DS1670E+

DS1670 Portable System Controller www.maxim-ic.com GENERAL DESCRIPTION FEATURES The DS1670 portable system controller is a circuit that incorporates many of the functions necessary for low-power portable products integrated into one chip. The device provides a real-time clock (RTC), NV RAM controller, microprocessor monitor, and a 3-channel, 8-bit analog-to-digital converter (ADC). Communication with the DS1670 is established through a simple 3-wire interface.  The RTC provides seconds, minutes, hours, day, date, month, and year information with leap year compensation. The RTC also provides an alarm interrupt. This interrupt works when the DS1670 is powered by the system power supply or when in battery-backup operation, so the alarm can be used to wake up a system that is powered down. Automatic backup and write protection of an external SRAM is provided through the VCCO, CEOL, and CEOH pins. The backup energy source used to power the RTC is also used to retain RAM data in the absence of VCC through the VCCO pin. The chipenable outputs to RAM (CEOL and CEOH) are controlled during power transients to prevent data corruption. Provides Real-Time Clock Counts Seconds, Minutes, Hours, Date of the Month, Month, Day of the Week, and Year with Leap Year Compensation Valid Up to 2100 Power-Control Circuitry Supports System Power-On from Day/Time Alarm Microprocessor Monitor Halts Microprocessor During Power Fail Automatically Restarts Microprocessor after Power Failure Monitors Pushbutton for External Override Halts and Resets an Out-of-Control Microprocessor NV RAM Control Automatic Battery Backup and Write Protection to External SRAM 3-Channel, 8-Bit ADC Simple 3-Wire Interface 3.3V Operation Underwriters Laboratory (UL) Recognized       PIN CONFIGURATION TOP VIEW ORDERING INFORMATION VOLTAGE (V) DS1670E 3.3 DS1670E+ 3.3 DS1670E/T&R 3.3 DS1670E+TRL 3.3 DS1670S 3.3 DS1670S+ 3.3 PART* PINPACKAGE 20 TSSOP 20 TSSOP 20 TSSOP 20 TSSOP 20 SO 20 SO TOP MARK† DS1670E DS1670E DS1670E DS1670E DS1670S DS1670S 20 ST 19 VCC 3 18 4 17 X1 X2 CS 5 16 AIN0 CEI 6 15 AIN1 CEOL 7 14 AIN2 CEOH 8 9 13 12 RST 10 11 BHE VBAT 1 VCCO 2 SCLK I/O INT GND * All devices are specified over the 0°C to +70°C operating range. † A “‘+” anywhere on the top mark denotes a lead-free device. + Denotes a lead(Pb)-free/RoHS-compliant device. DS1670 BLE TSSOP (4.4mm) SO (300 mils) 1 of 16 REV: 080805 DS1670 DETAILED DESCRIPTION The microprocessor monitor circuitry of the DS1670 provides three basic functions. First, a precision temperature-compensated reference and comparator circuit monitors the status of VCC. When an out-oftolerance condition occurs, an internal power-fail signal is generated that forces the reset to the active state. When VCC returns to an in-tolerance condition, the reset signals are kept in the active state for 250ms to allow the power supply and processor to stabilize. The second microprocessor monitor function is pushbutton reset control. The DS1670 debounces a pushbutton input and guarantees an active-reset pulse width of 250ms. The third function is a watchdog timer. The DS1670 has an internal timer that forces the reset signals to the active state if the strobe input is not driven low prior to watchdog timeout. The DS1670 also provides a 3-channel, 8-bit successive approximation analog-to-digital converter. The converter has an internal 2.55V (typical) reference voltage generated by an on-board band-gap circuit. The ADC is monotonic (no missing codes) and has an internal analog filter to reduce high frequency noise. OPERATION The block diagram in Figure 1 shows the main elements of the DS1670. The following paragraphs describe the function of each pin. DS1670 BLOCK DIAGRAM Figure 1 2 of 16 DS1670 PIN DESCRIPTION PIN NAME 1 VBAT 2 VCCO 3 4 SCLK I/O 5 CS 6 7 8 CEI CEOL