LINER LTC2905ITS8TRPBF Precision dual supply monitors with pin-selectable threshold Datasheet

LTC2904/LTC2905
Precision Dual Supply
Monitors with Pin-Selectable
Thresholds
DESCRIPTION
FEATURES
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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 (ThinSOT™) and
Plastic (3mm × 2mm) DFN Packages
The LTC®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.
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.
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.
TYPICAL APPLICATION
5V, 3.3V Dual Supply Monitor with 5% Tolerance
Table 1. Voltage Threshold Programming
5V
DC/DC
CONVERTER
SYSTEM
LOGIC
3.3V
V1
V2
LTC2905
0.1μF
0.1μF
S1
TMR
S2
GND
TOL
RST
22nF
29045 TA01
V1
V2
S1
S2
5.0
3.3
V1
V1
3.3
2.5
Open
GND
3.3
1.8
V1
Open
3.3
1.5
Open
V1
3.3
1.2
Open
Open
2.5
1.8
GND
GND
2.5
1.5
GND
Open
2.5
1.2
GND
V1
2.5
1.0
V1
GND
29045fd
1
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 .............................. 0°C to 70°C
LTC2904I/LTC2905I.............................–40°C to 85°C
LTC2905H .......................................... –40°C to 125°C
Storage Temperature Range .................. –65°C to 150°C
TSOT Lead Temperature (Soldering, 10 sec) ......... 300°C
PIN CONFIGURATION
TOP VIEW
GND 1
RST 2
8
TOL
7
S1
RST/TMR* 3
6
S2
V2 4
5
V1
9
TOP VIEW
V2 1
RST/TMR* 2
RST 3
GND 4
8 V1
7 S2
6 S1
5 TOL
TS8 PACKAGE
8-LEAD PLASTIC TSOT-23
* RST FOR LTC2904
TMR FOR LTC2905
TJMAX = 150°C, θJA = 195°C/W
DDB8 PACKAGE
8-LEAD (3mm s 2mm) PLASTIC DFN
EXPOSED PAD IS GND (PIN 9),
MUST BE SOLDERED TO PCB
* RST FOR LTC2904
TMR FOR LTC2905
TJMAX = 150°C, θJA = 76°C/W
ORDER INFORMATION
Lead Free Finish
TAPE AND REEL (MINI)
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC2904CDDB#TRMPBF
LTC2904CDDB#TRPBF
LBCZ
8-Lead (3mm × 2mm) Plastic DFN
0°C to 70°C
LTC2904IDDB#TRMPBF
LTC2904IDDB#TRPBF
LBDB
8-Lead (3mm × 2mm) Plastic DFN
–40°C to 85°C
LTC2905CDDB#TRMPBF
LTC2905CDDB#TRPBF
LAJF
8-Lead (3mm × 2mm) Plastic DFN
0°C to 70°C
LTC2905HDDB#TRMPBF
LTC2905HDDB#TRPBF
LBCY
8-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LTC2905IDDB#TRMPBF
LTC2905IDDB#TRPBF
LBCY
8-Lead (3mm × 2mm) Plastic DFN
–40°C to 85°C
LTC2904CTS8#TRMPBF
LTC2904CTS8#TRPBF
LTBCJ
8-Lead Plastic TSOT-23
0°C to 70°C
LTC2904ITS8#TRMPBF
LTC2904ITS8#TRPBF
LTBCK
8-Lead Plastic TSOT-23
–40°C to 85°C
LTC2905CTS8#TRMPBF
LTC2905CTS8#TRPBF
LTAJD
8-Lead Plastic TSOT-23
0°C to 70°C
LTC2905HTS8#TRMPBF
LTC2905HTS8#TRPBF
LTAJE
8-Lead Plastic TSOT-23
–40°C to 125°C
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/
–40°C to 85°C
29045fd
2
LTC2904/LTC2905
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. V1 = 2.5V, V2 = 1V, S1 = TOL = V1, S2 = 0V, unless otherwise noted.
