LTC6907HS6#TRM Linear Technology, LTC6907HS6#TRM Datasheet - Page 9

• Manufacturer Part Number: LTC6907HS6#TRM
• Description: SC-Timing, Low Power 10kHz - 1MHz Resistor Programmable Osc
• Manufacturer: Linear Technology

Specifications of LTC6907HS6#TRM

• Lead Free Status / Rohs Status: Not Compliant

APPLICATIO S I FOR ATIO
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 R
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:
The digital divider ratio, N, does not affect the start-
up time.
t
START
Figure 9. Supply Current vs Frequency over DIV Settings
Figure 10. PC Board Layout with Guard Ring
≅ 64 • t
1000
100
10
1
2
3
R
10
SET
C
T = 25°C
OUT
GND
DIV
SET
LOAD
LTC6907
OSC
to which it is connected. The guard ring
= 5pF
U
OUTPUT FREQUENCY (kHz)
GRD
SET
+ 100µs
V
3.3V, –10
100
+
U
:
6
5
4
3.3V, –3 :
6907 F10
1000
3.3V, –1 :
W
NO LEAKAGE
CURRENT
LEAKAGE
CURRENT
NO SOLDER MASK
OVER THE GUARD RING
GUARD
RING
6907 F09
10000
U
Power Supply Rejection
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.
High frequency noise on the power supply (V
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 ex-
ample, an RC filter with R = 160Ω and C = 10µF provides
a 100Hz lowpass filter while dropping the supply voltage
only about 10mV.
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 Charac-
teristics section of this data sheet.
Figure 11. Using the LTC6907 at Higher Supply Voltages
3.6V TO 5.5V DC
V
+
100Ω
1µF
V
GND
DIV
+
LTC6907
GRD
OUT
SET
LTC6907
6907 F11
R
SET
+
) pin has the
6907fa
9