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FEATURES

 Integrated NV SRAM, Real-Time Clock

(RTC), Crystal, Power-Fail Control Circuit,

and Lithium Energy Source

 Clock Registers are Accessed Identically to

the Static RAM; These Registers Reside in the

16 Top RAM Locations

 Century Byte Register (i.e., Y2K Compliant)

 Totally Nonvolatile with Over 10 Years of

Operation in the Absence of Power

 Precision Power-On Reset

 Programmable Watchdog Timer and RTC

Alarm

 BCD-Coded Year, Month, Date, Day, Hours,

Minutes, and Seconds with Automatic Leap

Year Compensation Valid Up to the Year

2100

 Battery Voltage-Level Indicator Flag

 Power-Fail Write Protection Allows for 10%

Power-Supply Tolerance

 Lithium Energy Source is Electrically

Disconnected to Retain Freshness Until Power

is Applied for the First Time

 Also Available in Industrial Temperature

Range: -40°C to +85°C

PIN CONFIGURATION

PIN DESCRIPTION

A0–A18 - Address Input

DQ0–DQ7 - Data Input/Outputs

IRQ/FT - Interrupt, Frequency Test

Output (Open Drain)

RST - Power-On Reset Output

(Open Drain)

CE - Chip Enable

OE - Output Enable

WE - Write Enable

- Power-Supply Input

GND - Ground

X1, X2 - Crystal Connection

BAT

- Battery Connection

DS1557

4Meg, Nonvolatile, Y2K-Compliant

Timekeeping RAM

www.maxim-ic.com

IRQ

/FT

A15

A16

DQ7

DQ6

DQ5

DQ4

DQ3

DQ2

DQ1

DQ0

GND

A17

A14

A13

A12

A11

A10

A18

GND

BAT

PowerCap Module Board

(Uses DS9034PCX PowerCap)

Maxim

DS1557

TOP VIEW

19-5501; Rev 9/10

Summary of content (17 pages)

