SP6125

SP6125 EXAR | Alldatasheet

Document overview

• Manufacturer or author: Provided By ALLDATASHEET.COM(FREE DATASHEET DOWNLOAD SITE)
• PDF pages: 12

Technical content

Jan28-08 RevG SP6125: TSOT-6 PFET Buck Controller  2007 Exar Corporation

FEATURES

/square6 Wide 4.5V – 29V Input Voltage Range /square6 Internal Compensation /square6 Built-in High Current PMOS Driver /square6 Adjustable Overcurrent Protection /square6 Internal soft-start /square6 300kHz Constant Frequency Operation /square6 0.6V Reference Voltage /square6 1% output setpoint accuracy /square6 Lead Free, RoHS Compliant Package: Small 6 pin TSOT

DESCRIPTION

The SP6125 is a PWM controlled step down (buck) voltage mode regulator with V IN 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 High=Of f L1, IHLP-2525CZ 8.2uH, 68mOhm, 4A 22uF Ds MBRA340T3G 300k, 1% RZ 66.5k, 1% FDS4685 CZ 47pF 0.1uF 4.7uF Rs 2k D1 1N4148 24V SHDN VIN VOUT GND GND VFB Vin LX GND VDR Gate SP6125 3.3V 0-3A 22uF 4.7uF SP6125 6 5 4 1 2 3 SP6125

6 PinTSOT

High-Voltage, Step Down Controller in TSOT6

Jan28-08 RevG SP6125: TSOT-6 PFET Buck Controller  2007 Exar Corporation ABSOLUTE MAXIMUM RATINGS Lead Temperature (Soldering, 1…0 sec)….…………..300 °C ESD Rating…… ….…….…1kV LX, 2kV all other nodes, HBM ELECTRICAL SPECIFICATIONS Specifications are for T AMB =T J=25 °C, and those denoted by ♦ apply over the full operating range, -40 °C< T j <125°C. Unless otherwise specified: VIN =4.5V to 29V, C IN = 4.7 µF. PARAMETER MIN TYP MAX UNITS ♦ CONDITIONS UVLO Turn-On Threshold 4.2 4.35 4.5 V 0°C< T j <125 °C UVLO Turn-Off Threshold 4.0 4.2 4.4 V 0°C< T j <125 °C UVLO Hysterisis 0.2 V Operating Input Voltage Range 4.5 29 V 0°C< T j <125 °C Operating Input Voltage Range 7 29 V Operating VCC Current 0.3 3 mA VFB=1.2V Reference Voltage Accuracy 0.5 1 % Reference Voltage Accuracy 0.5 2 % ♦ Reference Voltage 0.594 0.6 0.606 V Reference Voltage 0.588 0.6 0.612 V ♦ Switching Frequency 255 300 345 kHz Peak-to-peak ramp Modulator V IN /5 V Minimum ON-Pulse Duration 40 100 ns ♦ Minimum Duty Cycle 0 % Maximum Duty Cycle 100 % Gate Driver Turn-Off Resistance 50 60 k Ω Internal resistor between GATE and V IN Gate Driver Pull-Down Resistance 4 8 Ω V IN =12V, V FB =0.5V, Measure resistance between GATE and VDR Gate Driver Pull-up Resistance 3 6 Ω V IN =12V, V FB =0.7V, Measure resistance between GATE and VIN VIN - VDR voltage difference 4.5 5.5 V ♦ Measure VIN – VDR, VIN >7V Overcurrent Threshold 270 300 330 mV Measure VIN - LX LX pin Input Current 25 30 35 uA VLX = VIN OFF interval during hiccup 200 ms Soft start time 3 5 9 ms VFB=0.58V, measure between VIN =4.5V and first GATE pulse SHDN Threshold 0.9 1.0 1.1 V ♦ Apply voltage to FB SHDN Threshold Hysteresis 100 mV 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.

Jan28-08 RevG SP6125: TSOT-6 PFET Buck Controller  2007 Exar Corporation PIN DESCRIPTION PIN # PIN NAME DESCRIPTION 1 V IN Input power supply for the controller. Place input decoupling capacitor as close as possible to this pin. 2 GATE Connect to the gate terminal of the external P-channel MOSFET.

3 VDR

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. 4 FB 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. 5 GND Ground pin. 6 LX 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: V TRSHLD = 300mV – 30uA * R BLOCK DIAGRAM FAULT Register Set Dominant POR ENBL 4-Bit counter VDR VIN GATE 5V Internal LDO VIN - 0.3V Overcurrent Comparator LX VDR 30uA GND VREF FAULT FB Oscillator VIN S R I = k x VIN Error Amplifier PWM Comparator PWM Latch Reset Dominant Vin - 5V LDO FAULT FAULT 200ms delay UVLO S R R

Jan28-08 RevG SP6125: TSOT-6 PFET Buck Controller  2007 Exar Corporation The SP6125 is a fixed frequency, Voltage- mode, 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 (V IN /5 peak-to- peak) 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 R DS(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 compen- sation. 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: where: OUT ESR ESRZERO CRf ... 2 π= ……….. (2) OUT DBPOLE CL f .. 2 π ………… (3) 13.1 R CLCZ × 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. Table1- Selection of RZ fESRZERO ÷fDBPOLE RZ 1X 50K 2X 40K 3X 30K 5X 10K >= 10X 2K General Overview

