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AS1920, AS1922
Tr i p l e - Vo l ta g e , M i c r o - P o w e r M i c r o p r o c e s s o r Supervi s ory Ci rcuits
D a ta S h e e t
1 General Description
The AS1920 and AS1922 microprocessor supervisory circuits were designed to generate a reset when at least one of the three monitored supply voltages falls below its respective trip threshold. These very-low-current (6.2A, typ) devices maintain reset for a minimum timeout period after all supplies have stabilized. Guaranteed to be in the correct state for VCC > +1.0V, these devices are perfect for multiple-voltage systems with low current requirements and strict monitoring requirements. The devices are available as the standard products listed in Table 1. Table 1. Standard Products Model AS1920-18 AS1922-18 Output Type Push/Pull Open-Drain Supervisory Voltages 3V, 1.8V, Adjustable 3V, 1.8V, Adjustable
2 Key Features
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Simultaneous Triple-Voltage Monitoring Very-Low Supply Current: 6.2A 1.5% Accuracy Over Temperature Reset Time Delay: 200ms Power Supply Transient Immunity Guaranteed Reset for VCC3 1V or VCC18 1V Active-Low Push/Pull Reset Output (AS1920) Active-Low Open-Drain Reset Output (AS1922) 5-pin SOT23 Package
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All devices monitor primary and secondary factorytrimmed voltages. Additionally, a third monitoring voltage can be selected via an external resistor divider. The AS1920 has an active-low push/pull reset output, whereas the AS1922 has an active-low open-drain reset output. The AS1920 and AS1922 are available in a 5-pin SOT23 package.
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3 Applications
The devices are ideal for personal computers, notebooks, battery-powered systems, embedded controllers, intelligent instruments, automotive systems, critical CPU monitoring, and any multi-supply monitoring application.
Figure 1. Typical Application Diagram
3V 1.8V 2.5V 5 VCC3 4 R1 130k 1% 0.1F R2 100k 1% VCC18 3 VCCA
System Logic
AS1920/ AS1922
1 RESETN 2 GND
0.1F
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AS1920/AS1922
Datasheet - P i n o u t
4 Pinout
Pin Assignments
Figure 2. Pin Assignments (Top View)
RESETN 1
5 VCC3
GND 2
AS1920/ AS1922
VCCA 3
4 VCC18
Pin Descriptions
Table 2. Pin Descriptions Pin Number Pin Name Description Reset Logic Output. This active-low pin serves as the 3V push/pull reset output. A reset is asserted when any one of the supplies are below its respective trip threshold and the reset is held for 200ms after all power supplies have stabilized. Ground. VCCA. 1V sense, high-impedance input. Note: If this pin is not used it should be tied to VCC3 or VCC18. VCC18. 1.8V sense input and power detect pin (AS1920-18, AS1922-18). This pin provides power to the output reset stage of the device in order to assert a valid reset when the voltage on the primary input is down. Note: Bypass this pin to GND with a 0.1F ceramic capacitor. VCC3. 3V sense input and power supply pin (AS1920-18, AS1922-18). This pin provides power to the device. Note: Bypass this pin to GND with a 0.1F ceramic capacitor.
