LTC1985ES5-1.8#TRM [Linear]
LTC1985-1.8 - Micropower Precision Triple Supply Monitor with Push-Pull Reset Output in a 5-Lead SOT-23 Package; Package: SOT; Pins: 5; Temperature Range: -40°C to 85°C;
| 型号： | LTC1985ES5-1.8#TRM |
| 厂家： | 
Linear |
| 描述： | LTC1985-1.8 - Micropower Precision Triple Supply Monitor with Push-Pull Reset Output in a 5-Lead SOT-23 Package; Package: SOT; Pins: 5; Temperature Range: -40°C to 85°C 光电二极管 |
| 文件： | 总8页 (文件大小：137K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC1985-1.8
Micropower Precision
Triple Supply Monitor
with Push-Pull Reset Output
in a 5-Lead SOT-23 Package
U
FEATURES
DESCRIPTIO
The LTC®1985-1.8 is a triple supply monitor intended for
systems with multiple supply voltages. The reset output
remains low until all three supplies have been in compli-
ance for 200ms. Tight 1.5% accuracy specifications and
glitch immunity ensure reliable reset operation without
false triggering.
■
Monitors Three Inputs Simultaneously:
3V, 1.8V and Adjustable
■
±1.5% Threshold Accuracy Over Temperature
■
Very Low Supply Current: 10µA Typ
■
200ms Reset Time Delay
■
Power Supply Glitch Immunity
■
Guaranteed RESET for VCC3 ≥ 1V or VCC18 ≥ 1V
The RST output is guaranteed to be in the correct state for
VCC18 or VCC3 down to 1V. The LTC1985 may also be
configured to monitor any one or two VCC inputs instead
of three, depending on system requirements.
■
3V Active-Low Push-Pull Reset Output
■
5-Lead SOT-23 Package
U
APPLICATIO S
Verylow(10µAtypical)supplycurrentmakestheLTC1985
ideal for power conscious systems.
■
Desktop Computers
■
The LTC1985 is available in a 5-lead SOT-23 package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Notebook Computers
■
Intelligent Instruments
■
Portable Battery-Powered Equipment
■
Network Servers
U
TYPICAL APPLICATION
3V
1.8V
2.5V
DC/DC
CONVERTER
SYSTEM
LOGIC
1
RST
5
4
3
V
V
V
CC3
LTC1985-1.8
CC18
R1
130k
1%
0.1µF
CCA
R2
100k
1%
GND
0.1µF
1985-1.8 TA01
2
1
LTC1985-1.8
W W
U W
U W
U
ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
(Notes 1, 2)
VCC3, VCC18, VCCA ...................................... –0.3V to 7V
RST .......................................... –0.3V to (VCC3 + 0.3V)
Operating Temperature Range
(Note 3) ............................................. – 40°C to 85°C
Storage Temperature Range ................ –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................ 300°C
ORDER
TOP VIEW
PART NUMBER
RST 1
GND 2
5 V
4 V
CC3
LTC1985ES5-1.8
V
CCA
3
CC18
S5 PART MARKING
LTNM
S5 PACKAGE
5-LEAD PLASTIC SOT-23
TJMAX = 125°C, θJA = 250°C/W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specificaitons are at TA = 25°C. VCC3 = 3V, VCC18 = 1.8V, VCCA = VCC3 unless otherwise noted.
SYMBOL PARAMETER
CONDITIONS
MIN
2.760
1.656
0.985
1
TYP
MAX
2.850
1.710
1.015
7
UNITS
V
V
V
V
Reset Threshold V
Reset Threshold V
Reset Threshold V
V
V
V
Input Threshold
●
●
●
●
2.805
1.683
1.000
V
V
V
V
RT3
RT18
RTA
CC3
CC3
Input Threshold
CC18
CCA
CC18
Input Threshold
CCA
V
V
, V Operating Voltage
CC3 CC18
RST in Correct Logic State
CCOP
VCC3
I
Supply Current
V
V
> V
CC3
●
●
1
10
2
20
µA
µA
CC3
CC18
CC18
< V , V
= 3V (Note 4)
CC3 CC3
I
I
t
t
V
V
Supply Current
V
V
< V , V = 1.8V (Note 4)
CC3 CC18
●
●
●
1
2
µA
nA
ms
µs
VCC18
VCCA
RST
CC18
CC18
Input Current
= 1V
CCA
–15
140
0
15
CCA
Reset Pulse Width
Undervoltage Detect to RST
RST Low (Note 5)
, V or V Less Than Reset (Note 5)
CCA
200
110
280
V
V
UV
CC
CC18 CC3
Threshold V by More Than 1%
RT
V
V
Output Voltage Low, RST
I
I
I
I
= 2.5mA, V
= 100µA, V
= 100µA, V
= 100µA, V
= 3V, V
= 1V, V
= 0V, V
= 1V, V
= 0V
= 0V
= 1V
= 1V
●
●
●
●
0.15
0.05
0.05
0.05
0.4
0.3
0.3
0.3
V
V
V
V
OL
SINK
SINK
SINK
SINK
CC3
CC3
CC3
CC3
CC18
CC18
CC18
CC18
Output Voltage High, RST
I
= 200µA
●
0.8V
V
OH
SOURCE
CC3
extended temperature limits of –40°C to 85°C but are not tested at these
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
temperatures.
