Linear LTC2908CTS8-B1 Precision six supply monitor Datasheet

LTC2908
Precision
Six Supply Monitor
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FEATURES
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DESCRIPTIO
The LTC®2908 is a six supply monitor for systems with a
large number of supply voltages that require a precise and
compact solution. The common reset output remains low
until all six inputs have been in compliance for 200ms.
Ultralow Voltage Reset: VCC = 0.5V Guaranteed*
Monitors Six Inputs Simultaneously:
5V, 3.3V, 2.5V, 1.8V, ADJ1, ADJ2 (LTC2908-A1)
3.3V, 2.5V, 1.8V, 1.5V, ADJ1, ADJ2 (LTC2908-B1)
Guaranteed Threshold Accuracy: ±1.5% of
Monitored Voltage Over Temperature
Internal VCC Auto Select
Power Supply Glitch Immunity
200ms Reset Time Delay
Active Low Open-Drain RST Output
Low Profile (1mm) SOT-23 (ThinSOTTM) and Plastic
(2mm × 3mm) DFN Packages
The LTC2908 features a tight 1.5% threshold accuracy
over the entire operating temperature range (– 40°C to
85°C) and glitch immunity to ensure reliable reset operation without false triggering. The open-drain RST output
state is guaranteed to be in the correct state as long as V1
and/or V2 is 0.5V or greater.
The LTC2908 also features two adjustable inputs with a
nominal threshold level at 0.5V. This product provides a
precise, space-conscious, micropower and general purpose solution for any kind of system requiring supply
monitors.
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APPLICATIO S
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Network Servers
Wireless Base Stations
Optical Networking Systems
Mulitvoltage Systems
Desktop and Notebook Computers
Handheld Devices
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
*Patent pending.
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TYPICAL APPLICATIO
Six Supply Monitor with 5% Tolerance
(12V, 3.3V, 2.5V, 1.8V, 1.5V, 1.2V)
RST Output Voltage vs V1
with 10k Pull-Up Resistor to V1
12V
DC/DC
DC/DC
DC/DC
DC/DC
3.3V
0.4
V3 = V4 = VADJ1 =
VADJ2 = GND
2.5V
SYSTEM
1.8V
1.5V
1.2V
0.1µF 0.1µF
2.15M
100k
124k
RST OUTPUT VOLTAGE (V)
DC/DC
0.3
0.2
V2 = GND
0.1
100k
V2 = V1
0
V1
V2 V3 V4
VADJ1
LTC2908-B1
GND
VADJ2
0
0.2
0.4
0.6
0.8
V1 (V)
RST
2908 TA01a
2908 TA01b
sn2908 2908fs
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LTC2908
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AXI U
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ABSOLUTE
RATI GS (Notes 1, 2)
Terminal Voltages
V1, V2, V3, V4 ........................................ – 0.3V to 7V
VADJ1, VADJ2 ........................... – 0.3V to (VCC + 0.3V)
RST ........................................................ – 0.3V to 7V
Operating Temperature Range
LTC2908C-A1/LTC2908C-B1 .................. 0°C to 70°C
LTC2908I-A1/LTC2908I-B1 ................ –40°C to 85°C
Storage Temperature Range
DFN Package .....................................–65°C to 125°C
TSOT-23 Package ..............................–65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
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PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
ORDER PART
NUMBER
TOP VIEW
GND 1
8
VADJ2
RST 2
7
V3
6
VADJ1
5
V1
V4 3
V2 4
9
DDB8 PACKAGE
8-LEAD (3mm × 2mm) PLASTIC DFN
TJMAX = 125°C, θJA = 76°C/ W
EXPOSED PAD (PIN 9)
(PCB CONNECTION OPTIONAL)
LTC2908CDDB-A1
LTC2908IDDB-A1
LTC2908CDDB-B1
LTC2908IDDB-B1
DDB8 PART
MARKING
LBFD
LBFF
LBFG
LBFH
TOP VIEW
V2 1
V4 2
RST 3
GND 4
8 V1
7 VADJ1
6 V3
5 VADJ2
LTC2908CTS8-A1
LTC2908ITS8-A1
LTC2908CTS8-B1
LTC2908ITS8-B1
TS8 PART
MARKING
TS8 PACKAGE
8-LEAD PLASTIC TSOT-23
TJMAX = 125°C, θJA = 250°C/ W
LTBFJ
LTBFK
LTBFM
LTBFN
Consult factory for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
