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| 型号： | LTC3858EUH-2#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | DUAL SWITCHING CONTROLLER, 900 kHz SWITCHING FREQ-MAX, PQCC32 |
| 封装： | 5 X 5 MM, LEAD FREE, PLASTIC, MO-220WHHD, QFN-32 |
| 文件页数： | 9/40页 |
| 文件大小： | 432K |
| 代理商： | LTC3858EUH-2#TRPBF |
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LTC3858-2
17
38582f
(4a) Using a Resistor to Sense Current
(4b) Using the Inductor DCR to Sense Current
Figure 4. Current Sensing Methods
APPLICATIONS INFORMATION
Inductor DCR Sensing
For applications requiring the highest possible efficiency
at high load currents, the LTC3850 is capable of sensing
the voltage drop across the inductor DCR, as shown in
Figure 4b. The DCR of the inductor represents the small
amount of DC resistance of the copper wire, which can be
less than 1mΩ for today’s low value, high current inductors.
In a high current application requiring such an inductor,
power loss through a sense resistor would cost several
points of efficiency compared to inductor DCR sensing.
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
the inductor DCR multiplied by R2/(R1 + R2). R2 scales the
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
Value Calculation section, the target sense resistor value is:
RSENSE(EQUIV) =
VSENSE(MAX)
IMAX +
ΔIL
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 Voltage (VSENSE(MAX)) in the Electrical Characteristics
table (30mV, 50mV or 75mV depending on the state of
the ILIM pin).
Next, determine the DCR of the inductor. When provided,
use the manufacturer’s maximum value, usually given at
20°C. Increase this value to account for the temperature
coefficient of copper, which is approximately 0.4%/°C. A
conservative value for TL(MAX) is 100°C.
To scale the maximum inductor DCR to the desired sense
resistor (RD) value, use the divider ratio:
RD =
RSENSE(EQUIV)
DCRMAX at TL(MAX)
VIN
INTVCC
BOOST
TG
SW
BG
PLACE CAPACITOR NEAR
SENSE PINS
SENSE+
SENSE–
SGND
LTC3858-2
VOUT
RSENSE
38582 F04a
VIN
INTVCC
BOOST
TG
SW
BG
*PLACE C1 NEAR
SENSE PINS
INDUCTOR
DCR
L
SENSE+
SENSE–
SGND
LTC3858-2
VOUT
38582 F04b
R1
R2
C1*
(R1||R2) C1 =
L
DCR
RSENSE(EQ) = DCR
R2
R1 + R2
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