Page 1
Final Electrical Specifications
FEATURES
LTC1985-1.8
Micropower Precision
Triple Supply Monitor
with Push-Pull Reset Output
in a 5-Lead SOT-23 Package
March 2000
U
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 V
■
3V Active-Low Push-Pull Reset Output
■
5-Lead SOT-23 Package
≥ 1V or V
CC3
CC18
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APPLICATIO S
■
Desktop Computers
■
Notebook Computers
■
Intelligent Instruments
■
Portable Battery-Powered Equipment
■
Network Servers
U
TYPICAL APPLICATIO
≥ 1V
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.
The RST output is guaranteed to be in the correct state for
V
CC18
or V
down to 1V. The LTC1985 may also be
CC3
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.
The LTC1985 is available in a 5-lead SOT-23 package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
3V
DC/DC
CONVERTER
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.
1.8V
2.5V
0.1µF
0.1µF
R1
130k
1%
R2
100k
1%
5
V
CC3
LTC1985-1.8
4
V
CC18
3
V
CCA
SYSTEM
LOGIC
1
RST
GND
2
1985-1.8 TA01
1
Page 2
LTC1985-1.8
RST 1
GND 2
TOP VIEW
S5 PACKAGE
5-LEAD PLASTIC SOT-23
V
CCA
3
5 V
CC3
4 V
CC18
WWWU
ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
UU
W
(Notes 1, 2)
V
, V
CC3
RST .......................................... –0.3V to (V
CC18
, V
...................................... –0.3V to 7V
CCA
CC3
+ 0.3V)
ORDER
PART NUMBER
Operating Temperature Range
(Note 3) ............................................. –40°C to 85°C
LTC1985ES5-1.8
Storage Temperature Range ................ –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................ 300°C
T
= 125°C, θ
JMAX
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
temperature range, otherwise specificaitons are at TA = 25°C. V
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
RT3
V
RT18
V
RTA
V
CCOP
I
VCC3
I
VCC18
I
VCCA
t
RST
t
UV
V
OL
V
OH
Reset Threshold V
Reset Threshold V
Reset Threshold V
V
, V
CC3
CC18
V
Supply Current V
CC3
V
Supply Current V
CC18
V
Input Current V
CCA
Reset Pulse Width RST Low ● 140 200 280 ms
VCC Undervoltage Detect to RST V
Output Voltage Low, RST I
Output Voltage High, RST I
CC3
CC18
CCA
Operating Voltage RST in Correct Logic State ● 17V
V
Input Threshold ● 2.760 2.805 2.850 V
CC3
V
CC18
V
Input Threshold ● 0.985 1.000 1.015 V
CCA
CC18
V
CC18
CC18
= 1V ● –15 0 15 nA
CCA
CC18
Threshold V
= 2.5mA, V
SINK
= 100µA, V
I
SINK
I
= 100µA, V
SINK
= 100µA, V
I
SINK
SOURCE
The ● denotes specifications which apply over the full operating
= 3V, V
CC3
Input Threshold ● 1.656 1.683 1.710 V
> V
CC3
< V
, V
CC3
< V
CC3
, V
CC3
= 200µA ● 0.8V
= 3V (Note 4) ● 10 20 µA
CC3
, V
= 1.8V (Note 4) ● 12 µA
CC18
or V
Less Than Reset 110 µs
CCA
by More Than 1%
RT
= 3V, V
CC3
CC3
CC3
CC3
= 1V, V
= 0V, V
= 1V, V
CC18
CC18
CC18
CC18
= 1.8V, V
CC18
= 0V ● 0.15 0.4 V
= 0V ● 0.05 0.3 V
= 1V ● 0.05 0.3 V
= 1V ● 0.05 0.3 V
JA
CCA
= 250°C/W
= V
unless otherwise noted.
CC3
● 12 µA
S5 PART MARKING
LTNM
CC3
V
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
extended temperature limits of –40°C to 85°C but are not tested at these
temperatures.
Note 4: Both V
has the greatest potential.
