ds1836a/b/c/d 3.3v/5v micromanager ds1836a/b/c/d product preview 022698 1/9 features ? 5 volt or 3.3 volt poweron reset ? true 3 volt operation power switch ? switches to battery at 3.8 volts (2.6 volts for 3.3 volt versions) ? excellent for systems designed to operate with dual power supplies ? asserts resets during power transients ? maintains reset for 350 ms after v cc returns to an in tolerance condition ? reduces need for discrete components ? precision temperaturecompensated voltage refer- ence and voltage sensor ? 8pin dip or space saving 8pin soic surface mount available ? cmos reset output for low current operation ? operating temperature of 40 c to +85 c ? perfect for pic microprocessor applications pin assignment 1 2 3 4 v cc v bat nc v out 8 7 6 5 8 7 6 5 1 2 3 4 v cc v bat nc v out rst (*rst) nmi in gnd 8pin dip (300 mil) 8pin soic (150 mil) rst (*rst) nmi in gnd ds1836a/c (*ds1836b/d) pin description v cc power supply input v bat battery supply input nc no connect v out power supply output gnd ground in sense input nmi nonmaskable interrupt rst (*rst) reset output description the ds1836 micromanager performs three vital system functions. first a precision temperature compensated reference and comparator circuit monitors the status of the voltage on v cc and when an outoftolerance condition is detected, an internal power fail signal is generated which forces the reset active. if v cc contin- ues to degrade it switches to the battery supply when v cc drops below 3.8 volts (2.6 volts for 3.3 volt ver- sions). when v cc exceeds 3.9 volts (2.8 volts for 3.3 volt versions); v out will again be supplied from v cc . reset will remain active for 350 ms after v cc returns to an intolerance condition. lastly, the ds1836 supports a sense input that sends a nonmaskable interrupt whenever the sense input drops below 1.25 volts.
ds1836a/b/c/d 022698 2/9 operation power monitor the ds1836 provides the functions of detecting outof tolerance conditions on a 3.3 volt or 5 volt power supply and warning a processor based system of impending power failure. when v cc is detected as outoftoler- ance; the rst will be forced active. when v cc returns to a valid state the rst will remain active for about 350 ms and then return to an inactive state until the next v cc outoftolerance condition. on powerup reset is kept active for approximately 350 ms after the power supply input has reached the selected tolerance. this allows the power supply and system power to stabilize before rst is released. power switch (ds1836a & b) the ds1836 switches the v out output between v cc and v bat . on the initial power up v out draws current from the v bat input until v cc exceeds 3.9 volts. when v cc exceeds 3.9 volts v out switches from v bat to v cc and will not switch back to v bat until v cc drops below 3.8 volts. when v cc is below 3.8 volts, power will be drawn from the supply with the highest voltage either v cc or v bat . power switch (DS1836C & d) the ds1836 switches the v out output between v cc and v bat . on the initial power up v out draws current from the v bat input until v cc exceeds 2.8 volts. when v cc exceeds 2.8 volts v out switches from v bat to v cc and will not switch back to v bat until v cc drops below 2.6 volts. when v cc is below 2.6 volts, power will be drawn from the supply with the highest voltage either v cc or v bat . block diagram figure 1 + v cc tolerance bias t. c . reference 350 ms delay level sense and control v out rst (*rst) v cc v bat in gnd + nmi * ds1836b and ds1836d
ds1836a/b/c/d 022698 3/9 nonmaskable interrupt the ds1836 generates a nonmaskable interrupt (nmi ) for early warning of a power failure. a precision comparator monitors the voltage level at the in pin rela- tive to an onchip reference generated by an internal band gap. the in pin is a high impedance input allowing for a userdefined sense point. an external resistor voltage divider network (figure 3) is used to interface with high voltage signals. this sense point may be derived from a regulated supply or from a higher dc voltage level closer to the main system power input. since the in trip point v tp is 1.25 volts, the proper val- ues for r1 and r2 can be determined by the equation as shown in figure 3. proper operation of the ds1836 requires that the maximum voltage at the in pin be lim- ited to the active supply (v cc or v bat ). therefore, the maximum allowable voltage at the supply being moni- tored (v max ) can also be derived as shown in figure 3. a simple approach to solving the equation is to select a value for r2 high enough to keep power consumption low, and solve for r1. the flexibility of the in input pin allows for detection of power loss at the earliest point in a power supply system, maximizing the amount of time for system shutdown between nmi and rst (or rst ). a pullup resistor is required for proper operation of the nmi opendrain output. a 10k w resistor would be a typ- ical value for the pullup resistor. typical application figure 2 v bat v out nmi in ds1836a 10k w v cc rst gnd system power primary voltage reset system power warning voltage sense point secondary system power primary system power
