LTC2908IDDB8-A1#PBF [Linear]
IC 6-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO8, 3 X 2 MM, PLASTIC, M0-229WECD-1, DFN-8, Power Management Circuit;
| 型号： | LTC2908IDDB8-A1#PBF |
| 厂家： | 
Linear |
| 描述： | IC 6-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO8, 3 X 2 MM, PLASTIC, M0-229WECD-1, DFN-8, Power Management Circuit CD 光电二极管 |
| 文件： | 总16页 (文件大小：201K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC2908
Precision
Six Supply Monitor
U
FEATURES
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
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 opera-
tion 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.
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
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 pur-
pose solution for any kind of system requiring supply
monitors.
(2mm × 3mm) DUFN Packages
APPLICATIO S
■
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.
■
■
■
■
U
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
3.3V
2.5V
1.8V
0.4
DC/DC
DC/DC
DC/DC
DC/DC
DC/DC
V3 = V4 = V
ADJ2
=
ADJ1
V
= GND
0.3
0.2
0.1
0
SYSTEM
1.5V
1.2V
V2 = GND
0.1µF 0.1µF
2.15M
V
LTC2908-B1
GND
124k
V
100k
100k
V2 = V1
0.4
V1 (V)
0
0.2
0.6
0.8
V1
V2 V3 V4
ADJ1
ADJ2
RST
2908 TA01b
2908 TA01a
2908f
1
LTC2908
W W U W
(Notes 1, 2)
ABSOLUTE AXI U RATI GS
Terminal Voltages
Storage Temperature Range
V1, V2, V3, V4 ........................................ –0.3V to 7V
ADJ1, VADJ2 ........................... –0.3V to (VCC + 0.3V)
DFN Package .....................................–65°C to 125°C
TSOT-23 Package ..............................–65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
V
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
U W
U
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
ORDER PART
NUMBER
TOP VIEW
LTC2908CDDB8-A1
LTC2908IDDB8-A1
LTC2908CDDB8-B1
LTC2908IDDB8-B1
LTC2908CTS8-A1
TOP VIEW
LTC2908ITS8-A1
GND
RST
V4
1
2
3
4
8
7
6
5
V
ADJ2
V2 1
V4 2
RST 3
GND 4
8 V1
7 V
V3
V
LTC2908CTS8-B1
LTC2908ITS8-B1
ADJ1
9
ADJ1
6 V3
5 V
V2
V1
ADJ2
TS8 PART
MARKING
DDB8 PART
MARKING
TS8 PACKAGE
8-LEAD PLASTIC TSOT-23
TJMAX = 125°C, θJA = 250°C/ W
DDB8 PACKAGE
8-LEAD (3mm × 2mm) PLASTIC DFN
LTBFJ
LTBFK
LTBFM
LTBFN
LBFD
LBFF
LBFG
LBFH
TJMAX = 125°C, θJA = 76°C/ W
EXPOSED PAD (PIN 9)
(PCB CONNECTION OPTIONAL)
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
4.750
3.135
2.375
1.710
0.508
UNITS
V
V
V
V
V
5V, 5% Reset Threshold
3.3V, 5% Reset Threshold
2.5V, 5% Reset Threshold
1.8V, 5% Reset Threshold
ADJ, 5% Reset Threshold
V1 Input Threshold
V2 Input Threshold
V3 Input Threshold
V4 Input Threshold
●
●
●
●
●
4.600
3.036
2.300
1.656
0.492
