LTC2931
1
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TYPICAL APPLICATION
FEATURES
APPLICATIONS
DESCRIPTION
Confi gurable Six Supply
Monitor with Adjustable Reset
and Watchdog Timers
The LTC
®
2931 is a confi gurable supply monitor for
systems with up to six supply voltages. One of 16 preset or
adjustable voltage monitor combinations can be selected
using an external resistive divider connected to the mode
select pin. The preset voltage thresholds are accurate
to ±1.5% over temperature. The LTC2931 also features
adjustable inputs with a 0.5V nominal threshold. All six
open-drain voltage comparator outputs are connected to
separate pins for individual supply monitoring.
The reset and watchdog timeout periods are adjustable
using external capacitors. Tight voltage threshold accuracy
and glitch immunity ensure reliable reset operation without
false triggering. The RST output is guaranteed to be in the
correct state for VCC down to 1V. Each status output has
a weak internal pull-up and may be externally pulled up
to a user defi ned voltage.
The 52μA supply current makes the LTC2931 ideal for
power conscious systems and it may be confi gured to
monitor fewer than six inputs.
Six Supply Monitor 12V (ADJ), 5V, 3.3V, 2.5V, 1.8V, 1.2V (ADJ)
■ Simultaneously Monitors Six Supplies
■ 16 User Selectable Combinations of
5V, 3.3V, 3V, 2.5V, 1.8V, 1.5V and ± Adjustable
Voltage Thresholds
■ Guaranteed Threshold Accuracy: ±1.5%
■ Adjustable Reset and Watchdog Timeout
■ Low Supply Current: 52μA
■ Comparator/Monitor Output for Each Supply
■ Power Supply Glitch Immunity
■ Guaranteed RST for VCC ≥ 1V
■ High Temperature Operation to 125°C
■ 20-Lead TSSOP Package
■ Desktop and Notebook Computers
■ Multivoltage Systems
■ Telecom Equipment
■ Portable Battery-Powered Equipment
■ Network Servers
■ Automotive
COMP1
COMP2
COMP3
COMP4
COMP5
COMP6
LTC2931
1.2V
1.8V
2.5V
3.3V
5V
12V
2931 TA01
tRST = 94ms
tWD = 940ms
CWT
47nF
CRT
47nF
RST
WDO
WDI
VPG
GND CWT CRT
V1
V2
V3
V4
V5
V6
VREF
SYSTEM
LOGIC
POWER
GOOD
R1
59k
1%
100k
1%
100k
1%
124k
1%
2150k
1%
R2
40.2k
1%
0.1μF
0.1μF
10k
V1 (V) V2 (V) V3 (V) V4 (V) V5 (V) V6 (V)
5.0 3.3 2.5 1.8 ADJ ADJ
5.0 3.3 2.5 1.5 ADJ ADJ
5.0 3.3 2.5 ADJ ADJ ADJ
5.0 3.3 1.8 ADJ ADJ ADJ
5.0 3.3 1.8 –ADJ ADJ ADJ
5.0 3.3 ADJ ADJ ADJ ADJ
5.0 3.3 ADJ –ADJ ADJ ADJ
5.0 3.0 2.5 ADJ ADJ ADJ
5.0 3.0 1.8 ADJ ADJ ADJ
5.0 3.0 ADJ ADJ ADJ ADJ
3.3 2.5 1.8 1.5 ADJ ADJ
3.3 2.5 1.8 ADJ ADJ ADJ
3.3 2.5 1.8 –ADJ ADJ ADJ
3.3 2.5 1.5 ADJ ADJ ADJ
3.3 2.5 ADJ ADJ ADJ ADJ
3.3 2.5 ADJ –ADJ ADJ ADJ
Voltage Threshold Confi guration Table
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 6967591, 7239251, 7119714.