(LTC2908-A1) The ● denotes specifications which apply over the full
operating temperature range, otherwise specifications are TA = 25°C. VCC = 5V, unless otherwise noted. (Note 2)
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
V2 Input Threshold
●
3.036
3.086
3.135
V
VRT25
2.5V, 5% Reset Threshold
V3 Input Threshold
●
2.300
2.338
2.375
V
VRT18
1.8V, 5% Reset Threshold
V4 Input Threshold
●
1.656
1.683
1.710
V
VRTADJ
ADJ, 5% Reset Threshold
VADJ1, VADJ2 Input Threshold
●
0.492
0.500
0.508
V
(LTC2908-B1) The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are
TA = 25°C. VCC = 3.3V, unless otherwise noted. (Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VRT33
3.3V, 5% Reset Threshold
V1 Input Threshold
●
3.036
3.086
3.135
V
VRT25
2.5V, 5% Reset Threshold
VRT18
1.8V, 5% Reset Threshold
V2 Input Threshold
●
2.300
2.338
2.375
V
V3 Input Threshold
●
1.656
1.683
1.710
V
VRT15
1.5V, 5% Reset Threshold
V4 Input Threshold
●
1.380
1.403
1.425
V
VRTADJ
ADJ, 5% Reset Threshold
VADJ1, VADJ2 Input Threshold
●
0.492
0.500
0.508
V
sn2908 2908fs
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LTC2908
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are TA = 25°C. VCC = 5V for the LT2908-A1 and VCC = 3.3V for the LTC2908-B1, unless
otherwise noted. (Notes 2, 3)
SYMBOL
PARAMETER
CONDITIONS
MIN
VCC
Internal Operating Voltage
RST in Correct Logic State
●
IV1
V1 Input Current
V1 = 5.0V (LTC2908-A1) (Note 4)
V1 = 3.3V (LTC2908-B1)
●
●
IV2
V2 Input Current
V2 = 3.3V (LTC2908-A1) (Note 4)
V2 = 2.5V (LTC2908-B1)
IV3
V3 Input Current
IV4
TYP
0.5
MAX
UNITS
6
V
26
24
50
50
µA
µA
●
●
10
8
20
20
µA
µA
V3 = 2.5V (LTC2908-A1)
V3 = 1.8V (LTC2908-B1)
●
●
2
2
5
5
µA
µA
V4 Input Current
V4 = 1.8V (LTC2908-A1)
V4 = 1.5V (LTC2908-B1)
●
●
2
2
5
5
µA
µA
IVADJ
VADJ1, VADJ2 Input Current
VADJ1 = VADJ2 = 0.55V
●
±15
nA
tRST
Reset Time-Out Period
260
ms
tUV
VX Undervoltage Detect to RST or RST
VX Less Than Reset Threshold VRTX by
More Than 1%
VOH
Output Voltage High RST (Note 5)
IRST = –1µA, VCC = 5V (LTC2908-A1)
IRST = –1µA, VCC = 3.3V (LTC2908-B1)
●
●
VOL
Output Voltage Low RST
VCC = 0.5V, IRST = 5µA
VCC = 1.0V, IRST = 100µA
VCC = 3.0V, IRST = 2500µA
●
●
●
●
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The greater of V1, V2 is the internal supply voltage (VCC).
Note 3: All currents into pins are positive; all voltages are referenced to
GND unless otherwise noted.
160
200
250
µs
VCC – 1.5
VCC – 1.0
V
V
0.01
0.01
0.10
0.15
0.15
0.30
V
V
V
Note 4: Under typical operating conditions, most of the quiescent current
is drawn from the V1 input. When V2 exceeds V1, V2 supplies most of the
quiescent current.
Note 5: The output pin RST has an internal pull-up to VCC of typically 6µA.
However, an external pull-up resistor may be used when a faster rise time
is required or for VOH voltages greater than VCC.
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TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at TA = 25°C unless otherwise noted.
5V Threshold Voltage
vs Temperature
3.3V Threshold Voltage
vs Temperature
4.725
4.700
4.675
4.650
4.625
4.600
–50
–25
50
25
0
TEMPERATURE (°C)
75
100
2908 G01
2.375
THRESHOLD VOLTAGE, VRT25 (V)
3.135
THRESHOLD VOLTAGE, VRT33 (V)
THRESHOLD VOLTAGE, VRT50 (V)
4.750
2.5V Threshold Voltage
vs Temperature
3.115
3.095
3.075
3.055
3.035
–50
–25
50
25
0
TEMPERATURE (°C)
75
100
2908 G02
2.360
2.345
2.330
2.315
2.300
–50
–25
50
25
0
TEMPERATURE (°C)
75
100
2908 G03
sn2908 2908fs
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LTC2908
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TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at TA = 25°C unless otherwise noted.
