ETC MP1591

TM
MP1591
2A, 32V, 330KHz
Step-Down Converter
The Future of Analog IC Technology
TM
DESCRIPTION
FEATURES
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.
EVALUATION BOARD REFERENCE
Board Number
Dimensions
EV0020
2.1”X x 1.4”Y x 0.5”Z
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
APPLICATIONS
•
•
•
•
Automotive Power Adapters
PDA and Cellular Phone Battery Chargers
Distributed Power Systems
Automotive Aftermarket Electronics
“MPS” and “The Future of Analog IC Technology” are Trademarks of Monolithic
Power Systems, Inc.
TYPICAL APPLICATION
C2
10nF
INPUT
6.5V to 32V
Efficiency vs
Load Current
100
VOUT=5V
90
2
OPEN
NOT USED
8
1
IN
BS
3
SW
EN
D1
MP1591
REF
GND
4
FB
COMP
OUTPUT
2.5V
2A
5
6
C3
OPEN
C4
4.7nF
EFFICIENCY (%)
OFF ON
7
VOUT=3.3V
80
70
60
50
40
VIN=12V
30
20
0
0.5
1
1.5
LOAD CURRENT (A)
MP1591_TAC_S01
MP1591 Rev. 1.8
7/22/2005
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2
MP1591_EC01
1
TM
MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER
ABSOLUTE MAXIMUM RATINGS (1)
PACKAGE REFERENCE
IN Supply Voltage........................ –0.3V to +34V
SW Voltage............................. –1V to VIN + 0.3V
BS Voltage ....................VSW – 0.3V to VSW + 6V
All Other Pins................................. –0.3V to +6V
Junction Temperature...............................150°C
Lead Temperature ....................................260°C
Storage Temperature ..............–65°C to +150°C
TOP VIEW
BS
1
8
REF
IN
2
7
EN
SW
3
6
COMP
GND
4
5
FB
EXPOSED PAD
ON BACKSIDE
(SOIC8N ONLY)
CONNECT TO PIN 4
Recommended Operating Conditions
Input Voltage ................................... 6.5V to 32V
Operating Temperature .............–40°C to +85°C
MP1591_PD01-SOIC8/N
Thermal Resistance
Part Number*
Package
Temperature
MP1591DN
SOIC8N
–40°C to +85°C
MP1591DS
SOIC8
–40°C to +85°C
*
(2)
For Tape & Reel, add suffix –Z (eg. MP1591DN–Z)
For Lead Free, add suffix –LF (eg. MP1591DN–LF–Z)
(3)
θJA
θJC
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.
ELECTRICAL CHARACTERISTICS
VIN = 12V, TA = +25°C, unless otherwise noted.
Parameter
Shutdown Supply Current
Supply Current
Symbol Condition
VEN = 0V
VEN = 5V, VFB = 1.4V
6.5V ≤ VIN ≤ 32V, VCOMP < 2V
Feedback Voltage
Min
Typ
20
1.0
Max
35
1.2
Units
µA
mA
1.202
1.230
1.258
V
Error Amplifier Voltage Gain
400
Error Amplifier Transconductance
∆IC = ±10µA
500
700
2.5
120
8.5
0
3.6
(4)
High-Side Switch On Resistance
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 Threshold Voltage
Enable Pull-Up Current
Under Voltage Lockout Threshold
Under Voltage Lockout Threshold
Hysteresis
MP1591 Rev. 1.8
7/22/2005
VEN = 0V, VSW = 0V
V/V
1100
µA/V
10
4.9
mΩ
Ω
µA
A
3.5
280
330
35
90
0.8
1.2
1.8
2.6
VFB = 0V
VFB = 1.0V
VFB = 1.5V
VEN = 0V
VIN Rising
2.4
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250
A/V
380
0
1.6
2.8
KHz
KHz
%
%
V
µA
V
mV
2
TM
MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER
ELECTRICAL CHARACTERISTICS (continued)
VIN = 12V, TA = +25°C, unless otherwise noted.
Parameter
Symbol Condition
Thermal Shutdown
Min
(4)
Typ
160
REF Voltage
REF Load Regulation (4)
REF Line Regulation (4)
IREF = 0
∆IREF = 0 to 1mA
IREF = 100µA, VIN = 6.5 to 32V
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 #
Name Description
1
BS
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.
