MP1484

3A, 23V, 340KHz Synchronous Rectified

Step-Down Converter

DESCRIPTION FEATURES
The MP1484 is a monolithic synchronous buck regulator. The z 3A Continuous Output Current
device integrates top and bottom 85mΩ MOSFETS that z Wide 4.75V to 23V operating input Range
provide 3A of continuous load current over a wide operating z Integrated 85mΩ Power MOSFET Switches
input voltage of 4.75V to 23V. Current mode control provides z Output Adjustable from 0.925V to 20V
fast transient response and cycle-by-cycle current limit. z Up to 95% Efficiency
z Programmable Soft-Start
An adjustable soft-start prevents inrush current at turn-on and z Stable with Low ESR Ceramic Output Capacitors
in shutdown mode, the supply current drops below 1µA. z Fixed 340KHz Frequency
The MP1484 is PIN compatible to the MP1482 z Cycle-by-Cycle Over Current Protection
2A/23V/Synchronous Step-Down Converter. z Input Under Voltage Lockout
z Thermally Enhanced 8-Pin SOIC Package

APPLICATIONS
z FPGA,ASIC, DSP POWER SUPPLIES
z LCD TV
z Green Electronics/Appliances
z Notebook Computers

TYPICAL APPLICATION

PACKAGE REFERENCE
Part Number* Package Temperature
MP1484EN SOIC8N -20℃ to +85℃
(Exposed Pad)
*For Tape & Reel, add suffix-Z (e.g. MP1484EN-Z)
For Lead Free, add suffix-LF (e.g. MP1484EN-LF-Z)

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 MP1484
3A, 23V, 340KHz Synchronous Rectified
Step-Down Converter

(1)
ABSOLUTE MAXIMUM RATINGS Recommended Operating Conditions(2)
Supply Voltage VIN………………………-0.3V to +24V Input Voltage VIN………………………………4.75V to 23V
Switch voltage VSW…………………-1V to VIN +0.3V Output Voltage VOUT……………………...0.925V to 20V
Boost Voltage VBS……………VSW -0.3V to VSW +6V Ambient operating Temp………………….-20℃ to +85℃
All Other Pins………………………….-0.3V to +6V
Junction Temperature…………………………. 150℃ Thermal Resistance (3) ӨJA ӨJC
Lead Temperature………………………………260℃ SOIC8N(Exposed Pad)……………50……….10……℃/W
Storage Temperature……………….-65℃ to +150℃
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℃, unless otherwise noted.
Parameter Symbol Condition Min Typ Max Units
Shutdown Supply Current VEN=0V 0.3 3.0 µA
Supply Current VEN=2.0V, VFB=1.0V 1.3 1.5 mA
Feedback Voltage VFB 4.75V≤VIN ≤23V 0.900 0.925 0.950 V
Feedback Overvoltage Threshold 1.1 V
(4)
Error Amplifier Voltage Gain AEA 400 V/V
Error Amplifier Transconductance GEA ∆IC=±10µA 820 µA/V
High-Side/Low-Side Switch 85 mΩ
(4)
On-Resistance
High-Side Switch Leakage Current VEN=0V, VSW=0V 0 10 µA
Upper Switch Current Limit Minimum Duty Cycle 3.8 5.3 A
Lower Switch Current Limit From Drain to Source 0.9 A
COMP to Current Sense GCS 5.2 A/V
Transconductance
Oscillation Frequency FOSC1 300 340 380 KHz
Short Circuit Oscillation Frequency FOSC2 VFB=0V 110 KHz
Maximum Duty Cycle DMAX VFB=1.0V 90 %
Minimum On Time (4) TON 220 ns
EN Shutdown Threshold Voltage VEN Rising 1.1 1.5 2.0 V
EN Shutdown Threshold Voltage 220 mV
Hysterisis

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 MP1484
3A, 23V, 340KHz Synchronous Rectified
Step-Down Converter

ELECTRICAL CHARACTERISTICS (continued)

VIN=12V, TA=+25℃, Unless Otherwise noted.
Parameter Symbol Condition Min Typ Max Units
EN Lockout Threshold Voltage 2.2 2.5 2.7 V
EN Lockout Hysterisis 210 mV
Input Under Voltage Lockout VIN Rising 3.80 4.05 4.40 V
Threshold
Input Under Voltage Lockout 210 mV
Threshold Hysterisis
Soft-Start Current Vss=0V 6 µA
Soft-Start Period Css=0.1µF 15 ms
Thermal Shutdown (4) 160 ℃
Note:
4) Guaranteed by design, not tested.

