TF6002 / TF6002A 2A, 26V Synchronous Rectified Step-Down Converter Features Description 2A continuous output current Wide input voltage range: 4.5V to 26V Wide output voltage range: 0.923V to 23V Tight VFB variation: 1.5% (TF6002A), 2.5% (TF6002) High, >90%, efficiency (VIN = 5V, 0.15A < IL < 2A) enabled by integrated 130 mW MOSFET switches Operates at fixed 340 kHz frequency for small filter size 3 mA (MAX) shut-down supply current Programmable soft-start, cycle-by-cycle over-current protection and input under-voltage lockout Industrial temperature range: -40 °C to +85 °C Drop-in replacement for MP2305, MP1482 The TF6002 and TF6002A are monolithic synchronous buck regulators featuring integrated 130 mW MOSFETs that provide continuous 2A output load current. They operates over a wide 4.5V to 26V input voltage range and provides output voltage from 0.923V to 23V at up to 93% efficiency. Their current mode control circuitry provides fast transient response and cycle-bycycle current limit. Applications High-Density Point-of-Load Regulators Distributed Power Systems Notebook and Netbook Computers Power Supplies for FPGAs, DSP Blocks and ASICs Set-Top Boxes xDSL Modems Typical Application The TF6002 and TF6002A have the VFB variation of only 2.5% and 1.5%, respectively, providing tight output regulation. The TF6002 and TF6002A operate at fixed 340 kHz switching frequency. They features programmable soft-start which prevents inrush current at turn-on. In shut-down mode they draw only 3 mA (MAX). Both devices are offered in 8-pin SOIC narrow package. It operates over an extended -40 °C to +85 °C temperature range. Ordering Information PART NUMBER PACKAGE PACKING TF6002-TAS SOIC-8(N) Tube TF6002-TAQ SOIC-8(N) Tape & Reel 330mm TF6002-TAP SOIC-8(N) Tape & Reel 180mm TF6002A-TAS SOIC-8(N) Tube TF6002A-TAQ SOIC-8(N) Tape & Reel 330mm TF6002A-TAP SOIC-8(N) Tape & Reel 180mm Pin Diagram Top View March 15, 2011 1 TF6002 / TF6002A Functional Block Diagram Pin Descriptions PIN NAME PIN NUMBER PIN DESCRIPTION 1 High-side gate drive boost input pin. The BS pin supplies the drive for the high-side N-Channel MOSFET switch. Connect a 0.01 mF or greater capacitor from SW to BS to power up the high-side switch. IN 2 Power input pin. The IN pin supplies the power to the IC and the step-down converter switches. Drive the IN pin with a 4.5V to 26V power source. Bypass the IN pin to GND pin with an appropriate large capacitor to minimize noise on the input to the device. SW 3 Power switching output pin. The SW pin is the switching node that supplies power to the output. Connect a LC filter from SW pin to the output load. Note that a capacitor is needed from SW pin to BS pin to power the high-side switch. GND 4 Ground pin. FB 5 Feedback input pin. The FB pin senses the output voltage to regulate that voltage. Drive the FB pin with a resistive voltage divider from the output voltage. The feedback threshold is 0.923V. COMP 6 Compensation input pin. The COMP pin is used to compensate the regulation control loop. Connect a series RC filter from COMP to GND pin to compensate the regulation loop. In some cases, additional capacitor is needed. EN 7 Enable input pin. The EN pin is a digital input pin that enables or disables the regulator. Set the EN pin to high to turn the regulator on; set it to low, to turn the regulator off. Use 100 kW pull-up resistor for automatic start-up. 8 Soft-start control input pin. The SS pin controls the soft-start period. Connect a capacitor from the SS pin to the GND pin to set the soft-start period. A 0.1 mF capacitor sets the soft-start period to 15 ms. To disable the soft-start feature, leave the SS pin unconnected. BS SS March 15, 2011 2 TF6002 / TF6002A Absolute Maximum Ratings (NOTE1) Recommended Operating Conditions VIN - Supply voltage ..........................................................-0.3V to +28V VSW - Switch voltage ..................................................................-1V to VIN VBS- Boost voltage ..............................................VSW - 0.3V to VSW + 6V All other pins .......................................................................