4.675
3.086
2.338
1.683
0.500
V
V
V
V
V
RT50
RT33
RT25
RT18
RTADJ
V
, V
Input Threshold
ADJ1 ADJ2
(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
3.135
2.375
1.710
1.425
0.508
UNITS
V
RT33
V
RT25
V
RT18
V
RT15
V
RTADJ
3.3V, 5% Reset Threshold
2.5V, 5% Reset Threshold
1.8V, 5% Reset Threshold
1.5V, 5% Reset Threshold
ADJ, 5% Reset Threshold
V1 Input Threshold
V2 Input Threshold
V3 Input Threshold
V4 Input Threshold
●
●
●
●
●
3.036
2.300
1.656
1.380
0.492
3.086
2.338
1.683
1.403
0.500
V
V
V
V
V
, V
Input Threshold
V
ADJ1 ADJ2
2908f
2
LTC2908
ELECTRICAL CHARACTERISTICS
otherwise noted. (Notes 2, 3)
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
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
Internal Operating Voltage
V1 Input Current
RST in Correct Logic State
●
0.5
6
V
CC
I
I
I
I
V1 = 5.0V (LTC2908-A1) (Note 4)
V1 = 3.3V (LTC2908-B1)
●
●
26
24
50
50
µA
µA
V1
V2 Input Current
V3 Input Current
V4 Input Current
V2 = 3.3V (LTC2908-A1) (Note 4)
V2 = 2.5V (LTC2908-B1)
●
●
10
8
20
20
µA
µA
V2
V3
V4
V3 = 2.5V (LTC2908-A1)
V3 = 1.8V (LTC2908-B1)
●
●
2
2
5
5
µA
µA
V4 = 1.8V (LTC2908-A1)
V4 = 1.5V (LTC2908-B1)
●
●
2
2
5
5
µA
µA
I
t
t
V
, V
Input Current
V
= V = 0.55V
ADJ2
●
●
±15
nA
ms
µs
VADJ
RST
UV
ADJ1 ADJ2
ADJ1
Reset Time-Out Period
160
200
250
260
V Undervoltage Detect to RST or RST
V Less Than Reset Threshold V
More Than 1%
by
RTX
X
X
V
V
Output Voltage High RST (Note 5)
Output Voltage Low RST
I
I
= –1µA, V = 5V (LTC2908-A1)
●
●
V
V
– 1.5
– 1.0
V
V
OH
OL
RST
RST
CC
CC
CC
= –1µA, V = 3.3V (LTC2908-B1)
CC
V
V
V
= 0.5V, I
= 1.0V, I
= 3.0V, I
= 5µA
= 100µA
= 2500µA
●
●
●
0.01
0.01
0.10
0.15
0.15
0.30
V
V
V
CC
CC
CC
RST
RST
RST
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
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 2: The greater of V1, V2 is the internal supply voltage (V ).
CC
Note 5: The output pin RST has an internal pull-up to V of typically 6µA.
However, an external pull-up resistor may be used when a faster rise time
CC
Note 3: All currents into pins are positive; all voltages are referenced to
GND unless otherwise noted.
is required or for V voltages greater than V
.
CC
OH
U W
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
2.5V Threshold Voltage
vs Temperature
4.750
4.725
4.700
4.675
4.650
4.625
4.600
3.135
3.115
3.095
3.075
3.055
3.035
2.375
2.360
2.345
2.330
2.315
2.300
50
TEMPERATURE (°C)
100
50
TEMPERATURE (°C)
100
50
TEMPERATURE (°C)
100
–50 –25
0
25
75
–50 –25
0
25
75
–50 –25
0
25
75
2908 G01
2908 G02
2908 G03
2908f
3
LTC2908
TYPICAL PERFOR A CE CHARACTERISTICS
U W
Specifications are at TA = 25°C unless otherwise noted.