CEOH 9 INT 10 GND 11 BHE 12 BLE 13 RST 14, 15, 16 AIN2, AIN1, AIN0 17, 18 X2, X1 19 VCC 20 ST FUNCTION Battery Input for Standard 3V Lithium Cell or Other Energy Source. UL recognized to ensure against reverse charging when used with a lithium battery. Go to www.maximic.com/qa/info/ul/. External SRAM Power Supply Output. This pin is internally connected to VCC when VCC is within nominal limits. However, during power-fail VCCO is internally connected to the VBAT pin. Switchover occurs when VCC drops below the lower of VBAT or 2.7V. Serial Clock Input. Used to synchronize data movement on the serial interface. Data Input/Output. This pin is the bidirectional data pin for the 3-wire interface. Chip Select. Must be asserted high during a read or a write for communication over the 3wire serial interface. CS has an internal 40k pulldown resistor. RAM Chip-Enable In. Must be driven low to enable the external RAM. RAM Chip-Enable Out Low. Active-low chip-enable output for low-order SRAM byte. RAM Chip-Enable Out High. Active-low chip-enable output for high-order SRAM byte. Interrupt Output. This pin is an active-high output that can be used as an interrupt input to a microprocessor. The INT output remains high as long as the status bit causing the interrupt is present and the corresponding interrupt-enable bit is set. The INT pin operates when the DS1670 is powered by VCC or VBAT. Ground. DC power is provided to the device on this pin. Byte High-Enable Input. This pin when driven low activates the CEOH output if CEI is also driven low. Byte Low-Enable Input. This pin when driven low activates the CEOL output if CEI is also driven low. Active-Low Reset. The RST pin functions as a microprocessor reset signal. This pin is driven low 1) when VCC is outside of nominal limits; 2) when the watchdog timer has timed out; 3) during the power up reset period; and 4) in response to a pushbutton reset. The RST pin also functions as a pushbutton reset input. When the RST pin is driven low, the signal is debounced and timed such that a RST signal of at least 250ms is generated. This pin has an open-drain output with an internal 47k pullup resistor. Analog Inputs. These pins are the three analog inputs for the 3-channel ADC. Connections for Standard 32.768kHz Quartz Crystal. For greatest accuracy, the DS1670 must be used with a crystal that has a specified load capacitance of 6pF. There is no need for external capacitors or resistors. Note: X1 and X2 are very high-impedance nodes. It is recommended that they and the crystal be guard-ringed with ground and that high frequency signals be kept away from the crystal area. For more information on crystal selection and crystal layout considerations, refer to Application Note 58: Crystal Considerations with Dallas Real Time Clocks. The DS1670 does not function without a crystal. +3.3V Input DC Power. When 3.3V is applied within nominal limits, the device is fully accessible and data can be written and read. When VCC drops below 2.88V (typical) access to the device is prohibited. When VCC drops below the lower of VBAT and 2.7V (typical), the device is switched over to the backup power supply. Active-Low Strobe Input. The strobe input pin is used with the watchdog timer. If the ST pin is not driven low within the watchdog time period, the RST pin is driven low. 3 of 16 DS1670 POWER-UP/POWER-DOWN CONSIDERATIONS The DS1670 was designed to operate with a power supply of 3.3V. When 3.3V are applied within nominal limits, the device becomes fully accessible after tRPU (250ms typical). Before tRPU elapses, all inputs are disabled. When VCC drops below 2.88V (typical), the RST pin is driven low. When VCC drops below the lower of 2.7V (typical) or the battery voltage, the device is switched over to the backup power supply. During power-up, when