LTC1985-1.8 - Micropower Precision Triple Supply Monitor with Push-Pull Reset Output in a 5-Lead SOT-23 Package

LTC1985-1.8
Micropower Precision
Triple Supply Monitor
with Push-Pull Reset Output
in a 5-Lead SOT-23 Package
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FEATURES
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DESCRIPTIO
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
3V Active-Low Push-Pull Reset Output
5-Lead SOT-23 Package
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APPLICATIO S
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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.
Very low (10µA typical) supply current makes the LTC1985
ideal for power conscious systems.
Desktop Computers
Notebook Computers
Intelligent Instruments
Portable Battery-Powered Equipment
Network Servers
The LTC1985 is available in a 5-lead SOT-23 package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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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 compliance for 200ms. Tight 1.5% accuracy specifications and
glitch immunity ensure reliable reset operation without
false triggering.
TYPICAL APPLICATION
DC/DC
CONVERTER
3V
1.8V
2.5V
SYSTEM
LOGIC
1
5
RST
VCC3
LTC1985-1.8
4
R1
130k
1% 3
0.1µF
0.1µF
R2
100k
1%
VCC18
VCCA
GND
1985-1.8 TA01
2
1
LTC1985-1.8
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ABSOLUTE
RATI GS
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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
PART NUMBER
TOP VIEW
RST 1
5 VCC3
LTC1985ES5-1.8
GND 2
VCCA 3
4 VCC18
S5 PART MARKING
S5 PACKAGE
5-LEAD PLASTIC SOT-23
TJMAX = 125°C, θJA = 250°C/W
LTNM
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
TYP
MAX
UNITS
VRT3
Reset Threshold VCC3
VCC3 Input Threshold
●
2.760
2.805
2.850
V
VRT18
Reset Threshold VCC18
VCC18 Input Threshold
●
1.656
1.683
1.710
V
VRTA
Reset Threshold VCCA
VCCA Input Threshold
●
0.985
1.000
1.015
V
VCCOP
VCC3, VCC18 Operating Voltage
RST in Correct Logic State
●
1
7
V
IVCC3
VCC3 Supply Current
VCC18 > VCC3
VCC18 < VCC3, VCC3 = 3V (Note 4)
●
●
1
10
2
20
µA
µA
IVCC18
VCC18 Supply Current
VCC18 < VCC3, VCC18 = 1.8V (Note 4)
●
1
2
µA
IVCCA
VCCA Input Current
VCCA = 1V
●
– 15
0
15
nA
tRST
Reset Pulse Width
RST Low (Note 5)
●
140
200
280
ms
tUV
VCC Undervoltage Detect to RST
VCC18, VCC3 or VCCA Less Than Reset (Note 5)
Threshold VRT by More Than 1%
VOL
Output Voltage Low, RST
ISINK = 2.5mA, VCC3 = 3V, VCC18 = 0V
ISINK = 100µA, VCC3 = 1V, VCC18 = 0V
ISINK = 100µA, VCC3 = 0V, VCC18 = 1V
ISINK = 100µA, VCC3 = 1V, VCC18 = 1V
●
●
●
●
VOH
Output Voltage High, RST
ISOURCE = 200µA
●
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2: All voltage values are with respect to GND.
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
2
µs
110
0.15
0.05
0.05
0.05
0.8VCC3
0.4
0.3
0.3
0.3
V
V
V
V
V
extended temperature limits of – 40°C to 85°C but are not tested at these
temperatures.
Note 4: Both VCC3 and VCC18 can act as the supply depending on which pin
has the greatest potential.
Note 5: Measured from when input passes through the input threshold
voltage (VRTX) until RST passes through 1.5V.
