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FEATURES
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LTC2904/LTC2905 Precision Dual Supply Monitors with Pin-Selectable Thresholds DESCRIPTION
The LTC(R)2904/LTC2905 are dual supply monitors intended for systems with two supply voltages. The dual supply monitors have a common reset output with delay (200ms for the LTC2904 and adjustable using an external capacitor for the LTC2905). This product provides a precise, space-conscious and micropower solution for supply monitoring. The LTC2904/LTC2905 feature a tight 1.5% threshold accuracy over the whole operating temperature range, and glitch immunity to ensure reliable reset operation without false triggering. The open drain RST output is guaranteed to be in the correct state for inputs down to 1V. The LTC2904/LTC2905 also feature three programming input pins, which program the threshold and tolerance level without requiring any external components. These three programming pins provide a total of 27 different voltage level and tolerance combinations, eliminating the need to have different parts for development and implementation of different systems with different voltage levels requiring monitoring function.
Monitors Two Inputs Simultaneously Nine Threshold Combinations Three Supply Tolerances (5%, 7.5%, 10%) Guaranteed Threshold Accuracy: 1.5% of Monitored Voltage Over Temperature Internal VCC Auto Select Power Supply Glitch Immunity 200ms Reset Time Delay (LTC2904 Only) Adjustable Reset Time Delay (LTC2905 Only) Open Drain RST Output Guaranteed RST for V1 1V or V2 1V Low Profile (1mm) SOT-23 (ThinSOTTM) and Plastic (3mm x 2mm) DFN Packages
APPLICATIONS
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Desktop and Notebook Computers Handheld Devices Network Servers Core, I/O Monitor
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
5V, 3.3V Dual Supply Monitor with 5% Tolerance
DC/DC CONVERTER 5V 3.3V SYSTEM LOGIC
Table 1. Voltage Threshold Programming
V1 5.0 3.3 3.3 V2 3.3 2.5 1.8 1.5 1.2 1.8 1.5 1.2 1.0 S1 V1 Open V1 Open Open GND GND GND V1 S2 V1 GND Open V1 Open GND Open V1 GND
V1 0.1F S1 S2 TOL LTC2905
V2 0.1F TMR 22nF GND RST
3.3 3.3 2.5 2.5
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2.5 2.5
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LTC2904/LTC2905 ABSOLUTE MAXIMUM RATINGS
(Note 1, 2)
Terminal Voltages V1, V2 ...................................................... -0.3V to 7V S1, S2, TOL ................................-0.3V to (VCC +0.3V) RST .......................................................... -0.3V to 7V RST (LTC2904) ........................................ -0.3V to 7V TMR (LTC2905) ....................................... -0.3V to 7V
Operating Temperature Range LTC2904C/LTC2905C .............................. 0C to 70C LTC2904I/LTC2905I.............................-40C to 85C LTC2905H .......................................... -40C to 125C Storage Temperature Range .................. -65C to 150C TSOT Lead Temperature (Soldering, 10 sec) ......... 300C
PIN CONFIGURATION
TOP VIEW GND 1 RST 2 RST/TMR* 3 V2 4 9 8 7 6 5 TOL S1 S2 V1 V2 1 RST/TMR* 2 RST 3 GND 4 TOP VIEW 8 V1 7 S2 6 S1 5 TOL
DDB8 PACKAGE 8-LEAD (3mm 2mm) PLASTIC DFN EXPOSED PAD IS GND (PIN 9), MUST BE SOLDERED TO PCB * RST FOR LTC2904 TMR FOR LTC2905 TJMAX = 150C, JA = 76C/W
TS8 PACKAGE 8-LEAD PLASTIC TSOT-23 * RST FOR LTC2904 TMR FOR LTC2905 TJMAX = 150C, JA = 195C/W
ORDER INFORMATION
Lead Free Finish
TAPE AND REEL (MINI) LTC2904CDDB#TRMPBF LTC2904IDDB#TRMPBF LTC2905CDDB#TRMPBF LTC2905HDDB#TRMPBF LTC2905IDDB#TRMPBF LTC2904CTS8#TRMPBF LTC2904ITS8#TRMPBF LTC2905CTS8#TRMPBF LTC2905HTS8#TRMPBF TAPE AND REEL LTC2904CDDB#TRPBF LTC2904IDDB#TRPBF LTC2905CDDB#TRPBF LTC2905HDDB#TRPBF LTC2905IDDB#TRPBF LTC2904CTS8#TRPBF LTC2904ITS8#TRPBF LTC2905CTS8#TRPBF LTC2905HTS8#TRPBF PART MARKING* LBCZ LBDB LAJF LBCY LBCY LTBCJ LTBCK LTAJD LTAJE PACKAGE DESCRIPTION 8-Lead (3mm x 2mm) Plastic DFN 8-Lead (3mm x 2mm) Plastic DFN 8-Lead (3mm x 2mm) Plastic DFN 8-Lead (3mm x 2mm) Plastic DFN 8-Lead (3mm x 2mm) Plastic DFN 8-Lead Plastic TSOT-23 8-Lead Plastic TSOT-23 8-Lead Plastic TSOT-23 8-Lead Plastic TSOT-23 TEMPERATURE RANGE 0C to 70C -40C to 85C 0C to 70C -40C to 125C -40C to 85C 0C to 70C -40C to 85C 0C to 70C -40C to 125C -40C to 85C