VCC returns to an in-tolerance condition, the RST pin is kept in the active state for 250ms (typical) to allow the power supply and microprocessor to stabilize. ADDRESS/COMMAND BYTE The command byte for the DS1670 is shown in Figure 2. Each data transfer is initiated by a command byte. Bits 0 through 6 specify the addresses of the registers to be accessed. The MSB (bit 7) is the Read/Write bit. This bit specifies whether the accessed byte will be read or written. A read operation is selected if bit 7 is a 0 and a write operation is selected if bit 7 is a 1. The address map for the DS1670 is shown in Figure 3. ADDRESS/COMMAND BYTE Figure 2 7 RD WR 6 5 4 3 2 1 0 A6 A5 A4 A3 A2 A1 A0 DS1670 ADDRESS MAP Figure 3 BIT 7 00 01 0 0 02 0 03 04 05 0 0 0 06 07 08 M M 09 M 0A 0B 0C 0D 0E 0F 7F M BIT 0 10 SECONDS SECONDS 10 MINUTES MINUTES 12 10 HR 10 HR HOURS 24 A/P 0 0 0 0 DAY 0 10 DATE DATE 0 0 10 MONTH MO. 10 YEAR YEAR 10 SEC ALARM SECONDS ALARM 10 MIN ALARM MINUTES ALARM 12 10 HR 10 HR HOUR ALARM 24 A/P 0 0 0 DAY ALARM CONTROL REGISTER STATUS REGISTER WATCHDOG REGISTER ADC REGISTER RESERVED 4 of 16 DS1670 CLOCK, CALENDAR, AND ALARM The time and calendar information is accessed by reading/writing the appropriate register bytes. Note that some bits are set to 0. These bits will always read 0 regardless of how they are written. Also note that registers 0 Fh to 7 Fh are reserved. These registers will always read 0 regardless of how they are written. The contents of the time, calendar, and alarm registers are in the Binary-Coded Decimal (BCD) format. The DS1670 can run in either 12-hour or 24-hour mode. Bit 6 of the hours register is defined as the 12-hour or 24-hour mode select bit. When high, the 12-hour mode is selected. In the 12-hour mode, bit 5 is the AM/PM bit with logic 1 being PM. In the 24-hour mode, bit 5 is the second 10-hour bit (20-23 hours). The DS1670 also contains a time of day alarm. The alarm registers are located in registers 07h to 0 Ah. Bit 7 of each of the alarm registers are mask bits (see Table 1). When all of the mask bits are logic 0, an alarm will occur once per week when the values stored in timekeeping registers 00h to 03h match the values stored in the time of day alarm registers. An alarm will be generated every day when mask bit of the day alarm register is set to 1. An alarm will be generated every hour when the day and hour alarm mask bits are set to 1. Similarly, an alarm will be generated every minute when the day, hour, and minute alarm mask bits are set to 1. When day, hour, minute, and seconds alarm mask bits are set to 1, an alarm will occur every second. TIME OF DAY ALARM BITS Table 1 ALARM REGISTER MASK BITS (BIT 7) SECONDS MINUTES HOURS DAYS 1 1 1 1 0 1 1 1 0 0 1 1 0 0 0 1 0 0 0 0 DESCRIPTION Alarm once per second. Alarm when seconds match. Alarm when minutes and seconds match Alarm when hours, minutes and seconds match. Alarm when day, hours, minutes and seconds. SPECIAL PURPOSE REGISTERS The DS1670 has two additional registers (control register and status register) that control the real-time clock and interrupts. CONTROL REGISTER BIT 7 EOSC BIT 6 BIT 5 WP AIS1 BIT 4 AIS0 BIT 3 0 BIT 2 0 BIT 1 0 BIT 0 AIE EOSC (Enable Oscillator). This bit when set to logic 0 will start the oscillator. When this bit is set to a logic 1, the oscillator is stopped and the DS1670 is placed into a low-power standby mode with a current drain of less than 200nA when in battery-backup mode. When the DS1670 is powered by VCC, the oscillator is always on regardless of the status of the EOSC bit; however, the real-time clock is incremented only when EOSC is a logic 0. WP (Write Protect). Before any write operation to the real time clock or any other registers, this bit must be logic 0. When high, the write-protect bit prevents a write operation to any register. 