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ICL7673
Data Sheet July 22, 2005 FN3183.4
Automatic Battery Back-Up Switch
The Intersil ICL7673 is a monolithic CMOS battery backup circuit that offers unique performance advantages over conventional means of switching to a backup supply. The ICL7673 is intended as a low-cost solution for the switching of systems between two power supplies; main and battery backup. The main application is keep-alive-battery power switching for use in volatile CMOS RAM memory systems and real time clocks. In many applications this circuit will represent a low insertion voltage loss between the supplies and load. This circuit features low current consumption, wide operating voltage range, and exceptionally low leakage between inputs. Logic outputs are provided that can be used to indicate which supply is connected and can also be used to increase the power switching capability of the circuit by driving external PNP transistors.
Features
* Automatically Connects Output to the Greater of Either Input Supply Voltage * If Main Power to External Equipment is Lost, Circuit Will Automatically Connect Battery Backup * Reconnects Main Power When Restored * Logic Indicator Signaling Status of Main Power * Low Impedance Connection Switches * Low Internal Power Consumption * Wide Supply Range: . . . . . . . . . . . . . . . . . . . 2.5V to 15V * Low Leakage Between Inputs * External Transistors May Be Added if Very Large Currents Need to Be Switched * Pb-Free Plus Anneal Available (RoHS Compliant)
Ordering Information
PART NUMBER ICL7673CPA ICL7673CPAZ (See Note) ICL7673CBA ICL7673CBA-T ICL7673CBAZA (See Note) ICL7673CBAZA-T (See Note) TEMP. RANGE (C) 0 to 70 0 to 70 0 to 70 PACKAGE 8 Ld PDIP 8 Ld PDIP* (Pb-free) 8 Ld SOIC (N) PKG. DWG. # E8.3 E8.3 M8.15 M8.15 M8.15 M8.15
Applications
* On Board Battery Backup for Real-Time Clocks, Timers, or Volatile RAMs * Over/Under Voltage Detector * Peak Voltage Detector * Other Uses: - Portable Instruments, Portable Telephones, Line Operated Equipment
8 Ld SOIC (N) Tape and Reel 0 to 70 0 to 70 8 Ld SOIC (N) (Pb-free) 8 Ld SOIC (N) (Pb-free)
Functional Block Diagram
VP P1 VO
*Pb-free PDIPs can be used for through hole wave solder processing only. They are not intended for use in Reflow solder processing applications. NOTE: Intersil Pb-free plus anneal products employ special Pb-free material sets; molding compounds/die attach materials and 100% matte tin plate termination finish, which are RoHS compliant and compatible with both SnPb and Pb-free soldering operations. Intersil Pb-free products are MSL classified at Pb-free peak reflow temperatures that meet or exceed the Pb-free requirements of IPC/JEDEC J STD-020.
VS
P2 SBAR
+ PBAR
Pinouts
ICL7673 (SOIC, PDIP) TOP VIEW
VO VS SBAR GDN 1 2 3 4 8 7 6 5 VP NC PBAR NC
GND
VP > VS , P1 SWITCH ON AND PBAR SWITCH ON VS > VP , P2 SWITCH ON AND SBAR SWITCH ON
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright (c) Intersil Americas Inc. 1999-2005. All Rights Reserved All other trademarks mentioned are the property of their respective owners.
ICL7673
Absolute Maximum Ratings
Input Supply (VP or VS) Voltage . . . . . . . . . . . . GND - 0.3V to +18V Output Voltages PBAR and SBAR . . . . . . . . . . . GND - 0.3V to +18V Peak Current Input VP (at VP = 5V) (Note 1) . . . . . . . . . . . . . . . . . . . . . . . 38mA Input VS (at VS = 3V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30mA PBAR or SBAR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150mA
Thermal Information
Thermal Resistance (Typical, Note 2) JA (C/W) JC (C/W) PDIP Package* . . . . . . . . . . . . . . . . . . 150 N/A Plastic SOIC Package . . . . . . . . . . . . . 180 N/A Maximum Storage Temperature. . . . . . . . . . . . . . . . . -65C to 150C Maximum Lead Temperature (Soldering, 10sec). . . . . . . . . . . 300C (SOIC - Lead Tips Only) *Pb-free PDIPs can be used for through hole wave solder processing only. They are not intended for use in Reflow solder processing applications.