LTC2905ITS8#TRMPBF LTC2905ITS8#TRPBF LTAJE 8-Lead Plastic TSOT-23 TRM = 500 pieces. *Temperature grades are identified by a label on the shipping container. Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
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LTC2904/LTC2905 ELECTRICAL CHARACTERISTICS
SYMBOL VRT50 PARAMETER 5V, 5% Reset Threshold 5V, 7.5% Reset Threshold 5V, 10% Reset Threshold 3.3V, 5% Reset Threshold 3.3V, 7.5% Reset Threshold 3.3V, 10% Reset Threshold 2.5V, 5% Reset Threshold 2.5V, 7.5% Reset Threshold 2.5V, 10% Reset Threshold 1.8V, 5% Reset Threshold 1.8V, 7.5% Reset Threshold 1.8V, 10% Reset Threshold 1.5V, 5% Reset Threshold 1.5V, 7.5% Reset Threshold 1.5V, 10% Reset Threshold 1.2V, 5% Reset Threshold 1.2V, 7.5% Reset Threshold 1.2V, 10% Reset Threshold 1V, 5% Reset Threshold 1V, 7.5% Reset Threshold 1V, 10% Reset Threshold Minimum Internal Operating Voltage (Note 2) V1 Input Current V2 Input Current TMR Pull-Up Current TMR Pull-Down Current Reset Timeout Period Reset Timeout Period LTC2905 LTC2905 LTC2905H LTC2904 LTC2905 LTC2905H
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. V1 = 2.5V, V2 = 1V, S1 = TOL = V1, S2 = 0V, unless otherwise noted. (Notes 2, 3)
CONDITIONS V1 Input Threshold
l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l
VRT33
V1, V2 Input Threshold
VRT25
V1, V2 Input Threshold
VRT18
V2 Input Threshold
VRT15
V2 Input Threshold
VRT12
V2 Input Threshold
VRT10
V2 Input Threshold RST in Correct Logic State Includes Input Current to Three-State Pins VTMR = 0V VTMR = 1.4V
MIN 4.600 4.475 4.350 3.036 2.954 2.871 2.300 2.238 2.175 1.656 1.611 1.566 1.380 1.343 1.305 1.104 1.074 1.044 0.920 0.895 0.870
TYP 4.675 4.550 4.425 3.086 3.003 2.921 2.338 2.275 2.213 1.683 1.638 1.593 1.403 1.365 1.328 1.122 1.092 1.062 0.935 0.910 0.885 65 0.4
VCCMIN IV1 IV2 ITMR(UP) ITMR(DOWN) tRST tRST tUV VOL VOH
MAX 4.750 4.625 4.500 3.135 3.053 2.970 2.375 2.313 2.250 1.710 1.665 1.620 1.425 1.388 1.350 1.140 1.110 1.080 0.950 0.925 0.900 1 130 1.0 -2.7 2.7 2.7 260 260 295
UNITS V V V V V V V V V V V V V V V V V V V V V V A A A A A ms ms ms s V V V
-1.5 1.5 1.4 140 140 140
-2.1 2.1 2.0 200 200 150
CTMR = 22nF Vx Less than Reset Threshold VRTX by More than 1% I = 2.5mA I = 100A; V1 = 1V (RST Only) I = -1A
Vx Undervoltage Detect to RST or RST Output Voltage Low RST, RST
l l l
0.15 0.05 VCC-1
0.4 0.3
Output Voltage High RST, RST (Notes 2, 5) Three-State Inputs S1, S2, TOL VIL Low Level Input Voltage VIH High Level Input Voltage VZ Pin Voltage When Left in Open State
l l
0.4 1.4 0.7 0.9 1.1 0.65 0.9 1.15 25
2905H
I = -10A I = 0A I = 10A I = -10A I = 0A I = 10A
l l l l l
IVPG
Programming Input Current (Note 6)
V V V V V V V V A
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LTC2904/LTC2905 ELECTRICAL CHARACTERISTICS
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: The greater of V1, V2 is the internal supply voltage (VCC). Note 3: All currents into pins are positive; all voltages are referenced to GND unless otherwise noted. Note 4: For reset thresholds test conditions refer to the voltage threshold programming table in the Applications Information section. Note 5: The output pins RST and RST have an internal pull-up to VCC of typically -6A. However, an external pull-up resistor may be used when faster rise time is required or for VOH voltages greater than VCC. Note 6: The input current to the three-state input pins are the pull-up and the pull-down current when the pins are either set to V1 or GND respectively. In the open state, the maximum leakage current to V1 or GND permissible is 10A.
