SP6125 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 2 VIN 3 VDR GATE 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 1 C1 4.7uF Q1 FDS4685 2 Gate C2 4.7uF GND Vin L1, IHLP-2525CZ 8.2uH, 68mOhm, 4A Rs 2k VOUT LX C6 0.1uF 24V 6 SP6125 Ds MBRA340T3G 3 RZ 2K VDR C4 22uF R1 300k, 1% CZ 47pF 4 C5 22uF 3.3V 0-3A GND VFB GND R2 66.5k, 1% 5 D1 1N4148 SHDN High=Of f Jan28-08 RevG SP6125: TSOT-6 PFET Buck Controller 1 2007 Exar Corporation ABSOLUTE MAXIMUM RATINGS 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.....................................-40°C to 125°C Lead Temperature (Soldering, 1…0 sec)….…………..300 °C ESD Rating……….…….…1kV LX, 2kV all other nodes, HBM 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. ELECTRICAL SPECIFICATIONS Specifications are for TAMB=TJ=25°C, and those denoted by ♦ apply over the full operating range, -40°C< Tj <125°C. Unless otherwise specified: VIN =4.5V to 29V, CIN = 4.7µF. PARAMETER ♦ MIN TYP MAX UNITS UVLO Turn-On Threshold 4.2 4.35 4.5 V 0°C< Tj <125°C UVLO Turn-Off Threshold 4.0 4.2 4.4 V 0°C< Tj <125°C UVLO Hysterisis Operating Input Voltage Range Operating Input Voltage Range Operating VCC Current Reference Voltage Accuracy 0.2 V 4.5 29 V 7 29 V 0.3 0.5 3 1 mA % 0.5 2 % 0.6 0.606 V Reference Voltage Accuracy Reference Voltage 0.594 Reference Voltage 0.588 0.6 0.612 V 255 300 VIN/5 345 kHz V 40 100 ns 0 % % 50 60 kΩ 4 8 Ω 3 6 Ω 5.5 V 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 CONDITIONS 100 0°C< Tj <125°C ♦ 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 ♦ VIN - VDR voltage difference 4.5 Overcurrent Threshold 270 300 330 mV Measure VIN - LX LX pin Input Current OFF interval during hiccup 25 30 200 35 uA ms VLX = VIN Soft start time 3 5 9 ms 1.0 1.1 SHDN Threshold SHDN Threshold Hysteresis Jan28-08 RevG 0.9 100 V Measure VIN – VDR, VIN>7V VFB=0.58V, measure between VIN=4.5V and first GATE pulse ♦ Apply voltage to FB mV SP6125: TSOT-6 PFET Buck Controller 2 2007 Exar Corporation PIN DESCRIPTION PIN # PIN NAME 1 VIN 2 GATE 3 VDR 4 FB 5 GND 6 LX 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 VIN 5V VDR Oscillator Vin - 5V LDO VIN 5V Internal LDO I = k x VIN FAULT PWM Latch Reset Dominant VREF GATE S + FB R + - PWM Comparator Error Amplifier VDR FAULT FAULT ENBL LX - 200ms delay + - 1V Jan28-08 RevG FAULT Register S R R + UVLO 4-Bit counter Overcurrent Comparator 30uA VIN - 0.3V GND POR Set Dominant SP6125: TSOT-6 PFET Buck Controller 3 2007 Exar 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. Type-II internal compensation is sufficient if the following condition is met: 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. Creating a Type-III compensation Network f ESRZERO < f DBPOLE ………………. (1) where: 1 f ESRZERO = f DBPOLE = CZ = 2.π .R ESR .C OUT 1 2.π . L ⋅ C OUT ……….. (2) ………… (3) L⋅C ……………………….. (4) 1.3 × R1 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. 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. fESRZERO÷fDBPOLE RZ 1X 2X 3X 5X >= 10X 50K 40K 30K 10K 2K Table1- Selection of RZ Jan28-08 RevG SP6125: TSOT-6 PFET Buck Controller 4 2007 Exar Corporation General Overview Vout SP6125 CP1 2pF RZ CZ2 130pF RZ2 200k CZ R1 300k, 1% VFB Vref =0.6V + R2 Error Amplif ier Figure 1- RZ and CZ in conjunction with internal compensation components form a Type-III compensation 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, 82mΩ Aluminum Electrolytic capacitor. Determine whether Type-III compensation is needed. Loop Compensation Example 1- A converter utilizing a SP6125 has a 8.2uH inductor and two 22uF/5mΩ 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 48.7pF (use 47 pF). Following the guideline given in table 1, a 2kΩ RZ should be used. The steps followed in example 1 were used to compensate the typical application circuit shown on page 1. Satisfactory frequency 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 89.9pF (use 100pF). Since fESRZERO ÷ fDBPOLE is approximately 3, RZ has to be set at 30kΩ. 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. Jan28-08 RevG SP6125: TSOT-6 PFET Buck Controller 5 2007 Exar Corporation General Overview Using the ON/OFF Function Overcurrent protection Vin 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 10kΩ bleeding resistor across the output helps keep the output capacitor discharged under no load condition. SP6125 Gate Q1 Ov er-Current Comparator LX Rs + Ds 30uA Vin - 0.3V Programming the Output Voltage To program the output voltage, calculate R2 using the following equation: Figure 3- Overcurrent protection circuit R2 = 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)=0.1Ω, then the overcurrent will trigger at I = 0.3V/0.1Ω=3A. To program a lower overcurrent use a resistor Rs as shown in figure 1. Calculate Rs from: Rs = Where: Vref=0.6 is the reference voltage of the SP6125 R1=200kΩ 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 200kΩ. 0.3 − (1.15 × Iout × 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). 