LINER LTC2901-1CGN

Final Electrical Specifications
LTC2901
Programmable Quad Supply
Monitor with Adjustable Reset
and Watchdog Timers
June 2002
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FEATURES
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DESCRIPTIO
The LTC®2901 is a programmable supply monitor for
systems with up to four supply voltages. One of 16 preset
or adjustable voltage monitor combinations can be selected using an external resistor divider connected to the
program pin. The preset voltage thresholds are accurate
to 1.5% over temperature. All four voltage comparator
outputs are connected to separate pins for individual
supply monitoring.
Simultaneously Monitors Four Supplies
16 User Selectable Combinations of 5V, 3.3V, 3V,
2.5V, 1.8V, 1.5V and/or ±Adjustable Voltage
Thresholds
Guaranteed Threshold Accuracy: ±1.5% of
Monitored Voltage Over Temperature
Low Supply Current: 43µA Typ
Adjustable Reset Time
Adjustable Watchdog Time
Open-Drain RST Output (LTC2901-1)
Push-Pull RST Output (LTC2901-2)
Individual Nondelayed Monitor Output for Each Supply
Power Supply Glitch Immunity
Guaranteed RST for VCC ≥ 1V
The reset and watchdog delay times 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. The LTC2901-1 features
an open-drain RST output, while the LTC2901-2 has a
push-pull RST output.
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APPLICATIO S
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The 43µA supply current makes the LTC2901 ideal for
power conscious systems and it may be configured to
monitor less than four inputs. The parts are available in
the 16-lead narrow SSOP package.
Desktop and Notebook Computers
Multivoltage Systems
Telecom Equipment
Portable Battery-Powered Equipment
Network Servers
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATIO
Quadruple Supply Monitor (5V, 3.3V, 2.5V, 1.8V)
5V
3.3V
DC/DC
CONVERTER
SYSTEM
LOGIC
2.5V
1.8V
3
4
14
C1
0.1µF
C2
0.1µF
R1
59k
1%
R2
40.2k
1%
12
11
V3
V1
V2
VREF
VPG
13
R3
10k
V4
COMP1
16
COMP2
LTC2901-2
1
COMP3
15
COMP4
8
WDI
7
WDO
6
RST
GND CRT
10
2
5
POWER
GOOD
2901 TA01
CWT
CRT
47nF
9
CWT
47nF
tRST = 216ms
tWD = 940ms
2901is sn2901
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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LTC2901
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ABSOLUTE
RATI GS
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PACKAGE/ORDER I FOR ATIO
(Notes 1, 2, 3)
V1, V2, V3, V4, VPG ..................................... – 0.3V to 7V
RST (LTC2901-1)........................................ – 0.3V to 7V
RST (LTC2901-2).......................... – 0.3V to (V2 + 0.3V)
COMPX ....................................................... – 0.3V to 7V
CWT, WDO .................................................. – 0.3V to 7V
VREF, CRT, WDI ............................ – 0.3V to (VCC + 0.3V)
Reference Load Current (IVREF) ............................ ±1mA
V4 Input Current (–ADJ Mode) ............................. –1mA
Operating Temperature Range
LTC2901-1C/LTC2901-2C ....................... 0°C to 70°C
LTC2901-1I/LTC2901-2I .................... –40°C to 85°C
Storage Temperature Range .................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................... 300°C
ORDER PART
NUMBER
TOP VIEW
COMP3
1
16 COMP2
COMP1
2
15 COMP4
V3
3
14 V2
V1
4
13 V4
CRT
5
12 VREF
RST
6
11 VPG
WDO
7
10 GND
WDI
8
9
LTC2901-1CGN
LTC2901-2CGN
LTC2901-1IGN
LTC2901-2IGN
GN16 PART MARKING
CWT
29011
29012
29011I
29012I
GN PACKAGE
