View MP2355DN_1282349.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

TM
MP2355
3A, 23V, 380KHz Step-Down Converter
The Future of Analog IC Technology
TM
DESCRIPTION
The MP2355 is a step-down regulator with a built in internal Power MOSFET. It achieves 3A 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. Adjustable soft-start reduces the stress on the input source at turn-on. In shutdown mode the regulator draws 20A of supply current. The MP2355 uses a minimum number of readily available external components to complete a 3A step-down DC to DC converter solution.
FEATURES
* * * * * * * * * * * * * * Programmable Soft-Start 100m Internal Power MOSFET Switch Stable with Low ESR Output Ceramic Capacitors Up to 95% Efficiency 20A Shutdown Mode 3A Output Current Wide 4.75V to 23V Operating Input Range Fixed 380KHz Frequency Thermal Shutdown Cycle-by-Cycle Over Current Protection Under Voltage Lockout Distributed Power Systems Battery Chargers Pre-Regulator for Linear Regulators
APPLICATIONS
EVALUATION BOARD REFERENCE
Board Number EV2355DN-00A Dimensions 2.0"X x 1.3"Y x 0.5"Z
"MPS" and "The Future of Analog IC Technology" are Trademarks of Monolithic Power Systems, Inc.
TYPICAL APPLICATION
INPUT 4.75V to 23V 10nF
3 2
Efficiency vs Load Current
95 90
VOUT=5.0V
EFFICIENCY (%)
OPEN AUTOMATIC STARTUP
8 1
VIN RUN
BST LX
4 6
MP2355
SS GND 5 FB COMP 7
D1 B330A
OUTPUT 3.3V / 3A
85 80 75 70 65 60 0 500 1000 1500 2000 2500 3000 3500
VOUT=3.3V
VOUT=2.5V
10nF
4.7nF
MP2355_TAC_S01
LOAD CURRENT (mA)
MP2355_EC01
MP2355 Rev. 1.4 1/6/2006
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
1
TM
MP2355 - 3A, 23V, 380KHz STEP-DOWN CONVERTER
PACKAGE REFERENCE
TOP VIEW
SS BST VIN LX 1 2 3 4 8 7 6 5 RUN COMP FB GND
ABSOLUTE MAXIMUM RATINGS (1)
Supply Voltage VIN ....................... -0.3V to +25V Switch Voltage VLX ....................... -0.3V to +26V Boost Voltage VBST ..........VLX - 0.3V to VLX + 6V All Other Pins................................. -0.3V to +6V Junction Temperature...............................150C Lead Temperature ....................................260C Storage Temperature .............-65C to +150C
Recommended Operating Conditions
(2)
EXPOSED PAD ON BACKSIDE CONNECT TO PIN 4
MP2355_PD01-SOIC8N
Input Voltage VIN ............................ 4.75V to 23V Operating Temperature .............-40C to +85C
Thermal Resistance
Temperature -40C to +85C
(3)
Part Number* MP2355DN *
Package SOIC8N (Exposed Pad)
SOIC8N .................................. 50 ...... 10... 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.
JA
JC
For Tape & Reel, add suffix -Z (eg. MP2355DN-Z) For Lead Free, add suffix -LF (eg. MP2355DN -LF-Z)
ELECTRICAL CHARACTERISTICS
VIN = 12V, TA = +25C, unless otherwise noted.
