AS1925, AS1926 D a ta S he e t U l t r a - L o w Vo l ta g e M i c r o p r o c e s s o r S u p e r v i s o r y Circuit with Manual Reset 1 General Description 2 Key Features The AS1925/AS1926 microprocessor supervisory circuits were designed to assert a single reset if the monitored supply voltage drops below its reset threshold or if the manual reset is activated. The reset remains asserted for a fixed timeout delay after VCC has risen above the reset threshold and the manual reset is deasserted. Their small size, excellent circuit reliability, and low supply current (3.5µA) make the AS1925/AS1926 a very low cost solution by eliminating external components and adjustments when used with low-voltage (+0.9 to +1.5V) systems. ! Factory-Trimmed Reset Thresholds for Monitoring Supplies from 0.9 to 1.5V ! Low Power Consumption: 3.5µA ! Reset Threshold Accuracy Over Temperature: ±2.5% ! Four Timeout Periods: 1.5ms, 30ms, 210ms, and 1.68s ! Three Reset Output Types: - Active-Low Push/Pull - Active-High Push/Pull - Active Low Open-Drain ! Guaranteed Reset Valid to VCC = 0.55V (ActiveLow) ! Manual Reset Input ! Immune to Fast VCC Transients ! 5-pin SOT23 Package The devices are available as the standard products listed in Table 1. Table 1. Standard Products Model Output Type AS1925 Active-Low Push/Pull, Active-High Push/Pull AS1926 Active-High Push/Pull, Active-Low Open-Drain The active-low open-drain reset output requires a pullup resistor that can be connected to a voltage from 0 to VCC. The reset comparator was specifically designed to ignore fast VCC transients. 3 Applications The devices are available in a 5-pin SOT23 package. The device is ideal for portable and battery-powered systems, embedded controllers, intelligent instruments, automotive systems, telecommunications equipment, networking equipment, computer workstations and servers, critical CPU monitoring applications, and any lowvoltage application. Figure 1. Block Diagram and Pinout 4 AS1925/ AS1926 MRN 5 VCC + – VREF MRN Pullup Manual Reset Detect + Reset Timeout Period – RESETN 1 3 Reset Output RESET GND 2 1 5 VCC AS1925/ AS1926 RESETN RESET 3 GND www.austriamicrosystems.com 4 MRN 2 Revision 1.00 1 - 12 AS1925/AS1926 Data Sheet - P i n o u t 4 Pinout Pin Assignments Figure 2. Pin Assignments (Top View) RESETN 1 GND 2 5 VCC AS1925/ AS1926 RESET 3 4 MRN Pin Descriptions Table 2. Pin Descriptions Pin Number Pin Name 1 RESETN 2 GND Description Active-Low Reset Output – AS1925 Push/Pull or AS1926 Open-Drain. RESETN changes from high to low if VCC drops below the selected reset threshold or MRN is pulled low. RESETN remains low for the reset timeout period (see page 4) after VCC exceeds the device reset threshold and MRN is released high. Ground RESET Active-High Push/Pull Reset Output. RESET changes from low to high when VCC input drops below the selected reset threshold or MRN is pulled low. RESET remains high for the reset timeout period (see page 4) after VCC exceeds the device reset threshold and MRN is released high. 4 MRN Active-Low Manual Reset Input. This pin is connected to the internal 20kΩ pullup to VCC. Pull this pin low to force a reset. The reset remains active as long as MRN is low and for the reset timeout period (see page 4) after MRN goes high. Note: If this pin is not used it should be connected to VCC or left unconnected. 5 VCC Supply Voltage. Monitored supply voltage. 3 www.austriamicrosystems.com Revision 1.00 2 - 12 AS1925/AS1926 Data Sheet - A b s o l u t e M a x i m u m R a t i n g s 5 Absolute Maximum Ratings Stresses beyond those listed in Table 3 may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in Electrical Characteristics on page 4 is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Table 3. Absolute Maximum Ratings Parameter Min VCC to GND -0.3 +5 V MRN, RESETN (Open-Drain) to GND -0.3 +5 V RESETN (Push/Pull), RESET to GND -0.3 VCC + 0.3 V 20 mA Input Current (All Pins) Max Units RESETN, RESET Output Current 20 mA Continuous Power Dissipation (TAMB = +70ºC) 571 mW +85 ºC +150 ºC +150 ºC Operating Temperature Range -40 Junction Temperature Storage Temperature Range Package Body Temperature www.austriamicrosystems.com -65 +260 Revision 1.00 ºC Comments Derate 7.1mW/ºC above +70ºC The reflow peak soldering temperature (body temperature) specified is in accordance with IPC/JEDEC J-STD-020C “Moisture/Reflow Sensitivity Classification for Non-Hermetic Solid State Surface Mount Devices”. The lead finish for Pb-free leaded packages is matte tin (100% Sn). 