2
IN
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.
3
SW
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.
4
GND
5
FB
6
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.
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.
7
EN
Enable Input. EN is a digital input that turns the regulator on or off. Drive EN high to turn on the
regulator and low to turn it off. For automatic startup, leave EN unconnected.
8
REF
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.
MP1591 Rev. 1.8
7/22/2005
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TM
MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER
OPERATION
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.
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.
IN 2
5V
REF 8
CURRENT
SENSE
AMPLIFIER
INTERNAL
REGULATORS
OSCILLATOR
35/330KHz
+
1.2V
--
EN 7
-2.60V/
2.35V
+
FREQUENCY
FOLDBACK
COMPARATOR
+
SLOPE
COMP
--
CLK
+
SHUTDOWN
COMPARATOR
--
S
Q
R
Q
CURRENT
COMPARATOR
1
BS
3
SW
4
GND
M1
M2
LOCKOUT
COMPARATOR
1.8V
--
+
--
0.7V 1.230V
5
FB
+
ERROR
AMPLIFIER
6
COMP
MP1591_BD01
Figure 1—Functional Block Diagram
MP1591 Rev. 1.8
7/22/2005
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TM
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:
VFB = VOUT ×
R2
(R1 + R2)
Where VFB is the feedback voltage and VOUT is
the output voltage.
Thus the output voltage is:
VOUT = 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 × ( VOUT − 1.230 )
The inductance value can be calculated by the
equation:
L1 = VOUT ×
( VIN − VOUT )
( VIN × f × ∆I)
Where VIN 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
Open
Ferrite
7.0
7.8
5.5
CDH74
Open
Ferrite
7.3
8.0
5.2
CDRH5D28 Shielded
Ferrite
5.5
5.7
5.5
For example, for a 3.3V output voltage, R2 is
10kΩ, and R1 is 17kΩ.
CDRH5D28 Shielded
Ferrite
5.5
5.7
5.5
CDRH6D28 Shielded
Ferrite
6.7
6.7
3.0
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. Also, make sure that the peak inductor
current (the load current plus half the peak-topeak inductor ripple current) is below the 2.3A
minimum current limit.
CDRH104R Shielded
Ferrite
10.1 10.0 3.0
MP1591 Rev. 1.8
7/22/2005
Toko
D53LC
Type A
Shielded
Ferrite
5.0
5.0
3.0
D75C
Shielded
Ferrite
7.6
7.6
5.1
D104C
Shielded
Ferrite
10.0 10.0 4.3
D10FL
Open
Ferrite
9.7
1.5
DO3308
Open
Ferrite
9.4
13.0 3.0
DO3316
Open
Ferrite
9.4
13.0 5.1
4.0
Coilcraft
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.
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5
TM
MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER
The input capacitor value should be greater
than 10µF. The capacitor can be electrolytic,
tantalum or ceramic. However, since it absorbs
the input switching current it requires an
adequate ripple current rating. Its RMS current
rating should be greater than approximately 1/2
of the DC load current.
For insuring stable operation C1 should be
placed as close to the IC as possible.
Alternately, a smaller high quality ceramic
0.1µF capacitor may be placed closer to the IC
and a larger capacitor placed farther away. If
using this technique, it is recommended that the
larger capacitor be a tantalum or electrolytic
type. All ceramic capacitors should be placed
close to the MP1591.
Output Capacitor (C5)
The output capacitor is required to maintain the
DC output voltage. Low ESR capacitors are
preferred to keep the output voltage ripple low.
The characteristics of the output capacitor also
affect the stability of the regulation control
system. Ceramic, tantalum or low ESR
electrolytic capacitors are recommended. In the
case of ceramic capacitors, the impedance at
the switching frequency is dominated by the
capacitance, and so the output voltage ripple is
mostly independent of the ESR. The output
voltage ripple is estimated to be:
VRIPPLE
⎛f
≅ 1.4 × VIN × ⎜⎜ LC
⎝ f SW
⎞
⎟
⎟
⎠
2
Where VRIPPLE is the output ripple voltage, fLC is
the resonant frequency of the LC filter, fSW is the
switching frequency.