Parameter Shutdown Supply Current Supply Current Feedback Voltage Error Amplifier Voltage Gain Error Amplifier Transconductance High-Side Switch-On Resistance Low-Side Switch-On Resistance High-Side Switch Leakage Current Current Limit (4) Current Sense to COMP Transconductance Oscillation Frequency Short Circuit Oscillation Frequency Maximum Duty Cycle Minimum Duty Cycle EN Shutdown Threshold Voltage Symbol Condition VRUN = 0V VRUN = 2.8, VFB = 1.5V VFB AVEA GEA RDS(ON)1 RDS(ON)2 VRUN = 0V, VLX = 0V 3.7 GCS fS VFB = 0V DMAX DMIN VFB = 1.0V VFB = 1.5V 0.9 330 20 ICOMP = 10A 500 4.75V VIN 23V, VCOMP < 2V Min Typ 20 1.0 1.222 400 800 95 10 0 4.3 3.8 380 35 90 0 1.2 1.5 430 50 10 1120 Max 30 1.2 1.250 Units A mA V V/V A/V m A A A/V KHz KHz % % V
1.194
MP2355 Rev. 1.4 1/6/2006
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
2
TM
MP2355 - 3A, 23V, 380KHz STEP-DOWN CONVERTER
ELECTRICAL CHARACTERISTICS (continued)
VIN = 12V, TA = +25C, unless otherwise noted.
Parameter Enable Pull Up Current EN UVLO Threshold EN UVLO Threshold Hysteresis Soft-Start Period Thermal Shutdown
Note: 4) 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 above 40% duty cycle.
Symbol Condition VRUN = 0V VEN Rising
Min 1.1 2.37
Typ 1.8 2.54 210
Max 2.5 2.71
Units A V mV ms C
CSS = 0.1F
10 150
TYPICAL PERFORMANCE CHARACTERISTICS
Circuit of Figure 2, VIN = 12V, VO = 3.3V, L1 = 15H, C1 = 10F, C2 = 22F, TA = +25C, unless otherwise noted.
Heavy Load Operation
3A Load
VIN, AC 200mV/div. VO, AC 20mV/div. IL 1A/div. VSW 10V/div. VIN, AC 20mV/div. VO, AC 20mV/div. IL 1A/div. VSW 10V/div.
Light Load Operation
No Load
MP2355-TPC01
MP2355-TPC02
Startup from Shutdown
No C4 3A Resistive Load
VEN 5V/div. VEN 5V/div.
Startup from Shutdown
C4 = 10nF 3A Resistive Load
VEN 5V/div.
Startup from Shutdown
C4 = 10nF No Load
VOUT 1V/div.
VOUT 1V/div.
VOUT 1V/div. IL 1A/div.
IL 1A/div.
IL 1A/div.
MP2355-TPC03
MP2355-TPC04
MP2355-TPC05
MP2355 Rev. 1.4 1/6/2006
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
3
TM
MP2355 - 3A, 23V, 380KHz STEP-DOWN CONVERTER
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Circuit of Figure 2, VIN = 12V, VO = 3.3V, L1 = 15H, C1 = 10F, C2 = 22F, TA = +25C, unless otherwise noted.
Load Transient
VO, AC 200mV/div.
Short Circuit Protection
VOUT 2V/div.
Short Circuit Recovery
VOUT 2V/div.
IL 1A/div. ILOAD 1A/div. IL 2A/div. IL 2A/div.
MP2355-TPC06
MP2355-TPC07
MP2355-TPC08
PIN FUNCTIONS
Pin # 1 Description Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor from SS to SS GND to set the soft-start period. A 0.1F capacitor sets the soft-start period to 10ms. To disable the soft-start feature, leave SS unconnected. High-Side Gate Drive Boost Input. BST supplies the drive for the high-side N-Channel BST MOSFET switch. Connect a 10nF or greater capacitor from LX to BST to power the high side switch. Power Input. VIN supplies the power to the IC, as well as the step-down converter switches. VIN Drive VIN with a 4.75V to 23V power source. Bypass VIN to GND with a suitably large capacitor to eliminate noise on the input to the IC. See Input Capacitor Power Switching Output. LX is the switching node that supplies power to the output. LX Connect the output LC filter from LX to the output load. Note that a capacitor is required from LX to BST to power the high-side switch. GND Ground. (Note: Connect the exposed pad on backside to Pin 5.) Feedback Input. FB senses the output voltage to regulate that voltage. Drive FB with a FB resistive voltage divider from the output voltage. The feedback threshold is 1.222V. See Setting the Output Voltage Compensation Node. COMP is used to compensate the regulation control loop. Connect a COMP 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 Enable/UVLO. A voltage greater than 2.71V enables operation. For complete low current RUN shutdown the EN pin voltage needs to be less than 900mV. Name
2
3
4 5 6
7 8
MP2355 Rev. 1.4 1/6/2006
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
4
TM
MP2355 - 3A, 23V, 380KHz STEP-DOWN CONVERTER
OPERATION
The MP2355 is a current-mode step-down regulator. It regulates input voltages from 4.75V to 23V down to an output voltage as low as 1.222V, and is able to supply up to 3A of load current. The MP2355 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 LX and BST drives the gate. The capacitor is internally charged while LX is low. An internal 10 switch from LX to GND is used to insure that LX is pulled to GND when LX is low to fully charge the BST.capacitor.