1.8V Threshold Voltage
vs Temperature
1.5V Threshold Voltage
vs Temperature
ADJ Threshold Voltage
vs Temperature
1.425
1.420
1.415
1.410
1.405
1.400
1.395
1.390
1.385
1.380
1.710
1.700
1.690
1.680
1.670
1.660
0.5080
0.5060
0.5040
0.5020
0.5000
0.4980
0.4960
0.4940
0.4920
50
TEMPERATURE (°C)
100
–50
–25
0
25
100
–25
0
50
–50 –25
0
25
75
–50
75
100
50
75
25
TEMPERATURE (°C)
TEMPERATURE (°C)
2908 G04
2908 G05
2908 G06
IV1 vs Temperature
IV2 vs Temperature
IV3 vs Temperature
33
31
29
27
25
23
21
19
17
2.2
2.1
2.0
1.9
14
V1 = 5.0V (A1)/V1 = 3.3V (B1)
V2 = 3.3V (A1)/V2 = 2.5V (B1)
V3 = 2.5V (A1)/V3 = 1.8V (B1)
V4 = 1.8V (A1)/V4 = 1.5V (B1)
V1 = 5.0V (A1)/V1 = 3.3V (B1)
V2 = 3.3V (A1)/V2 = 2.5V (B1)
V3 = 2.5V (A1)/V3 = 1.8V (B1)
V4 = 1.8V (A1)/V4 = 1.5V (B1)
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)
V
= V
= 0.55V
V
= V
= 0.55V
V
ADJ1
= V
ADJ2
= 0.55V
ADJ1
ADJ2
ADJ1
ADJ2
11
10
9
A1
B1
A1
B1
1.8
1.7
8
7
1.6
1.5
1.4
6
5
4
–50
0
25
50
75
100
–50
–25
0
50
75
100
–25
–25
0
50
25
–50
75
100
25
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
2908 G07
2908 G09
2908 G08
Typical Transient Duration
vs Comparator Overdrive
Reset Time-Out Period (tRST
vs Temperature
)
IV4 vs Temperature
700
600
500
400
300
200
100
0
2.2
2.1
2.0
1.9
250
240
230
220
210
200
190
180
170
160
150
T
= 25°C
A
V1 = 5.0V (A1)/V1 = 3.3V (B1)
V2 = 3.3V (A1)/V2 = 2.5V (B1)
V3 = 2.5V (A1)/V3 = 1.8V (B1)
V4 = 1.8V (A1)/V4 = 1.5V (B1)
RESET OCCURS
ABOVE CURVE
V
= V
= 0.55V
ADJ1
ADJ2
1.8
1.7
1.6
1.5
1.4
–25
0
50
0.1
1
10
100
–25
0
50
–50
75
100
–50
75
100
25
25
TEMPERATURE (°C)
COMPARATOR OVERDRIVE VOLTAGE (% OF V
)
TEMPERATURE (°C)
RTX
2908 G11
2908 G10
2908 G12
2908f
4
LTC2908
U W
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 vs V1 with
10k Pull-Up Resistor to V1
RST Pull-Down Current (IRST
vs Supply Voltage (VCC
)
)
6
5
4
3
2
1
0
5.0
4.0
3.0
2.0
1.0
0
0.4
0.3
0.2
0.1
0
V
= V1 = V2
V1 = V2
V3 = V4 = V
ADJ2
=
CC
V3 = V4 = V
ADJ1
= V
ADJ2
= GND
V3 = 2.5V (A1)/V3 = 1.8V (B1)
V4 = 1.8V (A1)/V4 = 1.5V (B1)
V
= GND
ADJ1
V
= V
= 0.55V
ADJ1
ADJ2
RST AT
150mV
V2 = GND
RST AT
50mV
V2 = V1
V
V
RT50
RT33
V
V
RT50
RT33
LTC2908-B1 LTC2908-A1
LTC2908-B1 LTC2908-A1
0
1
2
3
4
5
0.4
V1 (V)
0
1
2
3
4
5
0
0.2
0.6
0.8
SUPPLY VOLTAGE, V (V)
V1 (V)
CC
2908 G13
2908 G15
2908 G14
RST Pull-Down Current (IRST) vs
Supply Voltage (VCC) with Dual
Channel Supply
RST Pull-Down Current (IRST) vs
Supply Voltage (VCC) with Single
Channel Supply
RST Output Voltage Low (VOL
)
vs RST Pull-Down Current (IRST
LTC2908-A1
)
0.8
10
1
10
1
V1 = 5.0V