16-LEAD PLASTIC SSOP
TJMAX = 125°C, θJA = 130°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, unless otherwise noted. (Note 3)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
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 Input Threshold
●
0.492
0.500
0.508
V
VRTAN
– ADJ Reset Threshold
V4 Input Threshold
●
– 18
0
18
mV
VCC
Minimum Internal Operating Voltage
RST, COMPX in Correct Logic State;
VCC Rising Prior to Program
●
1
V
VCCMINP
Minimum Required for Programming
VCC Rising
●
2.42
V
VCCMINC
Minimum Required for Comparators
VCC Falling
●
VREF
Reference Voltage
VCC ≥ 2.3V, IVREF = ±1mA, CREF ≤ 1000pF
●
1.192
VPG
Programming Voltage Range
VCC ≥ VCCMINP
●
0
IVPG
VPG Input Current
VPG = VREF
●
±20
nA
IV1
V1 Input Current
V1 = 5V, IVREF = 12µA, (Note 4)
●
43
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)
●
●
0.52
–15
1.2
15
µA
nA
V4 = 1.8V
V4 = 0.55V (ADJ Mode)
V4 = –0.05V (–ADJ Mode)
●
●
●
0.34
–15
–15
0.8
15
15
µA
nA
VCRT = 0V
●
–1.4
–2
–2.6
µA
IV4
V4 Input Current
1.210
2.32
V
1.228
V
VREF
V
ICRT(UP)
CRT Pull-Up Current
ICRT(DN)
CRT Pull-Down Current
VCRT = 1.3V
●
10
20
30
µA
tRST
Reset Time-Out Period
CRT = 1500pF
●
4.9
6.9
8.9
ms
2901is sn2901
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LTC2901
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, unless otherwise noted. (Note 3)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
tUV
VX Undervoltage Detect to RST or COMPX
VX Less Than Reset Threshold VRTX
by More Than 1%
VOL
Output Voltage Low RST, COMPX
ISINK = 2.5mA; V1 = 3V, V2 = 3V;
V3, V4 = 0V; VPG = 0V
●
0.15
0.4
V
ISINK = 100µA; V2 = 1V; V1, V3, V4 = 0V
ISINK = 100µA; V1 = 1V; V2, V3, V4 = 0V
●
●
0.05
0.05
0.3
0.3
V
V
µs
150
VOH
Output Voltage High RST, WDO, COMPX
(Note 5)
ISOURCE = 1µA
●
VOL
Output Voltage Low WDO
ISINK = 2.5mA; V1 = 5V, V2 = 3.3V;
V3, V4 = 1V; VPG = 0V
●
VOH
Output Voltage High RST (LTC2901-2)
(Note 6)
ISOURCE = 200µA
●
0.8 • V2
ICWT(UP)
CWT Pull-Up Current
VCWT = 0V
●
–1.4
–2
–2.6
µA
ICWT(DN)
CWT Pull-Down Current
VCWT = 1.3V
●
10
20
30
µA
tWD
Watchdog Time-Out 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
tWP
WDI Input Pulse Width
VCC = 3.3V
●
150
IWDI
WDI Pull-Up Current
VWDI = 0V
Note 1: Absolute Maximum Ratings are those values beyond which the life of
a device may be impaired.
Note 2: All voltage values are with respect to GND.
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.
V2 – 1
V
0.15
0.4
V
V
V
ns
–10
µA
Note 5: The output pins RST, WDO and COMPX have 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.
Note 6: The push-pull RST output pin on the LTC2901-2 is actively pulled up
to V2.
2901is sn2901
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LTC2901
TEST CIRCUITS
V1
V2
V3
V4
RST, WDO
LTC2901-1 OR COMPX
LTC2901-1
V1
V2
V3
V4
ISOURCE
1µA
RST, WDO
OR COMPX
2901 F01
V1
V2
V3
V4
ISINK
2.5mA,
100µA
LTC2901-2 RST
ISOURCE
200µA
2901 F02
Figure 1. RST, WDO, COMPX VOH Test
2901 F03
Figure 2. RST, WDO, COMPX VOL Test
Figure 3. Active Pull-Up RST VOH Test
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TI I G DIAGRA S
VX Monitor Timing
VX
VRTX
tUV
tRST
1.5V
RST
2901 TD
COMPX
Watchdog Timing
tRST
RST
WDI
tWP
WDO
tWD
tWD
2901 TD2
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LTC2901
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TYPICAL PERFOR A CE CHARACTERISTICS
5V Threshold Voltage
vs Temperature
3.3V Threshold Voltage
vs Temperature
THESHOLD VOLTAGE, VRT50 (V)
4.725
4.700
4.675
4.650
4.625
3.135
2.850
3.125
2.840
