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AS1925, AS1926
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
D a ta S he e t
1 General Description
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 (3.5A) 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. The devices are available as the standard products listed in Table 1. Table 1. Standard Products Model AS1925 AS1926 Output Type Active-Low Push/Pull, Active-High Push/Pull Active-High Push/Pull, Active-Low Open-Drain
2 Key Features
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Factory-Trimmed Reset Thresholds for Monitoring Supplies from 0.9 to 1.5V Low Power Consumption: 3.5A 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
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!
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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. The devices are available in a 5-pin SOT23 package.
3 Applications
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 MRN 5 VCC + - VREF + - MRN Pullup
AS1925/ AS1926
Manual Reset Detect Reset Timeout Period Reset Output 3 RESET 1 RESETN
RESETN 1
5 VCC
GND 2
AS1925/ AS1926
4 MRN
RESET 3
GND
2
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AS1925/AS1926
Data Sheet - P i n o u t
4 Pinout
Pin Assignments
Figure 2. Pin Assignments (Top View)
RESETN 1
5 VCC
GND 2
AS1925/ AS1926
4 MRN
RESET 3
Pin Descriptions
Table 2. Pin Descriptions Pin Number Pin Name 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 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. Active-Low Manual Reset Input. This pin is connected to the internal 20k 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. Supply Voltage. Monitored supply voltage.
1
RESETN
2
GND
3
RESET
4
MRN
5
VCC
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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 VCC to GND MRN, RESETN (Open-Drain) to GND RESETN (Push/Pull), RESET to GND Input Current (All Pins) RESETN, RESET Output Current Continuous Power Dissipation (TAMB = +70C) Operating Temperature Range Junction Temperature Storage Temperature Range -65 -40 Min -0.3 -0.3 -0.3 Max Units +5 +5 VCC + 0.3 20 20 571 +85 +150 +150 V V V mA mA mW C C C 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). Derate 7.1mW/C above +70C Comments
Package Body Temperature
+260
C
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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 +85C (unless otherwise specified). Typ values @ TAMB = +25C. Table 4. Electrical Characteristics Symbol VCC Parameter
1 2
Conditions
Min 0.75
Typ
Max 1.80
Units V
Supply Voltage Range
VCC = 0.9V, No Load, Reset Not Asserted ICC Supply Current VCC = 1.5V, No Load, Reset Not Asserted VCC = 1.8V, No Load, Reset Not Asserted Suffix 14 Suffix 13 VTH Reset Threshold (VCC Falling) Suffix 11 Suffix 10 Suffix 08 Suffix 07, TAMB = 0 to +85C VHYS Reset Threshold Hysteresis VCC to Reset Delay VCC Falling, Step Signal from (VTH + 10%) to (VTH - 10%) within 1s Suffix B tRP Reset Active Timeout Period Suffix C Suffix D Suffix E VIL MRN Input Voltage VIH MRN Minimum Input Pulse Width MRN Glitch Rejection MRN to Reset Delay MRN Pullup Resistance to VCC RESETN Open-Drain Output Voltage RESETN Open-Drain Output Leakage Current VCC = 0.55V, ISINK = 10A, Reset Asserted VCC = 0.83V, ISINK = 80A, Reset Asserted VCC > VTH, Reset Not Asserted VCC = 0.55V, ISINK = 10A, Reset Asserted VOL RESETN Push/Pull Output Voltage VOH VCC = 0.83V, ISINK = 80A, Reset Asserted VCC = 0.83V, ISOURCE = 40A, Reset Not Asserted 0.8 x VCC MRN driven from VCC to 0V MRN driven from VCC to 0V MRN driven from VCC to 0V
3 3 3 3
3.5 4.5 5 1.350 1.275 1.080 1.020 0.810 0.765 1.388 1.313 1.110 1.050 0.833 0.788 0.75 120 1 20 140 1120 1.5 30 210 1680
12 12 12 1.425 1.350 1.140 1.080 0.855 0.810 %VTH s 2 40 280 2240 0.3 x VCC ms V A
0.7 x VCC 1 150 500 10 20 26 0.2 x VCC 0.2 x VCC 1 0.2 x VCC 0.2 x VCC
V
s ns ns k
VOL
V
ILEAK
A
V
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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
Conditions VCC = 0.75V, ISOURCE = 10A, Reset Asserted
Min 0.8 x VCC 0.8 x VCC
Typ
Max
Units
VOH RESET Push/Pull Output Voltage VOL
VCC = 0.83V, ISOURCE = 40A, Reset Asserted VCC = 0.83V, ISINK = 80A, Reset Not Asserted
V 0.2 x VCC
1. 100% production tested at +25C. 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 +85C; for VCC > 0.833V, TAMB = -40 to +85C.
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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 = +25C (unless otherwise specified). Figure 3. Supply Current vs. Temperature
5
VCC =1.8V
Figure 4. Power Down Reset Delay vs. Temperature
. Power Down Reset Delay (s)
140 120 100 80 60 40
VOD = 10mV VOD = 20mV VOD = 100mV
Supply Current (A) .
4
VCC = 1.5V
3
VCC = 0.9V
2
1
20 0 -40
VOD = Overdrive Voltage
0 -40
-15
10
35
60
85
-15
10
35
60
85
Temperature (C)
Temperature (C)
Figure 5. Normalized Reset Timeout Periode vs. Temp.
1.08
Figure 6. Normalized VCC Reset TH. vs. Temperature
1.01
Normalized Reset Timeout Delay .
1.06 1.04 1.02 1
Normalized Vcc Reset Threshold .
-15 10 35 60 85
1.005
1
0.995
0.98 0.96 -40
0.99 0 15 30 45 60 75 90
Temperature (C)
Temperature (C)
Figure 7. Power-Up/Down Characteristics
Figure 8. Glitch rejection vs. Supply Voltage
700
.
600
Max. Transient Duration (s)
1V/Div
VCC
500 400 300 200 100 0
Reset occures above this line
RESETN
1V/Div
No reset occures below this line
100ms/Div
1
10
100
Overdrive VTH-VCC (mV)
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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 20k 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 0.1F capacitor from MRN to ground will provide additional noise immunity.
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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
AS1926
4 External Reset MRN GND 2
CPU
1 RESETN RESETN GND
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 0.1F 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 200k 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 RESETN RPULLDOWN
AS1925
GND
2
Note: A 200k pullup resistor to VCC is also recommended if the push/pull RESET is required to remain valid for VCC 0.75V.
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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
CPU
RESETN
1 RESETN
AS1926
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
CPU
RESETN
1 RESETN
AS1926
GND GND 2
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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.
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
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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 AS1925-BSTT-xyy
1
Description Ultra-Low Reset Threshold with Manual Reset Ultra-Low Reset Threshold (0.81V) with Manual Reset Ultra-Low Reset Threshold (0.81V) with Manual Reset, Open-Drain
Timeout Period
Delivery Form Tape and Reel
Package 5-pin SOT23 5-pin SOT23 5-pin SOT23
AS1925-BSTT-D07 AS1926-BSTT-D07
140ms Reset 140ms Reset
Tape and Reel Tape and Reel
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 B C D E 1 20 140 1120 typ 1.5 30 210 1680 max 2 40 280 2240 14 13 11 10 08 07 Suffix (yy) Reset Threshold (V) min 1.350 1.275 1.080 1.020 0.810 0.765 typ 1.388 1.313 1.110 1.050 0.833 0.788 max 1.425 1.350 1.140 1.080 0.855 0.810
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AS1925/AS1926
Data Sheet
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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