5 of 16 DS1670 AIS0-AIS1 (Analog Input Select). These 2 bits are used to determine the analog input for the analog-todigital conversion. Table 2 lists the specific analog input that is selected by these two bits. AIE (Alarm Interrupt Enable). When set to a logic 1, this bit permits the Interrupt Request Flag (IRQF) bit in the status register to assert INT. When the AIE bit is set to logic 0, the IRQF bit does not initiate the INT signal. ANALOG INPUT SELECTION Table 2 AIS1 0 0 1 1 AIS0 0 1 0 1 ANALOG INPUT NONE AIN0 AIN1 AIN2 STATUS REGISTER BIT 7 CU BIT 6 LOBAT BIT 5 0 BIT 4 0 BIT 3 0 BIT 2 0 BIT 1 0 BIT 0 IRQF CU (Conversion Update In Progress). When this bit is a 1, an update to the ADC Register (register 0Eh) will occur within 488ms. When this bit is a 0, an update to the ADC Register will not occur for at least 244ms. LOBAT (Low Battery Flag). This bit reflects the status of the backup power source connected to the V BAT pin. When VBAT is greater than 2.5V, LOBAT is set to a logic 0. When VBAT is less than 2.3 volts, LOBAT is set to a logic 1. IRQF (Interrupt Request Flag). A logic 1 in the Interrupt Request Flag bit indicates that the current time has matched the time of day Alarm registers. If the AIE bit is also a logic 1, the INT pin will go high. IRQF is cleared by reading or writing to any of the alarm registers. POWER-UP DEFAULT STATES These bits are set to a one upon initial power-up: EOSC , TD1 and TD0. These bits are cleared upon initial power-up: WP, AIS1, and AIS0. NONVOLATILE SRAM CONTROLLER The DS1670 provides automatic backup and write protection for external SRAM. This function is provided by gating the chip enable signals and by providing a constant power supply through the VCCO pin. The DS1670 was specifically designed with the Intel 80186 and 386EX microprocessors in mind. As such, the DS1670 can provide access to the external SRAM in either byte-wide or word-wide format. This capability is provided by the chip enable scheme. Three input signals and two output signals are used for enabling the external SRAM(s) (see Figure 4). CEI (chip enable in), BHE (byte high enable), and BLE (byte low enable) are used for enabling either one or two external SRAMs through the CEOL (chip enable low) and the CEOH (chip enable high) outputs. Table 3 illustrates the function of these pins. 6 of 16 DS1670 The DS1670 nonvolatilizes the external SRAM(s) by write protecting the SRAM(s) and by providing a back-up power supply in the absence of VCC. When VCC falls below 2.88V (typical), access to the external SRAM(s) are prohibited by forcing CEOL and CEOH high regardless of the level of CEI , BLE , and BHE . Also at this point, the SRAM power supply (VCCO) is switched from VCC to VBAT. Upon powerup, access is prohibited until the end of tRPU. EXTERNAL SRAM CHIP ENABLE Table 3 CEI BHE BLE CEOL CEOH 0 0 0 0 1 0 0 1 1 X 0 1 0 1 X 0 1 0 1 1 0 0 1 1 1 FUNCTION Word Transfer Byte Transfer in upper half of data bus (D15-D8) Byte Transfer in lower half of data bus (D7-D0) External SRAMs disabled External SRAMs disabled EXTERNAL SRAM INTERFACE (WORD-WIDE) TO THE DS1670 Figure 4 MICROPROCESSOR MONITOR The DS1670 monitors three vital conditions for a microprocessor: power supply, software execution, and external override. First, a precision temperature-compensated reference and comparator circuit monitors the status of VCC. When an out-of-tolerance condition occurs, an internal power-fail signal is generated which forces the RST pin to the active state, thus warning a processor-based system of impending power failure. The power-fail trip point is 2.88V (typical). When VCC returns to an in-tolerance condition upon power-up, the reset signal is kept in the active state for 250ms (typical) to allow the power supply and microprocessor to