M41T66 Serial real-time clock with alarms Features ■ Counters for tenths/hundredths of seconds, seconds, minutes, hours, day, date, month, year, and century ■ 32 KHz crystal oscillator integrating load capacitance and high crystal series resistance operation ■ Oscillator stop detection monitors clock operation QFN16 3 mm x 3 mm 2 ■ Serial interface supports I C bus (400 kHz) ■ 525 nA timekeeping current at 3 V ■ Low operating current of 35 µA (at 400 kHz) ■ Timekeeping down to 1.0 V ■ 1.
Contents M41T66 Contents 1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.1 3 2-wire bus characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.1.1 Bus not busy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.1.
M41T66 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 M41T66 register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Alarm repeat modes . . . . . . . . .
List of figures M41T66 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. Figure 18. Figure 19. Figure 20. Figure 21. 4/34 M41T66 logic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 M41T66 connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
M41T66 1 Description Description The M41T66 is a low-power serial real-time clock (RTC) with a built-in 32.768 kHz oscillator (external crystal controlled). Eight registers are used for the clock/calendar function and are configured in binary coded decimal (BCD) format. An additional 8 registers provide status/control of alarm, square wave, calibration, and watchdog functions. Addresses and data are transferred serially via a two line, bidirectional I2C interface.
Description .# .# 6## .# M41T66 connections .# 8/ )21 /54 633 3#, 317 3$! .# .# .# 8) 633 Figure 2. M41T66 !) 1. SQW output defaults to 32 KHz upon power-up 2. Open drain Table 1.
M41T66 Description Figure 4. Hardware hookup for SuperCap™ backup operation 6## -#5 - 4 6## # 8) 8/ # 633 6## )21 /54 317 0ORT 317). 3#, 3ERIAL #LOCK ,INE 3$! 3ERIAL $ATA ,INE !) B 1. Open drain 2. For a crystal with a load capacitance (CL) of 12.5 pF, two parallel external 12.5 pF capacitors (C1 and C2) must be added to achieve better clock accuracy. 3. It can also be connected to another power supply. 4.
Operation 2 M41T66 Operation The M41T66 clock operates as a slave device on the serial bus. Access is obtained by implementing a start condition followed by the correct slave address (D0h). The 16 bytes contained in the device can then be accessed sequentially in the following order: 2.
M41T66 2.1.4 Operation Data valid The state of the data line represents valid data when after a start condition, the data line is stable for the duration of the high period of the clock signal. The data on the line may be changed during the low period of the clock signal. There is one clock pulse per bit of data. Each data transfer is initiated with a start condition and terminated with a stop condition. The number of data bytes transferred between the start and stop conditions is not limited.
Operation M41T66 Figure 6. Acknowledgement sequence #,/#+ 05,3% &/2 !#+./7,%$'%-%.4 34!24 3#, &2/-!34%2 $!4! /54054 "9 42!.3-)44%2 -3" ,3" $!4! /54054 "9 2%#%)6%2 !) 2.2 READ mode In this mode the master reads the M41T66 slave after setting the slave address (see Figure 8 on page 11). Following the WRITE mode control bit (R/W=0) and the acknowledge bit, the word address 'An' is written to the on-chip address pointer.
M41T66 Figure 7. Operation Slave address location 2 7 3,!6% !$$2%33 ! ,3" -3" 34!24 !) 2 7 3,!6% !$$2%33 $!4! N !#+ $!4! N !#+ !#+ "53 !#4)6)49 3 !#+ 7/2$ !$$2%33 !N 3 !#+ 3$! ,).% 2 7 "53 !#4)6)49 -!34%2 34!24 READ mode sequence 34!24 Figure 8. 34/0 3,!6% !$$2%33 0 !) ./ !#+ $!4! N 8 2 7 3,!6% !$$2%33 $!4! N 8 0 ./ !#+ "53 !#4)6)49 $!4! N !#+ $!4! N !#+ 3 !#+ 3$! ,).