3 - 12 AS1925/AS1926 Data Sheet - E l e c t r i c a l C h a r a c t e r i s t i c s 6 Electrical Characteristics VCC = +0.55 to +1.8V, TAMB = -40 to +85ºC (unless otherwise specified). Typ values @ TAMB = +25ºC. Table 4. Electrical Characteristics 1 Symbol Parameter VCC Supply Voltage Range ICC VTH VHYS Conditions 2 Supply Current Reset Threshold (VCC Falling) Reset Active Timeout Period Typ 0.75 4.5 12 VCC = 1.8V, No Load, Reset Not Asserted 5 12 Suffix 14 1.350 1.388 1.425 Suffix 13 1.275 1.313 1.350 Suffix 11 1.080 1.110 1.140 Suffix 10 1.020 1.050 1.080 Suffix 08 0.810 0.833 0.855 Suffix 07, TAMB = 0 to +85ºC 0.765 0.788 0.810 VCC Falling, Step Signal from (VTH + 10%) to (VTH - 10%) within 1µs 120 µs 1.5 2 Suffix C 20 30 40 Suffix D 140 210 280 Suffix E 1120 1680 2240 0.3 × VCC 0.7 × VCC MRN driven from VCC to 0V MRN Glitch Rejection MRN driven from VCC to 0V MRN to Reset Delay MRN driven from VCC to 0V 3 RESETN Open-Drain Output Leakage Current 1 VOH www.austriamicrosystems.com V µs 150 ns 3 500 ns 10 20 26 VCC = 0.55V, ISINK = 10µA, Reset Asserted 0.2 × VCC VCC = 0.83V, ISINK = 80µA, Reset Asserted 0.2 × VCC VCC > VTH, Reset Not Asserted 1 VCC = 0.55V, ISINK = 10µA, Reset Asserted 0.2 × VCC VCC = 0.83V, ISINK = 80µA, Reset Asserted 0.2 × VCC VCC = 0.83V, ISOURCE = 40µA, Reset Not Asserted Revision 1.00 ms 3 VOL RESETN Push/Pull Output Voltage V %VTH 1 MRN Minimum Input Pulse Width µA 0.75 Suffix B MRN Pullup Resistance to VCC ILEAK V VCC = 1.5V, No Load, Reset Not Asserted 3 RESETN Open-Drain Output Voltage 1.80 12 VIH VOL Units 3.5 VIL MRN Input Voltage Max VCC = 0.9V, No Load, Reset Not Asserted Reset Threshold Hysteresis VCC to Reset Delay tRP Min kΩ V µA V 0.8 × VCC 4 - 12 AS1925/AS1926 Data Sheet - E l e c t r i c a l C h a r a c t e r i s t i c s Table 4. Electrical Characteristics (Continued) Symbol Parameter 1 VOH RESET Push/Pull Output Voltage VOL Conditions Min VCC = 0.75V, ISOURCE = 10µA, Reset Asserted 0.8 × VCC VCC = 0.83V, ISOURCE = 40µA, Reset Asserted 0.8 × VCC VCC = 0.83V, ISINK = 80µA, Reset Not Asserted Typ Max Units V 0.2 × VCC 1. 100% production tested at +25ºC. Over-temperature limits are guaranteed by design. 2. The active-low output RESETN VCC(MIN) = 0.55V. 3. For VCC > 0.788V, TAMB = 0 to +85ºC; for VCC > 0.833V, TAMB = -40 to +85ºC. www.austriamicrosystems.com Revision 1.00 5 - 12 AS1925/AS1926 Data Sheet - Ty p i c a l O p e r a t i n g C h a r a c t e r i s t i c s 7 Typical Operating Characteristics VCC = 1.5V, TAMB = +25ºC (unless otherwise specified). Figure 3. Supply Current vs. Temperature Power Down Reset Delay (µs) VCC =1.8V Supply Current (µA) . Figure 4. Power Down Reset Delay vs. Temperature . 5 4 VCC = 1.5V 3 VCC = 0.9V 2 1 0 -40 -15 10 35 60 140 120 VOD = 100mV 100 80 VOD = 20mV 60 40 VOD = 10mV 20 0 -40 85 VOD = Overdrive Voltage -15 Figure 5. Normalized Reset Timeout Periode vs. Temp. 35 60 85 Figure 6. Normalized VCC Reset TH. vs. Temperature 1.08 1.01 Normalized Vcc Reset Threshold . Normalized Reset Timeout Delay . 10 Temperature (°C) Temperature (°C) 1.06 1.005 1.04 1.02 1 0.995 0.98 0.96 -40 1 0.99 -15 10 35 60 85 0 Temperature (°C) 15 30 45 60 75 90 Temperature (°C) Figure 7. Power-Up/Down Characteristics Figure 8. Glitch rejection vs. Supply Voltage . 