TYPICAL PERFORMANCE CHARACTERISTICS
Specifications are at TA = 25C unless otherwise noted. 5V Threshold Voltage vs Temperature
4.75 THRESHOLD VOLTAGE, VRT50 (V) THRESHOLD VOLTAGE, VRT33 (V) 4.70 4.65 4.60 4.55 4.50 4.45 4.40 4.35 -50 -25 25 50 0 TEMPERATURE ( C) 75 100
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3.3V Threshold Voltage vs Temperature
3.120 5% 3.070 THRESHOLD VOLTAGE, VRT25 (V) 2.375
2.5V Threshold Voltage vs Temperature
5% 2.325 7.5% 2.275
5%
3.020
7.5%
7.5%
2.970 10% 2.920
10%
2.225
10%
2.870 -50
-25
25 50 0 TEMPERATURE ( C)
75
100
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2.175 -50
-25
25 50 0 TEMPERATURE ( C)
75
100
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1.8V Threshold Voltage vs Temperature
1.705 THRESHOLD VOLTAGE, VRT18 (V) THRESHOLD VOLTAGE, VRT15 (V) 1.685 1.665 1.645 1.625 1.605 1.585 1.565 -50 10% 7.5% 5% 1.405 1.385 1.425
1.5V Threshold Voltage vs Temperature
1.135 THRESHOLD VOLTAGE, VRT12 (V) 5% 1.125 1.115 1.105 1.095 1.085 1.075 1.065 1.055 -25 25 50 0 TEMPERATURE ( C) 75 100
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1.2V Threshold Voltage vs Temperature
5%
7.5% 1.365 1.345 10% 1.325 1.305 -50
7.5%
10%
-25
25 50 0 TEMPERATURE ( C)
75
100
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1.045 -50
-25
25 50 0 TEMPERATURE ( C)
75
100
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LTC2904/LTC2905 TYPICAL PERFORMANCE CHARACTERISTICS
Specifications are at TA = 25C unless otherwise noted. 1V Threshold Voltage vs Temperature
0.950 THRESHOLD VOLTAGE, VRT10 (V) 0.940 0.930 0.920 IV1 ( A) 0.910 0.900 0.890 0.880 0.870 -50 -25 25 50 0 TEMPERATURE ( C) 75 100
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IV1 vs Temperature
21.5 V1 = 5V V2 = 3.3V S1 = S2 = TOL = 1.4V 1.8 1.7 1.6
IV2 vs Temperature
V1 = 5V V2 = 3.3V S1 = S2 = TOL = 1.4V
5% 21.0
7.5%
IV2 ( A) 25 50 0 TEMPERATURE ( C)
20.5
1.5 1.4
20.0
10%
19.5
1.3 1.2 -50
19.0 -50
-25
75
100
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-25
25 50 0 TEMPERATURE ( C)
75
100
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IV2 vs Temperature
20.0 19.5 19.0 IV2 ( A) 18.5 18.0 17.5 17.0 -50 700 TYPICAL TRANSIENT DURATION ( s) V1 = 2.5V V2 = 3.3V S1 = S2 = TOL = 1.4V 600 500 400 300 200 100 0 -25 25 50 0 TEMPERATURE ( C) 75 100
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Typical Transient Duration vs Comparator Overdrive (V1, V2)
10000 RESET TIME OUT PERIOD, tRST (ms)
Reset Time Out Period (tRST) vs Capacitance (CTMR)
1000
RESET OCCURS ABOVE CURVE
100
10
1
1 10 100 0.1 COMPARATOR OVERDRIVE VOLTAGE (% OF VRTX)
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0.1 10p
100p
1n 10n CTMR (FARAD)
100n
1
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Reset Timeout Period (tRST) vs Temperature
235 RESET TIME-OUT PERIOD, tRST (ms) 5 CRT = 22nF 230 (FILM) 225 220 215 210 205 200 195 -50 -25 0 25 50 75 100
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RST Output Voltage vs V1
5 V2 = S1 = S2 = TOL = V1 10k PULL-UP RESISTOR 4 RST OUTPUT VOLTAGE (V) RST OUTPUT VOLTAGE (V) 3 2 1 0 -1
RST Output Voltage vs V1
V2 = S1 = S2 = TOL = V1 10k PULL-UP RESISTOR 4 3 2 1 0 -1
0
1
2 V1 (V)
3
4
5
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0
1
2 V1 (V)
3
4
5
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TEMPERATURE ( C)