Operation 2.3 M41T66 WRITE mode In this mode the master transmitter transmits to the M41T66 slave receiver. Bus protocol is shown in Figure 10. Following the START condition and slave address, a logic '0' (R/W=0) is placed on the bus and indicates to the addressed device that word address “An” will follow and is to be written to the on-chip address pointer.
M41T66 3 Clock operation Clock operation The M41T66 is driven by a quartz-controlled oscillator with a nominal frequency of 32.768 kHz. The accuracy of the real-time clock depends on the frequency of the quartz crystal that is used as the time-base for the RTC. The eight byte clock register (see Table 2: M41T66 register map) is used to both set the clock and to read the date and time from the clock, in a binary coded decimal format.
Clock operation 3.1 M41T66 Clock registers The M41T66 offers 16 internal registers which contain clock, calibration, alarm, watchdog, flags, and square wave. The clock registers are memory locations which contain external (user accessible) and internal copies of the data. The external copies are independent of internal functions except that they are updated periodically by the simultaneous transfer of the incremented internal copy.
M41T66 Clock operation M41T66 register map(1) Table 2. Addr D7 00h D6 D5 D4 D3 0.1 seconds D2 D1 D0 Function/range BCD format 0.
Clock operation 3.2 M41T66 Calibrating the clock The M41T66 is driven by a quartz controlled oscillator with a nominal frequency of 32,768 Hz. The accuracy of the real-time clock depends on the frequency of the quartz crystal that is used as the time-base for the RTC. The accuracy of the clock is dependent upon the accuracy of the crystal, and the match between the capacitive load of the oscillator circuit and the capacitive load for which the crystal was trimmed.
M41T66 Clock operation Figure 11. Crystal accuracy across temperature &REQUENCY PPM n n n & + X 4 n 4 / & n + n PPM q# PPM q# n 4/ q# q# n n n n n n n 4EMPERATURE q# !) Figure 12. Calibration waveform ./2-!, 0/3)4)6% #!,)"2!4)/. .%'!4)6% #!,)"2!4)/.
Clock operation 3.3 M41T66 Setting alarm clock registers Address locations 0Ah-0Eh contain the alarm settings. The alarm can be configured to go off at a prescribed time on a specific month, date, hour, minute, or second, or repeat every year, month, day, hour, minute, or second. Bits RPT5–RPT1 put the alarm in the repeat mode of operation. Table 3 shows the possible configurations. Codes not listed in the table default to the once per second mode to quickly alert the user of an incorrect alarm setting.
M41T66 3.4 Clock operation Watchdog timer The watchdog timer can be used to detect an out-of-control microprocessor. The user programs the watchdog timer by setting the desired amount of time-out into the Watchdog Register, address 09h.
Clock operation 3.5 M41T66 Square wave output The M41T66 offers the user a programmable square wave function which is output on the SQW pin. RS3-RS0 bits located in 04h establish the square wave output frequency. These frequencies are listed in Table 4. Once the selection of the SQW frequency has been completed, the SQW pin can be turned on and off under software control with the square wave enable bit (SQWE) located in register 0Ah. The SQW output is an open drain output driver.
M41T66 3.7 Clock operation Output driver pin When the OFIE bit, AFE bit, and watchdog register are not set to generate an interrupt, the IRQ/OUT pin becomes an output driver that reflects the contents of D7 of the calibration register. In other words, when D7 (OUT bit) is a '0,' then the IRQ/OUT pin will be driven low. Note: The IRQ/OUT pin is an open drain which requires an external pull-up resistor. 3.
Clock operation 3.9 M41T66 Initial power-on defaults Upon application of power to the device, the register bits will initially power-on in the state indicated in Table 5. Table 5. Initial power-on default values Condition Initial power-up(1) ST OF OFIE OUT AFE SQWE RS3-1 RS0 Watchdog 0 1 0 1 0 1 0 1 0 1. All other control bits power-up in an undetermined state. Table 6.
M41T66 4 Maximum ratings 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 7.
DC and AC parameters 5 M41T66 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 8.
