1
LTC2901
2901is sn2901
Programmable Quad Supply
Monitor with Adjustable Reset
and Watchdog Timers
June 2002
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 represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
■
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 V
CC
≥ 1V
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 se-
lected 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.
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 V
CC
down to 1V. The LTC2901-1 features
an open-drain RST output, while the LTC2901-2 has a
push-pull RST output.
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.
Quadruple Supply Monitor (5V, 3.3V, 2.5V, 1.8V)
■
Desktop and Notebook Computers
■
Multivoltage Systems
■
Telecom Equipment
■
Portable Battery-Powered Equipment
■
Network Servers
Final Electrical Specifications
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
, LTC and LT are registered trademarks of Linear Technology Corporation.
V1
V2
V
REF
V
PG
COMP1
COMP2
COMP3
COMP4
WDI
WDO
RST
GND
10
11
R1
59k
1%
R3
10k POWER
GOOD
R2
40.2k
1%
12
6
7
8
15
1
16
2
133
14
4
95 C
WT
47nF
C
RT
47nF
C2
0.1µF
C1
0.1µF
V4V3
LTC2901-2
CWTCRT
t
RST
= 216ms
t
WD
= 940ms
2901 TA01
DC/DC
CONVERTER 1.8V
2.5V
3.3V
5V
SYSTEM
LOGIC
2
LTC2901
2901is sn2901
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
RT50
5V, 5% Reset Threshold V1 Input Threshold ●4.600 4.675 4.750 V
V
RT33
3.3V, 5% Reset Threshold V1, V2 Input Threshold ●3.036 3.086 3.135 V
V
RT30
3V, 5% Reset Threshold V2 Input Threshold ●2.760 2.805 2.850 V
V
RT25
2.5V, 5% Reset Threshold V2, V3 Input Threshold ●2.300 2.338 2.375 V
V
RT18
1.8V, 5% Reset Threshold V3, V4 Input Threshold ●1.656 1.683 1.710 V
V
RT15
1.5V, 5% Reset Threshold V3, V4 Input Threshold ●1.380 1.403 1.425 V
V
RTA
ADJ Reset Threshold V3, V4 Input Threshold ●0.492 0.500 0.508 V
V
RTAN
–ADJ Reset Threshold V4 Input Threshold ●–18 0 18 mV
V
CC
Minimum Internal Operating Voltage RST, COMPX in Correct Logic State; ●1V
V
CC
Rising Prior to Program
V
CCMINP
Minimum Required for Programming V
CC
Rising ●2.42 V
V
CCMINC
Minimum Required for Comparators V
CC
Falling ●2.32 V
V
REF
Reference Voltage V
CC
≥ 2.3V, I
VREF
= ±1mA, C
REF
≤ 1000pF ●1.192 1.210 1.228 V
V
PG
Programming Voltage Range V
CC
≥ V
CCMINP
●0V
REF
V
I
VPG
V
PG
Input Current V
PG
= V
REF
●±20 nA
I
V1
V1 Input Current V1 = 5V, I
VREF
= 12µA, (Note 4) ●43 75 µA
I
V2
V2 Input Current V2 = 3.3V ●0.8 2 µA
I
V3
V3 Input Current V3 = 2.5V ●0.52 1.2 µA
V3 = 0.55V (ADJ Mode) ●–15 15 nA
I
V4
V4 Input Current V4 = 1.8V ●0.34 0.8 µA
V4 = 0.55V (ADJ Mode) ●–15 15 nA
V4 = –0.05V (–ADJ Mode) ●–15 15
I
CRT(UP)
CRT Pull-Up Current V
CRT
= 0V ●–1.4 –2 –2.6 µA
I
CRT(DN)