LTC2931
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PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS
V1, V2, V3, V4, V5, V6, VPG ........................ –0.3V to 7V
RST , COMP1-6............................................ –0.3V to 7V
CWT, WDO .................................................... –0.3V to 7V
CRT, VREF, WDI .............................–0.3V to (VCC + 0.3V)
Reference Load Current (IVREF) ..............................±1mA
V4 Input Current (–ADJ Mode) ..............................–1mA
RST , WDO, COMP1-6 Currents ...........................±10mA
Operating Temperature Range
LTC2931C ................................................ 0°C to 70°C
LTC2931I.............................................. –40°C to 85°C
LTC2931H .......................................... –40°C to 125°C
Storage Temperature Range ................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
(Notes 1, 2, 3)
F PACKAGE
20-LEAD PLASTIC TSSOP
1
2
3
4
5
6
7
8
9
10
TOP VIEW
20
19
18
17
16
15
14
13
12
11
COMP5
V5
COMP3
COMP1
V3
V1
CRT
RST
WDO
WDI
COMP6
V6
COMP2
COMP4
V2
V4
VREF
VPG
GND
CWT
TJMAX = 130°C, θJA = 90°C/W
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC2931CF#PBF LTC2931CF#TRPBF LTC2931F 20-Lead Plastic TSSOP 0°C to 70°C
LTC2931IF#PBF LTC2931IF#TRPBF LTC2931F 20-Lead Plastic TSSOP –40°C to 85°C
LTC2931HF#PBF LTC2931HF#TRPBF LTC2931F 20-Lead Plastic TSSOP –40°C to 125°C
Consult LTC Marketing for information on non-standard lead based fi nish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
This product is only offered in trays. For more information go to: http://www.linear.com/packaging/
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VCC Minimum Internal Operating Voltage RST, COMPn in Correct Logic State ●1V
VCCMINP Minimum Required for Mode Selection VCC Rising ●2.4 V
VCCMINC Minimum Required for Comparators VCC Falling ●2.3 V
VRT50 5V, 5% Reset Threshold V1 Input Threshold ●4.600 4.675 4.750 V
VRT33 3.3V, 5% Reset Threshold V1, V2 Input Threshold ●3.036 3.086 3.135 V
VRT30 3V, 5% Reset Threshold V2 Input Threshold ●2.760 2.805 2.850 V
VRT25 2.5V, 5% Reset Threshold V2, V3 Input Threshold ●2.300 2.338 2.375 V
VRT18 1.8V, 5% Reset Threshold V3, V4 Input Threshold ●1.656 1.683 1.710 V
VRT15 1.5V, 5% Reset Threshold V3, V4 Input Threshold ●1.380 1.403 1.425 V
VRTA ADJ Reset Threshold V3, V4, V5, V6 Input Threshold ●492.5 500 507.5 mV
VRTAN –ADJ Reset Threshold V4 Input Threshold ●–18 0 18 mV
The ● denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at TA = 25°C. VCC = 5V, unless otherwise specifi ed. (Note 3)
LTC2931
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SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VREF Reference Voltage VCC ≥ 2.3V, IVREF = ±1mA,
CREF ≤ 1000pF
●1.192 1.210 1.228 V
VPG Mode Selection Voltage Range VCC ≥ VCCMINP ●0V
REF V
IVPG VPG Input Current VPG = VREF ●±20 nA
IV1 V1 Input Current V1 = 5V, IVREF = 12μA (Note 4) ●52 75 μA
IV2 V2 Input Current V2 = 3.3V ●0.8 2 μA
IV3 V3 Input Current V3 = 2.5V
V3 = 0.55V (ADJ Mode)
●
●–15
0.52 1.2
15
μA
nA
IV4 V4 Input Current V4 = 1.8V
V4 = 0.55V (ADJ Mode)
V4 = –0.02V (–ADJ Mode)
●
●
●
–15
–15
0.34 0.8
15
15
μA
nA
nA
IV5, IV6 V5, V6 Input Current V5, V6 = 0.55V ●–15 15 nA
ICRT(UP) CRT Pull-Up Current VCRT = GND ●–1.4 –2 –2.6 μA
ICRT(DN) CRT Pull-Down Current VCRT = 1.3V ●10 20 30 μA
tRST Reset Timeout Period CRT = 1500pF ●234 ms
tUV Vn Undervoltage Detect to RST or
COMPn
Vn Less Than Reset Threshold by More
than 1%
150 μs
VOL Voltage Output Low RST, COMPnISINK = 3mA, VCC = 3V
ISINK = 100μA, VCC = 1V
●
●
0.15
0.05
0.4
0.3
V
V
ICOMPn COMPn Pull-Up Current VCOMPn = GND ●–2 –6 –12 μA
VOL Voltage Output Low WDO ISINK = 3mA ●0.15 0.4 V
VOH Voltage Output High RST, WDO, COMPn
(Note 5)
ISOURCE = –1μA ●V2-1 V
ICWT(UP) CWT Pull-Up Current VCWT = GND ●–1.4 –2 –2.6 μA
ICWT(DN) CWT Pull-Down Current VCWT = 1.3V ●10 20 30 μA
tWD Watchdog Timeout Period CWT = 1500pF ●20 30 40 ms
VIH WDI Input Threshold High VCC = 3.3V to 5.5V ●1.6 V
VIL WDI Input Threshold Low VCC = 3.3V to 5.5V ●0.4 V
tWP WDI Input Pulse Width VCC = 3.3V ●150 ns
IWDI WDI Pull-Up Current VWDI = 1V ●–4 –10 –16 μA
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device reliability
and lifetime.
Note 2: All currents into pins are positive, all voltages are referenced to GND
unless otherwise noted.
Note 3: The greater of V1, V2 is the internal supply voltage (VCC).
Note 4: Under static no-fault conditions, V1 will necessarily supply quiescent
current. If at any time V2 is larger than V1, V2 must be capable of supplying
the quiescent current, programming (transient) current and reference load
current.
