LTC6907
Micropower, 40kHz to 4MHz
Resistor Set Oscillator
in SOT-23
U
FEATURES
DESCRIPTIO
■
The LTC®6907 is a precision programmable oscillator that
is versatile, compact and easy to use. Micropower operation benefits portable and battery-powered equipment. At
400kHz, the LTC6907 consumes 36µA on a 3V supply.
■
■
■
■
■
■
■
■
Supply Current: 36µA at 400kHz
1% Frequency Accuracy (from 0°C to 70°C)
Frequency Range: 40kHz to 4MHz
One Resistor Sets the Oscillator Frequency
–40°C to 125°C Operating Temperature Range
Start-Up Time Under 200µs at 4MHz
First Cycle After Power-Up is Accurate
150Ω CMOS Output Driver
Low Profile (1mm) SOT-23 (ThinSOTTM) Package
The LTC6907 is easily programmed according to this
simple formula:
U
APPLICATIO S
■
■
■
■
■
A single resistor programs the oscillator frequency over a
10:1 range with better than 0.65% initial accuracy. The
output frequency can be divided by 1, 3 or 10 to span a
100:1 total frequency range, 40kHz to 4MHz.
Low Cost Precision Programmable Oscillator
Rugged, Compact Micropower Replacement for
Crystal and Ceramic Oscillators
High Shock and Vibration Environments
Portable and Battery-Powered Equipment
PDAs and Cellular Phones
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
ƒOUT
⎧10, DIV Pii n = V +
4MHz ⎛ 50k ⎞
⎪
, N = ⎨3, DIV Pin = Open
=
•⎜
⎟
N
⎝ R SET ⎠
⎪1, DIV Pin = GND
⎩
The LTC6907 is available in the 6-lead SOT-23 (ThinSOT)
package.
Contact LTC Marketing for a version of the part with a
shutdown feature or lower frequency operation.
U
TYPICAL APPLICATIO
Typical Supply Current vs Frequency
Micropower Clock Generator
LTC6907
3V TO 3.6V
V+
OUT
GND
GRD
DIV
SET
1000
40kHz TO 4MHz
÷10
÷3
÷1
RSET
50k TO 500k
6907 TA01
SUPPLY CURRENT (µA)
0.1µF
CLOAD = 5pF
T = 25°C
:
3.3V, –1
:
3.3V, –3
:
3.3V, –10
100
10
10
100
1000
OUTPUT FREQUENCY (kHz)
10000
6907 TA02
6907fa
1
LTC6907
W W
W
AXI U
U
U
W
PACKAGE/ORDER I FOR ATIO
U
ABSOLUTE
RATI GS
(Note 1)
V + ................................................................– 0.3V to 6V
DIV to GND .................................... – 0.3V to (V + + 0.3V)
SET to GND ................................... – 0.3V to (V + + 0.3V)
GRD to GND .................................. – 0.3V to (V + + 0.3V)
Operating Temperature Range (Note 7)
LTC6907C .......................................... – 40°C to 85°C
LTC6907I ............................................ – 40°C to 85°C
LTC6907H ........................................ – 40°C to 125°C
Specified Temperature Range (Note 7)
LTC6907C ............................................... 0°C to 70°C
LTC6907I ............................................ – 40°C to 85°C
LTC6907H ........................................ – 40°C to 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART NUMBER
TOP VIEW
OUT 1
6 V+
GND 2
5 GRD
DIV 3
4 SET
LTC6907CS6
LTC6907IS6
LTC6907HS6
S6 PACKAGE
6-LEAD PLASTIC TSOT-23
S6 PART MARKING*
TJMAX = 150°C, θJA = 200°C/W
LTBTX
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
*The temperature grade is indicated by a label on the shipping container.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full specified
temperature range, otherwise specifications are at TA = 25°C. V+ = 3V to 3.6V, CL = 5pF, Pin 3 = V + unless otherwise noted.
All voltages are with respect to GND.