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 0.01µF 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 4.75v to 23V power source. 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(Connect the exposed pad to Pin 4).
5 FB Feedback Input. FB senses the output voltage and regulates it. Drive FB with a resistive
Voltage divider connected to it from the output voltage. The feedback threshold is 0.925V. 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. In some cases, and additional capacitor form COMP to
GND is required. See Compensation Components.
7 EN Enable input. En is a digital input that turns the regulator on or off. Drive EN high to turn on the
regulator; low to turn it off. Attach to IN with a 100K Ω pull up resistor for automatic startup.
8 SS Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor from SS to GND to
set the soft-start period. A 0.1µF capacitor sets the soft-start period to 15ms. To disable the
soft-start feature, leave SS unconnected.

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 MP1484
3A, 23V, 340KHz Synchronous Rectified
Step-Down Converter

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 MP1484
3A, 23V, 340KHz Synchronous Rectified
Step-Down Converter

OPENRATION
FUNCTIONAL DESCRIPTION
The MP1484 regulates input voltages from 4.75V to 23V down to an output voltage as low as 0.925V, and supplies up to 3A of
load current.
The MP1484 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 transconductance error amplifier. The voltage at the COMP pin is compared to
the switch current (measured internally) to control the output voltage.
The converter uses internal N-Channel MOSFET switches to step-down the input voltage to the regulated output voltage. Since
the high side MOSFET requires a gate voltage greater than the input voltage, a boost capacitor connected between SW and BS is
needed to drive the high side gate. The boost capacitor is charged from the internal 5V rail when SW is low.
When the FB pin voltage exceeds 20% of the nominal regulation value of 0.925V, the over voltage comparator is tipped and the
COMP pin and the SS pin are discharged to GND, forcing the high-side switch off.

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 MP1484
3A, 23V, 340KHz Synchronous Rectified
Step-Down Converter

APPLICATIONS INFORMATION Thus the output voltage is:

COMPONENT SELECTION VOUT=0.925 X [(R1+R2)/R2]
Setting the Output Voltage
The output voltage is set using a resistive voltage divider R2 can be as high as 100k Ω, but a typical value is 10k Ω.
connected from the output voltage to FB. The voltage divider Using the typical value for R2, R1 is determined by:
divides the output voltage down to the feedback voltage by R1=10.81 X (VOUT -0.925) (k Ω)
the ratio: For example, for a 3.3V output voltage, R2 is 10k Ω, and R1
VFB = VOUT *[R2/(R1+R2)] is 26.1k Ω. Table 1 lists recommended resistance values of R1
and R2 for standard output voltages.

Table 1-Recommended Resistance Values

VOUT R1 R2
1.8V 9.52K Ω 10K Ω
2.5V 16.9K Ω 10K Ω
3.3V 26.1K Ω 10K Ω
5V 44.2K Ω 10K Ω
12V 121K Ω 10K Ω

Inductor
The inductor is required to supply constant current to the load while being driven by the switched input voltage. A larger value
inductor will result in less ripple current that will in turn 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. A good rule for determining inductance is to
allow the peak-to-peak ripple current to be approximately 30% or 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/(fs x ∆IL)x (1-VOUT/VIN)

Where VOUT is the output voltage, VIN is the input voltage, fs is the switching frequency, and ∆IL is the peak-to-peak inductor ripple
current.
Choose an inductor that will not saturate under the maximum inductor peak current, calculated by:
ILP=ILOAD + VOUT/(2xfs x L)x(1-VOUT/VIN)
Where ILOAD is the load current.
The choice of which style inductor to use mainly depends on the price vs. size requirements and any EMI constraints.

Optional Schottky Diode

During the transition between the high-side switch and low-side switch, the body diode of the low-side power MOSFET conducts
the inductor current. The forward voltage of this body diode is high. An optional schottky diode may be paralleled between the SW
pin and Gnd pin to improve overall efficiency. Table 2 lists example Schottky diodes and their Manufcturers.

Table 2---Diode Selection Guide

Part Number Voltage/Current Rating Vendor
B130 30V,1A Diodes, Inc.
SK13 30V,1A Diodes,Inc.
MBRS130 30V,1A International Rectifier

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 MP1484
3A, 23V, 340KHz Synchronous Rectified
Step-Down Converter

Input Capacitor
The input current to the step-down converter is discontinuous,
therefore a capacitor is required to supply the AC current
while maintaining the DC input voltage. Use low ESR
capacitors for the best performance. Ceramic capacitors are When using tantalum or electrolytic capacitors. The ESR
preferred, but tantalum or low-ESR electrolytic capacitors will dominates the impedance at the switching frequency. For
also suffice. Choose X5R or X7R dielectrics when using simplification, the output ripple can be approximated to:
ceramic capacitors. Since the input capacitor (C1) absorbs
the input switching current, it requires and adequate ripple
current rating. The RMS current in the input capacitor can be
estimated by:

