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LTC2909 Precision Triple/Dual Input UV, OV and Negative Voltage Monitor FEATURES

DESCRIPTIO

Two Low Voltage Adjustable Inputs (0.5V) Pin Selectable Input Polarity Allows Negative and OV Monitoring Guaranteed Threshold Accuracy: 1.5% 6.5V Shunt Regulator for High Voltage Operation Low 50A Quiescent Current Buffered 1V Reference for Negative Supply Offset Input Glitch Rejection Adjustable Reset Timeout Period Selectable Internal Timeout Saves Components Open-Drain RST Output Accurate UVLO for 2.5V, 3.3V, 5V Systems Ultralow Voltage Reset: VCC = 0.5V Guaranteed Space Saving 8-Lead TSOT-23 and 3mm x 2mm DFN Packages
The LTC(R)2909 is a dual input monitor intended for a variety of system monitoring applications. Polarity selection and a buffered reference output allow the LTC2909 to monitor positive and negative supplies for undervoltage (UV) and overvoltage (OV) conditions. The two inputs have a nominal 0.5V threshold, featuring tight 1.5% threshold accuracy over the entire operating temperature range. Glitch filtering ensures reliable reset operation without false triggering. A third fixed-threshold UVLO monitor on the part's VCC (also 1.5% accuracy) is available for standard logic supplies. The common reset output has a timeout that may use a preset 200ms, be set by an external capacitor or be disabled. A three-state input pin sets the input polarity of each adjustable input without requiring any external components. The LTC2909 provides a highly versatile, precise, spaceconscious, micropower solution for supply monitoring.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
APPLICATIO S

Desktop and Notebook Computers Handheld Devices Network Servers Core, I/O Monitor Automotive
TYPICAL APPLICATIO
3.3V UV/OV (Window) Monitor Application with 200ms Internal Timeout (3.3V Logic Out)
CBYP 100nF 3.3V RP6 453k ADJ1 RP5 10.7k VCC RST LTC2909-2.5 REF ADJ2 RP4 76.8k GND
2909 TA01a
SEL Pin Connection for Input Polarity Combinations
POLARITY
RPU 10k FAULT OUTPUT
ADJ1
+ + -
SEL TMR
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ADJ2 SEL PIN VCC OPEN GND
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+ - -
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LTC2909 ABSOLUTE AXI U RATI GS
Terminal Voltages VCC (Note 3)............................................. -0.3V to 6V SEL, RST .............................................. -0.3V to 7.5V ADJ1, ADJ2 .......................................... -0.3V to 7.5V TMR ..........................................-0.3V to (VCC + 0.3V) Terminal Currents IVCC (Note 3) ....................................................10mA IREF ....................................................................1mA
PACKAGE/ORDER I FOR ATIO
TOP VIEW SEL 1 TMR 2 VCC 3 RST 4 9 8 7 6 5 ADJ1 ADJ2 REF GND
DDB PACKAGE 8-LEAD (3mm 2mm) PLASTIC DFN TJMAX = 125C, JA = 76C/W EXPOSED PAD (PIN 9) MAY BE LEFT OPEN OR TIED TO GND (PCB CONNECTION REQUIRED FOR STATED JA)
TOP VIEW ADJ1 1 ADJ2 2 REF 3 GND 4 8 SEL 7 TMR 6 VCC 5 RST
TS8 PACKAGE 8-LEAD PLASTIC TSOT-23 TJMAX = 125C, JA = 250C/W
Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for parts specified with wider operating temperature ranges.
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(Notes 1, 2)
Operating Temperature Range LTC2909C ................................................ 0C to 70C LTC2909I .............................................- 40C to 85C Storage Temperature Range DFN....................................................- 65C to 125C TSOT-23.............................................- 65C to 150C Lead Temperature (Soldering, 10 sec) TSOT-23............................................................ 300C
ORDER PART NUMBER LTC2909CDDB-2.5 LTC2909IDDB-2.5 LTC2909CDDB-3.3 LTC2909IDDB-3.3 LTC2909CDDB-5 LTC2909IDDB-5
DDB PART* MARKING LBXG LBXG LBZS LBZS LBZT LBZT
ORDER PART NUMBER LTC2909CTS8-2.5 LTC2909ITS8-2.5 LTC2909CTS8-3.3 LTC2909ITS8-3.3 LTC2909CTS8-5 LTC2909ITS8-5
TS8 PART* MARKING LTBXF LTBXF LTBZV LTBZV LTBZW LTBZW
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LTC2909 ELECTRICAL CHARACTERISTICS
