LTC1985-1.8
Micropower Precision
Triple Supply Monitor
with Push-Pull Reset Output
in a 5-Lead SOT-23 Package
FEATURES
s
s
s
s
s
s
s
s
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
CC3
≥
1V or V
CC18
≥
1V
3V Active-Low Push-Pull Reset Output
5-Lead SOT-23 Package
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.
The RST output is guaranteed to be in the correct state for
V
CC18
or V
CC3
down to 1V. The LTC1985 may also be
configured to monitor any one or two V
CC
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.
APPLICATIO S
s
s
s
s
s
Desktop Computers
Notebook Computers
Intelligent Instruments
Portable Battery-Powered Equipment
Network Servers
TYPICAL APPLICATION
DC/DC
CONVERTER
3V
1.8V
2.5V
SYSTEM
LOGIC
1
5
V
CC3
RST
LTC1985-1.8
4
0.1µF
R1
130k
1% 3
0.1µF
R2
100k
1%
V
CC18
V
CCA
GND
2
1985-1.8 TA01
U
U
U
1
LTC1985-1.8
ABSOLUTE
(Notes 1, 2)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RST 1
GND 2
V
CCA
3
4 V
CC18
5 V
CC3
V
CC3
, V
CC18
, V
CCA
...................................... – 0.3V to 7V
RST .......................................... – 0.3V to (V
CC3
+ 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
LTC1985ES5-1.8
S5 PART MARKING
LTNM
S5 PACKAGE
5-LEAD PLASTIC SOT-23
T
JMAX
= 125°C,
θ
JA
= 250°C/W
Consult factory for Industrial and Military grade parts.
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specificaitons are at T
A
= 25°C. V
CC3
= 3V, V
CC18
= 1.8V, V
CCA
= V
CC3
unless otherwise noted.
SYMBOL
V
RT3
V
RT18
V
RTA
V
CCOP
I
VCC3
I
VCC18
I
VCCA
t
RST
t
UV
V
OL
PARAMETER
Reset Threshold V
CC3
Reset Threshold V
CC18
Reset Threshold V
CCA
V
CC3
, V
CC18
Operating Voltage
V
CC3
Supply Current
V
CC18
Supply Current
V
CCA
Input Current
Reset Pulse Width
V
CC
Undervoltage Detect to RST
Output Voltage Low, RST
CONDITIONS
V
CC3
Input Threshold
V
CC18
Input Threshold
V
CCA
Input Threshold
RST in Correct Logic State
V
CC18
> V
CC3
V
CC18
< V
CC3
, V
CC3
= 3V (Note 4)
V
CC18
< V
CC3
, V
CC18
= 1.8V (Note 4)
V
CCA
= 1V
RST Low (Note 5)
V
CC18
, V
CC3
or V
CCA
Less Than Reset (Note 5)
Threshold V
RT
by More Than 1%
I
SINK
= 2.5mA, V
CC3
= 3V, V
CC18
= 0V
I
SINK
= 100µA, V
CC3
= 1V, V
CC18
= 0V
I
SINK
= 100µA, V
CC3
= 0V, V
CC18
= 1V
I
SINK
= 100µA, V
CC3
= 1V, V
CC18
= 1V
I
SOURCE
= 200µA
q
q
q
q
q
q
q
q
q
q
q
q
q
q
ELECTRICAL CHARACTERISTICS
MIN
2.760
1.656
0.985
1
TYP
2.805
1.683
1.000
1
10
1
MAX
2.850
1.710
1.015
7
2
20
2
15
280
UNITS
V
V
V
V
µA
µA
µA
nA
ms
µs
– 15
140
0
200
110
0.15
0.05
0.05
0.05
0.4
0.3
0.3
0.3
V
OH
Output Voltage High, RST
0.8V
CC3
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
extended temperature limits of – 40°C to 85°C but are not tested at these
temperatures.
Note 4:
Both V
CC3
and V
CC18
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 (V
RTX
) until RST passes through 1.5V.
