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TM
MP1580
2A, 380 KHz Step-Down Converter
The Future of Analog IC Technology
TM
DESCRIPTION
The MP1580 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 23A of supply current. The MP1580 requires a minimum number of readily available standard external components. A synchronization pin allows the part to be driven to 600KHz.
FEATURES
* * * * * * * * * * * * * * * * 2A Output Current 0.18 Internal Power MOSFET Switch Stable with Low ESR Output Ceramic Capacitors Up to 95% Efficiency 23A Shutdown Mode Fixed 380KHz Frequency Thermal Shutdown Cycle-by-Cycle Over Current Protection Wide 4.75 to 25V Operating Input Range Output Adjustable from 1.22V to 21V Programmable Under Voltage Lockout Frequency Synchronization Input Available in an 8-Pin SO Package Distributed Power Systems Battery Chargers Pre-Regulator for Linear Regulators
APPLICATIONS
EVALUATION BOARD REFERENCE
Board Number EV0007 Dimensions 2.3"X x 1.5"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 25V OFF ON OPEN NOT USED
7 8
C5 10nF
95
2 IN EN 1 BS SW
Efficiency vs Output Current Voltage
VOUT = 5.0V VOUT = 3.3V VOUT = 2.5V
90
MP1580
SYNC GND 4 FB COMP 6
5
D1
EFFICIENCY (%)
3
OUTPUT 2.5V / 2A
85 80 75 70 0
C6 OPEN
C3 2.2nF
VIN = 10V
0.5 1 1.5 2
MP1580_TAC_S01
OUTPUT CURRENT (A)
MP1580_TAC_EC01
MP1580 Rev. 3.0 12/5/2005
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TM
MP1580 - 2A, 380KHz STEP-DOWN CONVERTER
PACKAGE REFERENCE
TOP VIEW
BS IN SW GND 1 2 3 4 8 7 6 5 SYNC EN COMP FB
BS IN SW GND 1 2 3 4
TOP VIEW
8 7 6 5 SYNC EN COMP FB
MP1580_PD01-SOIC8
MP1580_PD02-PDIP8
Part Number* MP1580HS *
Package SOIC8
Temperature -40C to +125C
Part Number** MP1580HP
Package PDIP8
Temperature -40C to +125C
For Tape & Reel, add suffix -Z (eg. MP1580HS-Z) For Lead Free, add suffix -LF (eg. MP1580HS -LF-Z)
** For Tape & Reel, add suffix -Z (eg. MP1580HP-Z)
For Lead Free, add suffix -LF (eg. MP1580HP -LF-Z)
ABSOLUTE MAXIMUM RATINGS (1)
Supply Voltage (VIN)..................................... 27V Switch Voltage (VSW).................. -1V to VIN + 1V Bootstrap Voltage (VBS) ....................... VSW + 6V Feedback Voltage (VFB) .................-0.3V to +6V Enable/UVLO Voltage (VEN)...........-0.3V to +6V Comp Voltage (VCOMP) ...................-0.3V to +6V Sync Voltage (VSYNC)......................-0.3V to +6V Junction Temperature ............................ +150C Lead Temperature ................................. +260C Storage Temperature.............. -65C to +150C
Recommended Operating Conditions
(2)
Input Voltage (VIN) ......................... 4.75V to 25V Operating Temperature...............-40C to +125C
Thermal Resistance
(3)
SOIC8.................................... 105 ..... 50... C/W PDIP8 ..................................... 95 ...... 55... 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
ELECTRICAL CHARACTERISTICS
VIN = 12V, TA = +25C, unless otherwise noted.
Parameter Feedback Voltage Upper Switch-On Resistance Lower Switch-On Resistance Upper Switch Leakage Current Limit (4) Current Limit Gain. Output Current to Comp Pin Voltage Error Amplifier Voltage Gain Error Amplifier Transconductance Oscillator Frequency Short Circuit Frequency Sync Frequency
MP1580 Rev. 3.0 12/5/2005
Symbol Condition 4.75V VIN 25V VCOMP < 2V
Min 1.198
Typ 1.222 0.18 10 0 3.0 1.95 400
Max 1.246
Units V A A A/V V/V
VEN = 0V, VSW = 0V 2.4
10 3.6
IC = 10A VFB = 0V Sync Drive 0V to 2.7V
500 342 20 445
770 380 35
1100 418 54 600
A/V KHz KHz KHz 2
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TM
MP1580 - 2A, 380KHz STEP-DOWN CONVERTER
ELECTRICAL CHARACTERISTICS (continued)
VIN = 12V, TA = +25C, unless otherwise noted.