Note 5: The output pins RST, WDO, and COMPn have diode protected internal
pull-ups to V2 of typically 6μA. However, external pull-up resistors may be used
when faster rise times are required or for VOH voltages greater than V2.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at TA = 25°C. VCC = 5V, unless otherwise specifi ed. (Note 3)
LTC2931
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TI
M
I
NG
DI
AGRAM
S
tRST
2931 TD
VRT
Vn
RST
COMPn
tUV
Vn Monitor Timing
tRST
tWP
t<t
RST
tWD tWD
2931 TD2
RST
WDI
WDO
tRST tRST
tWD
Watchdog Timing
LTC2931
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TEMPERATURE (°C)
–50
NORMALIZED THRESHOLD VOLTAGES (V/V)
1.005
1.010
1.015
25 75
2931 G01
1.000
0.995
–25 0 50 100 125
0.990
0.985
TEMPERATURE (oC)
–50
THRESHOLD VOLTAGE, VRTAN (mV)
6
12
18
25 75
2931 G02
0
–6
–25 0 50 100 125
–12
–18
TEMPERATURE (°C)
–50
VREF (V)
1.216
1.222
1.228
25 75
2931 G03
1.210
1.204
–25 0 50 100 125
1.198
1.192
TEMPERATURE (oC)
–50
SUPPLY CURRENT, IV1 (MA)
60
65
70
25 75
2931 G04
55
50
–25 0 50 100 125
45
40
V1 = 5V
V2 = 3.3V
V3 = 2.5V
V4 = 1.8V
V5 = V6 = 1V
V4 (mV)
IV4 (A)
2931 G05
–100μ
–10μ
–1μ
–100n
–10n
–1n
–100p
–300
125°C
90°C
25°C
–250 –200 –50 0–100–150
RESET COMPARATOR OVERDRIVE (% OF VRTX)
0.1
0
TYPICAL TRANSIENT DURATION (Ms)
200
250
300
1 10 100
2931 G06
150
100
50
TA = 25oC
RESET OCCURS ABOVE CURVE
RESET COMPARATOR OVERDRIVE (% OF VRTX)
0.1
0
TYPICAL TRANSIENT DURATION (Ms)
300
375
450
1 10 100
2931 G07
225
150
75
TA = 25oC
RESET OCCURS ABOVE CURVE
V1 (V)
0
0
RST OUTPUT VOLTAGE (V)
1
2
3
4
5
6
1234
2931 G08
5
TA = 25oC
10k PULL-UP FROM RST TO V1
TEMPERATURE (oC)
–50
WATCHDOG TIMEOUT PERIOD, tWD (ms)
32
34
36
25 75
2931 G09
30
28
–25 0 50 100 125
26
24
CWT = 1500pF
(SILVER MICA)
TYPICAL PERFORMANCE CHARACTERISTICS
Normalized Threshold Voltages
vs Temperature
–ADJ Threshold Voltage
vs Temperature VREF vs Temperature
Supply Current vs Temperature
Transient Duration vs Comparator
Overdrive (V1,V2)
Transient Duration vs Comparator
Overdrive (V3, V4, V5, V6)
RST Output Voltage vs V1,
VPG = GND
Watchdog Timeout Period
vs Temperature
I(V4) vs V4 in Negative
Adjust Mode
LTC2931
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TEMPERATURE (oC)
–50
1
RESET TIMEOUT PERIOD, tRST (ms)
2
3
4
5
–25 0 25 50
2931 G10
75 100 125
CRT = 1500pF
(SILVER MICA)
CWT (F)
WATCHDOG TIMEOUT PERIOD tWD (s)
2931 G11
100
10
1
100m
10m
1m
100μ10p 100p 1n 100n 1M10n
TA = 25oC
CRT (F)
RESET TIMEOUT PERIOD tRST (s)
2931 G12
10
1
100m
10m
1m
100M
10M10p 100p 1n 100n 1M10n
TA = 25oC
V1 OR V2 (V)
0
ISINK (mA)
9
12
15
4
2931 G13
6
3
01235
TA = 25oC
VOL = 0.4V
VOL = 0.2V
ISINK (mA)
0
VOL (mV)
300
400
500
8
2931 G14
200
100
024610
V1 = 5V
V2 = 3V 125oC
85oC
25oC
–40oC
V2 (V)
1
0
PULL-UP CURRENT (MA)
3
6
9
12
15
18
23 45
2931 G15
TA = 25oC
COMPn = WDO = GND
INPUT OVERDRIVE ABOVE THRESHOLD (mV)
COMPn PROPAGATION DELAY (Ms)
250
200
150
2931 G16
0
100
50
1000
10 100
TA = 25oC
V1, V2
V3, V4, V5, V6
V2 (V)
2.0
0
PULL-UP CURRENT (MA)
3
6
9
12
18
2.5 3.0 3.5 4.0
2931 G17
4.5 5.0
15
TA = 25oC
VRT25
VRT30
VRT33
TYPICAL PERFORMANCE CHARACTERISTICS
Watchdog Timeout Period vs CWT Reset Timeout Period vs CRT
Voltage Output Low vs Output
Sink Current (RST, WDO, COMPn)
COMPn and WDO Pull-Up Current
vs V2
RST Pull-Up Current vs V2
COMPn Propagation Delay vs
Input Overdrive Above Threshold
ISINK vs Supply Voltage
(RST, WDO, COMPn)
Reset Timeout Period
vs Temperature
LTC2931
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PIN FUNCTIONS
COMP5 (Pin 1): Comparator Output 5. Real-time logic
output with weak 6μA pull-up to V2. Pulls high when V5
is above reset threshold. May be pulled greater than V2
using external pull-up. Leave open if unused.
V5 (Pin 2): Adjustable Voltage Input 5. High impedance
comparator input with 0.5V typical threshold. See
Applications Information for details. Tie to V1 if unused.
