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LTC2906/LTC2907 Precision Dual Supply Monitors with One Pin-Selectable Threshold and One Adjustable Input
FEATURES
s s
DESCRIPTIO
s s s
s s s s s s s
Monitors Two Inputs Simultaneously Three Threshold Selections for 5V, 3.3V or 2.5V Supplies Low Voltage Adjustable Input (0.5V) 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 (LTC2906 Only) Adjustable Reset Time Delay (LTC2907 Only) Open Drain RST Output Guaranteed RST for V1 1V or VCC 1V Low Profile (1mm) SOT-23 (ThinSOTTM) and Plastic (3mm x 2mm) DFN Packages Desktop and Notebook Computers Handheld Devices Network Servers Core, I/O Monitor
, LTC and LT are registered trademarks of Linear Technology Corporation.
The LTC(R)2906/LTC2907 are dual supply monitors intended for systems with multiple supply voltages. The dual supply monitors have a common reset output with delay (200ms for the LTC2906 and adjustable using an external capacitor for the LTC2907). These products provide a precise, space-conscious and micropower solution for supply monitoring. The LTC2906/LTC2907 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 state is guaranteed to be in the correct state for V1 and/or VCC down to 1V. The LTC2906/LTC2907 also feature one adjustable input with a nominal threshold level at 0.5V, another input with three possible input threshold levels, and three supply tolerances for possible margining. These features provide versatility for any kind of system requiring dual supply monitors. Two three-state input pins program the threshold and tolerance level without requiring any external components.
APPLICATIO S
s s s s
TYPICAL APPLICATIO
Dual Supply Monitor with Adjustable Tolerance (2.5V, 0.8V)
DC/DC CONVERTER 2.5V 0.8V 49.9k V1 LTC2907 0.1F VCC S1 TOL TMR 22nF GND RST VADJ 0.1F 100k SYSTEM LOGIC
Supply Selection Programming
V1 5.0 3.3 2.5 S1 V1 OPEN GND
Tolerance Programming
TOLERANCE 5% 7.5%
29067 TA01
TOLERANCE = 10%
10%
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TOL V1 OPEN GND
29067f
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1
LTC2906/LTC2907
ABSOLUTE
AXI U RATI GS
Terminal Voltages V1, VCC ........................................................ -0.3V to 7V S1, VADJ, TOL ............................ -0.3V to (VMAX + 0.3V) RST ............................................................. -0.3V to 7V RST (LTC2906) ............................................ -0.3V to 7V TMR (LTC2907) ........................................... -0.3V to 7V
PACKAGE/ORDER I FOR ATIO
TOP VIEW GND 1 RST 2 RST/TMR* 3 VCC 4 9 8 TOL 7 S1 6 VADJ 5 V1
ORDER PART NUMBER LTC2906CDDB LTC2906IDDB LTC2907CDDB LTC2907IDDB DDB8 PART MARKING LBDC LBDD LBDF LBDG
DDB8 PACKAGE 8-LEAD (3mm x 2mm) PLASTIC DFN EXPOSED PAD IS GND (PIN 9), MUST BE SOLDERED TO PCB *RST FOR LTC2906 TMR FOR LTC2907 TJMAX = 125C, JA = 250C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = V1 = 2.5V, VADJ = 0.55V, S1 = TOL = 0V, unless otherwise noted. (Notes 2, 3, 4)