1.8V Threshold Voltage
vs Temperature
1.5V Threshold Voltage
vs Temperature
1.700
1.690
1.680
1.670
1.425
0.5080
1.420
0.5060
THRESHOLD VOLTAGE, VRTADJ (V)
THRESHOLD VOLTAGE, VRT15 (V)
THRESHOLD VOLTAGE, VRT18 (V)
1.710
ADJ Threshold Voltage
vs Temperature
1.415
1.410
1.405
1.400
1.395
1.390
1.385
1.380
–25
50
25
0
TEMPERATURE (°C)
75
100
–50
–25
0
25
50
TEMPERATURE (°C)
75
IV1 vs Temperature
0.4980
0.4960
0.4940
0.4920
–50
V1 = 5.0V (A1)/V1 = 3.3V (B1)
31 V2 = 3.3V (A1)/V2 = 2.5V (B1)
V3 = 2.5V (A1)/V3 = 1.8V (B1)
29 V4 = 1.8V (A1)/V4 = 1.5V (B1)
VADJ1 = VADJ2 = 0.55V
75
IV2 (µA)
27
V1 = 5.0V (A1)/V1 = 3.3V (B1)
2.1 V2 = 3.3V (A1)/V2 = 2.5V (B1)
V3 = 2.5V (A1)/V3 = 1.8V (B1)
2.0 V4 = 1.8V (A1)/V4 = 1.5V (B1)
VADJ1 = VADJ2 = 0.55V
1.9
10
A1
9
B1
8
23
1.8
1.7
7
21
100
IV3 vs Temperature
V1 = 5.0V (A1)/V1 = 3.3V (B1)
13 V2 = 3.3V (A1)/V2 = 2.5V (B1)
V3 = 2.5V (A1)/V3 = 1.8V (B1)
12 V4 = 1.8V (A1)/V4 = 1.5V (B1)
11 VADJ1 = VADJ2 = 0.55V
25
0
50
25
TEMPERATURE (°C)
2.2
14
B1
–25
2908 G06
IV2 vs Temperature
33
IV1 (µA)
0.5000
2908 G05
2908 G04
A1
100
0.5020
IV3 (µA)
1.660
–50
0.5040
1.6
6
19
1.5
5
–25
0
25
50
TEMPERATURE (°C)
75
4
–50
100
–25
0
50
25
TEMPERATURE (°C)
75
2908 G07
700
2.2
TYPICAL TRANSIENT DURATION (µs)
IV4 (µA)
1.9
1.8
1.7
1.6
1.5
–25
0
50
25
TEMPERATURE (°C)
75
100
2908 G10
0
50
25
TEMPERATURE (°C)
75
Reset Time-Out Period (tRST)
vs Temperature
250
TA = 25°C
600
500
100
2908 G09
Typical Transient Duration
vs Comparator Overdrive
V1 = 5.0V (A1)/V1 = 3.3V (B1)
2.1 V2 = 3.3V (A1)/V2 = 2.5V (B1)
V3 = 2.5V (A1)/V3 = 1.8V (B1)
2.0 V4 = 1.8V (A1)/V4 = 1.5V (B1)
VADJ1 = VADJ2 = 0.55V
–25
2908 G08
IV4 vs Temperature
1.4
–50
1.4
–50
100
RESET TIME-OUT PERIOD, tRST (ms)
17
–50
RESET OCCURS
ABOVE CURVE
400
300
200
100
0
0.1
1
10
100
COMPARATOR OVERDRIVE VOLTAGE (% OF VRTX)
2908 G11
240
230
220
210
200
190
180
170
160
150
–50
–25
0
50
25
TEMPERATURE (°C)
75
100
2908 G12
sn2908 2908fs
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LTC2908
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TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at TA = 25°C unless otherwise noted.
