參數(shù)資料
型號: LTC3616IUDD#TRPBF
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: 13.5 A SWITCHING REGULATOR, 2700 kHz SWITCHING FREQ-MAX, PQCC24
封裝: 3 X 5 MM, LEAD FREE, PLASTIC, QFN-24
文件頁數(shù): 16/28頁
文件大?。?/td> 490K
代理商: LTC3616IUDD#TRPBF
LTC3616
23
3616fa
applicaTions inForMaTion
Design Example
As a design example, consider using the LTC3616 in an
application with the following specifications:
VIN = 2.25V to 5.5V, VOUT = 1.8V, IOUT(MAX) = 6A, IOUT(MIN)
= 200mA, f = 2.6MHz.
Efficiency is important at both high and low load current,
so Burst Mode operation will be utilized.
First, calculate the timing resistor:
RT =
3.8211Hz
2.6MHz
k – 16k = 130kΩ
Next, calculate the inductor value for about 30% ripple
current at maximum VIN:
L =
1.8V
2.6MHz 2A
1–
1.8V
5.5V
= 0.233H
Using a standard value of 0.22H inductor results in a
maximum ripple current of:
IL =
1.8V
2.6MHz 0.22H
1–
1.8V
5.5V
= 2.12A
COUT will be selected based on the ESR that is required
to satisfy the output voltage ripple requirement and the
bulk capacitance needed for loop stability. For this design,
a 150F (or 47F plus 100F) ceramic capacitor is used
with a X5R or X7R dielectric.
Assumingworst-caseconditionsofVIN=2VOUT,CINshould
be selected for a maximum current rating of:
IRMS = 6A
1.8V
3.6V
3.6V
1.8V
– 1
= 3ARMS
Decoupling PVIN with four 22F capacitors is adequate
for most applications.
If we set R2 = 196k, the value of R1 can now be determined
by solving the following equation.
R1 = 196k
1.8V
0.6V
1
A value of 392k will be selected for R1.
Finally, define the soft start-up time choosing the proper
value for the capacitor and the resistor connected to
TRACK/SS. If we set minimum tSS = 5ms and a resistor
of 2M, the following equation can be solved with the
maximum SVIN = 5.5V :
CSS =
5ms
2MΩ In
5.5V
5.5V – 0.6V
= 21.6nF
The standard value of 22nF guarantees the minimum
soft-start up time of 5ms.
Figure 1 shows the schematic for this design example.
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC3616:
1. Agroundplaneisrecommended.Ifagroundplanelayer
is not used, the signal and power grounds should be
segregated with all small-signal components returning
to the SGND pin at one point which is then connected
to the PGND pin close to the LTC3616.
2. Connect the (+) terminal of the input capacitor(s), CIN,
as close as possible to the PVIN pin, and the (–) terminal
as close as possible to the exposed pad, PGND. This
capacitorprovidestheACcurrentintotheinternalpower
MOSFETs.
3. Keep the switching node, SW, away from all sensitive
small-signal nodes.
4. Flood all unused areas on all layers with copper. Flood-
ing with copper will reduce the temperature rise of
power components. Connect the copper areas to PGND
(exposed pad) for best performance.
5. Connect the VFB pin directly to the feedback resistors.
The resistor divider must be connected between VOUT
and SGND.
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