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 ADJ, 5% Reset Threshold ADJ, 7.5% Reset Threshold ADJ, 10% Reset Threshold VCC Input Current V1 Input Current VADJ Input Current CONDITIONS V1 Input Threshold
q q q q q q q q q q q q q q q q q q
ELECTRICAL CHARACTERISTICS
VRT33
V1 Input Threshold
VRT25
V1 Input Threshold
VRTADJ
VADJ Input Threshold
VMAX(MIN) IVCC IV1 IVADJ
Minimum VMAX Operating Voltage (Note 2) RST, RST in Correct Logic State VCC > V1 V1 > VCC VCC > V1 V1 > VCC
2
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U
W
WW
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(Notes 1, 2)
Operating Temperature Range LTC2906C/LTC2907C .............................. 0C to 70C LTC2906I/LTC2907I ............................-40C to 85C Storage Temperature Range ..................-65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
TOP VIEW VCC 1 RST/TMR* 2 RST 3 GND 4 8 V1 7 VADJ 6 S1 5 TOL
ORDER PART NUMBER LTC2906CTS8 LTC2906ITS8 LTC2907CTS8 LTC2907ITS8 TS8 PART MARKING LTBCM LTBCN LTBCP LTBCQ
TS8 PACKAGE 8-LEAD PLASTIC TSOT-23 *RST FOR LTC2906 TMR FOR LTC2907 TJMAX = 125C, JA = 250C/W
MIN 4.600 4.475 4.350 3.036 2.954 2.871 2.300 2.238 2.175 0.492 0.479 0.465
TYP 4.675 4.550 4.425 3.086 3.003 2.921 2.338 2.275 2.213 0.500 0.487 0.473 54 1 55
MAX 4.750 4.625 4.500 3.135 3.053 2.970 2.375 2.313 2.250 0.508 0.495 0.481 1 100 1 3 100 15
UNITS V V V V V V V V V V V V V A A A A nA
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LTC2906/LTC2907
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = V1 = 2.5V, VADJ = 0.55V, S1 = TOL = 0V, unless otherwise noted. (Notes 2, 3, 4)
SYMBOL ITMR(UP) ITMR(DOWN) tRST tRST tUV VOL VOH PARAMETER TMR Pull-Up Current TMR Pull-Down Current Reset Time-Out Period Reset Time-Out Period VX Undervoltage Detect to RST or RST Output Voltage Low RST, RST Output Voltage High RST, RST (Notes 2, 5) Low Level Input Voltage High Level Input Voltage Pin Voltage when Left in Hi-Z State I = -10A I = 0A I = 10A (LTC2907) (LTC2907) (LTC2906) (LTC2907) CTMR = 22nF VX Less Than Reset Threshold VRTX by More than 1% I = 2.5mA I = 100A; V1 and/or VCC = 1V (RST Only) I = -1A
q q q VMAX - 1
ELECTRICAL CHARACTERISTICS
CONDITIONS VTMR = 0V VTMR = 1.4V
q q q q
MIN -1.5 1.5 140 140
TYP -2.1 2.1 200 200 150 0.15 0.05
MAX -2.7 2.7 260 260
UNITS A A ms ms s
0.4 0.3
V V V
Three-State Inputs S1, TOL VIL VIH VZ
q q q q q
0.4 1.4 0.7 0.9 1.1 25
V V V V V A
IVPG
Programming Input Current (Note 6)
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The greater of V1, VCC is the internal supply voltage (VMAX). 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 VMAX of typically -6A. However, an external pull-up resistor may be used when faster rise time is required or for VOH voltages greater than VMAX. 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 PERFOR A CE CHARACTERISTICS
Specifications are at TA = 25C unless otherwise noted. 5V Threshold Voltage vs Temperature
4.75 3.12 5%
THRESHOLD VOLTAGE, VRT50 (V)
THRESHOLD VOLTAGE, VRT33 (V)
4.65 4.60 4.55 4.50 4.45 4.40 4.35 -50 -25 25 50 0 TEMPERATURE (C) 75 100