RST Output Voltage vs V1 with
10k Pull-Up Resistor to V1
RST OUTPUT VOLTAGE (V)
4.0
RST OUTPUT VOLTAGE (V)
0.4
V1 = V2
V3 = 2.5V (A1)/V3 = 1.8V (B1)
V4 = 1.8V (A1)/V4 = 1.5V (B1)
VADJ1 = VADJ2 = 0.55V
3.0
2.0
1.0
VRT33
LTC2908-B1
0
0
1
4
6
V3 = V4 = VADJ1 =
VADJ2 = GND
0.3
0.2
V2 = GND
0.1
V2 = V1
VRT50
LTC2908-A1
3
2
0
5
0.2
0.4
10
RST AT
50mV
VRT50
VRT33
LTC2908-B1 LTC2908-A1
1
0
0.1
RST AT 50mV
0.01
RST Output Voltage Low (VOL)
vs RST Pull-Down Current (IRST)
LTC2908-A1
0.8
VCC = V1
V2 = V3 = V4 = VADJ1 = VADJ2 = GND
1
RST AT 150mV
0.1
RST AT 50mV
0.01
0.001
0
1
0.2
0.4
0.6
0.8
SUPPLY VOLTAGE, VCC (V)
2908 G16
–30
RST PULL-UP CURRENT, IRST (µA)
V1 = 3.3V
0.7 V2 = 2.5V
V3 = 1.8V
0.6 V4 = 1.5V
VADJ1 = VADJ2 = 0.4V
0.5
–40°C
0.4
25°C
0.3
0.2
0.1
0
10
85°C
–40°C
0.4
25°C
0.3
0.2
0.1
0
1
5
10
20
25
30
35
15
RST PULL-DOWN CURRENT, IRST (mA)
20
15
RST PULL-DOWN CURRENT, IRST (mA)
2908 G18
RST Pull-Up Current (IRST)
vs Supply Voltage (VCC)
0.8
5
0.5
2908 G17
RST Output Voltage Low (VOL)
vs RST Pull-Down Current (IRST)
LTC2908-B1
85°C
V1 = 5.0V
0.7 V2 = 3.3V
V3 = 2.5V
0.6 V4 = 1.8V
VADJ1 = VADJ2 = 0.4V
0
0.001
0.2
0.4
0.6
0.8
SUPPLY VOLTAGE, VCC (V)
5
1
2
3
4
SUPPLY VOLTAGE, VCC (V)
2908 G15
RST OUTPUT VOLTAGE LOW, VOL (V)
RST AT 150mV
RST OUTPUT VOLTAGE LOW, VOL (V)
2
2908 G14
RST PULL-DOWN CURRENT, IRST (mA)
RST PULL-DOWN CURRENT, IRST (mA)
3
RST Pull-Down Current (IRST) vs
Supply Voltage (VCC) with Single
Channel Supply
VCC = V1 = V2
V3 = V4 = VADJ1 = VADJ2 = GND
0
RST AT
150mV
4
V1 (V)
RST Pull-Down Current (IRST) vs
Supply Voltage (VCC) with Dual
Channel Supply
0
5
0.8
0.6
2908 G13
1
VCC = V1 = V2
V3 = V4 = VADJ1 = VADJ2 = GND
0
0
V1 (V)
10
RST Pull-Down Current (IRST)
vs Supply Voltage (VCC)
RST PULL-DOWN CURRENT, IRST (mA)
5.0
RST Output Voltage vs V1 with
10k Pull-Up Resistor to V1
25
2908 G19
VCC = V1 = V2
V3 = 2.5V (A1)/V3 = 1.8V (B1)
V4 = 1.8V (A1)/V4 = 1.5V (B1)
VADJ1 = VADJ2 = 0.55V
RST HELD AT 0V
–25
–20
–15
–10
–5
VRT33
LTC2908-B1
0
2
2.5
VRT50
LTC2908-A1
4.5
3
3.5
4
SUPPLY VOLTAGE, VCC (V)
5
2908 G20
sn2908 2908fs
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LTC2908
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TYPICAL PERFOR A CE CHARACTERISTICS
RST Output Voltage High (VOH) vs
RST Output Source Current (IRST)
LTC2908-A1
RST Output Voltage High (VOH) vs
RST Output Source Current (IRST)
LTC2908-B1
3.0
4
3
25°C
–40°C
V1 = 5.0V
V2 = 3.3V
V3 = 2.5V
V4 = 1.8V
VADJ1 = VADJ2 = 0.55V
2
1
0
85°C
–4
–12
–16
–20
–8
OUTPUT SOURCE CURRENT, IRST (µA)
RST OUTPUT VOLTAGE HIGH, VOH (V)
RST OUTPUT VOLTAGE HIGH, VOH (V)
5
2.5
2.0
25°C
1.5
85°C
–40°C
V1 = 3.3V
V2 = 2.5V
1.0 V3 = 1.8V
V4 = 1.5V
VADJ1 = VADJ2 = 0.55V
0.5
–4
–6
–8
–10
–12
0
–2
OUTPUT SOURCE CURRENT, IRST (µA)
2908 G22
2908 G21
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PI FU CTIO S
(TS8 Package/DDB8 Package)
V2 (Pin 1/Pin 4): Voltage Input 2. The greater of V1, V2 is
also the internal VCC. The operating voltage on this pin
shall not exceed 6V. When in normal operation (V1 > V2),
this pin draws approximately 8µA. When this pin is acting
as the VCC (V2 > V1), this pin draws an additional 15µA.