SYMBOL VCC(MIN) VCC(SHUNT) ICC VRT VRT IADJ VCC(UVLO) PARAMETER Operating Supply Voltage VCC Shunt Regulation Voltage VCC Input Current ADJ Input Threshold ADJ Hysteresis (Note 4) ADJ Input Current VCC UVLO Threshold TMR = VCC VADJ = 0.55V LTC2909-2.5 LTC2909-3.3 LTC2909-5 TMR = VCC VCC > 2.175V, IVREF = 1mA VTMR = 1V VTMR = 1V CTMR = 2.2nF VTMR = 0V VTMR Rising VTMR Falling VTMR Falling VTMR Rising ADJx Driven Beyond Reset Threshold (VRTX) by 5mV VCC Less Than UVLO Threshold (VCC(UVLO)) by 1% VCC = 0.5V, I = 5A VCC = 1V, I = 100A VCC = 3V, I = 2500A RST = VCC

The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 2.5V (LTC2909-2.5), VCC = 3.3V (LTC2909-3.3), VCC = 5V (LTC2909-5), ADJ1 = ADJ2 = 0.55V, SEL = floating, unless otherwise noted. (Note 2)
CONDITIONS RST in Correct State IVCC = 1mA, IVREF = 0 2.175 < VCC < 6V

MIN 0.5 6.0 0.492 1.5 2.175 2.871 4.350 0.3 0.985 -1.5 1.5 16 150 VCC - 0.36 60 0.14 40 50 50
TYP 6.5 50 0.500 3.5 2.213 2.921 4.425 0.7 1.000 -2.1 2.1 20 200 VCC - 0.25 110 0.21 70 150 150 0.01 0.01 0.10
MAX 6.9 150 0.508 10.0 15 2.250 2.970 4.500 2.0 1.015 -2.7 2.7 25 260 VCC - 0.16 150 0.27 110 500 500 0.15 0.15 0.30 1 0.4
UNITS V V A V mV nA V V V % V A A ms ms V mV V mV s s V V V A V V V A A
VCC(UVLO) VREF ITMR(UP) ITMR(DOWN) tRST(EXT) tRST(INT) VTMR(DIS) VTMR(DIS) VTMR(INT) VTMR(INT) tPROP tUV VOL(RST)
UVLO Hysteresis (Note 4) Buffered Reference Voltage TMR Pull-Up Current TMR Pull-Down Current Reset Timeout Period, External Reset Timeout Period, Internal Timer Disable Voltage Timer Disable Hysteresis Timer Internal Mode Voltage Timer Internal Mode Hysteresis ADJx Comparator Propagation Delay to RST VCC Undervoltage Detect to RST RST Output Voltage Low
IOH(RST) VIL VIH VZ ISEL(Z) ISEL
RST Output Voltage High Leakage Low Level Input Voltage High Level Input Voltage Pin Voltage when Left in Open State Allowable Leakage in Open State SEL Input Current
Three-State Input SEL

1.4 0.9 5 10 25
ISEL = 0A
SEL = VCC or SEL = GND
A
Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: All currents into pins are positive; all voltages are referenced to GND unless otherwise noted. Note 3: VCC maximum pin voltage is limited by input current. Since the VCC pin has an internal 6.5V shunt regulator, a low impedance supply
which exceeds 6V may exceed the rated terminal current. Operation from higher voltage supplies requires a series dropping resistor. See Applications Information. Note 4: Threshold voltages have no hysteresis unless the part is in comparator mode. Hysteresis is one-sided, affecting only invalid-to-valid transitions. See Applications Information.
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LTC2909 TYPICAL PERFOR A CE CHARACTERISTICS TA = 25C unless otherwise noted
THRESHOLD VOLTAGE VARIATION (% OF 25C VALUE)
ADJ Threshold Voltage vs Temperature
508 THRESHOLD VOLTAGE, VRT (mV) 506 504 502 500 498 496 494 492 -50 -25 0 50 75 25 TEMPERATURE (C) 100 125
REF VOLTAGE, VREF (V)
REF Output Load Regulation
1.015 1.010 REF VOLTAGE, VREF (V) 1.005 1.000 TA = -40C 0.995 0.990 0.985 -1 -0.5 0 0.5 LOAD CURRENT, IREF (mA) 1
2909 G04
1.010 TA = 125C TA = 25C REF VOLTAGE, VREF (V) 1.005 TA = 125C TA = 25C TA = -40C
QUIESCENT SUPPLY CURRENT, ICC (A)
VCC = 2.5V
Allowable Glitch Duration vs Magnitude
700 600 MAXIMUM ALLOWABLE GLITCH DURATION (s) 500 400 300 200 100 0 0.1 1 10 100 GLITCH PERCENTAGE PAST THRESHOLD (%)
2909 G07
RESET TIMEOUT PERIOD, tRST (ms)
RESET TIMEOUT PERIOD, tRST (ms)
RESET OCCURS ABOVE CURVE
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UW
2909 G01
VCC UVLO Threshold Variation vs Temperature
1.5 1.0 0.5 0 -0.5 -1.0 -1.5 -50 0.015 1.010 1.005 1.000 0.995 0.990
REF Output Voltage vs Temperature
IREF = 0A
-25
50 25 75 0 TEMPERATURE (C)
100
125
0.985 -50
-25
50 25 75 0 TEMPERATURE (C)
100
125
2909 G02
2909 G03
REF Output Line Regulation
1.015 IREF = 0A 60
Quiescent Supply Current vs Temperature
ADJ1 = 0.55V 55 ADJ2 = 0.45V SEL = OPEN 50 45 40 35 30 25 20 -50 -25 0 50 75 25 TEMPERATURE (C) 100 125 VCC = 2.5V
VCC = 5V VCC = 3.3V
1.000 0.995
0.990 0.985 2 2.5
4.5 5 3 3.5 4 SUPPLY VOLTAGE, VCC (V)
5.5
6
2909 G05
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External Timeout Period vs Capacitance
10000 260 240
Reset Timeout Period vs Temperature
1000
EXTERNAL WITH 22nF CAPACITOR 220 200 180 160 140 -50 INTERNAL
100
10
1 0.1
1 10 100 TMR PIN CAPACITANCE, CTMR (nF)
1000
2909 G08
-25
50 25 75 0 TEMPERATURE (C)
100
125
2909 G09
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LTC2909 TYPICAL PERFOR A CE CHARACTERISTICS
Shunt Regulation Voltage vs Temperature