1
RESETN
2 3
GND VCCA
4
VCC18
5
VCC3
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AS1920/AS1922
Datasheet - 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 VCC18, VCC3, VCCA to GND RESETN Open-Drain RESETN to GND Min -0.3V -0.3 -0.3 Max +5 +7 VCC3 + 0.3 Units V V V Guaranteed to meet specified performance from 0 to 70C and is designed, characterized and assured to meet the extended temperature limits of -40 to 85C but are not tested at these temperatures. 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). Comments
Operating Temperature Range
-40
+85
C
Storage Temperature Range
-65
+150
C
Package Body Temperature
+260
C
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AS1920/AS1922
Datasheet - 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
VCC18 = 1.8V, VCC3 = 3V, VCCA = VCC3, TAMB = -40 to +85C (unless otherwise specified). Table 4. Electrical Characteristics Symbol VRT18 VRT3 VRTA VCC3, VCC18 IVCC18 IVCC3 IVCCA IOUT ILEAK tRST tUV
1
Parameter Reset Threshold VCC18 Reset Threshold VCC3 Reset Threshold VCCA Operating Voltage VCC18 Supply Current VCC3 Supply Current VCCA Input Current Open-Drain RESETN Output Current Open-Drain RESETN Output Leakage Current Reset Pulse Width VCC Undervoltage Detect to RESETN
Conditions
Min 1.653 2.763 0.982
Typ 1.683 2.805 1.00
Max 1.713 2.847 1.018 3.3
Unit V V V V A A nA A A ms s
RESETN in Correct Logic State VCC18 < VCC3, VCC18 = 1.8V VCC18 < VCC3, VCC3 = 3V VCCA = 1V Reset Not Asserted, Forced to 0V Reset Not Asserted, RESETN Forced to 5.5V, TAMB = 25C RESETN Low, TAMB = 25C VCC18, VCC3, or VCCA < 2 Reset Threshold by > 1% TAMB = 25C ISINK = 2.5mA, VCC3 = 3V, VCC18 = 0V ISINK = 100A, VCC3 = 1V, VCC18 = 0V ISINK = 100A, VCC3 = 0V, VCC18 = 1V ISINK = 100A, VCC3 = 1V, VCC18 = 1V
2
1 0.7 6.2 -15 2 -0.1 140 200 130 0 4
2 15 15 13 0.1 280
0.15 0.05 0.05 0.05 VCC3 1 VCC3 0.65
0.4 0.3 V 0.3 0.3 V
VOL
Output Voltage Low, RESETN
VOH
Output Voltage High, RESETN
ISOURCE = 1A (AS1922-xx)
1. Guaranteed by design. 2. Measured from the time (t1) when the input passes through the input threshold voltage (VRTX) to the time (t2) when RESETN passes through 1.5V.
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Datasheet - 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
TAMB = +25C (unless otherwise specified). Figure 3. IVCC18 vs. Temperature
1
Figure 4. IVCC3 vs. Temperature; VCC3 = 3V
6.5 6.4
VCC18 Supply Current (A) e
0.9
VCC3 Supply Current (A) e
6.3 6.2 6.1 6 5.9 5.8 5.7 5.6 5.5 -100 -50 0 50 100
0.8
0.7
0.6
0.5 -100
-50
0
50
100
Temperature (C) Figure 5. Supply Current VCCA vs. Temperature
10
Temperature (C) Figure 6. VOH/RST vs. Temperature; VCC3 = 3V
2.5 2.45
VCCA Supply Current (nA) e
9
7 6 5 4 3 2 1 0 -100 -50 0 50 100
Output Voltage High e
8
2.4 2.35 2.3 2.25 2.2 -100
-50
0
50
100
Temperature (C) Figure 7. tRST vs. Temperature; VCC3 = VCCA = 3V
280
Temperature (C) Figure 8. tUV vs. Temperature; VCC3 = VCCA = 3V
150
Reset Pulse Width (ms) e
260 240 220 200 180 160 140 -100
VCC Undervoltage Detect [s] e
125
100
75
-50
0
50
100
50 -100
-50
0
50
100
Temperature (C)
Temperature (C)
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AS1920/AS1922
Datasheet - D e t a i l e d D e s c r i p t i o n
8 Detailed Description
The AS1920/AS1922 microprocessor supervisory circuits were designed to generate a reset when at least one of the three monitored supply voltages falls below its respective trip threshold. These very-low-current (6.5A, typ) devices maintain reset for a minimum timeout period after all supplies have stabilized. Guaranteed to be in the correct state for VCC > +1.0V, these devices are perfect for multiple-voltage systems with low current requirements and strict monitoring requirements. Figure 9. AS1920 Block Diagram
5 -
VCC3
Power Detect 4 VCC Internal +
VCC3
VCC18
200ms Pulse Generator - 200ms Delay 1 RESETN
+
3 -
VCCA
+
2 GND
Bandgap Reference
AS1920
Figure 10. VCC Monitor Timing Diagram
VCCX
VRTX
tRST tUV
RESETN
1.5V
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AS1920/AS1922
Datasheet - D e t a i l e d D e s c r i p t i o n
Figure 11. AS1922 Block Diagram
5 -
VCC3
Power Detect 4 VCC Internal +
VCC3 IOUT
200ms Pulse Generator 1 RESETN 200ms Delay
VCC18
-
+
3 -
VCCA
+
2 GND
Bandgap Reference
AS1922
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AS1920/AS1922
Datasheet - 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
Supply Monitoring
The AS1920/AS1922 are low-power, high-accuracy triple-supply monitoring circuits with a single 200ms microprocessor reset output. All VCC inputs (VCC18, VCC3, and VCCA) must be above their thresholds to prevent a reset from being asserted. The AS1920/AS1922 will assert a reset during powerup, powerdown and brownout conditions on one or all of the VCC inputs.