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LTC2904/LTC2905 TYPICAL PERFORMANCE CHARACTERISTICS
Specifications are at TA = 25C unless otherwise noted. RST Output Voltage vs V1
5 RST PULL-DOWN CURRENT, IRST (mA) 4 RST OUTPUT VOLTAGE (V) 3 2 1 0 -1 RST PULL-DOWN CURRENT, IRST (mA) V2 = S1 = S2 = TOL = V1 10pF CAPACITOR AT RST 5 4 RST AT 150mV 3 2 1 0 0 1 2 3 4 SUPPLY VOLTAGE, VCC (V) 5
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RST Pull-Down Current (IRST) vs Supply Voltage (VCC)
V2 = S1 = S2 = TOL = V1 NO PULL-UP R 5 4
RST Pull-Down Current (IRST) vs Supply Voltage (VCC)
S1 = V2 = V1 TOL = S2 = GND NO PULL-UP R
RST AT 150mV 3 2 1 0 0 1 2 3 4 SUPPLY VOLTAGE, VCC (V) 5
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RST AT 50mV
RST AT 50mV
0
1
2 V1 (V)
3
4
5
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RST Output Voltage Low (VOL) vs RST Pull-Down Current (IRST)
1.8 RST OUTPUT VOLTAGE LOW, VOL (V) 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0 10 30 40 50 20 RST PULL-DOWN CURRENT, IRST (mA) 60 RST OUTPUT VOLTAGE LOW, VOL (V) V1 = 5V V2 = 3V S1 = S2 = TOL = V1 NO PULL-UP R 1.8 85 C 25 C 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0
RST Output Voltage Low (VOL) vs RST Pull-Down Current (IRST)
-18 RST PULL-UP CURRENT, IRST ( A) V1 = 5V V2 = 3.3V S1 = S2 = TOL = V1 NO PULL-UP R 85 C 25 C -16 -14 -12 -10 -8 -6 -4 -2
RST Pull-Up Current (IRST) vs Supply Voltage (VCC)
TOL = GND
-40 C
-40 C
VRT25 0 0 10 30 40 50 60 20 RST PULL-DOWN CURRENT, IRST (mA)
29045 G20
VRT33
VRT50 5.0
2.0
2.5
3.0 3.5 4.0 4.5 SUPPLY VOLTAGE, VCC (V)
29045 G19
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RST Pull-Up Current (IRST) vs Supply Voltage (VCC)
-16 RST PULL-UP CURRENT, IRST ( A) -14 -12 -10 -8 -6 -4 -2 0 2.0 VRT25 2.5 VRT33 VRT50 5.0 3.0 3.5 4.0 4.5 SUPPLY VOLTAGE, VCC (V) 3.0 TOL = V1 RST OUTPUT VOLTAGE HIGH, VOH (V) 2.5
RST Output Voltage High (VOH) vs RST Output Source Current (IRST)
RST OUTPUT VOLTAGE HIGH, VOH (V) V1 = 3.3V V2 = 1.8V S1 = TOL =V1 S2 = OPEN NO PULL-UP R 3.5 3.0 2.5 2.0
RST Output Voltage High (VOH) vs RST Output Source Current (IRST)
V1 = 3.3V V2 = 1.5V S1 = TOL = V1 S2 = OPEN NO PULL-UP R
2.0
1.5
85 C -40 C 25 C
-40 C 1.5 1.0 0.5 85 C 25 C
1.0
0.5 -12
-8 -6 -4 -2 -10 OUTPUT SOURCE CURRENT, IRST ( A)
0
-8
-7 -6 -5 -4 -3 -2 -1 OUTPUT SOURCE CURRENT, IRST ( A)
0
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LTC2904/LTC2905 TYPICAL PERFORMANCE CHARACTERISTICS
Specifications are at TA = 25C unless otherwise noted. IS1, IS2, ITOL vs Temperature
20 S1 = S2 = TOL = 3.3V 19 18 IS1, IS2, ITOL ( A) IS1, IS2, ITOL ( A) 17 16 15 14 13 12 11 10 -50 -25 25 50 0 TEMPERATURE ( C) 75 100
29045 G25
IS1, IS2, ITOL vs Temperature
-20 S1 = S2 = TOL = GND -19 -18 -17 -16 -15 -14 -13 -12 -11 -10 -50 -25 25 50 0 TEMPERATURE ( C) 75 100
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PIN FUNCTIONS
(TS8/DDB8)