THRESHOLD VOLTAGE, VRT30 (V)
THRESHOLD VOLTAGE, VRT33 (V)
4.750
3V Threshold Voltage
vs Temperature
3.115
3.105
3.095
3.085
3.075
3.065
3.055
3.035
– 60 –40 – 20 0 20 40 60
TEMPERATURE (°C)
80 100
2901 G01
2.810
2.800
2.790
2.780
80
2.760
– 60 –40 – 20 0 20 40 60
TEMPERATURE (°C)
100
2901 G02
2.5V Threshold Voltage
vs Temperature
1.425
1.705
1.420
2.3450
2.3375
2.3300
2.3225
2.3150
2.3075
THRESHOLD VOLTAGE, VRT15 (V)
1.710
2.3675
2.3525
1.700
1.695
1.690
1.685
1.680
1.675
1.670
1.665
80
1.655
–60 –40 –20 0
20 40 60
TEMPERATURE (°C)
100
ADJ Threshold Voltage
vs Temperature
1.405
1.400
1.395
1.390
80
1.380
– 60 –40 – 20 0 20 40 60
TEMPERATURE (°C)
100
0.504
0.502
0.500
0.498
0.496
0.494
80
100
2901 G07
1.228
0.012
1.222
0.006
1.216
0
1.210
–0.006
1.204
–0.012
1.198
–0.018
– 60 –40 – 20 0 20 40 60
TEMPERATURE (°C)
100
VREF vs Temperature
0.018
VREF (V)
THRESHOLD VOLTAGE, VRTAN (V)
0.506
80
2901 G06
– ADJ Threshold Voltage
vs Temperature
0.508
THRESHOLD VOLTAGE, VRTA (V)
1.410
2901 G05
2901 G04
0.492
– 60 –40 – 20 0 20 40 60
TEMPERATURE (°C)
1.415
1.385
1.660
2.3000
– 60 –40 – 20 0 20 40 60
TEMPERATURE (°C)
100
1.5V Threshold Voltage
vs Temperature
2.3750
2.3600
80
2901 G03
1.8V Threshold Voltage
vs Temperature
THRESHOLD VOLTAGE, VRT18 (V)
THRESHOLD VOLTAGE, VRT25 (V)
2.820
2.770
3.045
4.600
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
2.830
80
100
2901 G08
1.192
– 60 –40 – 20 0 20 40 60
TEMPERATURE (°C)
80
100
2901 G23
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LTC2901
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TYPICAL PERFOR A CE CHARACTERISTICS
IV1 vs Temperature
IV2 vs Temperature
IV3 vs Temperature
1.5
1.1
V1 = 5V
1.4 V2 = 3.3V
V3 = 2.5V
1.3
V4 = 1.8V
1.2
V1 = 5V
1.0 V2 = 3.3V
V3 = 2.5V
0.9
V4 = 1.8V
0.8
60
1.1
0.7
50
40
IV3 (µA)
V1 = 5V
90 V2 = 3.3V
V3 = 2.5V
80
V4 = 1.8V
70
IV2 (µA)
1.0
0.9
0.4
20
0.7
0.3
10
0.6
0.2
0.5
– 60 –40 – 20 0 20 40 60
TEMPERATURE (°C)
100
IV4 vs Temperature
0.5
0.4
0.3
0.2
0.1
0
– 60 –40 – 20 0 20 40 60
TEMPERATURE (°C)
80
100
Typical Transient Duration
vs Comparator Overdrive (V3, V4)
220
TA = 25°C
RESET OCCURS
ABOVE CURVE
300
250
200
150
100
50
WATCHDOG TIME-OUT PERIOD, tWD (ms)
2
1
0
0
140
120
100
80
60
40
20
Reset Time-Out Period
vs Temperature
Watchdog Time-Out Period
vs Temperature
3
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
V1 (V)
2901 G14
RESET OCCURS
ABOVE CURVE
160
2901 G22
8.9
38
4
180
2901 G13
2901 G12
V1 = V2 = V3 = V4
10k PULL-UP FROM RST TO V1
TA = 25°C
TA = 25°C
200
0
1
10
100
0.1
RESET COMPARATOR OVERDRIVE VOLTAGE (% OF VRTX)
0
0.1
1
10
100
RESET COMPARATOR OVERDRIVE VOLTAGE (% OF VRTX)
5
100
Typical Transient Duration
vs Comparator Overdrive (V1, V2)
350
RST Output Voltage
vs V1, VPG = 0V
80
2901 G11
400
TYPICAL TRANSIENT DURATION (µs)
0.6
0.1
– 60 –40 – 20 0 20 40 60
TEMPERATURE (°C)
100
2901 G10
450
1.0
V1 = 5V
0.9 V2 = 3.3V
V3 = 2.5V
0.8
V4 = 1.8V
0.7
80
TYPICAL TRANSIENT DURATION (µs)
80
2901 G09
IV4 (µA)
0.5
0.8
0
– 60 –40 – 20 0 20 40 60
TEMPERATURE (°C)
RST OUTPUT VOLTAGE (V)
0.6
30
CWT = 1500pF
36 (SILVER MICA)
RESET TIME-OUT PERIOD, tRST (ms)
IV1 (µA)
100
34
32
30
28
26
24
22
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
80
100
2901 G15
CRT = 1500pF
8.4 (SILVER MICA)
7.9
7.4
6.9
6.4
5.9
5.4
4.9
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
2901 G16
2901is sn2901
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LTC2901
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TYPICAL PERFOR A CE CHARACTERISTICS
Reset Time-Out Period