COMP3 (Pin 3): Comparator Output 3. Real-time logic
output with weak 6μA pull-up to V2. Pulls high when V3
is above its reset threshold. May be pulled greater than
V2 using external pull-up. Leave open if unused.
COMP1 (Pin 4): Comparator Output 1. Real-time logic
output with weak 6μA pull-up to V2. Pulls high when V1
is above its reset threshold. May be pulled greater than
V2 using external pull-up. Leave open if unused.
V3 (Pin 5): Voltage Input 3. Select from 2.5V, 1.8V, 1.5V,
or ADJ. See Applications Information for details. Tie to
V1 if unused.
V1 (Pin 6): Voltage Input 1. Select from 5V or 3.3V. See
Applications Information for details. The greater of V1 or
V2 is also VCC for the device. Bypass this pin to ground
with a 0.1μF (or greater) capacitor.
CRT (Pin 7): Reset Timeout Capacitor. Attach an external
capacitor (CRT) to GND to set a reset timeout of 2ms/nF.
Leaving the pin open generates a minimum delay of
approximately 25μs. A 47nF capacitor generates a 94ms
reset delay time.
RST (Pin 8): Reset Output. Logic output with weak 6μA
pull-up to V2. Pulls low when any voltage input is below
the reset threshold and held low for the confi gured delay
time after all voltage inputs are above threshold. May be
pulled greater than V2 using external pull-up. Leave open
if unused.
WDO (Pin 9): Watchdog Output. Logic output with weak
6μA pull-up to V2. May be pulled greater than V2 using
external pull-up. The watchdog timer is enabled when RST
is high. The watchdog output pulls low if the watchdog timer
times out and remains low for one reset timeout period.
The watchdog output is cleared with a WDI transition or
anytime RST is low.The output will toggle between high
and low as long as the watchdog and reset timers are
allowed to time out. Leave open if unused.
WDI (Pin 10): Watchdog Input. A logic input whose rising
or falling edge must occur on this pin (while RST is high)
within the selected watchdog time-out period, prohibiting
a high-to-low transition on the WDO pin. The capacitor
attached to the CWT pin sets the watchdog time-out period.
A rising or falling edge on the WDI pin clears the voltage
on the CWT capacitor, preventing WDO from going low. Tie
WDI to V1 or GND if unused. Tie CWT to GND to disable
the watchdog function.
CWT (Pin 11): Watchdog Timeout Capacitor. Attach
a capacitor (CWT) between CWT and GND to set a
watchdog time-out period of 20ms/nF. Leaving the pin open
generates a minimum timeout of approximately 200μs.
A 47nF capacitor generates a 940ms watchdog time-out
period. Tie CWT to GND to disable the watchdog function.
GND (Pin 12): Ground.
VPG (Pin 13): Threshold Select Input. Connect to an
external 1% resistive divider between VREF and GND to
select 1 of 16 combinations and/or ±adjustable voltage
thresholds (See Table 1). Do not add capacitance on the
VPG pin.
VREF (Pin 14): Buffered Reference Voltage Output. A
1.210V nominal reference used for the mode selection
voltage (VPG) and for the offset of negative adjustable
applications. The buffered reference can source and sink
up to 1mA. The reference can drive a bypass capacitor of
up to 1000pF without oscillation.
V4 (Pin 15): Voltage Input 4. Select from 1.8V, 1.5V, ADJ
or –ADJ. See Applications Information for details. Tie to
V1 if unused and confi gured for positive voltage.
V2 (Pin 16): Voltage Input 2. Select from 3.3V, 3V or 2.5V.
See Applications Information for details. The greater of V1,
V2 is also VCC for the device. Bypass this pin to ground
with a 0.1μF (or greater) capacitor. All status outputs are
weakly pulled up to V2.
COMP4 (Pin 17): Comparator Output 4. Real-time logic
output with weak 6μA pull-up to V2. Pulls high when V4
is above its reset threshold. May be pulled greater than
V2 using external pull-up. Leave open if unused.
LTC2931
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PIN FUNCTIONS
V2
6μA
20
COMP6
1
COMP5
V2
6μA
17
COMP4
V2
6μA
3
COMP3
V2
6μA
18
COMP2
V2
6μA
4
COMP1
A/D
BUFFER
1.210V
13
VPG
6
V1
16
V2
5
V3
15
V4
2
V5
19
V6
14
VREF
4
0.5V
4
2931 BD
BANDGAP
REFERENCE
ADJUSTABLE
RESET PULSE
GENERATOR
TRANSITION
DETECT
WATCHDOG
TIMER
POWER
DETECT
V1
V2
VCC
1110 CWTWDI
CWT
CRT
VCC
VCC
22μA
2μA
10μA
RESISTIVE
DIVIDER
MATRIX
4
4
4
–
+
–
+
–
+
VCC
2μA
22μA
7
CRT
V2
6μA
9
WDO
12
GND
V2
6μA
V2
6μA
8
RST
CMP1-4
CMP5
CMP6
BLOCK DIAGRAM
COMP2 (Pin 18): Comparator Output 2. Real-time logic
output with weak 6μA pull-up to V2. Pulls high when V2
is above its reset threshold. May be pulled greater than
V2 using external pull-up. Leave open if unused.
