参数资料
型号: LTC3412AMPFE
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: 6 A SWITCHING REGULATOR, 4000 kHz SWITCHING FREQ-MAX, PDSO16
封装: 4.40 MM, PLASTIC, TSSOP-16
文件页数: 6/20页
文件大小: 316K
代理商: LTC3412AMPFE
LTC3412A
3412afe
When a load step occurs, VOUT immediately shifts by an
amount equal to
ILOAD(ESR), where ESR is the effective
series resistance of COUT. ILOAD also begins to charge or
discharge COUTgeneratingafeedbackerrorsignalusedby
theregulatortoreturnVOUTtoitssteady-statevalue.During
this recovery time, VOUT can be monitored for overshoot
or ringing that would indicate a stability problem. The ITH
pin external components and output capacitor shown in
Figure 1 will provide adequate compensation for most
applications.
Design Example
As a design example, consider using the LTC3412A in an
application with the following specifications:
VIN = 3.3V, VOUT = 2.5V, IOUT(MAX) = 3A,
IOUT(MIN) = 100mA, f = 1MHz.
Because efficiency is important at both high and low load
current, Burst Mode operation will be utilized.
First, calculate the timing resistor:
R
k
OSC =
=
3 08 10
1 10
10
298
11
6
.
Use a standard value of 294k. Next, calculate the inductor
value for about 40% ripple current at maximum VIN:
L =
2.5V
(1MHz)(1.2A)
1–
2.5V
3.3V
=
0.51H
Using a 0.47H inductor results in a maximum ripple
current of:
ΔIL =
2.5V
(1MHz)(0.47H)
1–
2.5V
3.3V
=
1.29A
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, two
100F ceramic capacitors will be used.
CIN should be sized for a maximum current rating of:
IRMS =(3A)
2.5V
3.3V
3.3V
2.5V
– 1= 1.29ARMS
Decoupling the PVIN and SVIN pins with two 22F capaci-
tors is adequate for most applications.
The burst clamp and output voltage can now be pro-
grammed by choosing the values of R1, R2 and R3. The
voltage on pin MODE will be set to 0.50V by the resistor
divider consisting of R2 and R3. According to the graph
of Minimum Peak Inductor Current vs Burst Clamp Volt-
age in the Typical Performance Characteristics section, a
burst clamp voltage of 0.5V will set the minimum inductor
current, IBURST, to approximately 1.1A.
If we set the sum of R2 and R3 to 185k, then the following
equations can be solved:
R
k
R
V
2
3 185
1
2
3
0 8
0 50
+
=
+
=
.
The two equations shown above result in the following
values for R2 and R3: R2 = 69.8k , R3 = 115k. The value
of R1 can now be determined by solving the following
equation.
1
185
2 5
0 8
1 392
+
=
R
k
V
R
k
.
A value of 392k will be selected for R1. Figure 4 shows
the complete 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 LTC3412A. Check the following in your layout:
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 LTC3412A.
2. Connectthe(+)terminaloftheinputcapacitor(s),CIN,as
closeaspossibletothePVINpin.Thiscapacitorprovides
the AC current into the internal power MOSFETs.
ApplicAtions inForMAtion
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