29067 G01
3.07
THRESHOLD VOLTAGE, VRT25 (V)
4.70
5%
7.5%
10%
UW
3.3V Threshold Voltage vs Temperature
2.375
2.5V Threshold Voltage vs Temperature
5% 2.325 7.5% 2.275
3.02
7.5%
2.97 10% 2.92
2.225
10%
2.87 -50
-25
25 50 0 TEMPERATURE (C)
75
100
29067 G02
2.175 -50
-25
25 50 0 TEMPERATURE (C)
75
100
29067 G03
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3
LTC2906/LTC2907 TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at TA = 25C unless otherwise noted. ADJ Threshold Voltage vs Temperature
0.505 5% THRESHOLD VOLTAGE, VRTADJ (V) 0.500 19.0 0.495 IV1 (A) 0.490 0.485 0.480 17.5 0.475 0.470 -50 10% 17.0 -50 IVCC (A) 18.5 19.5
7.5%
-25
25 50 0 TEMPERATURE (C)
Typical Transient Duration vs Comparator Overdrive (V1, VADJ)
700 TYPICAL TRANSIENT DURATION (s) 600 500 400 300 200 100 0 1 10 100 0.1 COMPARATOR OVERDRIVE VOLTAGE (% OF VRTX)
29067 G07
RESET TIME OUT PERIOD, tRST (ms)
1000
RESET TIME OUT PERIOD, tRST (ms)
RESET OCCURS ABOVE CURVE
RST Output Voltage vs V1
5 4 RST OUTPUT VOLTAGE (V) 3 2 1 0 -1 S1 = TOL = VCC = V1 VADJ = 0.55V 10k PULL-UP RESISTOR RST OUTPUT VOLTAGE (V) 5 4 3 2 1 0 -1
RST OUTPUT VOLTAGE (V)
0
1
2 V1 (V)
3
4
UW
75
29067 G04
IV1 vs Temperature
V1 = 5V VCC = 3.3V VADJ =0.55V S1 =TOL = 1.4V 15.8 15.6 15.4 15.2 15.0 14.8 14.6 14.4 14.2 14.0 -25 25 50 0 TEMPERATURE (C) 75 100 100
IVCC vs Temperature
V1 = 2.5V VCC = 3.3V VADJ =0.55V S1 =TOL = 1.4V
18.0
-50
-25
25 50 0 TEMPERATURE (C)
75
100
29067 G05
29067 G06
Reset Time Out Period (t RST) vs Capacitance (CTMR)
10000 235
Reset Time Out Period (t RST) vs Temperature
CRT = 22nF 230 (FILM) 225 220 215 210 205 200 195 -50 -25 25 50 0 TEMPERATURE (C) 75 100
100
10
1
0.1 10p
100p
10n CTMR (FARAD)
1n
100n
1
29067 G08
29067 G09
RST Output Voltage vs V1
5 S1 = TOL = VCC = V1 VADJ = 0.55V 10k PULL-UP RESISTOR 4 3 2 1 0 -1
RST Output Voltage vs V1
S1 = TOL = VCC = V1 VADJ = 0.55V 10pF CAPACITOR AT RST
4
29067 G10
5
0
1
2 V1 (V)
3
4
5
29067 G11
0
1
2 V1 (V)
3
4
29067 G12
5
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LTC2906/LTC2907 TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at TA = 25C unless otherwise noted. RST Pull-Down Current (IRST) vs VMAX
RST PULL-DOWN CURRENT, IRST (mA) RST PULL-DOWN CURRENT, IRST (mA)
RST OUTPUT VOLTAGE LOW, VOL (V)
5 4
S1 = TOL = VCC = V1 VADJ = 0.55V NO PULL-UP R
RST AT 150mV 3 2 1 0 0 1 2 3 VMAX (V) 4 5
29067 G13
RST AT 50mV
RST Output Voltage Low (VOL) vs RST Pull-Down Current (IRST)
1.8
RST OUTPUT VOLTAGE LOW, VOL (V) RST PULL-UP CURRENT, IRST (A)
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0
-14 -12 -10 -8 -6 -4 -2 VRT25 0 VRT33 3.0 3.5 4.0 VMAX (V) VRT50 4.5 5.0
29067G17
RST PULL-UP CURRENT, IRST (A)
1.6
V1 = VCC = 5V VADJ = 0.55V S1 = TOL = V1 NO PULL-UP R
85C
10 30 40 50 60 20 RST PULL-DOWN CURRENT, IRST (mA)
29067 G16
RST Output Voltage High (VOH) vs RST Output Source Current (IRST)
3.0
RST OUTPUT VOLTAGE HIGH, VOH (V) RST OUTPUT VOLTAGE HIGH, VOH (V)
2.5
TOL = V1 = 3.3V VADJ = 0.55V S1 = OPEN NO PULL-UP R
IS1, ITOL (A)
2.0
1.5
85C -40C 25C
1.0
0.5 -12
