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| Solved by SP6125 TM High-Voltage, Step Down Controller in TSOT6 FEATURES Wide 4.5V - 29V Input Voltage Range Internal Compensation Built-in High Current PMOS Driver Adjustable Overcurrent Protection Internal soft-start 300kHz Constant Frequency Operation 0.6V Reference Voltage 1% output setpoint accuracy Lead Free, RoHS Compliant Package: Small 6 pin TSOT LX GND FB 6 5 4 SP6125 6 PinTSOT 1 VIN 2 GATE 3 VDR DESCRIPTION The SP6125 is a PWM controlled step down (buck) voltage mode regulator with VIN feedforward and internal Type-II compensation. It operates from 4.5V to 29V, making is suitable for 5V, 12V, and 24V applications. By using a PMOS driver, this device is capable of operating at 100% duty cycle. The high side driver is designed to drive the gate 5V below VIN. The programmable overcurrent protection is based on high-side MOSFET's ON resistance sensing and allows setting the overcurrent protection value up to 300mV threshold (measured from VIN-LX). The SP6125 is available in a space-saving 6-pin TSOT package making it the smallest controller available capable of operating from 24VDC supplies. TYPICAL APPLICATION CIRCUIT VIN Q1 FDS4685 C1 4.7uF C2 4.7uF 24-29 V 2 1 Vin Rs 2k LX C6 0.1uF 6 Gate GND L1, IHLP-2525CZ 8.2uH, 68mOhm, 4A VOUT C4 22uF R1 200k, 1% C5 22uF SP6125 3 VDR 4 VFB GND 5 Ds MBRA340T3G RZ 2K 3.3V 0-3A CZ 100pF R2 44.2k, 1% D1 1N4148 GND SHDN High=Of f Mar22-07 RevC SP6125: TSOT-6 PFET Buck Controller 2007 Sipex Corporation 1 ABSOLUTE MAXIMUM RATINGS These are stress ratings only, and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. Input Voltage......................................................-0.3V to 30V Lx...............................................................-2V to 30V FB...................................................................-0.3V to 5.5V Storage Temperature...............................-65 C to 150 C Junction Temperature.....................................-40C to 125C Lead Temperature (Soldering, 1...0 sec)..................300 C ESD Rating....................1kV LX, 2kV all other nodes, HBM ELECTRICAL SPECIFICATIONS Specifications are for TAMB=TJ=25C, and those denoted by apply over the full operating range, -40C< Tj <85C. Unless otherwise specified: VIN =4.5V to 29V, CIN = 4.7F. PARAMETER UVLO Turn-On Threshold UVLO Turn-Off Threshold UVLO Hysterisis Operating Input Voltage Range Operating Input Voltage Range Operating VCC Current Reference Voltage Accuracy Reference Voltage Accuracy Reference Voltage Reference Voltage Switching Frequency Peak-to-peak ramp Modulator Minimum ON-Pulse Duration Minimum Duty Cycle Maximum Duty Cycle Gate Driver Turn-Off Resistance Gate Driver Pull-Down Resistance Gate Driver Pull-up Resistance VIN - VDR voltage difference Overcurrent Threshold LX pin Input Current OFF interval during hiccup Soft start time SHDN Threshold SHDN Threshold Hysteresis MIN 4.2 4.0 TYP 4.35 4.2 0.2 MAX 4.5 4.4 UNITS V V V CONDITIONS 0C< Tj <85C 0C< Tj <85C 0C< Tj <85C 4.5 7 0.3 0.5 0.5 0.594 0.588 255 0.6 0.6 300 VIN/5 40 100 50 4 3 4.5 270 25 3 0.9 300 30 200 5 1.0 100 29 29 3 1 2 0.606 0.612 345 100 0 60 8 6 5.5 330 35 9 1.1 V V mA % % V V kHz V ns % % k VFB=1.2V Internal resistor between GATE and VIN VIN=12V, VFB=0.5V, Measure resistance between GATE and VDR VIN=12V, VFB=0.7V, Measure resistance between GATE and VIN V mV uA ms ms V mV Measure VIN - VDR, VIN>7V Measure VIN - LX VLX = VIN VFB=0.58V, measure between VIN=4.5V and first GATE pulse Apply voltage to FB Mar22-07 RevC SP6125: TSOT-6 PFET Buck Controller 2007 Sipex Corporation 2 PIN DESCRIPTION PIN # 1 2 3 PIN NAME VIN GATE VDR DESCRIPTION Input power supply for the controller. Place input decoupling capacitor as close as possible to this pin. Connect to the gate terminal of the external P-channel MOSFET. Power supply for the internal driver. This voltage is internally regulated to about 