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. Example: A switching MOSFET used with SP6125 has Rds(on) of 0.1Ω. Program the overcurrent circuit so that maximum output is 2A. MOSFET Gate Drive 0.3 − (1.15 × 2 A × 0.1Ohm ) Rs = 30uA 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. Rs = 2333Ω Using the above equation there is good agreement between calculated and test results for Rs in the range of 0.5kΩ to 3kΩ. For Rs larger than 3kΩ test results are lower than those predicted by (5), due to circuit parasitics. Therefore maximum value of Rs should be limited to 3kΩ. Jan28-08 RevG R1 Vout − 1 Vref SP6125: TSOT-6 PFET Buck Controller 6 2007 Exar Corporation General Overview Power MOSFET Selection where: Vf is diode forward voltage at IOUT 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: 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: Vout 1 1 L = (Vin − Vout ) × × × Vin f Irip 300mV RDS (ON ) ≤ 1.5 × 1.15 × Iout 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) 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: 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 ½ 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 ½ of IRIP. Vout Pcond = Iout × RDS (ON ) × Vin MOSFET’s junction estimated from: temperature can be T = (2 × Pc × 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 ½ L IOUT . A sudden decrease in IOUT forces the energy surplus in L to be absorbed by COUT. Vout Pc = Vf × Iout × 1 − Vin Jan28-08 RevG SP6125: TSOT-6 PFET Buck Controller 7 2007 Exar Corporation General Overview Input Capacitor Selection This causes an overshoot in output voltage that is corrected by power switch reduced duty cycle. Use the following equation to calculate COUT: 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 2 − I12 Cout = L × 2 2 Vos Vout Icin = Iout × D(1 − D ) 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 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: 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. ∆V , Cin = Iout × Vout × (Vin − Vout ) fs × Cin × Vin 2 ∆V , ESR = ESR(Iout − 0.5Irip ) 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: ∆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 × ESR 2 + 8 × Cout × fs 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 100µF 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. Jan28-08 RevG SP6125: TSOT-6 PFET Buck Controller 8 2007 Exar Corporation VIN 1 C1 4.7uF Q1 FDS4685 2 C2 4.7uF Gate 24V GND Vin L1, IHLP-2525CZ 8.2uH, 68mOhm, 4A Rs 2k VOUT LX C6 0.1uF 6 SP6125 Ds MBRA340T3G 3 RZ 2K VDR C4 22uF C5 22uF CZ 47pF 4 3.3V 0-3A R1 300k, 1% GND VFB GND R2 66.5k, 1% 5 D1 1N4148 SHDN High=Of f Figure 4- Application circuit for Vin=24V TYPICAL PERFORMANCE CHARACTERISTICS SP6125 Efficiency versus Iout, Vin=24V,Ta=25C 90 Efficiency (%) 80 70 Vout=3.3V 60 50 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Iout (A) Figure 5- Efficiency at VIN = 24 V , TA= 25˚C, natural convection Jan28-08 RevG SP6125: TSOT-6 PFET Buck Controller 9 2007 Exar Corporation 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 Jan28-08 RevG SP6125: TSOT-6 PFET Buck Controller 10 2007 Exar Corporation PACKAGE: 6PIN TSOT EXAR Jan28-08 RevG SP6125: TSOT-6 PFET Buck Controller 11 2007 Exar Corporation ORDERING INFORMATION Part Number Temperature Range Package SP6125EK1-L………………………………….-40°C to +125°C…………..….…(Lead Free) 6 Pin TSOT SP6125EK1-L/TR…………………………....-40°C to +125°C………..……..….(Lead Free) 6 Pin TSOT /TR = Tape and Reel Pack Quantity for Tape and Reel is 2500 For further assistance: Email: EXAR Technical Documentation: [email protected] http://www.exar.com/TechDoc/default.aspx? Exar Corporation Headquarters and Sales Office 48720 Kato Road Fremont, CA 94538 main: 510-668-7000 fax: 510-668-7030 EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration purposes and may vary depending upon a user’s specific application. While the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies. EXAR Corporation does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances. Jan28-08 RevG SP6125: TSOT-6 PFET Buck Controller 12 2007 Exar Corporation