LTC1985-1.8 Micropower Precision Triple Supply Monitor with Push-Pull Reset Output in a 5-Lead SOT-23 Package U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO Monitors Three Inputs Simultaneously: 3V, 1.8V and Adjustable ±1.5% Threshold Accuracy Over Temperature Very Low Supply Current: 10µA Typ 200ms Reset Time Delay Power Supply Glitch Immunity Guaranteed RESET for VCC3 ≥ 1V or VCC18 ≥ 1V 3V Active-Low Push-Pull Reset Output 5-Lead SOT-23 Package U APPLICATIO S ■ ■ ■ ■ The RST output is guaranteed to be in the correct state for VCC18 or VCC3 down to 1V. The LTC1985 may also be configured to monitor any one or two VCC inputs instead of three, depending on system requirements. Very low (10µA typical) supply current makes the LTC1985 ideal for power conscious systems. Desktop Computers Notebook Computers Intelligent Instruments Portable Battery-Powered Equipment Network Servers The LTC1985 is available in a 5-lead SOT-23 package. , LTC and LT are registered trademarks of Linear Technology Corporation. U ■ The LTC®1985-1.8 is a triple supply monitor intended for systems with multiple supply voltages. The reset output remains low until all three supplies have been in compliance for 200ms. Tight 1.5% accuracy specifications and glitch immunity ensure reliable reset operation without false triggering. TYPICAL APPLICATION DC/DC CONVERTER 3V 1.8V 2.5V SYSTEM LOGIC 1 5 RST VCC3 LTC1985-1.8 4 R1 130k 1% 3 0.1µF 0.1µF R2 100k 1% VCC18 VCCA GND 1985-1.8 TA01 2 1 LTC1985-1.8 W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (Notes 1, 2) VCC3, VCC18, VCCA ...................................... – 0.3V to 7V RST .......................................... – 0.3V to (VCC3 + 0.3V) Operating Temperature Range (Note 3) ............................................. – 40°C to 85°C Storage Temperature Range ................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................ 300°C ORDER PART NUMBER TOP VIEW RST 1 5 VCC3 LTC1985ES5-1.8 GND 2 VCCA 3 4 VCC18 S5 PART MARKING S5 PACKAGE 5-LEAD PLASTIC SOT-23 TJMAX = 125°C, θJA = 250°C/W LTNM Consult factory for Industrial and Military grade parts. ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specificaitons are at TA = 25°C. VCC3 = 3V, VCC18 = 1.8V, VCCA = VCC3 unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS VRT3 Reset Threshold VCC3 VCC3 Input Threshold ● 2.760 2.805 2.850 V VRT18 Reset Threshold VCC18 VCC18 Input Threshold ● 1.656 1.683 1.710 V VRTA Reset Threshold VCCA VCCA Input Threshold ● 0.985 1.000 1.015 V VCCOP VCC3, VCC18 Operating Voltage RST in Correct Logic State ● 1 7 V IVCC3 VCC3 Supply Current VCC18 > VCC3 VCC18 < VCC3, VCC3 = 3V (Note 4) ● ● 1 10 2 20 µA µA IVCC18 VCC18 Supply Current VCC18 < VCC3, VCC18 = 1.8V (Note 4) ● 1 2 µA IVCCA VCCA Input Current VCCA = 1V ● – 15 0 15 nA tRST Reset Pulse Width RST Low (Note 5) ● 140 200 280 ms tUV VCC Undervoltage Detect to RST VCC18, VCC3 or VCCA Less Than Reset (Note 5) Threshold VRT by More Than 1% VOL Output Voltage Low, RST ISINK = 2.5mA, VCC3 = 3V, VCC18 = 0V ISINK = 100µA, VCC3 = 1V, VCC18 = 0V ISINK = 100µA, VCC3 = 0V, VCC18 = 1V ISINK = 100µA, VCC3 = 1V, VCC18 = 1V ● ● ● ● VOH Output Voltage High, RST ISOURCE = 200µA ● Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Note 2: All voltage values are with respect to GND. Note 3: The LTC1985E is guaranteed to meet specified