-0.3V to +6V VIN - Input voltage ...............................................................4.5V to +26V VSW - Output voltage ........................................................0.923V to 23V TA - Operating ambient temperature range..........-40 °C to +85 °C SOIC-8 Thermal Resistance (NOTE2) QJC.................................................................................................45 °C/W QJA.................................................................................................90 °C/W TJ - Junction operating temperature .......................................+150 °C TL - Lead temperature (soldering, 10s) .................................. +260 °C Tstg - Storage temperature range ............................-65 °C to +150 °C NOTE1 Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. NOTE2 When mounted on a standard JEDEC 2-layer FR-4 board. Electrical Characteristics TA = 25 °C, VIN = 12V, unless otherwise specified. Symbol Parameter Conditions Isd Shutdown supply current VEN = 0V IIN Supply current VEN = 2V, VFB = 1V VFB Feedback voltage 4.5V < VIN < 26V (NOTE3) VFBth Feedback over-voltage threshold AEA Error amplifier voltage gain GEA MIN TF6002 TF6002A TYP MAX Unit 1 3 mA 1.3 1.5 mA 0.9 0.923 0.946 0.909 0.923 0.937 V 1.1 V (NOTE4) 400 V/V Error amplifier transconductance DIC = 10 mA 800 mA / V RDS(ON)1 High-side switch ON resistance (NOTE4) 130 mW RDS(ON)2 Low-side switch ON resistance (NOTE4) 130 mW IDS(off ) High-side switch leakage current VEN = 0V, VSW = 0V IDS(lim)1 Upper switch current limit Minimum duty cycle IDS(lim)2 Lower switch current limit From drain to source GCS COMP to current sense transconductance March 15, 2011 10 2.4 mA 3.4 A 1.1 A 3.5 A/V 3 TF6002 / TF6002A Symbol Parameter fosc Oscillation frequency fosc(sc) Short-circuit oscillation frequency DMAX Conditions MIN TYP MAX Unit 340 kHz VFB = 0V 100 kHz Maximum duty cycle VFB = 1V 90 % tONmin Minimum ON time (NOTE4) 110 ns VEN(sd_th) Enable shutdown threshold voltage VEN rising VEN(sd_th_hyst) Enable shutdown threshold voltage hysteresis VEN(lo_th) Enable lockout threshold voltage VEN(lo_th_hyst) Enable lockout threshold voltage hysteresis VIN(lo_th) Input under-voltage lockout threshold voltage VIN(lo_th_hyst) Input under-voltage lockout threshold voltage hysteresis ISS Soft-start current tSS Tsd 1.1 1.5 2.0 210 2.2 2.5 mV 2.7 210 VIN rising 3.8 4.0 V V mV 4.4 V 210 mV VSS = 0V 6 mA Soft-start period CSS = 0.1 mF 15 ms Thermal shutdown (NOTE4) 160 °C NOTE3 TF6002A: Typical performance 0-85°C = 0.923V +/-1.95%, not tested over temperature during regular production NOTE4 Not subject to production test - verified by design/characterization March 15, 2011 4 TF6002 / TF6002A Typical Performance VIN = 12V, VOUT = 3.3V, L = 15 mH, CIN = 10 mF, COUT = 22 mF, TA = 25 °C, unless otherwise specified. Figure 1. No-Load Steady State Operation Figure 5. 1A-Resistive-Load Startup Via Enable Operation Figure 2. 1A-Load Steady State Operation Figure 6. 1A-Resistive-Load Shutdown Via Enable Operation Figure 3. 2A-Load Steady State Operation Figure 7. Short Circuit Entry Operation Figure 4. Transient Load Response Figure 8. Efficiency as a Function of Load March 15, 2011 5 TF6002 / TF6002A Application Information The TF6002 is a monolithic synchronous buck regulator featuring integrated 130 mW Power MOSFETs that can provide up to 2A of load current. It regulates input voltages from 4.5V to 26V down to an output voltage as low as 0.923V while providing soft-start, cycle-by-cycle over-current, under-voltage lockout and over-temperature protection. SETTING THE OUTPUT VOLTAGE Based on the circuit of Figure 9, the output voltage depends on the feedback voltage, VFB, and the resistor divider network consisting of R1 and R2, as expressed with the following equation: VOUT = VFB This section of the datasheet describes typical application circuits, provides recommendations on component selection, and discusses thermal and layout design considerations. TYPICAL APPLICATIONS The TF6002 uses a fixed frequency, current-mode step-down regulator architecture to deliver constant voltage to the load. Figure 9 shows a typical application circuit. Figure 9. Typical Application Circuit R1 + R2 R2 The R2 resistor value may be as high as 100 kW, however 10 kW resistor value is