Bypass this pin to ground with a 0.1µF (or greater)
capacitor.
V4 (Pin 2/Pin 3): Voltage Input 4.
RST (Pin 3/Pin 2): Reset Logic Output. Pulls low when any
voltage input is below the reset threshold and is held low
for 200ms after all voltage inputs are above threshold. This
pin has a weak pull-up to VCC and may be pulled above VCC
using an external pull-up.
GND (Pin 4/Pin 1): Device Ground.
VADJ2 (Pin 5/Pin 8): Adjustable Voltage Input 2. See
Table 1 for recommended ADJ resistors values.
V3 (Pin 6/Pin 7): Voltage Input 3.
VADJ1 (Pin 7/Pin 6): Adjustable Voltage Input 1. See
Table 1 for recommended ADJ resistors values.
V1 (Pin 8/Pin 5): Voltage Input 1. The greater of V1, V2 is
also the internal VCC. The operating voltage on this pin
shall not exceed 6V. When in normal operation (V1 > V2),
this pin draws approximately 21µA. When this pin is not
acting as the VCC (V2 > V1), this pin draws approximately
8µA. Bypass this pin to ground with a 0.1µF (or greater)
capacitor.
Exposed Pad (Pin 9, DDB8 Only): Exposed Pad may be left
open or connected to device ground.
sn2908 2908fs
6
LTC2908
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BLOCK DIAGRA
LTC2908-A1/LTC2908-B1
–
V1
POWER
DETECT
+
C1
VCC
–
V2
+
C2
VCC
–
V3
+
6µA
C3
RST
200ms
RESET PULSE
GENERATOR
–
V4
+
C4
–
VADJ1
+
C5
–
VADJ2
+
GND
C6
BANDGAP
REFERENCE
2908 BD
WU
W
TI I G DIAGRA
VX Monitor Timing
VX
VRTX
tUV
RST
tRST
1V
2908 TD
sn2908 2908fs
7
LTC2908
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APPLICATIO S I FOR ATIO
Supply Monitoring
The LTC2908 is a low power, high accuracy, six input
supply monitoring circuit with two adjustable inputs. The
reset delay is set to a nominal of 200ms with an internal
capacitor, eliminating the need for an external timing
capacitor.
All input voltages must be above predetermined thresholds for the reset not to be invoked. The LTC2908 asserts
the reset output during power-up, power-down and brownout conditions on any one of the voltage inputs.
Ultralow Voltage Pull-Down on RST
The LTC2908 issues a logic low on the RST output when
any one of the inputs falls below its threshold. Ideally, the
RST logic output would remain low with the input supply
voltage down to zero volts. Most supervisors lack pulldown capability below 1V.
The LTC2908 power supply supervisor incorporates a
novel low voltage pull-down circuit that can hold the RST
line low with as little as 200mV of input supply voltage on
V1 and/or V2 (see Figures 1 and 2). The pull-down circuit
helps maintain a low impedance path to ground, reducing
the risk of the RST node from floating to an indeterminate
voltage.
During power-up, RST starts asserting low as soon as
there is at least 200mV on V1 and/or V2. The RST pulldown capability is a function of V1 and V2 as shown in the
Typical Performance Characteristics.
The greater of V1, V2 is the internal supply voltage (VCC)
that powers the other internal circuitry. Once all the VX
inputs rise above their thresholds, an internal timer is
started. After the internal timer counts a 200ms delay time,
RST weakly pulls high to VCC.
Power-Down
On power-down, once any of the VX inputs drop below
their threshold, RST asserts logic low. VCC of at least 0.5V
guarantees a logic low of 0.15V at RST.
10
VCC = V1 = V2
V3 = V4 = VADJ1 = VADJ2 = GND
1
Power-Up
RST PULL-DOWN CURRENT, IRST (mA)
RST PULL-DOWN CURRENT, IRST (mA)
10
Such an indeterminate voltage may trigger external logic
causing erroneous reset operation(s). Furthermore, a
mid-scale voltage level 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.
