LTC2903-1
Precision Quad Supply
Monitor in 6-Lead SOT-23
U
FEATURES
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DESCRIPTIO
Ultralow Voltage Reset: VCC = 0.5V Guaranteed
Monitor Four Inputs Simultaneously
3.3V, 2.5V, 1.8V, ADJ (LTC2903-A1)
5V, 3.3V, 2.5V, 1.8V (LTC2903-B1)
5V, 3.3V, 1.8V, –5.2V (LTC2903-C1)
3.3V, ADJ, ADJ, ADJ (LTC2903-D1)
5V, ADJ, ADJ, ADJ (LTC2903-E1)
Guaranteed Threshold Accuracy: ±1.5% of
Monitored Voltage over Temperature
10% (A1, B1, C1) and 5% (D1, E1) Undervoltage
Monitoring
Low Supply Current: 20µA Typical
200ms Reset Time Delay
Active Low Open-Drain RST Output
Power Supply Glitch Immunity
Low Profile (1mm) SOT-23 (ThinSOTTM) Package
The LTC®2903-1 monitors up to four supply voltages. The
common reset output remains low until all four inputs
have been in compliance for 200ms. Voltage thresholds
maintain ±1.5% accuracy over temperature (with respect
to the monitored voltage). The LTC2903-1 features an
open-drain RST output with a weak internal pullup.
Internal supply voltage (VCC) is generated from the greater
voltage on the V1, V2 inputs. VCC = V1 for LTC2903-D1 and
LTC2903-E1. The RST output is guaranteed to sink at least
5µA (VOL = 0.15V) for VCC down to 0.5V and will typically
conduct current down to 0V. Quiescent current is 20µA
typical, making the LTC2903-1 ideal for power conscious
systems. The LTC2903-1 is available in a 6-lead low profile
(1mm) SOT-23 package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
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APPLICATIO S
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Multivoltage Systems
Optical Networking Systems
Cell Phone Base Stations
Network Servers
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TYPICAL APPLICATIO
Low Voltage Reset Pull-Down Performance
vs External Pull-Up Current and Input Supply Voltage
0.10
5V
VIN = V1 = V2 = V3
LTC2903-B1
0.09
DC/DC
2.5V
CONVERTER
1.8V
SYSTEM
LOGIC
C1
0.1µF
C2
0.1µF
LTC2903-B1
RST
V1
GND
V4
V2
V3
0.08
RESET PIN VOLTAGE (V)
3.3V
0.07
20µA
0.06
10µA
0.05
0.04
5µA
0.03
0.02
2903 TA01
0.01
0
2µA
1µA
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
VIN, INPUT SUPPLY VOLTAGE (V)
1
2903 TA01b
29031f a
1
LTC2903-1
U
W
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ABSOLUTE MAXIMUM RATINGS
PACKAGE/ORDER INFORMATION
(Notes 1, 2, 3)
V1, V2 ...................................................... – 0.3V to 6.5V
V3 ................................................. 2.7V or (VCC + 0.3V)
V4 (LTC2903-A1, -B1, -D1, -E1) ...............– 0.3V to 6.5V
V4 (LTC2903-C1) .................................... – 6.5V to 0.3V
RST ........................................................ – 0.3V to 6.5V
Operating Temperature Range
LTC2903C-X1 .......................................... 0°C to 70°C
LTC2903I-X1 ...................................... – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
TOP VIEW
6 RST
V1 1
GND 2
5 V4
V2 3
4 V3
S6 PACKAGE
6-LEAD PLASTIC TSOT-23
TJMAX = 125°C, θJA = 230°C/W
ORDER PART NUMBER
S6 PART MARKING
LTC2903CS6-A1
LTC2903CS6-B1
LTC2903CS6-C1
LTC2903CS6-D1
LTC2903CS6-E1
LTC2903IS6-A1
LTC2903IS6-B1
LTC2903IS6-C1
LTC2903IS6-D1
LTC2903IS6-E1
LTAFV
LTAJN
LTAJQ
LTBMX
LTBMZ
LTAFW
LTAJP
LTAJR
LTBMY
LTBNB
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
(LTC2903-A1) The ● denotes the specifications which apply over the full
operating temperature range, otherwise specifications are at TA = 25°C. VCC = 3.3V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VRT33