SYMBOL
∆f
PARAMETER
CONDITIONS
Frequency Accuracy (Notes 2, 3)
V+ = 3V to 3.6V
MIN
400kHz ≤ f ≤ 4MHz
400kHz ≤ f ≤ 4MHz, LTC6907C
400kHz ≤ f ≤ 4MHz, LTC6907I, H
TYP
MAX
UNITS
±0.25
±0.65
±1
±1.3
%
%
%
500
kΩ
●
●
●
RSET
Frequency-Setting Resistor Range
∆f/∆T
Frequency Drift Over Temp (Note 3)
RSET = 158k
±0.005
%/°C
∆f/∆V
Frequency Drift Over Supply (Note 3)
V+ = 3V to 3.6V, 50k ≤ RSET ≤ 500k
0.06
%/V
Timing Jitter (Peak-to-Peak) (Note 4)
Pin 3 = V +, 50k ≤ R
SET ≤ 500k
Pin 3 = Open, 50k ≤ RSET ≤ 500k
Pin 3 = 0V, 50k ≤ RSET ≤ 500k
0.12
0.28
0.60
%
%
%
Sf
Long-Term Stability of Output Frequency
(Note 9)
Pin 3 = V +
Stability Over 1 Year
Stability Over 10 Years
300
888
2809
ppm/√kHr
ppm
ppm
DC
Duty Cycle
V+
Operating Supply Range (Note 8)
IS
Power Supply Current
50
●
●
43
●
3
50
57
%
3.6
V
RSET = 500k, Pin 3 = 0V, RL = 10M
(DIV = 1, fOUT = 400kHz)
V + = 3.6V
V + = 3V
●
●
40
36
55
48
µA
µA
RSET = 50k, Pin 3 = 0V, RL = 10M
(DIV = 1, fOUT = 4MHz)
V + = 3.6V
V + = 3V
●
●
305
275
406
366
µA
µA
VIH
High Level DIV Input Voltage
V+ = 3.6V
V+ = 3V
●
●
VIL
Low Level DIV Input Voltage
V+ = 3.6V
V+ = 3V
●
●
IDIV
DIV Input Current (Note 5)
V + = 3.6V
●
●
Pin 3 = V +
Pin 3 = 0V
3.1
2.6
–2
V
V
1
–1
0.5
0.2
V
V
2
µA
µA
6907fa
2
LTC6907
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full specified
temperature range, otherwise specifications are at TA = 25°C. V+ = 3V to 3.6V, CL = 5pF, Pin 3 = V + unless otherwise noted.
All voltages are with respect to GND.
SYMBOL
VOH
VOL
PARAMETER
CONDITIONS
High Level Output Voltage (Note 5)
V + = 3.6V
IOH = – 100µA
IOH = – 1mA
●
●
3.40
3.10
3.57
3.45
V
V
V + = 3V
IOH = – 100µA
IOH = – 1mA
●
●
2.8
2.5
2.97
2.80
V
V
V + = 3.6V
IOL = 100µA
IOL = 1mA
●
●
0.08
0.25
0.2
0.8
V
V
V + = 3V
IOL = 100µA
IOL = 1mA
●
●
0.07
0.25
0.2
0.8
V
V
Low Level Output Voltage (Note 5)
MIN
TYP
MAX
UNITS
tr
OUT Rise Time (Note 6)
V + = 3.6V
V+ = 3V
10
25
ns
ns
tf
OUT Fall Time (Note 6)
V + = 3.6V
V+ = 3V
10
25
ns
ns
VGS
GRD Pin Voltage Relative to SET Pin
Voltage
–10µA ≤ IGRD ≤ 0.3µA
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: Some frequencies may be generated using two different values of
RSET. For these frequencies, the error is specified assuming that the larger
value of RSET is used.
Note 3: Frequency accuracy is defined as the deviation from the fOUT
equation.
Note 4: Jitter is the ratio of the peak-to-peak deviation of the period to the
mean of the period. This specification is based on characterization and is
not 100% tested.
Note 5: Current into a pin is given as a positive value. Current out of a pin
is given as a negative value.
Note 6: Output rise and fall times are measured between the 10% and
90% power supply levels.
●
–10
10
mV
Note 7: The LTC6907C is guaranteed to meet specified performance from
0°C to 70°C. The LTC6907C is designed, characterized and expected to
meet specified performance from –40°C to 85°C but is not tested or QA
sampled at these temperatures. The LTC6907I is guaranteed to meet
specified performance from –40°C to 85°C.
Note 8: Consult the Applications Information section for operation with
supplies higher than 3.6V.
Note 9: Long term drift on 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 non-linear 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 888ppm at 300ppm/√kHr. Ten
years is 87.7kHr and would yield a drift of 2,809 ppm at 300 ppm/√kHr.