RST AT 150mV
0.1
RST AT 50mV
0.01
VCC = V1
V2 = V3 = V4 = VADJ1 = VADJ2 = GND
1
RST AT 150mV
0.1
RST AT 50mV
0.01
0.001
0.001
0
0.4
0.6
0.8
0.2
SUPPLY VOLTAGE, VCC (V)
1
2908 G16
Figure 1. RST Pull-Down Current (IRST) vs
Supply Voltage (VCC) with Dual Channel Supply
0
0.4
0.6
0.8
0.2
SUPPLY VOLTAGE, VCC (V)
1
2908 G17
Figure 2. RST Pull-Down Current (IRST) vs
Supply Voltage (VCC) with Single Channel Supply
sn2908 2908fs
8
LTC2908
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APPLICATIO S I FOR ATIO
Adjustable Input
VTRIP
The noninverting input on the VADJ comparator is set to
0.5V. And the high impedance inverting input directly ties
to the VADJ pin.
LTC2908-A1/LTC2908-B1
R1
1%
–
VADJ
R2
1%
+
In a typical application, this pin connects to a tap point on
an external resistive divider between the positive voltage
being monitored and ground. The following formula derives the value of the R1 resistor in the divider from a
particular value of R2 and the desired trip voltage:
+
–
0.5V
2908 F03
Figure 3. Setting the Adjustable Trip Point
⎛V
⎞
R1 = ⎜ TRIP – 1⎟ R2
⎝ 0.5V ⎠
Threshold Accuracy
R2 = 100k is recommended. Table 1 shows suggested 1%
resistor values for various adjustable applications and
their corresponding trip thresholds.
Table 1. Suggested 1% Resistor Values for the VADJ 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
If an application has less than six supply voltages, the
unused supervisor inputs should be tied to the closest
higher supply voltage available.
Specifying system voltage margin for worst-case operation
requires the 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 ±5% 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 4.75V (5%
below 5V), is the exact voltage at which a perfectly
accurate supervisor generates a reset (see Figure 4).
Such a perfectly accurate supervisor does not exist—the
actual reset threshold may vary over a specified band
(±1.5% for the LTC2908 supervisors). Figure 5 shows the
typical relative threshold accuracy for all six inputs over
temperature.
5.000V
4.750V
±1.5%
THRESHOLD 4.675V
BAND
4.600V
4.500V
MINIMUM
IDEAL
SUPPLY
RELIABLE TOLERANCE SUPERVISOR
SYSTEM
THRESHOLD
VOLTAGE
NOMINAL
SUPPLY
VOLTAGE
–5.0%
–6.5%
REGION OF POTENTIAL MALFUNCTION
WITH 2.5% MONITOR
2908 F04
–8.0%
±2.5%
THRESHOLD
BAND
–10%
Figure 4. Threshold Band Diagram
sn2908 2908fs
9
LTC2908
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APPLICATIO S I FOR ATIO
is to introduce hysteresis around the nominal threshold.
Notice however, this hysteresis introduces an error term
in the threshold accuracy. Therefore, a ±2.5% accurate
monitor with ±1% hysteresis is equivalent to a ±3.5%
monitor with no hysteresis.
TYPICAL THRESHOLD ACCURACY (%)
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
2908 F05
Figure 5. Typical Threshold Accuracy vs Temperature
Therefore, the LTC2908 takes a different approach to
solving this problem of supply noise causing spurious
reset. The first line of defense against this spurious reset
is a first order lowpass filter at the output of the comparators. Therefore, each comparator output is integrated over
time before triggering the output logic. Therefore, any kind
of transient at the input of the comparator needs to be of
sufficient magnitude and duration before it can trigger a
change in the output logic.
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 (for
example at 4.8V).
The second line of defense is the 200ms delay time tRST.
This delay eliminates the effect of any supply noise, whose
frequency is above 1/200ms = 5Hz, on the RST output.
Adding half of the reset threshold accuracy spread (1.5%)
to the ideal 5% thresholds puts the LTC2908 thresholds at
6.5% (typ) below the nominal input voltage. For example,
the 5V typical threshold is 4.675V, or 75mV below the ideal
threshold of 4.750V. The guaranteed threshold lies in the
band between 4.600V (8% below 5V) and 4.750V (5%
below 5V) over temperature.
If all the supplies remain above their corresponding threshold when the timer finishes counting, the RST pin weakly
pulls high. However, if any of the supplies falls below its
threshold any time during the period when the timer is still
counting, the timer resets and it starts fresh when all the
supplies rise above their corresponding threshold.
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 4.60V (8% below 5V). System ICs working with
a ±2.5% accurate supervisor must operate down to 4.50V
(10% below 5V), 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 is near the reset threshold. A less desirable but common solution to this problem
When any one of the supply voltages drops below its
threshold, the RST pin asserts low. When the supply
recovers above its threshold, the reset-pulse-generator
timer starts counting.