SHUNT REGULATION VOLTAGE, VCC(SHUNT) (V) SHUNT REGULATION VOLTAGE, VCC(SHUNT) (V) 7.0 7.0
6.8 ICC = 10mA 6.6 ICC = 1mA ICC = 100A
RST VOLTAGE (V)
6.4
6.2
6.0 -50 -25
50 25 0 75 TEMPERATURE (C)
RST Output Voltage vs VCC
0.4 PULL-DOWN CURRENT, IRST (mA) 6
PULL-DOWN CURRENT, IRST (mA)
0.3 RST VOLTAGE (V) VCC 0.2 RST WITH 10k PULL-UP 0.1 RST WITH 100k PULL-UP 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 SUPPLY VOLTAGE, VCC (V) 0.8
RST VOL vs IRST
1.0 VCC = 3V NO PULL-UP R TA = 125C RST VOL (V) TA = 25C ISEL (A) 0.6 TA = -40C 0.4 -20
0.8
-14
ISEL (A)
0.2
0
0
5
10
15 20 IRST (mA)
UW
100
2909 G13
TA = 25C unless otherwise noted
Shunt Regulation Voltage vs Supply Current
TA = 25C 5
RST Output Voltage vs VCC
ADJ1 = 0.55 ADJ2 = 0.45 4 SEL = OPEN 10k PULL-UP R TO VCC 3
6.8
6.6
6.4
2 LTC2909-2.5 1 LTC2909-3.3 LTC2909-5
6.2
125
6.0 0.01
0 0.1 1 10 SUPPLY CURRENT, ICC (mA) 100
2909 G11
0
1
3 4 2 SUPPLY VOLTAGE, VCC (V)
5
2909 G12
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RST Pull-Down Current vs VCC
ADJ1 = 0.55 ADJ2 = 0.55 5 SEL = OPEN 4 RST AT 150mV 3 2 1 0 0 1 2 3 4 SUPPLY VOLTAGE, VCC (V) 5
2909 G14
RST Pull-Down Current vs VCC
1
RST AT 150mV 0.1
RST AT 50mV 0.01
0.001
RST AT 50mV
0.0001 0 0.2 0.4 0.6 0.8 SUPPLY VOLTAGE, VCC (V) 1
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ISEL vs Temperature
SEL = GND 20
ISEL vs Temperature
SEL = VCC
-18
18
-16
16
14
-12
12
25
30
1635 G07
-10 -50
-25
50 25 0 75 TEMPERATURE (C)
100
125
10 -50
-25
50 25 0 75 TEMPERATURE (C)
100
125
2909 G17
2909 G18
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LTC2909 PI FU CTIO S (TSOT-23/DFN Package)
ADJ1 (Pin 1/Pin 8): Adjustable Voltage Input 1. Input to voltage monitor comparator 1 (0.5V nominal threshold). The polarity of the input is selected by the state of the SEL pin (refer to Table 1). Tie to REF if unused (with SEL = VCC or Open). ADJ2 (Pin 2/Pin 7): Adjustable Voltage Input 2. Input to voltage monitor comparator 2 (0.5V nominal threshold). The polarity of the input is selected by the state of the SEL pin (refer to Table 1). Tie to GND if unused (with SEL = GND or Open). REF (Pin 3/Pin 6): Buffered Reference Output. 1V nominal reference used for the offset of negative-monitoring applications. The buffered reference can source and sink 1mA. The reference can drive a capacitive load of up to 1000pF. Larger capacitance may degrade transient performance. This pin does not require a bypass capacitor, nor is one recommended. Leave open if unused. GND (Pin 4/Pin 5): Device Ground. RST (Pin 5/Pin 4): Open-Drain Inverted Reset Logic Output. Asserts low when any positive polarity input voltage is below threshold or any negative polarity input voltage is above threshold or VCC is below UVLO threshold. Held low for a timeout after all voltage inputs are valid. Requires an external pull-up resistor and may be pulled above VCC. VCC (Pin 6/Pin 3): Power Supply. Bypass this pin to ground with a 0.1F (or greater) capacitor. Operates as a direct supply input for voltages up to 6V. Operates as a shunt regulator for supply voltages greater than 6V and should have a resistor between this pin and the supply to limit VCC input current to no greater than 10mA. When used without a current-limiting resistor, pin voltage must not exceed 6V. UVLO options allow VCC to be used as an accurate third fixed 10% UV supply monitor. TMR (Pin 7/Pin 2): Reset Timeout Control. Attach an external capacitor (CTMR) to GND to set a reset timeout of 9ms/nF. A low leakage ceramic capacitor is recommended for timer accuracy. Capacitors larger than 1F (9 second timeout) are not recommended. See Applications Information for further details. Leaving this pin open generates a minimum timeout of approximately 400s. A 2.2nF capacitor will generate a 20ms timeout. Tying this pin to ground will enable the internal 200ms timeout. Tying this pin to VCC will disable the reset timer and put the part in comparator mode. Signals from the comparator outputs will then go directly to RST. SEL (Pin 8/Pin 1): Input Polarity Select Three-State Input. Connect to VCC, GND or leave unconnected in open state to select one of three possible input polarity combinations (refer to Table 1). Exposed Pad (Pin 9, DFN Only): The Exposed Pad may be left unconnected. For better thermal contact, tie to a PCB trace. This trace must be grounded or unconnected.