vs Capacitance
Watchdog Time-Out Period
vs Capacitance
10
TA = 25°C
10
1
10m
1m
10p
100p
10n
1n
CWT (FARAD)
100n
1µ
ISINK (mA)
10m
1m
100p
100n
10n
1n
CRT (FARAD)
– 40°C
VOH (V)
VOL (V)
V1 = 5V
V2 = 3V
V3 = 2.5V
V4 = 1V
3.0
16
2.0
– 40°C
1.5
25°C
85°C
0.5
70
80
90
0.5
2
1
1.5
ISOURCE (mA)
2
2.5
3
3.5
V2 (V)
4
4.5
5
2901 G24
RST Pull-Up Current vs V2
(LTC2901-2)
6
TA = 25°C
TA = 25°C
5
PULL-UP CURRENT (mA)
16
14
12
10
8
VRT33
6
VRT30
VRT25
4
50
1.5
18
PULL-UP CURRENT (µA)
COMPX PROPAGATION DELAY (µs)
20
200
V1, V2
1
2.5
RST Pull-Up Current vs V2
(LTC2901-1)
TA = 25°C
100
6
2901 G21
COMPX Propagation Delay vs Input
Overdrive Above Threshold
150
8
0
0
2901 G20
250
10
2
0
50 60
ISINK (mA)
40
14
12
4
0.5
30
6
TA = 25°C
18
1.0
20
5
3
4
V1 OR V2 (V)
2901 G19
20
3.5
25°C
1.0
10
2
COMPX and WDO Pull-Up
Current vs V2 (COMPX and
WDO Held at 0V)
2.5
0
1
0
RST High Level Output Voltage
vs Output Source Current
(LTC2901-2)
2.0
4
3
VRT33
VRT30
2
VRT25
1
2
V3, V4
0
0
1µ
2901 G18
2.5
0
VOL = 0.2V
2
100µ
10p
3.0
1.5
4
1
RST, WDO, COMPX Voltage
Output Low vs Output Sink Current
85°C
6
5
3
2901 G17
V2 = 3V
V1 = 5V
VOL = 0.4V
7
100m
100m
TA = 25°C
8
PULL-UP CURRENT (µA)
1
10
TA = 25°C
9
RESET TIME-OUT PERIOD, tRST (sec)
WATCHDOG TIME-OUT PERIOD, tWD (sec)
100
RST, WDO, COMPX ISINK
vs Supply Voltage
0
1000
10
100
INPUT OVERDRIVE ABOVE THRESHOLD (mV)
2901 G25
0
2
2.5
3
3.5
V2 (V)
4
4.5
5
2901 G26
2
2.5
3
3.5
V2 (V)
4
4.5
5
2901 G27
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LTC2901
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PI FU CTIO S
COMP3 (Pin 1): Comparator Output 3. Nondelayed, active
high logic output with weak pull-up to V2. Pulls high when
V3 is above reset threshold. May be pulled greater than V2
using external pull-up.
COMP1 (Pin 2): Comparator Output 1. Nondelayed, active
high logic output with weak pull-up to V2. Pulls high when
V1 is above reset threshold. May be pulled greater than V2
using external pull-up.
V3 (Pin 3): Voltage Input 3. Select from 2.5V, 1.8V, 1.5V
or ADJ. See Table 1 for details.
V1 (Pin 4): Voltage Input 1. Select from 5V or 3.3V. See
Table 1 for details. The greater of (V1, V2) is also VCC for
the chip. Bypass this pin to ground with a 0.1µF (or
greater) capacitor.
CRT (Pin 5): Reset Delay Time Programming Pin. Attach
an external capacitor (CRT) to GND to set a reset delay time
of 4.6ms/nF. Leaving the pin open generates a minimum
delay of approximately 50µs. A 47nF capacitor will generate a 216ms reset delay time.
RST (Pin 6): Reset Logic Output. Active low with weak
pull-up to V2 (LTC2901-1) or active pull-up to V2
(LTC2901-2). Pulls low when any voltage input is below
the reset threshold and held low for programmed delay
time after all voltage inputs are above threshold. May be
pulled above V2 using an external pull-up (LTC2901-1
only).
WDO (Pin 7): Watchdog Output. Active low logic output
with weak pull-up to V2. May be pulled greater than V2
using external pull-up. The watchdog output pulls low if
the watchdog timer is allowed to time out and remains low
until set high by the next WDI transistion or anytime RST
is low. The watchdog timer is enabled when RST is high.
WDI (Pin 8): 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 watchdog
time-out period is set by the value of the capacitor that is
attached to the CWT pin. A rising or falling edge on the WDI
pin clears the voltage on the CWT capacitor, preventing
WDO from going low. When disabling the watchdog
function, tie CWT to GND.