stabilize. Note, however, that if the EOSC bit is set to a logic 1 (to disable the oscillator during battery-backup mode), the reset signal will be kept in an active state for 250ms plus the startup time of the oscillator. The second monitoring function is pushbutton reset control. The DS1670 provides for a pushbutton switch to be connected to the RST output pin. When the DS1670 is not in a reset cycle, it continuously monitors the RST signal for a low-going edge. If an edge is detected, the DS1670 will debounce the 7 of 16 DS1670 switch by pulling the RST line low. After the internal 250ms timer has expired, the DS1670 will continue to monitor the RST line. If the line is still low, the DS1670 will continue to monitor the line looking for a rising edge. Upon detecting release, the DS1670 will force the RST line low and hold it low for 250ms. The third microprocessor monitoring function provided by the DS1670 is a watchdog timer. The watchdog timer function forces RST to the active state when the ST input is not stimulated within the predetermined time period. The time period is set by the Time Delay (TD) bits in the Watchdog Register. The time delay can be set to 250ms, 500ms, or 1000ms (see Figure 5). If TD0 and TD1 are both set to 0, the watchdog timer is disabled. When enabled, the watchdog timer starts timing out from the set time period as soon as RST is inactive. The default setting is for the watchdog timer to be enabled with 1000ms time delay. If a high-to-low transition occurs on the ST input pin prior to timeout, the watchdog timer is reset and begins to time-out again. If the watchdog timer is allowed to timeout, then the RST signal is driven to the active state for 250ms (typical). The ST input can be derived from microprocessor address signals, data signals, and/or control signals. To guarantee that the watchdog timer does not timeout, a high-to-low transition must occur at or less than the minimum period. WATCHDOG TIMEOUT CONTROL Figure 5 WATCHDOG REGISTER BIT 7 BIT 6 BIT 5 0 0 0 BIT 4 0 BIT 3 0 BIT 2 0 BIT 1 TD1 BIT 0 TD0 WATCHDOG TIMEOUT TD1 TD0 WATCHDOG TIMEOUT 0 0 Watchdog disabled 0 1 250ms 1 0 500ms 1 1 1000ms ANALOG-TO-DIGITAL CONVERTER The DS1670 provides a 3-channel, 8-bit analog-to-digital converter. The ADC reference voltage (2.55V typical) is derived from an on-chip band-gap circuit. Three multiplexed analog inputs are provided through the AIN0, AIN1, and AIN2 pins. The ADC is monotonic (no missing codes) and uses a successive approximation technique to convert the analog signal into a digital code. An A/D conversion is the process of assigning a digital code to an analog input voltage. This code represents the input value as a fraction of the full-scale voltage (FSV) range. Thus, the FSV range is then divided by the ADC into 256 codes (8 bits). The FSV range is bounded by an upper limit equal to the reference voltage and the lower limit, which is ground. The DS1670 has a FSV of 2.55V (typical) that provides a resolution of 10mV. An input voltage equal to the reference voltage converts to FFh while an input voltage equal to ground converts to 00h. The relative linearity of the ADC is ±0.5 LSB. The ADC selects from one of three different analog inputs (AIN0–AIN2). The input that is selected is determined by the Analog Input Select (AIS) bits in the Control Register. Table 2 lists the specific analog 8 of 16 DS1670 input that is selected by these 2 bits. Note also that the converter can be turned off by these bits to reduce power. When the ADC is turned on by setting AIS0 and AIS1 to any value other than 0,0 the analog input voltage is converted and written to the ADC Register within 488ms. An internal analog filter at the input reduces high frequency noise. Subsequent updates occur approximately every 10ms. If AIS0 and/or AIS1 are changed, updates