V2 (Pin 1/Pin 4): Voltage Input 2. Input for V2 monitor. Select from 3.3V, 2.5V, 1.8V, 1.5V, 1.2V or 1.0V. Refer to Table 1 for details. The greater of V1, V2 is also the internal supply voltage, VCC. Bypass this pin to ground with a 0.1F (or greater) capacitor. RST (Pin 2/Pin 3): (LTC2904 Only) Reset Logic Output. When all voltage inputs are above the reset threshold for at least the programmed delay time, this pin pulls low. This pin has a weak pull-up to VCC and may be pulled above VCC using an external pull-up. TMR (Pin 2/Pin 3): (LTC2905 Only) Reset Delay Time Programming Pin. Attach an external capacitor (CTMR) to GND to set a reset delay time of 9ms/nF Leaving the pin . open generates a minimum delay of approximately 200s. A 22nF capacitor will generate a 200ms reset delay time. RST (Pin 3/Pin 2): Inverted Reset Logic Output. Pulls low when any voltage input is below the reset threshold and is held low for programmed delay time after all voltage inputs
are above threshold. This pin has a weak pull-up to VCC and may be pulled above VCC using an external pull-up. GND (Pin 4/Pin 1, Pin 9): Ground. TOL (Pin 5/Pin 8): Three-state Input for Supply Tolerance Selection (5%, 7.5% or 10%). See the Applications Information section for tolerance selection chart (Table 2). S1 (Pin 6/Pin 7): Voltage Threshold Select Three-State Input. Connect to V1, GND or leave unconnected in open state (See Table 1). S2 (Pin 7/Pin 6): The Second Voltage Threshold Select Three-State Input. Connect to V1, GND or leave unconnected in open state (See Table 1). V1 (Pin 8/Pin 5): Voltage Input 1. Input for V1 monitor. Select from 5V, 3.3V, or 2.5V. See Table 1 for details. The greater of V1, V2 is also the internal supply voltage, VCC. Bypass this pin to ground with a 0.1F (or greater) capacitor.
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LTC2904/LTC2905 BLOCK DIAGRAM
LTC2904 6A VCC
V1 VCC POWER DETECT RESISTOR NETWORK
V2 RST
BAND GAP REFERENCE
LTC2905
V1 VCC POWER DETECT RESISTOR NETWORK
V2
BAND GAP REFERENCE
8
+
+
+
200ms RESET PULSE GENERATOR 6A VCC
+
-
-
- -
THREE-STATE DECODER
2904 BD
RST
GND
S1
S2
TOL
TMR VCC 6A RESET PULSE GENERATOR RST
THREE-STATE DECODER
GND
2905 BD
S1
S2
TOL
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LTC2904/LTC2905 TIMING DIAGRAM
VX Monitor Timing
VRTX VX
tUV
tRST
RST
1V
RST
1V
29045 TD
APPLICATIONS INFORMATION
Supply Monitoring The LTC2904/LTC2905 are low power, high accuracy dual supply monitors with a common reset output and selectable thresholds. Reset delay is set to a nominal of 200ms for the LTC2904 and is adjustable using an external capacitor for the LTC2905. The two 3-state input pins (S1 and S2) select one of nine possible threshold voltage combinations. Another threestate input pin sets the supply tolerance (5%, 7.5% or 10%). Both input voltages (V1 and V2) must be above predetermined thresholds for the reset not to be invoked. The LTC2904/LTC2905 assert the reset outputs during power-up, power-down and brownout conditions on either of the voltage inputs. Power-Up The greater of V1, V2 is the internal supply voltage (VCC). VCC powers the drive circuits for the RST pin. Therefore as soon as V1 or V2 reaches 1V during power-up, the RST output asserts low. VCC also powers the drive circuits for the RST pin in the LTC2904. Therefore, RST weakly pulls high when V1 or V2 reaches at least 1V. Threshold programming is complete when V1 reaches at least 2.17V. After programming, if either V1 or V2 falls below its programmed threshold, RST asserts low (RST weakly pulls high) as long as VCC is at least 1V. Once V1 and V2 rise above their thresholds, an internal timer is started. After the programmed delay time, RST weakly pulls high (RST asserts low).