5V below VIN. Place a 0.1uF decoupling capacitor between VDR and Vin as close as possible to the IC. Regulator feedback input. Connect to a resistive voltage-divider network to set the output voltage. This pin can be also used for ON/OFF control. If this pin is pulled above 1V the P-channel driver is disabled and controller resets internal soft start circuit. Ground pin. This pin is used as a current limit input for the internal current limit comparator. Connect to the drain pin of the external MOSFET through an optional resistor. Internal threshold is pre-set to 300mV nominal and can be decreased by changing the external resistor based on the following formula: VTRSHLD = 300mV - 30uA * R BLOCK DIAGRAM 5V VIN 4 5 FB GND 6 LX VDR Oscillator Vin - 5V LDO VIN 5V Internal LDO I = k x VIN FAULT VREF PWM Latch Reset Dominant S GATE FB + + - R Error Amplifier PWM Comparator VDR FAULT FAULT ENBL UVLO FAULT Register S 4-Bit counter - LX 200ms delay Overcurrent Comparator VIN - 0.3V + - R R Set Dominant POR 1V Mar22-07 RevC SP6125: TSOT-6 PFET Buck Controller 3 + 30uA GND 2007 Sipex Corporation General Overview The SP6125 is a fixed frequency, Voltagemode, non-synchronous PWM controller optimized for minimum component, small form factor and cost effectiveness. It has been designed for single-supply operation ranging from 4.5V to 29V. SP6125 has Type-II internal compensation for use with Electrolytic or Tantalum output capacitors. For ceramic capacitors Type-III compensation can be implemented by simply adding an R and C between output and Feedback. A precision 0.6V reference, present on the positive terminal of the Error Amplifier, permits programming of the output voltage down to 0.6V via the FB pin. The output of the Error Amplifier is internally compared to a feed-forward (VIN/5 peak-topeak) ramp and generates the PWM control. Timing is governed by an internal oscillator that sets the PWM frequency at 300kHz. SP6125 contains useful protection features. Overcurrent protection is based on high-side MOSFET's RDS(ON) and is programmable via a resistor placed at LX node. Under-Voltage Lock-Out (UVLO) ensures that the controller starts functioning only when sufficient voltage exists for powering IC's internal circuitry. SP6125 Loop Compensation The SP6125 includes Type-II internal compensation components for loop compensation. External compensation components are not required for systems with tantalum or aluminum electrolytic output capacitors with sufficiently high ESR. Use the condition below as a guideline to determine whether or not the internal compensation is sufficient for your design. Type-II internal compensation is sufficient if the following condition is met: f ESRZERO < f DBPOLE ................... (1) where: f ESRZERO = 1 2. .R ESR .C OUT ........... (2) f DBPOLE = 1 2. . L C OUT ............ (3) CZ = LC ............................. (4) R1 Creating a Type-III compensation Network The above condition requires the ESR zero to be at a lower frequency than the double-pole from the LC filter. If this condition is not met, Type-III compensation should be used and can be accomplished by placing a series RC combination in parallel with R1 as shown below. The value of CZ can be calculated as follows and RZ selected from table 1. fESRZERO/fDBPOLE RZ 1X 2X 3X 5X >= 10X 50K 40K 30K 10K 2K Table1- Selection of RZ Mar22-07 RevC SP6125: TSOT-6 PFET Buck Controller 2007 Sipex Corporation 4 General Overview SP6125 Vout CP1 2pF RZ CZ2 130pF RZ2 200k VFB CZ R1 200k, 1% Error Amplif ier Figure 1- RZ and CZ in conjunction with internal compensation components form a Type-III compensation Loop Compensation Example 1- A converter utilizing a SP6125 has a 8.2uH inductor and two 22uF/5m ceramic capacitor. Determine whether Type-III compensation is needed. From equation (2) fESRZERO = 1.45MHz. From equation (3) fDBPOLE = 8.4kHz. Since the condition specified in (1) is not met, Type-III compensation