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參數(shù)資料
| 型號： | LTC3522EUD#TR |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 0.85 A DUAL SWITCHING CONTROLLER, 1330 kHz SWITCHING FREQ-MAX, PQCC16 |
| 封裝： | 3 X 3 MM, PLASTIC, M0-220WEED-2, QFN-16 |
| 文件頁數(shù)： | 2/20頁 |
| 文件大?。?/td> | 270K |
| 代理商： | LTC3522EUD#TR |
LTC3522
10
3522f
Soft-Start
The buck converter has an internal voltage mode soft-start
circuit with a nominal duration of 600μs. The converter
remains in regulation during soft-start and will therefore
respond to output load transients which occur during
this time. In addition, the output voltage rise time has
minimal dependency on the size of the output capacitor
or load current.
Error Amplier and Compensation
The LT3522 buck converter utilizes an internal transcon-
ductance error amplier. Compensation of the feedback
loop is performed internally to reduce the size of the
application circuit and simplify the design process. The
compensation network has been designed to allow use of
a wide range of output capacitors while simultaneously
ensuring rapid response to load transients.
PGOOD2 Comparator
The PGOOD2 pin is an open-drain output which indicates
the status of the buck converter. If the buck output volt-
age falls 7.7% below the regulation voltage, the PGOOD2
open-drain output will pull low. The output voltage must
rise 2.5% above the falling threshold before the pull-down
will turn off. In addition, there is a 60μs typical deglitch-
ing delay in the ag in order to prevent false trips due
to voltage transients on load steps. The PGOOD2 output
will also pull low during overtemperature shutdown and
undervoltage lockout to indicate these fault conditions.
The PGOOD2 output is only active if the buck converter
is enabled.
BUCK-BOOST CONVERTER OPERATION
PWM Mode Operation
When the PWM pin is held high, the LTC3522 buck-boost
converter operates in a constant frequency PWM mode with
voltage mode control. A proprietary switching algorithm
allows the converter to switch between buck, buck-boost
and boost modes without discontinuity in inductor cur-
rent or loop characteristics. The switch topology for the
buck-boost converter is shown in Figure 1.
When the input voltage is signicantly greater than the
output voltage, the buck-boost converter operates in
buck mode. Switch D turns on continuously and switch
C remains off. Switches A and B are pulse width modu-
lated to produce the required duty cycle to support the
output regulation voltage. As the input voltage decreases,
switch A remains on for a larger portion of the switching
cycle. When the duty cycle reaches approximately 85%,
the switch pair AC begins turning on for a small fraction
of the switching period. As the input voltage decreases
further, the AC switch pair remains on for longer durations
and the duration of the BD phase decreases proportionally.
As the input voltage drops below the output voltage, the
AC phase will eventually increase to the point that there is
no longer any BD phase. At this point, switch A remains on
continuously while switch pair CD is pulse width modu-
lated to obtain the desired output voltage. At this point,
the converter is operating solely in boost mode.
This switching algorithm provides a seamless transition
between operating modes and eliminates discontinuities
in average inductor current, inductor current ripple, and
loop transfer function throughout all three operational
modes. These advantages result in increased efciency
and stability in comparison to the traditional 4-switch
buck-boost converter.
Error Amplier and Compensation
The buck-boost converter utilizes a voltage mode error
amplier with an internal compensation network as shown
in Figure 2.
Notice that resistor R2 of the external resistor divider
network plays an integral role in determining the frequency
OPERATION
L
D
PGND2
PGND1
LTC3522
A
SW1A
SW1B
BC
3522 F01
VOUT1
PVIN1
Figure 1. Buck-Boost Switch Topology
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