MP2106DQ MPS [Monolithic Power Systems], MP2106DQ Datasheet - Page 8

• Manufacturer Part Number: MP2106DQ
• Description: 1.5A, 15V, 800KHz Synchronous Buck Converter
• Manufacturer: MPS [Monolithic Power Systems]

Calculate the required inductance value by the
equation:
Where ∆I is the peak-to-peak inductor ripple
current. It is recommended to choose ∆I to be
30%~40% of the maximum load current.
Compensation
The system stability is controlled through the
COMP pin. COMP 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 loop gain is:
Where V
transconductance error amplifier voltage gain,
G
(roughly the output current divided by the
voltage at COMP) and R
resistance:
Where I
The system has 2 poles of importance, one is
due to the compensation capacitor (C3), and
the other is due to the load resistance and the
output capacitor (C2), where:
P1 is the first pole, and G
transconductance (300µA/V) and
MP2106 Rev. 1.6
2/22/2006
CS
is the current sense transconductance
A
OUT
VDC
FB
is the output load current.
is the feedback voltage, A
=
TM
L
⎛
⎜
⎜
⎝
f
f
P
=
V
P
2
V
1
OUT
V
R
FB
=
=
OUT
LOAD
2
2
V
⎞
⎟
⎟
⎠
π
π
IN
×
×
×
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
×
×
A
(
R
=
A
V
G
f
VEA
LOAD
SW
IN
VEA
EA
V
I
EA
1
OUT
OUT
−
is the error amplifier
×
×
×
V
LOAD
×
∆
G
OUT
C
C
I
CS
3
2
MP2106 – 1.5A, 15V, 800KHz SYNCHRONOUS BUCK CONVERTER
)
×
is the load
R
LOAD
VEA
© 2006 MPS. All Rights Reserved.
www.MonolithicPower.com
is the
The system has one zero of importance, due to
the compensation capacitor (C3) and the
compensation resistor (R3). The zero is:
If large value capacitors with relatively high
equivalent-series-resistance (ESR) are used,
the zero due to the capacitance and ESR of the
output capacitor can be compensated by a third
pole set by R3 and C4. The pole is:
The system crossover frequency (the frequency
where the loop gain drops to 1, or 0dB, is
important. Set the crossover frequency to below
one tenth of the switching frequency to insure
stable operation. Lower crossover frequencies
result in slower response and worse transient
load recovery. Higher crossover frequencies
degrade the phase and/or gain margins and
can result in instability.
Choosing the Compensation Components
The values of the compensation components
given in Table 1 yield a stable control loop for
the given output voltage and capacitor. To
optimize the compensation components for
conditions not listed in Table 1, use the
following procedure.
Table 1—Compensation Values for Typical
1.8V 22µF Ceramic
2.5V 22µF Ceramic
3.3V 22µF Ceramic
1.8V
2.5V
3.3V
V
Output Voltage/Capacitor Combinations
OUT
47µF Tantalum
(300mΩ)
47µF Tantalum
(300mΩ)
47µF Tantalum
(300mΩ)
C2
f
f
P
Z
3
1
=
=
2
2
π
π
×
×
R
R
6.8kΩ
9.1kΩ
12kΩ
13kΩ
18kΩ
24kΩ
1
1
3
3
R3
×
×
C
C
3
4
3.3nF
2.2nF
1.8nF
1.2nF
2nF
1nF
C3
750pF
560pF
None
None
None
1nF
C4
8