3.3V, 10% Reset Threshold
V1 Input Threshold
●
2.871
2.921
2.970
V
VRT25
2.5V, 10% Reset Threshold
V2 Input Threshold
●
2.175
2.213
2.250
V
VRT18
1.8V, 10% Reset Threshold
V3 Input Threshold
●
1.566
1.593
1.620
V
VRTA
Adjustable Reset Threshold
V4 Input Threshold
●
0.492
0.500
0.508
V
(LTC2903-B1) The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at
TA = 25°C. VCC = 5V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VRT50
5V, 10% Reset Threshold
V1 Input Threshold
VRT33
3.3V, 10% Reset Threshold
V2 Input Threshold
●
4.350
4.425
4.500
V
●
2.871
2.921
2.970
VRT25
2.5V, 10% Reset Threshold
V
V3 Input Threshold
●
2.175
2.213
2.250
V
VRT18
1.8V, 10% Reset Threshold
V4 Input Threshold
●
1.566
1.593
1.620
V
(LTC2903-C1) The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at
TA = 25°C. VCC = 5V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VRT50
5V, 10% Reset Threshold
V1 Input Threshold
VRT33
3.3V, 10% Reset Threshold
V2 Input Threshold
●
4.350
4.425
4.500
V
●
2.871
2.921
2.970
V
VRT18
1.8V, 10% Reset Threshold
V3 Input Threshold
●
VRT52N
–5.2V, 10% Reset Threshold
V4 Input Threshold
●
1.566
1.593
1.620
V
–4.524 –4.602 –4.680
V
29031f a
2
LTC2903-1
ELECTRICAL CHARACTERISTICS
(LTC2903-D1) The ● denotes the specifications which apply over the full
operating temperature range, otherwise specifications are at TA = 25°C. VCC = 3.3V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VRT33
3.3V, 5% Reset Threshold
V1 Input Threshold
●
3.036
3.086
3.135
V
VRTAV2
V2 Adjustable Threshold
V2 Input Threshold
●
0.492
0.500
0.508
V
VRTAV3
V3 Adjustable Threshold
V3 Input Threshold
●
0.492
0.500
0.508
V
VRTAV4
V4 Adjustable Threshold
V4 Input Threshold
●
0.492
0.500
0.508
V
(LTC2903-E1) The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at
TA = 25°C. VCC = 5V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VRT50
5V, 5% Reset Threshold
V1 Input Threshold
●
4.600
4.675
4.750
V
VRTAV2
V2 Adjustable Threshold
V2 Input Threshold
●
0.492
0.500
0.508
V
VRTAV3
V3 Adjustable Threshold
V3 Input Threshold
●
0.492
0.500
0.508
V
VRTAV4
V4 Adjustable Threshold
V4 Input Threshold
●
0.492
0.500
0.508
V
The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VCC = 3.3V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
IV1
V1 Input Current (Note 4)
V1 = 3.3V (LTC2903-A1, LTC2903-D1)
V1 = 5V (LTC2903-B1, LTC2903-C1,
LTC2903-E1)
IV2
MIN
TYP
MAX
●
●
20
25
80
80
µA
µA
V2 Input Current (Note 4)
V2 = 2.5V (LTC2903-A1)
●
V2 = 3.3V (LTC2903-B1, LTC2903-C1) ●
V2 = 0.55V (LTC2903-D1, LTC2903-E1) ●
8
10
30
30
±30
µA
µA
nA
IV3
V3 Input Current
V3 = 1.8V (LTC2903-A1, LTC2903-C1) ●
V3 = 2.5V (LTC2903-B1)
●
V3 = 0.55V (LTC2903-D1, LTC2903-E1) ●
8
10
30
30
±30
µA
µA
nA
IV4
V4 Input Current
V4 = 0.55V (LTC2903-A1)
V4 = 1.8V (LTC2903-B1)
V4 = –5.2V (LTC2903-C1)
V4 = 0.55V (LTC2903-D1, LTC2903-E1)
2
–3
±30
4
–6
±30
nA
µA
µA
nA
200
260
ms
●
●
●
●
●
tRST
Reset Time-Out Period
tUV
VX Undervoltage Detect to RST
VX Less Than Threshold VRTX by
More Than 1%
VOH
Output Voltage High RST (LTC2903-1) (Note 5)
IRST(DN) = –1µA (LTC2903-A1,
LTC2903-B1, LTC2903-C1)
(LTC2903-D1, LTC2903-E1)
●
V2 – 1
V
●
V1 – 1
V
VCC = 0.2V, IRST = 0.1µA
VCC = 0.5V, IRST = 5µA
VCC = 1V, IRST = 200µA
VCC = 3V, IRST = 2500µA
●
●
●
●
VOL
Output Voltage Low RST (Note 6)
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2: All currents into pins are positive, all voltages are referenced to
GND unless otherwise noted.
