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| 型号： | LTC3880EUJ#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 40/112页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 40-QFN |
| 软件下载： | LTpowerPlay™ |
| 标准包装： | 61 |
| 系列： | PolyPhase® |
| PWM 型： | 电流模式 |
| 输出数： | 2 |
| 频率 - 最大： | 1MHz |
| 电源电压： | 4.5 V ~ 24 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 105°C |
| 封装/外壳： | 40-WFQFN 裸露焊盘 |
| 包装： | 管件 |
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LTC3880/LTC3880-1
APPLICATIONS INFORMATION
R SENSE(EQUIV)
DCR (MAXERROR) at T L(MAX)
? V SENSE =
V IN – V OUT V OUT
R1||R2 =
R1 =
; R2 =
R1 = ( V IN(MAX) – V OUT ) ? V OUT
P LOSS
V OUT ( V IN – V OUT )
I RIPPLE =
V OUT ( V IN – V OUT )
V IN ? f OSC ?I RIPPLE
additional errors associated with the proximity of the
temperature sensor element to the inductor.
To scale the maximum inductor DCR to the desired sense
resistor value, use the divider ratio:
RD =
C1 is usually selected to be in the range of 0.047μF to
4.7μF. This forces R1||R2 to be approximately 2k. This
resistance minimizes errors caused by the SENSE pin
leakage currents. Adding optional elements R3 and C2
shown in Figure 18a will minimize offset errors associated
with these leakage currents.
The equivalent resistance R1||R2 is scaled to the room
temperature inductance and maximum DCR:
L
( DCR at 20 ° C ) ? C1
The sense resistor values are:
R1||R2 R1?RD
RD 1– RD
The maximum power loss in R1 is related to the duty
cycle, and will occur in continuous mode at the maximum
input voltage:
R1
Ensure that R1 has a power rating higher than this value.
If high efficiency is necessary at light loads, consider this
power loss when deciding whether to use DCR sensing or
sense resistors. Light load power loss can be modestly
higher with a DCR network than with a sense resistor
due to the extra switching losses incurred through R1.
However, DCR sensing eliminates a sense resistor, reduc-
ing conduction losses and provides higher efficiency at
heavy loads. Peak efficiency is about the same with either
method. Selecting Burst Mode operation or discontinuous
mode will improve the converter efficiency at light loads
regardless of the current sensing method.
To maintain a good signal-to-noise ratio for the current
sense signal, use a minimum ? V SENSE of 10mV to 15mV.
For a DCR sensing application, the actual ripple voltage
will be determined by the equation:
?
R1? C1 V IN ? f OSC
SLOPE COMPENSATION AND INDUCTOR PEAK
CURRENT
Slope compensation provides stability in constant
frequency current mode architectures by preventing
sub-harmonic oscillations at high duty cycles. This is
accomplished internally by adding a compensation ramp
to the inductor current signal at duty cycles in excess of
35%. The LTC3880 uses a patented current limit technique
that counteracts the compensating ramp. This allows the
maximum inductor peak current to remain unaffected
throughout all duty cycles.
INDUCTOR VALUE CALCULATION
Given the desired input and output voltages, the inductor
value and operating frequency, f OSC , directly determine
the inductor peak-to-peak ripple current:
V IN ? f OSC ?L
Lower ripple current reduces core losses in the inductor,
ESR losses in the output capacitors, and output voltage
ripple. Thus, highest efficiency operation is obtained at the
lowest frequency with a small ripple current. Achieving
this, however, requires a large inductor.
A reasonable starting point is to choose a ripple current
that is about 40% of I OUT(MAX) . Note that the largest ripple
current occurs at the highest input voltage. To guarantee
that the ripple current does not exceed a specified maxi-
mum, the inductor should be chosen according to:
L ≥
3880fb
40
For more information www.linear.com/LTC3880
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| LTC3880IUJ#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 40-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
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