH1 SNAPHAT® top tDR = 7 years (typ).

Expected data retention time Grade 1 10(4)

4. Using larger M4T32-BR12SH6 SNAPHAT® top (recommended for industrial temperature range - grade 6 device).

Ye a r s

Grade 6 10(5)

5. At 25°C, VCC = 0 V.

Ye a r s

M48T35 M48T35Y Package mechanical data

21/30

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

B1 B e1

Symbol

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 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

N28 28

Package mechanical data M48T35 M48T35Y

22/30

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

mechanical data

SOH-A

LA1 α

Symbol

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

e 1.27 – – 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

a0°8°0°8°

N 28 28

CP 0.10 0.004

M48T35 M48T35Y Package mechanical data

23/30

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

mechanical data

SHTK

A1 A

Symbol

mm inches

Typ Min Max Typ Min Max

A 9.78 0.385

A1 6.73 7.24 0.265 0.285

A2 6.48 6.99 0.255 0.275

A3 0.38 0.015

B 0.46 0.56 0.018 0.022

D 21.21 21.84 0.835 0.860

E 14.22 14.99 0.560 0.590

eB 3.20 3.61 0.126 0.142

L 2.03 2.29 0.080 0.090

Package mechanical data M48T35 M48T35Y

24/30

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

mechanical data

SHTK

A1 A

Symbol

mm inches

Typ Min Max Typ Min Max

A 10.54 0.415

A1 8.00 8.51 0.315 0.335

A2 7.24 8.00 0.285 0.315

A3 0.38 0.015

B 0.46 0.56 0.018 0.022

D 21.21 21.84 0.835 0.860

E 17.27 18.03 0.680 0.710

eB 3.20 3.61 0.126 0.142

L 2.03 2.29 0.080 0.090

M48T35 M48T35Y Package mechanical data

25/30

Figure 17. PMDIP28 – 28-pin plastic DIP, hybrid, package outline

Note: Drawing is not to scale.

Table 16. PMDIP28 – 28-pin plastic DIP, hybrid, package mechanical data

PMDIP

Be1

Symbol

mm inches

Typ Min Max Typ Min Max

A 9.27 9.53 0.365 0.375

A1 0.38 0.015

B 0.43 0.58 0.017 0.023

C 0.20 0.33 0.008 0.013

D 37.34 37.85 1.470 1.490

E 18.03 18.80 0.710 0.740

e1 2.29 2.79 0.090 0.110

e3 33.02 1.300

eA 14.99 16.00 0.590 0.630

L 3.05 3.81 0.120 0.150

S 1.91 2.67 0.075 0.105

N 28 28

Part numbering M48T35 M48T35Y

26/30

7 Part numbering

Table 17. 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 35 –70 PC 1 E

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

1. The M48T35 part is offered with the PCDIP28 (e.g., CAPHAT™) package only.

35Y = VCC = 4.5 to 5.5 V; VPFD = 4.2 to 4.5 V

Speed

–70 = 70 ns

Package

PC = PCDIP28

MH(2) = SOH28

2. The SOIC package (SOH28) requires the SNAPHAT® battery package which is ordered

separately under the part number “M4TXX-BR12SH” in plastic tube or “M4TXX-BR12SHTR” in

Tape & Reel form (see Table 18 on page 27).

PM = PMDIP28 (NND)(3)

3. This package is not to be used for new design.

Temperature range

1 = 0 to 70°C

6 = –40 to 85°C(4)

4. Available in SOIC package only.

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

M48T35 M48T35Y Part numbering

27/30

Table 18. SNAPHAT® battery table

Part number Description Package

M4T28-BR12SH Lithium battery (48 mAh) SNAPHAT®SH

M4T32-BR12SH Lithium battery (120 mAh) SNAPHAT®SH

Environmental information M48T35 M48T35Y

28/30

8 Environmental information

Figure 18. 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".

M48T35 M48T35Y Revision history
 29/30
9 Revision history
Table 19. Document revision history
Date Revision Changes
Nov- 1999 1 First issue
07-Feb-2000 1.1 tDR description changed (Ta b l e 9 )
04-Jun-2001 2 Reformatted; temp/voltage info. added to tables (Ta b l e 8 , 9, 3, 4, 10, 11); 
add century bit text
31-Jul-2001 2.1 Formatting changes based on latest document reviews
06-Mar-2002 2.2 Add PMDIP packaging option, which is “Not for New Design” (NND) 
(Ta bl e 1 7 , 16, and Figure 17)
20-May-2002 2.3 Modify reflow time and temperature footnotes (Ta bl e 6)
26-Jun-2002 2.4 Add footnote to table (Ta b l e 1 1 )
31-Mar-2003 3 v2.2 template applied; data retention condition updated (Ta b l e 1 1 )
10-Dec-2003 4 Reformatted; update DC characteristics (Ta b l e 9 )
31-Mar-2004 5 Reformatted; update Pb-free package information (Ta ble 6 , 17)
05-Dec20-05 6 Updated template, lead-free text, and remove footnote (Ta b le 9 , 17)
01-Aug-2007 7 Reformatted; added lead-free second level interconnect information to 
cover page and Section 6: Package mechanical data.
12-Feb-2009 8 Updated Ta bl e 6 ; text in Section 6: Package mechanical data; added 
Section 8: Environmental information; minor formatting changes.

M48T35 M48T35Y

30/30

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