v in > 1.25v nmi v ol v oh v tp(max) v tp(max) v tp v tp v tp(min) v tp(min) t ipd t ipd ds1836a/b/c/d 022698 4/9 nonmaskable interrupt circuit example figure 3 in nmi v bat ds1836 gnd to m p or sram r1 v sense v sense r1 r2 r2 x1.25 example: v sense = 4.50 volts at the trip point 100k w = r2 therefore: 4.5 r1 100k 100k x1.25 r1 260k v cc v out rst r2 10k w to m p or sram timing diagram: nonmaskable interrupt figure 4
ds1836a/b/c/d 022698 5/9 output valid conditions the ds1836 can maintain valid outputs as long as one input remains above 1.2 volts. however, the rst out- puts on the ds1836a (or c) use a pushpull output structure which can maintain a valid output below 1.2 volts on an input. to sink current below 1.2 volts a resis- tor can be connected from rst to gnd (see figure 5). this arrangement will maintain a valid value on the rst outputs even if all supply inputs are at 0 volts. during conditions when the rst is in the inactive or high state this arrangement will draw current through the pull down resistor. a value of about 100k w should be adequate to maintain a valid condition. the ds1836 nmi output requires a pullup resistor on the output to maintain a valid output. the value of the resistor is not critical in most cases but must be set low enough to pull the output to a high state. a common value used is 10k w s (see figure 3). application diagram: rst valid to 0 volts v cc on the ds1836a or DS1836C figure 5 rst input 100k w timing diagram: power up figure 6 v cc t r v ol v oh t rpu v cctp (max) v cctp (min) v cctp rst (ds1836b/d) = v bat rst (ds1836a/c)
ds1836a/b/c/d 022698 6/9 timing diagram: power down figure 7 t f rst (ds1836b/d) rst (ds1836a/c) v cc t rpd v ol v oh rst slews with v cc v cctp (max) v cctp v cctp (min) rst = v bat timing diagram: power switch figure 8 v cc v ccrtp v ccftp t rsw t fsw v cc =0.0v v out =v cc v out =v bat
ds1836a/b/c/d 022698 7/9 absolute maximum ratings* voltage on v cc or v bat pin relative to ground 0.5v to +7.0v voltage on any i/o pin relative to ground** 0.5v to v out + 0.5v operating temperature 40 c to +85 c storage temperature 55 c to +125 c soldering temperature 260 c 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 maxi- mum rating conditions for extended periods of time may affect reliability. **the voltage input on in can exceed v cc /v bat if the input current is less than 10 ma. recommended dc operating conditions (40 c to +85 c) parameter symbol min typ max units notes supply voltage v cc 1.2 5.5 v 1 secondary supply voltage v bat 1.2 5.5 v 1 dc electrical characteristics (40 c to +85 c; v cc =1.2v to 5.5v) parameter symbol min typ max units notes output voltage @ 500 m a v oh v cc 0.5 v cc 0.1 v 1 input leakage i il 1.0 +1.0 m a 2 output current @ 2.4v i oh 350 m a 3 output current @ 0.4v i ol +10 ma 3 operating current @ 5.5v in i cc 35 55 m a 4 operating current @ 3.6v in i cc 25 40 m a 5 supply output current i cc01 100 ma 6 supply output current i cc02 100 ma 7 supply output voltage (v cc ) v out v cc 0.5 v cc 0.3 v 1, 8 supply output voltage (v bat ) v out v bat 0.5 v bat 0.3 v 1, 9 rst v cc trip point ds1836a(or b)05 v cctp 4.50 4.63 4.75 v 1 rst v cc trip point ds1836a(or b)10 v cctp 4.25 4.37 4.50 v 1 rst v cc trip point DS1836C(or d)10 v cctp 2.80 2.88 2.97 v 1 rst v cc trip point DS1836C(or d)20 v cctp 2.67 2.72 2.80 v 1 power supply trip points (v cc to v bat ) ds1836 c or d v ccftp 2.60 2.65 2.70 v 1, 10 power supply trip points (v bat to v cc ) ds1836 c or d v ccrtp 2.70 2.75 2.80 v 1, 10 v bat leakage current i cc03 0.10 m a 11
ds1836a/b/c/d 022698 8/9 dc electrical characteristics (40 c to +85 c; v cc =1.2v to 5.5v) parameter symbol min typ max units notes power supply trip points (v cc to v bat ) ds1836 a or b v ccftp 3.80 3.85 3.0 v 1, 10 power supply trip points (v bat to v cc ) ds1836 a or b v ccrtp 3.90 3.95 4.0 v 1, 10 in input trip point v tp 1.15 1.25 1.35 v 1 output capacitance c out 10 pf ac electrical characteristics (40 c to +85 c; v cc =1.2v to 5.5v) parameter symbol min typ max units notes v tp to nmi delay t ipd 1 m s reset active time t rst 200 350 500 ms v cc slew rate (v intp(min) to v intp(max) ) t r 0 ns v cc detect to rst t rpu 200 350 500 ms 12 v cc slew rate (v intp(max) to v intp(min) ) t f 300 m s v cc detect to rst t rpd 2 10 m s v cc to v bat (v cc falling through 2.6v) t psw 1 m s 13 v bat to v cc (v cc rising through 2.8v) t rsw 1 m s 13 notes: 1. all voltages are referenced to ground. 2. measured with outputs open and inputs at v cc or gnd. 3. measured with outputs open and v cc or v bat > 2.7v. 4. measured with outputs open and both v cc and v bat < 5.5 volts. 5. measured with outputs open and both v cc and v bat < 3.6 volts. 6. v out = v cc 0.3v 7. v out = v bat 0.3v 8. v cc > 2.7v 9. v bat > 2.0v and v cc < 1.9v 10. v ccftp is offset by approximately 0.1 volt from v ccrtp . 11. v bat in the off state and v bat < v cc (v bat > v cc and v bat in the off state 1 m a maximum) 12. t r = 5 m s with one supply > 2.5v 13. typical only parameter not tested.
ds1836a/b/c/d 022698 9/9 data sheet revision summary the following represent the key differences between 01/17/95 and 06/17/97 version of the ds1836a/b/c/d data sheet. please review this summary carefully. 1. correction to various typo's 2. change battery switch characteristics for 5 volt versions
|