Note 3: The internal supply voltage (VCC) is generated from the greater
voltage on the V1 and V2 inputs. VCC = V1 for options D1 and E1.
Note 4: Under typical operating conditions, quiescent current is drawn
140
UNITS
150
5
10
25
100
µs
60
150
300
300
mV
mV
mV
mV
from the V1 input. When V2 exceeds V1, V2 supplies the quiescent
current. V1 only for options D1 and E1.
Note 5: The RST output pin on the LTC2903-1 has an internal pull-up to
V2 (for options A1, B1 and C1) of typically 10µA. However, for faster rise
times or for VOH voltages greater than V2, use an external pull-up resistor.
The internal pull-up is connected to V1 for options D1 and E1.
Note 6: For options A1, B1 and C1, the RST pulldown current is derived
from V1, V2 and V3. For options D1 and E1, pulldown strength is derived
from V1.
29031f a
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LTC2903-1
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TYPICAL PERFOR A CE CHARACTERISTICS
5V Threshold Voltage
vs Temperature
3.3V Threshold Voltage
vs Temperature
2.975
4.475
4.450
4.425
4.400
4.375
4.350
–50
–25
0
25
50
TEMPERATURE (°C)
75
2.250
THRESHOLD VOLTAGE, VRT25 (V)
THRESHOLD VOLTAGE, VRT33 (V)
4.500
THRESHOLD VOLTAGE, VRT50 (V)
2.5V Threshold Voltage
vs Temperature
2.950
2.925
2.900
2.875
–50
100
0
25
50
TEMPERATURE (°C)
–25
75
29031 G01
1.605
1.595
1.585
1.575
75
0.505
0.500
0.495
0
25
50
TEMPERATURE (°C)
–25
75
30
25
20
–4.605
–4.630
–4.655
–4.680
–50
10
30
V1 = 5V
V2 = 3.3V
V3 = 2.5V
V4 = 1.8V
25
15
15
10
IV2
10
5
IV2
IV3
5
IV3
0
IV3
–25
V1 = 5V
V2 = 3.3V
V3 = 1.8V
V4 = –5.2V
IV1
IV1
IV4
IV4
0
25
50
TEMPERATURE (°C)
75
100
29031 G07
0
–50
100
20
IV2
5
75
Supply Currents
vs Temperature (LTC2903-C1)
IVX (µA)
15
0
25
50
TEMPERATURE (°C)
–25
29031 G06
20
IVX (µA)
IVX (µA)
–4.580
Supply Currents
vs Temperature (LTC2903-B1)
V1 = 3.3V
V2 = 2.5V
V3 = 1.8V
0
–50
100
–4.555
29031 G05
Supply Currents
vs Temperature (LTC2903-A1)
100
–4.530
0.490
–50
100
IV1
75
–5.2V Threshold Voltage
vs Temperature
29031 G04
25
0
25
50
TEMPERATURE (°C)
–25
29031 G03
THRESHOLD VOLTAGE, VRT52N (V)
THRESHOLD VOLTAGE, VRTA (V)
THRESHOLD VOLTAGE, VRT18 (V)
1.615
30
2.190
2.175
–50
100
0.510
0
25
50
TEMPERATURE (°C)
2.205
ADJ Threshold Voltage
vs Temperature
1.625
–25
2.220
29031 G02
1.8V Threshold Voltage
vs Temperature
1.565
–50
2.235
–25
0
25
50
TEMPERATURE (°C)
75
100
29031 G08
–5
–50
–25
50
25
0
TEMPERATURE (°C)
75
100
29031 G09
29031f a
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LTC2903-1
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TYPICAL PERFOR A CE CHARACTERISTICS
260
TYPICAL TRANSIENT DURATION (µs)
LTC2903-E1
20
LTC2903-D1
15
10
5
0
–50
–25
75
0
25
50
TEMPERATURE (°C)
350
300
250
