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MP2451DT-LF-Z

P1-P3P4-P6P7-P9P10-P12P13-P15
MP245136V, 2MHz, 0.6A, STEP-DOWN CONVERTER
MP2451 Rev. 1.33 www.MonolithicPower.com
4/29/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2014 MPS. All Rights Reserved.
10
Table 2—Inductor Selection Guide
Part Number Inductance (µH) Max DCR () Current Rating (A)
Dimensions
L x W x H (mm
3
)
Wurth Electronics
7440430022 2.2 0.028 2.5 4.8x4.8x2.8
744043003 3.3 0.035 2.15 4.8x4.8x2.8
7447785004 4.7 0.078 2.4 5.9x6.2x3.2
TOKO
D63CB-#A916CY-2R0M 2.0 0.019 2.36 6.2x6.3x3.0
D62CB-#A916CY-3R3M 3.3 0.026 2.17 6.2x6.3x3.0
D62CB-#A916CY-4R7M 4.7 0.032 2.1 6.2x6.3x3.0
DK
LTF5022T-2R2N3R2
2.2 0.04 3.2 5.2x5.0x2.2
LTF5022T-3R3N2R5
3.3 0.06 2.5 5.2x5.0x2.2
LTF5022T-4R7N2R0
4.7 0.081 2.0 5.2x5.0x2.2
C
OOPER BUSSMANN
SD25-2R2
2.2 0.031 2.8 5.2x5.2x2.5
SD25-3R3
3.3 0.038 2.21 5.2x5.2x2.5
SD25-4R7
4.7 0.047 1.83 5.2x5.2x2.5
The input capacitor (C1) 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:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−××
×
=Δ
IN
OUT
IN
OUT
S
LOAD
IN
V
V
1
V
V
1Cf
I
V
Output Capacitor
The output capacitor (C2) 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:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
××
+×
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−×
×
=Δ
2Cf8
1
R
V
V
1
Lf
V
V
S
ESR
IN
OUT
S
OUT
OUT
Where L is the inductor value and R
ESR is the
equivalent series resistance (ESR) value of the
output capacitor.
In the case of ceramic capacitors, the impedance
at the switching frequency is dominated by the
capacitance. The output voltage ripple is mainly
caused by the capacitance. For simplification, the
output voltage ripple can be estimated by:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−×
×××
=
IN
OUT
2
S
OUT
OUT
V
V
1
2CLf8
V
ΔV
In the case of tantalum or electrolytic capacitors,
the ESR dominates the impedance at the
switching frequency. For simplification, the output
ripple can be approximated to:
ESR
IN
OUT
S
OUT
OUT
R
V
V
1
Lf
V
ΔV ×
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−×
×
=
The characteristics of the output capacitor also
affect the stability of the regulation system.
MP245136V, 2MHz, 0.6A, STEP-DOWN CONVERTER
MP2451 Rev. 1.33 www.MonolithicPower.com
4/29/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2014 MPS. All Rights Reserved.
11
Compensation Components
The goal of compensation design is to shape the
converter transfer function to get a desired loop
gain. Lower crossover frequencies result in
slower line and load transient responses, while
higher crossover frequencies could cause system
unstable. A good rule of thumb is to set the
crossover frequency to approximately one-tenth
of the switching frequency. If an electrolytic
capacitor is used, the loop bandwidth is no higher
than 1/4 of the ESR zero frequency (f
ESR
). f
ESR
is
given by:
ESR
ESR
R2C2
1
f
××π
=
The Table 3 lists the typical values of
compensation components for some standard
output voltages with various output capacitors
(ceramic) and inductors. The values of the
compensation components have been optimized
for fast transient responses and good stability at
given conditions.
Table 3—Compensation Values for Typical
Output Voltage/Capacitor Combinations
V
OUT
(V) L(µH) C2(µF) R2(k) C3(pF)
1.2 2.2 10 249 22
2.5 2.2 10 57.6 22
3.3 2.2 10 40.2 33
5 3.3 10 23.7 33
12 6.2 10 8.87 47
Note:
With the compensation, the control loop has the bandwidth at about
1/10 switching frequency and the phase margin higher than 45
degree.
External Bootstrap Diode
An external bootstrap diode may enhance the
efficiency of the regulator. In below cases, an
external BST diode is recommended from the 5V
to BST pin:
z There is a 5V rail available in the system;
z V
IN
is no greater than 5V;
z V
OUT
is between 3.3V and 5V;
This diode is also recommended for high duty
cycle operation (when V
OUT
/ V
IN
> 65%)
applications.
The bootstrap diode can be a low cost one such
as IN4148 or BAT54.
MP2451
BS
SW
5V
0.1uF
Figure 2—External Bootstrap Diode
At no load or light load, the converter may
operate in pulse skipping mode in order to
maintain the output voltage in regulation. Thus
there is less time to refresh the BS voltage. In
order to have enough gate voltage under such
operating conditions, the difference of V
IN
–V
OUT
should be greater than 3V. For example, if the
V
OUT
is set to 3.3V, the V
IN
needs to be higher
than 3.3V+3V=6.3V to maintain enough BS
voltage at no load or light load. To meet this
requirement, EN pin can be used to program the
input UVLO voltage to V
OUT
+3V.
MP245136V, 2MHz, 0.6A, STEP-DOWN CONVERTER
MP2451 Rev. 1.33 www.MonolithicPower.com
4/29/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2014 MPS. All Rights Reserved.
12
TYPICAL APPLICATION CIRCUITS
MP2451
SW
VIN
EN
FB
GND
BST
1
5
6
3
2
4
C1
C3
33pF
C4
100nF
D1
V
6-24V
IN
V
OUT
3.3V
Control
Figure 3—3.3V Output Typical Application Schematic
MP2451
SW
VIN
EN
FB
GND
BST
1
5
6
3
2
4
C1
C3
C4
100nF
D1
V
18-36V
47pF
IN
V
OUT
12V
Control
Figure 4—12V Output Typical Application Schematic
P1-P3P4-P6P7-P9P10-P12P13-P15

MP2451DT-LF-Z

Mfr. #:
Buy MP2451DT-LF-Z
Manufacturer:
Monolithic Power Systems (MPS)
Description:
Switching Voltage Regulators 600mA 36V 2MHz Non-sync Buck
Lifecycle:
New from this manufacturer.
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