V6 (Pin 19): Adjustable Voltage Input 6. High impedance
comparator input with 0.5V typical threshold. See
Applications Information for details. Tie to V1 if unused.
COMP6 (Pin 20): Comparator Output 6. Real-time logic
output with weak 6μA pull-up to V2. Pulls high when V6
is above its reset threshold. May be pulled greater than
V2 using external pull-up. Leave open if unused.
LTC2931
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APPLICATIONS INFORMATION
Supply Monitoring
The LTC2931 is a low power, high accuracy confi gurable
six supply monitoring circuit with six real-time monitor
outputs, a common reset output and a watchdog timer.
External capacitors set the reset and watchdog timeout
periods. An external resistive divider between VREF, VPG
and GND selects 1 of 16 possible input voltage monitor
combinations. All six voltage inputs must be above their
predetermined thresholds for the reset not to be activated.
The LTC2931 asserts the reset and comparator outputs
during power-up, power-down and brownout conditions
on any one of the voltage inputs.
Power-Up
The greater of V1 and V2 serves as the internal supply
voltage (VCC). On power-up, VCC powers the drive circuits
for the RST pin. This ensures that the RST output will be
low as soon as either V1 or V2 reaches 1V. The RST output
remains low until the part is confi gured. Once voltage
thresholds are set, if any of the supply monitor inputs is
below its confi gured threshold, RST will be a logic low.
Once all the monitor inputs rise above their thresholds,
an internal timer is started and RST is released after the
delay time. If VCC < (V3 – 1.0V) and VCC < 2.4V, the V3
input impedance will be low (10kΩ typical).
Threshold Accuracy
Consider a 5V system with ±5% tolerance. The 5V supply
may vary between 4.75V to 5.25V. System ICs powered
by this supply must operate reliably within this band (and
a little more as explained below). A perfectly accurate
supervisor for this supply generates a reset at exactly
4.75V, however no supervisor is this perfect. The actual
reset threshold of a supervisor varies over a specifi ed band;
the LTC2931 varies ±1.5% around its nominal threshold
voltage (see Figure 1) over temperature.
The reset threshold band and the power supply tolerance
bands should not overlap. This prevents false or nuisance
resets when the power supply is actually within its speci-
fi ed tolerance band.
The LTC2931 has a ±1.5% reset threshold accuracy, so a
“5%” threshold is typically set to 6.5% below the nominal
input voltage. Therefore, a typical 5V, “5%” threshold is
R1
1%
R2
1%
2931 F02
VREF
VPG
GND
LTC2931
Figure 2. Mode Selection
4.675V. The threshold is guaranteed to lie in the band
between 4.750V and 4.600V over temperature. The
powered system must work reliably down to the low end
of the threshold band, or risk malfunction before a reset
signal is properly issued.
A less accurate supervisor increases the required system
voltage margin and increases the probability of system
malfunction. The LTC2931 ±1.5% specifi cation improves
the reliability of the system over supervisors with wider
threshold tolerances.
Monitor Confi guration
Select the LTC2931 input voltage combination by placing
the recommended resistive divider from VREF to GND
and connecting the tap point to VPG, as shown in Figure
2. Table 1 offers recommended 1% resistor values for
each of the 16 modes. The last column in Table 1 specifi es
optimum VPG/VREF ratios (± 0.01), when confi guring with
a ratiometric DAC.
At power-up, once V1 or V2 reaches 2.4V, the monitor
enters a setup period of approximately 150μs. During the
setup time, the voltage on the VPG pin is sampled and
the monitor is confi gured to the desired input combina-
5V
4.75V
4.675V
±1.5%
THRESHOLD
BAND
4.6V
NOMINAL
SUPPLY
VOLTAGE
SUPPLY TOLERANCE
MINIMUM
RELIABLE
SYSTEM
VOLTAGE
IDEAL
SUPERVISOR
THRESHOLD
REGION OF POTENTIAL MALFUNCTION
–5%
–6.5%
–8%
Figure 1. 1.5% Threshold Accuracy Improves System Reliability
LTC2931
10
2931fb
APPLICATIONS INFORMATION
tion. The comparators are enabled and supply monitoring
begins. Do not add capacitance to the VPG pin.