In the case of tantalum or low-ESR electrolytic
capacitors, the ESR dominates the impedance
at the switching frequency, and so the output
ripple is calculated as:
VRIPPLE ≅ ∆I × R ESR
Output Rectifier Diode (D1)
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 rectifier.
Table 2 provides some recommended Schottky
rectifiers based on the maximum input voltage
and current rating.
Table 2—Diode Selection Guide
VIN
(Max)
15V
20V
30V
34V
2A Load Current
Part
Vendor
Number
30BQ15
4
B220
1
SK23
6
SR22
6
20BQ030
4
B230
1
SK23
6
SR23
3, 6
SS23
2, 3
21DQ04
4
MBRS240L
5
SK24
6
SS24
2, 3
3A Load Current
Part
Vendor
Number
B320
SK33
SS32
B330
B340L
MBRD330
SK33
SS33
B340L
MBRS340
SK34
SS34
1
1, 6
3
1
1
4, 5
1, 6
2, 3
1
4
1, 6
2, 3
Table 3 lists manufacturer’s websites.
Table 3—Schottky Diode Manufacturers
#
Vendor
Web Site
1
Diodes, Inc.
www.diodes.com
2
Fairchild Semiconductor
www.fairchildsemi.com
3
General Semiconductor
www.gensemi.com
4
International Rectifier
www.irf.com
5
On Semiconductor
www.onsemi.com
6
Pan Jit International
www.panjit.com.tw
Choose a rectifier whose maximum reverse
voltage rating is greater than the maximum
input voltage, and whose current rating is
greater than the maximum load current.
Where VRIPPLE is the output voltage ripple and
RESR is the equivalent series resistance of the
output capacitors.
MP1591 Rev. 1.8
7/22/2005
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TM
MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER
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:
A VDC =
VREF
× A VEA × G CS × R LOAD
VOUT
Where VREF is the feedback threshold voltage,
1.230V, AVEA is the transconductance error
amplifier voltage gain, 400 V/V, and GCS is the
current sense gain (roughly the output current
divided by the voltage at COMP), 3.5 A/V.
The system has 2 poles of importance; one is
due to the compensation capacitor (C4) and the
other is due to the output capacitor (C5). These
are:
fP1
R3
C3
C4
2.5V
22µF Ceramic
3.9kΩ
None
4.7nF
3.3V
22µF Ceramic
5.1kΩ
None
3.9nF
5V
22µF Ceramic
7.5kΩ
None
2.7nF
12V
22µF Ceramic
18kΩ
None
1.2nF
2.5V
47µF SP-Cap
8.2kΩ
None
2.2nF
1
3.3V
47µF SP-Cap
10kΩ
None
2.2nF
(2π × R LOAD × C5)
5V
47µF SP-Cap
16kΩ
None
1.5nF
12V
47µF SP-Cap
36kΩ
None
1nF
2.5V
560µF/6.3V, AL
30mΩ ESR
100kΩ
150pF
1nF
3.3V
560µF/6.3V, AL
30mΩ ESR
120kΩ
120pF
1nF
5V
470µF/10V, AL
30mΩ ESR
150kΩ
82pF
1nF
12V
220µF/25V, AL
30mΩ ESR
180kΩ
33pF
1nF
The system has one zero of importance due to
the compensation capacitor (C4) and the
compensation resistor (R3) which is
1
=
(2π × R3 × C4)
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 C3
f P3 =
MP1591 Rev. 1.8
7/22/2005
Table 4—Compensation Values for Typical
Output Voltage/Capacitor Combinations
C5
Where fP1 is the first pole, and GMEA is the error
amplifier transconductance (770µS) and
f Z1
Choosing the Compensation Components
The values of the compensation components
given in Table 4 yield a stable control loop for
the output voltage and given capacitor.
VOUT
G MEA
=
(2π × A VEA × C4)
fP2 =
The system crossover frequency fC, (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 one
tenth of the switching frequency. In this case,
the switching frequency is 330KHz, so use a
crossover frequency of 33KHz. Lower
crossover frequencies result in slower response
and worse transient load recovery. Higher
crossover frequencies can result in instability.
Note: “AL” = Electrolytic
1
(2π × R3 × C3)
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7
TM
MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER
To optimize the compensation components that
are not listed in Table 4, use the following
procedure.