has to be used by adding external components RZ and CZ. Using equation (4) CZ is calculated 95pF (use 100 pF). Following the guideline given in table 1, a 2k RZ should be used. The steps followed in example 1 were used to compensate the typical application circuit shown on page 1. Satisfactory frequency response of the circuit, seen in figure 2, validates the above procedure. Loop Compensation Example 2- A converter utilizing a SP6125 has a 8.2uH inductor and a 150uF, 82m Aluminum Electrolytic capacitor. Determine whether Type-III compensation is needed. From equation (2) fESRZERO = 13kHz. From equation (3) fDBPOLE = 4.5kHz. Since the condition specified in (1) is not met, Type-III compensation has to be used by adding external components RZ and CZ. Using equation (4) CZ is calculated 175pF (use 180 pF). Since fESRZERO / fDBPOLE is approximately 3, RZ has to be set at 30k . Figure 2- Satisfactory frequency response of typical application circuit shown on page 1. Crossover frequency fc is about 35kHz with a corresponding phase margin of 60 degrees. The two sets of curves, which are essentially identical, correspond to load current of 1A and 2.5A. Mar22-07 RevC SP6125: TSOT-6 PFET Buck Controller + Vref =0.6V R2 2007 Sipex Corporation 5 General Overview Using the ON/OFF Function Overcurrent protection Vin SP6125 Gate Q1 Ov er-Current Comparator LX Rs The Feedback pin serves a dual role of ON/OFF control. The MOSFET driver is disabled when a voltage greater than 1V is applied at the FB pin. Maximum voltage rating of this pin is 5.5V. The controlling signal should be applied through a small signal diode as shown on page 1. Please note that an optional 10k bleeding resistor across the output helps keep the output capacitor discharged under no load condition. Figure 3- Overcurrent protection circuit The overcurrent protection circuit functions by monitoring the voltage across the high-side FET Q1. When this voltage exceeds 0.3V, the overcurrent comparator triggers and the controller enters hiccup mode. For example if Q1 has Rds(on)=0.1 , then the overcurrent will trigger at I = 0.3V/0.1 =3A. To program a lower overcurrent use a resistor Rs as shown in figure 1. Calculate Rs from: Rs = 0.3 - (1.15 x Iout x Rds (on) ) ......... (5) 30uA The overcurrent circuit triggers at peak current through Q1 which is usually about 15% higher than average output current. Hence the multiplier 1.15 is used in (5). Example: A switching MOSFET used with SP6125 has Rds(on) of 0.1 . Program the overcurrent circuit so that maximum output is 2A. Rs = Rs = 2333 Using the above equation there is good agreement between calculated and test results for Rs in the range of 0.5k to 3k . For Rs larger than 3k test results are lower than those predicted by (5), due to circuit parasitics. Therefore maximum value of Rs should be limited to 3k . Mar22-07 RevC + Ds 30uA Vin - 0.3V Programming the Output Voltage To program the output voltage, calculate R2 using the following equation: R2 = R1 Vout Vref - 1 Where: Vref=0.6 is the reference voltage of the SP6125 R1=200k is a fixed-value resistor that, in addition to being a voltage divider, it is part of the compensation network. In order to simplify compensation calculations, R1 is fixed at 200k . Soft Start Soft Start is preset internally to 5ms (nominal). Internal Soft Start eliminates the need for the external capacitor CSS that is commonly used to program this function. MOSFET Gate Drive P-channel drive is derived through an internal regulator that generates VIN-5V. This pin (VDR) has to be connected to VIN with a 0.1uF decoupling capacitor. The gate drive circuit swings between VIN and VIN-5 and employs powerful drivers for efficient switching of the Pchannel MOSFET. 