-8 -6 -4 -2 -10 OUTPUT SOURCE CURRENT, IRST (A)
UW
25C -40C 0
29067 G19
RST Pull-Down Current (IRST) vs VMAX
5 4 3 2 1 0 0 1 2 3 VMAX (V) 4 5
29067 G14
RST Output Voltage Low (VOL) vs RST Pull-Down Current (IRST)
1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0 10 30 40 50 60 20 RST PULL-DOWN CURRENT, IRST (mA)
29067G15
VCC = V1 S1 = TOL = GND VADJ = 0.55V NO PULL-UP R RST AT 150mV
V1 = VCC = 5V VADJ = 0.45V S1 = TOL = V1 NO PULL-UP R
85C
25C
-40C
RST AT 50mV
RST Pull-Up Current (IRST) vs VMAX
-18 TOL = GND -16 -14 -12 -10 -8 -6 -4 -2 0 -16
RST Pull-Up Current (IRST) vs VMAX
TOL = V1
VRT25 2.0 2.5 3.0
VRT33 3.5 4.0 VMAX (V)
VRT50 4.5 5.0
2.0
2.5
29067 G18
RST Output Voltage High (VOH) vs RST Output Source Current (IRST)
3.5 TOL = V1 = 3.3V VADJ = 0.45V 3.0 S1 = OPEN NO PULL-UP R 2.5 2.0 -40C 1.5 1.0 0.5 -8 -7 -6 -5 -4 -3 -2 -1 OUTPUT SOURCE CURRENT, IRST (A) 0 85C 25C 20 19 18 17 16 15 14 13 12 11
IS1, ITOL vs Temperature
S1 = TOL = V1 = 3.3V
10 -50
-25
0
25
50
75
100
TEMPERATURE (C)
29067 G21
290467 G20
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LTC2906/LTC2907 TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at TA = 25C unless otherwise noted. IS1, ITOL vs Temperature
-20 -19 -18 -17
IS1, ITOL (A)
PI FU CTIO S
(TS8 Package/DDB8 Package)
VCC (Pin 1/Pin 4): Optional Power Supply Pin. VCC powers and maintains the correct operation of the RST and RST pins in the complete absence of V1. If V1 is present, the greater of VCC or V1 (VMAX) powers the internal circuitry and the reset outputs. Bypass this pin to ground with a 0.1F (or greater) capacitor. Tie to V1 when no optional power is available. RST (Pin 2/Pin 3): (LTC2906 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 VMAX and may be pulled above VMAX using an external pull-up. TMR (Pin 2/Pin 3): (LTC2907 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 either V1 or VADJ is below the reset threshold and
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S1 = TOL = GND V1 = 3.3V
-16 -15 -14 -13 -12 -11 -10 -50 -25 25 50 0 TEMPERATURE (C) 75 100
29067 G22
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holds low for programmed delay time after all voltage inputs are above threshold. This pin has a weak pull up to VMAX and may be pulled above VMAX using an external pull-up. GND (Pin 4/Pin 1 and Pin 9): Ground. TOL (Pin 5/Pin 8): Three-State Input for Supply Tolerance Selection (5%, 7.5% or 10%). Refer to Applications Information for tolerance selection chart (Table 3). S1 (Pin 6/Pin 7): The Voltage Threshold Select ThreeState Input. Connect to V1, GND or leave unconnected in open state to select one of three possible input threshold levels (refer to Table 1). VADJ (Pin 7/Pin 6): Adjustable Voltage Input. Bypass this pin to ground with a 0.1F (or greater) capacitor in a noisy environment. V1 (Pin 8/Pin 1): Voltage Input 1. Select from 5V, 3.3V or 2.5V. Refer to Table 1 for details. The greater of (V1, VCC) is also the internal VCC (VMAX). Bypass this pin to ground with a 0.1F (or greater) capacitor.