Using The Adjustable Thresholds
The reference inputs on the V3 and/or V4 comparators
are set to 0.5V when the positive adjustable modes are
selected (Figure 3). The reference inputs on the V5 and V6
comparators are always set to 0.5V. The tap point on an
external resistive divider, connected between the positive
voltage being sensed and ground, is connected to the high
Figure 3. Setting the Positive Adjustable Trip Point
+
–0.5V
2931 F03
V3, V4, V5 OR V6
VTRIP
R3
1%
R4
1%
LTC2931
2931 F04
V4
VREF
VTRIP
R4
1%
R3
1%
LTC2931
Figure 4. Setting the Negative Adjustable Trip Point
VSUPPLY (V) VTRIP (V) R3 (kΩ) R4 (kΩ)
12 11.25 2150 100
10 9.4 1780 100
8 7.5 1400 100
7.5 7 1300 100
6 5.6 1020 100
5 4.725 845 100
3.3 3.055 511 100
3 2.82 464 100
2.5 2.325 365 100
1.8 1.685 237 100
1.5 1.410 182 100
1.2 1.120 124 100
1 0.933 86.6 100
0.9 0.840 68.1 100
Table 2. Suggested 1% Resistor Values for the ADJ Inputs
VSUPPLY (V) VTRIP (V) R3 (kΩ) R4 (kΩ)
–2 –1.87 187 121
–5 –4.64 464 121
–5.2 –4.87 487 121
–10 –9.31 931 121
–12 –11.30 1130 121
Table 3. Suggested 1% Resistor Values for the –ADJ Inputs
impedance, adjustable inputs (V3, V4, V5, V6). Calculate
the trip voltage from:
V
TRIP =0.5V • 1+R3
R4
In the negative adjustable mode, the reference level on the
V4 comparator is connected to ground (Figure 4). The tap
point on an external resistive divider, connected between
Table 1. Voltage Threshold Modes*
MODE V1 (V) V2 (V) V3 (V) V4 (V) R1 (kΩ) R2 (kΩ)
VPG
VREF
0 5.0 3.3 ADJ ADJ Open Short 0.000
1 5.0 3.3 ADJ –ADJ 93.1 9.53 0.094
2 3.3 2.5 ADJ ADJ 86.6 16.2 0.156
3 3.3 2.5 ADJ –ADJ 78.7 22.1 0.219
4 3.3 2.5 1.5 ADJ 71.5 28.0 0.281
5 5.0 3.3 2.5 ADJ 66.5 34.8 0.344
6 5.0 3.3 2.5 1.8 59.0 40.2 0.406
7 5.0 3.3 2.5 1.5 53.6 47.5 0.469
8 5.0 3.0 2.5 ADJ 47.5 53.6 0.531
9 5.0 3.0 ADJ ADJ 40.2 59.0 0.594
10 3.3 2.5 1.8 1.5 34.8 66.5 0.656
11 3.3 2.5 1.8 ADJ 28.0 71.5 0.719
12 3.3 2.5 1.8 –ADJ 22.1 78.7 0.781
13 5.0 3.3 1.8 –ADJ 16.2 86.6 0.844
14 5.0 3.3 1.8 ADJ 9.53 93.1 0.906
15 5.0 3.0 1.8 ADJ Short Open 1.000
*V5 and V6 are always adjustable (ADJ).
LTC2931
11
2931fb
APPLICATIONS INFORMATION
low as long as the watchdog and reset timers are allowed
to time out repeatedly.
To disable the watchdog timer, simply ground the CWT
pin (Pin 11). With CWT held at ground, any reset event
forces WDO high indefi nitely. It is safe to leave the WDI
pin unconnected because the weak internal pull-up (10μA
typical) pulls WDI high. Tying WDI to V1 or ground is also
allowed, but grounding the WDI pin forces the pull-up
current to be drawn continuously.
Selecting the Reset Timing Capacitor
The reset timeout period is adjustable in order to
accommodate a variety of microprocessor applications.
The reset timeout period, tRST
, is adjusted by connecting
a capacitor, CRT
, between the CRT pin and ground. The
value of this capacitor is determined by:
CRT =tRST
2MΩ=500 pF / ms
⎡
⎣⎤
⎦•t
RST
Leaving the CRT pin unconnected generates a minimum
reset timeout of approximately 25μs. Maximum reset
timeout is limited by the largest available low leakage
capacitor. The accuracy of the timeout period is affected
by capacitor leakage (the nominal charging current is 2μA)
and capacitor tolerance. A low leakage ceramic capacitor
is recommended.
Selecting The Watchdog Timing Capacitor
The watchdog timeout period is adjustable and can be
optimized for software execution. The watchdog timeout
period, tWD, is adjusted by connecting a capacitor, CWT
,
between the CWT pin and ground. The value of this
capacitor is determined by:
CWT =tWD
20MΩ=50 pF / ms
⎡
⎣⎤
⎦•t
WD
Leaving the CWT pin unconnected generates a minimum
watchdog timeout of approximately 200μs. Maximum
watchdog timeout is limited by the largest available low
leakage capacitor. The accuracy of the timeout period is
affected by capacitor leakage (the nominal charging current
is 2μA) and capacitor tolerance. A low leakage ceramic
capacitor is recommended.
the negative voltage being sensed and the VREF pin, is
connected to the high impedance adjustable input (V4).
VREF provides the necessary level shift required to operate
at ground. The negative trip voltage is calculated from:
VTRIP =–V
REF •R3
R4
; VREF = 1.210V Nominal
In a negative adjustable application, the minimum value for
R4 is limited by the sourcing capability of VREF (±1mA).
With no other load on VREF, R4 (minimum) is:
1.210V
1mA =1.210kΩ
Tables 2 and 3 offer suggested 1% resistor values for
various positive and negative supply adjustable
applications assuming 5% monitor thresholds.
Although all six supply monitor comparators have built-
in glitch immunity, bypass capacitors on V1 and V2 are
recommended because the greater of V1 or V2 is also the
VCC for the device. Filter capacitors on the V3, V4, V5 and
V6 inputs are allowed.
Power-Down
On power-down, once any of the monitor inputs drops
below its threshold, RST is held at a logic low. A logic low
of 0.4V is guaranteed until both V1 and V2 drop below
1V. If the bandgap reference becomes invalid (VCC < 2V
typical), the LTC2931 will enter the 150μs setup period
when VCC rises above 2.4V max.