CRT Pull-Down Current V
CRT
= 1.3V ●10 20 30 µA
t
RST
Reset Time-Out Period C
RT
= 1500pF ●4.9 6.9 8.9 ms
ORDER PART
NUMBER
GN16 PART MARKING
29011
29012
29011I
29012I
T
JMAX
= 125°C, θ
JA
= 130°C/W
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)
(Notes 1, 2, 3)
V1, V2, V3, V4, V
PG
..................................... –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
V
REF
, CRT, WDI ............................ –0.3V to (V
CC
+ 0.3V)
Reference Load Current (I
VREF
) ............................ ±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
LTC2901-1CGN
LTC2901-2CGN
LTC2901-1IGN
LTC2901-2IGN
ABSOLUTE AXI U RATI GS
WWWU
PACKAGE/ORDER I FOR ATIO
UU
W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
GN PACKAGE
16-LEAD PLASTIC SSOP
1
2
3
4
5
6
7
8
TOP VIEW
16
15
14
13
12
11
10
9
COMP3
COMP1
V3
V1
CRT
RST
WDO
WDI
COMP2
COMP4
V2
V4
VREF
VPG
GND
CWT
3
LTC2901
2901is sn2901
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
t
UV
V
X
Undervoltage Detect to RST or COMPX V
X
Less Than Reset Threshold V
RTX
150 µs
by More Than 1%
V
OL
Output Voltage Low RST, COMPX I
SINK
= 2.5mA; V1 = 3V, V2 = 3V; ●0.15 0.4 V
V3, V4 = 0V; V
PG
= 0V
I
SINK
= 100µA; V2 = 1V; V1, V3, V4 = 0V ●0.05 0.3 V
I
SINK
= 100µA; V1 = 1V; V2, V3, V4 = 0V ●0.05 0.3 V
V
OH
Output Voltage High RST, WDO, COMPX I
SOURCE
= 1µA●V2 – 1 V
(Note 5)
V
OL
Output Voltage Low WDO I
SINK
= 2.5mA; V1 = 5V, V2 = 3.3V; ●0.15 0.4 V
V3, V4 = 1V; V
PG
= 0V
V
OH
Output Voltage High RST (LTC2901-2) I
SOURCE
= 200µA●0.8 • V2 V
(Note 6)
I
CWT(UP)
CWT Pull-Up Current V
CWT
= 0V ●–1.4 –2 –2.6 µA
I
CWT(DN)
CWT Pull-Down Current V
CWT
= 1.3V ●10 20 30 µA
t
WD
Watchdog Time-Out Period C
WT
= 1500pF ●20 30 40 ms
V
IH
WDI Input Threshold High V
CC
= 3.3V to 5.5V ●1.6 V
V
IL
WDI Input Threshold Low V
CC
= 3.3V to 5.5V ●0.4 V
t
WP
WDI Input Pulse Width V
CC
= 3.3V ●150 ns
I
WDI
WDI Pull-Up Current V
WDI
= 0V –10 µA
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)
ELECTRICAL CHARACTERISTICS
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 (V
CC
).
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 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 V
OH
voltages greater than V2.
Note 6: The push-pull RST output pin on the LTC2901-2 is
actively
pulled up
to V2.
4
LTC2901
2901is sn2901
TI I G DIAGRA S
WUW
VX Monitor Timing
t
RST
2901 TD
V
RTX
V
X
RST
COMPX
t
UV
1.5V
Watchdog Timing
tRST
tWP
tWD tWD 2901 TD2
RST
WDI
WDO
TEST CIRCUITS
Figure 1. RST, WDO, COMPX VOH Test
V1
V2
V3
V4
2901 F01
LTC2901-1 RST, WDO
OR COMPX
I
SOURCE
1µA
Figure 2. RST, WDO, COMPX VOL Test
V1
V2
V3
V4
2901 F02
LTC2901-1 ISINK
2.5mA,
100µA
RST, WDO
OR COMPX
Figure 3. Active Pull-Up RST VOH Test
V1
V2
V3
V4