Choose the compensation resistor to set the
desired crossover frequency. Determine the
value by the following equation:
R3 =
2π × C5 × VOUT × f C
G EA × G CS × VREF
Putting in the know constants and setting the
crossover frequency to the desired 33KHz:
R3 ≅ 6.88 × 10 7 × C5 × VOUT
Choose the compensation capacitor to set the
zero below one fourth of the crossover
frequency. Determine the value by the following
equation:
C4 >
2
1.93 × 10 −5
≈
R3
π × R3 × f C
Determine if the second compensation
capacitor, C3, is required. It is required if the
ESR zero of the output capacitor occurs at less
than four times the crossover frequency, or
Example:
VOUT = 5V, C5 = 22µF Ceramic (ESR = 10mΩ)
R3 ≈ 6.88x107 (22x10-6) (5) = 7568Ω
Use the nearest standard value of 7.5kΩ.
C4 > 1.93x10-5 / 7.5K = 2.57nF
Use standard value of 2.7nF.
8π x C5 x RESR x fC = 0.22, which is less than 1.
Therefore, no second compensation capacitor
(C3) is required.
External Bootstrap Diode
It is recommended that an external bootstrap
diode be added when the system has a 5V
fixed input or the power supply generates a 5V
output. This helps improve the efficiency of the
regulator. The bootstrap diode can be a low
cost one such as IN4148 or BAT54.
5V
BS
10nF
MP1591
SW
8π × C5 × R ESR × f C ≥ 1
If this is the case, then add the second
compensation resistor. Determine the value by
the equation:
C3 =
C5 × R ESR(MAX )
R3
MP1591_F02
Figure 2—External Bootstrap Diode
This diode is also recommended for high duty
cycle operation (when
VOUT
>65%) and high
VIN
output voltage (VOUT>12V) applications.
Where RESR(MAX) is the maximum ESR of the
output capacitor.
MP1591 Rev. 1.8
7/22/2005
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8
TM
MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER
TYPICAL APPLICATION CIRCUITS
C2
10nF
INPUT
6.5V to 32V
2
OFF ON
OPEN
NOT USED
7
8
1
IN
BS
3
SW
EN
MP1591
REF
GND
FB
COMP
4
5
D1
OUTPUT
2.5V
2A
6
C4
4.7nF
C3
OPEN
MP1591_F03
Figure 3—MP1591 with Murata 22µF / 10V Ceramic Output Capacitor
C2
10nF
INPUT
6.5V to 32V
2
OFF ON
OPEN
NOT USED
7
8
1
IN
BS
3
SW
EN
D1
MP1591
REF
GND
4
FB
COMP
OUTPUT
2.5V
2A
5
6
C3
OPEN
C4
2.2nF
MP1591_F04
Figure 4—MP1591 with Panasonic 47µF / 6.3V Special Polymer Output Capacitor
MP1591 Rev. 1.8
7/22/2005
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TM
MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER
PACKAGE INFORMATION
SOIC8 OR SOIC8N (WITH EXPOSED PAD)
PIN 1 IDENT.
0.229(5.820)
0.244(6.200)
0.0075(0.191)
0.0098(0.249)
0.150(3.810)
0.157(4.000)
SEE DETAIL "A"
NOTE 2
0.110(2.794)
0.150(3.810)
0.011(0.280) x 45o
0.020(0.508)
0.013(0.330)
0.020(0.508)
0.050(1.270)BSC
0.189(4.800)
0.197(5.004)
0.053(1.350)
0.068(1.730)
0o-8o
0.049(1.250)
0.060(1.524)
0.016(0.410)
0.050(1.270)
DETAIL "A"
SEATING PLANE
0.001(0.030)
0.004(0.101)
NOTE:
1) Control dimension is in inches. Dimension in bracket is millimeters.
2) Heat Slug Option Only (N Package)
NOTICE: The information in this document is subject to change without notice. Please contact MPS for current specifications.
Users should warrant and guarantee that third party Intellectual Property rights are not infringed upon when integrating MPS
products into any application. MPS will not assume any legal responsibility for any said applications.
MP1591 Rev. 1.8
7/22/2005
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