Parameter Maximum Duty Cycle Minimum Duty Cycle EN Shutdown Threshold Voltage Enable Pull-Up Current EN UVLO Threshold Rising EN UVLO Threshold Hysteresis Supply Current (Shutdown) Supply Current (Quiescent) Thermal Shutdown
Note: 4) Derate current limit 0.011A/C.
Symbol Condition VFB = 1.0V VFB = 1.5V ICC > 100A VEN = 0V VEN Rising VEN 0.4V VEN 2.6V, VFB = 1.4V
Min
Typ 90
Max 0 1.3 1.8 2.62 36 1.2
Units % % V A V mV A mA C
0.7 1.15 2.37
1.0 1.46 2.495 210 23 1.0 160
PIN FUNCTIONS
Pin # 1 Name BS Description Bootstrap (C5). This capacitor is needed to drive the power switch's gate above the supply voltage. It is connected between 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. Supply Voltage. The MP1580 operates from a +4.75V to +25V unregulated input. C1 is needed to prevent large voltage spikes from appearing at the input. Switch. This connects the inductor to either IN through M1 or to GND through M2. 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. Feedback. An external resistor divider from the output to GND, tapped to the FB pin sets the output voltage. To prevent current limit run away during a short circuit fault condition the frequency foldback comparator lowers the oscillator frequency when the FB voltage is below 700mV. 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. Enable/UVLO. A voltage greater than 2.62V enables operation. For complete low current shutdown the EN pin voltage needs to be less than 700mV. Synchronization Input. This pin is used to synchronize the internal oscillator frequency to an external source. There is an internal 11k pull down resistor to GND; therefore leave SYNC unconnected if unused.
2 3 4
IN SW GND
5
FB
6 7 8
COMP EN SYNC
MP1580 Rev. 3.0 12/5/2005
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TM
MP1580 - 2A, 380KHz STEP-DOWN CONVERTER
OPERATION
The MP1580 is a current mode regulator; 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 (refer to 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 MP1580 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 1.222V bandgap reference. The polarity is such that an FB pin voltage less than 1.222V increases the COMP pin voltage. Since the COMP pin voltage is proportional to the peak inductor current, an increase in its voltage increases the current delivered to the output. The lower 10 switch ensures that the bootstrap capacitor voltage is charged during light load conditions. An external Schottky Diode D1 carries the inductor current when M1 is off (see Figure 1).
IN 2 INTERNAL REGULATORS SYNC 8 OSCILLATOR SLOPE COMP CLK CURRENT SENSE AMPLIFIER + -5V
40/380kHz +
1 Q Q 3
BS
+
S R
0.7V EN 7
--
SHUTDOWN COMPARATOR LOCKOUT COMPARATOR
--
CURRENT COMPARATOR
SW
-2.285V/ 2.495V
1.8V + -4 GND
+
FREQUENCY FOLDBACK COMPARATOR
--
0.7V 1.222V 5 FB
+
ERROR AMPLIFIER 6 COMP
MP1580_BD01
Figure 1--Functional Block Diagram
MP1580 Rev. 3.0 12/5/2005
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TM
MP1580 - 2A, 380KHz STEP-DOWN CONVERTER
APPLICATION INFORMATION
COMPONENT SELECTION
Sync Pin Operation The SYNC pin driving waveform should be a square wave with a rise time less than 20ns. The Minimum High voltage level is 2.7V and the Low level is less than 0.8V. The frequency of the external sync signal needs to be greater than 445KHz. A rising edge on the SYNC pin forces a reset of the oscillator. The upper transistor M1 is switched off immediately if it is not already off. 250ns later M1 turns on connecting SW to VIN. Setting the Output Voltage The output voltage is set using a resistive voltage divider from the output to FB (see Figure 3). The voltage divider divides the output voltage down by the ratio:
VFB = VOUT R2 R1 + R2
A good rule 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-to-peak inductor ripple current) is below the 2.4A minimum current limit. The inductance value can be calculated by the equation:
L = VOUT x ( VIN - VOUT ) VIN x f x I
Where VIN is the input voltage, f is the oscillator 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) W L H 7.0 7.3 5.5 5.5 6.7 10.1 5.0 7.6 10.0 9.7 9.4 9.4 7.8 8.0 5.7 5.7 6.7 10.0 5.0 7.6 10.0 11.5 13.0 13.0 5.5 5.2 5.5 5.5 3.0 3.0 3.0 5.1 4.3 4.0 3.0 5.1
Where VFB is the feedback voltage and VOUT is the output voltage. Thus the output voltage is:
VOUT = 1.222 x R1 + R2 R2
Vendor/ Model Sumida CR75 CDH74 CDRH5D28 CDRH5D28 CDRH6D28 CDRH104R Toko D53LC Type A D75C D104C D10FL Coilcraft DO3308 DO3316
Core Type Open Open Shielded Shielded Shielded Shielded Shielded Shielded Shielded Open Open Open
Core Material Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite
R2 can be as high as 100k, but a typical value is 10k. Using this value, R1 is determined by:
R1 8.18 x ( VOUT - 1.222)
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 results in less ripple current that in turn 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.
