iDESYN iD8803 3A, 23V, Synchronous Step-Down DC/DC ...

1 iDESYN iD88033A, 23V, Synchronous Step-Down DC/DCApr. 20141 DescriptionThe iD8803 is a 340kHz fixed frequency PWMsynchronous Step-Down regulator. The iD8803 isoperated from to 23V, the generated output isadjustable from to ; and the continuousoutput current can be up to MOSFETs of 90m on resistance are integratedin this device. The current mode control provides fasttransient response and cycle-by-cycle current shutdown current is A typical. Adjustable softstart prevents inrush current at turn iD8803 is with thermal shutdown.

2 The iD8803 isavailable in the PSOP-8L package, and it is RoHScompliant and 100% lead (Pb) InformationiD8803 - PackageP80:PSOP-8 Output Voltage Voltage CodeAdjustableADTapingR: Tape and ReelApplications Distributed power systems Networking systems FPGA, DSP, ASIC power supplies Notebook computers Green electronics or applianceFeatures to 23V input voltage Output adjustable from to 18V Output current up to 3A Integrated 90m power MOSFET switches UVLO protection Shutdown current A typical Efficiency up to 96% 340kHz fixed frequency Programmable soft start Over current protection Over temperature protection RoHS Compliant and 100% Lead (Pb) FreeMarking InformationFor marking information, please contact our salesrepresentative directly or through distributor aroundyour iD8803 Apr.

3 20142 Application CircuitAbsolute Maximum Ratings Recommended Operating ConditionsSupply Voltage VIN to +26V Input Voltage VIN to 23 VSwitch Node VSW to VIN+ Temperature -20 C to 125 CBoost VBSVSW to VSW+6 VAmbient Operating Temperatures -40 C to 85 CEnable VEN to VIN+ Other Pins to +6 VPower Dissipation, PD @ TA=25 CPSOP-8 Resistance,TjaPSOP-875 C/WMax. Junction Temperature150 CStorage Temperature -65 C to 150 CiDESYN iD8803 Apr.

4 20143 ConfigurationsPin DescriptionNumberNameDescription1 BSHigh-Side Gate Drive Boost Input. BS supplies the drive for the high-side MOSswitch. Connect a 10nF or greater capacitor from SW to BS to power Input. Bypass to GND with a suitable large Switching Output. SW is the switching node that supplies power to theoutput. Connect the output LC filter from SW to the output load. Note that acapacitor is required from SW to BS to power the high-side Input. Connect FB to the center point of the external resistor Node. COMP is used to compensate the regulation controlloop.

5 Connect a series RC network from COMP to GND to compensate theregulation control Input. When higher than , this pin turns the IC on. When lowerthan , this pin turns the IC off. Output voltage is discharged when the ICis off. This pin should not be left open. Recommend to put a 100K pull upresistor to Vin for start Start Control Input. SS controls the soft start period. Connect a capacitorfrom SS to GND to set the soft-start period. A F capacitor sets the soft-start period to 15ms. To disable the soft-start feature, leave SS iD8803 Apr. 20144 Block DiagramiDESYN iD8803 Apr.

6 20145 Characteristics (VIN=12V, VOUT= , unless otherwise specified. Typical values are at TA=25 C)ParametersSymbolConditionMinTypMax UnitsFeedback VoltageVFB to 23V Overvoltage Switch Current Limit Mimunum Duty to Current Amp Transconductance ICOMP = +-10 A900 A/VError Amp DC Gain*400V/VSwitching FrequencyfSW340 KHzShort Circuit Switching Frequency VFB = GND100 KHzMaximum Duty Cycle VFB = Duty Shutdown Threshold VEN Shutdown ThresholdHysteresis180mVEN Lockout Threshold Lockout Threshold Hysteresis150mVStandby Current VEN = GND, AQuiescent Current VEN = 3V, VFB = UVLO Threshold RisingUVLO VEN = UVLO Threshold Hysteresis150mVSoft Start Current VSS = 0V6 ASoft Start Time CSS = F13mSThermal Shutdown Temperature*Hysteresis = 25 C155 CHigh-Side Switch-On Resistance*90P Low-Side Switch-On Resistance*70P High-Side Switch Leakage VEN = 0V, VSW = AiDESYN iD8803 Apr.

7 20146 InformationOverviewThe iD8803 is a Synchronous rectified, current-mode, Step-Down regulator. It regulates input voltages to 23V down to an output voltage as low , and supplies up to 3A of load iD8803 uses current-mode control to regulate theoutput voltage. The output voltage is measured at FBthrough a resistive voltage divider and amplifiedthrough the internal transconductance error voltage at the COMP pin is compared to theswitch current measured internally to control the converter uses internal N-Channel MOSFET switches to Step-Down the input voltage to theregulated output voltage.

8 Since the high side MOSFET requires a gate voltage greater than the input voltage,a boost capacitor connected between SW and BS isneeded to drive the high side gate. The boost capacitoris charged from the internal 5V rail when SW is the iD8803 FB pin exceeds 20% of the nominalregulation voltage of , the over voltagecomparator is tripped and the COMP pin and the SSpin are discharged to GND, forcing the high-sideswitch the Output VoltageThe output voltage is set using a resistive voltagedivider from the output voltage to FB pin. The voltagedivider divides the output voltage down to the feedbackvoltage by the ratio:VFB = VOUT R2 / (R1 + R2)Where VFB is the feedback voltage and VOUT is theoutput the output voltage is:VOUT = VFB (R1 + R2) / R2R2 can be as high as 100k , but a typical value is10k.

9 Using the typical value for R2, R1 is determined by:R1 = (VOUT ) (k )InductorThe inductor is required to supply constant current tothe output load while being driven by the switchedinput voltage. A larger value inductor will result in lessripple current that will result in lower output ripplevoltage. However, the larger value inductor will have alarger physical size, higher series resistance, and/orlower saturation current. A good rule for determiningthe inductance to use is to allow the peak-to-peakripple current in the inductor to be approximately 30%of the maximum switch current limit. Also, make surethat the peak inductor current is below the maximumswitch current limit.

10 The inductance value can becalculated by:L = [ VOUT / (fS IL) ] (1 VOUT/VIN)Where VOUT is the output voltage, VIN is the inputvoltage, fS is the switching frequency, and IL is thepeak-to-peak inductor ripple an inductor that will not saturate under themaximum inductor peak current. The peak inductorcurrent can be calculated by:ILP = ILOAD + [ VOUT / (2 fS L) ] (1 VOUT/VIN)Where ILOAD is the load choice of which style inductor to use mainlydepends on the price vs. size requirements and anyEMI Schottky DiodeDuring the transition between high-side switch andlow-side switch, the body diode of the low-side powerMOSFET conducts the inductor current.