Operating Conditions
Temperature Range: ICL7673C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0C to 70C
CAUTION: Stresses above those listed in "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
NOTES: 1. Derate above 25C by 0.38mA/C. 2. JA is measured with the component mounted on an evaluation PC board in free air.
Electrical Specifications
PARAMETER Input Voltage
TA = 25C Unless Otherwise Specified SYMBOL VP VS TEST CONDITIONS VS = 0V, ILOAD = 0mA VP = 0V, ILOAD = 0mA VP = 0V, VS = 3V, ILOAD = 0mA VP = 5V, VS = 3V, ILOAD = 15mA At TA = +85C VP = 9V, VS = 3V, ILOAD = 15mA VP = 12V, VS = 3V, ILOAD = 15mA MIN 2.5 2.5 TYP 1.5 8 16 6 5 0.5 40 60 26 16 0.7 0.01 35 0.01 120 85 120 50 40 150 210 85 50 MAX 15 15 5 15 100 20 50 400 400 UNITS V V A %/C %/C nA nA nA nA mV mV mV mV mV mV mV mV
Quiescent Supply Current Switch Resistance P1 (Note 1)
I+ rDS(ON)P1
Temperature Coefficient of Switch Resistance P1 Switch Resistance P2 (Note 1)
TC(P1) rDS(ON)P2
VP = 5V, VS = 3v, ILOAD = 15mA VP = 0V, VS = 3V, ILOAD = 1mA At TA = +85C VP = 0V, VS = 5V, ILOAD = 1mA VP = 0V, VS = 9V, ILOAD = 1mA
Temperature Coefficient of Switch Resistance P2 Leakage Current (VP to VS)
TC(P2) IL(PS)
VP = 0V, VS = 3V, ILOAD = 1mA VP = 5V, VS = 3V, ILOAD = 10mA At TA = +85C
Leakage Current (VP to VS)
IL(SP)
VP = 0V, VS = 3V, ILOAD = 10mA at TA = +85C
Open Drain Output Saturation Voltages
VOPBAR
VP = 5V, VS = 3V, ISINK = 3.2mA, ILOAD = 0mA At TA = 85C VP = 9V, VS = 3V, ISINK = 3.2mA, ILOAD = 0mA VP = 12V, VS = 3V, ISINK = 3.2mA ILOAD = 0mA
Open Drain Output Saturation Voltages
VOSBAR
VP = 0V, VS = 3V, ISINK = 3.2mA, ILOAD = 0mA at TA = +85C VP = 0V, VS = 5V, ISINK = 3.2mA ILOAD = 0mA VP = 0V, VS = 9V, ISINK = 3.2mA ILOAD = 0mA
2
FN3183.4 July 22, 2005
ICL7673
Electrical Specifications
PARAMETER Output Leakage Currents of PBAR and SBAR TA = 25C Unless Otherwise Specified (Continued) SYMBOL ILPBAR TEST CONDITIONS VP = 0V, VS = 15V, ILOAD = 0mA at TA = +85C ILSBAR VP = 15V, VS = 0V, ILOAD = 0mA at TA = +85C Switchover Uncertainty for Complete Switching of Inputs and Open Drain Outputs NOTE: 3. The Minimum input to output voltage can be determined by multiplying the load current by the switch resistance. V P - VS VS = 3V, ISINK = 3.2mA, ILOAD = 15mA MIN TYP 50 900 50 900 10 MAX 500 500 50 UNITS nA nA nA nA mV
Typical Performance Curves
100 ILOAD = 15mA ON-RESISTANCE P1 () ON-RESISTANCE P2 () 100 ILOAD = 1mA
10
10
1 0 2 4 6 8 10 12 14 16 INPUT VOLTAGE VP (V)
1 0 2 4 6 INPUT VOLTAGE VS 8 10
FIGURE 1. ON-RESISTANCE SWITCH P1 AS A FUNCTION OF INPUT VOLTAGE VP
1
FIGURE 2. ON-RESISTANCE SWITCH P2 AS A FUNCTION OF INPUT VOLTAGE VS
5 OUTPUT SATURATION VOLTAGE (V)
VO = 5V VO = 3V
VO = 9V
0.8 SUPPLY CURRENT (A)
4
VO = 12V 3
0.6
0.4
2
VO = 15V
0.2
-40C 25C 85C 0 2 4 6 8 10 12 14 SUPPLY VOLTAGE (V) 16
1
0
40
80 120 OUTPUT CURRENT (mA)
140
180
FIGURE 3. SUPPLY CURRENT AS A FUNCTION OF SUPPLY VOLTAGE
FIGURE 4. PBAR OR SBAR SATURATION VOLTAGE AS A FUNCTION OF OUTPUT CURRENT
3
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ICL7673
low load currents the output voltage is nearly equal to the greater of the two inputs. The maximum voltage drop across switch P1 or P2 is 0.5V, since above this voltage the bodydrain parasitic diode will become forward biased. Complete switching of the inputs and open-drain outputs typically occurs in 50s.
