FEATURES
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LTC6991
TimerBlox: Resettable, Low
Frequency Oscillator
DESCRIPTION
The LTC
®
6991 is a silicon oscillator with a programmable
period range of 1.024ms to 9.54 hours (29.1μHz to 977Hz),
specifically intended for long duration timing events. The
LTC6991 is part of the TimerBlox
®
family of versatile silicon
timing devices.
A single resistor, R
SET
, programs the LTC6991’s internal
master oscillator frequency. The output clock period
is determined by this master oscillator and an internal
frequency divider, N
DIV
, programmable to eight settings
from 1 to 2
21
.
t
OUT
=
N
DIV
• R
SET
• 1.024ms, N
DIV
=
1,8,64,...,2
21
50kΩ
Period Range: 1ms to 9.5 Hours
Configured with 1 to 3 Resistors
<1.5% Maximum Frequency Error
Output Reset Function
2.25V to 5.5V Single Supply Operation
55μA to 80μA Supply Current
(2ms to 9.5hr Clock Period)
500μs Start-Up Time
CMOS Output Driver Sources/Sinks 20mA
–55°C to 125°C Operating Temperature Range
Available in Low Profile (1mm) SOT-23 (ThinSOT
™
)
and 2mm
×
3mm DFN Packages
APPLICATIONS
n
n
n
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n
“Heartbeat” Timers
Watchdog Timers
Intervalometers
Periodic “Wake-Up” Call
High Vibration, High Acceleration Environments
Portable and Battery-Powered Equipment
In normal operation, the LTC6991 oscillates with a 50%
duty cycle. A reset function is provided to truncate the
pulse (reducing the duty cycle). The reset pin can also be
used to prevent the output from oscillating.
The RST and OUT pins can be configured for active-low
or active-high operation using a polarity function.
POL BIT
0
0
1
1
RST PIN
0
1
0
1
OUTPUT STATE
Oscillating
0 (reset)
1 (reset)
Oscillating
L,
LT, LTC, LTM, Linear Technology, TimerBlox and the Linear logo are registered trademarks
and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
For easy configuration of the LTC6991, download the
TimerBlox Designer tool at
www.linear.com/timerblox.
TYPICAL APPLICATION
Low Frequency Pulse Generator
OUT
R
PW
2.26k
RST
C
PW
470pF
R
SET
715k
SET
DIV
R2
392k
t
PULSE
≈ R
PW
PW
≈ 1μs
Clock Period Range over Eight Divider Settings
10Hr
1Hr
CLOCK PERIOD (LOG SCALE)
1μs PULSE WIDTH
60 SECONDS
10Min
1Min
10Sec
1Sec
100ms
10ms
1ms
0
1.25
0.625
1.875
DIV PIN VOLTAGE, V
DIV
(V)
2.5
6991 TA01b
OUT
6991 TA01a
LTC6991
GND
V
+
R1
1M
5V
0.1μF
6991fb
1
LTC6991
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Supply Voltage (V
+
) to GND ........................................6V
Maximum Voltage
on Any Pin ................ (GND – 0.3V) ≤ V
PIN
≤ (V
+
+ 0.3V)
Operating Temperature Range (Note 2)
LTC6991C ............................................–40°C to 85°C
LTC6991I .............................................–40°C to 85°C
LTC6991H .......................................... –40°C to 125°C