2
U
V
V
V
V
V
W
U
U
W W
W
LTC1985-1.8
TYPICAL PERFOR A CE CHARACTERISTICS
I
VCC3
vs Temperature
15
14
13
12
I
VCC18
(µA)
I
VCC3
(µA)
1.2
1.1
1.0
0.9
0.8
0.7
0.6
INPUT CURRENT (nA)
11
10
9
8
7
6
5
– 60 –40 – 20 0 20 40 60
TEMPERATURE (°C)
80
100
V
CCA
Threshold Voltage
vs Temperature
1.015
2.845
2.835
2.825
2.815
2.805
2.795
2.785
2.775
V
CC18
THRESHOLD VOLTAGE, V
RT18
(V)
V
CCA
THRESHOLD VOLTAGE, V
RTA
(V)
V
CC3
THRESHOLD VOLTAGE, V
RT3
(V)
1.010
1.005
1.000
0.995
0.990
0.985
–60 –40 –20 0
20 40 60
TEMPERATURE (°C)
Typical Transient Duration
vs Comparator Overdrive
450
TYPICAL TRANSIENT DURATION (µs)
400
350
300
250
200
150
100
50
0
0.1
1
10
100
RESET COMPARATOR OVERDRIVE VOLTAGE (% OF V
CC
)
1985-18 G07
RESET OCCURS
ABOVE CURVE
RESET PULSE WIDTH, t
RST
(ms)
220
200
180
160
140
–60 –40 –20
I
SINK
(mA)
U W
1985-18 G01
I
VCC18
vs Temperature
1.5
1.4
1.3
V
CC3
= 3V
V
CCA
= 3V
V
CC18
= 1.8V
2.0
1.5
1.0
0.5
0
– 0.5
–1.0
–1.5
80
100
V
CCA
Input Current
vs Input Voltage
T
A
= 25°C
0.5
– 60 –40 – 20 0 20 40 60
TEMPERATURE (°C)
– 2.0
0.80 0.85 0.90 0.95 1 1.05 1.10 1.15 1.20
INPUT VOLTAGE (V)
1985-18 G03
1985-18 G02
V
CC3
Threshold Voltage
vs Temperature
1.710
1.700
1.690
1.680
1.670
1.660
V
CC18
Threshold Voltage
vs Temperature
80
100
2.765
– 60 –40 – 20 0 20 40 60
TEMPERATURE (°C)
80
100
1.650
–60 –40 –20 0
20 40 60
TEMPERATURE (°C)
80
100
1985-18 G04
1985-18 G05
1985-18 G06
Reset Pulse Width
vs Temperature
T
A
= 25°C
280
260
240
I
SINK
vs Supply Voltage
8
7
6
V
OL
= 0.4V
5
4
V
OL
= 0.2V
3
2
1
0
T
A
= 25°C
0
20
40
60
80
100
0
0.5
TEMPERATURE (°C)
1985-18 G08
1.0
1.5
2.0
V
CC3
OR V
CC18
(V)
2.5
3.0
1985-18 • G09
3
LTC1985-1.8
TYPICAL PERFOR A CE CHARACTERISTICS
RST High Level Output Voltage vs
Output Source Current
3.5
3.0
2.5
V
OH
(V)
V
CC3
= V
CC18
= V
CCA
= 3.0V
V
OL
(V)
1.0
0.8
0.6
0.4
V
OL
(V)
2.0
– 40°C
1.5
1.0
85°C
0.5
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
I
SOURCE
(mA)
1985-81 G10
25°C
PI FU CTIO S
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.
V
CCA
(Pin 3):
1V Sense, High Impedance Input. If unused
it can be tied to either V
CC3
or V
CC18
.
V
CC18
(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 V
CC18
is greater than the voltage
on V
CC3
. Bypass to ground with a
≥
0.1µF ceramic
capacitor.
V
CC3
(Pin 5):
3V Sense Input and Power Supply Pin. This
pin provides power to the part when the voltage on V
CC3
is greater than the voltage on V
CC18
. Bypass to ground
with a
≥
0.1µF ceramic capacitor.
4
U W
RST Voltage Output Low vs
Output Sink Current
1.8
1.6
1.4
85°C
1.2
– 40°C
2.0
1.5
1.0
0.5
3.0
RST Voltage Output Low vs
Output Sink Current
V
CC3
= V
CC18
= 3V
V
CCA
= 0V
85°C
– 40°C
25°C
V
CC3
= V
CC18
= 1.8V
V
CCA
= 0V
25°C
2.5
0.2
0
0
2
4
8
I
SINK
(mA)
6
10
12
14
0
0
5
10
15
25 30
I
SINK
(mA)
20
35
40
45
1985-81 G11
1985-81 G12
U
U
U
LTC1985-1.8
BLOCK DIAGRA
V
CC3
5
POWER
DETECT
V
CC18
4
V
CC
INTERNAL
V
CC3
V
CCA
3
GND 2
TI I G DIAGRA
V
CCX
V
RTX
t
UV
t
RST
1.5V
1985-18 TD
RST
+
+
+
–
–
–
W
W
LTC1985-1.8
200ms PULSE GENERATOR
200ms
DELAY
1 RST
BANDGAP
REFERENCE
1985-18 BD
UW
V
CC
Monitor Timing
5
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