Drift without power applied to the device may be approximated as 1/10th of
the drift with power, or 30ppm/√kHr for a 300ppm/√kHr device.
6907fa
3
LTC6907
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Typical Frequency Error
vs Temperature
Typical Frequency Error
vs Power Supply Voltage
0.060%
–0.020%
FREQUENCY ERRROR (%)
FREQUENCY ERROR (%)
FREQUENCY ERROR (%)
0.000%
0.4%
0.2%
RSET = 50k
0%
–0.2%
RSET = 500k
–0.4%
–0.6%
–0.040%
RSET = 50k
RSET = 500k
3
3.1
3.2
3.3
3.4
SUPPLY VOLTAGE (V)
3.5
3.6
0.050%
0.000%
–0.050%
–0.100%
–0.8%
–1.0%
–45 –25 –5
15 35 55 75 95 115 135
TEMPERATURE (°C)
6907 G01
–0.150%
0.75
RSET VOLTAGE (V)
SUPPLY CURRENT (µA)
SUPPLY CURRENT (µA)
0.7
700
600
500
400
RSET = 50k, 3.0V
RSET = 50k, 3.6V
RSET = 500k, 3.0V
RSET = 500k, 3.6V
300
200
100
1000
OUTPUT FREQUENCY (kHz)
0
10000
10
30
40
50
20
LOAD CAPACITANCE (pF)
0.6
0.55
0.45
0
10
0.65
0.5
100
10
V+ = 3V
T = 25°C
800
100
600
VSET vs Temperature (VSET is the
Voltage Measured at the SET Pin)
900
:
3.3V, –3
500
200
300
400
SET RESISTOR (k OHMS)
0.8
1000
CLOAD = 5pF
T = 25°C
:
3.3V, –10
100
6907 G03
Typical Supply Current
vs Load Capacitance
:
3.3V, –1
0
6907 G02
Typical Supply Current
vs Frequency
1000
T = 25°C
V+ = 3V
CLOAD = 5pF
0.100%
0.6%
0.020%
–0.060%
0.150%
+ = 3V
V+
V
0.8% CLOAD = 5pF
T = 25°C
CLOAD = 5pF
0.040%
Typical Frequency Error vs RSET
1.0%
60
0.4
–45 –25 –5
15 35 55 75 95 115 135
TEMPERATURE (°C)
6907 G06
6907 G05
6907 G04
Output Waveform, 400kHz
Output Waveform, 4MHz
V+ = 3.3V
0.5V/DIV
0.5V/DIV
V+ = 3.3V
6907 G08
6907 G07
500ns/DIV
50ns/DIV
6907fa
4
LTC6907
U
U
U
PI FU CTIO S
OUT (Pin 1): Oscillator Output. The OUT pin swings from
GND to V+ with an output resistance of approximately
150Ω. For micropower operation, the load resistance
must be kept as high as possible and the load capacitance
as low as possible.
GND (Pin 2): Ground.
or better temperature coefficient. For lower accuracy
applications, an inexpensive 1% thick-film resistor may be
used. Limit the capacitance in parallel with RSET to less
than 10pF to reduce jitter and to ensure stability. The
voltage on the SET pin is approximately 650mV at 25°C
and decreases with temperature by about –2.3mV/°C.
DIV (Pin 3): Divider Setting Input. This three-level input
selects one of three internal digital divider settings, determining the value of N in the frequency equation. Tie to GND
for ÷1, leave floating for ÷3 and tie to V+ for ÷10. When left
floating, the LTC6907 pulls Pin 3 to mid-supply with a
2.5M resistor. When Pin 3 is floating, care should be taken
to reduce coupling from the OUT pin and its trace to Pin 3.
Coupling can be reduced by increasing the physical space
between traces or by shielding the DIV pin with grounded
metal.
GRD (Pin 5): Guard Signal. This pin can be used to reduce
PC board leakage across the frequency setting resistor,
RSET. The GRD pin is held within a few millivolts of the SET
pin and shunts leakage current away from the SET pin. To
control leakage, connect a bare copper trace (a trace with
no solder mask) to GRD and loop it around the SET pin and
all PC board metal connected to SET. Careful attention to
board layout and assembly can prevent leakage currents.
The use of a guard ring provides additional shielding of
leakage currents from the SET pin and is optional. If
unused, the GRD pin should be left unconnected.