PAGE 1
9-5501; Rev 9/10 DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM www.maxim-ic.com FEATURES            Integrated NV SRAM, Real-Time Clock (RTC), Crystal, Power-Fail Control Circuit, and Lithium Energy Source Clock Registers are Accessed Identically to the Static RAM; These Registers Reside in the 16 Top RAM Locations Century Byte Register (i.e.
PAGE 2
DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM ORDERING INFORMATION PART TEMP RANGE DS1557P-70+ DS1557P-70IND+ DS1557WP-120+ DS1557WP-120IND+ 0°C to +70°C -40°C to +85°C 0°C to +70°C -40°C to +85°C VOLTAGE (V) 5.0 5.0 3.3 3.3 PIN-PACKAGE TOP MARK** 34 PowerCap* 34 PowerCap* 34 PowerCap* 34 PowerCap* DS1557P+70 DS1557P+70 IND DS1557WP+120 DS1557WP+120 IND + Denotes a lead(Pb)-free/RoHS-compliant package. *DS9034PCX+ or DS9034I-PCX+ (PowerCap) required. Must be ordered separately.
PAGE 3
DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM Figure 1. Block Diagram Maxim DS1557 Table 1. Operating Modes VCC VCC > VPF VSO < VCC
PAGE 4
DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM DATA WRITE MODE The DS1557 is in the write mode whenever WE and CE are in their active state. The start of a write is referenced to the latter occurring transition of WE or CE. The addresses must be held valid throughout the cycle. CE and WE must return inactive for a minimum of tWR prior to the initiation of a subsequent read or write cycle. Data in must be valid tDS prior to the end of the write and remain valid for tDH afterward.
PAGE 5
DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM CLOCK OPERATIONS Table 2 and the following paragraphs describe the operation of RTC, alarm, and watchdog functions. Table 2.
PAGE 6
DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM CLOCK OSCILLATOR CONTROL The clock oscillator may be stopped at any time. To increase the shelf life of the backup lithium battery source, the oscillator can be turned off to minimize current drain from the battery. The OSC bit is the MSB of the Seconds Register (B7 of 7FFF9h). Setting it to a 1 stops the oscillator, setting to a 0 starts the oscillator. The DS1557 is shipped from Maxim with the clock oscillator turned off, OSC bit set to a 1.
PAGE 7
DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM USING THE CLOCK ALARM The alarm settings and control for the DS1557 reside within Registers 7FFF2h-7FFF5h. Register 7FFF6h contains two alarm enable bits: Alarm Enable (AE) and Alarm in Backup Enable (ABE). The AE and ABE bits must be set as described below for the IRQ/FT output to be activated for a matched alarm condition. The alarm can be programmed to activate on a specific day of the month or repeat every day, hour, minute, or second.
PAGE 8
DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM Figure 3. Clearing IRQ Waveforms 7FFF0h 18 CE =0 The IRQ/FT pin can also be activated in the battery-backed mode. The IRQ/FT will go low if an alarm occurs and both ABE and AE are set. The ABE and AE bits are cleared during the power-up transition, however an alarm generated during power-up will set AF. Therefore, the AF bit can be read after system power-up to determine if an alarm was generated during the power-up sequence.
PAGE 9
DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM USING THE WATCHDOG TIMER The watchdog timer can be used to detect an out-of-control processor. The user programs the watchdog timer by setting the desired amount of timeout into the 8-bit Watchdog Register (Address 7FFF7h). The five Watchdog Register bits BMB4 to BMB0 store a binary multiplier and the two lower order bits RB1 to RB0 select the resolution, where 00=1/16 second, 01=1/4 second, 10=1 second, and 11=4 seconds.
PAGE 10
DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM ABSOLUTE MAXIMUM RATINGS Voltage Range on Any Pin Relative to Ground………………………………………………………………-0.3V to +6.0V Storage Temperature Range…………...………………………………………………………….....……..-55°C to +125°C Lead Temperature (soldering, 10s).....................................................................................................…………+260°C Soldering Temperature (reflow)……………………………………………………………………………………….
PAGE 11
DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM DC ELECTRICAL CHARACTERISTICS (VCC = 3.3V ±10%, TA = Over the Operating Range.) PARAMETER SYMBOL CONDITIONS Active Supply Current TTL Standby Current (CE = VIH) CMOS Standby Current (CE VCC - 0.2V) Input Leakage Current (Any Input) Output Leakage Current (Any Output) Output Logic 1 Voltage (IOUT = -1.
PAGE 12
DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM AC CHARACTERISTICS—READ CYCLE (TA = Over the Operating Range) PARAMETER SYMBOL VCC = 5.0V 10% MIN MAX 70 VCC = 3.
PAGE 13
DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM Figure 6. Write Cycle Timing, Write-Enable Controlled Figure 7.
PAGE 14
DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM POWER-UP/DOWN CHARACTERISTICS—5V (VCC = 5.0V ±10%, TA = Over the Operating Range.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS CE or WE at VIH, Before Power-Down tPD 0 s VCC Fall Time: VPF(MAX) to VPF(MIN) VCC Fall Time: VPF(MIN) to VSO VCC Rise Time: VPF(MIN) to VPF(MAX) tF tFB tR 300 10 0 s s s VPF to RST High Expected Data-Retention Time (Oscillator On) tREC 40 tDR (Note 6) Figure 8.
PAGE 15
DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM POWER-UP/DOWN CHARACTERISTICS—3.3V (VCC = 3.3V ±10%, TA = Over the Operating Range.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS CE or WE at VIH, Before Power-Down tPD 0 s VCC Fall Time: VPF(MAX) to VPF(MIN) VCC Rise Time: VPF(MIN) to VPF(MAX) tF tR 300 0 s s VPF to RST High tREC 40 Expected Data-Retention Time (Oscillator On) tDR (Note 6) 200 10 ms years Figure 9. Power-Up/Down Waveform Timing—3.
PAGE 16
DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM AC TEST CONDITIONS Output Load: 50 pF + 1TTL Gate Input Pulse Levels: 0 to 3.0V Timing Measurement Reference Levels: Input: 1.5V Output: 1.5V Input Pulse Rise and Fall Times: 5 ns NOTES: 1) Voltage referenced to ground. 2) 3) 4) 5) Typical values are at 25C and nominal supplies. Outputs are open. Battery switchover occurs at the lower of either the battery voltage or VPF. The IRQ/FT and RST outputs are open drain.
PAGE 17
DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM REVISION HISTORY REVISION DATE 9/10 DESCRIPTION Updated the Ordering Information table to include only lead-free parts; updated the storage temperature range and soldering temperature and added the lead temperature to the Absolute Maximum Ratings section; added Note 11 to the ICC parameter in the DC Electrical Characteristics tables (for 5.0V and 3.