MP1591
2A, 32V, 330KHz
Step-Down Converter
The Future of Analog IC Technology
DESCRIPTION
The MP1591 is a high voltage step-down
converter ideal for automotive power adapter
battery chargers. Its wide 6.5V to 32V input
voltage range covers the automotive battery’s
requirements and it achieves 2A continuous
output for quick charge capability.
Current mode operation provides fast transient
response and eases loop stabilization. Fault
protection includes cycle-by-cycle current
limiting and thermal shutdown. In shutdown
mode, the converter draws only 20µA of supply
current.
The MP1591 requires a minimum number of
readily available external components to
complete a 2A step-down DC to DC converter
solution.
FEATURES
•
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•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Wide 6.5V to 32V Input Operating Range
34V Absolute Maximum Input
2A Output Current
120mΩ Internal Power MOSFET Switch
Stable with Low ESR Output Ceramic
Capacitors
Up to 95% Efficiency
20µA Shutdown Mode
Fixed 330KHz Frequency
Thermal Shutdown
Cycle-by-Cycle Over Current Protection
Output Adjustable From 1.23V to 21V
Under Voltage Lockout
Reference Voltage Output
Available in 8-Pin SOIC Packages
Automotive Power Adapters
PDA and Cellular Phone Battery Chargers
Distributed Power Systems
Automotive Aftermarket Electronics
APPLICATIONS
EVALUATION BOARD REFERENCE
Board Number
EV0020
Dimensions
2.1”X x 1.4”Y x 0.5”Z
“MPS” and “The Future of Analog IC Technology” are Registered Trademarks of
Monolithic Power Systems, Inc.
TYPICAL APPLICATION
INPUT
6.5V to 32V
C2
10nF
Efficiency vs
Load Current
100
90
V
OUT
=5V
V
OUT
=3.3V
2
1
OFF ON
OPEN
NOT USED
7
EN
EFFICIENCY (%)
IN
BS
3
SW
8
MP1591
REF
GND
4
FB
COMP
6
5
D1
OUTPUT
2.5V
2A
80
70
60
50
40
30
20
0
C3
OPEN
C4
4.7nF
V
IN
=12V
0.5
1
1.5
LOAD CURRENT (A)
2
MP1591 Rev. 2.3
9/27/2006
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2006 MPS. All Rights Reserved.
1
MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER
PACKAGE REFERENCE
TOP VIEW
BS
IN
SW
GND
1
2
3
4
8
7
6
5
REF
EN
COMP
FB
ABSOLUTE MAXIMUM RATINGS
(1)
IN Supply Voltage........................ –0.3V to +34V
SW Voltage............................. –1V to V
IN
+ 0.3V
BS Voltage ....................V
SW
– 0.3V to V
SW
+ 6V
All Other Pins................................. –0.3V to +6V
Junction Temperature...............................150°C
Lead Temperature ....................................260°C
Storage Temperature ..............–65°C to +150°C
Recommended Operating Conditions
(2)
EXPOSED PAD
ON BACKSIDE
(SOIC8N ONLY)
CONNECT TO PIN 4
Input Voltage ................................... 6.5V to 32V
Operating Temperature .............–40°C to +85°C
Thermal Resistance
Temperature
–40°C to +85°C
–40°C to +85°C
(3)
Part Number*
MP1591DN
MP1591DS
*
Package
SOIC8E
SOIC8
SOIC8 (w/ Exposed Pad) ....... 50 ...... 10...
°C/W
SOIC8..................................... 90 ...... 45...
°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. MP1591DN–Z)
For RoHS Compliant Packaging, add suffix –LF
(eg. MP1591DN–LF–Z)
ELECTRICAL CHARACTERISTICS
V
IN
= 12V, T
A
= +25°C, unless otherwise noted.
