參數(shù)資料
型號: LTC1702IGN
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: Dual 550kHz Synchronous 2-Phase Switching Regulator Controller
中文描述: 5 A DUAL SWITCHING CONTROLLER, 750 kHz SWITCHING FREQ-MAX, PDSO24
封裝: 0.150 INCH, PLASTIC, SSOP-24
文件頁數(shù): 23/36頁
文件大?。?/td> 350K
代理商: LTC1702IGN
23
LTC1702
Finally, choose a convenient resistor value for R1 (10k is
usually a good value). Now calculate the remaining values:
(K is a constant used in the calculations)
= chosen crossover frequency
G = 10
(GAIN/20)
(this converts GAIN in dB to G in absolute
gain)
Type 2 Loop:
K
TanBOOST
1
2
2
C
GKR
2
C
C K
R
K
C
R
V
R
( )
V
V
B
REF
OUT
REF
=
+
°
=
=
(
π
)
=
π
=
2
45
2
1
1
1
2
2
1
1
Type 3 Loop:
K
Tan
BOOST
4
C
GR
C
C K
2
R
K
C
1
R
R
K
C
KR
R
( )
R
V
V
V
B
REF
OUT
REF
=
+
°
1
=
=
(
π
)
=
π
=
(
)
=
π
=
2
45
2
2
1
1
1
2
2
1
3
1
3
1
2
3
1
APPLICATIO
S I
FOR
ATIO
U
nodes don’t corrupt the measurements or damage the
analyzer.
If breadboard measurement is not practical, a SPICE
simulation can be used to generate approximate gain/
phase curves. Plug the expected capacitor, inductor and
MOSFET values into the following SPICE deck and gener-
ate an AC plot of V(V
OUT
)/V(COMP) in dB and phase of
V(OUT) in degrees. Refer to your SPICE manual for details
of how to generate this plot.
W
U
U
*1702 modulator gain/phase
*
1999 Linear Technology
*this file written to run with PSpice 8.0
*may require modifications for other SPICE
simulators
*MOSFETs
rfet mod sw 0.02
;MOSFET rdson
*inductor
lext sw out1 1u
rl out1 out 0.005
;inductor value
;inductor series R
*output cap
cout out out2 1000u
resr out2 0 0.01
;capacitor value
;capacitor ESR
*1702 internals
emod mod 0 comp 0 5
vstim comp 0 0 ac 1
.ac dec 100 1k 1meg
.probe
.end
With the gain/phase plot in hand, a loop crossover fre-
quency can be chosen. Usually the curves look something
like Figure 8. Choose the crossover frequency in the rising
or flat parts of the phase curve, beyond the external LC
poles. Frequencies between 10kHz and 50kHz usually
work well. Note the gain (GAIN, in dB) and phase (PHASE,
in degrees) at this point. The desired feedback amplifier
gain will be –GAIN to make the loop gain 0dB at this
frequency. Now calculate the needed phase boost, assum-
ing 60
°
as a target phase margin:
BOOST = –(PHASE + 30
°
)
If the required BOOST is less than 60
°
, a type 2 loop can
be used successfully, saving two external components.
BOOST values greater than 60
°
usually require type 3
loops for satisfactory performance.
;3.3 for 3.3V supply
;ac stimulus
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