performance from 0°C to 70°C and is designed, characterized and assured to meet the 2 µs 110 0.15 0.05 0.05 0.05 0.8VCC3 0.4 0.3 0.3 0.3 V V V V V extended temperature limits of – 40°C to 85°C but are not tested at these temperatures. Note 4: Both VCC3 and VCC18 can act as the supply depending on which pin has the greatest potential. Note 5: Measured from when input passes through the input threshold voltage (VRTX) until RST passes through 1.5V. LTC1985-1.8 U W TYPICAL PERFOR A CE CHARACTERISTICS VCCA Input Current vs Input Voltage IVCC18 vs Temperature 1.5 1.4 13 1.3 12 1.2 11 10 9 1.0 0.9 0.8 7 0.7 6 0.6 80 – 2.0 0.80 0.85 0.90 0.95 1 1.05 1.10 1.15 1.20 INPUT VOLTAGE (V) 100 1985-18 G03 VCC18 Threshold Voltage vs Temperature 1.010 1.005 1.000 0.995 0.990 80 100 1.710 VCC18 THRESHOLD VOLTAGE, VRT18 (V) VCC3 THRESHOLD VOLTAGE, VRT3 (V) VCCA THRESHOLD VOLTAGE, VRTA (V) 80 2.845 0.985 –60 –40 –20 0 20 40 60 TEMPERATURE (°C) 2.835 2.825 2.815 2.805 2.795 2.785 2.775 2.765 – 60 –40 – 20 0 20 40 60 TEMPERATURE (°C) 80 100 1.700 1.690 1.680 1.670 1.660 1.650 –60 –40 –20 0 20 40 60 TEMPERATURE (°C) 1985-18 G05 1985-18 G04 Typical Transient Duration vs Comparator Overdrive RESET OCCURS ABOVE CURVE 250 200 150 100 50 0 0.1 1 10 100 RESET COMPARATOR OVERDRIVE VOLTAGE (% OF VCC) 1985-18 G07 280 8 260 7 TA = 25°C 6 240 VOL = 0.4V 220 200 180 5 4 VOL = 0.2V 3 2 160 140 –60 –40 –20 100 ISINK vs Supply Voltage ISINK (mA) TA = 25°C 400 80 1985-18 G06 Reset Pulse Width vs Temperature RESET PULSE WIDTH, tRST (ms) TYPICAL TRANSIENT DURATION (µs) – 0.5 VCC3 Threshold Voltage vs Temperature 1.015 300 0 1985-18 G02 VCCA Threshold Voltage vs Temperature 350 0.5 –1.5 1985-18 G01 450 1.0 –1.0 0.5 – 60 –40 – 20 0 20 40 60 TEMPERATURE (°C) 100 TA = 25°C 1.5 1.1 8 5 – 60 –40 – 20 0 20 40 60 TEMPERATURE (°C) 2.0 VCC3 = 3V VCCA = 3V VCC18 = 1.8V INPUT CURRENT (nA) 15 14 IVCC18 (µA) IVCC3 (µA) IVCC3 vs Temperature 1 0 0 20 40 60 80 100 TEMPERATURE (°C) 1985-18 G08 0 0.5 1.0 1.5 2.0 VCC3 OR VCC18 (V) 2.5 3.0 1985-18 • G09 3 LTC1985-1.8 U W TYPICAL PERFOR A CE CHARACTERISTICS RST High Level Output Voltage vs Output Source Current 3.5 RST Voltage Output Low vs Output Sink Current RST Voltage Output Low vs Output Sink Current 3.0 1.8 VCC3 = VCC18 = VCCA = 3.0V VCC3 = VCC18 = 1.8V VCCA = 0V 1.6 3.0 VCC3 = VCC18 = 3V VCCA = 0V 2.5 25°C 85°C 1.4 85°C 2.0 1.2 – 40°C 1.5 25°C – 40°C 1.0 VOL (V) 2.0 VOL (V) VOH (V) 2.5 0.8 85°C – 40°C 1.5 1.0 0.6 1.0 25°C 0.4 0.5 0.5 0.2 0 0 0 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 ISOURCE (mA) 0 2 4 1985-81 G10 6 8 ISINK (mA) 10 12 14 1985-81 G11 0 5 10 15 20 25 30 ISINK (mA) 35 40 45 1985-81 G12 U U U PI FU CTIO S RST (Pin 1): Reset Logic Output. Active low, 3V pushpull output. Asserted when one or all of the supplies are below trip thresholds and held for 200ms after all supplies become valid. GND (Pin 2): Ground. VCCA (Pin 3): 1V Sense, High Impedance Input. If unused it can be tied to either VCC3 or VCC18. 