CWT (Pin 9): Watchdog Time-Out Programming Pin.
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 time-out of approximately
200µs. A 47nF capacitor will generate a 940ms watchdog
time-out period.
GND (Pin 10): Ground.
VPG (Pin 11): Voltage Threshold Combination Select
Input. Connect to an external 1% resistive divider between VREF and GND to select 1 of 16 combinations of
preset and/or ±adjustable voltage thresholds (see Table␣ 1).
Do not add capacitance on the VPG pin.
VREF (Pin 12): Buffered Reference Voltage. A 1.210V
nominal reference used for programming 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 13): Voltage Input 4. Select from 1.8V, 1.5V, ADJ
or – ADJ. See Table 1 for details.
V2 (Pin 14): Voltage Input 2. Select from 3.3V, 3V or 2.5V.
See Table 1 for details. The greater of (V1, V2) is also VCC
for chip. Bypass this pin to ground with a 0.1µF (or greater)
capacitor. All logic outputs (COMP1, COMP2, COMP3,
COMP4, RST, WDO) are weakly pulled up to V2
(LTC2901-1). RST is actively pulled up to V2 in the
LTC2901-2.
COMP4 (Pin 15): Comparator Output 4. Nondelayed,
active high logic output with weak pull-up to V2. Pulls high
when V4 is above reset threshold. May be pulled greater
than V2 using external pull-up.
COMP2 (Pin 16): Comparator Output 2. Nondelayed,
active high logic output with weak pull-up to V2. Pulls high
when V2 is above reset threshold. May be pulled greater
than V2 using external pull-up.
2901is sn2901
8
LTC2901
W
BLOCK DIAGRA
V1
V2
POWER
DETECT
VCC
6µA
COMP1
–
V2
2
+
V2
–
V1
4
V2
14
V3
6µA
+
COMP2
16
RESISTIVE
DIVIDER
MATRIX
3
–
V4
13
+
V2
6µA
GND
10
COMP3
–
+
VPG
11
1
A/D
V2
BUFFER
6µA
VREF
12
BANDGAP
REFERENCE
COMP4
15
ADJUSTABLE
RESET PULSE
GENERATOR
VCC
V2 LTC2901-1
2µA
6µA
22µA
RST
6
LTC2901-2
V2
10µA
TRANSITION
DETECT
VCC
WATCHDOG
TIMER
RST
6
VCC
2µA
6µA
22µA
5 CRT
CRT
8
V2
WDO
WDI
7
9 CWT
CWT
2901 DB-1
2901is sn2901
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LTC2901
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APPLICATIO S I FOR ATIO
Power-Up
The greater of V1, V2 is the internal supply voltage (VCC).
On power-up, VCC will power the drive circuits for the RST
and the COMPX pins. This ensures that the RST and COMPX
outputs will be low as soon as V1 or V2 reaches 1V. The
RST and COMPX outputs will remain low until the part is
programmed. After programming, if any one of the VX inputs
is below its programmed threshold, RST will be a logic low.
Once all the VX inputs rise above their thresholds, an internal timer is started and RST is released after the programmed delay time. If VCC < (V3 – 1) and VCC < 2.4V, the
V3 input impedance will be low (1kΩ typ).
Monitor Programming
The LTC2901 input voltage combination is selected by
placing the recommended resistive divider from VREF to
GND and connecting the tap point to VPG, as shown in
Figure 4. Table 1 offers recommended 1% resistor values
for the various modes. The last column in Table 1 specifies
optimum VPG/VREF ratios (±0.01) to be used when programming with a ratiometric DAC.
During power-up, once V1 or V2 reaches 2.4V max, the
monitor enters a programming period of approximately
Table 1. Voltage Threshold Programming
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
LTC2901
12
VREF
11
VPG
10
GND
R1
1%
R2
1%
2901 F04
Figure 4. Monitor Programming
150µs during which the voltage on the VPG pin is sampled
and the monitor is configured to the desired input combination. Do not add capacitance to the VPG pin. Immediately
after programming, the comparators are enabled and
supply monitoring will begin.
Supply Monitoring
The LTC2901 is a low power, high accuracy programmable quad supply monitoring circuit with four nondelayed
monitor outputs, a common reset output and a watchdog
timer. Watchdog and reset timing are both adjustable
using external capacitors. Single pin programming selects
1 of 16 input voltage monitor combinations. All four
voltage inputs must be above predetermined thresholds
for the reset not to be invoked. The LTC2901 will assert the
reset and comparator outputs during power-up, powerdown and brownout conditions on any one of the voltage
inputs.
