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参数资料
| 型号： | LTC6992CDCB6-2#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, PDSO6 |
| 封装： | 2 X 3 MM, LEAD FREE, PLASTIC, MO-229TBD, DFN-6 |
| 文件页数： | 13/32页 |
| 文件大小： | 322K |
| 代理商： | LTC6992CDCB6-2#PBF |
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LTC6992-1/LTC6992-2/
LTC6992-3/LTC6992-4
20
69921234p
APPLICATIONS INFORMATION
Step 4: Select RSET
Calculate the correct value for RSET using Equation (1b).
RSET =
1MHz 50k
4 20kHz
= 625k
Since 625k is not available as a standard 1% resistor,
substitute 619k if a 0.97% frequency shift is acceptable.
Otherwise, select a parallel or series pair of resistors such
as 309k and 316k to attain a more precise resistance.
The completed design is shown in Figure 7.
6992 F07
LTC6992-4
MOD
GND
SET
OUT
V+
DIV
R1
976k
DIVCODE = 1
R2
102k
RSET
625k
VMOD
2.25V TO 5.5V
Figure 7. 20kHz PWM Oscillator
Figure 8. Duty Cycle Variation Due to ΔVSET
VMOD (V)
0
DUT
Y
CYCLE
(%)
100
90
70
80
60
50
30
40
20
10
0
0.6
0.2
6992 F08
1
0.4
0.8
ΔVSET = 0mV
ΔVSET = 30mV
ΔVSET = –30mV
Figure 9. Fixed-Frequency, Arbitrary Duty Cycle Oscillator
6992 F09
LTC6992-X
MOD
GND
SET
OUT
V+
DIV
R1
R2
RSET2
RSET1
2.25V TO 5.5V
D
5
4
RSET2
RSET1 RSET2
1
8
Some applications can eliminate
ΔVSET sensitivity by
making VMOD proportional to VSET. For example, Figure 9
shows a simple circuit for generating an arbitrary duty
cycle. The equation for duty cycle does not depend on
VSET at all.
Duty Cycle Sensitivity to ΔVSET
The output duty cycle is proportional to the ratio of VMOD/
VSET. Since VSET can vary up to ±30mV from 1V it can
effectively gain or attenuate VMOD, as shown below when
ΔVSET is added to the equation.
D
=
VMOD
0.8 VSET +ΔVSET
(
)
1
8
The simplifying assumption of
ΔVSET = 0V creates the po-
tential for additional duty cycle error, which increases with
VMOD, reaching a maximum of 3.4% if ΔVSET = –30mV.
ΔD
VMOD
800mV
ΔVSET
VSET
Dideal +
1
8
ΔVSET
VSET
Figure 8 demonstrates the worst-case impact of this varia-
tion (if VSET is at its 0.97V or 1.03V limits).
This error is in addition to the inherent PWM duty cycle
accuracy spec
ΔD (±4.5%), so care should be taken if ac-
curacy at high duty cycles (VMOD near 0.9V) is critical.
ISET Extremes (Master Oscillator Frequency Extremes)
Pushing ISET outside of the recommended 1.25μA to 20μA
range forces the master oscillator to operate outside of the
62.5kHz to 1MHz range in which it is most accurate.
The oscillator will still function with reduced accuracy
for ISET < 1.25μA. At approximately 500nA, the oscillator
output will be frozen in its current state. The output could
halt in a high or low state. This avoids introducing short
pulses while frequency modulating a very low frequency
output.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC6992CDCB6-2-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:TimerBlox Voltage-Controlled Pulse Width Modulator (PWM) |
| LTC6992CDCB6-3-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:TimerBlox Voltage-Controlled Pulse Width Modulator (PWM) |
| LTC6992CDCB6-3-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:TimerBlox Voltage-Controlled Pulse Width Modulator (PWM) |
| LTC6992CDCB6-4-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:TimerBlox Voltage-Controlled Pulse Width Modulator (PWM) |
| LTC6992CDCB6-4-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:TimerBlox Voltage-Controlled Pulse Width Modulator (PWM) |
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