700 Max. Transient Duration (µs) 1V/Div RESETN VCC 1V/Div 600 500 Reset occures above this line 400 300 No reset occures below this line 200 100 0 1 100ms/Div 10 100 Overdrive VTH-VCC (mV) www.austriamicrosystems.com Revision 1.00 6 - 12 AS1925/AS1926 Data Sheet - D e t a i l e d D e s c r i p t i o n 8 Detailed Description Reset Output The AS1925/AS1926 assert a reset during power-up, power-down, and brownout conditions if the VCC supply voltage falls below a preset threshold (AS1925/AS1926). The reset remains asserted for a fixed timeout delay (see page 4) once VCC has stabilized. The devices are available with four timeout options: 1.5ms, 30ms, 210ms, and 1.68s. The AS1925/AS1926 have two reset outputs (RESETN and RESET); RESETN is the inverse of RESET. The AS1925 has an active-high push/pull output and an active-low push/pull output. The AS1926 has an active-high push/pull output and an active-low open-drain output. Manual Reset Input The devices feature a manual reset input (MRN). When pin MRN is pulled low, a reset is asserted and the reset remains asserted as long as MRN is kept low, and for a fixed timeout delay after MRN goes high. MRN is connected to an internal 20kΩ pullup resistor, thus this pin can be left open if it is not used. MRN can be driven with CMOS logic-level or with open-drain/collector outputs. To create a manual reset circuit, connect a normally open momentary switch from MRN to ground (see Figure 9 on page 8). External debounce circuitry is not required. If pin MRN is driven via long cables or the device is used in a noisy environment, a 0.1µF capacitor from MRN to ground will provide additional noise immunity. www.austriamicrosystems.com Revision 1.00 7 - 12 AS1925/AS1926 Data Sheet - A p p l i c a t i o n I n f o r m a t i o n 9 Application Information Figure 9. Typical Application Diagram +3.3V 0.9V DC/DC Converter 5 VCC VCC I/O Supply CPU AS1926 1 RESETN RESETN 4 External Reset GND MRN GND 2 Fast Transient Immunity The AS1925/AS1926 are virtually immune to fast, falling VCC transients. Figure 8 on page 6 shows typical transient duration versus reset comparator overdrive, for which the devices do not generate a reset pulse. The graph was generated using a falling pulse applied to VCC, starting 0.1V above the actual reset threshold and ending below it by the magnitude indicated (reset comparator overdrive). The graph indicates the maximum pulse width that a falling VCC transient can have without causing a reset pulse. As the magnitude of the transient goes further below the reset threshold, the maximum allowable pulse width decreases. Note: For additional transient immunity, place a 0.1µF bypass capacitor as close as is practical to pin VCC. Ensuring a Valid Reset Output Down to 0V If VCC falls below 0.55V, the AS1925 push/pull RESETN output will no longer sink current and becomes an open circuit, which means that high-impedance CMOS-logic inputs connected to RESETN can drift to undetermined voltages. This is not relevant for most applications since most microprocessors and other circuits do not operate with a supply voltage < 0.55V. In systems where RESETN must be valid down to 0V, adding a pulldown resistor to RESETN (see Figure 10) causes any stray leakage currents to flow to ground, holding RESETN low. The value of the pulldown resistor is not critical; a 200kΩ resistor is large enough not to load RESETN and small enough to pull RESETN to ground. Figure 10. Reset Valid to VCC = 0V 5 VCC 1 AS1925 RESETN RPULLDOWN GND 2 Note: A 200kΩ pullup resistor to VCC is also recommended if the push/pull RESET is required to remain valid for VCC 0.75V. www.austriamicrosystems.com Revision 1.00 8 - 12 AS1925/AS1926 Data Sheet - A p p l i c a t i o n I n f o r m a t i o n Interfacing to Bi-Directional Microprocessor Reset Pins Because the RESETN output of the AS1926 is open drain, this device interfaces easily with microprocessors that have bidirectional reset pins. Connecting the AS1926 RESETN output directly to the microprocessor RESETN pin with a single pullup resistor allows either device to assert reset (Figure 11 on page 9). Figure 11. Interfacing to Microprocessors with Bidirectional Reset Pins VCC VCC 5 VCC 1 CPU RESETN AS1926 RESETN GND GND 2 Using the