will occur at the next 10ms conversion time. The Conversion Update In Progress (CU) bit in the Status Register indicates when the ADC Register can be read. When this bit is a 1, an update to the ADC Register will occur within 488ms maximum. However, when this bit is 0 an update will not occur for at least 244ms. The CU bit should be polled before reading the ADC Register to ensure that the contents are stable during a read cycle. Once a read cycle to the ADC Register has been started, the DS1670 will not update that register until the read cycle has been completed. It should also be mentioned that taking CS low will abort the read cycle and will allow the ADC Register to be updated. Figure 6 illustrates the timing of the CU bit relative to an instruction to begin conversion and the completion of that conversion. CU BIT TIMING Figure 6 3-WIRE SERIAL INTERFACE Communication with the DS1670 is accomplished through a simple 3-wire interface consisting of the Chip Select (CS), Serial Clock (SCLK) and Input/Output (I/O) pins. All data transfers are initiated by driving the CS input high. The CS input serves two functions. First, CS turns on the control logic, which allows access to the shift register for the address/command sequence. Second, the CS signal provides a method of terminating either single byte or multiple byte (burst) data transfer. A clock cycle is a sequence of a rising edge followed by a falling edge. For data input, data must be valid during the rising edge of the clock and data bits are output on the falling edge of the clock. If the CS input goes low, all data transfer terminates and the I/O pin goes to a high-impedance state. 9 of 16 DS1670 Address and data bytes are always shifted LSB first into the I/O pin. Any transaction requires the address/command byte to specify a read or write to a specific register followed by one or more bytes of data. The address byte is always the first byte entered after CS is driven high. The most significant bit ( RD /WR) of this byte determines if a read or write will take place. If this bit is 0, one or more read cycles will occur. If this bit is 1, one or more write cycles will occur. Data transfers can occur 1 byte at a time or in multiple-byte burst mode. After CS is driven high an address is written to the DS1670. After the address, one or more data bytes can be read or written. For a single-byte transfer 1 byte is read or written and then CS is driven low. For a multiple-byte transfer, multiple bytes can be read or written to the DS1670 after the address has been written. Each read or write cycle causes the register address to automatically increment. Incrementing continues until the device is disabled. After accessing register 0Eh, the address wraps to 00h. Data transfer for single-byte transfer and multiple-byte burst transfer is illustrated in Figures 7 and 8. SINGLE-BYTE DATA TRANSFER Figure 7 CS SCLK A0 A1 A2 A3 A4 A5 A6 RD WR D0 D1 D2 D3 D4 D5 MULTIPLE-BYTE BURST TRANSFER Figure 8 CS SCLK I/O ADDRESS BYTE DATA BYTE 0 DATA BYTE 1 10 of 16 DATA BYTE N D6 D7 DS1670 ABSOLUTE MAXIMUM RATINGS Voltage on Any Pin Relative to Ground………………………………………………………-0.3V to +6V Operating Temperature………………………………………………………………………..0°C to +70°C Storage Temperature………………………………………………………………………-55°C to +125°C Soldering Temperature………………………………………….See IPC/JEDEC J-STD-020 Specification This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect device reliability. RECOMMENDED DC OPERATING CONDITIONS PARAMETER (TA = 0C to +70C) SYMBOL MIN TYP MAX UNITS NOTES Power-Supply Voltage VCC 2.97 3.3 3.63 V 1 Input Logic 1 VIH 2.0 VCC + 0.3 V 1 Input Logic 0 VIL -0.3 +0.8 V 1 VBAT 2.5 3.7 V 1 Battery Voltage 11 of 16 DS1670 DC ELECTRICAL CHARACTERISTICS PARAMETER (TA = 0C to +70C) SYMBOL MIN Input Leakage ILI -1 CS Leakage ILO Logic 