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參數(shù)資料
| 型號： | LTC3835EDHC-1#TRPBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 3 A SWITCHING CONTROLLER, 580 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | 5 X 3 MM, LEAD FREE, PLASTIC, MO-229WJED-1, DFN-16 |
| 文件頁數(shù)： | 3/28頁 |
| 文件大?。?/td> | 303K |
| 代理商： | LTC3835EDHC-1#TRPBF |
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LTC3835-1
11
38351fc
APPLICATIONS INFORMATION
OPERATION (Refer to Functional Diagram)
The typical capture range of the LTC3835-1’s phase-
locked loop is from approximately 115kHz to 800kHz,
with a guarantee to be between 140kHz and 650kHz. In
other words, the LTC3835-1’s PLL is guaranteed to lock
to an external clock source whose frequency is between
140kHz and 650kHz.
The typical input clock thresholds on the PLLIN/MODE
pin are 1.6V (rising) and 1.2V (falling).
Output Overvoltage Protection
An overvoltage comparator guards against transient over-
shoots as well as other more serious conditions that may
overvoltage the output. When the VFB pin rises to more
than 10% higher than its regulation point of 0.800V, the top
MOSFET is turned off and the bottom MOSFET is turned
on until the overvoltage condition is cleared.
RSENSE Selection for Output Current
RSENSE is chosen based on the required output current.
The current comparator has a maximum threshold of
100mV/RSENSE and an input common mode range of
SGND to 10V. The current comparator threshold sets the
peak of the inductor current, yielding a maximum average
output current IMAX equal to the peak value less half the
peak-to-peak ripple current,
ΔIL.
Allowing a margin for variations in the IC and external
component values yields:
R
mV
I
SENSE
MAX
=
80
When using the controller in very low dropout conditions,
the maximum output current level will be reduced due to the
internal compensation required to meet stability criterion
for buck regulators operating at greater than 50% duty
factor. A curve is provided to estimate this reduction in
peak output current level depending upon the operating
duty factor.
Operating Frequency and Synchronization
The choice of operating frequency, is a trade-off between
efciency and component size. Low frequency operation
improves efciency by reducing MOSFET switching losses,
both gate charge loss and transition loss. However, lower
frequency operation requires more inductance for a given
amount of ripple current.
The internal oscillator of the LTC3835-1 runs at a nominal
400kHz frequency when the PLLLPF pin is left oating
and the PLLIN/MODE pin is a DC low or high. Pulling the
PLLLPF to INTVCC selects 530kHz operation; pulling the
PLLLPF to SGND selects 250kHz operation.
Alternatively, the LTC3835-1 will phase-lock to a clock
signal applied to the PLLIN/MODE pin with a frequency
between 140kHz and 650kHz (see Phase-Locked Loop
and Frequency Synchronization).
Inductor Value Calculation
The operating frequency and inductor selection are inter-
related in that higher operating frequencies allow the use
of smaller inductor and capacitor values. So why would
anyone ever choose to operate at lower frequencies with
larger components? The answer is efciency. A higher
frequency generally results in lower efciency because
of MOSFET gate charge losses. In addition to this basic
trade-off, the effect of inductor value on ripple current and
low current operation must also be considered.
The inductor value has a direct effect on ripple current.
The inductor ripple current
ΔIL decreases with higher
inductance or frequency and increases with higher VIN:
ΔI
fL
V
L
OUT
IN
= ()( )
1
1–
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