LTC6908IDCB-1#TRPBF Linear Technology, LTC6908IDCB-1#TRPBF Datasheet - Page 7

• Manufacturer Part Number: LTC6908IDCB-1#TRPBF
• Description: IC OSC PREC LP RES SET 6-DFN
• Manufacturer: Linear Technology
• Type: Oscillator, Siliconr

Specifications of LTC6908IDCB-1#TRPBF

• Frequency: 10MHz
• Voltage - Supply: 2.7 V ~ 5.5 V
• Current - Supply: 1.25mA
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 6-DFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Count: -

OPERATIO
As shown in the Block Diagram, the LTC6908’s master
oscillator is controlled by the ratio of the voltage between
the V
(I
tion (SSFM) is disabled, I
the (V
enabled, I
noise (PRN) signal. Here the I
value uniformly distributed between (I
+ 10%). In this way the frequency of the master oscillator
is modulated to produce an approximately fl at frequency
spectrum that is centered at the frequency set by the I
current, with a bandwidth equal to approximately 20% of
the center frequency.
The voltage on the SET pin is forced to approximately 1.1V
below V
age. This voltage is accurate to ±5% at a particular input
current and supply voltage (see Figure 1). The LTC6908
is optimized for use with resistors between 20k and 400k,
corresponding to output frequencies between 250kHz and
5MHz. Accurate frequencies up to 10MHz (R
are attainable if the supply voltage is greater than 4V. The
R
locks together the (V
This allows the parts to attain excellent frequency accuracy
regardless of the precision of the SET pin voltage. The
master oscillation frequency is:
f
The master oscillator signal is divided by 2 before driving
the output pins, resulting in the simple formula for the
MASTER
MASTER
SET
+
+
resistor, connected between the V
and SET pins and the current entering the SET pin
– V
+
= 20MHz • 10k/R
). When the spread spectrum frequency modula-
MASTER
SET
by the PMOS transistor and its gate bias volt-
Figure 1. V
1.4
1.3
1.2
1.1
1.0
0.9
0.8
) voltage and the R
0.1
T
A
is modulated by a fi ltered pseudorandom
U
= 25°C
+
+
– V
1
– V
SET
MASTER
SET
SET
I
RES
V
) voltage and the current I
+
Variation with I
10
MASTER
= 3V
(µA)
SET
V
+
is strictly determined by
= 5V
resistor. When SSFM is
100
SET
current is a random
– 10%) and (I
+
690812 F01
RES
and SET pins,
1000
SET
= 10k)
SET
SET
SET
.
output frequency, f
When the spread spectrum frequency modulation (SSFM)
is disabled, the frequency f
quency. When SSFM is enabled, 0.9 • f
output frequency and 1.1 • f
frequency.
Both outputs are nominally 50% duty cycle. There are 2
possible output confi gurations for the LTC6908, shown
in Figure 3.
Output Confi gurations
The only difference between the two versions of the
LTC6908 is the phase relationship between the two outputs.
The LTC6908-1 outputs are 180 degrees out of phase and
the LTC6908-2 outputs are 90 degrees out of phase. These
convenient output options are useful in synchronizing the
clocking of multiple phase switching regulator designs. In
very high current applications, a signifi cant improvement
f
OUT
Figure 3. Output Waveforms for LTC6908-1, LTC6908-2
= 10MHz • 10k/R
OUT1
OUT2
OUT1
OUT2
Figure 2. R
100k
10M
LTC6908-1 (COMPLEMENTARY)
LTC6908-2 (QUADRATURE)
10k
1M
LTC6908-1/LTC6908-2
10k
DESIRED OUTPUT FREQUENCY (Hz)
OUT
SET
, below (see Figure 2):
vs Desired Output Frequency
100k
SET
OUT
OUT
is the maximum output
1M
is the fi nal output fre-
OUT
690812 F02
is the minimum
10M
690812 F03
690812fa
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