(Notes 2, 3)
SYMBOL
VRT50
CONDITIONS
V1 Input Threshold
VCCMIN
IV1
IV2
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
ITMR(UP)
ITMR(DOWN)
TMR Pull-Up Current
TMR Pull-Down Current
VTMR = 0V
VTMR = 1.4V
tRST
Reset Timeout Period
LTC2905
LTC2905
LTC2905H
LTC2904
tRST
Reset Timeout Period
LTC2905
LTC2905H
CTMR = 22nF
tUV
Vx Undervoltage Detect to
RST or RST
Output Voltage Low RST, RST
VRT33
VRT25
VRT18
VRT15
VRT12
VRT10
VOL
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
VOH
2905H
IVPG
Programming Input Current (Note 6)
65
0.4
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
UNITS
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
μA
μA
l
–1.5
1.5
1.4
140
–2.1
2.1
2.0
200
–2.7
2.7
2.7
260
μA
μA
μA
ms
l
l
140
140
200
260
295
ms
ms
μs
0.4
0.3
V
V
V
0.4
V
V
V
V
V
V
V
V
μA
l
l
l
V1, V2 Input Threshold
l
l
l
V1, V2 Input Threshold
l
l
l
V2 Input Threshold
l
l
l
V2 Input Threshold
l
l
l
V2 Input Threshold
l
l
l
V2 Input Threshold
l
l
l
RST in Correct Logic State
Includes Input Current to Three-State Pins
l
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
l
l
Vx Less than Reset Threshold VRTX
by More than 1%
I = 2.5mA
I = 100μA; V1 = 1V (RST Only)
I = –1μA
l
l
l
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
150
l
l
l
0.15
0.05
VCC–1
l
l
I = –10μA
I = 0μA
I = 10μA
I = –10μA
I = 0μA
I = 10μA
l
1.4
0.7
0.9
l
l
l
l
1.1
0.65
0.9
1.15
±25
29045fd
3
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 –6μA. 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 10μA.
TYPICAL PERFORMANCE CHARACTERISTICS
Specifications are at TA = 25°C unless otherwise noted.
5V Threshold Voltage
vs Temperature
3.3V Threshold Voltage
vs Temperature
4.75
2.5V Threshold Voltage
vs Temperature
2.375
3.120
5%
4.65
4.60
7.5%
4.55
4.50
4.45
10%
4.40
4.35
–50
–25
25
50
0
TEMPERATURE (oC)
75
3.070
7.5%
3.020
2.970
10%
2.920
2.870
–50
100
THRESHOLD VOLTAGE, VRT25 (V)
4.70
THRESHOLD VOLTAGE, VRT33 (V)
THRESHOLD VOLTAGE, VRT50 (V)
5%
–25
25
50
0
TEMPERATURE (oC)
75
29045 G01
7.5%
2.275
2.175
–50
7.5%
1.645
1.625
1.605
10%
1.585
–25
25
50
0
TEMPERATURE (oC)
75
100
29045 G04
25
50
0
TEMPERATURE (oC)
1.135
1.125
5%
1.405
1.385
7.5%
1.365
1.345
10%
1.325
1.305
–50
100
75
1.2V Threshold Voltage
vs Temperature
THRESHOLD VOLTAGE, VRT12 (V)
THRESHOLD VOLTAGE, VRT15 (V)
1.665
–25
29045 G03
1.425
5%
1.685
10%
2.225
1.5V Threshold Voltage
vs Temperature
1.705
THRESHOLD VOLTAGE, VRT18 (V)
2.325
29045 G02
1.8V Threshold Voltage
vs Temperature
1.565
–50
100
5%
5%
1.115
1.105
7.5%
1.095
1.085
1.075
1.065
10%
1.055
–25
25
50
0
TEMPERATURE (oC)
75
100
29045 G05
1.045
–50
–25
25
50
0
TEMPERATURE (oC)
75
100
29045 G06
29045fd
4
LTC2904/LTC2905
TYPICAL PERFORMANCE CHARACTERISTICS
Specifications are at TA = 25°C unless otherwise noted.