MP1580 Rev. 3.0 12/5/2005
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TM
MP1580 - 2A, 380KHz STEP-DOWN CONVERTER Input Capacitor The input current to the step-down converter is discontinuous, 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 lowESR electrolytic capacitors will also suffice. The input capacitor value should be greater than 10F. 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. To ensure stable operation, C1 should be placed as close to the IN pin as possible. Alternately, a smaller high quality ceramic 0.1F capacitor may be placed closer to the IN pin and a larger capacitor placed further away. If using this technique, it is recommended that the larger capacitor be a tantalum or electrolytic type capacitor. All ceramic capacitors should be placed close to the MP1580. Output Capacitor 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 oscillator frequency is dominated by the capacitance, so the output voltage ripple is mostly independent of the ESR. The output voltage ripple is estimated to be:
f VRIPPLE 1.4 x VIN x LC f
2
In the case of tantalum or low-ESR electrolytic capacitors, the ESR dominates the impedance at the oscillator frequency, therefore the output ripple is calculated as:
VRIPPLE I x R ESR
Where VRIPPLE is the output voltage ripple and RESR is the equivalent series resistance of the output capacitors. Output Rectifier Diode The output rectifier diode supplies the current to the inductor when the upper transistor M1 is off. To reduce losses due to the diode forward voltage and recovery times, use a Schottky rectifier. Table 2 provides the Schottky rectifier part numbers based on the maximum input voltage and current rating. Table 2--Schottky Rectifier Selection Guide
VIN (Max) 2A Load Current Part Number Vendor
15V 20V
30BQ015 B220 SK23 SR22 20BQ030 B230
4 1 6 6 4 1 6 3, 6 2, 3
26V
SK23 SR23 SS23
Table 3 lists some rectifier manufacturers. Table 3--Schottky Diode Manufacturers
Vendor Web Site
Where VRIPPLE is the output ripple voltage, fLC is the resonant frequency of the LC filter and f is the oscillator frequency.
Diodes, Inc. Fairchild Semiconductor General Semiconductor International Rectifier On Semiconductor Pan Jit International
www.diodes.com www.fairchildsemi.com www.gensemi.com www.irf.com www.onsemi.com www.panjit.com.tw
Choose a rectifier that has a maximum reverse voltage rating greater than the maximum input voltage, and a current rating greater than the maximum load current.
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TM
MP1580 - 2A, 380KHz 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 = R LOAD x G CS x A VEA x VFB VOUT
In this case, the switching frequency is 380KHz, so use a crossover frequency, fC, of 40KHz. 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 capacitor given. Table 4--Compensation Values for Typical Output Voltage/Capacitor Combinations
VOUT C2 R3 C3 C6
Where AVEA is the transconductance error amplifier voltage gain, 400 V/V, GCS is the current sense gain, (roughly the output current divided by the voltage at COMP), 1.95 A/V and RLOAD is the load resistance (VOUT / IOUT where IOUT is the output load current). The system has 2 poles of importance, one is due to the compensation capacitor (C3), and the other is due to the output capacitor (C2). These are:
fP1 = GEA 2 x C3 x A VEA
2.5V 3.3V 5V 12V 2.5V 3.3V 5V 12V
Where P1 is the first pole and GEA is the error amplifier transconductance (770A/V). and
fP2 1 = 2 x C2 x R LOAD
22F Ceramic 22F Ceramic 22F Ceramic 22F Ceramic 560F/6.3V (30m ESR) 560F/6.3V (30m ESR) 470F/10V (30m ESR) 220F/25V (30m ESR)
7.5k 10k 15k 33k 200k 200k 250k 250k
2.2nF 2nF 1.2nF 1nF 1nF 1nF 1nF 1nF
None None None None 100pF 82pF 56pF 27pF
To optimize the compensation components for conditions 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 = 2 x C2 x f C VOUT x G EA x G CS VFB
The system has one zero of importance, due to the compensation capacitor (C3) and the compensation resistor (R3). The zero is:
f Z1 = 1 2 x C3 x R3
If a large value capacitor (C2) with relatively high equivalent-series-resistance (ESR) is used, the zero due to the capacitance and ESR of the output capacitor can be compensated by a third pole set by R3 and C6. The pole is:
f P3 1 = 2 x C6 x R3
Putting in the known constants and setting the crossover frequency to the desired 40KHz:
R3 1.37 x 10 8 x C2 x VOUT
Choose the compensation capacitor to set the zero below 1/4 of the crossover frequency. Determine the value by the following equation:
C3 > 0.22 x C2 x VOUT R3
The system crossover frequency (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 1/10 of the switching frequency.