Parameter
Shutdown Supply Current
Supply Current
Feedback Voltage
Error Amplifier Voltage Gain
Error Amplifier Transconductance
High-Side Switch On Resistance
(4)
Low-Side Switch On Resistance
(4)
High-Side Switch Leakage Current
Current Limit
(5)
Current Sense to COMP
Transconductance
Oscillation Frequency
Short Circuit Oscillation Frequency
Maximum Duty Cycle
(4)
Minimum Duty Cycle
(4)
EN Shutdown Threshold Voltage
Enable Pull-Up Current
EN UVLO Threshold
EN UVLO Threshold Hysteresis
∆I
C
=
±10µA
500
Symbol Condition
V
EN
=
0V
V
EN
= 5V, V
FB
= 1.4V
6.5V
≤
V
IN
≤
32V, V
COMP
< 2V
Min
Typ
20
1.0
1.230
400
700
120
8.5
0
3.6
3.5
280
V
FB
= 0V
V
FB
= 1.0V
V
FB
= 1.5V
0.8
V
EN
= 0V
V
EN
Rising
2.4
330
35
90
1.2
1.8
2.6
250
380
1100
Max
35
1.2
1.258
Units
µA
mA
V
V/V
µA/V
mΩ
Ω
µA
A
A/V
KHz
KHz
%
%
V
µA
V
mV
1.202
V
EN
= 0V, V
SW
= 0V
2.5
10
4.9
0
1.6
2.8
MP1591 Rev. 2.3
9/27/2006
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2006 MPS. All Rights Reserved.
2
MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER
ELECTRICAL CHARACTERISTICS
(continued)
V
IN
= 12V, T
A
= +25°C, unless otherwise noted.
Parameter
Thermal Shutdown
(4)
REF Voltage
REF Load Regulation
(4)
REF Line Regulation
(4)
I
REF
= 0
∆I
REF
= 0 to 1mA
I
REF
= 100µA, V
IN
= 6.5 to 32V
Symbol Condition
Min
Typ
160
5.0
100
30
Max
Units
°C
V
mV
mV
Notes:
4) These parameters are guaranteed by design, not production tested.
5) Equivalent output current = 1.5A
≥
50% Duty Cycle
2.0A
≤
50% Duty Cycle
Assumes ripple current = 30% of load current.
Slope compensation changes current limit.
PIN FUNCTIONS
Pin #
1
2
Name Description
BS
IN
High-Side Gate Drive Boost Input. BS supplies the drive for the high-side N-Channel MOSFET
switch. Connect a 10nF or greater capacitor from SW to BS to power the high-side switch.
Power Input. IN supplies the power to the IC, as well as the step-down converter switches.
Drive IN with a 6.5V to 32V power source. Bypass IN to GND with a suitably large capacitor to
eliminate noise on the input to the IC. See
Input Capacitor.
Power Switching Output. SW is the switching node that supplies power to the output. Connect
the output LC filter from SW to the output load. Note that a capacitor is required from SW to BS
to power the high-side switch.
Ground. For the MP1591DN, connect the Exposed Pad to pin 4.
Feedback Input. FB senses the output voltage to regulate that voltage. Drive FB with a resistive
voltage divider from the output voltage. The feedback threshold is 1.230V. See
Setting the
Output Voltage.
3
SW
4
5
GND
FB
6
COMP Compensation Node. COMP is used to compensate the regulation control loop. Connect a
series RC network from COMP to GND to compensate the regulation control loop. In some
cases, an additional capacitor from COMP to GND is required. See
Compensation.
EN
REF
Enable/UVLO. A voltage greater than 2.8V enables operation. For complete low current
shutdown the EN pin voltage needs to be less than 800mV.
Reference Output. REF is the 5V reference voltage output. It can supply up to 1mA to external
circuitry. If used, bypass REF to GND with 10nF or greater capacitor. Leave REF unconnected
if not used.
7
8
MP1591 Rev. 2.3
9/27/2006
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2006 MPS. All Rights Reserved.
3
MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER
OPERATION
The MP1591 is a current mode step-down
regulator. It regulates input voltages from 6.5V
to 32V down to an output voltage as low as
1.230V and is able to supply up to 2A of load
current.
The MP1591 uses current-mode control to
regulate the output voltage. The output voltage
is measured at FB through a resistive voltage
divider and amplified through the internal error
amplifier. The output current of the
transconductance error amplifier is presented at
COMP where a network compensates the
regulation control system.