4 VCC18 (Pin 4): 1.8V Sense Input and Power Supply Pin. This pin is used on the LTC1985 to provide power to the part when the voltage on VCC18 is greater than the voltage on VCC3. Bypass to ground with a ≥ 0.1µF ceramic capacitor. VCC3 (Pin 5): 3V Sense Input and Power Supply Pin. This pin provides power to the part when the voltage on VCC3 is greater than the voltage on VCC18. Bypass to ground with a ≥ 0.1µF ceramic capacitor. LTC1985-1.8 W BLOCK DIAGRA LTC1985-1.8 – VCC3 5 + POWER DETECT VCC INTERNAL VCC3 VCC18 4 – 200ms PULSE GENERATOR 1 RST 200ms DELAY + – VCCA 3 + GND 2 BANDGAP REFERENCE 1985-18 BD WU W TI I G DIAGRA VCC Monitor Timing VCCX VRTX t UV RST tRST 1.5V 1985-18 TD 5 LTC1985-1.8 U W U U APPLICATIO S I FOR ATIO Supply Monitoring Override Functions The LTC1985 is a low power, high accuracy triple supply monitoring circuit with a single 200ms microprocessor reset output. The VCCA pin, if unused, can be tied to either VCC3 or VCC18. This is an obvious solution since the trip points for VCC3 and VCC18 will always be greater than the trip point for VCCA. Likewise, the VCC18, if unused, can be tied to VCC3. VCC3 must always be used. Tying VCC3 to VCC18 and operating off of a 1.8V supply will result in the continuous assertion of RST. All three VCC inputs must be above predetermined thresholds for reset not to be invoked. The LTC1985 will assert reset during power-up, power-down and brownout conditions on any one or all of the VCC inputs. Ensuring RST Valid for Supply Voltages Under 1V 3V or 1.8V Power Detect The LTC1985 is powered from the 3V input pin (VCC3) or the 1.8V input pin (VCC18), whichever pin has the highest potential. This ensures the part pulls the RST pin low as soon as either input pin is ≥1V. Power-Up Upon power-up, either the VCC18 or VCC3 pin, can power the part. This ensures that RST will be low when either VCC18 or VCC3 reaches 1V. As long as any one of the VCC inputs is below its predetermined threshold, RST will stay a logic low. Once all of the VCC inputs rise above their thresholds, an internal timer is started and RST is driven high after 200ms. RST is reasserted whenever any one of the VCC inputs drops below its predetermined threshold and remains asserted until 200ms after all of the VCC inputs are above their thresholds. When the supplies drops below 1V the RST output current sink capability is drastically reduced. The combination of stray currents and stray capacitance to signals other than ground can cause the RST output pin to float around. In a lot of applications this is not a problem since most microprocessors and other circuits do not operate with the supply voltage less than 1V. In applications where the RST output must be valid down to 0V the addition of a pulldown resistor from RST to ground will ensure RST is held low. The circuit in Figure 1 shows an application employing this technique. The value chosen for the pull-down resistor (R3) is a trade-off between pull-down strength and loading of the RST pin. If the value of the resistor is too large the pin may still float and if the resistor value is too low it may load down the RST as well as burn excess supply current, a value of 100k is a good compromise. 4 VCC3 = VCC18 = VCCA Power-Down LTC1985-1.8 3V ADJUSTABLE SUPPLY R1 1.8V 5 4 3 R2 2 VCC3 RST 1 3 RST VOLTAGE (V) On power-down, once any of the VCC inputs drop below its threshold, RST is held at a logic low. A logic low of 0.3V is guaranteed until both VCC3 and VCC18 drop below 1V. 2 1 R3 100k VCC18 VCCA 0 GND 0 1 2 3 4 VCC3 (V) 1985-18 TA06 1985-18 TA06b Resistor on RST Output to Ground Ensures RST Valid to VCC = 0V Figure 1. Typical Application Showing Resistor on RST Output to Ground 6 Figure 2. RST Voltage vs VCC3 with a 100k