SET (Pin 4): Frequency Setting Resistor Input. Connect a
resistor, RSET, from this pin to GND to set the oscillator
frequency. For best performance use a precision metal or
thin-film resistor of 0.1% or better tolerance and 50ppm/°C
V+ (Pin 6): Voltage Supply (3V to 3.6V). A 0.1µF
decoupling capacitor should be placed as close as possible to this pin for best performance.
W
BLOCK DIAGRA
6
2
V+
FREQUENCY-TO-CURRENT
CONVERTERS
V+
5M
fOSC
GND
IFB
THREE-LEVEL
INPUT
DETECTOR
IFB
DIV
3
5M
VSET ≅ VGRD ≅ 650mV
VSET
4
SET
RSET
ISET = IFB
DIVIDER
SELECT
VSET
BUFFER
5
GRD
VSET
–
+
OP AMP
VOLTAGE
CONTROLLED
OSCILLATOR
(MASTER OSCILLATOR)
fOSC = 4MHz •
150Ω DRIVER
fOSC
PROGRAMMABLE
DIVIDER (n)
(÷1, ÷3, ÷10)
OUT
1
50kΩ
RSET
6907 BD
6907fa
5
LTC6907
TEST CIRCUIT
CTEST
LTC6907
SUPPLY
VOLTAGE
+
OUT
GND
GRD
DIV
SET
V
EQUIVALENT CIRCUIT OF
OSCILLOSCOPE OR
FREQUENCY COUNTER PROBE
0.1µF
RPROBE
10M
CPROBE
RSET
0.01%
10ppm/°C
6907 F01
CTEST = 1/(1/5pF – 1/CPROBE)
= 7.5pF FOR A 15pF SCOPE PROBE
Figure 1. Test Circuit with 5pF Effective Load
U
U U
EQUIVALE T I PUT A D OUTPUT CIRCUITS
6
V+
6
V+
20Ω
4
SET
6
1k
5
V+
GRD
200Ω
TOTAL OUTPUT
RESISTANCE
800pF
2
GND
2
6907 F02
Figure 2. V + Pin
6
GND
2
6907 F03
Figure 3. SET Pin
V+
6
DIV
6907 F04
Figure 4. GRD Pin
V+
fOUT
5M
3
GND
1
OUT
150Ω
5M
2
GND
6907 F05
Figure 5. DIV Pin
2
GND
6907 F06
Figure 6. OUT Pin
6907fa
6
LTC6907
U
THEORY OF OPERATIO
The LTC6907 is a precision, resistor programmable oscillator (see Block Diagram). It generates a square wave at
the OUT pin with a period directly proportional to the value
of an external resistor, RSET. A feedback circuit measures
and controls the oscillator frequency to achieve the highest possible accuracy. In equilibrum, this circuit ensures
that the current in the SET pin, ISET, is balanced by IFB. IFB
is proportional to the master oscillator frequency, so we
have the relationship:
ISET = IFB = VSET • ƒOSC • COSC
(1)
Where COSC is a precision internal capacitor:
COSC = 5pF for the LTC6907
Solving for the oscillator period:
tOSC =
1
ƒOSC
=
so
tOSC =
(2)
This is the fundamental equation for the LTC6907. It holds
regardless of how the SET pin is driven. When a resistor,
RSET, is connected from the SET pin to ground, we have
the relationship:
VSET
= RSET
ISET
ƒOSC
= RSET • COSC
(4)
The period and frequency are determined exclusively by
RSET and the precision internal capacitor. Importantly, the
value of VSET is immaterial, and the LTC6907 maintains its
accuracy even though VSET is not a precision reference
voltage.
The digital dividers shown in the Block Diagram further
divide the master oscillator frequency by 1, 3 or 10
producing:
ƒOUT =
VSET
• COSC
ISET
1
ƒOSC
N
(5)
and
tOUT = N • tOSC
(6)
Table 1 gives specific frequency and period equations for
the LTC6907. The Applications Information section gives
further detail and discusses alternative ways of setting the
LTC6907 output frequency.