CC3
and V
can act as the supply depending on which pin
CC18
Page 3
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TYPICAL PERFOR A CE CHARACTERISTICS
I
I
vs Temperature
VCC3
15
14
13
12
11
(µA)
10
VCC3
I
9
8
7
6
5
–60
–40 0
–20
TEMPERATURE (°C)
V
Threshold Voltage
CCA
vs Temperature
1.015
(V)
1.010
RTA
1.005
1.000
0.995
THRESHOLD VOLTAGE, V
0.990
CCA
V
0.985
–60
–40 0
–20 20
TEMPERATURE (°C)
1.5
1.4
1.3
1.2
1.1
(µA)
1.0
VCC18
0.9
I
0.8
0.7
0.6
80
20
60
40
40
60
1985-18 G01
80
1985-18 G04
100
100
0.5
2.845
2.835
(V)
RT3
2.825
2.815
2.805
2.795
2.785
THRESHOLD VOLTAGE, V
CC3
2.775
V
2.765
vs Temperature
VCC18
V
= 3V
CC3
= 3V
V
CCA
= 1.8V
V
CC18
–60
–40 0
–20
TEMPERATURE (°C)
V
Threshold Voltage
CC3
vs Temperature
–60
–40 0
–20
TEMPERATURE (°C)
20
20
60
40
60
40
80
1985-18 G02
80
1985-18 G05
2.0
1.5
1.0
0.5
–0.5
INPUT CURRENT (nA)
–1.0
–1.5
100
100
–2.0
1.710
(V)
1.700
RT18
1.690
1.680
1.670
THRESHOLD VOLTAGE, V
1.660
CC18
V
1.650
LTC1985-1.8
V
Input Current
CCA
vs Input Voltage
TA = 25°C
0
0.80 0.85 0.95 1.05 1.15
0.90
V
Threshold Voltage
CC18
vs Temperature
–40 0
–60
–20 20
1
INPUT VOLTAGE (V)
40
TEMPERATURE (°C)
1.10
1985-18 G03
60
1985-18 G06
1.20
80
100
Typical Transient Duration
vs Comparator Overdrive
450
400
350
300
250
200
150
100
TYPICAL TRANSIENT DIRATION (µs)
50
0
0.1
RESET COMPARATOR OVERDRIVE VOLTAGE (% OF VCC)
RESET OCCURS
ABOVE CURVE
1 10 100
TA = 25°C
1985-18 G07
Reset Pulse Width
vs Temperature
280
260
(ms)
240
RST
220
200
180
RESET PULSE WIDTH, t
160
140
–60 –40
–20 20 40 800 100
TEMPERATURE (°C)
60
1985-18 G08
3
Page 4
LTC1985-1.8
U
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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.
V
(Pin 3): 1V Sense, High Impedance Input. If unused
CCA
it can be tied to either V
CC3
or V
CC18
.
W
BLOCK DIAGRA
CC3
5V
–
V
(Pin 4): 1.8V Sense Input and Power Supply Pin.
CC18
This pin is used on the LTC1985 to provide power to the
part when the voltage on V
on V
. Bypass to ground with a ≥0.1µF ceramic
CC3
is greater than the voltage
CC18
capacitor.
V
(Pin 5): 3V Sense Input and Power Supply Pin. This
CC3
pin provides power to the part when the voltage on V
is greater than the voltage on V
. Bypass to ground
CC18
CC3
with a ≥0.1µF ceramic capacitor.
LTC1985-1.8
V
CC18
CCA
+
POWER
DETECT
4
3V
2GND
INTERNAL
V
CC
–
+
–
+
BANDGAP
REFERENCE
200ms PULSE GENERATOR
200ms
DELAY
V
CC3
RST
1
1985-18 BD
4
Page 5
UWW
TI I G DIAGRA
LTC1985-1.8
VCC Monitor Timing
V
V
CCX
RTX
t
RST
RST
WUUU
APPLICATIO S I FOR ATIO
Supply Monitoring
The LTC1985 is a low power, high accuracy triple supply
monitoring cirucit with a single 200ms microprocessor
reset output.
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.
3V or 1.8V Power Detect
The LTC1985 is powered from the 3V input pin (V
the 1.8V input pin (V
), whichever pin has the highest
CC18
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 V
CC18
or V
pin, can power
CC3
the part. This ensures that RST will be low when either
V
CC18
or V
reaches 1V. As long as any one of the V
CC3
inputs is below its predetermined threshold, RST will stay
a logic low. Once all of the VCC inputs rise above their
CC3
) or
CC
1985-18 TD
thresholds, an internal timer is started and RST is released
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.
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 V
CC3
and V
drop below 1V.
CC18
Override Functions
The V
This is an obvious solution since the trip points for V
and V
V
CCA
V
CC3
pin, if unused, can be tied to either V
CCA
will always be greater than the trip point for
CC18
. Likewise, the V
, if unused, can be tied to V
CC18
must always be used. Tying V
CC3
CC3
to V
or V
CC18
CC18
CC3
CC3
and
.