1 Output (Iout=-0.4 mA) VOH Logic 0 Output (Iout=1.5 mA) VOL Active Supply Current (CS = VCC-0.2) ICCA A/D Converter Current MAX UNITS +1 A 150 A 7 V 2 0.4 V 3 1.0 mA 4 IADC 200 A 5 Standby Current (CS=VIL) ICCS 100 A 6 Battery Current (Oscillator On) IBAT1 500 nA Battery Current (Oscillator Off) IBAT2 200 nA Internal RST Pull-up Resistor TYP 2.4 0.75 300 RP 35 47 60 k VCC Trip Point VCCTP 2.80 2.88 2.97 V VCC Switchover VCCSW 2.62 2.70 2.78 V A/D Reference Voltage VADC 2.47 2.55 2.63 V Pushbutton Detect PBDV 0.8 2.0 V Pushbutton Release PBRD 0.8 V Output Voltage VCCO VCCO Output Current (Source = VCC) ICCO1 VCCO Output Current (Source = VBAT) ICCO2 0.3 VCC-0.3 Input Capacitance 12 V 11 100 mA 13 150 A 14 CAPACITANCE PARAMETER NOTES (TA = +25C) SYMBOL MIN TYP MAX UNITS CI 10 pF I/O Capacitance CI/O 15 pF Crystal Capacitance CX 6 pF 12 of 16 NOTES DS1670 AC ELECTRICAL CHARACTERISTICS PARAMETER (VCC = 3.3V ±10%, TA = 0C to +70C.) SYMBOL MIN TYP MAX UNITS NOTES Data to Clock Setup tDC 100 ns 8 CLK to Data Hold tCDH 140 ns 8 CLK to Data Delay tCDD ns 8, 9, 10 CLK to Low Time tCL 500 ns 8 CLK to High Time tCH 500 ns 8 CLK Frequency tCLK 1.0 MHz 8 CLK Rise and Fall tR, tF 1000 ns CS to CLK Setup tCC 2 s 8 CLK to CS Hold tCCH 120 ns 8 CS Inactive Time tCWH 2 s 8 CS to I/O High-Z tCDZ 140 ns 8 SCLK to I/O High-Z tCCZ 140 ns 8 400 VCC Slew Rate (2.85V to 2.3V) tF 300 s VCC Slew Rate (2.3V to 2.85V) tR 0 ns VCC Detect to RST (VCC Falling) tRPD Reset Active Time tRST 250 ms 15 Pushbutton Debounce PBDB 250 ms 15 VCC Detect to RST (VCC Rising) tRPU 250 ms 15, 16 ST Pulse Width tST Chip Enable Propagation Delay to External SRAM tCED Nominal Voltage to VCC Switchover Fall Time tFB 100 20 ns 8 200 13 of 16 ns 15 ns s DS1670 TIMING DIAGRAM: READ DATA Figure 9 TIMING DIAGERAM: WRITE DATA Figure 10 14 of 16 DS1670 PUSHBUTTON RESET Figure 11 RST VOH PBDV PBRD PBDB tRST POWER-UP Figure 12 VCCTP VCC tRPU VOH RST POWER-DOWN Figure 13 VCC VCCTPMAX VCCTP VCCSWMIN RST VOL tRPD tFB 15 of 16 DS1670 NOTES: 1. All voltages are referenced to ground. 2. Logic 1 voltages are specified at VCC = 3.3V, VOH = VCC for capacitive loads. Excludes 3. Logic 0 voltages are specified at VCC = 3.3V, VOL = GND for capacitive loads. 4. ICCA is specified with outputs open, CS set to a logic 1, SCLK = 500kHz, oscillator enabled, and DAC enabled. 5. IADC is specified with CS, VCCO open and I/O, SCLK at logic 0. ADC is enabled. 6. ICCS is specified with CS, VCCO open and I/O, SCLK at logic 0. ADC is disabled. 7. CS has a 40k pulldown resistor to ground. 8. Measured at VIH = 2.0V or VIL = 0.8V and 10ns maximum rise and fall time. 9. Measured at VOH = 2.4V or VOL = 0.4V. RST pin. 10. Load capacitance = 50 pF. 11. ICCO = 100 mA, VCC > VCCTP. 12. VCCO switchover from VCC to VBAT occurs when VCC drops below the lower of VCCSW and VBAT. 13. Current from VCC input pin to VCCO output pin. 14. Current from VBAT input pin to VCCO output pin. 15. Time base is generated by very accurate crystal oscillator. Accuracy of this time period is based on the crystal that is used. A typical crystal with a specified load capacitance of 6pF will provide an accuracy within ±100ppm over the 0°C to +70°C temperature range. 16. If the EOSC bit in the Control Register is set to a logic 1, tRPU is equal to 250ms plus the startup time of the crystal oscillator. PACKAGE INFORMATION For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE PACKAGE CODE DOCUMENT NO. 20 TSSOP U20+1 21-0066 20 SO W20+1 21-0042 16 of 16 Maxim/Dallas Semiconductor cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim/Dallas Semiconductor product. No circuit patent licenses are implied. Maxim/Dallas Semiconductor reserves the right to change the circuitry and specifications without notice at any time. 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