MP1580 Rev. 3.0 12/5/2005
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TM
MP1580 - 2A, 380KHz STEP-DOWN CONVERTER Determine if the second compensation capacitor, C6, is required. It is required if the ESR zero of the output capacitor happens at less than four times the crossover frequency. Or:
8 x C2 x R ESR x f C 1
Negative Output Voltage The MP1580 can be configured as a buckboost regulator to supply negative output voltage. Because the GND pin of the IC is now connected to the negative output voltage, the maximum allowable input voltage is the IC input voltage rating (25V) minus the negative output voltage value. A typical application circuit is shown in Figure 3. 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
or
7.34 x 10 -5 x R3 x R ESR 1 VOUT
If this is the case, add the second compensation capacitor. Determine the value by the equation:
C6 = C2 x R ESR(MAX ) R3
Where RESR(MAX) is the maximum ESR of the output capacitor. For example: VOUT = 3.3V C2= 22F Ceramic (ESR = 10m)
R3 (1.37 x 10 8 ) x (22 x 10 -6 ) x (3.3) = 9.9k
BS
MP1580
SW
10nF
MP1580_F02
Use the nearest standard value of 10k.
C3 > 0.22 x (22 x 10 -6 ) x 3.3 10 x 10 3 = 1.6nF
Figure 2--External Bootstrap Diode This diode is also recommended for high duty cycle operation (when
VOUT >65%) and high VIN
Use a standard value of 2nF
2 x C2 x R ESR x f C = 0.014
output voltage (VOUT>12V) applications.
which is less than 1, therefore no second compensation capacitor is required. Table 5--Recommended Components for Standard Output Voltages
VOUT R1 L1 Minimum
1.22V 1.5V 1.8V 2.5V 3.3V 5.0V
0 2.32k 4.75k 10.5k 16.9k 30.9k
6.8H 6.8H 10H 10H 15H 22H
MP1580 Rev. 3.0 12/5/2005
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TM
MP1580 - 2A, 380KHz STEP-DOWN CONVERTER
TYPICAL APPLICATION CIRCUITS
INPUT 4.75V to 25V OFF ON OPEN NOT USED
7 8
C5 10nF
2 IN EN 1 BS SW 3 5
MP1580
SYNC GND 4 FB COMP 6
D1
OUTPUT 2.5V / 2A
C6 OPEN
C3 2.2nF
MP1580_F03
Figure 3--Application Circuit for -5V Supply
INPUT 4.75V to 20V OFF ON OPEN NOT USED
7 8
C5 10nF
2 IN EN 1 BS SW 3 5
MP1580
SYNC GND 4 FB COMP 6
D1 B230
C6 OPEN
C3 10nF OUTPUT -5V / 0.8A
MP1580_F04
Figure 4--MP1580 with Murata 22F/10V Ceramic Output Capacitor
MP1580 Rev. 3.0 12/5/2005
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TM
MP1580 - 2A, 380KHz STEP-DOWN CONVERTER
PACKAGE INFORMATION
SOIC8
PIN 1 IDENT. 0.229(5.820) 0.244(6.200)
0.150(3.810) 0.157(4.000)
0.0075(0.191) 0.0098(0.249)
SEE DETAIL "A"
0.013(0.330) 0.020(0.508) 0.050(1.270)BSC 0.011(0.280) x 45o 0.020(0.508)
0.189(4.800) 0.197(5.004) 0.053(1.350) 0.068(1.730) 0.049(1.250) 0.060(1.524)
0o-8o
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.
PDIP8
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.
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