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11/04/08

PD-60357

IR3802AMPbF

HIGHLY INTEGRATED 6A

WIDE-INPUT VOLTAGE, SYNCHRONOUS BUCK REGULATOR

Features

• Wide Input Voltage Range 2.5V to 21V

• Wide Output Voltage Range 0.6V to 12V

• Continuous 6A Load Capability

• 300kHz High Frequency Operation

• Programmable Over-Current Protection

• Hiccup Current Limit

• Precision Reference Voltage (0.6V)

• Programmable Soft-Start

• Pre-Bias Start-up

• Thermal Protection

• Thermally Enhanced Package

• Small Size 5mmx6mm QFN

• Pb-Free (RoHS Compliant)

Fig. 1. Typical application diagram

Description

The IR3802A SupIRBuck

is an easy-to-use,

fully integrated and highly efficient DC/DC

regulator. The onboard switching controller and

MOSFETs make the IR3802A a space-efficient

solution, providing accurate power delivery for

low output voltage applications.

The IR3802A operates from a single 4.5V to 14V

input supply and generates an output voltage

adjustable from 0.6V to 0.8*Vin at loads up to 6A.

A versatile regulator offering programmability of

startup time, power good threshold and current

limit, the IR3802A’s fixed 300kHz switching

frequency allows the use of small external

components.

The IR3802A also features important protection

functions, such as Pre-Bias startup, hiccup

current limit and thermal shutdown to provide the

required system level security in the event of fault

conditions.

SupIRBuck

Applications

• Game Consoles

• Set-top Boxes

• Graphics Cards

• LCD TVs

• Desktop PCs

• Distributed Point-of-Loads

• Embedded Systems

• Computing Peripheral Voltage Regulators

Summary of content (21 pages)