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LTC2909 BLOCK DIAGRA W
SEL THREE-STATE DECODE CONTROL 2 ADJ1 CONTROL 1 VCC VCC 6.5V
+
TMR
-
ADJUSTABLE PULSE GENERATOR THREE-STATE DECODE RST
ADJ2
+ -
VCC
200ms PULSE GENERATOR
GND
+ - + -
REF 500mV
+ + - -
1.000V
SEL GND OPEN VCC
CONTROL 1 H L L
CONTROL 2 H H L
2909 BD
TI I G DIAGRA S
Normal Positive Polarity Input Timing
VADJ VRT tPROP RST 1V tRST RST VADJ
Normal Negative Polarity Input Timing
VADJ VRT tPROP RST 1V tRST RST VADJ
Normal UVLO Timing
VCC VCC(UVLO) tUV RST 1V tRST RST VCC VCC(UVLO) tUV 1V
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UW
Comparator Mode Positive Polarity Input Timing
VRT tPROP 1V
,VRT
tPROP
Comparator Mode Negative Polarity Input Timing
VRT tPROP 1V
,VRT
tPROP
Comparator Mode UVLO Timing
,VCC(UVLO)
tUV
2909 TD
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LTC2909 APPLICATIO S I FOR ATIO
The LTC2909 is a low power, high accuracy dual/triple supply monitor with two adjustable inputs and an accurate UVLO. Reset timeout may be selected with an external capacitor, set to an internally generated 200ms, or disabled entirely. The three-state polarity select pin (SEL) chooses one of three possible polarity combinations for the adjustable input thresholds, as described in Table 1. Both input voltages (VADJ1 and VADJ2) must be valid (above threshold if configured for positive polarity, below threshold if configured for negative polarity), and VCC above the UVLO threshold for the reset timeout before RST is released. The LTC2909 asserts the reset output during power-up, power-down and brownout conditions on any of the voltage inputs. Power-Up The LTC2909 uses proprietary low voltage drive circuitry for the RST pin which holds RST low with as little as 200mV of VCC. This helps prevent an unknown voltage on the RST line during power-up. In applications where the low voltage pull-down capability is important, the supply to which the external pull-up resistor connects should be the same supply which powers the part. Using the same supply for both ensures that RST never floats above 200mV during power-up, as the pulldown ability of the pin will then increase as the required pull-down current to maintain a logic low increases. Once VCC passes the UVLO threshold, polarity selection and timer initialization will occur. If the monitored supplies (ADJ1 and ADJ2) are valid, the appropriate timeout delay will begin, after which RST will be released. Otherwise, the part will wait until all supplies are valid (including VCC above the UVLO threshold) before beginning the timeout. Power-Down On power-down, once VCC drops below the UVLO threshold or either VADJ becomes invalid, RST asserts logic low. VCC of at least 0.5V guarantees a logic low of 0.15V at RST. Shunt Regulator The LTC2909 contains an internal 6.5V shunt regulator on the VCC pin to allow operation from a high voltage supply. To
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operate the part from a supply higher than 6V, the VCC pin must have a series resistor, RCC, to the supply. This resistor should be sized according to the following equation: VS(MAX ) - 6.2V 10mA RCC VS(MIN) - 6.8V 200A + IVREF where VS(MIN) and VS(MAX) are the operating minimum and maximum of the supply, and IVREF is the maximum current the user expects to draw from the reference output. As an example, consider operation from an automobile battery which might dip as low as 10V or spike to 60V. Assume that the user will be drawing 100A from the reference. We must then pick a resistance between 5.4k and 10.7k. When the VCC pin is connected to a low impedance supply, it is important that the supply voltage never exceed 6V, or the shunt regulator may begin to draw large currents. Some supplies may have nominal value sufficiently close to the shunt regulation voltage to prevent sizing of the resistor according to the above equation. For such supplies, a 470 series resistor may be used. Polarity Selection The external connection of the SEL pin selects the polarities of the LTC2909 adjustable inputs. SEL may be connected to GND, connected to VCC or left unconnected during normal operation. When left unconnected, the maximum leakage allowable from the pin to either GND or VCC is 10A. Table 1 shows the three possible selections of polarity based on SEL connection.
Table 1. Voltage Threshold Selection
ADJ1 INPUT Positive Polarity (+) UV or (-) OV Positive Polarity (+) UV or (-) OV Negative Polarity (-) UV or (+) OV ADJ2 INPUT Positive Polarity (+) UV or (-) OV Negative Polarity (-) UV or (+) OV Negative Polarity (-) UV or (+) OV SEL VCC Open Ground Note: Open = open circuit or driven by a three-state buffer in high impedance state with leakage current less than 10A.
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If the user's application requires, the SEL pin may be driven using a three-state buffer which satisfies the VIL, VIH and leakage of the three-state pin.