1mA ILOAD = 10mA VS = 0V 100mA
Input Voltage
85C
10nA
1nA
1000pA
The input operating voltage range for VP or VS is 2.5V to 15V. The input supply voltage (VP or VS) slew rate should be limited to 2V per microsecond to avoid potential harm to the circuit. In line-operated systems, the rate-of-rise (or fall) of the supply is a function of power supply design. For battery applications it may be necessary to use a capacitor between the input and ground pins to limit the rate-of-rise of the supply voltage. A low-impedance capacitor such as a 0.047F disc ceramic can be used to reduce the rate-of-rise.
IS LEAKAGE CURRENT
Status Indicator Outputs
10pA 25C 1pA 0 2 4 5 6 INPUT VP (V) 8 10 12
FIGURE 5. IS LEAKAGE CURRENT VP TO VS AS A FUNCTION OF INPUT VOLTAGE
The N-Channel open drain output transistors can be used to indicate which supply is connected, or can be used to drive external PNP transistors to increase the power switching capability of the circuit. When using external PNP power transistors, the output current is limited by the beta and thermal characteristics of the power transistors. The application section details the use of external PNP transistors.
Detailed Description
As shown in the Functional Diagram, the ICL7673 includes a comparator which senses the input voltages VP and VS. The output of the comparator drives the first inverter and the open-drain N-Channel transistor PBAR . The first inverter drives a large P-Channel switch, P1, a second inverter, and another open-drain N-Channel transistor, SBAR . The second inverter drives another large P-Channel switch P2. The ICL7673, connected to a main and a backup power supply, will connect the supply of greater potential to its output. The circuit provides break-before-make switch action as it switches from main to backup power in the event of a main power supply failure. For proper operation, inputs VP and VS must not be allowed to float, and, the difference in the two supplies must be greater than 50mV. The leakage current through the reverse biased parasitic diode of switch P2 is very low.
Applications
A typical discrete battery backup circuit is illustrated in Figure 6. This approach requires several components, substantial printed circuit board space, and high labor cost. It also consumes a fairly high quiescent current. The ICL7673 battery backup circuit, illustrated in Figure 7, will often replace such discrete designs and offer much better performance, higher reliability, and lower system manufacturing cost. A trickle charge system could be implemented with an additional resistor and diode as shown in Figure 8. A complete low power AC to regulated DC system can be implemented using the ICL7673 and ICL7663S micropower voltage regulator as shown in Figure 9.
+5V PRIMARY DC POWER VO +5V OR +3V STATUS INDICATOR
Output Voltage
The output operating voltage range is 2.5V to 15V. The insertion loss between either input and the output is a function of load current, input voltage, and temperature. This is due to the P-Channels being operated in their triode region, and, the ON-resistance of the switches is a function of output voltage VO . The ON-resistance of the P-Channels have positive temperature coefficients, and therefore as temperature increases the insertion loss also increases. At 4
NiCAD BATTERY STACK
GND
FIGURE 6. DISCRETE BATTERY BACKUP CIRCUIT
FN3183.4 July 22, 2005
ICL7673
Applications for the ICL7673 include volatile semiconductor memory storage systems, real-time clocks, timers, alarm systems, and over/under the voltage detectors. Other systems requiring DC power when the master AC line supply fails can also use the ICL7673.