RESET OCCURS
ABOVE CURVE
200
150
100
50
0
1
10
100
0.1
RESET COMPARATOR OVERDRIVE (% OF VRTX)
100
RST Output Voltage with 10k
Pull-Up to V1
2.5
2.0
1.5
1.0
0
25
50
TEMPERATURE (°C)
0.10
75
100
VIN = V1 = V2 = V3
0.08
0.20
0.15
V1 ONLY
0.10
2.5 3
V1 (V)
3.5
4
4.5
0
5
20µA
0.06
10µA
0.05
0.04
5µA
0.03
0.01
V1 = V2 = V3
2
0.07
0.02
0.05
0.5
1.5
–25
Low Voltage Reset Pull-Down
Performance vs External Pull-Up
Current and Input Supply Voltage
RESET PIN VOLTAGE (V)
RST OUTPUT VOLTAGE (V)
RST OUTPUT VOLTAGE (V)
3.0
1
160
0.09
3.5
0.5
180
29301 G11
0.25
0
200
140
–50
0.30
4.0
0
220
RST Output Voltage with
10k Pull-Up to V1
V1 = V2 = V3
LTC2903-B1, -C1
4.5
240
29031 G10
29031 G20
5.0
RESET TIME-OUT PERIOD, tRST (ms)
400
25
IV1 (µA)
Reset Time-Out Period
vs Temperature
Transient Duration
vs Comparator Overdrive
Supply Currents vs Temperature
0
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
V1 (V)
29031 G12
2µA
1µA
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
VIN, INPUT SUPPLY VOLTAGE (V)
29301 G13
RST Current Sink Capability
vs VCC
29031 G14
RST Voltage Output Low
vs RST Sink Current
15
1.5
12
1.2
LTC2903-A1, -E1
V1 = 3.3V
RST Voltage Output Low
vs RST Sink Current
1.5
85°C
1
25°C
LTC2903-B1, -C1, -D1
V1 = 5V
25°C
1.2
–45°C
85°C
–45°C
VOL = 0.2V
6
3
0
0.9
VOL (V)
9
VOL (V)
IRST (mA)
VOL = 0.4V
0.6
0.6
0.3
0.3
0
0
0.5
1
1.5
2
2.5 3
VCC (V)
3.5
4
4.5
5
29031 G15
0.9
0
0
5
10
15
25 30
IRST (mA)
20
35
40
45
29031 G16
0
10
20
40
30
IRST (mA)
50
60
29031 G16
29031f a
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LTC2903-1
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TYPICAL PERFOR A CE CHARACTERISTICS
RST Pull-Up Current vs V2
RST Pull-Up Current vs V1
–90
–80
LTC2903-A1, -B1, -C1
–80 V1, V3, V4 ABOVE THRESHOLD
LTC2903-D1, -E1
–70 V2, V3, V4 ABOVE THRESHOLD
–70
–60
IRST (µA)
IRST (µA)
–60
–50
–40
LTC2903-D1
–40
–30
–30
–20
–20
VRT25
VRT33
0
0.5
1
1.5
2
2.5 3
V2 (V)
3.5
LTC2903-E1
–10
–10
0
–50
4.5
4
0
5
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5
V1 (V)
29031 G18
29031 G21
RST Pull-Up Current vs External
Pull-Down Voltage on RST
RST Pull-Up Current vs External
Pull-Down Voltage on RST
–40
–80
–35
–70
–30
–60
LTC2903-E1
IRST (µA)
IRST (µA)
LTC2903-B1, -C1
–25
–20
–15
–50
–40
–30
LTC2903-A1
–10
–20
–5
–10
LTC2903-D1
0
0
0
0.5
1
2
1.5
VRST (V)
2.5
3
3.5
0
1
2
3
4
5
6
VRST (V)
29031 G19
29031 G22
29031f a
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LTC2903-1
U
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PI FU CTIO S
V1 (Pin 1): Voltage Input 1. Internal VCC is generated from
the greater voltage on the V1 and V2 inputs. VCC = V1 for
options D1 and E1. Bypass this pin to ground with a 0.1µF
(or greater) capacitor.