VIN 3 INTERNAL REGULATORS OSCILLATOR SLOPE COMP CLK CURRENT SENSE AMPLIFIER + -5V
42/380kHz +
2 Q Q 4
BST
+
S R
0.7V RUN 8
--
SHUTDOWN COMPARATOR LOCKOUT COMPARATOR
--
CURRENT COMPARATOR
LX
-2.37V/ 2.62V
1.8V + -5 GND
+
FREQUENCY FOLDBACK COMPARATOR
--
0.7V 1.222V 6 FB
+
ERROR AMPLIFIER 7 COMP 1 SS
MP2355_BD01
Figure 1--Functional Block Diagram
MP2355 Rev. 1.4 1/6/2006
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
5
TM
MP2355 - 3A, 23V, 380KHz STEP-DOWN CONVERTER
APPLICATIONS INFORMATION
INPUT 4.75V to 23V
3 2 BST LX 4 6
C5 10nF
OPEN AUTOMATIC STARTUP
8 1
VIN RUN
MP2355
SS GND 5 FB COMP 7
D1 B330A
OUTPUT 3.3V / 3A
C4 10nF
C6 OPEN
C3 4.7nF
MP2355_TAC_F02
Figure 2--MP2355 with Murata 22F, 10V Ceramic Output Capacitor
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:
VFB = VOUT R2 R1 + R2
R1 + R2 R2
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= VOUT V x 1 - OUT fS x IL VIN
Thus the output voltage is:
VOUT = 1.22 x
Where VFB is the feedback voltage and VOUT is the output voltage. A typical value for R2 can be as high as 100k, but a typical value is 10k. Using that value, R1 is determined by:
R1 = 8.18 x ( VOUT - 1.22)(k )
Where VIN is the input voltage, fS is the 380KHz switching frequency, and IL is the peak-topeak inductor ripple current. Choose an inductor that will not saturate under the maximum inductor peak current. The peak inductor current can be calculated by:
ILP = ILOAD + VOUT V x 1 - OUT 2 x fS x L VIN
For example, for a 3.3V output voltage, R2 is 10k, and R1 is 17k. 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.
Where ILOAD is the load current. Table 1 lists a number of suitable inductors from various manufacturers. The choice of which style inductor to use mainly depends on the price vs. size requirements and any EMI requirement.
