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DS1632
PC Power-Fail and Reset Controller
www.maxim-ic.com
FEATURES
* * * * * * * * * * * * Power-fail detector for personal computers and workstations Connects directly to popular personal computer chip sets On chip 32.768 kHz oscillator for real time clock Provides battery backup power to clock chip Pushbutton reset input Accurate 5% or 10% +5-volt power supply monitoring Complementary outputs for reset, power-fail, and low battery Provides for reset pulse width of either 95 ms or 190 ms Eliminates the need for discrete components Low-power CMOS circuitry 16-pin DIP or SOIC surface mount package 0C to 70C operation
PIN ASSIGNMENT
PBRST X1 X2 VBAT LB LB TOL GND 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 VCC PF PF VCCO RST RST RD OSCOUT
16-Pin DIP (300-mil) See Mech. Drawings Section PBRST X1 X2 VBAT LB LB TOL GND 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 VCC PF PF VCCO RST RST RD OSCOUT
16-Pin SOIC (300-mil) See Mech. Drawings Section
PIN DESCRIPTION
PBRST
DESCRIPTION
X1, X2 VBAT LB, LB RST, RST RD TOL GND OSCOUT VCCO PF, PF VCC
- Pushbutton Reset Input - Crystal Inputs - Battery Input - Low Battery Outputs - Reset Outputs - Reset Duration - Selects 5% Or 10% Detection - Ground - Oscillator Out - Switched Power Out - Power-Fail Outputs - +5-Volt Power In
The DS1632 PC Power-Fail and Reset Controller is designed to do various functions involving battery backup and other functions typically accomplished with discrete components. The DS1632 provides a 32.768 kHz battery-backed crystal oscillator and switched VCC/VBAT power via VCCO for the real time clock function located in accompanying chip sets. In addition, the DS1632 provides for reset on both 1 of 6 060303
DS1632
power-up and via pushbutton input, power-fail status signals for the processor, and low battery warning signals. The DS1632 is capable of detecting power failure at both the 5% and 10% power supply tolerances, and the reset pulse width can be set for either 95 ms or 190 ms. The device is designed to connect directly to popular laptop and notebook chip sets which eliminates the need for discrete components and reduces cost.
BLOCK DIAGRAM Figure 1
OPERATION - CRYSTAL OSCILLATOR SECTION
The DS1632 crystal oscillator is designed to be hooked directly to a 32.768 kHz crystal. By using the Daiwa Part No. DT26S, Seiko Part No. DS-VT-200 or equivalent, the oscillator will be accurate enough to run a real time clock to within 2 minutes per month. If another crystal is to be selected, it should have a specified load capacitance (CL) of 6 pF. The crystal oscillator will run as long as either VCC or VBAT is present, providing that VBAT is greater than 2.3V. The oscillator output provides a rail to rail swing with regards to VCC or VBAT, whichever is greater. The crystal oscillator is also used internally as a time base. 2 of 6
DS1632
OPERATION - POWER-FAIL, BATTERY BACKUP
The DS1632 provides a switch to direct power from the battery (VBAT) or the incoming supply (VCC), depending on which is greater. This switch has a voltage drop of less than 0.3 volts. The VCC input is constantly monitored by a precision comparator for an out-of-tolerance condition. When such a condition occurs, the power-fail signals are driven to their active state immediately. The reset signals are also driven active, but this action is delayed by a time determined by the level of the input on the reset duration pin (RD). If RD is tied to ground then reset signals will become active after 9 ms. If RD is tied to VCC, then reset signals will become active after 18 ms. Once active, both the reset signals and the power-fail signals will remain active as long as a (VCC) out-of-tolerance condition persists. If an out-of-tolerance condition is not long enough to activate the reset signals, then only the power-fail signals would be affected. When power returns to within nominal limits the power-fail signals will return immediately to the inactive state. However, the reset signals remain in the active state for a time which is dependent on the state of the RD pin. If RD is tied to ground, the reset signals will remain active for 95 ms. If RD is tied to VCC, then the reset signals will remain active for 190 ms after power is within nominal limits. The delay action on the reset signals allows time for the power supply and microprocessor clock oscillators to stabilize. The tolerance pin (TOL) selects the point at which power-fail detection occurs. With the tolerance pin grounded, power-fail detection occurs in the range of 4.75V to 4.5V. If the tolerance pin is connected to VCC, then power-fail detection occurs in the range of 4.5V to 4.25V. During most power supply conditions the VCC input will supply power to all functions within the chip and also to the VCCO pin. The battery pin (VBAT) only supplies power when VCC is less than VBAT. When VCC is below the level of VBAT only the VCCO and the OSC OUT pin remain powered by VBAT. All other outputs will be driven to ground when in a logic low state and will be driven to VCC when in a logic high state. This is done to preserve battery capacity by avoiding battery drain resulting from loads on these outputs. The output ground level will be maintained for all levels of VCC, even VCC = GND. However, the output VCC level will be maintained only for VCC > 2.0V. Internal battery power consumption is less than 2 mA while VBAT is supplying power. The external load on OSC OUT and VCCO must be added to internal consumption to determine the total load on the battery.