Watchdog Timer
The watchdog circuit monitors a microprocessor’s (μP)
activity. The μP is required to change the logic state of the
WDI pin on a periodic basis in order to clear the watchdog
timer. Whenever RST is low, the watchdog timer is cleared
and WDO is set high. The watchdog timer starts when RST
goes high. Subsequent edges received on the WDI pin
clear the watchdog timer. The watchdog timer continues
to run until it times out. Once it times out, internal circuitry
brings the WDO pin low. WDO remains low for one reset
timeout period unless it is cleared by another edge on the
WDI pin or RST goes low. WDO toggles between high and
LTC2931
12
2931fb
Supply and Temperature Monitor
Figure 5 illustrates how to confi gure the LTC2931 to
monitor temperature. Temperature is sensed by a
thermistor, RNTC, as part of a voltage divider driving
adjustable input V6. Output COMP6 goes low when the
temperature is higher than the trip point, and is fed back
through RHYST to provide hysteresis.
Assume a thermistor (RNTC) with values RHOT at the up-
per threshold and RCOLD at the lower threshold. Minimize
errors arising from V6 input current (15nA maximum)
by choosing RCOLD ≤ 100kΩ, and to limit the loading
on VREF, choose RHOT ≥ 1kΩ. RBIAS and RHYST are
calculated from:
RBIAS = (RHOT/VRTA) • (VREF – VRTA) = 1.42 • RHOT
RHYST =V1
V
RTA
•RCOLD • RHOT
()
RCOLD −RHOT
()
V1 is the nominal operating voltage at input V1, VREF =
1.210V, VRTA = 0.5V, and RPU < RHYST. The closest 1%
value was chosen for RHYST.
In Figure 5, the trip points are 115°C with RHOT = 11.1kΩ
(COMP6 goes low) and 100°C with RCOLD = 18.5kΩ
(COMP6 goes high). A reset is generated in the event of
an over-temperature condition. COMP6 (Temp Good) and
COMP5 (Power Good) distinguish over-temperature and
undervoltage faults.
Five Supply Power-up Sequencer
In Figure 6, the LTC2931’s real-time COMP outputs are
used to enable DC/DC converters sequentially. The system
is powered by a 12V source.
The system is started when the push-button is pressed and
the LTC2950-1 brings the RUN pin of the LTM4600 high.
Subsequently, the LTM4600 generates a 5V output which
applies power to each of the 4 DC/DC converters.
The LTC2931 is confi gured to mode 13 (see Table 1). When
the threshold is reached on V1, COMP1 pulls high. COMP1
then enables the 3.3V converter fi rst. When the threshold
is reached on V2, COMP2 pulls high and enables the 1.8V
converter next. When all the converters have been enabled
and are good, COMP5 pulls high. RST pulls high 9.4ms
after COMP5. Figure 7 shows the power-up sequence of
the fi ve supplies and the DONE and RST outputs.
If the KILL input on the LTC2950-1 does not receive a logic
high within 512ms of initial power-up, EN pulls low and
the LTM4600 is powered down.
In the event that the external 12V supply drops below
9.6V, COMP6 and RST will pull low. The LTC2950-1 then
receives a logic low on the KILL input, which powers down
the LTM4600 and the sequencing circuit.
APPLICATIONS INFORMATION
COMP1
COMP2
COMP3
COMP4
COMP5
COMP6
VREF
V6
LTC2931
POWER GOOD
*PANASONIC ERTJOEV474J
**OPTIONAL FOR ESD PROTECTION
TEMP GOOD
2931 F05
121k
1%
467k 1%
RBIAS
15.8k
1%
R1
93.1k
1%
R2
9.53k
1%
RNTC*
470k
10k
5V
0.1μF
3.3V
12V
28V
–5.2V
100k
1%
RPU
10k 10k
100k
1%
tRST = 94ms
tWD = 940ms
CWT
47nF
CRT
47nF
RST
WDO
WDI
VPG GND CRT CWT
V1
V2
V3
V5
V4
RHYST
280k
1%
10k**
MANUAL RESET
PUSH BUTTON
2150k 1%
5110k 1%
SYSTEM
LOGIC
Figure 5. Supply and Temperature Monitor (5V, 3.3V, 28V, -5.2V, 12V, 115°C)
LTC2931
13
2931fb
COMP1 COMP2 COMP3 COMP4 COMP5 COMP6
LTC2931
12V (9.6V THRESHOLD)
12V SUPPLY STATUS
DONE
2.5V
–5.2V
1.8V
3.3V
5V
2931 F06
365k
1%
487k
1%
5V
10k 10k
10k 0.1μF
tRST = 9.4ms
4.7nF
WDI
WDO
VPG GND
CRT CWT
V1
V2
V3
V4
V5
V6
RST
VREF
SYSTEM
LOGIC
10k
LT3028
VIN 3.3V