LTC6991MP ....................................... –55°C to 125°C
Specified Temperature Range (Note 3)
LTC6991C ................................................ 0°C to 70°C
LTC6991I .............................................–40°C to 85°C
LTC6991H .......................................... –40°C to 125°C
LTC6991MP ....................................... –55°C to 125°C
Junction Temperature ........................................... 150°C
Storage Temperature Range .................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
S6 Package ........................................................... 300°C
PIN CONFIGURATION
TOP VIEW
V
+
1
DIV 2
SET 3
7
6 OUT
5 GND
4 RST
RST 1
GND 2
SET 3
TOP VIEW
6 OUT
5 V
+
4 DIV
DCB PACKAGE
6-LEAD (2mm 3mm) PLASTIC DFN
T
JMAX
= 150°C,
θ
JA
= 64°C/W,
θ
JC
= 10.6°C/W
EXPOSED PAD (PIN 7) CONNECTED TO GND,
PCB CONNECTION OPTIONAL
S6 PACKAGE
6-LEAD PLASTIC TSOT-23
T
JMAX
= 150°C,
θ
JA
= 192°C/W,
θ
JC
= 51°C/W
ORDER INFORMATION
Lead Free Finish
TAPE AND REEL (MINI)
LTC6991CDCB#TRMPBF
LTC6991IDCB#TRMPBF
LTC6991HDCB#TRMPBF
LTC6991CS6#TRMPBF
LTC6991IS6#TRMPBF
LTC6991HS6#TRMPBF
TAPE AND REEL
LTC6991CDCB#TRPBF
LTC6991IDCB#TRPBF
LTC6991HDCB#TRPBF
LTC6991CS6#TRPBF
LTC6991IS6#TRPBF
LTC6991HS6#TRPBF
PART MARKING*
LDWZ
LDWZ
LDWZ
LTDWY
LTDWY
LTDWY
PACKAGE DESCRIPTION
6-Lead (2mm
×
3mm) Plastic DFN
6-Lead (2mm
×
3mm) Plastic DFN
6-Lead (2mm
×
3mm) Plastic DFN
6-Lead Plastic TSOT-23
6-Lead Plastic TSOT-23
6-Lead Plastic TSOT-23
SPECIFIED TEMPERATURE RANGE
0°C to 70°C
–40°C to 85°C
–40°C to 125°C
0°C to 70°C
–40°C to 85°C
–40°C to 125°C
–55°C to 125°C
LTC6991MPS6#TRMPBF
LTC6991MPS6#TRPBF
LTDWY
6-Lead Plastic TSOT-23
TRM = 500 pieces. *Temperature grades are identified by a label on the shipping container.
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
6991fb
2
LTC6991
ELECTRICAL CHARACTERISTICS
SYMBOL
t
OUT
f
OUT
Δf
OUT
Δf
OUT
/ΔT
Δf
OUT
/ΔV
+
PARAMETER
Output Clock Period
Output Frequency
Frequency Accuracy (Note 4)
Frequency Drift Over Temperature
Frequency Drift Over Supply
Long-Term Frequency Stability
Period Jitter (Note 10)
BW
t
S
Analog Inputs
V
SET
ΔV
SET
/ΔT
R
SET
V
DIV
ΔV
DIV
/ΔV
+
Voltage at SET Pin
V
SET
Drift Over Temperature
Frequency-Setting Resistor
DIV Pin Voltage
DIV Pin Valid Code Range (Note 5)
DIV Pin Input Current
Power Supply
V
+
I
S
Operating Supply Voltage Range
Power-On Reset Voltage
Supply Current
R
L
= ∞, R
SET
= 50k
R
L
= ∞, R
SET
= 100k
R
L
= ∞, R
SET
= 800k
V
+
= 5.5V
V
+
= 2.25V
V
+
= 5.5V
V
+
= 2.25V
V
+
= 5.5V
V
+
= 2.25V
l
l
l
l
l
l
l
l
l
l
l
l
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. Test conditions are V
+
= 2.25V to 5.5V, RST = 0V, DIVCODE = 0 to 15
(N
DIV
= 1 to 2
21
), R
SET
= 50k to 800k, R
LOAD
= 5k, C
LOAD
= 5pF unless otherwise noted.