Resistor on RST to Ground LTC1985-1.8 U TYPICAL APPLICATIO S Triple Supply Monitor (3V, 1.8V and Adjustable) Dual Supply Monitor (3V and 1.8V, Defeat VCCA Input) LTC1985-1.8 5 3V ADJUSTABLE SUPPLY OR DC/DC FEEDBACK DIVIDER R1* 4 1.8V 3 R2* 2 VCC3 RST LTC1985-1.8 1 SYSTEM RESET 5 3V VCC18 4 1.8V 3 VCCA 2 GND VCC3 RST 1 SYSTEM RESET VCC18 VCCA GND 1985-18 TA02 1985-18 TA03 *TO PRESERVE THRESHOLD ACCURACY, SET PARALLEL COMBINATION OF R1 AND R2 ≤ 66.5k Dual Supply Monitor (3V Plus Adjustable) Using VCCA Tied to DC/DC Feedback Divider LTC1985-1.8 3V 5 4 ADJUSTABLE SUPPLY R1* 3 R2* 2 VCC3 RST 1 2.5V SYSTEM RESET VCC18 LTC1435 VOSENSE VCCA GND 1985-18 TA04 *TO PRESERVE THRESHOLD ACCURACY, SET PARALLEL COMBINATION OF R1 AND R2 ≤ 66.5k ADJUSTABLE RESET TRIP THRESHOLD 2.31V 6 27.4k 1% 3V 2.26k 1.8V 1% 22.6k 1% Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. LTC1985-1.8 5 4 3 2 VCC3 RST 1 SYSTEM RESET VCC18 VCCA GND 1985-18 TA05 7 LTC1985-1.8 U TYPICAL APPLICATIO Triple Supply Monitor with Manual Reset Button 2.5V VTRIP = 2.3V SYSTEM RESET 1 3V 1.8V 5 RST VCC3 100nF R3* 10k 5% *OPTIONAL RESISTOR RECOMMENDED TO EXTEND ESD TOLERANCE VCC18 100nF 3 R2 100k 0.1% MANUAL RESET BUTTON (NORMALLY OPEN) U PACKAGE DESCRIPTIO LTC1985-1.8 4 R1 130k 0.1% VCCA GND 1985-18 TA07 2 V VTRIP = CCA (R1 + R2) R2 V R1 = R2 TRIP – 1 VCCA ( ) Dimensions in inches (millimeters) unless otherwise noted. S5 Package 5-Lead Plastic SOT-23 (LTC DWG # 05-08-1633) 2.60 – 3.00 (0.102 – 0.118) 1.50 – 1.75 (0.059 – 0.069) 0.35 – 0.55 (0.014 – 0.022) 0.09 – 0.20 (0.004 – 0.008) (NOTE 2) 0.00 – 0.15 (0.00 – 0.006) 0.90 – 1.45 (0.035 – 0.057) 0.35 – 0.50 0.90 – 1.30 (0.014 – 0.020) (0.035 – 0.051) FIVE PLACES (NOTE 2) NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DIMENSIONS ARE INCLUSIVE OF PLATING 3. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 4. MOLD FLASH SHALL NOT EXCEED 0.254mm 5. PACKAGE EIAJ REFERENCE IS SC-74A (EIAJ) 2.80 – 3.00 (0.110 – 0.118) (NOTE 3) 0.95 (0.037) REF 1.90 (0.074) REF S5 SOT-23 0599 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC690 5V Supply Monitor, Watchdog Timer and Battery Backup 4.65V Threshold LTC694-3.3 3.3V Supply Monitor, Watchdog Timer and Battery Backup 2.9V Threshold LTC699 5V Supply Monitor and Watchdog Timer 4.65V Threshold LTC1232 5V Supply Monitor, Watchdog Timer and Push-Button Reset 4.37V/4.62V Threshold LTC1326 Micropower Precision Triple Supply Monitor for 5V, 3.3V and ADJ 4.725V, 3.118V, 1V Thresholds (±0.75%) LTC1326-2.5 Micropower Precision Triple Supply Monitor for 2.5V, 3.3V and ADJ 2.363V, 3.118V, 1V Thresholds (±0.75%) LTC1536 Precision Triple Supply Monitor for PCI Applications Meets PCI tFAIL Timing Specifications LTC1726-2.5 Micropower Triple Supply Monitor for 2.5V, 3.3V and ADJ Adjustable RESET and Watchdog Time Outs LTC1726-5 Micropower Triple Supply Monitor for 5V, 3.3V and ADJ Adjustable RESET and Watchdog Time Outs LTC1727-2.5/1727-5 Micropower Triple Supply Monitor with Open-Drain Reset Individual Monitor Outputs in MSOP LTC1728-1.8 Micropower Triple Supply Monitor with Open-Drain Reset 5-Lead SOT-23 Package LTC1728-2.5/1728-5 Micropower Triple Supply Monitor with Open-Drain Reset 5-Lead SOT-23 Package 8 Linear Technology Corporation 1985f LT/TP 0900 4K • PRINTED IN THE USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com LINEAR TECHNOLOGY CORPORATION 2000