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LTC2906/LTC2907
BLOCK DIAGRA W
VMAX 6A RESISTOR NETWORK VMAX POWER DETECT RESISTOR NETWORK
LTC2906
V1 VMAX POWER DETECT
VCC VADJ
BAND GAP REFERENCE
LTC2907
VCC
VADJ
BAND GAP REFERENCE
+
+
-
V1
-
+
200ms RESET PULSE GENERATOR 6A VMAX
+
- -
THREE-STATE DECODER
2906 BD
RST
RST
GND
S1
TOL
TMR VMAX 6A 200ms RESET PULSE GENERATOR RST
THREE-STATE DECODER
GND
2907 BD
S1
TOL
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LTC2906/LTC2907 TI I G DIAGRA W
Vx Monitor Timing
VRTX VX tUV tRST 1V 1V
29067 TD
APPLICATIO S I FOR ATIO
Supply Monitoring
The LTC2906/LTC2907 are low power, high accuracy dual supply monitoring circuits with an adjustable input and another input with selectable threshold. Reset delay is set to a nominal of 200ms for LTC2906 and is adjustable using an external capacitor for LTC2907. The three-state input pin (S1) selects one of three possible threshold voltage levels for V1. Another three-state input pin sets the supply tolerance (5%, 7.5% or 10%). Both input voltages (V1 and VADJ) must be above predetermined thresholds for the reset not to be invoked. The LTC2906/LTC2907 assert the reset outputs during powerup, power-down and brownout conditions on any one of the voltage inputs. Power-Up The greater of V1, VCC is the internal supply voltage (VMAX). VMAX powers the drive circuits for the RST pin. Therefore, as soon as V1 or VCC reaches 1V during power up, the RST output asserts low. VMAX also powers the drive circuits for the RST pin in the LTC2906. Therefore, RST weakly pulls high when either V1 or VCC reaches at least 1V. Threshold programming is complete, when V1 reaches at least 2.17V. After programming, if any one of the Vx inputs
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U
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RST
RST
falls below its programmed threshold, RST asserts low (RST weakly pulls high) as long as VMAX is at least 1V. Once both V1 and VADJ inputs rise above their thresholds, an internal timer is started. After the programmed delay time, RST weakly pulls high (RST asserts low). Power-Down On power-down, once either V1 or VADJ drops below its threshold, RST asserts logic low and RST weakly pulls high. VMAX of at least 1V guarantees a logic low of 0.4V at RST. Auxiliary Power If an auxiliary power is available it can be connected to the VCC pin. Since the internal supply voltage (VMAX) is the greater of V1, VCC; a VCC of at least 1V guarantees logic low of 0.4V at RST for voltage inputs (V1 and/or VADJ) down to 0V. Programming Pins The two three-state input pins, S1 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.
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LTC2906/LTC2907
APPLICATIO S I FOR ATIO
In margining application, the three-state input pins can be driven using a three-state buffer. Note however, the low and high output of the three-state buffer has to satisfy the VIL and VIH of the three-state pin listed in the Electrical Characteristics Table. Moreover, when the three-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 to either GND, or V1, or leaving it in open state selects the LTC2906/LTC2907 V1 input voltage threshold. Table 1 shows the three possible selections of V1 nominal input voltage and their corresponding S1 connection.
Table 1. Supply Selection Programming
V1 5.0 3.3 2.5 S1 V1 OPEN GND
Note: Open = open circuit or driven by a three-state buffer in high impedance state with leakage current less than 10A.
The noninverting input on the VADJ comparator is set to 0.5V when the TOL pin is set high (5% tolerance) (Figure 1) and the high impedance inverting input directly ties to the VADJ pin.