2901 F03
LTC2901-2 RST
I
SOURCE
200µA
5
LTC2901
2901is sn2901
2.5V Threshold Voltage
vs Temperature 1.8V Threshold Voltage
vs Temperature 1.5V Threshold Voltage
vs Temperature
ADJ Threshold Voltage
vs Temperature –ADJ Threshold Voltage
vs Temperature
TEMPERATURE (°C)
–60
THRESHOLD VOLTAGE, V
RT25
(V)
2.3750
2.3675
2.3600
2.3525
2.3450
2.3375
2.3300
2.3225
2.3150
2.3075
2.3000 –20 20 40
2901 G04
–40 0 60 80 100
TEMPERATURE (°C)
–60
1.655
THRESHOLD VOLTAGE, V
RT18
(V)
1.665
1.675
1.685
1.695
–20 20 60 100
2901 G05
1.705
1.710
1.660
1.670
1.680
1.690
1.700
–40 0 40 80
TEMPERATURE (°C)
–60
THRESHOLD VOLTAGE, VRT15 (V)
1.425
1.420
1.415
1.410
1.405
1.400
1.395
1.390
1.385
1.380 –20 20 40
2901 G06
–40 0 60 80 100
TEMPERATURE (°C)
–60
THRESHOLD VOLTAGE, V
RTA
(V)
0.508
0.506
0.504
0.502
0.500
0.498
0.496
0.494
0.492 –20 20 40
2901 G07
–40 0 60 80 100
TEMPERATURE (°C)
–60
THRESHOLD VOLTAGE, V
RTAN
(V)
0.018
0.012
0.006
0
–0.006
–0.012
–0.018 –20 20 40
2901 G08
–40 0 60 80 100
TYPICAL PERFOR A CE CHARACTERISTICS
UW
5V Threshold Voltage
vs Temperature 3.3V Threshold Voltage
vs Temperature 3V Threshold Voltage
vs Temperature
TEMPERATURE (°C)
–60
THESHOLD VOLTAGE, V
RT50
(V)
4.675
4.700
4.750
4.725
0 40 100
2901 G01
4.650
4.625
4.600 –40 –20 20 60 80
TEMPERATURE (°C)
–60
THRESHOLD VOLTAGE, VRT33 (V)
3.135
3.125
3.115
3.105
3.095
3.085
3.075
3.065
3.055
3.045
3.035 –20 20 40
2901 G02
–40 0 60 80 100
TEMPERATURE (°C)
–60
THRESHOLD VOLTAGE, VRT30 (V)
2.850
2.840
2.830
2.820
2.810
2.800
2.790
2.780
2.770
2.760 –20 20 40
2901 G03
–40 0 60 80 100
TEMPERATURE (°C)
–60
VREF (V)
1.228
1.222
1.216
1.210
1.204
1.198
1.192 –20 20 40
2901 G23
–40 0 60 80 100
VREF vs Temperature
6
LTC2901
2901is sn2901
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Typical Transient Duration
vs Comparator Overdrive (V1, V2)
RST Output Voltage
vs V1, VPG = 0V Reset Time-Out Period
vs Temperature
IV2 vs Temperature IV3 vs Temperature
IV4 vs Temperature
TEMPERATURE (°C)
–60
0.5
I
V2
(µA)
0.6
0.8
0.9
1.0
1.5
1.2
–20 20 40
2901 G10
0.7
1.3
1.4
1.1
–40 0 60 80 100
V1 = 5V
V2 = 3.3V
V3 = 2.5V
V4 = 1.8V
RESET COMPARATOR OVERDRIVE VOLTAGE (% OF V
RTX
)
0.1
250
TYPICAL TRANSIENT DURATION (µs)
300
350
400
450
110100
2901 G13
200
150
50
0
100
RESET OCCURS
ABOVE CURVE
T
A
= 25°C
V1 (V)
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
RST OUTPUT VOLTAGE (V)
2901 G14
5
4
3
2
1
0
V1 = V2 = V3 = V4
10k PULL-UP FROM RST TO V1
TA = 25°C
TEMPERATURE (°C)
–60 –40
WATCHDOG TIME-OUT PERIOD, t
WD
(ms)
34
38
36
60 80
2901 G15
32
30
–20 0 20 40 100
26
22
28
24
C
WT
= 1500pF
(SILVER MICA)
Watchdog Time-Out Period
vs Temperature
TEMPERATURE (°C)
–60
0.1
I
V3
(µA)
0.2
0.4
0.5
0.6
1.1
0.8
–20 20 40
2901 G11