Note that this second line of defense is only effective for a
rising supply and does not affect the sensitivity of the
system to a falling supply. Therefore, the first line of
defense that works for both cases of rising and falling is
necessary. These two approaches prevent spurious reset
caused by supply noise without sacrificing the threshold
accuracy.
Although all six comparators for the six inputs have builtin glitch filtering, use bypass capacitors on the V1 and V2
inputs because the greater of V1 or V2 supplies the VCC for
the part (a 0.1µF ceramic capacitor satisfies most applications). Apply filter capacitors on the V3, V4, VADJ1 and
VADJ2 inputs in extremely noisy situations.
sn2908 2908fs
10
LTC2908
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APPLICATIO S I FOR ATIO
RST Output Characteristics
The DC characteristics of the RST pull-up and pull-down
strength are shown in the Typical Performance Characteristics section. The RST output has a weak internal pull-up
to VCC = Max(V1, V2) and a strong pull-down to ground.
The weak pull-up and strong pull-down arrangement
allows this pin to have open-drain behavior while possessing several other beneficial characteristics.
The weak pull-up eliminates the need for external pull-up
resistors when the rise time on these pins is not critical. On
the other hand, the open-drain RST configuration allows
for wired-OR connections and can be useful when more
than one signal needs to pull down on the RST line.
As noted in the discussion of power-up and power-down,
the circuits that drive RST are powered by VCC. During
fault condition, VCC of at least 0.5V guarantees a maximum VOL = 0.15V at RST.
Output Rise and Fall Time Estimation
The following formula estimates the output fall time (90%
to 10%) for a particular external load capacitance (CLOAD):
The rise time on the RST pin is limited by a weak internal
pull-up current source to VCC. The following formula estimates the output rise time (10% to 90%) at the RST pin:
tRISE ≈ 2.2 • RPU • CLOAD
where RPU is the on-resistance of the pull-up transistor.
Notice that this pull-up transistor is modeled as a 6µA
current source in the Block Diagram as a typical
representation.
The on-resistance as a function of the VCC = Max(V1, V2)
voltage (for VCC > 1V) at room temperature is estimated as
follows:
RPU =
6 • 105
Ω
MAX( V1, V2) – 1V
At VCC = 3.3V, RPU is about 260k. Using 150pF for load
capacitance, the rise time is 86µs. A smaller external pullup resistor may be used if the output needs to pull up faster
and/or to a higher voltage. For example, the rise time
reduces to 3.3µs for a 150pF load capacitance when using
a 10k pull-up resistor.
tFALL ≈ 2.2 • RPD • CLOAD
where RPD is the on-resistance of the internal pull-down
transistor estimated to be typically 40Ω at room temperature (25°C) and CLOAD is the external load capacitance on
the pin. Assuming a 150pF load capacitance, the fall time
is about 13ns.
sn2908 2908fs
11
LTC2908
U
TYPICAL APPLICATIO S
Six Supply Monitor, 5% Tolerance, 12V, 5V, 3.3V, 2.5V, 1.8V, 1V
12V
DC/DC
DC/DC
DC/DC
DC/DC
DC/DC
5V
3.3V
SYSTEM
2.5V
1.8V
1.0V
C1
C2
0.1µF 0.1µF
V1
R1
2.15M
R3
R2
100k 86.6k
V2 V3 V4
VADJ1
LTC2908-A1
GND
R4
100k
VADJ2
RST
2908 TA02
sn2908 2908fs
12
LTC2908
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TYPICAL APPLICATIO S
Quad Supply Monitor with One Adjustable Input, 5% Tolerance, 3.3V, 2.5V, 1.8V, 1.2V
3.3V
DC/DC
2.5V
SYSTEM
DC/DC
DC/DC
1.8V
1.2V
C1
C2
0.1µF 0.1µF
V1
V2
R3
124k
V3 V4
VADJ1
LTC2908-B1
GND
R4
100k
VADJ2
RST
2908 TA03
sn2908 2908fs
13
LTC2908
U
PACKAGE DESCRIPTIO
DDB Package