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LTC2909 APPLICATIO S I FOR ATIO
If the state of the SEL pin configures a given input as "negative polarity," the voltage at the ADJx pin must be below the trip point (0.5V nominal), or the RST output will be pulled low. Conversely, if a given input is configured as "positive polarity," the pin voltage must be above the trip point or RST will assert low. Thus, a "negative polarity" input may be used to determine whether a monitored negative voltage is smaller in absolute value than it should be (-UV), or a monitored positive voltage is larger than it should be (+OV). The opposite is true for a "positive polarity" input (-OV or +UV). These usages are also shown in Table 1. For purposes of this
Table 2a. Possible Combinations of Supply Monitoring. For Example Purposes, All Supplies are Monitored at 5% Tolerance and Connections are Shown Only for ADJ1, ADJ2, REF, SEL
SEL = VCC
15V (UV) 5V (UV) RP2A 3.09M RP2B 1.15M ADJ1 ADJ2 RP1A 115k RP1B 137k REF SEL RN1A 107k RN1B 133k REF RN2A 3.09M
2 Positive UV
-15V (OV) -5V (OV) RN2A 10.2M RN2B 1.37M ADJ1 ADJ2 RN1A 309k RN1B 118k REF SEL RP1A 200k
2 Negative OV
15V (UV) -15V (OV) RP2 3.09M RN2 10.2M ADJ1 ADJ2 RP1 115k RN1 309k REF SEL RP1 200k
1 Positive UV, 1 Negative OV
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data sheet, a negative voltage is considered "undervoltage" if it is closer to ground than it should be (e.g., -4.3V for a -5V supply). Proper configuration of the SEL pin and setting of the trip-points via external resistors allows for any two fault conditions to be detected. For example, the LTC2909 may monitor two supplies (positive, negative or one of each) for UV or for OV (or one UV and one OV). It may also monitor a single supply (positive or negative) for both UV and OV. Tables 2a and 2b show example configurations for monitoring possible combinations of fault condition and supply polarity.
SEL = GND
-15V (UV) -5V (UV) RN2B 1.37M ADJ1 ADJ2 SEL
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15V (OV) 5V (OV) RP2A 6.19M RP2B 1.33M ADJ1 ADJ2 RP1B 137k REF SEL
2 Positive OV
15V (OV) -15V (UV) RP2 6.19M RN2 3.09M ADJ1 ADJ2 RN1 107k REF SEL
1 Positive OV, 1 Negative UV
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LTC2909 APPLICATIO S I FOR ATIO
Table 2b. Possible Combinations of Supply Monitoring. For Example Purposes, All Supplies are Monitored at 5% Tolerance and Connections are Shown Only for ADJ1, ADJ2, REF, SEL
SEL OPEN
15V (UV/OV) RP6 2.37M RP5 10.7k RP4 76.8k REF ADJ1 ADJ2 SEL RN4 309k REF RN5 40.2k -15V (UV/OV) RN6 10.2M ADJ1 ADJ2 SEL
1 Positive UV and OV
15V (UV) -15V (UV) RP2 3.09M RN2 3.09M ADJ1 ADJ2 RP1 115k RN1 107k REF SEL RN1 309k
1 Positive UV, 1 Negative UV
15V (UV) 5V (OV) RP2A 3.09M RP2B 1.33M ADJ1 ADJ2 RP1A 115k RP1B 137k REF SEL
1 Positive UV, 1 Positive OV
Adjust Input Trip Point The trip threshold for the supplies monitored by the adjustable inputs is set with an external resistor divider, allowing the user complete control over the trip point. Selection of this trip voltage is crucial to the reliability of the system. Any power supply has some tolerance band within which it is expected to operate (e.g., 5V 10%). It is generally undesirable that a supervisor issue a reset when the power supply is inside this tolerance band. Such a "nuisance" reset reduces reliability by preventing the system from functioning under normal conditions. To prevent nuisance resets, the supervisor threshold must be guaranteed to lie outside the power supply tolerance
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1 Negative UV and OV
-15V (OV) 15V (OV) RN2 10.2M RP2 6.19M ADJ1 ADJ2 RP1 200k REF SEL
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1 Negative OV, 1 Positive OV
-15V (OV) -5V (UV) RN2A 10.2M RN2B 1.37M ADJ1 ADJ2 RN1A 309k RN1B 133k REF SEL
1 Negative UV, 1 Negative OV
band. To ensure that the threshold lies outside the power supply tolerance range, the nominal threshold must lie outside that range by the monitor's accuracy specification. All three of the LTC2909 inputs (ADJ1, ADJ2, VCC UVLO) have the same relative threshold accuracy of 1.5% of the programmed nominal input voltage (over the full operating temperature range). Therefore, using the LTC2909, the typical 10% UV threshold is at 11.5% below the nominal input voltage level. For a 5V input, the threshold is nominally 4.425V. With 1.5% accuracy, the trip threshold range is 4.425V 75mV over temperature (i.e., 10% to 13% below 5V). The monitored system must thus operate reliably down to 4.35V or 13% below 5V over temperature.