The characteristics of the output capacitor also affect the

stability of the regulation system. The MP1484 can be
optimized for a wide range of capacitance and ESR values.
The worst-case condition occurs at VIN=2VOUT, where IC1 =
ILOAD/2. For simplification, use an input capacitor with a RMS
current rating greater than half of the maximum load current. Compensation Components
The input capacitor can be electrolytic, tantalum or ceramic. MP1484 employs current mode control for easy
When using electrolytic or tantalum capacitor, i.e. 0.1µF, compensation and fast transient response. The system
should be placed as close to the IC as possible. When using stability and transient response are controlled through the
ceramic capacitors, make sure that they have enough COMP pin. COMP is the output of the internal
capacitance to provide sufficient charge to prevent excessive transconductance error amplifier. A series capacitor-resistor
voltage ripple at input. The input voltage ripple for low ESR combination sets a pole-zero combination to govern the
capacitors can be estimated by: characteristics of the control system. The DC gain of the
voltage feedback loop is given by:

Where C1 is the input capacitance Value.

Output Capacitor
The output capacitor (C2) is required to maintain the DC Where VFB is the feedback voltage (0.925V), AVEA is the error
output voltage. Ceramic, tantalum, or low ESR electrolytic amplifier voltage gain, GCS is the current sense
capacitors are recommended. Under typical application transconductance and RLOAD is the load resistor value.
conditions, a minimum ceramic capacitor value of 20µF is The system has two poles of importance. One is due to the
recommended on the output. Low ESR capacitors are compensation capacitor (C3) and the output resistor of the
preferred to keep the output voltage ripple low. The output error amplifier, and the other is due to the output capacitor and
voltage ripple can be estimated by: the load resistor. These poles are located at:
∆VOUT=VOUT /(fs x L )x (1- VOUT/VIN)X (RESR
+1/(8XFSXC2))
Where C2 is the output capacitance value and RESR is the
equivalent series resistance (ESR) value of the output
capacitor.
When using ceramic capacitors, the impedance at the
switching frequency is dominated by the capacitance which is Where GEA is the error amplifier transconductance.
the main cause for the output voltage ripple. For simplification,
the output voltage ripple can be estimated by:

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 MP1484
3A, 23V, 340KHz Synchronous Rectified
Step-Down Converter

The system has one zero of importance, due to the below one-forth of the crossover frequency provides
compensation capacitor (C3) and the compensation resistor sufficient phase margin.
(R3). This zero is located at: Determine C3 by the following equation:

The system may have another zero of importance, if the Where R3 is the compensation resistor
output capacitor has a large capacitance and/or a high ESR 3. Determine if the second compensation capacitor (C6) is
value. The zero, due to the ESR and capacitance of the output required. It is required if the ESR zero of the output
capacitor, is located at: capacitor is located at less than half of the switching
frequency, or the following relationship is valid:

In this case, a third pole set by the compensation capacitor

(C6) and the compensation resistor (R3) is used to If this is the case, then add the second compensation
compensate the effect of the ESR zero on the loop gain. This capacitor (C6) to set pole fp3 at the location of the ESR zero.
pole is located at : Determine C6 by the equation:

The goal of compensation design is to shape the converter External Bootstrap Diode
transfer function to get a desired loop gain. The system An external bootstrap diode may enhance the efficiency of the
crossover frequency where the feedback loop has the unity regulator, the applicable conditions of external BS diode are:
gain is important. Lower crossover frequencies result in VOUT is 5V or 3.3V; and
slower line and load transient responses, while higher
crossover frequencies could cause system instability. A good Duty cycle is high:
standard is to set the crossover frequency below one-tenth of In these cases, and external BS diode is recommended from
the switching frequency. the output of the voltage regulator to BS pin, as shown in Fig.2
To optimize the compensation components, the following
procedure can be used.
1. Choose the compensation resistor (R3) to set the desired
crossover frequency.
Determine R3 by the following equation:

Where fC is the desired crossover frequency which is typically

below one tenth of the switching frequency. Figure 2-Add Optional External Bootstrap Diode to
2. Choose the compensation capacitor (C3) to achieve the Enhance Efficiency
desired phase margin. For applications with typical The recommended external BS diode is IN4148, and the BS
inductor values, setting the compensation zero (Fz1) cap is 0.1~1µF.

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 MP1484
3A, 23V, 340KHz Synchronous Rectified
Step-Down Converter

TYPICAL APPLICATIONS CIRCUIT

Figure 3-MP1484 with 3.3V Output, 2X10µF Ceramic Output Capacitor

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 MP1484
3A, 23V, 340KHz Synchronous Rectified
Step-Down Converter

PACKAGE INFORMATION
SOIC8N(EXPOSED PAD)

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