8-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1702)
0.61 ±0.05
(2 SIDES)
0.675 ±0.05
2.50 ±0.05
1.15 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
2.20 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
R = 0.115
TYP
5
0.56 ± 0.05
(2 SIDES)
3.00 ±0.10
(2 SIDES)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
0.38 ± 0.10
8
2.00 ±0.10
(2 SIDES)
0.75 ±0.05
0 – 0.05
4
0.25 ± 0.05
1
PIN 1
CHAMFER OF
EXPOSED PAD
(DDB8) DFN 1103
0.50 BSC
2.15 ±0.05
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
sn2908 2908fs
14
LTC2908
U
PACKAGE DESCRIPTIO
TS8 Package
8-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1637)
0.52
MAX
2.90 BSC
(NOTE 4)
0.65
REF
1.22 REF
1.4 MIN
3.85 MAX 2.62 REF
2.80 BSC
1.50 – 1.75
(NOTE 4)
PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.22 – 0.36
8 PLCS (NOTE 3)
0.65 BSC
0.80 – 0.90
0.20 BSC
0.01 – 0.10
1.00 MAX
DATUM ‘A’
0.30 – 0.50 REF
0.09 – 0.20
(NOTE 3)
1.95 BSC
TS8 TSOT-23 0802
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
sn2908 2908fs
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
LTC2908
U
TYPICAL APPLICATIO
Six Supply Monitor with Manual Reset Button, 5% Tolerance, 12V, 5V, 3.3V, 2.5V, 1.8V, 1.5V
12V
DC/DC
DC/DC
DC/DC
DC/DC
DC/DC
5V
3.3V
SYSTEM
2.5V
1.8V
1.5V
C1
C2
0.1µF 0.1µF
R1
182k
R3
MANUAL
2.15M RESET BUTTON
R5 (NORMALLY OPEN)
10k
R2
100k
R4
100k
V1
V2 V3 V4
VADJ1
LTC2908-A1
GND
VADJ2
RST
2908 TA04
RELATED PARTS
PART NUMBER
LTC690
LTC694-3.3
LTC699
LTC1232
LTC1326/LTC1326-2.5
LTC1536
LTC1726-2.5/LTC1726-5
LTC1727-2.5/LTC1727-5
LTC1728-1.8/LTC1728-3.3
LTC1728-2.5/LTC1728-5
LTC1985-1.8
LTC2900
DESCRIPTION
5V Supply Monitor, Watchdog Timer and Battery Backup
3.3V Supply Monitor, Watchdog Timer and Battery Backup
5V Supply Monitor and Watchdog Timer
5V Supply Monitor, Watchdog Timer and Pushbutton Reset
Micropower Precision Triple Supply Monitor for 5V/2.5V, 3.3V
and ADJ
Precision Triple Supply Monitor for PCI Applications
Micropower Triple Supply Monitor for 2.5V/5V, 3.3V and ADJ
Micropower Triple Supply Monitor with Open-Drain Reset
Micropower Triple Supply Monitor with Open-Drain Reset
Micropower Triple Supply Monitor with Open-Drain Reset
Micropower Triple Supply Monitor with Push-Pull Reset Output
Programmable Quad Supply Monitor
LTC2901
Programmable Quad Supply Monitor
LTC2902
Programmable Quad Supply Monitor
LTC2903
LTC2904
Precision Quad Supply Monitor
Three-State Programmable Precision Dual Supply Monitor
LTC2905
Three-State Programmable Precision Dual Supply Monitor
LTC2906
Dual Supply Monitor with One Pin Selectable Threshold and
One Adjustable Input
Dual Supply Monitor with One Pin Selectable Threshold and
One Adjustable Input
LTC2907
COMMENTS
4.65 Threshold
2.9V Threshold
4.65 Threshold
4.37V/4.62V Threshold
4.725V, 3.118V, 1V Threshold (±0.75%)
Meets PCI tFAIL Timing Specifications
Adjustable RESET and Watchdog Time-Outs
Individual Monitor Outputs in MSOP
5-Lead SOT-23 Package
5-Lead SOT-23 Package
5-Lead SOT-23 Package
Adjustable RESET, 10-Lead MSOP and DFN
Packages
Adjustable RESET and Watchdog Timer,
16-Lead SSOP Package
Adjustable RESET and Tolerance,
16-Lead SSOP Package
6-Lead SOT-23 Package
Adjustable Tolerance, 8-Lead SOT-23 and DFN
Packages
Adjustable RESET and Tolerance,
8-Lead SOT-23 and DFN Packages
0.5V Adjustable Threshold and Three Supply
Tolerances, 8-Lead SOT-23 and DFN Packages
0.5V Adjustable Threshold, RESET and Three Supply
Tolerances, 8-Lead SOT-23 and DFN Packages
sn2908 2908fs
16
Linear Technology Corporation
LT/TP 0504 1K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2004
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