0.3
0.9
1.0
0.7
–40 0 60 80 100
V1 = 5V
V2 = 3.3V
V3 = 2.5V
V4 = 1.8V
TEMPERATURE (°C)
–60
0
I
V4
(µA)
0.1
0.3
0.4
0.5
1.0
0.7
–20 20 40
2901 G12
0.2
0.8
0.9
0.6
–40 0 60 80 100
V1 = 5V
V2 = 3.3V
V3 = 2.5V
V4 = 1.8V
RESET COMPARATOR OVERDRIVE VOLTAGE (% OF VRTX)
0.1
80
TYPICAL TRANSIENT DURATION (µs)
100
120
140
160
1 10 100
2901 G22
60
40
20
0
200
180
220 TA = 25°C
RESET OCCURS
ABOVE CURVE
Typical Transient Duration
vs Comparator Overdrive (V3, V4)
TEMPERATURE (°C)
–60
4.9
RESET TIME-OUT PERIOD, t
RST
(ms)
5.9
6.4
6.9
8.9
7.9
–20 20 40
2901 G16
5.4
8.4
7.4
–40 0 60 80 100
C
RT
= 1500pF
(SILVER MICA)
IV1 vs Temperature
TEMPERATURE (°C)
–60
0
I
V1
(µA)
10
30
40
50
100
70
–20 20 40
2901 G09
20
80
90
60
–40 0 60 80 100
V1 = 5V
V2 = 3.3V
V3 = 2.5V
V4 = 1.8V
7
LTC2901
2901is sn2901
RST, WDO, COMPX Voltage
Output Low vs Output Sink Current
RST High Level Output Voltage
vs Output Source Current
(LTC2901-2)
RST, WDO, COMPX ISINK
vs Supply Voltage
TYPICAL PERFOR A CE CHARACTERISTICS
UW
V1 OR V2 (V)
0
0
ISINK (mA)
2
4
6
1234
2901 G19
5
8
10
1
3
5
7
9
6
VOL = 0.4V
TA = 25°C
VOL = 0.2V
I
SINK
(mA)
0
V
OL
(V)
20 40 50 90
2901 G20
10 30 60 70 80
3.0
2.5
2.0
1.5
1.0
0.5
0
85°C
25°C
–40°C
V2 = 3V
V1 = 5V
Reset Time-Out Period
vs Capacitance
CRT (FARAD)
10p 100p 10n 1µ
10
1
100m
10m
1m
100µ
2901 G18
1n 100n
RESET TIME-OUT PERIOD, tRST (sec)
TA = 25°C
ISOURCE (mA)
0 0.5 2
VOH (V)
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
2901 G21
2.5
1.51
85°C
25°C
–40°C
V1 = 5V
V2 = 3V
V3 = 2.5V
V4 = 1V
Watchdog Time-Out Period
vs Capacitance
CWT (FARAD)
10p 100p 10n 1µ
100
10
1
100m
10m
1m
2901 G17
1n 100n
WATCHDOG TIME-OUT PERIOD, tWD (sec)
TA = 25°C
V2 (V)
1
0
PULL-UP CURRENT (µA)
2
6
8
10
20
14
233.5
2901 G24
4
16
18
12
1.5 2.5 44.5 5
T
A
= 25°C
COMPX and WDO Pull-Up
Current vs V2 (COMPX and
WDO Held at 0V)
COMPX Propagation Delay vs Input
Overdrive Above Threshold
INPUT OVERDRIVE ABOVE THRESHOLD (mV)
COMPX PROPAGATION DELAY (µs)
250
200
V1, V2
V3, V4
150
2901 G25
0
100
50
1000
10 100
T
A
= 25°C
RST Pull-Up Current vs V2
(LTC2901-1) RST Pull-Up Current vs V2
(LTC2901-2)
V2 (V)
2
0
PULL-UP CURRENT (µA)
4
8
12
2.5 33.5 4
2901 G26
4.5
16
20
2
6
10
14
18
5
TA = 25°C
VRT25
VRT30
VRT33
V2 (V)
2
0
PULL-UP CURRENT (mA)
2
4
5
2.5 33.5 4
2901 G27
4.5
1
3
6
5
TA = 25°C
VRT25
VRT30
VRT33
8
LTC2901
2901is sn2901
UU
U
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 V
CC
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 (C
RT
) 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 gener-
ate 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 C
WT
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 (C
WT
) 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.