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LTC2909 APPLICATIO S I FOR ATIO
The above discussion is concerned only with the DC value of the monitored supply. Real supplies also have relatively high frequency variation from sources such as load transients, noise and pickup. These variations should not be considered by the monitor in determining whether a supply voltage is valid or not. The variations may cause spurious outputs at RST, particularly if the supply voltage is near its trip threshold. A common solution to the problem of spurious reset is to introduce hysteresis around the nominal threshold. However, this hysteresis degrades the effective accuracy of the monitor and increases the range over which the system must operate. The LTC2909 therefore does not have hysteresis, except in comparator mode (see Setting the Reset Timeout). If hysteresis is desired in other modes, it may be added externally. See Typical Applications for an example. The LTC2909 uses two techniques to combat spurious reset without sacrificing threshold accuracy. First, the timeout period helps prevent high frequency variation whose frequency is above 1/ tRST from appearing at the RST output. When either ADJ1 or ADJ2 becomes invalid, the RST pin asserts low. When the supply recovers past the threshold, the reset timer starts (assuming it is not disabled) and RST does not go high until it finishes. If the supply becomes invalid any time during the timeout period, the timer resets and starts fresh when the supply next becomes valid. While the reset timeout is useful at preventing toggling of the reset output in most cases, it is not effective at preventing nuisance resets due to short glitches (from load transients or other effects) on a valid supply. To reduce sensitivity to these short glitches, the comparator outputs go through a lowpass filter before triggering the output logic. Any transient at the input of a comparator needs to be of sufficient magnitude and duration to pass the filter before it can change the monitor state. The combination of the reset timeout and comparator filtering prevents spurious changes in the output state without sacrificing threshold accuracy. If further supply glitch immunity is needed, the user may place an external capacitor from the ADJ input to ground. The resultant RC
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lowpass filter with the resistor divider will further reject high frequency components of the supply, at the cost of slowing the monitor's response to fault conditions. Selecting External Resistors In a typical positive supply monitoring application, the ADJx pin connects to a tap point on an external resistive divider between a positive voltage being monitored and ground, as shown in Figure 1. When monitoring a negative supply, the ADJx pin connects to a tap point on a resistive divider between the negative voltage being monitored and the buffered reference (REF), as shown in Figure 2.
VMON RP2 ADJx
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+ -
RP1
0.5V
+ -
2909 F01
Figure 1. Setting Positive Supply Trip Point
REF RN1 ADJx
+ -
RN2 VMON 0.5V
+ -
2909 F02
Figure 2. Setting Negative Supply Trip Point
Normally the user will select a desired trip voltage based on their supply and acceptable tolerances, and a value of RN1 or RP1 based on current draw. Current used by the resistor divider will be approximately: I= 0.5V R X1
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Recommended range is 1k to 1M.
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LTC2909 APPLICATIO S I FOR ATIO
RP2 = RP1(2VTRIP - 1) For a negative-monitoring application: RN2 = RN1(1 - 2VTRIP) Note that the value VTRIP should be negative for a negative application. The LTC2909 can also be used to monitor a single supply for both UV and OV. This may be accomplished with three resistors, instead of the four required for two independent supplies. Configurations are shown in Figures 3 and 4. RP4 or RN4 may be chosen as is RP1 above. For a given RP4, monitoring a positive supply: RP5 = RP 4 VOV - VUV VUV VOV VUV
RN4
For a positive-monitoring application, RP2 is then chosen by:
RP6 = RP 4 ( 2VUV - 1)
For monitoring a negative supply with a given RN4: RN5 = RN4 VUV - VOV 1 - VUV 1 - VOV 1 - VUV
RN6 = RN4 (1 - 2VUV )
For example, consider monitoring a -5V supply at 10%. For this supply application: VOV = -5.575V and VUV = -4.425V.
ADJ1 VMON RP6
+ -
RP5
ADJ2
+ -
RP4
0.5V
+ -
2909 F03
Figure 3. Setting UV and OV Trip Point for a Positive Supply
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REF ADJ1
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+ -
RN5
ADJ2
+ -
RN6 VMON 0.5V
+ -
2909 F04
Figure 4. Setting UV and OV Trip Point for a Negative Supply
Suppose we wish to consume about 5A in the divider, so RN4 = 100k. We then find RN5 = 21.0k, RN6 = 1.18M (nearest 1% standard values have been chosen). Suggested values of resistors for 5% monitoring are shown in Table 3.
VCC Monitoring/UVLO The LTC2909 contains an accurate third 10% undervoltage monitor on the VCC pin. This monitor is fixed at a nominal 11.5% below the VCC specified in the part number. The standard part (LTC2909-2.5) is configured to monitor a 2.5V supply (UVLO threshold of 2.213V), but versions to monitor 3.3V and 5.0V (UVLO of 2.921V and 4.425V, respectively) are available. For applications that do not need VCC monitoring, the 2.5V version should be used, and the UVLO will simply guarantee that the VCC is above the minimum required for proper threshold and timer accuracy before the timeout begins. Setting the Reset Timeout The reset timeout of the LTC2909 may be configured in one of three ways: internal 200ms, programmed by external capacitor and no timeout (comparator mode). The mode of the timer is determined by the connection of the TMR pin. In externally-controlled mode, the TMR pin is connected by a capacitor to ground. The value of that capacitor allows for selection of a timeout ranging from about 400s to 10 seconds. See the following section for details.