MP2355 Rev. 1.4 1/6/2006
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
6
TM
MP2355 - 3A, 23V, 380KHz STEP-DOWN CONVERTER Table 1--Inductor Selection Guide
Package Dimensions (mm) W
7.0 7.3 5.5 5.5 6.7 10.1
Vendor/ Model Sumida
CR75 CDH74 CDRH5D28 CDRH5D28 CDRH6D28 CDRH104R
Core Type
Open Open Shielded Shielded Shielded Shielded
Core Material
Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite
L
7.8 8.0 5.7 5.7 6.7 10.0
H
5.5 5.2 5.5 5.5 3.0 3.0
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 (C1) absorbs the input switching current it requires an adequate ripple current rating. The RMS current in the input capacitor can be estimated by:
I C1 = ILOAD x VOUT VOUT x 1- VIN VIN

Sumida (continued)
Toko
D53LC Type A D75C D104C D10FL Shielded Shielded Shielded Open Open Open Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite 5.0 7.6 10.0 9.7 9.4 9.4 5.0 7.6 10.0 1.5 13.0 13.0 3.0 5.1 4.3 4.0 3.0 5.1
The worst-case condition occurs at VIN = 2VOUT, where:
I C1 = ILOAD 2
Coilcraft
DO3308 DO3316
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 which has a maximum reverse voltage rating is greater than the maximum input voltage, and who's current rating is greater than the maximum load current. Table 2 lists example Schottky diodes and manufacturers. Table 2--Diode Selection Guide
Diode SK33 SK34 B330 B340 MBRS330 MBRS340 Voltage/Current Manufacture Rating 30V, 3A 40V, 3A 30V, 3A 40V, 3A 30V, 3A 40V, 3A Diodes Inc. Diodes Inc. Diodes Inc. Diodes Inc. On Semiconductor On Semiconductor
For simplification, choose the input capacitor whose RMS current rating greater than half of the maximum load current. The input capacitor can be electrolytic, tantalum or ceramic. When using electrolytic or tantalum capacitors, a small, high quality ceramic capacitor, i.e. 0.1F, 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:
VIN = ILOAD V V x OUT x 1 - OUT f s x C1 VIN VIN
MP2355 Rev. 1.4 1/6/2006
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
7
TM
MP2355 - 3A, 23V, 380KHz STEP-DOWN CONVERTER Output Capacitor The output capacitor 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:
VOUT = VOUT V x 1 - OUT fS x L VIN 1 x R ESR + 8 x f S x C2
The DC gain of the voltage feedback loop is given by:
A VDC = R LOAD x G CS x A VEA x VFB VOUT
Where AVEA is the error amplifier voltage gain, is the current sense 400V/V; GCS transconductance, 3.8A/V; RLOAD is the load resistor value. The system has two poles of importance. One is due to the compensation capacitor (C3) and the output resistor of error amplifier, and the other is due to the output capacitor and the load resistor. These poles are located at:
fP1 = fP2 = GEA 2 x C3 x A VEA 1 2 x C2 x R LOAD
Where L is the inductor value, C2 is the output capacitance value, and RESR 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:
VOUT = VOUT 8 x fS
2
V x 1 - OUT VIN x L x C2

Where GEA is the transconductance, 800A/V.
error
amplifier
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:
VOUT = VOUT V x 1 - OUT fS x L VIN x R ESR
The system has one zero of importance, due to the compensation capacitor (C3) and the compensation resistor (R3). This zero is located at:
f Z1 = 1 2 x C3 x R3
The characteristics of the output capacitor also affect the stability of the regulation system. The MP2355 can be optimized for a wide range of capacitance and ESR values. Compensation Components MP2355 employs current mode control for easy compensation and fast transient response. The system stability and transient response are controlled through the COMP pin. COMP pin 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 system may have another zero of importance, if the output capacitor has a large capacitance and/or a high ESR value. The zero, due to the ESR and capacitance of the output capacitor, is located at:
fESR = 1 2 x C2 x RESR
In this case (as shown in Figure 2), a third pole set by the compensation capacitor (C6) and the compensation resistor (R3) is used to compensate the effect of the ESR zero on the loop gain. This pole is located at:
f P3 = 1 2 x C6 x R3
MP2355 Rev. 1.4 1/6/2006
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
8
TM
MP2355 - 3A, 23V, 380KHz STEP-DOWN CONVERTER The goal of compensation design is to shape the converter transfer function to get a desired loop gain. The system crossover frequency where the feedback loop has the unity gain is important. 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. Switching frequency for the MP2355 is 380KHz, so the desired crossover frequency is around 38KHz. Table 3 lists the typical values of compensation components for some standard output voltages with various output capacitors 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
VOUT
2.5V 3.3V 5V 12V 2.5V 3.3V 5V 12V
2) Choose the compensation capacitor (C3) to achieve the desired phase margin. For applications with typical inductor values, setting the compensation zero, fZ1, to less than one forth of the crossover frequency provides sufficient phase margin. Determine the C3 value by the following equation:
C3 > 4 2 x R3 x f C
Where R3 is the compensation resistor value and fC is the desired crossover frequency, 38KHz. 3) Determine if the second compensation capacitor (C6) is required. It is required if the ESR zero of the output capacitor is located at less than half of the 380KHz switching frequency, or the following relationship is valid:
f 1 L1
10H min. 15H min. 15H min. 22H min. 10H min. 15H min. 15H min. 22H min.