Jan28-08 RevG SP6125: TSOT-6 PFET Buck Controller  2007 Exar Corporation Overcurrent protection 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 Ω, then the overcurrent will trigger at I = 0.3V/0.1 Ω=3A. To program a lower overcurrent use a resistor Rs as shown in figure 1. Calculate Rs from: ( ) uA on Rds Iout Rs 30 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 Ω. Program the over- current circuit so that maximum output is 2A. ( ) uA Ohm ARs 30 Rs = 2333 Ω Using the above equation there is good agreement between calculated and test results for Rs in the range of 0.5k Ω to 3k Ω. For Rs larger than 3k Ω test results are lower than those predicted by (5), due to circuit parasitics. Therefore maximum value of Rs should be limited to 3k Ω. Using the ON/OFF Function 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 Ω bleeding resistor across the output helps keep the output capacitor discharged under no load condition. Programming the Output Voltage To program the output voltage, calculate R2 using the following equation:  − Vref Vout RR Where: Vref=0.6 is the reference voltage of the SP6125 R1=200k Ω 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 Ω. 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 V IN -5V. This pin (VDR) has to be connected to VIN with a 0.1uF decoupling capacitor. The gate drive circuit swings between V IN and V IN -5 and employs powerful drivers for efficient switching of the P- channel MOSFET. Ds Rs SP6125 Gate LX 30uA Vin - 0.3V Vin Ov er-Current Comparator General Overview

Jan28-08 RevG SP6125: TSOT-6 PFET Buck Controller  2007 Exar Corporation Power MOSFET Selection Select the Power MOSFET for Voltage rating BV DSS , On resistance R DS(ON) , and thermal resistance Rthja. BV DSS should be about twice as high as V IN in order to guard against switching transients. Recommended MOSFET voltage rating for V IN 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 R DS(ON) and 15% for inductor current ripple, the following expression can be used: ××≤ Iout mV ON RDS 15 . 15 . 1 300 )( Within this constraint, selecting MOSFETs with lower R DS(ON) will reduce conduction losses at the expense of increased switching losses. As a rule of thumb select the highest R DS(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: ××= Vin Vout ON RDS Iout Pcond )( MOSFET’s junction temperature can be estimated from: ( ) Tambient Rthja Pc T +××= 2 Schottky Rectifier selection Select the Schottky for Voltage rating V R , Forward voltage V f, 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: −××= Vin Vout Iout Vf Pc 1 where: Vf is diode forward voltage at I OUT 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: ( )  × ×−= Irip fVin Vout Vout Vin L 11 where: V IN is converter input voltage VOUT is converter output voltage f is switching frequency I RIP is inductor peak-to-peak current ripple (nominally set to 30% of IOUT ) Keep in mind that a higher I RIP 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 I RIP . 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 I RIP . 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 I OUT corresponds to inductor stored energy of ½ L IOUT 2. A sudden decrease in IOUT forces the energy surplus in L to be absorbed by COUT . General Overview

Jan28-08 RevG SP6125: TSOT-6 PFET Buck Controller  2007 Exar Corporation This causes an overshoot in output voltage that is corrected by power switch reduced duty cycle. Use the following equation to calculate C OUT :  −×= Vout -Vos IILCout Where: L is the output inductance I 2 is the step load high current I1 is the step load low current Vos is output voltage including overshoot V OUT 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 C OUT . Select ESR such that output voltage ripple RIP ) 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 V RIP is due to inductor ripple current flowing through output capacitor’s ESR. It can be calculated from: ××+×= fs Cout ESR Irip Vrip Where: I RIP is inductor ripple current fs is switching frequency C OUT is output capacitor calculated above Note that a smaller inductor results in a higher I RIP , therefore requiring a larger COUT and/or lower ESR in order to meet VRIP . 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: ( )DDIout Icin −×= 1 In general total input voltage ripple should be kept below 1.5% of V IN (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 I OUT - IIN . The contribution to Input voltage ripple by each term can be calculated from: ( ) 2, Vin Cin fs Vout Vin Vout Iout Cin V ×× −××=Δ ( )Irip Iout ESR ESR V 5 . 0, −=Δ ( ) Trise Irip Iout ESL ESL V 5 . 0, −=Δ Where Trise is the rise time of current through capacitor Total input voltage ripple is sum of the above: ESL VESR VCin VTot V ,,,, Δ+Δ+Δ=Δ 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 100 µF Aluminum Electrolytic capacitor at the input will help reduce ringing and restore a smooth startup. General Overview

Jan28-08 RevG SP6125: TSOT-6 PFET Buck Controller  2007 Exar Corporation PACKAGE: 6PIN TSOT EXAR

Jan28-08 RevG SP6125: TSOT-6 PFET Buck Controller  2007 Exar Corporation

ORDERING INFORMATION

Part Number Temperature Range Package /TR = Tape and Reel Pack Quantity for Tape and Reel is 2500 For further assistance: Email: customersupport@exar.com EXAR Technical Documentation: 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.