Note 4: Both V
and V
can act as the supply depending on which pin
CC18
Note 2: All voltage values are with respect to GND.
CC3
has the greatest potential.
Note 5: Measured from when input passes through the input threshold
voltage (V ) until RST passes through 1.5V.
Note 3: The LTC1985E is guaranteed to meet specified performance from
0°C to 70°C and is designed, characterized and assured to meet the
RTX
2
LTC1985-1.8
U W
TYPICAL PERFOR A CE CHARACTERISTICS
VCCA Input Current
vs Input Voltage
IVCC3 vs Temperature
IVCC18 vs Temperature
15
14
13
12
11
10
9
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
2.0
1.5
V
V
V
= 3V
= 3V
T
= 25°C
CC3
CCA
CC18
A
= 1.8V
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
8
7
6
5
–60
20
TEMPERATURE (°C)
60 80
–40 –20
0
40
100
–60
20
TEMPERATURE (°C)
60 80
0.80 0.85 0.90 0.95
1
1.05 1.10 1.15 1.20
–40 –20
0
40
100
INPUT VOLTAGE (V)
1985-18 G01
1985-18 G02
1985-18 G03
VCC18 Threshold Voltage
vs Temperature
VCCA Threshold Voltage
vs Temperature
VCC3 Threshold Voltage
vs Temperature
2.845
2.835
2.825
2.815
2.805
2.795
2.785
2.775
2.765
1.710
1.700
1.690
1.680
1.670
1.660
1.650
1.015
1.010
1.005
1.000
0.995
0.990
0.985
–60
20
TEMPERATURE (°C)
60 80
–40 –20
0
40
100
40 60
TEMPERATURE (°C)
–60 –40 –20
0
20
80 100
40 60
TEMPERATURE (°C)
–60 –40 –20
0
20
80 100
1985-18 G05
1985-18 G06
1985-18 G04
Typical Transient Duration
vs Comparator Overdrive
Reset Pulse Width
vs Temperature
ISINK vs Supply Voltage
450
400
350
300
250
200
150
100
50
280
260
8
7
6
5
4
3
2
1
0
T
A
= 25°C
T
= 25°C
A
RESET OCCURS
ABOVE CURVE
240
V
= 0.4V
OL
220
200
180
160
V
OL
= 0.2V
0
140
0.1
1
10
100
2.5
0
0.5
1.0
V
1.5
OR V
2.0
(V)
3.0
–20
0
20 40
80 100
–60 –40
60
RESET COMPARATOR OVERDRIVE VOLTAGE (% OF V
)
CC
TEMPERATURE (°C)
CC3
CC18
1985-18 G07
1985-18 • G09
1985-18 G08
3
LTC1985-1.8
TYPICAL PERFOR A CE CHARACTERISTICS
U W
RST High Level Output Voltage vs
Output Source Current
RST Voltage Output Low vs
Output Sink Current
RST Voltage Output Low vs
Output Sink Current
3.0
2.5
2.0
1.5
1.0
0.5
0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
V
CC3
V
CCA
= V
= 3V
V
CC3
= V
= V
= 3.0V
CCA
V
CC3
V
CCA
= V
= 1.8V
CC18
CC18
CC18
25°C
= 0V
= 0V
25°C
85°C
85°C
–40°C
–40°C
–40°C
25°C
85°C
0
5
10 15 20 25 30 35 40 45
(mA)
0
0.2 0.4 0.6
1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
0.8
0
2
4
6
I
8
(mA)
12
14
10
I
I
(mA)
SINK
SOURCE
SINK
1985-81 G12
1985-81 G10
1985-81 G11
U
U
U
PI FU CTIO S
VCC18 (Pin 4): 1.8V Sense Input and Power Supply Pin.