1V Threshold Voltage
vs Temperature
IV1 vs Temperature
0.940
1.8
V1 = 5V
V2 = 3.3V
S1 = S2 = TOL = 1.4V
5%
21.0
V1 = 5V
V2 = 3.3V
S1 = S2 = TOL = 1.4V
1.7
0.930
1.6
7.5%
0.910
0.900
20.5
IV2 (MA)
0.920
IV1 (MA)
THRESHOLD VOLTAGE, VRT10 (V)
IV2 vs Temperature
21.5
0.950
20.0
1.5
1.4
0.890
10%
19.5
1.3
0.880
0.870
–50
–25
25
50
0
TEMPERATURE (oC)
75
19.0
–50
100
–25
25
50
0
TEMPERATURE (oC)
75
29045 G07
700
IV2 (MA)
19.0
18.5
18.0
17.5
17.0
–50
25
50
0
TEMPERATURE (oC)
75
600
500
400
RESET OCCURS
ABOVE CURVE
300
200
100
Reset Timeout Period (tRST)
vs Temperature
215
210
205
50
75
100
4
3
2
1
–1
29045 G13
3
2
1
0
–1
0
1
2
3
4
5
0
1
2
3
4
5
V1 (V)
V1 (V)
TEMPERATURE (oC)
1M
V2 = S1 = S2 = TOL = V1
10k PULL-UP RESISTOR
0
200
100n
RST Output Voltage vs V1
RST OUTPUT VOLTAGE (V)
RST OUTPUT VOLTAGE (V)
RESET TIME-OUT PERIOD, tRST (ms)
220
1n
10n
CTMR (FARAD)
5
4
225
100p
29045 G12
V2 = S1 = S2 = TOL = V1
10k PULL-UP RESISTOR
25
1
RST Output Voltage vs V1
CRT = 22nF
230 (FILM)
0
10
0.1
10p
5
235
–25
100
29045 G11
29045 G10
195
–50
1000
1
10
100
0.1
COMPARATOR OVERDRIVE VOLTAGE (% OF VRTX)
100
100
10000
0
–25
75
Reset Time Out Period (tRST)
vs Capacitance (CTMR)
RESET TIME OUT PERIOD, tRST (ms)
TYPICAL TRANSIENT DURATION (Ms)
19.5
25
50
0
TEMPERATURE (oC)
29045 G09
Typical Transient Duration
vs Comparator Overdrive (V1, V2)
V1 = 2.5V
V2 = 3.3V
S1 = S2 = TOL = 1.4V
–25
29045 G08
IV2 vs Temperature
20.0
1.2
–50
100
29045 G14
29045 G15
29045fd
5
LTC2904/LTC2905
TYPICAL PERFORMANCE CHARACTERISTICS
Specifications are at TA = 25°C unless otherwise noted.