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LTC2904/LTC2905 APPLICATIONS INFORMATION
Power-Down On power-down, once either V1 or V2 inputs drops below its threshold, RST asserts logic low and RST weakly pulls high. VCC of at least 1V guarantees a logic low of 0.4V at RST. Programming Pins The three 3-state input pins: S1, S2 and TOL should be connected to GND, V1 or left unconnected during normal operation. Note that when left unconnected, the maximum leakage current allowable from the pin to either GND or V1 is 10A. In margining applications, all the 3-state input pins can be driven using a tri-state buffer. Note however the low and high output of the tri-state buffer has to satisfy the VIL and VIH of the 3-state pin listed in the Electrical Characteristics Table. Moreover, when the tri-state buffer is in the high impedance state, the maximum leakage current allowed from the pin to either GND or V1 is 10A. Monitor Programming Connecting S1 and S2 to GND, V1 or leaving them open selects the LTC2904/LTC2905 input voltage combinations. Table 1 shows the nine possible combinations of nominal input voltages and their corresponding S1, S2 connections.
Table 1. Voltage Threshold Programming
V1 5.0 3.3 3.3 3.3 3.3 2.5 2.5 2.5 2.5 V2 3.3 2.5 1.8 1.5 1.2 1.8 1.5 1.2 1.0 S1 V1 Open V1 Open Open GND GND GND V1 S2 V1 GND Open V1 Open GND Open V1 GND
Tolerance Programming The three-state input pin, TOL programs the common supply tolerance for both V1 and V2 input voltages (5%, 7.5% or 10%). The larger the tolerance the lower the trip threshold. Table 2 shows the tolerances selection corresponding to a particular connection at the TOL pin.
Table 2. Tolerance Programming
Tolerance 5% 7.5% 10% TOL V1 Open GND
Threshold Accuracy Reset threshold accuracy is of the utmost importance in a supply sensitive system. Ideally such a system should not reset while supply voltages are within a specified margin below the rated nominal level. Both of the LTC2904/LTC2905 inputs have the same relative threshold accuracy. The specification for LTC2904/LTC2905 is 1.5% of the programmed nominal input voltage (over the full operating temperature range). For example, when the LTC2904/LTC2905 are programmed to handle a 5V input with 10% tolerance (S1 = S2 = V1 and TOL = GND, refer to Table 1 and Table 2), it does not issue a reset command when V1 is above 4.5V. The typical 10% trip threshold is at 11.5% below the nominal input voltage level. Therefore, the typical trip threshold for the 5V input is 4.425V. With 1.5% accuracy, the trip threshold range is 4.425V 75mV over temperature (i.e. 10% to 13% below 5V). This implies that the monitored system must operate reliably down to 4.35V over temperature. The same system using a supervisor with only 2.5% accuracy needs to work reliably down to 4.25V (4.375V 125mV) or 15% below 5V, requiring the monitored system to work over a much wider operating voltage range.
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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LTC2904/LTC2905 APPLICATIONS INFORMATION
In any supervisory application, supply noise riding on the monitored DC voltage can cause spurious resets, particularly when the monitored voltage is near the reset threshold. A less desirable but common solution to this problem is to introduce hysteresis around the nominal threshold. Notice however, this hysteresis introduces an error term in the threshold accuracy. Therefore, a 2.5% accurate monitor with 1.0% hysteresis is equivalent to a 3.5% monitor with no hysteresis. The LTC2904/LTC2905 takes a different approach to solve this problem of supply noise causing spurious reset. The first line of defense against this spurious reset is a first order low pass filter at the output of the comparator. Thus, the comparator output goes through a form of integration before triggering the output logic. Therefore, any kind of transient at the input of the comparator needs to be of sufficient magnitude and duration before it can trigger a change in the output logic. The second line of defense is the programmed delay time tRST (200ms for LTC2904 and using an external capacitor for LTC2905). This delay will eliminate the effect of any supply noise whose frequency is above 1/tRST on the RST and RST output. When either V1 or V2 drops below its programmed threshold, the RST pin asserts low (RST weakly pulls high). Then when the supply recovers above the programmed threshold, the reset-pulse-generator timer starts counting. If the supply remains above the programmed threshold when the timer finishes counting, the RST pin weakly pulls high (RST asserts low). However, if the supply falls below the programmed threshold any time during the period when the timer is still counting, the timer resets and it starts fresh when the supply next rises above the programmed threshold. Note that this second line of defense is only effective for a rising supply and does not affect the sensitivity of the system to a falling supply. Therefore, the first line of defense that works for both cases of rising and falling is necessary. These two approaches prevent spurious reset caused by supply noise without sacrificing the threshold accuracy.