VTRIP R1 1% VADJ R2 1% LTC2906/LTC2907
-
+ + -
0.5V
29067 F01
Figure 1. Setting the Adjustable Trip Point
In a typical application, the VADJ pin connects to a tap point on an external resistive divider between the positive voltage being monitored and ground. The following formula obtains R1 resistor value for a particular value of R2 and a desired trip voltage at 5% tolerance:
VTRIP(5%) - 1 R2 R1 = 0.5V
U
R2 =100k is recommended. Once the resistor divider is set in the 5% tolerance mode, there is no need to change the divider for the other tolerance modes (7.5%, 10%) because the internal reference at the noninverting input on the VADJ comparator is scaled accordingly, moving the trip point in 2.5% decrements. Table 2 shows suggested 1% resistor values for various adjustable applications.
Table 2. Suggested 1% Resistor Values for the VADJ Inputs
VSUPPLY (V) 12 10 8 7.5 6 5 3.3 3 2.5 1.8 1.5 1.2 1 0.9 0.8 0.7 0.6 VTRIP (V) 11.25 9.4 7.5 7 5.6 4.725 3.055 2.82 2.325 1.685 1.410 1.120 0.933 0.840 0.750 0.655 0.561 R1 (k) 2150 1780 1400 1300 1020 845 511 464 365 237 182 124 86.6 68.1 49.9 30.9 12.1 R2 (k) 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100
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Tolerance Programming The three-state input pin TOL, programs the common supply tolerance for both V1 and VADJ input voltages (5%, 7.5% or 10%). The larger the tolerance the lower the trip threshold. Table 3 shows the tolerances selection corresponding to a particular connection at the TOL pin.
Table 3. Tolerance Programming
TOLERANCE 5% 7.5% 10% TOL V1 OPEN GND
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LTC2906/LTC2907
APPLICATIO S I FOR ATIO
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 LTC2906/ LTC2907 inputs have the same relative threshold accuracy. The specification for LTC2906/LTC2907 is 1.5% of the programmed nominal input voltage (over the full operating temperature range). For example, when the LTC2906/LTC2907 are programmed to handle a 5V input with 10% tolerance (S1 = V1 and TOL = GND, refer to Table 1 and Table 3), 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 or 13% below 5V 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. 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% hysteresis is equivalent to a 3.5% monitor with no hysteresis. The LTC2906/LTC2907 take 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
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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 LTC2906 and adjustable using an external capacitor for LTC2907). 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 VADJ drops below its programmed threshold, the RST pin asserts low (RST weakly pulls high). 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 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. Selecting the Reset Timing Capacitor The reset time-out period for LTC2907 is adjustable in order to accommodate a variety of microprocessor applications. Connecting a capacitor, CTMR, between the TMR pin and ground sets the reset time-out period, tRST. The following formula determines the value of capacitor needed for a particular reset time-out period: CTMR = tRST * 110 * 10-9 [F/s] For example, using a standard capacitor value of 22nF gives a 200ms delay. The graph in Figure 2 shows the desired delay time as a function of the value of the timer capacitor that should be used:
29067f
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LTC2906/LTC2907
APPLICATIO S I FOR ATIO
10000
RESET TIME OUT PERIOD, tRST (ms)
1000
100
10
1
0.1 10p
100p
1n 10n CTMR (FARAD)
100n
1
29067 F02
Figure 2. Reset Time-Out Period vs Capacitance
Leaving the TMR pin open with no external capacitor generates a reset time-out of approximately 200s. For long reset time-out, the only limitation is the availability of a large value capacitor with low leakage. The TMR capacitor will never charge if the leakage current exceeds the TMR charging current of 2.1A (typical). 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 VMAX and a strong pull-down to ground. The weak pull-up and strong pull-down arrangement allows 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 VMAX = MAX (V1, VCC). During fault condition, VMAX of at least 1V guarantees a maximum VOL = 0.4V at RST. However, at VMAX = 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 pullup strength of the RST pin is crucial at very low VMAX.