+5V PRIMARY SUPPLY 8 VP VO 1 VO +5V OR +3V
2 LITHIUM BATTERY GND +
VS
GND
Pbar
6
4
RI STATUS INDICATOR
-
A typical application, as illustrated in Figure 12, would be a microprocessor system requiring a 5V supply. In the event of primary supply failure, the system is powered down, and a 3V battery is employed to maintain clock or volatile memory data. The main and backup supplies are connected to VP and VS, with the circuit output VO supplying power to the clock or volatile memory. The ICL7673 will sense the main supply, when energized, to be of greater potential than VS and connect, via its internal MOS switches, VP to output VO. The backup input, VS will be disconnected internally. In the event of main supply failure, the circuit will sense that the backup supply is now the greater potential, disconnect VP from VO, and connect VS. Figure 11 illustrates the use of external PNP power transistors to increase the power switching capability of the circuit. In this application the output current is limited by the beta and thermal characteristics of the power transistors. If hysteresis is desired for a particular low power application, positive feedback can be applied between the input VP and open drain output SBAR through a resistor as illustrated in Figure 12. For high power applications hysteresis can be applied as shown in Figure 13. The ICL7673 can also be used as a clipping circuit as illustrated in Figure 14. With high impedance loads the circuit output will be nearly equal to the greater of the two input signals.
VP
FIGURE 7. ICL7673 BATTERY BACKUP CIRCUIT
+5V PRIMARY SUPPLY RC
8
VP
VO
1
VO +5V OR +3V
2 RECHARGEABLE BATTERY
GND
VS
+ -
GND 4
FIGURE 8. APPLICATION REQUIRING RECHARGEABLE BATTERY BACKUP
FUSE BRIDGE RECTIFIER 120/240 VAC STEPDOWN TRANSFORMER C1
8
2 R2 R3 +
8
1
VO
ICL7663 REGULATOR 4 6
VS
ICL7673 BATTERY BACK-UP 2 4 GND
R1
D1
-
BATTERY STACK
FIGURE 9. POWER SUPPLY FOR LOW POWER PORTABLE AC TO DC SYSTEMS
+5V MAIN POWER
POWER FAIL DETECTOR
MICROPROCESSOR
VP VS VO ICL7673 BACKUP CIRCUIT
INTERRUPT SIGNAL
+
VOLATILE RAM
-
FIGURE 10. TYPICAL MICROPROCESSOR MEMORY APPLICATION
5
FN3183.4 July 22, 2005
ICL7673
R2
PNP
PNP MAIN SUPPLY VP 8 VS + 3V BACKUP SUPPLY ICL7673 2 GND VO 6 3 1 PSR1 NC R3 (NOTE 4) EXTERNAL EQUIPMENT R4
NOTE 4. > 1MW FIGURE 11. HIGH CURRENT BATTERY BACKUP SYSTEM
RF RS VP 8 ICL7673 VS BATTERY BACKUP GND + 2 3 GND S-
MAIN SUPPLY
VO
GND
FIGURE 12. LOW CURRENT BATTERY BACKUP SYSTEM WITH HYSTERESIS
R2 PNP
PNP RF R1 +V MAIN SUPPLY RS VP 8 1 PVS 2 + MAIN SUPPLY GND BACKUP SUPPLY ICL7673 6 4 3 SNC R3 EXTERNAL EQUIPMENT R4
-
FIGURE 13. HIGH CURRENT BACKUP SYSTEM WITH HYSTERESIS
6
FN3183.4 July 22, 2005
ICL7673
VP VP ICL7673 VS GND VO VS
VO
FIGURE 14. CLIPPLING CIRCUITS
All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems. Intersil Corporation's quality certifications can be viewed at www.intersil.com/design/quality
Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.
For information regarding Intersil Corporation and its products, see www.intersil.com 7
FN3183.4 July 22, 2005

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