M41T66 DC and AC parameters Table 9. Capacitance Parameter(1)(2) Symbol CIN COUT(3) tLP Min Max Unit Input capacitance 7 pF Output capacitance 10 pF Low-pass filter input time constant (SDA and SCL) 50 ns 1. Effective capacitance measured with power supply at 3.6 V; sampled only, not 100% tested. 2. At 25 °C, f = 1 MHz. 3. Outputs deselected. Table 10. Sym VCC(2) DC characteristics Test condition(1) Parameter Clock Min Typ 1.0 4.4 V –20 °C to 85 °C 1.3 4.
DC and AC parameters Table 11. M41T66 Crystal electrical characteristics Parameter(1)(2) Sym fO Min Typ Resonant frequency Max Units 32.768 RS Series resistance (TA = –40 to 70 °C) CL Load capacitance kHz 75 (3)(4) kΩ 6 pF 7-12.5(5) 1. Externally supplied if using the QFN16 package. STMicroelectronics recommends the Citizen CFS-145 (1.5 x 5 mm) and the KDS DT-38 (3 x 8 mm) for thru-hole, or the KDS DMX-26S (3.2 x 8 mm) for surface-mount, tuning fork-type quartz crystals.
M41T66 DC and AC parameters Table 13. AC characteristics Parameter(1) Sym Min 0 Typ Max Units 400 kHz fSCL SCL clock frequency tLOW Clock low period 1.
Package mechanical data 6 M41T66 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 17. QFN16 – 16-lead, quad, flat package, no lead, 3 x 3 mm body size, outline $ % ! ! ! DDD # E B , + % #H + $ 1&. ! 1.
M41T66 Package mechanical data Table 14. QFN16 – 16-lead, quad, flat package, no lead, 3 x 3 mm body size, mech. data mm inches Symb Typ Min Max Typ Min Max A 0.90 0.80 1.00 0.035 0.032 0.039 A1 0.02 0.00 0.05 0.001 0.000 0.002 A3 0.20 – – 0.008 – – b 0.25 0.18 0.30 0.010 0.007 0.012 D 3.00 2.90 3.10 0.118 0.114 0.122 D2 1.70 1.55 1.80 0.067 0.061 0.071 E 3.00 2.90 3.10 0.118 0.114 0.122 E2 1.70 1.55 1.80 0.067 0.061 0.071 e 0.50 – – 0.
Package mechanical data M41T66 Figure 20. Carrier tape for QFN16 (3 mm x 3 mm) package P0 E P2 D T A0 F TOP COVER TAPE W B0 P1 CENTER LINES OF CAVITY K0 USER DIRECTION OF FEED AM03073v1 Table 15. Carrier tape dimensions for QFN16 (3 mm x 3 mm) package Package W D QFN16 12.00 ±0.30 1.50 +0.10 /-0.00 30/34 E P0 P2 F 1.75 4.00 2.00 5.50 ±0.10 ±0.10 ±0.10 ±0.05 A0 B0 K0 P1 T 3.30 ±0.10 3.30 ±0.10 1.10 ±0.10 8.00 ±0.10 0.30 ±0.
M41T66 Package mechanical data Figure 21. Reel schematic T 40mm min. Access hole At slot location B D C N A G measured Tape slot In core for Full radius Tape start 2.5mm min.width At hub AM04928v1 Table 16. Reel dimensions for 12 mm carrier tape - QFN16 package A B (max) (min) 330 mm (13-inch) 1.5 mm Note: C 13 mm ± 0.2 mm D N (min) (min) 20.2 mm 60 mm G 12.4 mm + 2/–0 mm T (max) 18.
Part numbering 7 M41T66 Part numbering Table 17. Ordering information scheme Example: M41T 66 Q 6 F Device family M41T Device type and supply voltage 66 = VCC = 1.5 V to 4.4 V Package Q = QFN16 (3 mm x 3 mm) Temperature range 6 = –40 °C to 85 °C Shipping method F = ECOPACK® package, tape & reel For other options, or for more information on any aspect of this device, please contact the ST sales office nearest you.
M41T66 8 Revision history Revision history Table 18.
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