TM
MP1411
2A, 18V, 380KHz
Step-Down Converter
The Future of Analog IC Technology
TM
DESCRIPTION
The MP1411 is a monolithic step-down switch
mode converter with a built in internal power
MOSFET. It achieves 2A continuous output
current over a wide input supply range with
excellent load and line regulation.
Current mode operation provides fast transient
response and eases loop stabilization.
Fault condition protection includes cycle-by-cycle
current limiting and thermal shutdown. In
shutdown mode the regulator draws 23µA of
supply
current.
Programmable
soft-start
minimizes the inrush supply current and the
output overshoot at initial startup.
The MP1411 requires a minimum number of
readily available standard external components.
FEATURES
•
•
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•
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•
•
•
•
•
•
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2A Output Current
0.2Ω Internal Power MOSFET Switch
Stable with Low ESR Output Ceramic
Capacitors
Up to 95% Efficiency
23µA Shutdown Mode
Fixed 380KHz Frequency
Thermal Shutdown
Cycle-by-Cycle Over Current Protection
Wide 4.75V to 18V Operating Input Range
Output Adjustable from 0.92V to 16V
Programmable Under Voltage Lockout
Available in an MSOP10 with Exposed Pad
Package
Distributed Power Systems
Battery Charger
DSL Modems
Pre-Regulator for Linear Regulators
APPLICATIONS
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“MPS” and “The Future of Analog IC Technology” are Trademarks of Monolithic
Power Systems, Inc.
TYPICAL APPLICATION
INPUT
4.75V - 18V
4
2
BS
SW
C5
10nF
IN
EN
Efficiency vs
Output Current
95
90
EFFICIENCY (%)
OPEN = AUTOMATIC
STARTUP
9
10
5.0V
3.3V
2.5V
5
7
MP1411
SS
GND
6
FB
COMP
8
D1
B220A
V
OUT
3.3V/2A
85
80
75
70
65
60
0
0.5
1.0
1.5
C6
OPEN
C3
3.9nF
2.0
2.5
MP1411_TAC_S01
OUTPUT CURRENT (A)
MP1411_EC01
MP1411 Rev. 1.3
1/22/2010
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2010 MPS. All Rights Reserved.
1
TM
MP1411 – 2A, 18V, 380KHz STEP-DOWN CONVERTER
PACKAGE REFERENCE
ABSOLUTE MAXIMUM RATINGS
(1)
Supply Voltage (V
IN
) .................................... 20V
Switch Node Voltage (V
SW
).......................... 21V
Bootstrap Voltage (V
BS
) ....................... V
SW
+ 6V
Feedback Voltage (V
FB
) ................. –0.3V to +6V
Enable/UVLO Voltage (V
EN
)........... –0.3V to +6V
Comp Voltage (V
COMP
) ................... –0.3V to +6V
SS Voltage (V
SS
)............................ –0.3V to +6V
Junction Temperature.............................+150°C
Lead Temperature ..................................+260°C
Storage Temperature ..............–65°C to +150°C
TOP VIEW
NC
BS
NC
IN
SW
1
2
3
4
5
10
9
8
7
6
SS
EN
COMP
FB
GND
EXPOSED PAD
CONNECT TO PIN 6
Recommended Operating Conditions
MP1411_PD01_MSOP10
(2)
Supply Voltage (V
IN
) ...................... 4.75V to 18V
Operating Temperature.................–40°C to +85°C
Thermal Resistance
Part Number*
MP1411DH
*
Package
MSOP10
Temperature
–40°C to +85°C
(3)
MSOP10 with Exposed Pad ... 55 ...... 12...
°C/W
Notes:
1) Exceeding these ratings may damage the device.
2) The device is not guaranteed to function outside of its
operating conditions.
3) Measured on approximately 1” square of 1 oz copper.
θ
JA
θ
JC
For Tape & Reel, add suffix –Z (eg. MP1411DH–Z)
For Lead Free, add suffix –LF (eg. MP1411DH–LF–Z)
ELECTRICAL CHARACTERISTICS
V
IN
= 12V, T
A
= +25°C, unless otherwise noted.