PAGE 1
PD-60357 IR3802AMPbF SupIRBuck TM HIGHLY INTEGRATED 6A WIDE-INPUT VOLTAGE, SYNCHRONOUS BUCK REGULATOR Features • • • • • • • • • • • • • Wide Input Voltage Range 2.5V to 21V Wide Output Voltage Range 0.6V to 12V Continuous 6A Load Capability 300kHz High Frequency Operation Programmable Over-Current Protection Hiccup Current Limit Precision Reference Voltage (0.
PAGE 2
PD-60357 IR3802AMPbF ABSOLUTE MAXIMUM RATINGS (Voltages referenced to GND) • VIN Supply Voltage -0.3V to 24V • Vcc Supply Voltage -0.3V to 16V • Vc Supply Voltage -0.3V to 30V • SW -0.3V to 30V • Fb,COMP,SS -0.3V to 3.5V • OCSet 10mA • AGnd to PGnd -0.3V to +0.
PAGE 3
PD-60357 IR3802AMPbF Block Diagram Fig. 3. Simplified block diagram of the IR3802A.
PAGE 4
PD-60357 IR3802AMPbF Pin Description Pin Name Description 1 NC No Connect 2 Fb 3 Comp Inverting input to the error amplifier. This pin is connected directly to the output of the regulator via resistor divider to set the output voltage and provide feedback to the error amplifier. Output of error amplifier. 4 AGnd Signal ground for internal reference and control circuitry. 5 AGnd Signal ground for internal reference and control circuitry. 6 SS/SD 7 OCSet Soft start / shutdown.
PAGE 5
PD-60357 IR3802AMPbF Recommended Operating Conditions Symbol Vin Vcc Vc Vo Io Note1 Tj Definition Input Voltage Supply Voltage Supply Voltage Output Voltage Output Current Junction Temperature Min Max 2.5 4.5 Vin + 5V 0.6 0 -40 21 14 28 12 6 125 Units V A C o Electrical Specifications Unless otherwise specified, these specification apply over Vin=Vcc=Vc=12V, 0oC
PAGE 6
PD-60357 IR3802AMPbF Parameter SYM Test Condition Min TYP MAX Units 270 300 330 kHz Oscillator Frequency FS Ramp Amplitude Vramp Note3 1.25 V Min Pulse Width Dmin(ctrl) Note3 80 ns Max Duty Cycle Dmax Fb=0V Input Bias Current IFB1 SS=3V Input Bias Current IFB2 SS=0V Source/Sink Current Transconductance 80 % Error Amplifier -0.1 -0.5 20 35 50 I(source/Sink) 50 70 90 gm 1000 1300 1600 μmho 15 20 28 μA 0.
PAGE 7
PD-60357 IR3802AMPbF TYPICAL OPERATING CHARACTERISTICS (-40oC - 125oC) Icc(static) Ic(static) 13.0 7.0 12.0 6.0 [mA] [mA] 11.0 10.0 9.0 4.0 3.0 8.0 7.0 -40 5.0 -20 0 20 40 60 80 100 2.0 -40 120 -20 0 20 Tem p[oC] 20.0 18.0 18.0 16.0 16.0 14.0 14.0 [mA] [mA] 20.0 12.0 10.0 8.0 8.0 0 20 40 80 100 120 80 100 120 12.0 10.0 -20 60 Ic(dynam ic) Icc(dynam ic) 6.0 -40 40 Tem p[oC] 60 80 100 6.
PAGE 8
PD-60357 IR3802AMPbF Circuit Description THEORY OF OPERATION The IR3802A is a voltage mode PWM synchronous regulator and operates with a fixed 300kHz switching frequency, allowing the use of small external components. The output voltage is set by feedback pin (Fb) and the internal reference voltage (0.6V). These are two inputs to error amplifier. The error signal between these two inputs is amplified and it is compared to a fixed frequency linear sawtooth ramp.
PAGE 9
PD-60357 IR3802AMPbF Soft-Start The IR3802A has programmable soft-start to control the output voltage rise and limit the inrush current during start-up. To ensure correct start-up, the soft-start sequence initiates when Vcc and Vc rise above their threshold and generate the Power On Ready (POR) signal. The soft-start function operates by sourcing current to charge an external capacitor to about 3V.
PAGE 10
PD-60357 IR3802AMPbF Over-Current Protection The over-current protection is performed by sensing current through the RDS(on) of the low side MOSFET. This method enhances the converter’s efficiency and reduces cost by eliminating a current sense resistor. As shown in figure 7, an external resistor (RSET) is connected between OCSet pin and the inductor point which sets the current limit set point. The internal current source develops a voltage across RSET.
PAGE 11
PD-60357 IR3802AMPbF Application Information Design Example: The following example is a typical application for the IR3802A. The application circuit is shown in page 17. Vin = 12 V,( 13 .2V, max ) Soft-Start Programming The soft-start timing can be programmed by selecting the soft-start capacitance value. The start-up time of the converter can be calculated by using: CSS ≅ 20μA * Tstart --(1) Vo = 1.
PAGE 12
PD-60357 IR3802AMPbF Input Capacitor Selection The input filter capacitor should be selected based on how much ripple the supply can tolerate on the DC input line. The ripple current generated during the on time of upper MOSFET should be provided by the input capacitor. The RMS value of this ripple is expressed by: IRMS = Io ∗ D ∗ (1 − D ) --(7 ) D= Where: Vo Vin D is the Duty Cycle IRMS is the RMS value of the input capacitor current. Io is the output current.
PAGE 13
PD-60357 IR3802AMPbF Feedback Compensation The IR3802A is a voltage mode controller; the control loop is a single voltage feedback path including error amplifier and error comparator. To achieve fast transient response and accurate output regulation, a compensation circuit is necessary. The goal of the compensation network is to provide a closed loop transfer function with the highest 0dB crossing frequency and adequate phase margin (greater than 45o).
PAGE 14
PD-60357 IR3802AMPbF To cancel one of the LC filter poles, place the zero before the LC filter resonant frequency pole: VOUT ZIN Fz = 75%FLC C7 1 Fz = 0.75 * 2π Lo * Co - - - (17) Use equations (15) and (16) to calculate C4. One more capacitor is sometimes added in parallel with C4 and R3. This introduces one more pole which is mainly used to suppress the switching noise.
PAGE 15
PD-60357 IR3802AMPbF Based on the frequency of the zero generated by output capacitor and its ESR versus crossover frequency, the compensation type can be different. The table below shows the compensation types and location of crossover frequency. Compensator type FESR vs.
PAGE 16
PD-60357 IR3802AMPbF Programming the Current-Limit The Current-Limit threshold can be set by connecting a resistor (RSET) from drain of the low-side MOSFET to the OCSet pin. The resistor can be calculated by using equation (3). The RDS(on) has a positive temperature coefficient and it should be considered for the worse case operation. This resistor must be placed close to the IC, place a small ceramic capacitor from this pin to power ground (PGnd) for noise rejection purposes.
PAGE 17
PD-60357 IR3802AMPbF Typical Application for IR3802A 12V to 1.8V @ 6A Fig.16: Typical Application circuit for 12V to 1.
PAGE 18
PD-60357 IR3802AMPbF PCB Metal and Components Placement The lead lands (the 11 IC pins) width should be equal to the nominal part lead width. The minimum lead to lead spacing should be ≥ 0.2mm to minimize shorting. Lead land length should be equal to the maximum part lead length + 0.3 mm outboard extension. The outboard extension ensures a large and inspectable toe fillet. The pad lands (the 4 big pads other than the 11 IC pins) length and width should be equal to maximum part pad length and width.
PAGE 19
PD-60357 IR3802AMPbF Solder Resist It is recommended that the lead lands are Non Solder Mask Defined (NSMD). The solder resist should be pulled away from the metal lead lands by a minimum of 0.025mm to ensure NSMD pads. The land pad should be Solder Mask Defined (SMD), with a minimum overlap of the solder resist onto the copper of 0.05mm to accommodate solder resist mis-alignment. Ensure that the solder resist in between the lead lands and the pad land is ≥ 0.
PAGE 20
PD-60357 IR3802AMPbF Stencil Design • • 11/04/08 The Stencil apertures for the lead lands should be approximately 80% of the area of the lead lads. Reducing the amount of solder deposited will minimize the occurrences of lead shorts. If too much solder is deposited on the center pad the part will float and the lead lands will be open. The maximum length and width of the land pad stencil aperture should be equal to the solder resist opening minus an annular 0.
PAGE 21
PD-60357 IR3802AMPbF IR WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245, USA Tel: (310) 252-7105 TAC Fax: (310) 252-7903 This product has been designed and qualified for the Consumer market. Visit us at www.irf.com for sales contact information Data and specifications subject to change without notice.