2909fa
LTC2909 APPLICATIO S I FOR ATIO
5% UV NOMINAL RX1 VOLTAGE 24 232k 15 115k 12 49.9k 9 115k 5 137k 3.3 221k 2.5 115k 1.8 63.4k 1.5 59.0k 1.2 127k 1 200k -5 133k -9 97.6k -12 107k -15 107k Trip points are nominal voltage 6.5%. RX2 10.2M 3.09M 1.07M 1.82M 1.15M 1.15M 422k 150k 107k 158k 174k 1.37M 1.74M 2.49M 3.09M
Table 3. Suggested Resistor Values for 5% Monitoring
5% OV RX1 102k 200k 102k 78.7k 137k 340k 51.1k 115k 137k 102k 100k 118k 115k 40.2k 309k RX2 5.11M 6.19M 2.49M 1.43M 1.33M 2.05M 221k 324k 301k 158k 113k 1.37M 2.32M 1.07M 10.2M RX4 82.5k 76.8k 76.8k 162k 76.8k 76.8k 137k 82.5k 76.8k 187k 107k 174k 182k 40.2k 309k 5% UV and OV RX5 11.5k 10.7k 10.7k 22.6k 10.7k 10.7k 19.1k 11.5k 10.7k 26.1k 15.0k 20.0k 22.6k 5.11k 40.2k RX6 4.12M 2.37M 1.87M 2.94M 732k 453k 576k 221k 158k 267k 105k 2.00M 3.65M 1.07M 10.2M
If the user wishes to avoid having an external capacitor, the TMR pin should be tied to ground, switching the part to an internal 200ms timer. If the user requires a shorter timeout than 400s, or wishes to perform application-specific processing of the reset output, the part may be put in comparator mode by tying the TMR pin to VCC. In comparator mode, the timer is bypassed and comparator outputs go straight to the reset output. The current required to hold TMR at ground or VCC is about 2A. To force the pin from the floating state to ground or VCC may require as much as 100A during the transition. When the part is in comparator mode, one of the two means of preventing false reset has been removed, so a small amount of one-sided hysteresis is added to the inputs to prevent oscillation as the monitored voltage passes through the threshold. This hysteresis is such that the valid-to-invalid transition threshold is unchanged, but the invalid-to-valid threshold is moved by about 0.7%. Thus, when the ADJ input polarity is positive, the threshold voltage is 500mV nominal when the input is above 500mV. As soon as the input drops below 500mV, the threshold moves up to 503.5mV nominal. Conversely, when configured as a negative-polarity input,
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the threshold is 500mV when the input is below 500mV, and switches to 496.5mV when the input goes above 500mV. The comparator mode feature should be enabled by directly shorting the TMR pin to the VCC pin. Connecting the pin to any other voltage may have unpredictable results. Selecting the Reset Timing Capacitor Connecting a capacitor, CTMR, between the TMR pin and ground sets the reset timeout, tRST. The following formula approximates the value of capacitor needed for a particular timeout: CTMR = tRST * 110 [pF/ms] Leaving the TMR pin open with no external capacitor generates a reset timeout of approximately 400s. Maximum length of the reset timeout is limited by the ability of the part to charge a large capacitor on start-up. Initially, with a large (discharged) capacitor on the TMR pin, the part will assume it is in internal timer mode (since the pin voltage will be at ground). If the 2A flowing out of the TMR pin does not charge the capacitor to the groundsense threshold within the first 200ms after supplies become good, the internal timer cycle will complete and RST will go high too soon.
2909fa
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13
LTC2909 APPLICATIO S I FOR ATIO
This imposes a practical limit of 1F (9 second timeout) if the length of timeout during power-up needs to be longer than 200ms. If the power-up timeout is not important, larger capacitors may be used, subject to the limitation that the capacitor leakage current must not exceed 500nA, or the function of the timer will be impaired. RST Output Characteristics The DC characteristics of the RST pull-down strength are shown in the Typical Performance Characteristics section. RST is an open-drain pin and thus requires an external pull-up resistor to the logic supply. RST may be
TYPICAL APPLICATIO S
Six Supply Undervoltage Monitor with 2.5V Reset Output and 20ms Timeout
15V 5V -5V -15V 3.3V 2.5V CBYP1 100nF RPU 10k CBYP2 100nF
RN2A 1.37M ADJ1 RN2B 3.09M RN1A 133k RN1B 107k ADJ2
VCC RST RST LTC2909-2.5 REF SEL
TMR GND CTMR1 CTMR2 2.2nF 2.2nF
48V Telecom UV/OV Monitor with Hysteresis
VIN 36V TO 72V SYSTEM CBYP 100nF 5V VCC ADJ1 RST 10k* MANUAL RESET PUSHBUTTON RN2 2.49M -12V
2909 TA03
RP2A 1.43M M2 RP2A2 169k
RP2B 1.91M
RCC 27k 0.25W
VUV(RISING): 43.3V VUV(FALLING): 38.7V VOV(RISING): 71.6V VOV(FALLING): 70.2V
LTC2909-2.5 ADJ2 RP1A 18.7k RP1B 13.7k M1 RP1B2 681k REF GND TMR SEL
M1, M2: FDG6301N OR SIMILAR IF LOADING OF RST WILL EXCEED 1nF, A 1nF BYPASS CAPACITOR ON M1's DRAIN IS RECOMMENDED
14
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pulled above VCC, providing the voltage limits of the pin are observed. The open-drain nature of the RST pin allows for wired-OR connection of several LTC2909s to monitor more than two supplies (see Typical Applications). Other logic with opendrain outputs may also connect to the RST line, allowing other logic-determined conditions to issue a reset. As noted in the discussion of power up and power down, the circuits that drive RST are powered by VCC. During a fault condition, VCC of at least 0.5V guarantees a VOL of 0.15V at RST .