CONDITIONS
MIN
1.024m
29.1μ
29.1μHz ≤ f
OUT
≤ 977Hz
l
l
l
l
TYP
MAX
34,360
977
UNITS
Seconds
Hz
%
%
%/°C
%/V
%/V
ppm/√kHr
ppm
RMS
ppm
RMS
Hz
Cycle
±0.8
±0.005
0.23
0.06
90
15
7
0.4 • f
OUT
1
0.97
50
0
1.00
±75
±1.5
±2.2
0.55
0.16
V
+
= 4.5V to 5.5V
V
+
= 2.25V to 4.5V
(Note 11)
N
DIV
= 1
N
DIV
= 8
Frequency Modulation Bandwidth
Frequency Change Settling Time (Note 9)
1.03
800
V
+
±1.5
±10
V
μV/°C
kΩ
V
%
nA
V
V
μA
μA
μA
μA
μA
μA
Deviation from Ideal
V
DIV
/V
+
= (DIVCODE + 0.5)/16
2.25
135
105
100
80
65
55
5.5
1.95
170
135
130
105
100
85
6991fb
3
LTC6991
ELECTRICAL CHARACTERISTICS
SYMBOL
Digital I/O
PARAMETER
RST Pin Input Capacitance
RST Pin Input Current
High Level RST Pin Input Voltage
Low Level RST Pin Input Voltage
Output Output Current
High Level Output Voltage (Note 7)
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. Test conditions are V
+
= 2.25V to 5.5V, RST = 0V, DIVCODE = 0 to 15
(N
DIV
= 1 to 2
21
), R
SET
= 50k to 800k, R
LOAD
=
∞,
C
LOAD
= 5pF unless otherwise noted.
CONDITIONS
MIN
TYP
2.5
RST = 0V to V
+
(Note 6)
(Note 6)
V
+
= 2.7V to 5.5V
V
+
= 5.5V
V
+
= 3.3V
V
+
= 2.25V
±10
l
l
MAX
UNITS
pF
nA
V
V
mA
V
V
V
V
V
V
V
V
V
V
V
V
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
V
IH
V
IL
I
OUT(MAX)
V
OH
0.7 • V
+
0.3 • V
+
5.45
4.84
3.24
2.75
2.17
1.58
±20
5.48
5.15
3.27
2.99
2.21
1.88
0.02
0.26
0.03
0.22
0.03
0.26
16
24
40
5
1.1
1.7
2.7
1.0
1.6
2.4
V
OL
Low Level Output Voltage (Note 7)
V
+
= 5.5V
V
+
= 3.3V
V
+
= 2.25V
I
OUT
= –1mA
I
OUT
= –16mA
I
OUT
= –1mA
I
OUT
= –10mA
I
OUT
= –1mA
I
OUT
= –8mA
I
OUT
= 1mA
I
OUT
= 16mA
I
OUT
= 1mA
I
OUT
= 10mA
I
OUT
= 1mA
I
OUT
= 8mA
l
l
l
l
l
l
l
l
l
l
l
l
0.04
0.54
0.05
0.46
0.07
0.54
t
RST
Reset Propagation Delay
t
WIDTH
t
r
Minimum Input Pulse Width
Output Rise Time (Note 8)
t
f
Output Fall Time (Note 8)
V
+
= 5.5V
V
+
= 3.3V
V
+
= 2.25V
V
+
= 3.3V
V
+
= 5.5V
V
+
= 3.3V
V
+
= 2.25V
V
+
= 5.5V
V
+
= 3.3V
V
+
= 2.25V
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LTC6991C is guaranteed functional over the operating
temperature range of –40°C to 85°C.
Note 3:
The LTC6991C is guaranteed to meet specified performance from
0°C to 70°C. The LTC6991C is designed, characterized and expected to
meet specified performance from –40°C to 85°C but it is not tested or
QA sampled at these temperatures. The LTC6991I is guaranteed to meet
specified performance from –40°C to 85°C. The LTC6991H is guaranteed
to meet specified performance from –40°C to 125°C. The LTC6991MP is
guaranteed to meet specified performance from –55°C to 125°C.
Note 4:
Frequency accuracy is defined as the deviation from the f
OUT
equation, assuming R
SET
is used to program the frequency.
Note 5:
See Operation section, Table 1 and Figure 2 for a full explanation
of how the DIV pin voltage selects the value of DIVCODE.