typically recommended. Given this and the typical VFB of 0.923V, the R1 resistor may easily be calculated for a desired output voltage. Table 1 exemplifies several standard resistor values needed to achieve desired output voltage. If standard resistor values are not available a parallel combination of two standard resistors may also be used. VOUT [V] R1 [kW] R2 [kW] 1.2 3.0 10 1.8 9.53 10 2.5 16.9 10 3.3 26.1 10 5 44.2 10 12 121 10 Table 1. Examples of Standard Value Resistors for a Desired Output Voltage The circuit of Figure 9 takes an input voltage between 4.5V and 26V and regulates it down to 3.3V while bringing 2A of load current. March 15, 2011 6 TF6002 / TF6002A COMPONENT SELECTION Inductor: High frequency operation of the TF6002 allows the use of small surface mount inductors. The minimum inductance value is inversely proportional to the operating frequency and is bounded by the following limits: L= VOUT (VIN − VOUT ) fS IL( MAX )ripple VIN [H ] Inductor Series Supplier Website SRU8043 Bourns Inc. www.bourns.com MSS7341 Coilcraft www.coilcraft.com LQH88P Murata www.murata.com DR1040 Coiltronics www.coiltronics.com CDRH8D43 Sumida www.sumida.com where Table 2. List of Recommended Inductor Series • fS = Operating frequency [Hz] • IL(MAX)ripple = Allowable maximum inductor current ripple [A] • VIN = Input voltage [V] • VOUT = Output voltage [V] The inductor current ripple is typically set to 20% to 40% of the maximum load current. Given this, the operating frequency and the input and output voltages for the TF6002 regulator circuits, it is easy to calculate the optimal inductor value which typically ranges between 10 and 47 mH. Note that a larger value inductor will result in less ripple current and ultimately in lower output ripple voltage. However, the larger value inductor will have a larger physical size, higher series resistance, and lower saturation current. Choose an inductor that will not saturate under the maximum inductor peak current. The peak inductor current is given in the following equation: IL( peak =) ILOAD + VOUT (VIN − VOUT ) 2fS L1VIN [ A] For high efficiency, it is recommended to select an inductor with a high frequency core material (e.g. ferrite) to minimize core losses. Low ESR (equivalent series resistance) is another preferred inductor characteristic when designing for low losses. The inductor must handle the peak inductor current at full load without saturating. Note that the peak inductor current must be below the maximum switch current limit. Chip inductors typically do not have enough core to support the peak inductor currents above 1A and are not suitable for the TF6002 applications. Lastly, select a toroid, pot core or shielded bobbin inductor for low radiated noise. Table 2 provides a list of recommended inductor series. March 15, 2011 Optional Schottky Diode: During the transition between the high-side switch and the low side switch, the body diode of the low-side switch (N-channel power MOSFET) conducts the inductor current. Forward voltage of this body diode is relatively high, therefore, an optional Schottky diode may be paralleled between SW and GND pins. The Schottky diode which features low forward voltage and fast recovery time will result in improved peak efficiency of the buck regulator circuits. Table 3 provides a list of recommended diode series. Diode Series Supplier Website MBR130 MCC www.mcc.com SBR Diodes Inc. www.diodes.com B130 Vishay www.vishay.com Table 3. List of Recommended Schottky Diode Series The connection of the optional Schottky diode (D1) is shown in Figure 10. 7 TF6002 / TF6002A Input Capacitor: The input current to the buck regulator is discontinuous, therefore, a capacitor is required to supply AC current to the regulator while maintaining the DC input voltage. Output Capacitor: The value of the output capacitor of Figure 1 (C2) has an effect on the output voltage ripple as expressed in the following equation: The input capacitor of Figure 1 (C1) absorbs the input switching current, therefore, it requires adequate ripple current rating. The RMS current in the input capacitor can be estimated using the following equation: V V = IC 1 ILOAD OUT 1− OUT VIN VIN The worst case condition occurs