V2 = 3.3V
V3 = 2.5V
V4 = 1.8V
V
= V1 = V2
V
= V1
CC
V3 = V4 = V
CC
V2 = V3 = V4 = V
= V
= GND
= V
= GND
ADJ2
ADJ1
ADJ2
ADJ1
0.7
0.6
V
ADJ1
= V
ADJ2
= 0.4V
RST AT 150mV
0.5
0.4
0.3
0.2
0.1
85°C
–40°C
25°C
RST AT 150mV
0.1
0.01
0.1
0.01
RST AT 50mV
RST AT 50mV
0
0.001
0.001
5
10
20
25
30
(mA)
35
0
15
0
0.2
0.4
0.6
0.8
1
0
0.2
0.4
0.6
0.8
1
RST PULL-DOWN CURRENT, I
SUPPLY VOLTAGE, V (V)
SUPPLY VOLTAGE, V (V)
RST
CC
CC
2908 G16
2908 G17
2908 G18
RST Output Voltage Low (VOL
)
vs RST Pull-Down Current (IRST
)
RST Pull-Up Current (IRST
vs Supply Voltage (VCC
)
LTC2908-B1
)
0.8
–30
V1 = 3.3V
V2 = 2.5V
V3 = 1.8V
V4 = 1.5V
V
= V1 = V2
CC
V3 = 2.5V (A1)/V3 = 1.8V (B1)
–25 V4 = 1.8V (A1)/V4 = 1.5V (B1)
= V = 0.55V
0.7
0.6
V
ADJ1
ADJ2
V
= V
= 0.4V
RST HELD AT 0V
ADJ1
ADJ2
–20
–15
–10
–5
0.5
0.4
0.3
0.2
0.1
85°C
–40°C
25°C
V
V
RT50
RT33
LTC2908-B1
LTC2908-A1
0
0
5
10
20
(mA)
25
0
15
2
3
3.5
4
4.5
5
2.5
SUPPLY VOLTAGE, V (V)
RST PULL-DOWN CURRENT, I
CC
RST
2908 G19
2908 G20
2908f
5
LTC2908
U W
TYPICAL PERFOR A CE CHARACTERISTICS
RST Output Voltage High (VOH) vs
RST Output Voltage High (VOH) vs
RST Output Source Current (IRST
LTC2908-A1
)
RST Output Source Current (IRST
)
LTC2908-B1
5
4
3
2
1
3.0
2.5
2.0
1.5
25°C
25°C
85°C
–40°C
85°C
V1 = 5.0V
V2 = 3.3V
V3 = 2.5V
V4 = 1.8V
V1 = 3.3V
V2 = 2.5V
V3 = 1.8V
V4 = 1.5V
–40°C
1.0
0.5
V
= V
= 0.55V
V
= V
= 0.55V
ADJ2
ADJ1
ADJ2
ADJ1
0
–4
–8
–12
–16
(µA)
–20
0
–4
–6
–8
–10
(µA)
–12
–2
OUTPUT SOURCE CURRENT, I
OUTPUT SOURCE CURRENT, I
RST
RST
2908 G21
2908 G22
U
U
U
(TS8 Package/DDB8 Package)
PI FU CTIO S
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.
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.
V4 (Pin 2/Pin 3): Voltage Input 4.
RST(Pin3/Pin2):ResetLogicOutput. Pullslowwhenany
voltage input is below the reset threshold and is held low
for200msafterallvoltageinputsareabovethreshold.This
pin has a weak pull-up to VCC and may be pulled above VCC
using an external pull-up.
ExposedPad(Pin9,DDB8Only):ExposedPadmaybeleft
open or connected to device ground.
GND (Pin 4/Pin 1): Device Ground.
2908f
6
LTC2908
W
BLOCK DIAGRA
LTC2908-A1/LTC2908-B1
V1
–
+
C1
C2
C3
C4
C5
POWER
DETECT
V
CC
–
+
V2
V3
V4
V
CC
–
+
6µA
RST
200ms
RESET PULSE
GENERATOR
–
+
V
ADJ1
–
+
V
ADJ2
–
+
C6
GND
BANDGAP
REFERENCE
2908 BD
W U
W
TI I G DIAGRA
VX Monitor Timing
V
RTX
V
X
t
UV
t
RST
1V
RST
2908 TD
2908f
7
LTC2908
W U U
U
APPLICATIO S I FOR ATIO
Supply Monitoring
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 character-
istic, consuming more quiescent current than normal.