The inverting inputs on the V3 and/or V4 comparators are
set to 0.5V when the positive adjustable modes are selected
(Figure 5). The tap point on an external resistive divider,
connected between the positive voltage being sensed and
ground, is connected to the high impedance noninverting
inputs (V3, V4). The trip voltage is calculated from:
 R3 
VTRIP = 0.5V 1 + 
 R4 
In the negative adjustable mode, the noninverting input on
the V4 comparator is connected to ground (Figure 6). The
tap point on an external resistive divider, connected between the negative voltage being sensed and the VREF pin,
is connected to the high impedance inverting input (V4).
VREF provides the necessary level shift required to operate
at ground. The trip voltage is calculated from:
 R3 
VTRIP = – VREF   ; VREF = 1.210 V No min al
 R4 
2901is sn2901
10
LTC2901
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APPLICATIO S I FOR ATIO
VTRIP
Table 2. Suggested 1% Resistor Values for the ADJ Inputs
LTC2901
R3
1%
+
V3 OR V4
R4
1%
–
+
–
0.5V
2901 F05
Figure 5. Setting the Positive Adjustable Trip Point
12
R4
1%
VREF
13 V4
R3
1%
LTC2901
–
+
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
VTRIP
Table 3. Suggested 1% Resistor Values for the –ADJ Input
2901 F06
Figure 6. Setting the Negative Adjustable Trip Point
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:
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
1.21V ÷ 1mA = 1.21kΩ.
Tables 2 and 3 offer suggested 1% resistor values for
various adjustable applications.
Although all four supply monitor comparators have builtin glitch immunity, bypass capacitors on V1 and V2 are
recommended because the greater of V1 or V2 is also the
VCC for the chip. Filter capacitors on the V3 and V4 inputs
are allowed.
Power-Down
On power-down, once any of the VX inputs drop below
their threshold, RST and COMPX are 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 typ), the part will reprogram once VCC rises
above 2.4V max.
Monitor Output Rise and Fall Time Estimation
All of the outputs (RST, COMPX, WDO) have strong pulldown capability. If the external load capacitance (CLOAD)
for a particular output is known, output fall time (10% to
90%) is estimated using:
tFALL ≈ 2.2 • RPD • CLOAD
where RPD is the on-resistance of the internal pull-down
transistor. The typical performance curve (VOL vs ISINK)
demonstrates that the pull-down current is somewhat
linear versus output voltage. Using the 25°C curve, RPD is
estimated to be approximately 40Ω. Assuming a 150pF
load capacitance, the fall time is about 13.2ns.
Although the outputs are considered to be “open-drain,”
they do have a weak pull-up capability (see COMPX or RST
2901is sn2901
11
LTC2901
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APPLICATIO S I FOR ATIO
Pull-Up Current vs V2 curve). Output rise time (10% to
90%) is estimated using:
tRISE ≈ 2.2 • RPU • CLOAD
where RPU is the on-resistance of the pull-up transistor.
The on-resistance as a function of the V2 voltage at room
temperature is estimated using:
6 • 105
RPU =
Ω
V2 – 1
with V2 = 3.3V, RPU is about 260k. Using 150pF for load
capacitance, the rise time is 86µs. If the output needs to
pull up faster and/or to a higher voltage, a smaller
external pull-up resistor may be used. Using a 10k pullup resistor, the rise time is reduced to 3.3µs for a 150pF
load capacitance.
The LTC2901-2 has an active pull-up to V2 on the RST
output. The typical performance curve (RST Pull-Up Current vs V2 curve) demonstrates that the pull-up current is
somewhat linear versus the V2 voltage and RPU is estimated to be approximately 625Ω. A 150pF load capacitance makes the rise time about 206ns.
Watchdog Timer
The watchdog circuit typically monitors a µP’s 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 and
prevent the WDO pin from going low. Whenever RST is low,
the watchdog timer is cleared and WDO is set high. The
watchdog timer is started when RST pulls high. Subsequent
edges received on the WDI pin will clear the watchdog timer.
The timer will continue to run until the watchdog timer times
out. Once the watchdog timer times out, internal circuitry
will bring the WDO pin low. WDO will remain low and the
watchdog timer will remain cleared until the next edge is
received on the WDI pin or until RST goes low.
To disable the watchdog timer, simply ground the CWT pin
(Pin 9). With CWT held at ground, any reset event will force
WDO high indefinitely. It is safe to leave the WDI pin (Pin␣ 8)
unconnected because the weak internal pull-up (10µA typ)
will pull WDI high. Tying WDI to V1 or ground is also
allowed, but grounding the WDI pin will force the pull-up
current to be drawn continuously.