V3 is an adjustable input for options D1 and E1. See Table
1b for recommended ADJ resistor values.
GND (Pin 2): Ground.
V4 (Pin 5): Voltage Input 4. Table 1 lists the recommended
ADJ resistor values for options A1, B1 and C1. See Table
1b for options D1 and E1.
V2 (Pin 3): Voltage Input 2. Internal VCC is generated from
the greater voltage on the V1 and V2 inputs. VCC = V1 for
options D1 and E1. For option A1, B1, C1 bypass this pin
to ground with a 0.1µF (or greater) capacitor. V2 is an
adjustable input for options D1 and E1. See Table 1b for
recommended ADJ resistor values.
RST (Pin 6): Reset Logic Output. Pulls low when any voltage input is below reset threshold and held low for 200ms
after all voltage inputs exceed threshold. The pin contains
a weak pull-up to V2 (V1 for options D1 and E1). Use an
external pull-up for faster rise times or output voltages
greater than V2 (V1 for options D1 and E1).
V3 (Pin 4): Voltage Input 3. This input assists the RST pulldown circuitry below 1V (for options A1, B1 and C1 only).
WU
W
TI I G DIAGRA
VX
VRTX
tUV
RST
tRST
1.5V
29031 TD
29031f a
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LTC2903-1
W
BLOCK DIAGRA S
V1 1
(LTC2903-A1, LTC2903-B1)
–
V1
+
POWER
DETECT
V2
VCC
V2
10µA
V2 3
–
RESET DELAY GENERATOR
+
V3 4
200ms
DELAY
–
V1
V2
V3
+
V4 5
6 RST
LOW VOLTAGE
PULL-DOWN
MONITORED VOLTAGES
–
+
BANDGAP
REFERENCE
GND 2
A1
B1
V1
3.3V
5V
V2
2.5V
3.3V
V3
1.8V
2.5V
V4
ADJ
1.8V
29031 BD1
0.5V
(LTC2903-C1)
V1 1
–
V1
+
POWER
DETECT
V2
VCC
V2
10µA
V2 3
–
RESET DELAY GENERATOR
+
V3 4
6 RST
200ms
DELAY
–
V1
V2
V3
+
LOW VOLTAGE
PULL-DOWN
MONITORED VOLTAGES
V4 5
+
–
GND 2
BANDGAP
REFERENCE
V1
5V
V2
3.3V
V3
1.8V
V4
–5.2V
29031 BD3
29031f a
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LTC2903-1
W
BLOCK DIAGRA S
(LTC2903-D1, LTC2903-E1)
–
V1 1
POWER
DETECT
V1
+
VCC
V1
10µA
–
V2 3
RESET DELAY GENERATOR
+
6 RST
200ms
DELAY
–
V3 4
V1
+
LOW VOLTAGE
PULL-DOWN
MONITORED VOLTAGES
–
V4 5
+
BANDGAP
REFERENCE
GND 2
D1
E1
V1
3.3V
5V
V2
ADJ
ADJ
V3
ADJ
ADJ
V4
ADJ
ADJ
29031 BD2
0.5V
U
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APPLICATIO S I FOR ATIO
The LTC2903-1 issues a logic low on the RST output when
an input supply voltage resides below the prescribed
threshold voltage. Ideally, the RST logic output would
remain low with the input supply voltage down to zero
volts. Most supervisors lack pull-down capability below
1V. The LTC2903-1 power supply supervisors incorporate
a new low voltage pull-down circuit that can hold the RST
line low with as little as 200mV of input supply voltage on
V1, V2 or V3 (V1 only for options D1 and E1). The pull-down
circuit helps maintain a low impedance path to ground,
reducing the risk of floating the RST node to undetermined
voltages. Such voltages may trigger external logic causing
erroneous reset operation(s). Furthermore, a mid-scale
voltage could cause external circuits to operate in the
middle of their voltage transfer characteristic, consuming
more quiescent current than normal. These conditions
could cause serious system reliability problems.