RST Pull-Down Current (IRST)
vs Supply Voltage (VCC)
RST Output Voltage vs V1
RST Pull-Down Current (IRST)
vs Supply Voltage (VCC)
5
3
2
1
0
0
1
2
3
3
2
1
RST AT 50mV
0
5
4
RST AT 150mV
V1 (V)
2
3
4
SUPPLY VOLTAGE, VCC (V)
29045 G16
RST OUTPUT VOLTAGE LOW, VOL (V)
1.6
1.4
25oC
–40oC
1.2
1.0
0.8
0.6
0.4
0.2
0
10
30
40
50
20
RST PULL-DOWN CURRENT, IRST (mA)
V1 = 5V
V2 = 3.3V
S1 = S2 = TOL = V1
NO PULL-UP R
1.6
1.4
1.2
0.6
0.4
0.2
3.0
–6
–4
–2
0
2.0
VRT25
2.5
VRT33
–16
–14
–12
–10
–8
–6
–4
–2
VRT25
VRT50
3.0
3.5
4.0
4.5
SUPPLY VOLTAGE, VCC (V)
5.0
29045 G22
VRT33
2.0
10
30
40
50
60
20
RST PULL-DOWN CURRENT, IRST (mA)
2.5
2.5
85oC
–40oC
1.0
25oC
0.5
–12
5.0
29045 G21
RST Output Voltage High (VOH)
vs RST Output Source Current (IRST)
3.5
V1 = 3.3V
V2 = 1.8V
S1 = TOL =V1
S2 = OPEN
NO PULL-UP R
2.0
1.5
VRT50
3.0
3.5
4.0
4.5
SUPPLY VOLTAGE, VCC (V)
29045 G20
TOL = V1
–8
5
29045 G18
RST Output Voltage High (VOH)
vs RST Output Source Current (IRST)
–10
2
3
4
SUPPLY VOLTAGE, VCC (V)
0
0
RST OUTPUT VOLTAGE HIGH, VOH (V)
RST PULL-UP CURRENT, IRST (MA)
25oC
0.8
RST Pull-Up Current (IRST)
vs Supply Voltage (VCC)
–12
1
0
TOL = GND
85oC
1.0
60
–14
RST AT 50mV
RST Pull-Up Current (IRST)
vs Supply Voltage (VCC)
–40oC
29045 G19
–16
1
5
0
0
2
–18
1.8
85oC
RST AT 150mV
3
RST Output Voltage Low (VOL)
vs RST Pull-Down Current (IRST)
RST OUTPUT VOLTAGE LOW, VOL (V)
V1 = 5V
V2 = 3V
S1 = S2 = TOL = V1
NO PULL-UP R
4
29045 G17
RST Output Voltage Low (VOL)
vs RST Pull-Down Current (IRST)
1.8
S1 = V2 = V1
TOL = S2 = GND
NO PULL-UP R
5
0
1
0
RST PULL-UP CURRENT, IRST (MA)
–1
4
RST OUTPUT VOLTAGE HIGH, VOH (V)
RST OUTPUT VOLTAGE (V)
4
V2 = S1 = S2 = TOL = V1
NO PULL-UP R
5
RST PULL-DOWN CURRENT, IRST (mA)
RST PULL-DOWN CURRENT, IRST (mA)
V2 = S1 = S2 = TOL = V1
10pF CAPACITOR AT RST
V1 = 3.3V
V2 = 1.5V
S1 = TOL = V1
S2 = OPEN
NO PULL-UP R
3.0
2.5
2.0
–40oC
1.5
85oC
1.0
25oC
0.5
–8
–6
–4
–2
–10
OUTPUT SOURCE CURRENT, IRST (MA)
0
29045 G23
–8
–7 –6 –5 –4 –3 –2
–1
OUTPUT SOURCE CURRENT, IRST (MA)
0
29045 G24
29045fd
6
LTC2904/LTC2905
TYPICAL PERFORMANCE CHARACTERISTICS
Specifications are at TA = 25°C unless otherwise noted.
IS1, IS2, ITOL vs Temperature
IS1, IS2, ITOL vs Temperature
–20
20
S1 = S2 = TOL = GND
–19
18
–18
17
–17
IS1, IS2, ITOL (MA)
IS1, IS2, ITOL (MA)
S1 = S2 = TOL = 3.3V
19
16
15
14
13
–16
–15
–14
–13
12
–12
11
–11
10
–50
–25
25
50
0
TEMPERATURE (oC)
75
100
29045 G25
PIN FUNCTIONS
–10
–50
–25
25
50
0
TEMPERATURE (oC)
75
100
29045 G26
(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 0.1μF
(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 200μs. 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 0.1μF (or greater)
capacitor.