.
operating off of a 1.8V supply will result in the continuous
assertion of RST.
5
Page 6
LTC1985-1.8
U
TYPICAL APPLICATIO S
ADJUSTABLE SUPPLY
OR DC/DC FEEDBACK
Triple Supply Monitor (3V, 1.8V and Adjustable)
LTC1985-1.8
DIVIDER
5
3V
1.8V
R1*
R2*
*TO PRESERVE THRESHOLD ACCURACY, SET PARALLEL
COMBINATION OF R1 AND R2 ≤ 66.5k
V
CC3
4
V
CC18
3
V
CCA
2
GND
RST
1
SYSTEM RESET
1985-18 TA02
Dual Supply Monitor (3V and 1.8V, Defeat V
LTC1985-1.8
3V SYSTEM RESET
1.8V
5
4
3
2
V
CC3
V
CC18
V
CCA
GND
RST
Dual Supply Monitor (3V Plus Adjustable)
LTC1985-1.8
ADJUSTABLE
SUPPLY
R1*
5
3V
4
3
2
R2*
V
CC3
V
CC18
V
CCA
GND
RST
1
1985-18 TA03
1
SYSTEM RESET
1985-18 TA04
CCA
Input)
6
*TO PRESERVE THRESHOLD ACCURACY, SET PARALLEL
COMBINATION OF R1 AND R2 ≤ 66.5k
Page 7
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TYPICAL APPLICATIO S
LTC1985-1.8
Using V
LTC1435
ADJUSTABLE
RESET TRIP
THRESHOLD 2.31V
Tied to DC/DC Feedback Divider
CCA
2.5V
27.4k
1%
V
OSENSE
6
2.26k
1%
22.6k
1%
3V
1.8V
LTC1985-1.8
5
V
CC3
4
V
CC18
3
V
CCA
2
GND
RST
1985-18 TA05
Resistor on RST Output to Ground Ensures RST Valid to VCC = 0V
Typical Application Showing Resistor on RST Output to Ground RST Voltage vs V
ADJUSTABLE
SUPPLY
LTC1985-1.8
5
3V
V
CC3
4
1.8V
V
R1
R2
CC18
3
V
CCA
2
GND
RST
1985-18 TA06
1
R3
100k
4
V
= V
CC3
3
2
1
SYSTEM RESET
with a Resistor on RST to Ground
CC3
= V
CC18
CCA
RST VOLTAGE (V)
1
0
0
1
2
V
CC3
(V)
3
4
1985-18 TA06b
7
Page 8
LTC1985-1.8
TYPICAL APPLICATIO
MANUAL
RESET BUTTON
(NORMALLY OPEN)
PACKAGE DESCRIPTIO
2.60 – 3.00
(0.102 – 0.118)
1.50 – 1.75
(0.059 – 0.069)
U
Triple Supply Monitor with Manual Reset Button
2.5V
= 2.3V
V
TRIP
R3*
10k
5%
*OPTIONAL RESISTOR RECOMMENDED
TO EXTEND ESD TOLERANCE
R1
130k
0.1%
R2
100k
0.1%
1.8V 3V
100nF
100nF
1
RST
5
V
CC3
LTC1985-1.8
4
V
CC18
3
V
CCA
GND
2
V
CCA
V
= (R1 + R2)
TRIP
R2
V
TRIP
R1 = R2
– 1
()
V
CCA
U
Dimensions in inches (millimeters) unless otherwise noted.
S5 Package
5-Lead Plastic SOT-23
(LTC DWG # 05-08-1633)
2.80 – 3.00
0.00 – 0.15
(0.00 – 0.006)
0.90 – 1.45
(0.035 – 0.057)
(0.110 – 0.118)
(NOTE 3)
1985-18 TA02
0.35 – 0.55
(0.014 – 0.022)
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)
0.09 – 0.20
(0.004 – 0.008)
(NOTE 2)
0.35 – 0.50
(0.014 – 0.020)
FIVE PLACES (NOTE 2)
0.90 – 1.30
(0.035 – 0.051)
1.90
(0.074)
REF
0.95
(0.037)
REF
S5 SOT-23 0599
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Timing Specifications
FAIL
8
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear-tech.com
1985i LT/TP 0300 4K • PRINTED IN THE USA
LINEAR TECHNOLOGY CORPORATION 2000
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