Selecting RSET and the Divider Ratio T" />
參數(shù)資料
型號: LTC6906CS6#TRM
廠商: Linear Technology
文件頁數(shù): 13/14頁
文件大?。?/td> 0K
描述: IC OSC SILICON 1MHZ TSOT23-6
標準包裝: 500
類型: 振蕩器 - 硅
頻率: 10kHz ~ 1MHz
電源電壓: 2.25 V ~ 3.6 V
電流 - 電源: 78µA
工作溫度: 0°C ~ 70°C
封裝/外殼: SOT-23-6 細型,TSOT-23-6
包裝: 帶卷 (TR)
供應商設備封裝: TSOT-23-6
安裝類型: 表面貼裝
其它名稱: LTC6906CS5
LTC6906CS5-ND
LTC6906CS6
LTC6906CS6-ND
LTC6906
8
6906fc
APPLICATIONS INFORMATION
Selecting RSET and the Divider Ratio
The LTC6906 contains a master oscillator followed by a
digital divider (see the Block Diagram). RSET determines
the master oscillator frequency and the DIV pin sets the
divider ratio, N. The range of frequencies accessible in
each divider ratio overlap, as shown in Figure7. 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, where we can clearly
see that supply current decreases for large values of RSET.
For a discussion of jitter and divide ratio, refer to page 11.
Minimizing Power Consumption
The supply current of the LTC6906 has four current
components:
Constant (Independent V+, OUT and CLOAD)
Proportional to ISET (which is the current in RSET)
Proportional to V+, OUT and CLOAD
Proportional to V+ and RLOAD
An approximate expression for the total supply current is:
I+
5μA + 6I
SET + V
+
OUT CLOAD + 5pF
()+
V+
2 RLOAD
5μA + 6
VSET
RSET
+ V+
OUT CLOAD + 5pF
()+
V+
2 RLOAD
VSET is approximately 650mV at 25°C, but varies with
temperature. This behavior is shown in the Typical Per-
formance Characteristics section.
Power can be minimized by maximizing RSET, minimizing
the load on the OUT pin and operating at lower frequen-
cies. Figure 9 shows total supply current vs frequency
under typical conditions. Below 100kHz the load current
is negligible for the 5pF load shown.
Figure 7. RSET vs Desired Output Frequency (LTC6906)
Figure 8. Unloaded Supply Current vs RSET
OUTPUT FREQUENCY (kHz)
R
SET
(kΩ)
1000
10000
1
100
1000
10000
6906 F07
10
100
10
3
1
RSET (kΩ)
50
I SUPPLY
(A)
70
100
1000
6906 F08
30
40
60
80
20
10
0
CLOAD = 0
V+ = 3V
TA = 25°C
Figure 9. Supply Current vs Frequency
MASTER OSCILLATOR FREQUENCY (kHz)
0
POWER
SUPPLY
CURRENT
(A)
10
30
40
50
800
6906 F09
20
400
200
1000
600
1200
60
1
3
10
70
80
V+ = 2.7V
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