(3)
Table 1. Output Frequency Equations
PART NUMBER
FREQUENCY
LTC6907
ƒOUT
4MHz ⎛ 50k ⎞
•⎜
=
N
⎝ RSET ⎟⎠
PERIOD
⎛R ⎞
tOUT = N • 250 ns • ⎜ SET ⎟
⎝ 50k ⎠
DIVIDER RATIOS
⎧10, DIV Pin = V +
⎪
N = ⎨3, DIV Pin = Open
⎪1, DIV Pin = GND
⎩
6907fa
7
LTC6907
U
W
U U
APPLICATIO S I FOR ATIO
10000
The LTC6907 contains a master oscillator followed by a
digital divider (see Block Diagram). RSET determines the
master oscillator frequency and the three level DIV pin sets
the divider ratio, N. The range of frequencies accessible in
each divider ratio overlap, as shown in Figure 7. This
figure is derived from the equations in Table 1. For any
given frequency, power can be minimized by minimizing the master oscillator frequency. This implies maximizing RSET and using the lowest possible divider ratio,
N. The relationship between RSET, N and the unloaded
power consumption is shown in Figure 8. The supply
current decreases for large values of RSET. Refer to the
section titled “Jitter and Divide Ratio.”
OUTPUT FREQUENCY (kHz)
Selecting RSET and the Divider Ratio
÷1
÷3
÷10
1000
100
10
10
100
RSET (kΩ)
1000
6907 F07
Figure 7. RSET vs Desired Output Frequency
160
140
The supply current of the LTC6907 has four current
components:
120
• Constant (Independent V+, ƒOUT and CLOAD)
• Proportional to ISET (which is the current in RSET)
• Proportional to V+, ƒOUT and CLOAD
• Proportional to V+ and R
SUPPLY CURRENT (µA)
Minimizing Power Consumption
ISUPPLY
CLOAD = 0
V+ = 3V
:
DIV = –1
TA = 25°C
100
80
60
40
20
0
LOAD
10
An approximate expression for the total supply current is:
100
RSET (kΩ)
1000
6907 F08
I+ ≅ 7µA + 6 • ISET + V + • ƒOUT • (CLOAD + 5pF ) +
V+
2 • RLOAD
or, in terms of VSET ,
V
V+
I ≅ 7µA + 6 • SET + V + • ƒOUT • (CLOAD + 5pF ) +
RSET
2 • RLOAD
+
VSET is approximately 650mV at 25°C, but varies with
temperature. This behavior is shown in the Typical Performance Characteristics.
Power can be minimized by maximizing RSET, minimizing
the load on the OUT pin and operating at lower frequencies. Figure 9 shows total supply current vs frequency
under typical conditions. Below 100kHz the load current is
negligible for the 5pF load shown.
Figure 8. Unloaded Supply Current vs RSET
Guarding Against PC Board Leakage
The LTC6907 uses relatively large resistance values for
RSET to minimize power consumption. For RSET = 500k,
the SET pin current is typically only 13µA. Thus, only 13nA
leaking into the SET pin causes a 0.1% frequency error.
Similarly, 500M of leakage resistance across RSET
(1000 • RSET) causes the same 0.1% error.
Achieving the highest accuracy requires controlling potential leakage paths. PC board leakage is aggravated by
both dirt and moisture. Effective cleaning is a good first
step to minimizing leakage.
Another effective method for controlling leakage is to shunt
the leakage current away from the sensitive node through
a low impedance path. The LTC6907 provides a signal on
the GRD pin for this purpose. Figure 10 shows a PC board
6907fa
8
LTC6907
U
W
U U
APPLICATIO S I FOR ATIO
SUPPLY CURRENT (µA)
1000
Power Supply Rejection
CLOAD = 5pF
T = 25°C
The LTC6907 has a very low supply voltage coefficient,
meaning that the output frequency is nearly insensitive to
the DC power supply voltage. In most cases, this error
term can be neglected.
:
3.3V, –1
:
3.3V, –3
:
3.3V, –10
100
10
10
100
1000
OUTPUT FREQUENCY (kHz)
10000
6907 F09
Figure 9. Supply Current vs Frequency over DIV Settings
layout that uses the GRD pin and a “guard ring” to absorb
leakage currents. The guard ring surrounds the SET pin
and the end of RSET to which it is connected. The guard ring
must have no solder mask covering it to be effective. The
GRD pin voltage is held within a few millivolts of the SET
pin voltage, so any leakage path between the SET pin and
the guard ring generates no leakage current.
Start-Up Time
When the LTC6907 is powered up, it holds the OUT pin
low. After the master oscillator has settled, the OUT pin is
enabled and the first output cycle is accurate. The time
from power-up to the first output transition is given
approximately by:
tSTART ≅ 64 • tOSC + 100µs
The digital divider ratio, N, does not affect the startup time.