SYSTEM VCC ADJ1 RP1A 137k RP1B 115k TMR GND ADJ2
2909 TA02
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RP2A 1.15M RP2B 3.09M
LTC2909-3.3 SEL REF
12V UV Monitor Powered from 12V, 20ms Timeout (1.8V Logic Out)
RCC 10k CBYP 100nF 1.8V RP2 1.07M ADJ1 RP1 49.9k RN1 107k VCC RST RPU 10k
RPU 10k
12V
FAULT OUTPUT
LTC2909-2.5 REF ADJ2 GND
2909 TA01b
SEL TMR CTMR 2.2nF
*OPTIONAL FOR ESD
2909fa
LTC2909 PACKAGE DESCRIPTIO U
DDB Package 8-Lead Plastic DFN (3mm x 2mm)
(Reference LTC DWG # 05-08-1702)
0.61 0.05 (2 SIDES) 0.675 0.05 2.50 0.05 1.15 0.05 PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.20 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE PIN 1 BAR TOP MARK (SEE NOTE 6) 2.00 0.10 (2 SIDES) 3.00 0.10 (2 SIDES) R = 0.115 TYP 5 0.56 0.05 (2 SIDES) 0.38 0.10 8 0.200 REF 0.75 0.05 4 0.25 0.05 2.15 0.05 (2 SIDES) BOTTOM VIEW--EXPOSED PAD 1 PIN 1 CHAMFER OF EXPOSED PAD
(DDB8) DFN 1103
0.50 BSC
0 - 0.05
TS8 Package 8-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1637)
0.52 MAX 0.65 REF 2.90 BSC (NOTE 4)
1.22 REF
3.85 MAX 2.62 REF
1.4 MIN
2.80 BSC
1.50 - 1.75 (NOTE 4) PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR
0.65 BSC
0.22 - 0.36 8 PLCS (NOTE 3)
0.80 - 0.90 0.20 BSC 1.00 MAX DATUM `A' 0.01 - 0.10
0.30 - 0.50 REF 0.09 - 0.20 (NOTE 3) NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193
1.95 BSC
TS8 TSOT-23 0802
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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.
15
LTC2909 TYPICAL APPLICATIO
D1: 1N5238B OR SIMILAR Q1, Q2: FFB2227 OR SIMILAR RS 0.01 M1 IRLZ34
Automotive Supply System with Overvoltage, Overcurrent and Overtemperature Protection and Undervoltage Reset
DC/DC DC/DC 2.5V 3.3V
VIN 12V
RG2 10 D1
2N6507
Q1 Q2 RL2 100k RPU1 4.7k RST VCC
RG1 1k CBYP1 100nF VCC GND SENSE GATE TIMER ON FB CT 680nF PWRGD LT1641-2 CG 10nF
RFB2 100k
RFB1 10k
CIRCUIT BREAKER AND CROWBAR
RELATED PARTS
PART NUMBER LTC1326/LTC1326-2.5 LTC1536 LTC1540 DESCRIPTION Micropower Precision Triple Supply Monitor for 5V/2.5V, 3.3V and ADJ Precision Triple Supply Monitor for PCI Applications Nanopower Comparator with Reference COMMENTS 4.725V, 3.118V, 1V Threshold (0.75%) Meets PCI tFAIL Timing Specifications Adjustable Hysteresis Adjustable Reset and Watchdog Time-Outs Individual Monitor Outputs in MSOP/5-Lead SOT-23 5-Lead SOT-23 Package Adjustable Reset, 10-Lead MSOP and 3mm x 3mm 10-Lead DFN Package Adjustable Reset and Watchdog Timer, 16-Lead SSOP Package Adjustable Reset and Tolerance, 16-Lead SSOP Package, Margining Functions 6-Lead SOT-23 Package, Ultralow Voltage Reset Adjustable Tolerance and Reset Timer, 8-Lead SOT-23 Package Separate VCC Pin, RST/RST Outputs/Adjustable Reset Timer 8-Lead SOT-23 and DDB Packages 6-Lead SOT-23 Package
LTC1726-2.5/LTC1726-5 Micropower Triple Supply Monitor for 2.5V/5V, 3.3V and ADJ LTC1727/LTC1728 LTC1985-1.8 LTC2900 LTC2901 LTC2902 LTC2903 LTC2904/LTC2905 LTC2906/LTC2907 LTC2908 LT6700 Micropower Triple Supply Monitor with Open-Drain Reset Micropower Triple Supply Monitor with Push-Pull Reset Output Programmable Quad Supply Monitor Programmable Quad Supply Monitor Programmable Quad Supply Monitor Precision Quad Supply Monitor 3-State Programmable Precision Dual Supply Monitor Precision Dual Supply Monitor 1-Selectable and 1 Adjustable Precision Six Supply Monitor (Four Fixed and 2 Adjustable) Micropower, Low Voltage, Dual Comparator with 400mV Reference
16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2005
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SYSTEM RL1 4.7k CBYP3 100nF RCC 4.7k RP2A 2.49M RP2B 2.05M CBYP2 100nF ADJ1 RST RP2C 221k RP2D 1.07M RP2E 1.15M VCC ADJ1 RREF 10.7k NTC THERMISTOR NTHS-1206N01 R25 = 100k R = 10.7k AT 85C RP1D 49.9k ADJ1 LTC2909-2.5 SEL REF VCC SEL LTC2909-2.5 REF RST RPU2 10k LTC2909-2.5 SEL REF TMR GND ADJ2 RP1A 102k RP1B 340k TMR GND ADJ2 RP1C 51.1k ADJ2 RP1E 221k GND
2909 TA05
TMR
12V OV AND 3.3V OV DETECT
2.5V OV AND T > 85C DETECT
12V, 3.3V and 2.5V UV DETECT
2909fa LT 0606 REV A * PRINTED IN USA

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