When V1, V2 and V3 are ramped simultaneously (for
options A1, B1 and C1 only), the reset pull-down current
increases up to three times the current that may be pulled
with a single input. Figure 1 demonstrates the reset pin
10000
TA = 25°C
VRST = 0.3VCC
1000
IRST (µA)
Power-Up
V1 = V2 = V3
100
V1 ONLY
10
1
0
0.2
0.4
0.6
VCC (V)
0.8
1.0
1.2
29031 F01
Figure 1. RST Pull-Down Current vs VCC
29031f a
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LTC2903-1
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current sinking ability for single supply and triple supplytracking applications. Figure 2 shows a detailed view of the
reset pin voltage with a 10k pull-up resistor to V1.
The LTC2903-1 supervisors derive their internal supply
voltage (VCC) automatically from the greater voltage on the
V1 and V2 inputs (VCC = V1 for options D1 and E1). With
all supply inputs above threshold, the quiescent current
drawn from VCC is 20µA (typ).
Supply Monitoring
The LTC2903-1 accurately monitors four inputs in a small
6-lead SOT-23 package. The low voltage reset output
includes an integrated 200ms reset delay timer. The reset
line pulls high 200ms after all voltage inputs exceed their
respective thresholds. The reset output remains low during power-up, power-down and brownout conditions on
any of the voltage inputs.
Triple Adjustable Options (LTC2903-D1, LTC2903-E1)
LTC2903-D1 and LTC2903-E1 provide 3 adjustable inputs: V2, V3 and V4. The V1 threshold is 3.086V (3.3V,
5%) for option D1 and 4.675 (5V, 5%) for option E1. For
each supply monitored by an adjustable input, connect an
external resistor divider (R1 and R2) between the positive
voltage being sensed and ground. The tap point for each
divider is then connected to each adjustable input. All
adjustable inputs are compared to an internal 0.5V
reference.
Figure 3 shows how each adjustable input is configured.
Calculate the trip voltage from:
⎛ R1⎞
VTRIP = 0.5V⎜ 1 + ⎟
⎝ R2 ⎠
VTRIP
LTC2903-A1
0.7
R1
TA = 25°C
RST OUTPUT VOLTAGE (V)
–
V4
0.6
R2
0.5
0.4
+
COMPETITION
PART
0.5V
+
–
0.3
29031 F03
0.2
0.1
V1 ONLY
V1 = V2 = V3
Figure 3. Setting the Positive Adjustable Trip Point
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
V1 (V)
29031 F02
Figure 2. RST Output Voltage with a 10k Pull-Up to V1
(Enlarged Area of Detail)
29031f a
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Table 1a. Suggested 1% Resistor Values for the –11.5% ADJ Inputs
VSUPPLY (V)
VTRIP (V)
R1 (kΩ)
R2(kΩ)
12
10.75
2050
100
10
8.95
1690
100
8
7.15
1330
100
7.5
6.7
1240
100
6
5.38
976
100
5
4.435
787
100
3.3
2.935
487
100
3
2.66
432
100
2.5
2.2
340
100
1.8
1.605
221
100
1.5
1.325
165
100
1.2
1.065
113
100
1
0.884
76.8
100
0.9
0.795
59
100
Table 1b contains suggested 1% resistor values for the
ADJ inputs to obtain nominal –6.5% thresholds.
Table 1b. Suggested 1% Resistor Values for the –6.5% ADJ Inputs
VSUPPLY (V)
VTRIP (V)
R1 (kΩ)
R2(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
0.933
86.6
100
0.9
0.840
68.1
100
0.8
0.750
49.9
100
0.7
0.655
30.9
100
0.6
0.561
12.1
100
Implications of Threshold Accuracy
Specifying system voltage margin for worst-case operation requires consideration of three factors: power supply
tolerance, IC supply voltage tolerance and supervisor reset threshold accuracy. Highly accurate supervisors ease
the design challenge by decreasing the overall voltage
margin required for reliable system operation. Consider a
5V system with a ±10% power supply tolerance band.