Note 6:
The RST pin has hysteresis to accommodate slow rising or falling
signals. The threshold voltages are proportional to V
+
. Typical values can
be estimated at any supply voltage using V
RST(RISING)
≈ 0.55 • V
+
+ 185mV
and V
RST(FALLING)
≈ 0.48 • V
+
– 155mV.
Note 7:
To conform to the Logic IC Standard, current out of a pin is
arbitrarily given a negative value.
Note 8:
Output rise and fall times are measured between the 10% and the
90% power supply levels with 5pF output load. These specifications are
based on characterization.
Note 9:
Settling time is the amount of time required for the output to settle
within ±1% of the final frequency after a 0.5× or 2× change in I
SET
.
Note 10:
Jitter is the ratio of the deviation of the period to the mean of the
period. This specification is based on characterization and is not 100%
tested.
Note 11:
Long-term drift of silicon oscillators is primarily due to the
movement of ions and impurities within the silicon and is tested at 30°C
under otherwise nominal operating conditions. Long-term drift is specified
as ppm/√kHr due to the typically nonlinear nature of the drift. To calculate
drift for a set time period, translate that time into thousands of hours, take
the square root and multiply by the typical drift number. For instance, a
year is 8.77kHr and would yield a drift of 266ppm at 90ppm/√kHr. Drift
without power applied to the device may be approximated as 1/10th of the
drift with power, or 9ppm/√kHr for a 90ppm/√kHr device.
6991fb
4
LTC6991
V = 3.3V, R
SET
= 200k, T
A
= 25°C unless otherwise noted.
Frequency Error vs Temperature
3
GUARANTEED MAX OVER TEMPERATURE
2
1
ERROR (%)
ERROR (%)
0
–1
–2
GUARANTEED MIN OVER TEMPERATURE
R
SET
= 50k
3 PARTS
2
1
ERROR (%)
0
–1
–2
GUARANTEED MIN OVER TEMPERATURE
3
GUARANTEED MAX OVER TEMPERATURE
2
R
SET
= 200k
3 PARTS
1
0
–1
–2
GUARANTEED MIN OVER TEMPERATURE
TYPICAL PERFORMANCE CHARACTERISTICS
+
Frequency Error vs Temperature
3
GUARANTEED MAX OVER TEMPERATURE
R
SET
= 800k
3 PARTS
Frequency Error vs Temperature
–3
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
–3
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
–3
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
6991 G01
6991 G02
6991 G03
Frequency Error vs R
SET
3
GUARANTEED MAX OVER TEMPERATURE
2
3 PARTS
1
ERROR (%)
DRIFT (%)
0
–1
–2
–3
0
200
400
R
SET
(kΩ)
600
800
6991 G04
Frequency Drift vs Supply Voltage
0.5
0.4
0.3
NUMBER OF UNITS
0.2
0.1
0
–0.1
–0.2
REFERENCED TO V
+
= 4.5V
R
SET
= 50k
R
SET
= 200k
R
SET
= 800k
2
4
3
5
SUPPLY VOLTAGE (V)
6
6991 G05
Typical V
SET
Distribution
250
2 LOTS
DFN AND SOT-23
1274 UNITS
200
150
100
GUARANTEED MIN OVER TEMPERATURE
–0.3
–0.4
–0.5
50
0
0.98
0.988
0.996
1.004
V
SET
(V)
1.012
1.02
6991 G06
V
SET
Drift vs I
SET
1.0
0.8
0.6
0.4
DRIFT (mV)
V
SET
(mV)
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
0
5
REFERENCED TO I
SET
= 10μA
10
I
SET
(μA)
15
20
6992 G07
V
SET
Drift vs Supply
1.0
0.8
0.6
0.4
V
SET
(V)
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
2
3
REFERENCED TO V
+
= 4V
4
SUPPLY (V)
5
6991 G08
V
SET
vs Temperature
1.020
1.015
1.010
1.005
1.000
0.995
0.990
0.985
6
0.980
–50
–25
75
0
25
50
TEMPERATURE (°C)
100
125
3 PARTS
6991 G09
6991fb
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