These conditions could cause serious system reliability
problems.
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 thresh-
olds for the reset not to be invoked. The LTC2908 asserts
theresetoutputduringpower-up,power-downandbrown-
out conditions on any one of the voltage inputs.
Power-Up
During power-up, RST starts asserting low as soon as
there is at least 200mV on V1 and/or V2. The RST pull-
down capability is a function of V1 and V2 as shown in the
Typical Performance Characteristics.
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 pull-
down capability below 1V.
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.Aftertheinternaltimercountsa200msdelaytime,
RST weakly pulls high to VCC.
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.
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
10
V
= V1 = V2
V
= V1
CC
V3 = V4 = V
CC
V2 = V3 = V4 = V
= V
= GND
= V
= GND
ADJ2
ADJ1
ADJ2
ADJ1
1
0.1
1
0.1
RST AT 150mV
RST AT 150mV
RST AT 50mV
RST AT 50mV
0.01
0.001
0.01
0.001
0
0.2
0.4
0.6
0.8
1
0
0.2
0.4
0.6
0.8
1
SUPPLY VOLTAGE, V (V)
SUPPLY VOLTAGE, V (V)
CC
CC
2908 G16
2908 G17
Figure 1. RST Pull-Down Current (IRST) vs
Supply Voltage (VCC) with Dual Channel Supply
Figure 2. RST Pull-Down Current (IRST) vs
Supply Voltage (VCC) with Single Channel Supply
2908f
8
LTC2908
W U U
APPLICATIO S I FOR ATIO
Adjustable Input
U
V
TRIP
LTC2908-A1/LTC2908-B1
R1
The noninverting input on the VADJ comparator is set to
0.5V. And the high impedance inverting input directly ties
to the VADJ pin.
1%
V
–
ADJ
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 de-
rives 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
VTRIP
0.5V
R1=
– 1 R2
Threshold Accuracy
Specifyingsystemvoltagemarginforworst-caseoperation
requires the consideration of three factors: power supply
tolerance, IC supply voltage tolerance and supervisor re-
set 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.
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 V
Inputs
ADJ
V
(V)
V
(V)
TRIP
R1 (kΩ)
R2 (kΩ)
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
SUPPLY
12
11.25
9.4
2150
1780
1400
1300
1020
845
10
8
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%fortheLTC2908supervisors). Figure5showsthe
typical relative threshold accuracy for all six inputs over
temperature.
7.5
7.5
6
7
5.6
5
4.725
3.055
2.82
3.3
3
511
464
2.5
1.8
1.5
1.2
1.0
0.9
0.8
0.7
0.6
2.325
1.685
1.410
1.120
0.933
0.840
0.750
0.655
0.561
365
237
182
124
86.6
68.1
49.9
30.9
12.1
NOMINAL
SUPPLY
VOLTAGE
5.000V
MINIMUM
SUPPLY
IDEAL
RELIABLE TOLERANCE SUPERVISOR
SYSTEM
VOLTAGE
THRESHOLD
4.750V
4.675V
4.600V
–5.0%
±1.5%
THRESHOLD
BAND
–6.5%
–8.0%
±2.5%
THRESHOLD
BAND
REGION OF POTENTIAL MALFUNCTION
WITH 2.5% MONITOR
If an application has less than six supply voltages, the
unused supervisor inputs should be tied to the closest
higher supply voltage available.
4.500V
–10%
2908 F04
Figure 4. Threshold Band Diagram
2908f
9
LTC2908
W U U
U
APPLICATIO S I FOR ATIO
1.5
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.