29045fd
7
LTC2904/LTC2905
BLOCK DIAGRAM
VCC
LTC2904
6μA
–
RST
V1
+
VCC
POWER
DETECT
200ms
RESET PULSE
GENERATOR
RESISTOR
NETWORK
–
VCC
6μA
V2
+
RST
BAND GAP
REFERENCE
THREE-STATE DECODER
GND
2904 BD
S1
S2
TOL
LTC2905
–
TMR
VCC
V1
+
VCC
POWER
DETECT
6μA
RESISTOR
NETWORK
RESET PULSE
GENERATOR
–
RST
V2
+
BAND GAP
REFERENCE
THREE-STATE DECODER
GND
2905 BD
S1
S2
TOL
29045fd
8
LTC2904/LTC2905
TIMING DIAGRAM
VX Monitor Timing
VRTX
VX
tUV
tRST
RST
1V
RST
1V
29045 TD
APPLICATIONS INFORMATION
Supply Monitoring
Power-Up
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 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.
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.
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).
29045fd
9
LTC2904/LTC2905
APPLICATIONS INFORMATION
Power-Down
Tolerance Programming
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.
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.
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 10μA.
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 10μA.
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
V2
S1
S2
5.0
3.3
V1
V1
3.3
2.5
Open
GND
3.3
1.8
V1
Open
3.3
1.5
Open
V1
3.3
1.2
Open
Open
2.5
1.8
GND
GND
2.5
1.5
GND
Open
2.5
1.2
GND
V1
2.5
1.0
V1
GND
Table 2. Tolerance Programming
Tolerance
TOL
5%
V1
7.5%
Open
10%
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 10μA.
29045fd
10
LTC2904/LTC2905
APPLICATIONS INFORMATION
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.
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 200μs. 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 2.1μA (typical).
10000
RESET TIME OUT PERIOD, tRST (ms)
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.
1000
100
10
1
0.1
10p
100p
1n
10n
CTMR (FARAD)
100n
1μ
29045 F01
Figure 1. Reset Timeout Period vs Capacitance
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.
29045fd
11
LTC2904/LTC2905
APPLICATIONS INFORMATION
RST and RST Output Characteristics
Output Rise and Fall Time Estimation
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 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):
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.
tFALL ≈ 2.2 • RPD • CLOAD
where RPD is the on-resistance of the internal pull-down
transistor estimated to be typically 40Ω at room temperature (25°C) 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
6μA 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
Ω
MAX( V1,V2) – 1V
At VCC = 3.3V, RPU is about 260k. Using 150pF for load
capacitance, the rise time is 86μs. 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 3.3μs for a 150pF load capacitance, when using
a 10k pull-up resistor.
29045fd
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
510Ω
V2
1.2V
V1
2.5V
V2
1.2V
LTC2904
LTC2904
RST
S2
RST
S1
GND
TOL
0.1μF
0.1μF
SYSTEM
RESET
V1
LED
S2
RST
S1
RST
GND
TOL
0.1μF
0.1μF
29045 TA02
SYSTEM
RESET
29045 TA03
5V, 3.3V Dual Supply Monitor with Voltage
Margining for Automated On-Board Testing
5V
DC/DC
CONVERTER
SYSTEM
LOGIC
3.3V
V1
V2
LTC2905
VIN
SUPPLY
CONTROLLER
0.1μF
S1
0.1μF
TMR
22nF
THREE-STATE
S2
GND
TOL
RST
29045 TA04
3.3V, 1.2V Dual Supply Monitor with Asymmetric Hysteresis, 5%
Tolerance (Supplies Rising), 10% Tolerance (After RST Goes Low)
1.2V
V2
V1
LTC2904
3.3V
10k
S2
RST
S1
TOL
GND
RST
0.1μF
0.1μF
SYSTEM
RESET
29045 TA05
29045fd
13
LTC2904/LTC2905
PACKAGE DESCRIPTION
DDB Package
