MP2364DF Monolithic Power Systems, MP2364DF Datasheet - Page 8

• Manufacturer Part Number: MP2364DF
• Description: Dual 1.5a, 23V, 1.4mhz Step-down Converter
• Manufacturer: Monolithic Power Systems

For simplification, choose the input capacitor
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 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 L1 is the inductor value, C2 is the output
capacitance value, and R
series resistance (ESR) 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
MP2364 Rev. 1.4
3/22/2006
∆
V
OUT
the
the
=
∆V
∆V
f
∆
V
ripple
S
case
OUT
case
V
OUT
OUT
×
IN
L
TM
=
=
1
=
×
8
I
LOAD
C
×
⎛
⎜ ⎜
⎝
of
f
of
V
S
is
1
1
f
OUT
S
×
−
2
V
L
×
V
OUT
ceramic
×
1
mainly
tantalum
V
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
OUT
V
L
×
IN
V
OUT
1
⎛
⎜
⎝
IN
×
1
⎞
⎟ ⎟
⎠
−
C
ESR
×
×
2
V
⎛
⎜
⎜
⎝
V
⎛
⎜ ⎜
⎝
OUT
×
1
R
IN
caused
is the equivalent
−
⎛
⎜ ⎜
⎝
ESR
capacitors,
1
⎞
⎟
⎠
V
or
−
V
×
OUT
IN
+
V
R
V
OUT
MP2364 — DUAL 1.5A, 23V, 1.4MHz STEP-DOWN CONVERTER
ESR
8
IN
electrolytic
⎞
⎟ ⎟
⎠
×
© 2006 MPS. All Rights Reserved.
⎞
⎟ ⎟
⎠
f
by
S
1
www.MonolithicPower.com
×
C
the
the
2
⎞
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MP2364 can be optimized for a wide range of
capacitance and ESR values.
Compensation Components
The MP2364 employs current mode control on
each channel 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
characteristics of the control system.
The DC gain of the voltage feedback loop is
given by:
Where A
G
R
The system has two 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.
The system has one zero of importance, due to
the compensation capacitor (C3) and the
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,
LOAD
CS
is the current sense transconductance and
is the load resistor value.
A
VDC
VEA
G
EA
is the error amplifier voltage gain,
combination
=
f
f
P
R
P
2
f
1
LOAD
Z
1
=
=
is
is
=
2
2
π
π
2
×
×
π
×
G
C
×
C
the
CS
G
2
C
3
1
1
EA
3
×
×
×
R
×
A
A
to
located
R
LOAD
VEA
VEA
error
3
×
control
V
V
OUT
FB
amplifier
the
at:
8