LTC1985-1.8
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TYPICAL PERFOR A CE CHARACTERISTICS
VCCA Input Current
vs Input Voltage
IVCC18 vs Temperature
1.5
1.4
13
1.3
12
1.2
11
10
9
1.0
0.9
0.8
7
0.7
6
0.6
80
– 2.0
0.80 0.85 0.90 0.95 1 1.05 1.10 1.15 1.20
INPUT VOLTAGE (V)
100
1985-18 G03
VCC18 Threshold Voltage
vs Temperature
1.010
1.005
1.000
0.995
0.990
80
100
1.710
VCC18 THRESHOLD VOLTAGE, VRT18 (V)
VCC3 THRESHOLD VOLTAGE, VRT3 (V)
VCCA THRESHOLD VOLTAGE, VRTA (V)
80
2.845
0.985
–60 –40 –20 0
20 40 60
TEMPERATURE (°C)
2.835
2.825
2.815
2.805
2.795
2.785
2.775
2.765
– 60 –40 – 20 0 20 40 60
TEMPERATURE (°C)
80
100
1.700
1.690
1.680
1.670
1.660
1.650
–60 –40 –20 0
20 40 60
TEMPERATURE (°C)
1985-18 G05
1985-18 G04
Typical Transient Duration
vs Comparator Overdrive
RESET OCCURS
ABOVE CURVE
250
200
150
100
50
0
0.1
1
10
100
RESET COMPARATOR OVERDRIVE VOLTAGE (% OF VCC)
1985-18 G07
280
8
260
7
TA = 25°C
6
240
VOL = 0.4V
220
200
180
5
4
VOL = 0.2V
3
2
160
140
–60 –40 –20
100
ISINK vs Supply Voltage
ISINK (mA)
TA = 25°C
400
80
1985-18 G06
Reset Pulse Width
vs Temperature
RESET PULSE WIDTH, tRST (ms)
TYPICAL TRANSIENT DURATION (µs)
– 0.5
VCC3 Threshold Voltage
vs Temperature
1.015
300
0
1985-18 G02
VCCA Threshold Voltage
vs Temperature
350
0.5
–1.5
1985-18 G01
450
1.0
–1.0
0.5
– 60 –40 – 20 0 20 40 60
TEMPERATURE (°C)
100
TA = 25°C
1.5
1.1
8
5
– 60 –40 – 20 0 20 40 60
TEMPERATURE (°C)
2.0
VCC3 = 3V
VCCA = 3V
VCC18 = 1.8V
INPUT CURRENT (nA)
15
14
IVCC18 (µA)
IVCC3 (µA)
IVCC3 vs Temperature
1
0
0
20
40
60
80
100
TEMPERATURE (°C)
1985-18 G08
0
0.5
1.0
1.5
2.0
VCC3 OR VCC18 (V)
2.5
3.0
1985-18 • G09
3
LTC1985-1.8
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TYPICAL PERFOR A CE CHARACTERISTICS
RST High Level Output Voltage vs
Output Source Current
3.5
RST Voltage Output Low vs
Output Sink Current
RST Voltage Output Low vs
Output Sink Current
3.0
1.8
VCC3 = VCC18 = VCCA = 3.0V
VCC3 = VCC18 = 1.8V
VCCA = 0V
1.6
3.0
VCC3 = VCC18 = 3V
VCCA = 0V
2.5
25°C
85°C
1.4
85°C
2.0
1.2
– 40°C
1.5
25°C
– 40°C
1.0
VOL (V)
2.0
VOL (V)
VOH (V)
2.5
0.8
85°C
– 40°C
1.5
1.0
0.6
1.0
25°C
0.4
0.5
0.5
0.2
0
0
0
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
ISOURCE (mA)
0
2
4
1985-81 G10
6
8
ISINK (mA)
10
12
14
1985-81 G11
0
5
10
15
20 25 30
ISINK (mA)
35
40
45
1985-81 G12
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PI FU CTIO S
RST (Pin 1): Reset Logic Output. Active low, 3V pushpull output. Asserted when one or all of the supplies are
below trip thresholds and held for 200ms after all supplies become valid.
GND (Pin 2): Ground.
VCCA (Pin 3): 1V Sense, High Impedance Input. If unused
it can be tied to either VCC3 or VCC18.
4
VCC18 (Pin 4): 1.8V Sense Input and Power Supply Pin.
This pin is used on the LTC1985 to provide power to the
part when the voltage on VCC18 is greater than the voltage
on VCC3. Bypass to ground with a ≥ 0.1µF ceramic
capacitor.
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.
LTC1985-1.8
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BLOCK DIAGRA
LTC1985-1.8
–
VCC3 5
+
POWER
DETECT
VCC INTERNAL
VCC3
VCC18 4
–
200ms PULSE GENERATOR
1 RST
200ms
DELAY
+
–
VCCA 3
+
GND 2
BANDGAP
REFERENCE
1985-18 BD
WU
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TI I G DIAGRA
VCC Monitor Timing
VCCX
VRTX
t UV
RST
tRST
1.5V
1985-18 TD
5
LTC1985-1.8
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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.
