LTC3866 Datasheet, PDF (30/36 Pages) Linear Technology – Current Mode Synchronous Controller for Sub Milliohm DCR Sensing

LTC3866
Typical Applications
Very Low Output Ripple Converter
The LTC3866 can work with very low DCR inductors be-
cause it can operate with only a small peak-to-peak sense
voltage. Two inductor characteristics can diminish this
signal: lower DC resistance and higher inductance. While
lower DCR improves efficiency, higher inductance reduces
output ripple. Because the LTC3866 only requires a ripple
signal about a quarter of the sense signal of the next best
current mode converters, output ripple can be drastically
reduced by increasing the inductance and capacitance of
the output filter. The very small output voltage ripple is
critical for low noise applications such as audio systems
and noise sensitive systems.
The schematic as shown Figure 15 is similar to that of the
front page circuit, except that three times the inductance
and double the output capacitance are used. The com-
pensation components are changed to maintain the same
crossover frequency and phase margin. Figure 16 shows
the transient response of 15A load step, and Figure 17
demonstrates that the output voltage ripple is a factor of
six smaller than that of typical current mode converters.
Increasing the inductance, while maintaining the same
physical size inductor, will invariably increase conduction
losses due to higher DC resistance. However, reduced ripple
current will decrease the core loss and the AC resistance
loss often enough to negate the extra DC conduction
losses. Figure 18 shows a high efficiency converter with
the benefit of low output ripple current.
75pF
R_B
30.1k
R_A
20k
10k
680pF
100k
0.1µF
C1
220nF
C2
220nF
FREQ MODE/PLLIN
RUN
PGOOD
TK/SS
ITEMP
ITH
EXTV_CC
V_FB LTC3866 V_IN
DIFFOUT INTVCC
DIFFP
BOOST
DIFFN
TG
SNSD⁺
SW
SNS^–
BG
SNSA⁺
PGND
ILIM
CLKOUT
SGND
4.7µF
V_IN
4.5V TO 20V
220µF
CMDSH-3
0.1µF
BSC050NE2LS
L1
1µH
DCR = 1mΩ
BSC010NE2LS
R2
909Ω
R1
4.53k
C_OUT
470µF
×4
V_OUT
1.5V
25A
3866 F15
Figure 15. High Efficiency, 1.5V/25A Step-Down Converter with Very Low Output Ripple
3866fa
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