1.0
0.5
0
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 compara-
tors. Therefore, eachcomparatoroutputisintegratedover
timebeforetriggeringtheoutputlogic.Therefore,anykind
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.
–0.5
–1.0
–1.5
–50
0
25
50
75
100
–25
TEMPERATURE (°C)
2908 F05
Figure 5. Typical Threshold Accuracy vs Temperature
Withthisvariationofresetthresholdinmind,thenominal
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
.
Thisdelayeliminatestheeffectofanysupplynoise, whose
frequency is above 1/200ms = 5Hz, on the RST output.
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.
Ifallthesuppliesremainabovetheircorrespondingthresh-
old 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.
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,
the5Vtypicalthresholdis4.675V,or75mVbelowtheideal
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.
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.
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.
Although all six comparators for the six inputs have built-
in 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 applica-
tions). Apply filter capacitors on the V3, V4, VADJ1 and
VADJ2 inputs in extremely noisy situations.
In any supervisory application, supply noise riding on the
monitored DC voltage can cause spurious resets, particu-
larly when the monitored voltage is near the reset thresh-
old. A less desirable but common solution to this problem
2908f
10
LTC2908
W U U
APPLICATIO S I FOR ATIO
U
RST Output Characteristics
The rise time on the RST pin is limited by a weak internal
pull-up current source to VCC. The following formula esti-
mates the output rise time (10% to 90%) at the RST pin:
The DC characteristics of the RST pull-up and pull-down
strength are shown in the Typical Performance Character-
istics section. The RST output has a weak internal pull-up
to VCC = Max(V1, V2) and a strong pull-down to ground.
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 weak pull-up and strong pull-down arrangement
allowsthispintohaveopen-drainbehaviorwhilepossess-
ing several other beneficial characteristics.
The weak pull-up eliminates the need for external pull-up
resistorswhentherisetimeonthesepinsisnotcritical.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.
The on-resistance as a function of the VCC = Max(V1, V2)
voltage (for VCC > 1V) at room temperature is estimated as
follows:
6 •105
RPU
=
Ω
MAX V1,V2 – 1V
(
)
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 maxi-
mum VOL = 0.15V at RST.
At VCC = 3.3V, RPU is about 260k. Using 150pF for load
capacitance, the rise time is 86µs. A smaller external pull-
upresistormaybeusediftheoutputneedstopullupfaster
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.
Output Rise and Fall Time Estimation
The following formula estimates the output fall time (90%
to 10%) for a particular external load capacitance (CLOAD):
tFALL ≈ 2.2 • RPD • CLOAD
where RPD is the on-resistance of the internal pull-down
transistor estimated to be typically 40Ω at room tempera-
ture (25°C) and CLOAD is the external load capacitance on
the pin. Assuming a 150pF load capacitance, the fall time
is about 13ns.
2908f
11
LTC2908
TYPICAL APPLICATIO S
U
Six Supply Monitor, 5% Tolerance, 12V, 5V, 3.3V, 2.5V, 1.8V, 1V
12V
5V
DC/DC
DC/DC
DC/DC
DC/DC
DC/DC
3.3V
2.5V
SYSTEM
1.8V
1.0V
C1
C2
0.1µF 0.1µF
R1
2.15M
R3
86.6k
R2
100k
R4
100k
V1
V2 V3 V4
V
V
ADJ1
ADJ2
LTC2908-A1