Parameter
Feedback Voltage
Upper Switch On Resistance
Lower Switch On Resistance
Upper Switch Leakage
Current Limit
(4)
Current Sense Transconductance
Output Current to Comp Pin Voltage
Error Amplifier Voltage Gain
Error Amplifier Transconductance
Oscillator Frequency
Short Circuit Frequency
Soft-Start Pin Equivalent
Output Resistance
Symbol Condition
V
FB
R
DS(ON)1
R
DS(ON)2
V
EN
= 0V, V
SW
= 0V
2.8
G
CS
A
VEA
G
EA
f
S
V
FB
= 0V
∆I
C
=
±10µA
550
4.75V
≤
V
IN
≤
18V
Min
0.892
Typ
0.920
0.2
10
0
3.4
1.95
400
830
380
240
9
1150
Max
0.948
Units
V
Ω
Ω
µA
A
A/V
V/V
µA/V
KHz
KHz
kΩ
10
MP1411 Rev. 1.3
1/22/2010
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2010 MPS. All Rights Reserved.
2
TM
MP1411 – 2A, 18V, 380KHz STEP-DOWN CONVERTER
ELECTRICAL CHARACTERISTICS
(continued)
V
IN
= 12V, T
A
= +25°C, unless otherwise noted.
Parameter
Maximum Duty Cycle
Minimum On Time
EN Shutdown Threshold
Enable Pull Up Current
EN UVLO Threshold Rising
EN UVLO Threshold Hysteresis
Supply Current (Shutdown)
Supply Current (Quiescent)
Thermal Shutdown
Note:
4) Slope compensation changes current limit above 40% duty cycle.
Symbol Condition
D
MAX
V
FB
= 0.8V
t
ON
I
CC
> 100µA
V
EN
= 0V
V
EN
Rising
V
EN
≤
0.4V
V
EN
≥
3V
Min
0.7
2.37
Typ
90
100
1.0
1.0
2.50
210
23
1.1
160
Max
1.3
2.62
36
1.3
Units
%
ns
V
µA
V
mV
µA
mA
°C
PIN FUNCTIONS
Pin #
1
2
Name Description
No Connect.
Bootstrap. This capacitor (C5) is needed to drive the power switch’s gate above the supply
voltage. It is connected between the SW and BS pins to form a floating supply across the
power switch driver. The voltage across C5 is about 5V and is supplied by the internal +5V
supply when the SW pin voltage is low.
NC
No Connect.
IN
Supply Voltage. The MP1411 operates from a +4.75V to +18V unregulated input. C1 is needed
to prevent large voltage spikes from appearing at the input.
SW Switch. This connects the inductor to either IN through M1 or to GND through M2.
GND Ground. This pin is the voltage reference for the regulated output voltage. For this reason care
must be taken in its layout. This node should be placed outside of the D1 to C1 ground path to
prevent switching current spikes from inducing voltage noise into the part.
FB
Feedback. An external resistor divider from the output to GND, tapped to the FB pin, sets the
output voltage. To prevent current limit runaway during a short circuit fault condition the
frequency foldback comparator lowers the oscillator frequency when the FB voltage is below
400mV.
COMP Compensation. This node is the output of the transconductance error amplifier and the input to the
current comparator. Frequency compensation is done at this node by connecting a series R-C to
ground. See the compensation section for exact details.
EN
Enable/UVLO. A voltage greater than 2.62V enables operation. Leave EN unconnected for
automatic startup. An Under Voltage Lockout (UVLO) function can be implemented by the
addition of a resistor divider from V
IN
to GND. For complete low current shutdown the EN pin
voltage needs to be less than 700mV.
SS
Soft-Start. Connect SS to an external capacitor to program the soft-start. If unused, leave it
open.
NC
BS
3
4
5
6
7
8
9
10
MP1411 Rev. 1.3
1/22/2010
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2010 MPS. All Rights Reserved.
3
TM
MP1411 – 2A, 18V, 380KHz STEP-DOWN CONVERTER
OPERATION
The MP1411 is a current mode regulator. That
is, the COMP pin voltage is proportional to the
peak inductor current. At the beginning of a
cycle: the upper transistor M1 is off; the lower
transistor M2 is on (see Figure 1); the COMP
pin voltage is higher than the current sense
amplifier output; and the current comparator’s
output is low. The rising edge of the 380KHz
CLK signal sets the RS Flip-Flop. Its output
turns off M2 and turns on M1 thus connecting
the SW pin and inductor to the input supply.
The increasing inductor current is sensed and
amplified by the Current Sense Amplifier. Ramp
compensation is summed to Current Sense
Amplifier output and compared to the Error
Amplifier output by the Current Comparator.
When the Current Sense Amplifier plus Slope
Compensation signal exceeds the COMP pin
voltage, the RS Flip-Flop is reset and the
MP1411 reverts to its initial M1 off, M2 on state.
If the Current Sense Amplifier plus Slope
Compensation signal does not exceed the
COMP voltage, then the falling edge of the CLK
resets the Flip-Flop.