Power Detect
The AS1920/AS1922 is powered from the 3V input pin (VCC3). The power detect circuitry ensures that the device pulls pin RESETN low as soon as the primary input pin is 1V or the secondary input pin is 1V.
Powerup
The power detect circuitry ensures that RESETN will be low when either VCC18 or VCC3 1V. As long as any one of the VCC inputs is below its reset threshold, RESETN will stay at a logic low. When all VCC inputs have stabilized, an internal timer will be started and RESETN will be driven high after 200ms.
Powerdown
On powerdown, if any of the VCC inputs drop below its threshold, RESETN is held at a logic low (0.3V) and is guaranteed until VCC3 and VCC18 < 1V.
Override Functions
As the trip points for VCC3 and VCC18 will always be greater than the trip point for VCCA, if pin VCCA is not used, it should be tied to VCC3 or VCC18. In a similar manner if pin VCC18 is not used it should be tied to VCC3. Tying VCC3 to VCC18 and operating from a 1.8V supply will assure the continuous assertion of RESETN. Note: Pin VCC3 must be used in all configurations.
Ensuring RESETN Valid for Supply Voltages < 1V
When the supplies drops below 1V the RESETN output current sink capability is greatly reduced. Stray currents and stray capacitance to signals other than GND can cause the RESETN output to float. This is not relevant for most applications since most microprocessors and other circuits do not operate with a supply voltage < 1V. In applications where the RESETN output must be valid down to 0V, a pulldown resistor from pin RESETN to ground will ensure RESETN is held low (see Figure 12). Figure 12. Typical Application w/Resistor on RESETN Output to GND
3V
5 VCC3 4 VCC18 3
1.8V
AS1920/ AS1922
1 RESETN 2 GND R3 100k
Adjustable Supply
R1
VCCA R2
The value of the pulldown resistor (R3) is a trade-off between pulldown strength and loading of the RESETN pin. If the value of R3 is too large RESETN may still float, and if the value of R3 is too small it may load RESETN and also use excess supply current, therefore a value of 100k is recommended for the pulldown resistor.