VOUT
SHDN
LTM4600
VIN
VOUT
RUN
10k
LT3028
VIN 1.8V
VOUT
SHDN
10k
LTC3704
VIN –5.2V
VOUT
RUN/UVLO
10k
LT3028
VIN 2.5V
VOUT
SHDN
100k
1%
121k
1%
1820k
1%
100k
1%
R1
16.2k
1%
R2
86.6k
1%
LTC2950-1
VIN INT
PB KILL
EN
APPLICATIONS INFORMATION
Figure 6. Five Supply Power-Up Sequencer with Push Button (Watchdog Functions Disabled)
LTC2931
14
2931fb
APPLICATIONS INFORMATION
2V/DIV
PB
5V
3.3V
2.5V
1.8V
–5.2V
DONE
RST
10ms/DIV 2931 FO7
Figure 7. Five Supply Power-Up Sequencing (Based on Circuit in Figure 6)
LTC2931
15
2931fb
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
PACKAGE DESCRIPTION
F Package
20-Lead Plastic TSSOP (4.4mm)
(Reference LTC DWG # 05-08-1650)
F20 TSSOP 0204
0.09 – 0.20
(.0035 – .0079)
0° – 8°
0.25
REF
0.50 – 0.75
(.020 – .030)
4.30 – 4.50**
(.169 – .177)
134
5678910
111214 13
6.40 – 6.60*
(.252 – .260)
20 19 1817 16 15
1.10
(.0433)
MAX
0.05 – 0.15
(.002 – .006)
0.65
(.0256)
BSC
6.40
(.252)
BSC
0.19 – 0.30
(.0075 – .0118)
TYP
2
MILLIMETERS
(INCHES)
DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED .152mm (.006") PER SIDE
DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED .254mm (.010") PER SIDE
*
**
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS
2. DIMENSIONS ARE IN
3. DRAWING NOT TO SCALE
RECOMMENDED SOLDER PAD LAYOUT
0.45 ±0.05 0.65 BSC
4.50 ±0.10
6.60 ±0.10
1.05 ±0.10
LTC2931
16
2931fb
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2008
LT 0508 REV B • PRINTED IN USA
TYPICAL APPLICATION
PART NUMBER DESCRIPTION COMMENTS
LTC690 5V Supply Monitor, Watchdog Timer and Battery Backup 4.65 Threshold
LTC694-3.3 3.3V Supply Monitor, Watchdog Timer and Battery Backup 2.9V Threshold
LTC1232 5V Supply Monitor, Watchdog Timer and Pushbutton Reset 4.37V/4.62V Threshold
LTC1326 Micropower Triple Supply Monitor for 5V/2.5V, 3.3V and ADJ 4.725V, 3.118V, 1V Threshold (±0.75%) and ADJ
LTC1726 Micropower Triple Supply Monitor for 2.5V/5V, 3.3V and ADJ Adjustable Reset and Watchdog Timeouts
LTC1727 Micropower Triple Supply Monitor with Open-Drain Reset Individual Monitor Outputs in MSOP
LTC1728 Micropower Triple Supply Monitor with Open-Drain Reset 5-Lead SOT-23 Package
LTC1985 Micropower Triple Supply Monitor with Push-Pull Reset Output 5-Lead SOT-23 Package
LTC2900 Programmable Quad Supply Monitor Adjustable Reset, 10-Lead MSOP and DFN Packages
LTC2901 Programmable Quad Supply Monitor Adjustable Reset and Watchdog Timer
LTC2902 Programmable Quad Supply Monitor Adjustable Reset and Tolerance
LTC2903 Precision Quad Supply Monitor 6-Lead SOT-23 Package
LTC2904-LTC2907 Three-State Programmable Precision Dual Supply Monitor 8-Lead SOT-23 and DFN Packages
LTC2908 Precision Six Supply Monitor (Four Fixed & Two Adjustable) 8-Lead TSOT-23 and DFN Packages
LTC2909 Precision Triple/Dual Input UV, OV and Negative Voltage Monitor Shunt Regulated VCC Pin, Adjustable Threshold and Reset,
8-Lead SOT-23 and DFN Packages
LTC2910 Precision Octal Positive/Negative Voltage Supply Monitor 16-Lead SSOP and 5mm × 3mm DFN Packages, H-Grade
Temperature Range
LTC2912-LTC2914 Single/Dual/Quad UV and OV Voltage Monitors Separate VCC Pin, Adjustable Reset Timer, H-Grade Temperature
Range
LTC2915-LTC2918 Single Supply Monitor with 27 Pin-Selectable Thresholds Manual Reset, Watchdog, TSOT-8/MSOP-10 and 3mm × 2mm
DFN Packages, H-Grade Temperature Range
LTC2928 Quad Power Supply Sequencer and Supervisor Easily Confi gure Power Management without Software, 36-Lead
5mm × 7mm QFN and SSOP Packages
RELATED PARTS
COMP1
COMP2
COMP3
COMP4
COMP5
COMP6
10
VREF
VPG
CRT
CWT
LTC2931
2931 TA02
182k
1%
R1
59k
1%
5V
0.1μF
RESET
POWER GOOD
3.3V
2.5V
1.8V
1.5V
R2
40.2k
1%
100k
1%
10k
tWD = 94ms
tRST = 9.4ms
RST
WDO
GND
V1
V2
V3
V4
V5
V6
4.7nF
4.7nF WDI
SYSTEM
LOGIC
System Reset Generated by Watchdog Timing or Supply Voltage Failure