0.3 - (1.15 x 2 A x 0.1Ohm ) 30uA SP6125: TSOT-6 PFET Buck Controller 2007 Sipex Corporation 6 General Overview Power MOSFET Selection Select the Power MOSFET for Voltage rating BVDSS, On resistance RDS(ON), and thermal resistance Rthja. BVDSS should be about twice as high as VIN in order to guard against switching transients. Recommended MOSFET voltage rating for VIN of 5V, 12V and 24V is 12V, 30V and 40V respectively. RDS(ON), must be selected such that when operating at peak current and junction temperature the Overcurrent threshold of the SP6125 is not exceeded. Allowing 50% for temperature coefficient of RDS(ON) and 15% for inductor current ripple, the following expression can be used: where: Vf is diode forward voltage at IOUT Schottky's AC losses due to its switching capacitance are negligible. Inductor Selection Select the Inductor for inductance L and saturation current Isat. Select an inductor with Isat higher than the programmed overcurrent. Calculate inductance from: 300mV RDS (ON ) 1.5 x 1.15 x Iout Within this constraint, selecting MOSFETs with lower RDS(ON) will reduce conduction losses at the expense of increased switching losses. As a rule of thumb select the highest RDS(ON) MOSFET that meets the above criteria. Switching losses can be assumed to roughly equal the conduction losses. A simplified expression for conduction losses is given by: Vout 1 1 L = (Vin - Vout ) x x x Vin f Irip where: VIN is converter input voltage VOUT is converter output voltage f is switching frequency IRIP is inductor peak-to-peak current ripple (nominally set to 30% of IOUT) Keep in mind that a higher IRIP results in a smaller inductor which has the advantages of small size, low DC equivalent resistance DCR, high saturation current Isat and allows the use of a lower output capacitance to meet a given step load transient. A higher Irip, however, increases the output voltage ripple and increases the current at which converter enters Discontinuous Conduction Mode. The output current at which converter enters DCM is 1/2 of IRIP. Note that a negative current step load that drives the converter into DCM will result in a large output voltage transient. Therefore the lowest current for a step load should be larger than 1/2 of IRIP. Vout Pcond = Iout x RDS (ON ) x Vin MOSFET's junction estimated from: temperature can be T = (2 x Pc x Rthja ) + Tambient Schottky Rectifier selection Select the Schottky for Voltage rating VR, Forward voltage Vf, and thermal resistance Rthja. Voltage rating should be selected using the same guidelines outlined for MOSFET voltage selection. For a low duty cycle application such as the circuit shown on first page, the Schottky is conducting most of the time and its conduction losses are the largest component of losses in the converter. Conduction losses can be estimated from: Output Capacitor Selection Select the output capacitor for voltage rating, capacitance and Equivalent Series Resistance (ESR). Nominally the voltage rating is selected to be twice as large as the output voltage. Select the capacitance to satisfy the specification for output voltage overshoot or undershoot caused by current step load. A steady-state output current IOUT corresponds to 2 inductor stored energy of 1/2 L IOUT . A sudden decrease in IOUT forces the energy surplus in L to be absorbed by COUT. 2007 Sipex Corporation Vout Pc = Vf x Iout x 1 - Vin Mar22-07 RevC SP6125: TSOT-6 PFET Buck Controller 7 General Overview This causes an overshoot in output voltage that is corrected by power switch reduced duty cycle. Use the following equation to calculate COUT: Input Capacitor Selection Select the input capacitor for Voltage, Capacitance, ripple current, ESR and ESL. Voltage rating is nominally selected to be twice the input voltage. The RMS value of input capacitor current, assuming a low inductor ripple current (Irip), can be calculated from: I 2 - I1 Cout = L x 2 2 Vos - Vout Where: L is the output inductance I2 is the step load high current I1 is the step load low current Vos is output voltage including overshoot VOUT is steady state output voltage Output voltage