OPERATION - PUSHBUTTON RESET
The DS1632 provides an input pin for direct connection to a pushbutton. The pushbutton reset input PBRST requires an active low level input. While TTL levels are sufficient to properly activate this input, it has been primarily designed for contact closure. Internally, this input is debounced and timed such that RST and RST signals of 95ms or 190 ms minimum are generated. If RD is tied to ground, then a reset pulse of 95 ms is generated. If RD is tied to VCC then a reset pulse of 190 ms is generated. The delay time is started as the pushbutton reset input is released from low level.
OPERATION - LOW BATTERY WARNING
The DS1632 provides outputs which warn of a low battery condition. Whenever VCC is within nominal limits, the VBAT input is continuously monitored. If the VBAT input is out of tolerance, the low battery outputs are driven to their active states, and will remain in the active state as long as VCC is within nominal limits or until the battery input is restored to an in limit status. On power-up, if the VBAT input is out of tolerance, the low battery outputs are not guaranteed active until power-fail is deactivated, but guaranteed active prior to reset inactive. When VCC is below the VCC fail trip point both LB and LB will be driven to ground. For application information, please reference Application Note 64, published separately.
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DS1632
ABSOLUTE MAXIMUM RATINGS*
Voltage on VCC Pin Relative to Ground Voltage on I/O Relative to Ground Operating Temperature Storage Temperature Soldering Temperature * -0.5V to +7.0V -0.5V to VCC + 0.5V 0C to 70C -55C to +125C 260C for 10 seconds
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 reliability.
RECOMMENDED DC OPERATING CONDITIONS
PARAMETER Supply Voltage
PBRST PBRST
(0C to 70C)
MAX 5.5 VCC+0.3 +0.8 3.0 3.5 UNITS V V V V NOTES 1 1, 3 1, 3 1 5.0
SYMBOL VCC VIH VIL VBAT
MIN 4.5 2.0 -0.3 2.3
TYP
Input High Level Input Low Level
Battery Supply Voltage
DC ELECTRICAL CHARACTERISTICS
PARAMETER Output Current @ 2.4V Output Current @ 0.4V Output Voltage @ -500 A Low Level @ RST Operating Current VCC Trip Point (TOL=GND) VCC Trip Point (TOL=VCC) Battery Fail Trip Point Supply Voltage Output Supply Current Output SYMBOL IOH IOL VOH VOL ICC VCCTP VCCTP VBATTP VCCO ICCO1 4.50 4.25 2.30 VCC-0.3 MIN 1 4
(0C to 70C; VCC=4.5 to 5.5V)
TYP MAX UNITS mA mA V 0.4 0.5 4.62 4.37 2.45 2.0 4.75 4.50 2.55 100 V mA V V V V mA 4 NOTES 5, 7 7 1, 6 1 2 1 1 1
VCC-0.5V VCC-0.1V
DC ELECTRICAL CHARACTERISTICS
PARAMETER Battery Current Battery Backup Current SYMBOL IBAT ICCO2 MIN TYP MAX 2 500
(0C; VCC=UNITS A A NOTES 4
CAPACITANCE
PARAMETER Input Capacitance Output Capacitance SYMBOL CIN COUT MIN TYP MAX 5 7 UNITS pF pF
(tA=25C)
NOTES
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AC ELECTRICAL CHARACTERISTICS
PARAMETER
PBRST
(0C to 70C; VCC=5V 10%)
TYP MAX 105 210 105 210 11 22 UNITS ms ms ms ms ms ms ms s s s NOTES RD=GND RD=VCC RD=GND RD=VCC RD=GND RD=VCC
= VIL
SYMBOL tPB tRST tRST tRPU tRPU tRPD tRPD tF tFB tR
MIN tRPD 95 190 95 190 9 18 300 10 10
Reset Pulse Width Reset Pulse Width Reset Active on Power-Up Reset Active on Power-Up Reset Active on Power-Down Reset Active on Power-Down VCC Slew Rate Power-Down VCC Slew Rate Power-Down VCC Slew Rate Power-Up
TIMING DIAGRAM: PUSHBUTTON RESET
TIMING DIAGRAM: POWER-DOWN
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TIMING DIAGRAM: POWER-UP
NOTES:
1. All voltages are referenced to ground. 2. Measured with outputs open. 3. The PBRST input has an internal pull-up of 10kW to VCC. 4. Supply current output is specified with 0.3V drop from VBAT or VCC. 5. RST , PF , and LB are open-drain outputs. 6. RST and PF remain within 0.5 volts of VCC on power down until VCC drops below 2.0V. 7. Sink and source currents apply to all outputs except OSC OUT which has a drive capability of sourcing 500 mA at VOH = VCCO - 0.5V and sinking 1 mA at VOL = 0.5 V.
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