OUT
V+
Operating the LTC6907 with Supplies Higher
Than 3.6V
The LTC6907 may also be used with supply voltages
between 3.6V and 5.5V under very specific conditions. To
ensure proper functioning above 3.6V, a filter circuit must
be attached to the power supply and located within 1cm of
the device. A simple RC filter consisting of a 100Ω resistor
and 1µF capacitor (Figure 11) will ensure that supply
resonance at higher supply voltages does not induce
unpredictable oscillator behavior. Accuracy under higher
supplies may be estimated from the typical Frequency vs
Supply Voltage curves in the Typical Performance Characteristics section of this data sheet.
V+
3.6V TO 5.5V DC
LTC6907
1
High frequency noise on the power supply (V+) pin has the
potential to interfere with the LTC6907’s master oscillator.
Periodic noise, such as that generated by a switching
power supply, can shift the output frequency or increase
jitter. The risk increases when the fundamental frequency
or harmonics of the noise fall near the master oscillator
frequency. It is relatively easy to filter the LTC6907 power
supply because of the very low supply current. For example, an RC filter with R = 160Ω and C = 10µF provides
a 100Hz lowpass filter while dropping the supply voltage
only about 10mV.
NO SOLDER MASK
OVER THE GUARD RING
6
100Ω
GRD
2
3
5
GND
DIV
SET
1µF
GUARD
RING
4
LTC6907
V+
OUT
GND
GRD
DIV
SET
RSET
RSET
NO LEAKAGE
CURRENT
6907 F11
Figure 11. Using the LTC6907 at Higher Supply Voltages
LEAKAGE
CURRENT
6907 F10
Figure 10. PC Board Layout with Guard Ring
6907fa
9
LTC6907
U
W
U U
APPLICATIO S I FOR ATIO
Alternative Methods for Setting the Output Frequency
Any means of sinking current from the SET pin will control
the output frequency of the LTC6907. Equation 2 (repeated below) gives the fundamental relationship between
frequency and the SET pin voltage and current:
tOSC =
1
ƒOSC
=
VSET
• 5pF
ISET
Figure 12 and Figure 13 show a current controlled oscillator and a voltage controlled oscillator. These circuits are
not highly accurate if used alone, but can be very useful if
they are enclosed in an overall feedback circuit such as a
phase-locked loop.
(2)
LTC6907
V+
This equation shows that the LTC6907 converts conductance (ISET/VSET) to frequency or, equivalently, converts
resistance (RSET = VSET/ISET) to period.
VSET is the voltage across an internal diode, and as such
it is given approximately by:
VSET ≅ VT • Loge
ISET
IS
4MHz TO 400kHz
V+
OUT
GND
GRD
DIV
SET
10k
49.9k
6907 F12
Figure 12. Current Controlled Oscillator
LTC6907
⎛
⎞
ISET
≅ 25.9mV • Loge ⎜
⎟ – 2.3mV/ °C
⎝ 82 • 10 –18 A ⎠
V+
V+
OUT
GND
GRD
DIV
SET
499k
where
0µA
TO 11.25µA
4MHz TO 400kHz
RSET
56.2k
VCTRL
0V TO 0.675V (VSET)
6907 F13
VT = kT/q = 25.9mV at T = 300°K (27°C)
IS ≅ 82 • 10–18 Amps
(IS is also temperature dependent)
VSET varies with temperature and the SET pin current. The
response of VSET to temperature is shown in the Typical
Performance graphs. VSET changes approximately –2.3mV/
°C. At room temperature VSET increases 18mV/octave or
60mV/decade of increase in ISET.
If the SET pin is driven with a current source generating
ISET, the oscillator output frequency will be:
ƒOSC ≅
Figure 13. Voltage Controlled Oscillator
Jitter and Divide Ratio
At a given output frequency, a higher master oscillator
frequency and a higher divide ratio will result in lower jitter
and higher power supply dissipation. Indeterminate jitter
percentage will decrease by a factor of slightly less than
the square root of the divider ratio, while determinate jitter
will not be similarly attenuated. Please consult the specification tables for typical jitter at various divider ratios.
