參數(shù)資料
型號: LT3580MPMS8E#PBF
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: 2.8 A SWITCHING REGULATOR, 2500 kHz SWITCHING FREQ-MAX, PDSO8
封裝: LEAD FREE, PLASTIC, MSOP-8
文件頁數(shù): 4/28頁
文件大?。?/td> 289K
代理商: LT3580MPMS8E#PBF
LT3580
12
3580fg
APPLICATIONS INFORMATION
Using the circuit in Figure 14 as an example, Table 3 shows
the parameters used to generate the bode plot shown in
Figure 5.
Table 3. Bode Plot Parameters
PARAMETER
VALUE
UNITS
COMMENT
RL
21.8
Ω
Application Specific
COUT
10
μF
Application Specific
RESR
10
m
Ω
Application Specific
RO
305
k
Ω
Not Adjustable
CC
1000
pF
Adjustable
CF
0
pF
Optional/Adjustable
CPL
0
pF
Optional/Adjustable
RC
10
k
Ω
Adjustable
R1
130
k
Ω
Adjustable
R2
14.6
k
Ω
Not Adjustable
VOUT
12
V
Application Specific
VIN
5
V
Application Specific
gma
230
μmho
Not Adjustable
gmp
7
mho
Not Adjustable
L
4.2
μH
Application Specific
fS
1.2
MHz
Adjustable
In Figure 5, the phase is –140° when the gain reaches 0dB
giving a phase margin of 40°. The crossover frequency
is 10kHz, which is more than three times lower than the
frequency of the RHP zero to achieve adequate phase
margin.
Diode Selection
Schottky diodes, with their low forward voltage drops and
fast switching speeds, are recommended for use with the
LT3580. The Microsemi UPS120 is a very good choice.
Where the input-to-output voltage differential exceeds 20V,
use the UPS140 (a 40V diode). These diodes are rated to
handle an average forward current of 1A.
Oscillator
The operating frequency of the LT3580 can be set by the
internal free-running oscillator. When the SYNC pin is
driven low (< 0.4V), the frequency of operation is set by
a resistor from RT to ground. An internally trimmed timing
capacitor resides inside the IC. The oscillator frequency is
calculated using the following formula:
f
OSC =
91.9
(R
T + 1)
where fOSC is in MHz and RT is in kΩ. Conversely, RT
(in k
Ω) can be calculated from the desired frequency
(in MHz) using:
R
T =
91.9
f
OSC
1
Clock Synchronization
The operating frequency of the LT3580 can be synchronized
to an external clock source. To synchronize to the external
source, simply provide a digital clock signal into the SYNC
pin. The LT3580 will operate at the SYNC clock frequency.
The LT3580 will revert to the internal free-running oscillator
clock after SYNC is driven low for a few free-running clock
periods.
Driving SYNC high for an extended period of time effectively
stops the operating clock and prevents latch SR1 from
becoming set (see the Block Diagram). As a result, the
switching operation of the LT3580 will stop.
The duty cycle of the SYNC signal must be between 35%
and 65% for proper operation. Also, the frequency of the
SYNC signal must meet the following two criteria:
Figure 5. Bode Plot for Example Boost Converter
FREQUENCY (Hz)
10
60
GAIN
(dB)
PHASE
(DEG)
80
100
120
140
100
1k
10k
100k
1M
3580 F05
40
20
0
–20
160
180
–120
–100
–80
–60
–40
–140
–160
–180
–200
–20
0
40 AT
10kHz
PHASE
GAIN
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