undershoot calculation is more complicated. Test results for SP6125 buck circuits show that undershoot is approximately equal to overshoot. Therefore above equation provides a satisfactory method for calculating COUT. Select ESR such that output voltage ripple (VRIP) specification is met. There are two components to VRIP: First component arises from charge transferred to and from COUT during each cycle. The second component of VRIP is due to inductor ripple current flowing through output capacitor's ESR. It can be calculated from: Icin = Iout x D(1 - D ) In general total input voltage ripple should be kept below 1.5% of VIN (not to exceed 180mV). Input voltage ripple has three components: ESR and ESL cause a step voltage drop upon turn on of the MOSFET. During on time capacitor discharges linearly as it supplies IOUT - IIN. The contribution to Input voltage ripple by each term can be calculated from: V , Cin = Iout x Vout x (Vin - Vout ) fs x Cin x Vin 2 V , ESR = ESR(Iout - 0.5Irip ) V , ESL = ESL (Iout - 0.5Irip ) Trise Where Trise is the rise time of current through capacitor Total input voltage ripple is sum of the above: 1 Vrip = Irip x ESR + 8 x Cout x fs 2 2 V , Tot = V , Cin + V , ESR + V , ESL In circuits where converter input voltage is applied via a mechanical switch excessive ringing may be present at turn-on that may interfere with smooth startup of SP6126. Addition of an inexpensive 100F Aluminum Electrolytic capacitor at the input will help reduce ringing and restore a smooth startup. Where: IRIP is inductor ripple current fs is switching frequency COUT is output capacitor calculated above Note that a smaller inductor results in a higher IRIP, therefore requiring a larger COUT and/or lower ESR in order to meet VRIP. Mar22-07 RevC SP6125: TSOT-6 PFET Buck Controller 2007 Sipex Corporation 8 VIN Q1 FDS4685 C1 4.7uF C2 4.7uF 24-29 V 2 1 Vin Rs 2k LX C6 0.1uF 6 Gate GND L1, IHLP-2525CZ 8.2uH, 68mOhm, 4A VOUT C4 22uF R1 200k, 1% C5 22uF SP6125 3 VDR 4 VFB GND 5 Ds MBRA340T3G RZ 2K 3.3V 0-3A CZ 100pF R2 44.2k, 1% D1 1N4148 GND SHDN High=Of f Figure 4- Application circuit for Vin=24V TYPICAL PERFORMANCE CHARACTERISTICS SP6125 Efficiency versus Iout, Vin=24V,Ta=25C 90 80 Efficiency (%) 70 Vout=3.3V 60 50 0.0 0.5 1.0 1.5 Iout (A) 2.0 2.5 3.0 Figure 5- Efficiency at VIN = 24 V , TA= 25C, natural convection Mar22-07 RevC SP6125: TSOT-6 PFET Buck Controller 2007 Sipex Corporation 9 TYPICAL PERFORMANCE CHARACTERISTICS Figure 6- Step load 1.2-2.8A, ch1: VIN; ch2: VOUT; ch3: IOUT Figure 9- Output ripple at 0A is 12mV, ch1: VIN; ch2: VOUT; ch3: IOUT Figure 7- Startup no load, ch1: VIN; ch2: VOUT, ch3: IOUT Figure 10- Output ripple at 3A is 32mV, ch1: VIN; ch2: VOUT; ch3: IOUT Figure 8- Start up 3A, ch1: VIN; ch2: VOUT; ch3: IOUT Mar22-07 RevC SP6125: TSOT-6 PFET Buck Controller 2007 Sipex Corporation 10 PACKAGE: 6 PIN TSOT Mar22-07 RevC SP6125: TSOT-6 PFET Buck Controller 2007 Sipex Corporation 11 ORDERING INFORMATION Part Number Temperature Range Package SP6125EK1-L........................................-40C to +85C......................(Lead Free) 6 Pin TSOT SP6125EK1-L/TR1..................................-40C to +85C......................(Lead Free) 6 Pin TSOT /TR = Tape and Reel Pack Quantity for Tape and Reel is 2500 For further assistance: Email: WWW Support page: Sipex Application Notes: Sipexsupport@sipex.com http://www.sipex.com/content.aspx?p=support http://www.sipex.com/applicationNotes.aspx Solved by Sipex Corporation Headquarters and Sales Office 233 South Hillview Drive Milpitas, CA95035 tel: (408) 934-7500 fax: (408) 935-7600 TM Sipex Corporation reserves the right to make changes to any products described herein. Sipex does not assume any liability arising out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others. Mar22-07 RevC SP6125: TSOT-6 PFET Buck Controller 2007 Sipex Corporation 12 |
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