ISET
5pF
ISET
⎛
⎞
25.9mV • Loge ⎜
– 2.3mV / °C
⎝ 82 • 10 –18 A ⎟⎠
6907fa
10
LTC6907
U
PACKAGE DESCRIPTIO
S6 Package
6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636)
0.62
MAX
2.90 BSC
(NOTE 4)
0.95
REF
1.22 REF
3.85 MAX 2.62 REF
1.4 MIN
2.80 BSC
1.50 – 1.75
(NOTE 4)
PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.30 – 0.45
6 PLCS (NOTE 3)
0.95 BSC
0.80 – 0.90
0.20 BSC
0.01 – 0.10
1.00 MAX
DATUM ‘A’
0.30 – 0.50 REF
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
0.09 – 0.20
(NOTE 3)
1.90 BSC
S6 TSOT-23 0302
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
6907fa
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.
11
LTC6907
U
TYPICAL APPLICATIO S
Sine Wave Oscillator
Trimming the Frequency
Setting Frequency to 0.1%
Resolution with Standard Resistors
LTC6907
1MHz
0.1µF
LTC6907
3V TO 3.6V
0.1µF
OUT
GND
GRD
DIV
SET
3V TO 3.6V
3V TO 3.6V
0.1µF
40kHz TO 4MHz
LTC6907
1k
V+
V+
OUT
GND
GRD
DIV
SET
0.1µF
L1
100µH
÷10
÷3
÷1
C1
220pF
RSET
200k
V+
OUT
GND
GRD
DIV
SET
RA
97.6k
RA
RA < RB/10
1% THIN FILM
RB
50k TO 500k
0.1% THIN FILM
6907 TA05
2MHz WITH
±2.5% RANGE
RB
5k
6907 TA03
6907 TA04
Low Power 62.5Hz to 6.25kHz Sine Wave Generator (IQ < 1.5mA)
fOSC = 400kHz TO 40kHz
3V
1
1µF
2
3
5
V+
OUT
LTC6907
GND GRD
DIV
56.2k
4
SET
VCTRL
0V–0.6V
499k
fOSC
C4
1µF
74HC4520
1
3V
2
16
C2
0.1µF
10
7
8
9
15
Q1A
CLOCK A
Q2A
ENABLE A
Q3A
VDD
ENABLE B
Q4A
RESET A
Q1B
VSS
Q2B
CLOCK B
Q3B
RESET B
Q4B
3
÷2
4
÷4
5
÷8
6
÷16
11 ÷32
12 ÷64
LTC1067-50
3V
C3
0.1µF
1
2
3
R61
10k
4
R51 5.11k
R31 51.1k
R11
100k
6
7
R21 20k
13 ÷128
14 ÷256
5
8
V+
CLK
NC
AGND
+
–
V
V
SA
SB
LPA
LPB
BPA
BPB
HPA/NA HPB/NB
INV A
INV B
16
15
14
R62 14k
13
R52
5.11k
12
11
R32 51.1k
SINEWAVE
OUT
10
9
R22 20k
fSINE = fOSC
64
RH1 249k
fOSC
64
RL1 51.1k
6907 TA06
CLOCK-TUNABLE LOWPASS FILTER WITH
A STOPBAND NOTCH AT THE 3rd HARMONIC
fOSC
•3
64
(
)
RELATED PARTS
PART NUMBER
LTC1799
LTC6900
LTC6902
LTC6903/LTC6904
LTC6905
LTC6905-XXX
LTC6906
DESCRIPTION
1kHz to 33MHz ThinSOT Oscillator, Resistor Set
1kHz to 20MHz ThinSOT Oscillator, Resistor Set
Multiphase Oscillator with Spread Spectrum Modulation
1kHz to 68MHz Serial Port Programmable Oscillator
17MHz to 170MHz ThinSOT Oscillator, Resistor Set
Fixed Frequency ThinSOT Oscillator Family, up to 133MHz
Micropower 10kHz to 1MHz ThinSOT Oscillator, Resistor Set
COMMENTS
Wide Frequency Range
Low Power, Wide Frequency Range
2-, 3- or 4-Phase Outputs
0.1% Frequency Resolution, I2C or SPI Interface
High Frequency, 100µsec Startup, 7ps RMS Jitter
No Trim Components Required
12µA Supply Current of 100kHz, 0.65% Frequency Accuracy
6907fa
12
Linear Technology Corporation
LT 0506 REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2005
工商网监
湘ICP备2023018690号
