MPS MP1591 User Manual

Page 1

MP1591

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 20A 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

2A, 32V, 330KHz

Step-Down Converter

FEATURES

• Wide 6.5V to 32V Input Operating Range

• 34V Absolute Maximum Input

• 2A Output Current

• 120m Internal Power MOSFET Switch

• Stable with Low ESR Output Ceramic

Capacitors

• Up to 95% Efficiency

• 20A 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

TYPICAL APPLICATION

INPUT

6.5V to 32V

OFF ON

OPEN

NOT USED

MP1591

REF

GND COMP

OPEN

BSIN

4.7nF

10nF

“MPS” and “The Future of Analog IC Technology” are Registered Trademarks of Monolithic Power Systems, Inc.

Efficiency vs Load Current

100

=5V

OUT

=3.3V

OUTPUT

2.5V 2A

EFFICIENCY (%)

0 0.5 1 1.5 2

OUT

VIN=12V

LOAD CURRENT (A)

Page 2

MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER

PACKAGE REFERENCE

TOP VIEW

GND

EXPOSED PAD

ON BACKSIDE

(SOIC8N ONLY)

CONNECT TO PIN 4

Part Number* Package Temperature

MP1591DN SOIC8E

MP1591DS SOIC8

For Tape & Reel, add suffix –Z (eg. MP1591DN–Z)

For RoHS Compliant Packaging, add suffix –LF (eg. MP1591DN–LF–Z)

REF

COMP

–40°C to +85°C –40°C to +85°C

ABSOLUTE MAXIMUM RATINGS

(1)

IN Supply Voltage........................ –0.3V to +34V

SW Voltage............................. –1V to V

BS Voltage

....................VSW – 0.3V to VSW + 6V

+ 0.3V

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)

Input Voltage ................................... 6.5V to 32V

Operating Temperature .............–40°C to +85°C

Thermal Resistance

(3)

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 Symbol Condition Min Typ Max Units

Shutdown Supply Current VEN = 0V 20 35 A

Supply Current VEN = 5V, VFB = 1.4V 1.0 1.2 mA

Feedback Voltage

6.5V ≤ V

≤ 32V, V

COMP

< 2V

Error Amplifier Voltage Gain 400 V/V

Error Amplifier Transconductance

High-Side Switch On Resistance

Low-Side Switch On Resistance

(4)

120

(4)

8.5

ΔI

= ±10A

High-Side Switch Leakage Current VEN = 0V, VSW = 0V 0 10 A

Current Limit

Current Sense to COMP Transconductance

(5)

2.5 3.6 4.9 A

3.5 A/V

Oscillation Frequency 280 330 380 KHz

Short Circuit Oscillation Frequency VFB = 0V 35 KHz

Maximum Duty Cycle

Minimum Duty Cycle

(4)

= 1.0V 90 %

= 1.5V 0 %

EN Shutdown Threshold Voltage 0.8 1.2 1.6 V

Enable Pull-Up Current VEN = 0V 1.8 A

EN UVLO Threshold VEN Rising 2.4 2.6 2.8 V

EN UVLO Threshold Hysteresis 250 mV

1.202 1.230 1.258 V

500 700 1100 A/V

mΩ

Ω

Page 3

MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER

ELECTRICAL CHARACTERISTICS (continued)

VIN = 12V, TA = +25°C, unless otherwise noted.

Parameter Symbol Condition Min Typ Max Units

Thermal Shutdown

REF Voltage I

REF Load Regulation

REF Line Regulation

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.

(4)

160

= 0 5.0 V

(4)

I

(4)

REF

= 0 to 1mA 100 mV

REF

= 100A, VIN = 6.5 to 32V 30 mV

REF

°C

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 Ground. For the MP1591DN, connect the Exposed Pad to pin 4.

5 FB 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.

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.

7 EN 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.

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.

Page 4

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.

REF

1.2V

2.60V/

2.35V

INTERNAL

REGULATORS

SHUTDOWN

COMPARATOR

LOCKOUT

COMPARATOR

OSCILLATOR

35/330KHz

SLOPE

COMP

CLK

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 10 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

CURRENT

SENSE

AMPLIFIER

CURRENT

-COMPARATOR

SRQ

1.8V

GND

THERMAL

PROTECTION

ERROR

AMPLIFIER

COMP

FREQUENCY

FOLDBACK

COMPARATOR

1.230V0.7V

Figure 1—Functional Block Diagram

Page 5

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:

×=

OUTFB

Where V

is the feedback voltage and V

the output voltage.

Thus the output voltage is:

×=

OUT

230.1V

A typical value for R2 can be as high as 100k, but 10k is recommended. Using that value, R1 is determined by:

−×≅

OUT

For example, for a 3.3V output voltage, R2 is 10k, and R1 is 17k.

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.

)2R1R(

OUT

)2R1R(

)230.1V(18.81R

The inductance value can be calculated by the equation:

)VV(

OUTIN

)IfV(

Δ××

Where V

V1L

OUT

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

Vendor/

Model

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

CDRH6D28 Shielded Ferrite 6.7 6.7 3.0

CDRH104R Shielded Ferrite 10.1 10.0 3.0

Toko

D53LC Type A

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 4.0

Coilcraft

DO3308 Open Ferrite 9.4 13.0 3.0

DO3316 Open Ferrite 9.4 13.0 5.1

Core Type

Shielded Ferrite 5.0 5.0 3.0

Core

Material

(mm)

WL H

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.

Page 6

MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER

The input capacitor value should be greater than 10F. 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

0.1F 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:

⎞

⎛

⎟

⎜

V4.1V

××≅

INRIPPLE

⎜ ⎝

Where V

is the output ripple voltage, fLC is

RIPPLE

the resonant frequency of the LC filter, f

⎟ ⎠

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:

RIV

Δ≅

ESRRIPPLE

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

(Max)

15V 30BQ15 4

20V

30V

34V

2A Load Current 3A Load Current

Part

Number

B220 1 B320 1 SK23 6 SK33 1, 6 SR22 6 SS32 3

20BQ030 4 B330 1

B230 1 B340L 1 SK23 6 MBRD330 4, 5 SR23 3, 6 SK33 1, 6 SS23 2, 3 SS33 2, 3

21DQ04 4 B340L 1

MBRS240L 5 MBRS340 4

SK24 6 SK34 1, 6 SS24 2, 3 SS34 2, 3

Vendor

Part

Number

Vendor

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 V R

is the equivalent series resistance of the

ESR

is the output voltage ripple and

RIPPLE

output capacitors.

Page 7

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

Where V

REF

1.230V, A

REF

OUT

is the feedback threshold voltage,

is the transconductance error

VEA

amplifier voltage gain, 400 V/V, and G

RGA

LOADCSVEA

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:

Where f

is the first pole, and G

MEA

VEA

)4CA2(

××π

is the error

MEA

amplifier transconductance (770S) and

LOAD

)5CR2(

××π

The system has one zero of importance due to the compensation capacitor (C4) and the compensation resistor (R3) which is

)4C3R2(

××π

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

The system crossover frequency f

(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.

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.

Table 4—Compensation Values for Typical

Output Voltage/Capacitor Combinations

OUT

2.5V 22F Ceramic 3.9k None 4.7nF

3.3V 22F Ceramic 5.1k None 3.9nF

5V 22F Ceramic 7.5k None 2.7nF

12V 22F Ceramic 18k None 1.2nF

2.5V 47F SP-Cap 8.2k None 2.2nF

3.3V 47F SP-Cap 10k None 2.2nF

5V 47F SP-Cap 16k None 1.5nF

12V 47F SP-Cap 36k None 1nF

2.5V

3.3V

12V

Note: “AL” = Electrolytic

C5 R3 C3 C4

560F/6.3V, AL

30m ESR

560F/6.3V, AL

30m ESR

470F/10V, AL

30m ESR

220F/25V, AL

30m ESR

100k 150pF 1nF

120k 120pF 1nF

150k 82pF 1nF

180k 33pF 1nF

)3C3R2(

××π

Page 8

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:

fV5C2

×××π

COUT

××

VGG

REFCSEA

Putting in the know constants and setting the crossover frequency to the desired 33KHz:

V5C1088.63R ×××≅

OUT

Choose the compensation capacitor to set the zero below one fourth of the crossover frequency. Determine the value by the following equation:

5C−

≈

f3R

××π

1093.1

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

1fR5C8

≥×××π

CESR

If this is the case, then add the second compensation resistor. Determine the value by the equation:

R5C

)MAX(ESR

Example:

= 5V, C5 = 22F Ceramic (ESR = 10m)

OUT

R3  6.88x10

(22x10-6) (5) = 7568

Use the nearest standard value of 7.5k.