C2
22F Ceramic 22F Ceramic 22F Ceramic 22F Ceramic 560F Al. 30m ESR 560F Al 30m ESR 470F Al. 30m ESR 220F Al. 30m ESR
R3
3.9k 4.7k 7.5k 15k 100k 120k 150k 169k
C3
5.6nF 4.7nF 2.7nF 1.5nF 1nF 1nF 1nF 1nF
C6
None None None None 150pF 120pF 82pF 39pF
If this is the case, then add the second compensation capacitor (C6) to set the pole fP3 at the location of the ESR zero. Determine the C6 value by the equation:
C6 = C2 x R ESR R3
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
MP2355
SW
10nF
To optimize the compensation components for conditions not listed in Table 2, the following procedure can be used. 1) Choose the compensation resistor (R3) to set the desired crossover frequency. Determine the R3 value by the following equation:
R3 = 2 x C2 x f C VOUT x G EA x G CS VFB
MP2355_F03
Figure 3--External Bootstrap Diode This diode is also recommended for high duty cycle operation (when
VOUT >65%) and high VIN
output voltage (VOUT>12V) applications.
MP2355 Rev. 1.4 1/6/2006
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
9
TM
MP2355 - 3A, 23V, 380KHz STEP-DOWN CONVERTER
PACKAGE INFORMATION
SOIC8N (EXPOSED PAD)
PIN 1 IDENT. 0.229(5.820) 0.244(6.200)
NOTE 4 0.150(3.810) 0.157(4.000)
0.0075(0.191) 0.0098(0.249)
SEE DETAIL "A"
NOTE 2 0.013(0.330) 0.020(0.508) 0.050(1.270)BSC 0.011(0.280) x 45o 0.020(0.508)
0o-8o
0.016(0.410) 0.050(1.270)
DETAIL "A"
.028
NOTE 3 0.189(4.800) 0.197(5.000) 0.053(1.350) 0.068(1.730) 0.049(1.250) 0.060(1.524) SEATING PLANE 0.001(0.030) 0.004(0.101)
.050
0.200 (5.07 mm)
0.140 (3.55mm)
0.060
Land Pattern
NOTE: 1) Control dimension is in inches. Dimension in bracket is millimeters. 2) Exposed Pad Option (N-Package) ; 2.31mm -2.79mm x 2.79mm - 3.81mm. Recommend Solder Board Area: 2.80mm x 3.82mm = 10.7mm 2 (16.6 mil2) 3) The length of the package does not include mold flash. Mold flash shall not exceed 0.006in. (0.15mm) per side. With the mold flash included, over-all length of the package is 0.2087in. (5.3mm) max. 4) The width of the package does not include mold flash. Mold flash shall not exceed 0.10in. (0.25mm) per side. With the mold flash included, over-all width of the package is 0.177in. (4.5mm) max.
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.
MP2355 Rev. 1.4 1/6/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
10

▲Up To Search▲

Price & Availability of MP2355DN

	To Download MP2355DN Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .