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參數(shù)資料
| 型號： | CM3706IM25 |
| 廠商： | Champion Microelectronic Corp. |
| 英文描述： | 1.5MHz, 600mA Synchronous Step-Down Regulator |
| 中文描述： | 1.5MHz的，600毫安同步降壓穩(wěn)壓器 |
| 文件頁數(shù)： | 8/11頁 |
| 文件大?。?/td> | 393K |
| 代理商： | CM3706IM25 |
CM3706
1.5MHz, 600mA
Synchronous
Step-Down Regulator
2006/12/20
Rev. 1.6
Champion Microelectronic Corporation
Page 8
APPLICATIONS INFORMATION
Setting the Output Voltage
Figure 2 above shows the basic application circuit with
CM3706 adjustable output version. The external resistor
sets the output voltage according to the following
equation:
+
=
1
2
6
R
R
V
V
OUT
R1=316K
; R2= 316K
; V
OUT
=1.2V
R1=316K
; R2= 470K
; V
OUT
=1.5V
R1=316K
; R2= 630K
; V
OUT
=1.8V
R1=316K
; R2= 1M
; V
OUT
=2.5V
R1=316K
; R2= 1.42M
; V
OUT
=3.3V.
Input Capacitor Selection
The input capacitor reduces the surge current drawn from
the input and switching noise from the device. The input
capacitor impedance at the switching frequency shall be
less than input source impedance to prevent high
frequency switching current passing to the input. A low
ESR input capacitor sized for maximum RMS current must
be used Ceramic capacitors with X5R or X7R dielectrics
are highly recommended because of their low ESR and
small temperature coefficients. A 4.7μF ceramic capacitor
for most applications is sufficient.
Inductor Selection
For most designs, the CM3706 operates with inductors
of 1μH to 4.7μH. Low inductance values are physically
smaller but require faster switching, which results in
some efficiency loss. The inductor value can be
derived from the following equation:
(
IN
OUT
I
V
×
is inductor Ripple Current. Large value
)
OSC
L
IN
OUT
f
V
V
V
L
×
×
=
Where
L
I
inductors lower ripple current and small value inductors
result in high ripple currents. Choose inductor ripple
current approximately 35% of the maximum load current
600mA, or
=210mA.
L
I
V
IN
SW
CM3706
RUN GND V
FB
2
2.5V TO
5.5V
Cin
4.7uF
C1
Cout
10uF
C3
22PF
C2
634k
2.2uH
316K
1%
1
4
3
5
OUT
IN
R1
1%
L1
Figure2 Application Circuit with
adjustable output versions
For output voltages above 2.0V, when light-load efficiency
is important, the minimum recommended inductor is
2.2μH.
For optimum voltage-positioning load transients, choose
an inductor with DC series resistance in the 50m
to
150m
range. For higher efficiency at heavy loads, or
minimal load regulation (but some transient overshoot),
the resistance should be kept below 100m
. The DC
current rating of the inductor should be at least equal to
the maximum load current plus half the ripple current to
prevent core saturation (600mA+105mA).
Output Capacitor Selection
The output capacitor is required to keep the output
voltage ripple small and to ensure regulation loop stability.
The output capacitor must have low impedance at the
switching frequency. Ceramic capacitors with X5R or
X7R dielectrics are recommended due to their low ESR
and high ripple current.The output ripple V
OUT
determined by:
×
≤
L
f
V
OSC
IN
Input Zener Selection
In USB device application, we will add zener. The zener
can be reduced the surge voltage when device plug in
and plug out. Application circuit is show in Figure3.
is
×
×
+
×
×
×
3
8
1
)
(
C
f
ESR
V
V
V
V
osc
OUT
IN
OUT
OUT
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