Selecting the Reset Timing Capacitor
The reset time-out period is adjustable in order to accommodate a variety of microprocessor applications. The
reset time-out 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 • 217.4 • 10 –9
with CRT in Farads and tRST in seconds. The CRT value per
millisecond of delay can also be expressed as CRT/ms =
217.4 (pF/ms).
Leaving the CRT pin unconnected will generate a minimum reset time-out of approximately 50µs. Maximum
reset time-out is limited by the largest available low
leakage capacitor. The accuracy of the time-out period will
be 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 time-out period is adjustable and can be
optimized for software execution. The watchdog time-out
period, tWD, is adjusted by connecting a capacitor, CWT,
between the CWT pin and ground. Given a specified
watchdog time-out period, the capacitor is determined by:
CWT = tWD • 50 • 10–9
with CWT in Farads and tWD in seconds. The CWT value per
millisecond of delay can also be expressed as CWT/ms =
50 (pF/ms).
Leaving the CWT pin unconnected will generate a minimum watchdog time-out of approximately 200µs. Maximum time-out is limited by the largest available low
leakage capacitor. The accuracy of the time-out period will
be affected by capacitor leakage (the nominal charging
current is 2µA) and capacitor tolerance. A low leakage
ceramic capacitor is recommended.
Monitoring Power Supply Controller Activity
Figure 7 demonstrates how the LTC2901 can be used to
monitor switcher activity. The monitor is configured to
supervise 3.3V, 2.5V, 1.8V and one adjustable input.
2901is sn2901
12
LTC2901
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APPLICATIO S I FOR ATIO
Because 2.5V does not exist in this application, the V2
input is tied to the V1 (3.3V) input. The feedback voltage
on the LTC1772 (0.8V typ) is monitored with the adjustable input (V4). The RST pin will go high 216ms
(CRT = 47nF) after the 3.3V and 1.8V supplies and the
feedback voltage are above threshold. Individual input
status is available at the COMPX pins.
While the voltage monitors can detect low voltage or
shorted inputs, the watchdog circuit can be used to detect
an open circuit to the primary load. With the CWT pin
LTC1772
6
ITH
PGATE
2
5
VIN
GND
3
4
VFB SENSE –
R6
10k
C3
220pF
M1
Burst Mode is a registered trademark of Linear Technology Corporation.
VIN
3.3V
C1
10µF
10V
R5
0.15Ω
1
unconnected, the watchdog time-out is approximately
200µs. At low load currents on the 1.8V supply, the
LTC1772 will go into Burst Mode® operation. With an
open-ciruit load, the duty cycle at the gate of M1 will drop,
and the pulse spacing will exceed the watchdog time-out
period. The WDO pin will go low indicating the low load
condition. The WDO pin will return high on the next pulse
to the gate of M1. The WDO pin will remain high if the load
is restored.
14
3
L1
10µH
+
D1
4
C2
47µF
6V
C1: TAIYO YUDEN CERAMIC LMK325BJ106K-T
C2: SANYO POSCAP 6TPA47M
D1: MOTOROLA MBRM120T3
L1: COILTRONICS UP1B-100
M1: Si3443DV
R5: DALE 0.25W
13
VOUT
1.8V
0.5A
R3
100k
8
12
R1
28k
1%
R4
80.6k
11
10
R2
71.5k
1%
LTC2901-2
2
V1
COMP1
16
V2
COMP2
1
V3
COMP3
15
V4
COMP4
6
WDI
RST
7
VREF
WDO
5
CRT
VPG
9
CWT
GND
3.3V MONITOR
1.8V MONITOR
FEEDBACK MONITOR
COMMON RESET OUT
LOW LOAD INDICATOR
CRT
47nF
2901 F07
Figure 7. Monitor Input, Output, Feedback Voltage and Low Load Conditions on DC/DC Controller
U
TYPICAL APPLICATIO S
Quad Supply Monitor with Watchdog Timer Disabled
5V, 3V, 1.8V, 12V (ADJ)
1
2
1.8V
5V
3
4
5
SYSTEM
RESET
CRT
6
7
8
COMP3
COMP2