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Datasheet - A p p l i c a t i o n I n f o r m a t i o n
Figure 13. Triple-Supply Monitor (3V, 1.8V, Adjustable)
5 3V VCC3 4 VCC18 Adjustable Supply or DC/DC Feedback Divider 3 R1 R2 VCCA
1 RESETN
System Reset
1.8V
AS1920-18
2 GND
To ensure threshold accuracy, set the parallel combination of R1 and R2 66.5k
Figure 14. Dual-Supply Monitor (3V and 1.8V; Disable VCCA Input)
5 3V VCC3 4 VCC18 3 VCCA
1 RESETN
System Reset
1.8V
AS1920-18
2 GND
Figure 15. Dual-Supply Monitor (3V and Adjustable)
3V
5 VCC3 4 VCC18
1 RESETN
System Reset
AS1920-18
2 GND
Adjustable Supply or DC/DC Feedback Divider To ensure threshold accuracy, set the parallel combination of R1 and R2 66.5k
3 R1 R2 VCCA
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AS1920/AS1922
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
Figure 16. VCCA Tied to DC/DC Feedback Divider
2.5V
27.4k 1% Adjustable Reset Trip Threshold 2.31V 2.26k 1%
3V
5 VCC3 4 VCC18 3 VCCA
1 RESETN
System Reset
1.8V
AS1920-18
2 GND
22.6k 1%
Figure 17. Triple-Supply Monitor w/Manual Reset Switch
VTRIP = VCCA/R2 (R1 + R2) 2.5V VTRIP = 2.3V
1.8V
3V 5 1 RESETN System Reset
R1 = R2 ((VTRIP/VCCA) - 1) R1 130k 0.1%
100nF
VCC3 4
R3 10k 5%
100nF
VCC18 3 VCCA
AS1920-18
2 GND
Normally Open Manual Reset Switch
R2 100k 0.1%
Optional Resistor Recommended to Extend ESD Tolerance
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AS1920/AS1922
Datasheet - 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 devices are available in an 5-pin SOT23 package. Figure 18. 5-pin SOT23 Package
Symbol A A1 A2 b C D E E1 L e e1
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 0 8
Notes: 1. 2. 3. 4. 5. 6. All dimensions in millimeters. Foot length measured at intercept point between datum A and lead surface. Package outline exclusive of mold flash and metal burr. Package outline inclusive of solder plating. Complies with EIAJ SC74. PKG ST 0003 Rev A supersedes SOT23-D-2005 Rev C.
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AS1920/AS1922
Datasheet - 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
Tape and Reel Pin1 Orientation
Figure 19. AS1920 Tape&Reel Pin1 Orientation
Top, Through View
User direction of feed
SOT23-5
SOT23-5
SOT23-5
SOT23-5
Figure 20. AS1922 Tape&Reel Pin1 Orientation
Top, Through View
User direction of feed
SOT23-5
SOT23-5
SOT23-5
SOT23-5
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AS1920/AS1922
Datasheet - O r d e r i n g I n f o r m a t i o n
11 Ordering Information
The devices are available as the standard products shown in Table 5. Table 5. Ordering Information Model AS1920-18-T AS1922-18-T Marking ASI1 ASI2 Description Triple-Voltage Supervisory Circuit: 3V, 1.8V, and Adjustable. Triple-Voltage Supervisory Circuit: 3V, 1.8V, and Adjustable. Reset Type Push/Pull Open-Drain Delivery Form Tape and Reel Tape and Reel Package 5-pin SOT23 5-pin SOT23
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AS1920/AS1922
Datasheet
Copyrights
Copyright (c) 1997-2007, austriamicrosystems AG, Schloss Premstaetten, 8141 Unterpremstaetten, Austria-Europe. Trademarks Registered (R). 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. For shipments of less than 100 parts the manufacturing flow might show deviations from the standard production flow, such as test flow or test location. The information furnished here by austriamicrosystems AG is believed to be correct and accurate. However, austriamicrosystems AG shall not be liable to recipient or any third party for any damages, including but not limited to personal injury, property damage, loss of profits, loss of use, interruption of business or indirect, special, incidental or consequential damages, of any kind, in connection with or arising out of the furnishing, performance or use of the technical data herein. No obligation or liability to recipient or any third party shall arise or flow out of austriamicrosystems AG rendering of technical or other services.
Contact Information
Headquarters austriamicrosystems AG A-8141 Schloss Premstaetten, Austria Tel: +43 (0) 3136 500 0 Fax: +43 (0) 3136 525 01
For Sales Offices, Distributors and Representatives, please visit: http://www.austriamicrosystems.com/contact
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