The voltage at COMP is compared to the switch
current measured internally to control the output
voltage. The converter uses an internal
N-Channel MOSFET switch to step-down the
input voltage to the regulated output voltage.
Since the MOSFET requires a gate voltage
greater than the input voltage, a boost capacitor
connected between SW and BS drives the gate.
The capacitor is internally charged while SW is
low. An internal 10Ω switch from SW to GND is
used to insure that SW is pulled to GND when
the switch is off to fully charge the BS capacitor
IN 2
REF 8
5V
INTERNAL
REGULATORS
OSCILLATOR
SLOPE
COMP
CLK
CURRENT
SENSE
AMPLIFIER
+
--
M1
35/330KHz
+
1
Q
Q
BS
+
S
R
1.2V
EN 7
--
SHUTDOWN
COMPARATOR
LOCKOUT
COMPARATOR
--
CURRENT
COMPARATOR
3
M2
SW
--
2.60V/
2.35V
1.8V
+
THERMAL
PROTECTION
ERROR
AMPLIFIER
4
GND
+
--
FREQUENCY
FOLDBACK
COMPARATOR
--
0.7V 1.230V
+
5
FB
6
COMP
Figure 1—Functional Block Diagram
MP1591 Rev. 2.3
9/27/2006
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2006 MPS. All Rights Reserved.
4
MP1591 – 2A, 32V, 330KHz 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.
The voltage divider divides the output voltage
down by the ratio:
V
FB
=
V
OUT
×
R2
(R1
+
R2)
The inductance value can be calculated by the
equation:
L1
=
V
OUT
×
( V
IN
−
V
OUT
)
( V
IN
×
f
× ∆
I)
Where V
IN
is the input voltage, f is the switching
frequency and
∆I
is the peak-to-peak inductor
ripple current.
Table 1 lists a number of suitable inductors
from various manufacturers.
Table 1—Inductor Selection Guide
Package
Dimensions
(mm)
Vendor/
Core
Core
Model
Type
Material W
L
H
Sumida
CR75
CDH74
Open
Open
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
7.0
7.3
5.5
5.5
6.7
7.8
8.0
5.7
5.7
6.7
5.5
5.2
5.5
5.5
3.0
Where V
FB
is the feedback voltage and V
OUT
is
the output voltage.
Thus the output voltage is:
V
OUT
=
1.230
×
(R1
+
R2)
R2
A typical value for R2 can be as high as 100kΩ,
but 10kΩ is recommended. Using that value, R1
is determined by:
R1
≅
8.18
×
( V
OUT
−
1.230 )
CDRH5D28 Shielded
CDRH5D28 Shielded
CDRH6D28 Shielded
CDRH104R Shielded
Toko
D53LC
Type A
D75C
D104C
D10FL
Coilcraft
DO3308
DO3316
Open
Open
Shielded
Shielded
Shielded
Open
For example, for a 3.3V output voltage, R2 is
10kΩ, and R1 is 17kΩ.
Inductor (L1)
The inductor is required to supply constant
current to the output load while being driven by
the switched input voltage. A larger value
inductor results in less ripple current that results
in lower output ripple voltage. However, the
larger value inductor has a larger physical size,
higher series resistance, and/or lower
saturation current. Choose an inductor that
does not saturate under the worst-case load
conditions. A good rule to use for determining
the inductance is to allow the peak-to-peak
ripple current in the inductor to be
approximately 30% of the maximum load
current that the IC can provide. Also, make sure
that the peak inductor current (the load current
plus half the peak-to-peak inductor ripple
current) is below the 2.3A minimum current
limit.
10.1 10.0 3.0
5.0
7.6
9.7
9.4
9.4
5.0
7.6
1.5
3.0
5.1
4.0
10.0 10.0 4.3
13.0 3.0
13.0 5.1
Input Capacitor (C1)
The input current to the step-down converter is
discontinuous, and so a capacitor is required to
supply the AC current to the step-down
converter while maintaining the DC input
voltage. A low ESR capacitor is required to
keep the noise at the IC to a minimum. Ceramic
capacitors are preferred, but tantalum or low
ESR electrolytic capacitors may also suffice.
MP1591 Rev. 2.3
9/27/2006
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2006 MPS. All Rights Reserved.
5
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