This pin is used on the LTC1985 to provide power to the
partwhenthevoltageonVCC18 isgreaterthanthevoltage
on VCC3. Bypass to ground with a ≥0.1µF ceramic
capacitor.
RST (Pin 1): Reset Logic Output. Active low, 3V push-
pull output. Asserted when one or all of the supplies are
below trip thresholds and held for 200ms after all sup-
plies become valid.
GND (Pin 2): Ground.
VCC3 (Pin 5): 3V Sense Input and Power Supply Pin. This
pin provides power to the part when the voltage on VCC3
is greater than the voltage on VCC18. Bypass to ground
with a ≥0.1µF ceramic capacitor.
VCCA (Pin 3): 1V Sense, High Impedance Input. If unused
it can be tied to either VCC3 or VCC18
.
4
LTC1985-1.8
W
BLOCK DIAGRA
LTC1985-1.8
–
+
V
5
CC3
POWER
DETECT
V
INTERNAL
CC
V
CC3
V
4
CC18
–
+
200ms PULSE GENERATOR
1
RST
200ms
DELAY
–
+
V
3
2
CCA
GND
BANDGAP
REFERENCE
1985-18 BD
W U
W
TI I G DIAGRA
VCC Monitor Timing
V
RTX
V
CCX
t
RST
t
UV
RST
1.5V
1985-18 TD
5
LTC1985-1.8
W U U
U
APPLICATIO S I FOR ATIO
Supply Monitoring
Override Functions
The LTC1985 is a low power, high accuracy triple supply
monitoring circuit with a single 200ms microprocessor
reset output.
TheVCCA pin, ifunused, canbetiedtoeitherVCC3 orVCC18.
This is an obvious solution since the trip points for VCC3
and VCC18 will always be greater than the trip point for
VCCA. Likewise, the VCC18, if unused, can be tied to VCC3
.
All three VCC inputs must be above predetermined thresh-
olds for reset not to be invoked. The LTC1985 will assert
reset during power-up, power-down and brownout condi-
tions on any one or all of the VCC inputs.
VCC3 must always be used. Tying VCC3 to VCC18 and
operating off of a 1.8V supply will result in the continuous
assertion of RST.
Ensuring RST Valid for Supply Voltages Under 1V
3V or 1.8V Power Detect
When the supplies drops below 1V the RST output current
sink capability is drastically reduced. The combination of
stray currents and stray capacitance to signals other than
ground can cause the RST output pin to float around. In a
lot of applications this is not a problem since most
microprocessors and other circuits do not operate with
the supply voltage less than 1V. In applications where the
RSToutputmustbevaliddownto0Vtheadditionofapull-
down resistor from RST to ground will ensure RST is held
low. The circuit in Figure 1 shows an application employ-
ing this technique. The value chosen for the pull-down
resistor (R3) is a trade-off between pull-down strength
andloadingoftheRSTpin. Ifthevalueoftheresistoristoo
large the pin may still float and if the resistor value is too
low it may load down the RST as well as burn excess
supply current, a value of 100k is a good compromise.
The LTC1985 is powered from the 3V input pin (VCC3) or
the 1.8V input pin (VCC18), whichever pin has the highest
potential. This ensures the part pulls the RST pin low as
soon as either input pin is ≥1V.
Power-Up
Upon power-up, either the VCC18 or VCC3 pin, can power
the part. This ensures that RST will be low when either
VCC18 or VCC3 reaches 1V. As long as any one of the VCC
inputs is below its predetermined threshold, RST will stay
a logic low. Once all of the VCC inputs rise above their
thresholds, an internal timer is started and RST is driven
high after 200ms.
RST is reasserted whenever any one of the VCC inputs
drops below its predetermined threshold and remains
asserted until 200ms after all of the VCC inputs are above
their thresholds.
4
V
CC3
= V
= V
CC18 CCA
Power-Down
On power-down, once any of the VCC inputs drop below its
threshold, RST is held at a logic low. A logic low of 0.3V is
guaranteed until both VCC3 and VCC18 drop below 1V.
