MP1580HS-LF Monolithic Power Systems (MPS), MP1580HS-LF Datasheet - Page 7

• Manufacturer Part Number: MP1580HS-LF
• Description: Switching Converters, Regulators & Controllers 2A 380kHz Step-Down Converter
• Manufacturer: Monolithic Power Systems (MPS)

Specifications of MP1580HS-LF

• Rohs: yes
• Output Voltage: 21 V
• Output Current: 2 A
• Input Voltage: 4.75 V to 25 V
• Switching Frequency: 380 kHz
• Operating Temperature Range: - 40 C to + 125 C
• Mounting Style: SMD/SMT
• Package / Case: SOIC-8

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 A
amplifier voltage gain, 400 V/V, G
current sense gain, (roughly the output current
divided by the voltage at COMP), 1.95 A/V and
R
I
The system has 2 poles of importance, one is
due to the compensation capacitor (C3), and
the other is due to the output capacitor (C2).
These are:
Where P1 is the first pole and G
amplifier transconductance (770µA/V).
and
The system has one zero of importance, due to
the compensation capacitor (C3) and the
compensation resistor (R3). The zero is:
If a large value capacitor (C2) with relatively
high equivalent-series-resistance (ESR) is used,
the zero due to the capacitance and ESR of the
output capacitor can be compensated by a third
pole set by R3 and C6. The pole is:
The system crossover frequency (the frequency
where the loop gain drops to 1, or 0dB) is
important. A good rule of thumb is to set the
crossover frequency to approximately 1/10 of
the switching frequency.
MP1580 Rev. 3.0
10/10/2007
OUT
LOAD
is the output load current).
is the load resistance (V
A
VDC
VEA
TM
=
f
f
P
R
is the transconductance error
P
f
2
f
1
P
LOAD
Z
3
=
1
=
=
=
2
2
π
π
2
2
×
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
×
π
π
×
G
C
×
×
C
CS
G
C
2
C
3
1
EA
1
1
3
×
6
×
×
R
×
×
A
A
R
LOAD
R
VEA
VEA
3
3
OUT
×
EA
V
/ I
V
OUT
is the error
FB
OUT
CS
© 2007 MPS. All Rights Reserved.
is the
where
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MP1580 – 2A, 380KHz STEP-DOWN CONVERTER
In this case, the switching frequency is 380KHz,
so use a crossover frequency, f
Lower crossover frequencies result in slower
response and worse transient load recovery.
Higher crossover frequencies can result in
instability.
Choosing the Compensation Components
The values of the compensation components
given in Table 4 yield a stable control loop for
the output voltage and capacitor given.
To optimize the compensation components for
conditions not listed in Table 4, use the
following procedure:
Choose the compensation resistor to set the
desired crossover frequency.
value by the following equation:
Putting in the known constants and setting the
crossover frequency to the desired 40KHz:
Choose the compensation capacitor to set the
zero below ¼ of the crossover frequency.
Determine the value by the following equation:
Table 4—Compensation Values for Typical
2.5V
3.3V
2.5V
3.3V
V
12V
12V
Output Voltage/Capacitor Combinations
5V
5V
OUT
22μF Ceramic
22μF Ceramic
22μF Ceramic
22μF Ceramic
(30mΩ ESR)
(30mΩ ESR)
(30mΩ ESR)
(30mΩ ESR)
560μF/6.3V
560μF/6.3V
470μF/10V
220μF/25V
R
R
3
3
C
C2
≈
3
=
. 1
>
2
G
37
π
. 0
EA
×
×
22
C
10
×
2
×
G
8
×
C
200kΩ
200kΩ
250kΩ
250kΩ
R
7.5kΩ
CS
10kΩ
15kΩ
33kΩ
×
f
2
3
R3
C
C
×
×
2
V
×
V
OUT
V
OUT
V
FB
Determine the
2.2nF
1.2nF
OUT
2nF
1nF
1nF
1nF
1nF
1nF
C
C3
, of 40KHz.
100pF
None
None
None
None
82pF
56pF
27pF
C6
7