MP2307DN Monolithic Power Systems, MP2307DN Datasheet - Page 8

• Manufacturer Part Number: MP2307DN
• Description: 3A, 23V, 340khz Synchronous Rectified Step-down Converter
• Manufacturer: Monolithic Power Systems

Since the input capacitor (C1) absorbs the input
switching current, it requires an adequate ripple
current rating. The RMS current in the input
capacitor can be estimated by:
The worst-case condition occurs at V
where I
input capacitor with a RMS current rating
greater than half of the maximum load current.
The input capacitor can be electrolytic, tantalum
or ceramic. When using electrolytic or tantalum
capacitors, a small, high quality ceramic
capacitor, i.e. 0.1µF, should be placed as close
to the IC as possible. When using ceramic
capacitors, make sure that they have enough
capacitance to provide sufficient charge to
prevent excessive voltage ripple at input. The
input voltage ripple for low ESR capacitors can
be estimated by:
Where C1 is the input capacitance value.
Output Capacitor
The output capacitor (C2) is required to
maintain the DC output voltage. Ceramic,
tantalum, or low ESR electrolytic capacitors are
recommended.
preferred to keep the output voltage ripple low.
The output voltage ripple can be estimated by:
Where C2 is the output capacitance value and
R
value of the output capacitor.
When using ceramic capacitors, the impedance
at the switching frequency is dominated by the
capacitance which is the main cause for the
output voltage ripple. For simplification, the
output voltage ripple can be estimated by:
MP2307 Rev. 1.7
3/14/2006
∆
ESR
V
OUT
is the equivalent series resistance (ESR)
∆V
=
C1
∆
f
V
OUT
V
S
I
C
= I
OUT
IN
×
1
TM
=
L
=
LOAD
=
MP2307 – 3A, 23V, 340KHz SYNCHRONOUS RECTIFIED STEP-DOWN CONVERTER
×
C
I
I
LOAD
8
LOAD
1
⎛
⎜ ⎜
⎝
1
×
×
Low
/2. For simplification, use an
−
f
f
S
S
V
×
V
2
×
V
OUT
OUT
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
×
IN
V
V
L
V
V
OUT
ESR
OUT
×
IN
IN
⎞
⎟ ⎟
⎠
C
×
2
×
×
⎛
⎜
⎜
⎝
⎛
⎜
⎜
⎝
R
1
⎛
⎜ ⎜
⎝
×
1
−
ESR
⎛
⎜ ⎜
⎝
−
V
capacitors
1
V
OUT
−
V
IN
V
OUT
+
V
IN
V
OUT
8
⎞
⎟
⎟
⎠
IN
IN
×
⎞
⎟ ⎟
⎠
© 2006 MPS. All Rights Reserved.
= 2V
f
⎞
⎟ ⎟
⎠
S
1
×
www.MonolithicPower.com
C
OUT
are
2
⎞
⎟
⎟
⎠
,
When using tantalum or electrolytic capacitors,
the ESR dominates the impedance at the
switching frequency. For simplification, the
output ripple can be approximated to:
The characteristics of the output capacitor also
affect the stability of the regulation system. The
MP2307 can be optimized for a wide range of
capacitance and ESR values.
Compensation Components
MP2307 employs current mode control for easy
compensation and fast transient response. The
system stability and transient response are
controlled through the COMP pin. COMP is the
output of the internal transconductance error
amplifier.
combination sets a pole-zero combination to
govern the characteristics of the control system.
The DC gain of the voltage feedback loop is
given by:
Where V
A
the current sense transconductance and R
is the load resistor value.
The system has two poles of importance. One
is due to the compensation capacitor (C3) and
the output resistor of the error amplifier, and the
other is due to the output capacitor and the load
resistor. These poles are located at:
Where
transconductance.
VEA
is the error amplifier voltage gain, G
A
∆V
FB
VDC
G
OUT
EA
is the feedback voltage (0.925V),
=
A
f
P
f
=
R
P
2
1
LOAD
f
V
=
S
=
is
OUT
×
2
2
series
L
π
π
×
×
×
×
G
C
⎛
⎜ ⎜
⎝
C
the
1
G
CS
2
3
−
EA
1
×
×
V
×
R
A
V
OUT
A
LOAD
IN
VEA
EA
capacitor-resistor
error
⎞
⎟ ⎟
⎠
×
×
R
V
V
ESR
OUT
FB
amplifier
CS
LOAD
is
8