3
2
1
0
LTC1985-1.8
5
4
3
2
1
3V
V
V
V
RST
CC3
R3
100k
1.8V
CC18
CCA
R1
ADJUSTABLE
SUPPLY
R2
GND
0
2
3
4
1
V
CC3
(V)
1985-18 TA06
1985-18 TA06b
Resistor on RST Output to Ground Ensures RST Valid to VCC = 0V
Figure 1. Typical Application Showing
Resistor on RST Output to Ground
Figure 2. RST Voltage vs VCC3 with
a 100k Resistor on RST to Ground
6
LTC1985-1.8
U
TYPICAL APPLICATIO S
Dual Supply Monitor (3V and 1.8V, Defeat VCCA Input)
Triple Supply Monitor (3V, 1.8V and Adjustable)
LTC1985-1.8
LTC1985-1.8
5
4
3
2
1
5
4
3
2
1
SYSTEM RESET
3V
V
V
V
RST
CC3
3V
V
V
V
RST
SYSTEM RESET
CC3
1.8V
1.8V
CC18
CCA
CC18
CCA
ADJUSTABLE SUPPLY
OR DC/DC FEEDBACK
DIVIDER
R1*
R2*
GND
GND
1985-18 TA02
1985-18 TA03
*TO PRESERVE THRESHOLD ACCURACY, SET PARALLEL
COMBINATION OF R1 AND R2 ≤ 66.5k
Dual Supply Monitor (3V Plus Adjustable)
Using VCCA Tied to DC/DC Feedback Divider
LTC1985-1.8
2.5V
5
4
3
2
1
V
V
V
RST
3V
SYSTEM RESET
CC3
27.4k
1%
LTC1985-1.8
LTC1435
V
5
4
3
2
1
6
CC18
CCA
SYSTEM RESET
3V
V
RST
R1*
CC3
OSENSE
ADJUSTABLE
SUPPLY
2.26k
1%
1.8V
V
V
CC18
CCA
R2*
GND
1985-18 TA04
22.6k
1%
GND
ADJUSTABLE
RESET TRIP
THRESHOLD 2.31V
1985-18 TA05
*TO PRESERVE THRESHOLD ACCURACY, SET PARALLEL
COMBINATION OF R1 AND R2 ≤ 66.5k
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 ofits circuits as described herein willnotinfringe on existing patentrights.
7
LTC1985-1.8
U
TYPICAL APPLICATIO
Triple Supply Monitor with Manual Reset Button
2.5V
= 2.3V
SYSTEM
RESET
1
3V
V
1.8V
TRIP
RST
5
4
3
V
V
V
CC3
100nF
LTC1985-1.8
CC18
R1
130k
0.1%
R3*
10k
5%
100nF
CCA
GND
2
R2
100k
0.1%
MANUAL
1985-18 TA07
RESET BUTTON
(NORMALLY OPEN)
V
R2
CCA
V
TRIP
=
(R1 + R2)
*OPTIONAL RESISTOR RECOMMENDED
TO EXTEND ESD TOLERANCE
V
V
TRIP
– 1
R1 = R2
(
)
CCA
U
Dimensions in inches (millimeters) unless otherwise noted.
PACKAGE DESCRIPTIO
S5 Package
5-Lead Plastic SOT-23
(LTC DWG # 05-08-1633)
2.60 – 3.00
(0.102 – 0.118)
2.80 – 3.00
(0.110 – 0.118)
(NOTE 3)
1.50 – 1.75
(0.059 – 0.069)
0.00 – 0.15
(0.00 – 0.006)
0.90 – 1.45
(0.035 – 0.057)
0.35 – 0.55
(0.014 – 0.022)
0.35 – 0.50
(0.014 – 0.020)
FIVE PLACES (NOTE 2)
0.90 – 1.30
(0.035 – 0.051)
0.09 – 0.20
(0.004 – 0.008)
(NOTE 2)
0.95
(0.037)
REF
S5 SOT-23 0599
1.90
(0.074)
REF
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DIMENSIONS ARE INCLUSIVE OF PLATING
3. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
4. MOLD FLASH SHALL NOT EXCEED 0.254mm
5. PACKAGE EIAJ REFERENCE IS SC-74A (EIAJ)
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1985f LT/TP 0900 4K • PRINTED IN THE USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
8
●
●
(408)432-1900 FAX:(408)434-0507 www.linear-tech.com
LINEAR TECHNOLOGY CORPORATION 2000
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