System ICs powered by this supply must operate reliably
within this band (and a little more, as explained below).
The bottom of the supply tolerance band, at 4.5V (5V –
10%), is the exact voltage at which a perfectly accurate
supervisor generates a reset. Such a perfectly accurate
supervisor does not exist—the actual reset threshold may
vary over a specified band (±1.5% for the LTC2903-1 supervisors). Figure 4 shows the typical relative threshold
accuracy for all four inputs, over temperature.
With this variation of reset threshold in mind, the nominal
reset threshold of the supervisor resides below the minimum supply voltage, just enough so that the reset threshold band and the power supply tolerance bands do not
overlap. If the two bands overlap, the supervisor could
generate a false or nuisance reset when the power supply
remains within its specified tolerance band (say, at 4.6V).
Adding half of the reset threshold accuracy spread (1.5%)
to the ideal 10% thresholds puts the LTC2903-1 thresholds at 11.5% (typ) below the nominal input voltage. For
example, the 5V typical threshold is 4.425V, or 75mV
below the ideal threshold of 4.500V. The guaranteed
threshold lies in the band between 4.500V and 4.350V
over temperature.
1.5
TYPICAL THRESHOLD ACCURACY (%)
Table 1a contains suggested 1% resistor values for the
ADJ inputs to obtain nominal –11.5% thresholds. Connect
unused supervisor inputs to the highest supply voltage
available.
1.0
0.5
0
–0.5
–1.0
–1.5
–50
–25
50
25
0
TEMPERATURE (°C)
75
100
29031 F04
Figure 4. LTC2903 Typical Threshold Accuracy vs Temperature
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The powered system must work reliably down to the
lowest voltage in the threshold band or risk malfunction
before the reset line falls. In the 5V example, using the
1.5% accurate supervisor, the system ICs must work
down to 4.35V. System ICs working with a ±2.5% accurate
supervisor must operate down to 4.25V, increasing the
required system voltage margin and the probability of
system malfunction.
In any supervisory application, supply noise riding on the
monitored DC voltage can cause spurious resets, particularly when the monitored voltage approaches the reset
threshold. A less than desirable but commonly used
technique used to mitigate this problem adds hysteresis to
the input comparator. The amount of added hysteresis,
usually specified as a percentage of the trip threshold,
effectively degrades the advertised accuracy of the part.
To maintain high accuracy, the LTC2903-1 does not use
hysteresis.
To minimize spurious resets while maintaining threshold
accuracy, the LTC2903-1 employs two forms of noise
filtering. The first line of defense incorporates proprietary
tailoring of the comparator transient response. Transient
events receive electronic integration in the comparator
and must exceed a certain magnitude and duration to
cause the comparator to switch. Figure 5 illustrates the
typical transient duration versus comparator overdrive
(as a percentage of the trip threshold VRT) required to trip
the comparators. Once any comparator is switched, the
reset line pulls low. The reset time-out counter starts once
TYPICAL TRANSIENT DURATION (µs)
400
TA = 25°C
350
300
250
200
RESET OCCURS
ABOVE CURVE
all inputs return above threshold. The nominal reset delay
time is 200ms. The counter clears whenever any input
drops back below threshold. This reset delay time effectively provides further filtering of the voltage inputs. A
noisy input with frequency components of sufficient magnitude above f = 1/tRST = 5Hz holds the reset line low,
preventing oscillatory behavior on the reset line.
Although all four comparators have built-in glitch filtering,
use bypass capacitors on the V1 and V2 inputs because
the greater of V1 or V2 supplies the VCC (options A1, B1
and C1) for the part (a 0.1µF ceramic capacitor satisfies
most applications). Apply filter capacitors on the V3 and
V4 inputs in extremely noisy situations. Options D1 and E1
require a bypass capacitor only on V1. Apply filter capacitors on V2, V3 and V4 adjustable inputs in extremely noisy
situations.