AS1926 Open-Drain RESETN Output with Multiple Supplies In a typical application, the pullup resistor connected to the AS1926 connects to the voltage being monitored at pin VCC. However, some systems use an open-drain output to level-shift from the monitored supply to reset circuitry powered by another supply (see Figure 12). As VCC decreases, so does the ability of the AS1926 to sink current at RESETN. RESETN is pulled high as VCC decreases toward 0V. The voltage where this occurs depends on the value of the pullup resistor and the supply voltage to which it is connected. Figure 12. AS1926 Open-Drain RESETN Output with Multiple Supplies +5.0V VCC RPULLUP +0.9V 5 VCC 1 CPU RESETN AS1926 RESETN GND GND www.austriamicrosystems.com Revision 1.00 2 9 - 12 AS1925/AS1926 Data Sheet - P a c k a g e D r a w i n g s a n d M a r k i n g s 10 Package Drawings and Markings The AS1925/AS1926 are available in an 5-pin SOT23 package. Figure 13. 5-pin SOT23 Package Notes: 1. All dimensions are in millimeters. 2. Foot length is measured at the intercept point between datum A and lead surface. 3. Package outline exclusive of mold flash and metal burr. 4. Package outline inclusive of solder plating. 5. Complies with EIAJ SC74. 6. Package ST003 Revision A supercedes SOT34-D-2005 Revision C. www.austriamicrosystems.com Revision 1.00 Symbol A A1 A2 b C D E E1 L e e1 α Min Max 0.90 1.45 0.00 0.15 0.90 1.30 0.30 0.50 0.09 0.20 2.80 3.05 2.60 3.00 1.50 1.75 0.30 0.55 0.95 Ref 1.90 Ref 0º 8º 10 - 12 AS1925/AS1926 Data Sheet - O r d e r i n g I n f o r m a t i o n 11 Ordering Information The AS1925/AS1926 are available as the standard products shown in Table 5. Table 5. Ordering Information Model Description AS1925-BSTT-xyy Ultra-Low Reset Threshold with Manual Reset AS1925-BSTT-D07 Ultra-Low Reset Threshold (0.81V) with Manual Reset AS1926-BSTT-D07 Ultra-Low Reset Threshold (0.81V) with Manual Reset, Open-Drain 1 Timeout Period Delivery Form Package Tape and Reel 5-pin SOT23 140ms Reset Tape and Reel 5-pin SOT23 140ms Reset Tape and Reel 5-pin SOT23 1. xx and y is a placeholder for variants, e.g., AS1926-BSTT-D07 offers 0.81V (max) reset threshold and a 140ms minimum timeout periode (see Table 6). Available upon request. Contact austriamicrosystems, AG for more information. Table 6. Model Variants Suffix (x) Reset timout (ms) min typ max B 1 1.5 2 C 20 30 D 140 E 1120 Suffix (yy) Reset Threshold (V) min typ max 14 1.350 1.388 1.425 40 13 1.275 1.313 1.350 210 280 11 1.080 1.110 1.140 1680 2240 10 1.020 1.050 1.080 08 0.810 0.833 0.855 07 0.765 0.788 0.810 www.austriamicrosystems.com Revision 1.00 11 - 12 AS1925/AS1926 Data Sheet Copyrights Copyright © 1997-2007, austriamicrosystems AG, Schloss Premstaetten, 8141 Unterpremstaetten, Austria-Europe. Trademarks Registered ®. All rights reserved. The material herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. All products and companies mentioned are trademarks or registered trademarks of their respective companies. Disclaimer Devices sold by austriamicrosystems AG are covered by the warranty and patent indemnification provisions appearing in its Term of Sale. austriamicrosystems AG makes no warranty, express, statutory, implied, or by description regarding the information set forth herein or regarding the freedom of the described devices from patent infringement. austriamicrosystems AG reserves the right to change specifications and prices at any time and without notice. Therefore, prior to designing this product into a system, it is necessary to check with austriamicrosystems AG for current information. This product is intended for use in normal commercial applications. Applications requiring extended temperature range, unusual environmental requirements, or high reliability applications, such as military, medical life-support or lifesustaining equipment are specifically not recommended without additional processing by austriamicrosystems AG for each application. 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