GND
RST
2908 TA02
2908f
12
LTC2908
U
TYPICAL APPLICATIO S
Quad Supply Monitor with One Adjustable Input, 5% Tolerance, 3.3V, 2.5V, 1.8V, 1.2V
3.3V
2.5V
DC/DC
SYSTEM
1.8V
DC/DC
1.2V
DC/DC
C1
C2
0.1µF 0.1µF
R3
124k
R4
100k
V1
V2
V3 V4
LTC2908-B1
GND
V
V
ADJ1
ADJ2
RST
2908 TA03
2908f
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
0.38 ± 0.10
3.00 ±0.10
(2 SIDES)
TYP
5
8
0.56 ± 0.05
(2 SIDES)
2.00 ±0.10
PIN 1 BAR
(2 SIDES)
TOP MARK
PIN 1
(SEE NOTE 6)
CHAMFER OF
EXPOSED PAD
4
1
(DDB8) DFN 1103
0.25 ± 0.05
0.75 ±0.05
0.200 REF
0.50 BSC
2.15 ±0.05
(2 SIDES)
0 – 0.05
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
2908f
14
LTC2908
U
PACKAGE DESCRIPTIO
TS8 Package
8-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1637)
2.90 BSC
(NOTE 4)
0.52
MAX
0.65
REF
1.22 REF
1.50 – 1.75
(NOTE 4)
2.80 BSC
1.4 MIN
3.85 MAX 2.62 REF
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
DATUM ‘A’
0.01 – 0.10
1.00 MAX
0.30 – 0.50 REF
1.95 BSC
0.09 – 0.20
(NOTE 3)
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
2908f
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-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
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
5V
DC/DC
3.3V
DC/DC
SYSTEM
2.5V
DC/DC
1.8V
DC/DC
1.5V
DC/DC
C1
C2
R1
182k
R3
R2
100k
MANUAL
RESET BUTTON
(NORMALLY OPEN)
0.1µF 0.1µF
2.15M
R5
10k
R4
100k
V1
V2 V3 V4
V
V
ADJ1
ADJ2
RST
LTC2908-A1
GND
2908 TA04
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC690
5V Supply Monitor, Watchdog Timer and Battery Backup
3.3V Supply Monitor, Watchdog Timer and Battery Backup
5V Supply Monitor and Watchdog Timer
4.65 Threshold
LTC694-3.3
LTC699
2.9V Threshold
4.65 Threshold
LTC1232
5V Supply Monitor, Watchdog Timer and Pushbutton Reset
4.37V/4.62V Threshold
4.725V, 3.118V, 1V Threshold (±0.75%)
LTC1326/LTC1326-2.5
Micropower Precision Triple Supply Monitor for 5V/2.5V, 3.3V
and ADJ
LTC1536
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
Meets PCI t
Timing Specifications
FAIL
LTC1726-2.5/LTC1726-5
LTC1727-2.5/LTC1727-5
LTC1728-1.8/LTC1728-3.3
LTC1728-2.5/LTC1728-5
LTC1985-1.8
Adjustable RESET and Watchdog Time-Outs
Individual Monitor Outputs in MSOP
5-Lead SOT-23 Package
5-Lead SOT-23 Package
Micropower Triple Supply Monitor with Push-Pull Reset Output
Programmable Quad Supply Monitor
5-Lead SOT-23 Package
LTC2900
Adjustable RESET, 10-Lead MSOP and DFN
Packages
LTC2901
LTC2902
Programmable Quad Supply Monitor
Programmable Quad Supply Monitor
Adjustable RESET and Watchdog Timer,
16-Lead SSOP Package
Adjustable RESET and Tolerance,
16-Lead SSOP Package
LTC2903
LTC2904
Precision Quad Supply Monitor
6-Lead SOT-23 Package
Three-State Programmable Precision Dual Supply Monitor
Adjustable Tolerance, 8-Lead SOT-23 and DFN
Packages
LTC2905
LTC2906
LTC2907
Three-State Programmable Precision Dual Supply Monitor
Adjustable RESET and Tolerance,
8-Lead SOT-23 and DFN Packages
Dual Supply Monitor with One Pin Selectable Threshold and
One Adjustable Input
0.5V Adjustable Threshold and Three Supply
Tolerances, 8-Lead SOT-23 and DFN Packages
Dual Supply Monitor with One Pin Selectable Threshold and
One Adjustable Input
0.5V Adjustable Threshold, RESET and Three Supply
Tolerances, 8-Lead SOT-23 and DFN Packages
2908f
LT/TP 0504 1K • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
16
●
●
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
LINEAR TECHNOLOGY CORPORATION 2004
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