The output of the Error Amplifier integrates the
voltage difference between the feedback and
the 0.92V bandgap reference. The polarity is
such that an FB pin voltage lower than 0.92V
increases the COMP pin voltage. Since the
COMP pin voltage is proportional to the peak
inductor current an increase in its voltage
increases current delivered to the output. The
lower 10Ω switch ensures that the bootstrap
capacitor voltage is charged during light load
conditions. External Schottky Diode D1 carries
the inductor current when M1 is off.
IN 4
INTERNAL
REGULATORS
OSCILLATOR
240KHz/
380KHz
+
SLOPE
COMP
CLK
CURRENT
SENSE
AMPLIFIER
+
--
5V
2
Q
Q
5
BS
+
S
R
0.7V
EN 9
--
SHUTDOWN
COMPARATOR
LOCKOUT
COMPARATOR
--
CURRENT
COMPARATOR
SW
--
2.50V/
2.30V
+
+
--
1.8V
6
GND
FREQUENCY
FOLDBACK
COMPARATOR
--
0.4V
7
0.92V
FB
SS 10
+
ERROR
AMPLIFIER
8
COMP
MP1411_BD01
Figure 1—Functional Block Diagram
MP1411 Rev. 1.3
1/22/2010
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2010 MPS. All Rights Reserved.
4
TM
MP1411 – 2A, 18V, 380KHz STEP-DOWN CONVERTER
APPLICATION INFORMATION
COMPONENT SELECTION
Setting the Output Voltage
The output voltage is set using a resistive voltage
divider from the output voltage to FB pin. The
voltage divider divides the output voltage down to
the feedback voltage by the ratio:
V
FB
=
V
OUT
R2
R1
+
R2
Choose an inductor that will not saturate under
the maximum inductor peak current. The peak
inductor current can be calculated by:
I
LP
=
I
LOAD
+
⎛
V
OUT
V
× ⎜
1
−
OUT
2
×
f
S
×
L
⎜
V
IN
⎝
⎞
⎟
⎟
⎠
Where I
LOAD
is the load current.
Output Rectifier Diode
The output rectifier diode supplies the current to
the inductor when the high-side switch is off. To
reduce losses due to the diode forward voltage
and recovery times, use a Schottky diode.
Choose a diode whose maximum reverse
voltage rating is greater than the maximum
input voltage, and whose current rating is
greater than the maximum load current.
Input Capacitor
The input current to the step-down converter is
discontinuous, therefore a capacitor is required
to supply the AC current to the step-down
converter while maintaining the DC input
voltage. Use low ESR capacitors for the best
performance. Ceramic capacitors are preferred,
but tantalum or low-ESR electrolytic capacitors
may also suffice.
Since the input capacitor absorbs the input
switching current it requires an adequate ripple
current rating. The RMS current in the input
capacitor can be estimated by:
I
CIN
=
I
LOAD
×
V
OUT
⎛
V
OUT
×⎜
1
−
V
IN
⎜
V
IN
⎝
⎞
⎟
⎟
⎠
Where V
FB
is the feedback voltage and V
OUT
is
the output voltage.
Thus the output voltage is:
V
OUT
=
0.92
×
R1
+
R2
R2
A typical value for R2 can be as high as 100kΩ,
but a typical value is 10kΩ. Using that value, R1
is determined by:
R1
=
10.87
×
( V
OUT
−
0.92)
For example, for a 3.3V output voltage, R2 is
10kΩ, and R1 is 25.8kΩ.
Inductor
The inductor is required to supply constant
current to the output load while being driven by
the switched input voltage. A larger value inductor
will result in less ripple current that will result in
lower output ripple voltage. However, the larger
value inductor will have a larger physical size,
higher series resistance, and/or lower saturation
current. A good rule for determining the
inductance to use is to allow the peak-to-peak
ripple current in the inductor to be approximately
30% of the maximum switch current limit. Also,
make sure that the peak inductor current is below
the maximum switch current limit. The inductance
value can be calculated by:
L
=
⎛
⎞
V
OUT
V
× ⎜
1
−
OUT
⎟
f
S
×
∆I
L
⎜
V
IN
⎟
⎝
⎠
The worst-case condition occurs at V
IN
= 2V
OUT
,
where:
I
CIN
=
I
LOAD
2
Where f
S
is the switching frequency,
∆I
L
is the
peak-to-peak inductor ripple current and V
IN
is
the input voltage.
For simplification, choose the input capacitor
whose RMS current rating greater than half of
the maximum load current.
MP1411 Rev. 1.3
1/22/2010
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2010 MPS. All Rights Reserved.
5
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