V
PG
(Pin 11):
Voltage Threshold Combination Select
Input. Connect to an external 1% resistive divider be-
tween 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 V
CC
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.
9
LTC2901
2901is sn2901
–
+
–
+
–
+
–
+
4
14
3
13
V1
V2
V3
RESISTIVE
DIVIDER
MATRIX
V4
10
GND
A/D
BUFFER
11
V
PG
12
V
REF
5CRT 8WDI
C
RT
2901 DB-1
BANDGAP
REFERENCE
ADJUSTABLE
RESET PULSE
GENERATOR
TRANSITION
DETECT WATCHDOG
TIMER
POWER
DETECT
V1
V2
V
CC
6
RST
V2 LTC2901-1
LTC2901-2
V2
6µA
22µA
10µA
9CWT
C
WT
2µA
15
COMP4
V2
6µA
1
COMP3
V2
6µA
16
COMP2
V2
6µA
2
COMP1
V2
6µA
7
WDO
V2
V
CC
V
CC
V
CC
6µA
22µA
2µA
6
RST
BLOCK DIAGRA
W
10
LTC2901
2901is sn2901
APPLICATIO S I FOR ATIO
WUUU
Power-Up
The greater of V1, V2 is the internal supply voltage (V
CC
).
On power-up, V
CC
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 V
X
inputs
is below its programmed threshold, RST will be a logic low.
Once all the V
X
inputs rise above their thresholds, an inter-
nal timer is started and RST is released after the pro-
grammed delay time. If V
CC
< (V3 – 1) and V
CC
< 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 V
REF
to
GND and connecting the tap point to V
PG
, as shown in
Figure 4. Table 1 offers recommended 1% resistor values
for the various modes. The last column in Table 1 specifies
optimum V
PG
/V
REF
ratios (±0.01) to be used when pro-
gramming with a ratiometric DAC.
During power-up, once V1 or V2 reaches 2.4V max, the
monitor enters a programming period of approximately
150µs during which the voltage on the V
PG
pin is sampled
and the monitor is configured to the desired input combi-
nation. Do not add capacitance to the V
PG
pin. Immediately
after programming, the comparators are enabled and
supply monitoring will begin.
Supply Monitoring
The LTC2901 is a low power, high accuracy program-
mable 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, power-
down 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:
VV
R
R
TRIP =+
05 1 3
4
.
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 be-
tween the negative voltage being sensed and the V
REF
pin,
is connected to the high impedance inverting input (V4).
V
REF
provides the necessary level shift required to operate
at ground. The trip voltage is calculated from:
VV
R
RV V No al
TRIP REF REF
=
=– ; . min
3
41 210
Figure 4. Monitor Programming
12
11
10
R1
1%
R2
1%
2901 F04
V
REF
V
PG
GND
LTC2901
Table 1. Voltage Threshold Programming
V
PG
MODE V1 (V) V2 (V) V3 (V) V4 (V) R1 (kΩ) R2 (kΩ)V
REF
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
11
LTC2901
2901is sn2901
APPLICATIO S I FOR ATIO
WUUU
In a negative adjustable application, the minimum value
for R4 is limited by the sourcing capability of V
REF
(±1mA).
With no other load on V
REF
, R4 (minimum) is:
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 built-
in glitch immunity, bypass capacitors on V1 and V2 are
recommended because the greater of V1 or V2 is also the
V
CC
for the chip. Filter capacitors on the V3 and V4 inputs
are allowed.
Power-Down
On power-down, once any of the V
X
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
(V
CC
< 2V typ), the part will reprogram once V
CC
rises
above 2.4V max.