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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 output 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 VMAX >1V, 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 VMAX. 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 VMAX = MAX (V1, VCC) voltage (for VMAX > 1V) at room temperature is estimated as follows:
RPU = 6 * 105 , MAX(V1 VCC ) - 1V
W
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At VMAX = 3.3V, RPU is about 260k. Using 150pF for load capacitance, the rise time is 86s. A smaller external pullup resistor maybe 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.
29067f
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LTC2906/LTC2907
TYPICAL APPLICATIO S
5V, 3.3V Supply Monitor, 5% Tolerance with LED Power Good Indicator
3.3V 0.1F 499 P0WER GOOD LED SYSTEM RESET
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V1 LTC2906 TOL S1 RST RST
VCC 845k VADJ 100k GND
5V
0.1F
2906 TA02
3.3V, 1.8V Monitor, 7.5% Tolerance with an Auxiliary 5V Supply (5V Not Monitored)
3.3V 0.1F
V1 LTC2906 TOL S1 TMR
VCC
5V 1.8V 237k
VADJ 100k GND
0.1F
22nF
SYSTEM RESET
RST
2907 TA03
29067f
LTC2906/LTC2907
TYPICAL APPLICATIO S
2.5V, 1V Monitor, 10% Tolerance with LED Undervoltage Indicator and 5V High Availability Auxiliary Supply (5V Not Monitored)
1V 86.6k 2.5V 0.1F VCC 5V 0.1F LED S1 GND
2907 TA04
3.3V 0.1F CGATE 10nF RONB 154k RONA 100k VCC GATE ON LTC2923 RAMPBUF RTB1 TRACK1 RTA1 RTB2 TRACK2 RTA2 GND RFA2 RFB2 100k S1 GND
292067 TA06
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V1 LTC2907
VADJ 100k TMR 22nF 0.1F TOL
499 RST
Dual Supply Monitor with Hysteresis, 5% Tolerance (Supplies Rising), 10% Tolerance (After RST Goes Low)
3.3V 511k VADJ LTC2906 100k GND VCC S1 RST SYSTEM RESET RST TOL
2906 TA05
V1
5V 0.1F
10k
Dual Supply Monitor for Tracked/Sequenced Supply
RAMP FB1 FB
IN DC/DC OUT RFB1
2.5V SYSTEM
RFA1
0.1F VCC V1 OUT 1.8V TOL 237k VADJ TMR 22nF LTC2907 RST
IN DC/DC FB2 FB
29067f
13
LTC2906/LTC2907
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
29067f
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LTC2906/LTC2907
PACKAGE DESCRIPTIO U
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 1.4 MIN 2.80 BSC 1.50 - 1.75 (NOTE 4) PIN ONE ID 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 0.09 - 0.20 (NOTE 3) 1.95 BSC
TS8 TSOT-23 0802
3.85 MAX 2.62 REF
RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR
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
29067f
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.
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LTC2906/LTC2907
TYPICAL APPLICATIO
0.8V 49.9k
VADJ 100k 22nF TMR S1 GND
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 LTC2904 LTC2905 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 Push-Button 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 Three-State Programmable Precision Dual Supply Monitor Three-State Programmable Precision Dual Supply Monitor 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 Time-Outs 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 and 3mm X 3mm 10-Lead 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 Adjustable Tolerance, 8-Lead SOT-23 and 3mm x 2mm DFN Packages Adjustable RESET and Tolerance, 8-Lead SOT-23 and 3mm x 2mm DFN Packages
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
q
FAX: (408) 434-0507 q www.linear.com
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Quad Supply Monitor with LED Undervoltage Indicator, 5% Tolerance, 3.3V, 2.5V, 0.8V, 0.6V
3.3V LTC2907 V1 VCC TOL 0.1F 0.1F 499 LED RST 2.5V V1 TOL LTC2907 VCC S1 TMR GND RST
2907 TA07
0.6V 12.1k VADJ 100k 22nF
29067f LT/TP 0304 1K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 2004

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