The VCCA pin, if unused, can be tied to either VCC3 or VCC18.
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.
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.
All three VCC inputs must be above predetermined thresholds for reset not to be invoked. The LTC1985 will assert
reset during power-up, power-down and brownout conditions on any one or all of the VCC inputs.
Ensuring RST Valid for Supply Voltages Under 1V
3V or 1.8V Power Detect
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.
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
RST output must be valid down to 0V the addition of a pulldown resistor from RST to ground will ensure RST is held
low. The circuit in Figure 1 shows an application employing this technique. The value chosen for the pull-down
resistor (R3) is a trade-off between pull-down strength
and loading of the RST pin. If the value of the resistor is too
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.
4
VCC3 = VCC18 = VCCA
Power-Down
LTC1985-1.8
3V
ADJUSTABLE
SUPPLY
R1
1.8V
5
4
3
R2
2
VCC3
RST
1
3
RST VOLTAGE (V)
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.
2
1
R3
100k
VCC18
VCCA
0
GND
0
1
2
3
4
VCC3 (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
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Figure 2. RST Voltage vs VCC3 with
a 100k Resistor on RST to Ground
LTC1985-1.8
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TYPICAL APPLICATIO S
Triple Supply Monitor (3V, 1.8V and Adjustable)
Dual Supply Monitor (3V and 1.8V, Defeat VCCA Input)
LTC1985-1.8
5
3V
ADJUSTABLE SUPPLY
OR DC/DC FEEDBACK
DIVIDER
R1*
4
1.8V
3
R2*
2
VCC3
RST
LTC1985-1.8
1
SYSTEM RESET
5
3V
VCC18
4
1.8V
3
VCCA
2
GND
VCC3
RST
1
SYSTEM RESET
VCC18
VCCA
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
3V
5
4
ADJUSTABLE
SUPPLY
R1*
3
R2*
2
VCC3
RST
1
2.5V
SYSTEM RESET
VCC18
LTC1435
VOSENSE
VCCA
GND
1985-18 TA04
*TO PRESERVE THRESHOLD ACCURACY, SET PARALLEL
COMBINATION OF R1 AND R2 ≤ 66.5k
ADJUSTABLE
RESET TRIP
THRESHOLD 2.31V
6
27.4k
1%
3V
2.26k
1.8V
1%
22.6k
1%
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.
LTC1985-1.8
5
4
3
2
VCC3
RST
1
SYSTEM RESET
VCC18
VCCA
GND
1985-18 TA05
7
LTC1985-1.8
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TYPICAL APPLICATIO
Triple Supply Monitor with Manual Reset Button
2.5V
VTRIP = 2.3V
SYSTEM
RESET
1
3V
1.8V
5
RST
VCC3
100nF
R3*
10k
5%
*OPTIONAL RESISTOR RECOMMENDED
TO EXTEND ESD TOLERANCE
VCC18
100nF
3
R2
100k
0.1%
MANUAL
RESET BUTTON
(NORMALLY OPEN)
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PACKAGE DESCRIPTIO
LTC1985-1.8
4
R1
130k
0.1%
VCCA
GND
1985-18 TA07
2
V
VTRIP = CCA (R1 + R2)
R2
V
R1 = R2 TRIP – 1
VCCA
(
)
Dimensions in inches (millimeters) unless otherwise noted.
S5 Package
5-Lead Plastic SOT-23
(LTC DWG # 05-08-1633)
2.60 – 3.00
(0.102 – 0.118)
1.50 – 1.75
(0.059 – 0.069)
0.35 – 0.55
(0.014 – 0.022)
0.09 – 0.20
(0.004 – 0.008)
(NOTE 2)
0.00 – 0.15
(0.00 – 0.006)
0.90 – 1.45
(0.035 – 0.057)
0.35 – 0.50
0.90 – 1.30
(0.014 – 0.020)
(0.035 – 0.051)
FIVE PLACES (NOTE 2)
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)
2.80 – 3.00
(0.110 – 0.118)
(NOTE 3)
0.95
(0.037)
REF
1.90
(0.074)
REF
S5 SOT-23 0599
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8
Linear Technology Corporation
1985f LT/TP 0900 4K • PRINTED IN THE USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com
 LINEAR TECHNOLOGY CORPORATION 2000