Monitor Output Rise and Fall Time Estimation
All of the outputs (RST, COMPX, WDO) have strong pull-
down capability. If the external load capacitance (C
LOAD
)
for a particular output is known, output fall time (10% to
90%) is estimated using:
t
FALL
≈ 2.2 • R
PD
• C
LOAD
where R
PD
is the on-resistance of the internal pull-down
transistor. The typical performance curve (V
OL
vs I
SINK
)
demonstrates that the pull-down current is somewhat
linear versus output voltage. Using the 25°C curve, R
PD
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
Figure 5. Setting the Positive Adjustable Trip Point
–
+
+
–0.5V
2901 F05
V3 OR V4
VTRIP
R3
1%
R4
1%
LTC2901
Figure 6. Setting the Negative Adjustable Trip Point
–
+
2901 F06
V4
V
REF
13
12
V
TRIP
R4
1%
R3
1%
LTC2901
Table 2. Suggested 1% Resistor Values for the ADJ Inputs
V
SUPPLY
(V) V
TRIP
(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 3. Suggested 1% Resistor Values for the –ADJ Input
V
SUPPLY
(V) V
TRIP
(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
12
LTC2901
2901is sn2901
Pull-Up Current vs V2 curve). Output rise time (10% to
90%) is estimated using:
t
RISE
≈ 2.2 • R
PU
• C
LOAD
where R
PU
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:
RV
PU
=Ω
610
21
5
•
–
with V2 = 3.3V, R
PU
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 pull-
up 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 Cur-
rent vs V2 curve) demonstrates that the pull-up current is
somewhat linear versus the V2 voltage and R
PU
is esti-
mated to be approximately 625Ω. A 150pF load capaci-
tance 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 accom-
modate a variety of microprocessor applications. The
reset time-out period, t
RST
, is adjusted by connecting a
capacitor, C
RT
, between the CRT pin and ground. The
value of this capacitor is determined by:
C
RT
= t
RST
• 217.4 • 10
–9
with C
RT
in Farads and t
RST
in seconds. The C
RT
value per
millisecond of delay can also be expressed as C
RT/ms
=
217.4 (pF/ms).
Leaving the CRT pin unconnected will generate a mini-
mum 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, t
WD
, is adjusted by connecting a capacitor, C
WT
,
between the CWT pin and ground. Given a specified
watchdog time-out period, the capacitor is determined by:
C
WT
= t
WD
• 50 • 10
–9
with C
WT
in Farads and t
WD
in seconds. The C
WT
value per
millisecond of delay can also be expressed as C
WT/ms
=
50 (pF/ms).
Leaving the CWT pin unconnected will generate a mini-
mum watchdog time-out of approximately 200µs. Maxi-
mum 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.
APPLICATIO S I FOR ATIO
WUUU
13
LTC2901
2901is sn2901
APPLICATIO S I FOR ATIO
WUUU
+
COMP1
COMP2
COMP3
COMP4
RST
WDO
CRT
CWT
V1
V2
V3
V4
WDI
VREF
VPG
GND
2
16
1
15
6
7
5
9
3.3V MONITOR
1.8V MONITOR
FEEDBACK MONITOR
COMMON RESET OUT
LOW LOAD INDICATOR
4
14
3
13
8
12
11
10
LTC2901-2
PGATE
VIN
SENSE–
ITH
GND
VFB
6
5
4
M1
D1
1
2
3
LTC1772
R1
28k
1%
R5
0.15Ω
R6
10k
R3
100k
R4
80.6k
C2
47µF
6V
VOUT
1.8V
0.5A
VIN
3.3V
L1
10µH
R2
71.5k
1%
CRT
47nF
2901 F07
C1
10µF
10V
C3
220pF
C1: TAIYO YUDEN CERAMIC LMK325BJ106K-T
C2: SANYO POSCAP 6TPA47M
D1: MOTOROLA MBRM120T3
L1: COILTRONICS UP1B-100
M1: Si3443DV
R5: DALE 0.25W
Burst Mode is a registered trademark of Linear Technology Corporation.
