LTC3774 查看數據表（PDF） - Linear Technology
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LTC3774 Datasheet PDF : 38 Pages
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LTC3774
APPLICATIONS INFORMATION
VIN 5V
VIN
RITEMP
RS
20k
RNTC RP
100k 43.2k
LTC3774
PWM
ITEMP
SNSD+
SNS–
SNSA+
GND
VLOGIC BOOST
VCC
TG
LTC4449
IN
TS
BG
C1
C2
INDUCTOR
L DCR
R1 R2
VOUT
3774 F04
PLACE C1, C2 NEXT TO IC
PLACE R1, R2 NEXT TO INDUCTOR
R1C1 = 5 • R2C2
Figure 4. Inductor DCR Current Sensing
The LTC3774 could also be used like any typical current
mode controller by disabling the SNSD+ pin, shorting it
to ground. An RSENSE resistor or a RC filter can be used
to sense the output inductor signal and connects to the
SNSA+ pin. If the RC filter is used, its time constant,
R • C, is equaled to L/DCR of the output inductor. In these
applications, the current limit, VSENSE (MAX), will be five
times larger for the specified ILIM, and the operating
voltage range of SNSA+ and SNS– is from 0V to 5.25V.
Inductor DCR Sensing
The LTC3774 is specifically designed for high load current
applications requiring the highest possible efficiency; it is
capable of sensing the signal of an inductor DCR in the
sub milliohm range (Figure 4). The DCR is the DC winding
resistance of the inductor’s copper, which is often less than
1mΩ for high current inductors. In high current and low
output voltage applications, a conduction loss of a high
DCR or a sense resistor will cause a significant reduction
in power efficiency. For a specific output requirement,
chose the inductor with the DCR that satisfies the maxi-
mum desirable sense voltage, and uses the relationship
of the sense pin filters to output inductor characteristics
as depicted below.
DCR
=
VSENSE(MAX )
IMAX
+
∆IL
2
L/DCR = R1• C1 = 5 • R2 • C2
where:
VSENSE(MAX): Maximum sense voltage for a given ILIM
threshold
IMAX: Maximum load current
∆IL: Inductor ripple current
L, DCR: Output inductor characteristics
R1•C1: Filter time constant of the SNSD+ pin
R2 • C2: Filter time constant of the SNSA+ pin
3774f
16
For more information www.linear.com/LTC3774
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