MP2303DQ MPS [Monolithic Power Systems], MP2303DQ Datasheet - Page 9

• Manufacturer Part Number: MP2303DQ
• Description: 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter
• Manufacturer: MPS [Monolithic Power Systems]

whose 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 caused by capacitance can
be estimated by:
Output Capacitor
The output capacitor is required to maintain the
DC output voltage. Ceramic, tantalum, or low
ESR electrolytic capacitors are recommended.
Low ESR capacitors are 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.
In
impedance at the switching frequency is
dominated by the capacitance. The output
voltage
capacitance. For simplification, the output
voltage ripple can be estimated by:
In
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
MP2303 Rev. 0.91
5/2/2006
For simplification, choose the input capacitor
∆
ESR
V
OUT
the
the
is the equivalent series resistance (ESR)
∆
=
∆V
V
∆V
f
V
ripple
IN
case
case
S
OUT
OUT
OUT
×
=
L
=
f
S
×
=
I
8
LOAD
⎛
⎜ ⎜
⎝
×
of
f
V
1
×
of
is
S
C
OUT
−
f
S
×
1
V
2
V
L
ceramic
OUT
V
mainly
×
tantalum
OUT
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
×
×
IN
L
MP2303 – 3A, 28V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER
⎛
⎜ ⎜
⎝
V
1
×
V
OUT
⎞
⎟ ⎟
⎠
−
IN
C
×
V
2
⎛
⎜
⎜
⎝
V
OUT
×
R
×
IN
caused
⎛
⎜ ⎜
⎝
⎛
⎜ ⎜
⎝
ESR
1
capacitors,
1
⎞
⎟ ⎟
⎠
−
or
−
×
V
+
V
R
V
V
OUT
OUT
ESR
8
IN
IN
electrolytic
INITIAL RELEASE – SPECIFICATIONS SUBJECT TO CHANGE
×
© 2006 MPS. All Rights Reserved.
f
⎞
⎟ ⎟
⎠
⎞
⎟ ⎟
⎠
by
S
1
×
www.MonolithicPower.com
C
2
the
the
⎞
⎟
⎟
⎠
MP2303 can be optimized for a wide range of
capacitance and ESR values.
Compensation Components
MP2303 employs current mode control for easy
compensation and fast transient response. The
system stability and transient response are
controlled through the COMP pin. COMP pin is
the output of the internal transconductance
error amplifier. A series capacitor-resistor
combination sets a pole-zero combination to
control the characteristics of the control system.
The DC gain of the voltage feedback loop is
given by:
Where A
400V/V;
transconductance, 7.0A/V; R
resistor value.
The system has 2 poles of importance. One is
due to the compensation capacitor (C3) and the
output resistor of error amplifier, and the other
is due to the output capacitor and the load
resistor. These poles are located at:
Where,
transconductance, 820µA/V, and R
resistor value.
The system has one zero of importance, due to the
compensation
compensation resistor (R3). This zero is located at:
The system may have another zero of
importance, if the output capacitor has a large
capacitance and/or a high ESR value. The zero,
due to the ESR and capacitance of the output
capacitor, is located at:
A
VEA
VDC
G
G
EA
is the error amplifier voltage gain,
=
CS
f
f
P
ESR
f
R
P
2
f
1
LOAD
Z
capacitor
=
1
=
=
is
=
is
2
2
2
π
π
×
2
π
×
π
×
G
×
×
C
C
CS
the
the
G
C
C
2
3
1
EA
1
2
3
×
×
1
×
×
R
×
A
A
R
R
LOAD
(C3)
VEA
VEA
LOAD
ESR
3
current
error
×
LOAD
V
V
is the load
OUT
FB
and
is the load
amplifier
sense
the
9