C4 > 1.93x10

-5

/ 7.5K = 2.57nF

Use standard value of 2.7nF.

8 x C5 x R

x fC = 0.22, which is less than 1.

ESR

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.

MP1591

10nF

Figure 2—External Bootstrap Diode

This diode is also recommended for high duty

OUT

cycle operation (when

output voltage (V

>12V) applications.

OUT

>65%) and high

Where R

ESR(MAX)

is the maximum ESR of the

output capacitor.

Page 9

MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER

TYPICAL APPLICATION CIRCUITS

INPUT

6.5V to 32V

10nF

OFF ON

OPEN

NOT USED

MP1591

REF

GND COMP

OPEN

BSIN

4.7nF

OUTPUT

2.5V 2A

Figure 3—MP1591 with Murata 22μF / 10V Ceramic Output Capacitor

BSIN

2.2nF

10nF

OUTPUT

2.5V 2A

INPUT

6.5V to 32V

OFF ON

OPEN

NOT USED

MP1591

REF

GND COMP

OPEN

Figure 4—MP1591 with Panasonic 47μF / 6.3V Special Polymer Output Capacitor

Page 10

PACKAGE INFORMATION

0.189(4.80)

0.197(5.00)

MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER

SOIC8

0.024(0.61)

0.063(1.60)

0.050(1.27)

PIN 1 ID

0.013(0.33)

0.020(0.51)

GAUGE PLANE

0.010(0.25) BSC

0o-8

0.150(3.80)

0.157(4.00)

TOP VIEW

0.053(1.35)

0.069(1.75) SEATING PLANE

0.004(0.10)

0.010(0.25)

0.050(1.27) BSC

FRONT VIEW

0.010(0.25)

0.020(0.50)

0.016(0.41)

0.050(1.27)

x 45

DETAIL "A"

0.228(5.80)

0.244(6.20)

0.213(5.40)

RECOMMENDED LAND PATTERN

0.0075(0.19)

0.0098(0.25)

SEE DETAIL "A"

SIDE VIEW

NOTE:

1) CONTROL DIMENSION IS IN INCHES. DIMENSION IN BRACKET IS IN MILLIMETERS.

2) PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.

3) PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.

4) LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.004" INCHES MAX.

5) DRAWING CONFORMS TO JEDEC MS-012, VARIATION AA.

6) DRAWING IS NOT TO SCALE.

Page 11

SOIC8E (WITH EXPOSED PAD)

0.189(4.80)

0.197(5.00)

MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER

0.124(3.15)

0.136(3.45)

PIN 1 ID

0.013(0.33)

0.020(0.51)

0.024(0.61)

0.063(1.60)

0.150(3.80)

0.157(4.00)

TOP VIEW

0.051(1.30)

0.067(1.70) SEATING PLANE

0.000(0.00)

0.006(0.15)

0.050(1.27) BSC

FRONT VIEW

0.050(1.27)

0.228(5.80)

0.244(6.20)

SEE DETAIL "A"

GAUGE PLANE

0.010(0.25) BSC

0o-8

BOTTOM VIEW

SIDE VIEW

0.010(0.25)

0.020(0.50)

0.016(0.41)

0.050(1.27)

DETAIL "A"

0.089(2.26)

0.101(2.56)

0.0075(0.19)

0.0098(0.25)

x 45

0.103(2.62)

0.213(5.40)

NOTE:

1) CONTROL DIMENSION IS IN INCHES. DIMENSION IN BRACKET IS IN MILLIMETERS.

2) PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.

3) PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASH

0.138(3.51)

RECOMMENDED LAND PATTERN

OR PROTRUSIONS.

4) LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.004" INCHES MAX.

5) DRAWING CONFORMS TO JEDEC MS-012, VARIATION BA.

6) DRAWING IS NOT TO SCALE.

NOTICE: The information in this document is subject to change without notice. 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.