CM3706AGIM25 CHAMP [Champion Microelectronic Corp.], CM3706AGIM25 Datasheet - Page 9

• Manufacturer Part Number: CM3706AGIM25
• Description: 1.5MHz, 600mA Synchronous Step-Down Regulator
• Manufacturer: CHAMP [Champion Microelectronic Corp.]

APPLICATIONS INFORMATION
Setting the Output Voltage
Figure 2 above shows the basic application circuit with
CM3706A adjustable output version. The external resistor
sets the output voltage according to the following equation:
R1=316KΩ ; R2= 316KΩ ; V
R1=316KΩ ; R2= 470KΩ ; V
R1=316KΩ ; R2= 630KΩ ; V
R1=316KΩ ; R2= 1MΩ ; V
R1=316KΩ ; R2= 1.42MΩ ; V
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 CM3706A 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:
Where
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
2008/03/07
I Δ
I Δ
L
Rev. 1.0
L
L
is inductor Ripple Current. Large value
=210mA.
=
V
OUT
V
V
OUT
IN
=
×
×
OUT
0
6 .
(
Δ
OUT
OUT
OUT
V
OUT
V
I
=2.5V
IN
L
⎛
⎜
⎝
=1.2V
=1.5V
=1.8V
1
=3.3V.
×
−
+
V
f
OSC
R
OUT
R
1
2
⎞
⎟
⎠
)
Champion Microelectronic Corporation
1.5MHz, 600mA Synchronous Step-Down Regulator
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
recommended due to their low ESR and high ripple current.The
output ripple V
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.
For output voltages above 2.0V, when light-load efficiency is
important, the minimum recommended inductor is 2.2µH.
inductor with DC series resistance in the 50mΩ to 150mΩ
range. For higher efficiency at heavy loads, or minimal load
regulation (but some transient overshoot), the resistance
should be kept below 100mΩ. 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).
For optimum voltage-positioning load transients, choose an
Δ
V
2.5V T O
5.5V
OUT
IN
≤
capacitors
Figure2 Application Circuit with
V
OUT
adjustable output versions
OUT
V
4.7uF
C 1
C in
IN
×
is determined by:
×
(
V
f
IN
4
1
OSC
with
R U N G N D V
V
IN
−
C M 3706A
×
V
2
OUT
L
X5R
)
S W
316K
1%
F B
×
R 1
or
⎛
⎜ ⎜
⎝
3
5
ESR
CM3706A
1%
X7R
2.2uH
C 2
L 1
R 2
634k
22P F
+
8
dielectrics
Page 9
×
f
O U T
osc
C out
10uF
1
C 3
×
C
3
are
⎞
⎟ ⎟
⎠