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參數(shù)資料
| 型號： | LTC3867IUF#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 0.1 A SWITCHING CONTROLLER, 1200 kHz SWITCHING FREQ-MAX, PQCC24 |
| 封裝： | 4 X 4 MM, LEAD FREE, PLASTIC, MO-220WGGD, QFN-24 |
| 文件頁數(shù)： | 8/36頁 |
| 文件大?。?/td> | 380K |
| 代理商： | LTC3867IUF#PBF |
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LTC3867
16
3867f
APPLICATIONS INFORMATION
of the parasitic inductance was determined to be 0.5nH
using the equation:
ESL
=
VESL(STEP)
IL
tON tOFF
tON + tOFF
(1)
If the RC time constant is chosen to be close to the
parasitic inductance divided by the sense resistor (L/R),
the resulting waveform looks resistive again, as shown
in Figure 5. For applications using low maximum sense
voltages, check the sense resistor manufacturer’s data
sheet for information about parasitic inductance. In the
absence of data, measure the voltage drop directly across
the sense resistor to extract the magnitude of the ESL step
and use Equation 1 to determine the ESL. However, do not
overfilter. Keep the RC time constant, less than or equal
to the inductor time constant to maintain a high enough
ripple voltage of
VSENSE. The above generally applies to
high density/high current applications where IMAX > 10A
and low values of inductors are used. For applications
where IMAX < 10A, set RF to 10Ω and CF to 1000pF. This
will provide a good starting point. The filter components
need to be placed close to the IC. The positive and nega-
tive sense traces need to be routed as a differential pair
and Kelvin connected to the sense resistor.
Inductor DCR Sensing
For applications requiring the highest possible efficiency
at high load currents, the LTC3867 is capable of sensing
the voltage drop across the inductor DCR, as shown in
Figure 3b. The DCR of the inductor represents the small
amount of DC winding resistance of the copper, which
can be less than 1mΩ for today’s low value, high current
inductors. In a high current application requiring such an
inductor, conduction loss through a sense resistor would
costseveralpointsofefficiencycomparedtoDCRsensing.
If the external R1|| R2 C1 time constant is chosen to be
exactly equal to the L/DCR time constant, the voltage drop
across the external capacitor is equal to the drop across
theinductorDCRmultipliedbyR2/(R1+R2).R2scalesthe
voltage across the sense terminals for applications where
the DCR is greater than the target sense resistor value.
To properly dimension the external filter components, the
DCR of the inductor must be known. It can be measured
using a good RLC meter, but the DCR tolerance is not
always the same and varies with temperature; consult
the manufacturers’ data sheets for detailed information.
Using the inductor ripple current value from the Inductor
ValueCalculationsection,thetargetsenseresistorvalueis:
RSENSE(EQUIV) =
VSENSE(MAX)
IMAX +
IL
2
To ensure that the application will deliver full load current
over the full operating temperature range, choose the
minimum value for the Maximum Current Sense Thresh-
old (VSENSE(MAX)) in the Electrical Characteristics table.
Next, determine the DCR of the inductor. Where provided,
use the manufacturer’s maximum value, usually given at
Figure 4. Voltage Waveform Measured
Directly Across the Sense Resistor
Figure 5. Voltage Waveform Measured After
the Sense Resistor Filter. CF = 1000pF, RF = 100Ω
500ns/DIV
VSENSE
20mV/DIV
3867 F04
VESL(STEP)
500ns/DIV
VSENSE
20mV/DIV
3867 F05
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