COMP1
COMP4
V3
V2
V1 LTC2901 V4
CRT
VREF
RST
VPG
WDO
GND
WDI
CWT
16
15
14
13
3V
R3
2.15M
1%
12V
VTRIP = 11.25V
12
11
10
R4
100k
1%
9
2901 TA02
2901is sn2901
13
LTC2901
U
TYPICAL APPLICATIO S
5V, –5V Monitor with Watchdog Timer Disabled and Unused
V2, V3 Inputs Pulled Above Trip Thresholds
1
2
3
CRT
COMP1
COMP4
V2
V1 LTC2901 V4
5
SYSTEM
RESET
COMP2
V3
4
5V
COMP3
CRT
6
7
8
VREF
RST
VPG
WDO
GND
WDI
CWT
16
15
R3
464k
1%
14
13
–5V
12
VTRIP = –4.64V
R1
R4
16.2k 121k
1%
1%
11
10
9
R2
86.6k
1%
2901 TA03
Quad Supply Monitor with LED Undervoltage Indicators
5V, 3.3V, 2.5V, 1.5V
RL1
1k
LED
RL3
1k
LED
1
2
2.5V
3
4
5V
5
SYSTEM RESET
WATCHDOG STATUS
WDI
CRT
RL2
1k
6
7
8
LED
COMP3
COMP2
COMP1
COMP4
V3
V2
V1 LTC2901 V4
CRT
VREF
RST
VPG
WDO
GND
WDI
CWT
RL4
1k
LED
16
15
14
3.3V
13
1.5V
12
R1
53.6k
1%
11
10
9
R2
47.5k
1%
CWT
2901 TA04
2901is sn2901
14
LTC2901
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PACKAGE DESCRIPTIO
GN Package
16-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641)
0.189 – 0.196*
(4.801 – 4.978)
16 15 14 13 12 11 10 9
0.229 – 0.244
(5.817 – 6.198)
0.150 – 0.157**
(3.810 – 3.988)
1
0.015 ± 0.004
× 45°
(0.38 ± 0.10)
0.007 – 0.0098
(0.178 – 0.249)
0.009
(0.229)
REF
0.053 – 0.068
(1.351 – 1.727)
2 3
4
5 6
7
8
0.004 – 0.0098
(0.102 – 0.249)
0° – 8° TYP
0.016 – 0.050
(0.406 – 1.270)
* DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
0.008 – 0.012
(0.203 – 0.305)
0.0250
(0.635)
BSC
GN16 (SSOP) 1098
2901is sn2901
15
LTC2901
U
TYPICAL APPLICATIO
Monitor Seven Supplies (12V, 5V, 3.3V, 2.5V, 1.8V, –2V, –5.2V) with
Sequenced Reset and AC Present Indication
5V
AC/DC
DC/DC
CONVERTERS
12V
5V
3.3V
2.5V
1.8V
–2V
–5.2V
10k
4
3.3V
14
3
1.8V
13
8
120V AC
12
LOW
VOLTAGE
SECONDARY
121k 16.2k
1%
1%
11
10
LTC2901-1
2
V1
COMP1
16
V2
COMP2
1
V3
COMP3
15
V4
COMP4
6
WDI
RST
7
VREF
WDO
5
CRT
VPG
9
CWT
GND
487k 86.6k
1%
1%
10k
4
5V MONITOR
3.3V MONITOR
2.5V
14
3
1.8V MONITOR
13
–5.2V MONITOR
8
12
12V
CRT1
47nF
2.15M
1%
121k 78.7k
1%
1%
100k
1%
187k 22.1k
1%
1%
100k
–5.2V
11
10
LTC2901-1
2
V1
COMP1
16
V2
COMP2
1
V3
COMP3
15
V4
COMP4
6
WDI
RST
7
VREF
WDO
5
CRT
VPG
9
CWT
GND
2.5V MONITOR
12V MONITOR
–2V MONITOR
COMMON RESET OUT
AC PRESENT
CWT
680pF
–2V
100k
1N4148
CRT2
47nF
2901 TA05
1N4148
tRST1 + tRST2 = 432ms
tWD = 13.6ms
Q1
2N3904
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PART NUMBER
DESCRIPTION
COMMENTS
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4.65V Threshold
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3.3V Supply Monitor, Watchdog Timer and Battery Backup
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5V Supply Monitor and Watchdog Timer
4.65V Threshold
LTC1232
5V Supply Monitor, Watchdog Timer and Push-Button Reset
4.37V/4.62V Threshold
LTC1326
Micropower Precision Triple Supply Monitor for 5V, 3.3V and ADJ
4.725V, 3.118V, 1V Thresholds (±0.75%)
LTC1326-2.5
Micropower Precision Triple Supply Monitor for 2.5V, 3.3V and AJD
2.363V, 3.118V, 1V Thresholds (±0.75%)
LTC1536
Precision Triple Supply Monitor for PCI Applications
Meets PCI tFAIL Timing Specifications
LTC1726-2.5
Micropower Triple Supply Monitor for 2.5V, 3.3V and ADJ
Adjustable RESET and Watchdog Time-Outs
LTC1726-5
Micropower Triple Supply Monitor for 5V, 3.3V and ADJ
Adjustable RESET and Watchdog Time-Outs
LTC1727-2.5/LTC1727-5
Micropower Triple Supply Monitors 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 Monitors 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
2901is sn2901
16
Linear Technology Corporation
LT/TP 0602 1.5K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2002