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Selecting the Reset Timing Capacitor The reset timeout period for LTC2905 is adjustable in order to accommodate a variety of microprocessor applications. Connecting a capacitor, CTMR, between the TMR pin and ground sets the reset timeout period, tRST. The following formula determines the value of capacitor needed for a particular reset timeout period: CTMR = tRST * 110 * 10-9 [F/s] For example, using a standard capacitor value of 22nF would give a 22000/110 = 200ms delay. Figure 1 shows the desired delay time as a function of the value of the timer capacitor that should be used: Leaving the TMR pin open with no external capacitor generates a reset timeout of approximately 200s. For long reset timeout, the only limitation is the availability of large value capacitor with low leakage. The TMR capacitor will never charge if the leakage current exceeds the minimum TMR charging current of 2.1A (typical).
10000 RESET TIME OUT PERIOD, tRST (ms)
1000
100
10
1
0.1 10p
100p
1n 10n CTMR (FARAD)
100n
1
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Figure 1. Reset Timeout Period vs Capacitance
11
LTC2904/LTC2905 APPLICATIONS INFORMATION
RST and RST Output Characteristics The DC characteristics of the RST and RST pull-up and pull-down strength are shown in the Typical Performance Characteristics section. Both RST and RST have a weak internal pull-up to VCC = Max (V1, V2) and a strong pulldown to ground. The weak pull-up and strong pull-down arrangement allow these two pins to have open-drain behavior while possessing several other beneficial characteristics. The weak pull-ups eliminate the need for external pull-up resistors when the rise time on these pins is not critical. On the other hand, the open-drain RST configuration allows for wired-OR connections and can be useful when more than one signal needs to pull down on the RST line. As noted in the Power-Up and Power-Down sections the circuits that drive RST and RST are powered by VCC. During fault condition, VCC of at least 1V guarantees a maximum VOL = 0.4V at RST. However, at VCC = 1V the weak pull-up current on RST is barely turned on. Therefore, an external pull-up resistor of no more than 100k is recommended on the RST pin if the state and pull-up strength of the RST pin is crucial at very low VCC. Note however, by adding an external pull-up resistor, the pull-up strength on the RST pin is increased. Therefore, if it is connected in a wired-OR connection, the pull-down strength of any single device needs to accommodate this additional pull-up strength. Output Rise and Fall Time Estimation The RST and RST outputs have strong pull-down capability. The following formula estimates the output fall time (90% to 10%) for a particular external load capacitance (CLOAD): tFALL 2.2 * RPD * CLOAD where RPD is the on-resistance of the internal pull-down transistor estimated to be typically 40 at room temperature (25C) and CLOAD is the external load capacitance on the pin. Assuming a 150pF load capacitance, the fall time is about 13ns. The rise time, on the RST and RST pins is limited by weak internal pull-up current sources to VCC. The following formula estimates the output rise time (10% to 90%) at the RST and RST pins: tRISE 2.2 RPU * CLOAD where RPU is the on-resistance of the pull-up transistor. Notice that this pull-up transistor is modeled as a 6A current source in the Block Diagram as a typical representation. The on-resistance as a function of the VCC = Max (V1, V2) voltage (for VCC > 1V) at room temperature is estimated as follows: R PU = 6 * 105 MAX( V1,V2) - 1V
At VCC = 3.3V, RPU is about 260k. Using 150pF for load capacitance, the rise time is 86s. An external pull-up resistor may be used if the output needs to pull up faster and/or to a higher voltage, for example: the rise time reduces to 3.3s for a 150pF load capacitance, when using a 10k pull-up resistor.