8-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1702 Rev B)
0.61 ±0.05
(2 SIDES)
3.00 ±0.10
(2 SIDES)
R = 0.115
TYP
5
R = 0.05
TYP
0.40 ± 0.10
8
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)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
2.00 ±0.10
(2 SIDES)
0.56 ± 0.05
(2 SIDES)
0.75 ±0.05
0 – 0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
4
0.25 ± 0.05
1
PIN 1
R = 0.20 OR
0.25 × 45°
CHAMFER
(DDB8) DFN 0905 REV B
0.50 BSC
2.15 ±0.05
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
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
29045fd
14
LTC2904/LTC2905
PACKAGE DESCRIPTION
TS8 Package
8-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1637)
0.52
MAX
2.90 BSC
(NOTE 4)
0.65
REF
1.22 REF
1.4 MIN
3.85 MAX 2.62 REF
2.80 BSC
1.50 – 1.75
(NOTE 4)
PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.22 – 0.36
8 PLCS (NOTE 3)
0.65 BSC
0.80 – 0.90
0.20 BSC
0.01 – 0.10
1.00 MAX
DATUM ‘A’
0.30 – 0.50 REF
0.09 – 0.20
(NOTE 3)
1.95 BSC
TS8 TSOT-23 0802
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
29045fd
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
V1
V2
1.2V
V2
LTC2905
TMR
0.1μF
TOL
S2
22nF
TMR
0.1μF
510Ω
0.1μF
LED
RST
GND
TOL
22nF
GND
S1
2.5V
V1
LTC2905
0.1μF
S2
S1
RST
29045 TA06
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC690
5V Supply Monitor, Watchdog Timer and Battery Backup
4.65V Threshold
LTC694-3.3
3.3V Supply Monitor, Watchdog Timer and Battery Backup
2.9V Threshold
LTC699
5V Supply Monitor and Watchdog Timer
4.65V Threshold
LTC1232
5V Supply Monitor, Watchdog Timer and Pushbutton Reset
4.37V/4.62V Threshold
LTC1326/LTC1326-2.5
Micropower Precision Triple Supply Monitor
for 5V/2.5V, 3.3V and ADJ
4.725V, 3.118V, 1V Threshold (±0.75%)
LTC1536
Precision Triple Supply Monitor for PCI Applications
Meets PCI tFAIL Timing Specifications
LTC1726-2.5/LTC1726-5
Micropower Triple Supply Monitor for 2.5V/5V, 3.3V and ADJ
Adjustable RESET and Watchdog Timeouts
LTC1727-2.5/LTC1727-5
Micropower Triple Supply Monitor with Open-Drain Reset
Individual Monitor Outputs in MSOP
LTC1728-1.8/LTC1728-3.3
Micropower Triple Supply Monitor with Open-Drain Reset
5-Lead SOT-23 Package
LTC1728-2.5/LTC1728-5
Micropower Triple Supply Monitor with Open-Drain Reset
5-Lead SOT-23 Package
LTC1985-1.8
Micropower Triple Supply Monitor with Push-Pull Reset Output
5-Lead SOT-23 Package
LTC2900
Programmable Quad Supply Monitor
Adjustable RESET, 10-Lead MSOP, DFN Packages
LTC2901
Programmable Quad Supply Monitor
Adjustable RESET and Watchdog Timer,
16-Lead SSOP Package
LTC2902
Programmable Quad Supply Monitor
Selectable Tolerance, RESET Disable for Margining
Functions, 16-Lead SSOP Package
LTC2903-1
Precision Quad Supply Monitor
Ultralow Voltage RESET, 6-Lead SOT-23 Package
LTC2906
Dual Supply Monitor with One Pin-Selectable Threshold and
One Adjustable Input
0.5V Adjustable Threshold and Three Supply
Tolerances, 8-Lead SOT-23 and DFN Packages
LTC2907
Dual Supply Monitor with One Pin-Selectable Threshold and
One Adjustable Input
0.5V Adjustable Threshold, Adjustable RESET Timer
and Three Supply Tolerances, 8-Lead SOT-23 and
DFN Packages
LTC2908
Precision Six Supply Monitors
Ultralow Voltage RESET, 8-Lead SOT-23 and DFN
Packages
29045fd
16 Linear Technology Corporation
LT 1109 REV D • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2003
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