Reset Output Rise and Fall Time Estimation
The reset output line contains a weak pull-up current
source to the V2 supply (V1 for options D1 and E1). Use
an external pull-up resistor when the output needs to pull
to another voltage and/or when the reset output needs a
faster rise time. The open-drain output allows for wiredOR connections when more than one signal needs to pull
down on the reset line. Estimate output rise time for the
open-drain output without an external pull-up using:
tRISE ≈ 2.2 • RPU • CLOAD
where RPU is the on-resistance of the pull-up transistor
and CLOAD is the external load capacitance on the pin. At
room temperature, the average RPU is approximately
50kΩ. When externally pulling up to voltages higher than
V2 (V1 for options D1 and E1), an internal network
automatically protects the weak pull-up circuitry from
reverse currents.
The reset output has very strong pull-down capability.
Estimate the output fall time using:
150
100
tFALL ≈ 2.2 • RPD • CLOAD
50
0
0.1
1
10
100
RESET COMPARATOR OVERDRIVE (% OF VRTX)
29031 F05
Figure 5. Typical Transient Duration vs Overdrive
Required to Trip Comparator
where RPD is the on-resistance of the pull-down transistor
and CLOAD is the external load capacitance on the pin. At
room temperature, the average RPD is approximately 40Ω.
With a 150pF load capacitance the reset line can pull down
in about 13ns.
29031f a
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TYPICAL APPLICATIO S
Quad Supply Monitor with Adjustable Input
1
3.3V
C1
0.1µF
V1
RST
6
SYSTEM RESET
LTC2903-A1
2
GND
V4
R1
76.8k
5
R2
100k
C2
0.1µF
3
2.5V
V2
V3
4
1V
(VTRIP = 0.884V)
1.8V
2903 TA02
Fixed Quad Supply Monitor with LED Indication on RST
5V
1k
LED
1
5V
C1
0.1µF
V1
RST
6
SYSTEM RESET
LTC2903-B1
2
GND
V4
V2
V3
5
1.8V
C2
0.1µF
3.3V
3
4
2.5V
2903 TA05
29031f a
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TYPICAL APPLICATIO S
Quad Supply Monitor with Unused Input Pulled Above Threshold
1
5V
C1
0.1µF
V1
RST
6
SYSTEM RESET
LTC2903-C1
2
GND
V4
V2
V3
5
–5.2V
C2
0.1µF
3
3.3V
4
2903 TA03
Quad Supply Monitor with 3 Adjustable Inputs Monitoring
5% Supplies
1
3.3V
C1
0.1µF
V1
RST
6
SYSTEM RESET
LTC2903-D1
2
GND
V4
2150k
5
12V
(VTRIP = 11.25V)
100k
237k
1.8V
(VTRIP = 1.685V)
3
100k
V2
V3
2903 TA06
365k
4
100k
2.5V
(VTRIP = 2.325V)
29031f a
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LTC2903-1
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PACKAGE DESCRIPTIO
S6 Package
6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636)
0.62
MAX
2.90 BSC
(NOTE 4)
0.95
REF
1.22 REF
3.85 MAX 2.62 REF
1.4 MIN
2.80 BSC
1.50 – 1.75
(NOTE 4)
PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.30 – 0.45
6 PLCS (NOTE 3)
0.95 BSC
0.80 – 0.90
0.20 BSC
0.01 – 0.10
1.00 MAX
DATUM ‘A’
0.30 – 0.50 REF
0.09 – 0.20
(NOTE 3)
1.90 BSC
S6 TSOT-23 0302
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
29031f a
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LTC2903-1
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TYPICAL APPLICATIO
Quad Supply Monitor with Manual Reset Button
3.3V
R3
10k
3.3V
V1
C1
0.1µF
RST
LTC2903-A1
GND
SYSTEM RESET
12V
(VTRIP = 10.75V)
V4
R2
100k
C2
0.1µF
V2
2.5V
MANUAL
RESET BUTTON
R1
RESD* (NORMALLY OPEN)
2050k 10k
1.8V
V3
2903 TA04
*OPTIONAL RESISTOR RECOMMENDED
TO EXTEND ESD TOLERANCE
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