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12
LTC2904/LTC2905 TYPICAL APPLICATIONS
2.5V, 1.2V Supply Monitor, 10% Tolerance 3.3V, 1.2V Dual Supply Monitor with LED Power Good Indicator, 7.5% Tolerance and Adjustable Timer
3.3V 510 1.2V V2 LTC2904 RST 0.1F SYSTEM RESET RST GND S1 TOL
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V1 S2
2.5V
1.2V
V2 LTC2904 S2
V1 LED RST 0.1F RST TOL
29045 TA03
0.1F
0.1F S1 GND SYSTEM RESET
5V, 3.3V Dual Supply Monitor with Voltage Margining for Automated On-Board Testing
DC/DC CONVERTER 5V 3.3V SYSTEM LOGIC
V1 VIN SUPPLY CONTROLLER THREE-STATE 0.1F S1 S2 TOL LTC2905
V2 TMR 22nF GND RST
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0.1F
3.3V, 1.2V Dual Supply Monitor with Asymmetric Hysteresis, 5% Tolerance (Supplies Rising), 10% Tolerance (After RST Goes Low)
1.2V
V2 LTC2904 S2
V1 10k RST TOL RST SYSTEM RESET
3.3V 0.1F
0.1F S1 GND
29045 TA05
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13
LTC2904/LTC2905 PACKAGE DESCRIPTION
DDB Package 8-Lead Plastic DFN (3mm x 2mm)
(Reference LTC DWG # 05-08-1702 Rev B)
0.61 0.05 (2 SIDES) 0.70 0.05 2.55 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) 0.56 0.05 (2 SIDES) 0.75 0.05 PIN 1 R = 0.20 OR 0.25 x 45 CHAMFER
(DDB8) DFN 0905 REV B
3.00 0.10 (2 SIDES)
R = 0.05 TYP
R = 0.115 TYP 5
0.40 0.10 8
0.200 REF
4 0.25 0.05 2.15 0.05 (2 SIDES)
1 0.50 BSC
0 - 0.05
BOTTOM VIEW--EXPOSED PAD
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14
LTC2904/LTC2905 PACKAGE DESCRIPTION
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
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
0.09 - 0.20 (NOTE 3)
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
LTC2904/LTC2905 TYPICAL APPLICATION
3.3V, 1.2V Dual Supply Monitor with LED Power Good Indicator, 7.5% Tolerance and Adjustable Timer
3.3V 1.8V 1.2V 0.1F 22nF S1 GND RST V2 LTC2905 TMR S2 TOL 0.1F 510 LED RST
29045 TA06
V1 0.1F
V2 LTC2905 TMR 22nF GND
V1 TOL
2.5V
0.1F S2 S1
RELATED PARTS
PART NUMBER LTC690 LTC694-3.3 LTC699 LTC1232 LTC1326/LTC1326-2.5 LTC1536 LTC1726-2.5/LTC1726-5 LTC1727-2.5/LTC1727-5 LTC1728-1.8/LTC1728-3.3 LTC1728-2.5/LTC1728-5 LTC1985-1.8 LTC2900 LTC2901 LTC2902 LTC2903-1 LTC2906 LTC2907 DESCRIPTION 5V Supply Monitor, Watchdog Timer and Battery Backup 3.3V Supply Monitor, Watchdog Timer and Battery Backup 5V Supply Monitor and Watchdog Timer 5V Supply Monitor, Watchdog Timer and Pushbutton Reset Micropower Precision Triple Supply Monitor for 5V/2.5V, 3.3V and ADJ Precision Triple Supply Monitor for PCI Applications Micropower Triple Supply Monitor for 2.5V/5V, 3.3V and ADJ Micropower Triple Supply Monitor with Open-Drain Reset Micropower Triple Supply Monitor with Open-Drain Reset 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 Dual Supply Monitor with One Pin-Selectable Threshold and One Adjustable Input Dual Supply Monitor with One Pin-Selectable Threshold and One Adjustable Input Precision Six Supply Monitors COMMENTS 4.65V Threshold 2.9V Threshold 4.65V Threshold 4.37V/4.62V Threshold 4.725V, 3.118V, 1V Threshold (0.75%) Meets PCI tFAIL Timing Specifications Adjustable RESET and Watchdog Timeouts Individual Monitor Outputs in MSOP 5-Lead SOT-23 Package 5-Lead SOT-23 Package 5-Lead SOT-23 Package Adjustable RESET, 10-Lead MSOP DFN Packages , Adjustable RESET and Watchdog Timer, 16-Lead SSOP Package Selectable Tolerance, RESET Disable for Margining Functions, 16-Lead SSOP Package Ultralow Voltage RESET, 6-Lead SOT-23 Package 0.5V Adjustable Threshold and Three Supply Tolerances, 8-Lead SOT-23 and DFN Packages 0.5V Adjustable Threshold, Adjustable RESET Timer and Three Supply Tolerances, 8-Lead SOT-23 and DFN Packages Ultralow Voltage RESET, 8-Lead SOT-23 and DFN Packages
LTC2908
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16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 1109 REV D * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2003

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