Figure 7. Monitor Input, Output, Feedback Voltage and Low Load Conditions on DC/DC Controller
TYPICAL APPLICATIO S
U
Quad Supply Monitor with Watchdog Timer Disabled
5V, 3V, 1.8V, 12V (ADJ)
COMP2
COMP4
V2
V4
V
REF
V
PG
GND
CWT
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
COMP3
COMP1
V3
V1
CRT
RST
WDO
WDI
R3
2.15M
1%
SYSTEM
RESET
1.8V 3V
12V
5V
C
RT
R4
100k
1%
LTC2901
V
TRIP
= 11.25V
2901 TA02
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 adjust-
able input (V4). The RST pin will go high 216ms
(C
RT
= 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
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
LTC2901
2901is sn2901
TYPICAL APPLICATIO S
U
Quad Supply Monitor with LED Undervoltage Indicators
5V, 3.3V, 2.5V, 1.5V
COMP2
COMP4
V2
V4
VREF
VPG
GND
CWT
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
COMP3
COMP1
V3
V1
CRT
RST
WDO
WDI
SYSTEM RESET
WATCHDOG STATUS
WDI
1.5V
3.3V
5V
2.5V
R2
47.5k
1%
R1
53.6k
1%
RL2
1k
LED
LTC2901
2901 TA04
CRT CWT
RL4
1k
LED
RL3
1k
LED
RL1
1k
LED
5V, –5V Monitor with Watchdog Timer Disabled and Unused
V2, V3 Inputs Pulled Above Trip Thresholds
COMP2
COMP4
V2
V4
V
REF
V
PG
GND
CWT
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
COMP3
COMP1
V3
V1
CRT
RST
WDO
WDI
R4
121k
1%
R3
464k
1%
SYSTEM
RESET
–5V
5V
R2
86.6k
1%
R1
16.2k
1%
LTC2901
V
TRIP
= –4.64V
2901 TA03
C
RT
15
LTC2901
2901is sn2901
U
PACKAGE DESCRIPTIO
GN Package
16-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641)
GN16 (SSOP) 1098
* 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
12
345678
0.229 – 0.244
(5.817 – 6.198)
0.150 – 0.157**
(3.810 – 3.988)
16 15 14 13
0.189 – 0.196*
(4.801 – 4.978)
12 11 10 9
0.016 – 0.050
(0.406 – 1.270)
0.015 ± 0.004
(0.38 ± 0.10) × 45°
0° – 8° TYP
0.007 – 0.0098
(0.178 – 0.249)
0.053 – 0.068
(1.351 – 1.727)
0.008 – 0.012
(0.203 – 0.305)
0.004 – 0.0098
(0.102 – 0.249)
0.0250
(0.635)
BSC
0.009
(0.229)
REF
16
LTC2901
2901is sn2901
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 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 t
FAIL
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
LT/TP 0602 1.5K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 2002
RELATED PARTS
COMP1
COMP2
COMP3
COMP4
RST
WDO
CRT
CWT
V1
V2
V3
V4
WDI
V
REF
V
PG
GND
2
16
1
15
6
7
5
9
2.5V MONITOR
12V MONITOR
–2V MONITOR
COMMON RESET OUT
AC PRESENT
4
14
3
13
8
12
11
10
LTC2901-1
C
WT
680pF
2901 TA05
C
RT2
47nF
78.7k
1%
121k
1%
187k
1%
Q1
2N3904
2.15M
1%
12V
2.5V
–2V
100k
1%
100k 22.1k
1%
10k
COMP1
COMP2
COMP3
COMP4
RST
WDO
CRT
CWT
V1
V2
V3
V4
WDI
V
REF
V
PG
GND
2
16
1
15
6
7
5
9
5V MONITOR
3.3V MONITOR
1.8V MONITOR
–5.2V MONITOR
12V
5V
3.3V
2.5V
1.8V
–2V
–5.2V
4
14
3
13
8
12
11
10
LTC2901-1
3.3V
5V
1.8V
1N4148
C
RT1
47nF
16.2k
1%
121k
1%
487k
1%
LOW
VOLTAGE
SECONDARY
AC/DC
DC/DC
CONVERTERS
–5.2V
86.6k
1%
10k
1N4148
100k
120V AC
t
RST1
+ t
RST2
= 432ms
t
WD
= 13.6ms
Monitor Seven Supplies (12V, 5V, 3.3V, 2.5V, 1.8V, –2V, –5.2V) with
Sequenced Reset and AC Present Indication
TYPICAL APPLICATIO
U
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear.com