when VIN is twice the value of VOUT. In this case, the IC1 is equal to the half of the load current. As a rule of thumb, select the input capacitor with the RMS current rating greater than the half of the maximum load current. The input capacitor reduces peak currents drawn from the input source and reduces input switching noise. The input voltage ripple caused by the input capacitor can be estimated using the following equation: V fS L1 OUT DVOUT = 1− where • fS = Operating frequency [Hz] • ESRC2 = Equivalent series resistance of C2 • VIN = Input voltage [V] • VOUT = Output voltage [V] The output capacitor, C2, can be ceramic, tantalum or electrolytic type. When using ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance, therefore, the above equation may be simplified as the following: = DVOUT = DVIN ILOAD VOUT VOUT 1− C1fS VIN VIN The input capacitor values in the range between 10 and 47 mF are sufficient in most cases. Low ESR capacitors are recommended for a low loss operation. Ceramic capacitors with X5R or X7R dielectrics are preferred, however, tantalum and electrolytic capacitors are acceptable as well. When using electrolytic or tantalum capacitors, a small (e.g. 0.1 mF), ceramic capacitors should also be used and placed as close to the IN pin as possible. Table 4 provides a list of recommended capacitor series. VOUT 1 ESRC 2 + 8fS C 2 VIN V VOUT 1− OUT 8fS L1C 2 VIN When using tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency, therefore, the original output voltage ripple equation can be re-written as the following expression: = DVOUT VOUT VOUT 1− ESRC 2 fS L1 VIN The output capacitor values in the range between 10 and 47 mF provide low output voltage ripple in most cases. Table 4 provides a list of recommended capacitor series. Capacitor Series Supplier Website 0201-2225 Ceramic, TPS, TPM Tantalum AVX www.avx.com MK107, MK212, MK316 Ceramic Taiyo Yuden www.t-yuden.com POSCAP Electrolytic Sanyo edc.sanyo.com Table 4. List of Recommended Capacitor Series March 15, 2011 8 TF6002 / TF6002A Compensation Components: TF6002 employs current mode control for easy compensation and fast transient response. System stability and transient response are controlled via COMP pin. COMP pin is the output of the internal transconductance error amplifier. A series RC network (C3 and R3 of Figure 1) sets a pole-zero combination and controls the characteristics of the control system. The DC gain of the voltage feedback loop is given by the following equation: AVDC = RLOAD GCS AVEA VFB VOUT where • GCS = Current sense transconductance • AVEA = Error amplifier voltage gain The system has two poles of importance. One is due to the compensation capacitor (C3 of Figure 1) and the output resistor of the error amplifier. The other one is due to output capacitor (C2 of Figure 1) and the load resistor. These poles are located at: fP1 = GEA 2πC 3 AVEA fP 2 = 1 2πC 2 RLOAD where • The C6 may be added to compensate for the ESR of C2. The C6 together with R3 creates another pole which is located at: fP 3 = 1 2πC 6 R3 The aim of the compensation design is to shape the converter transfer function to get a desired loop gain. The system crossover frequency where the feedback loop has the unity gain is important. Lower crossover frequencies result in slower line and load transient responses, while higher crossover frequencies could cause system to be unstable. As a rule of thumb, the crossover frequency (fC) below one tenth of the switching frequency is recommended. This is expressed using in the following inequality: fC < fS 10 The following steps may be used for optimizing the compensation components: 1. Select the compensation resistor, R3 to set the desired crossover frequency. The R3 resistor value can be determined using the following equation: R3 = 2πC 2 fC VOUT GEA GCS VFB GEA = Error amplifier transconductance The system has one zero of importance, due to the compensation capacitor (C3) and the compensation resistor (R3). The zero is located at: fZ 1 = 1 2πC 3 R3 The system may also have another zero of importance due to high output capacitance and ESR of C2 (output capacitor of Figure 1). The zero is located at: fZ 2 = March 15, 2011 1 2πC 2 ESRC 2 2. Select the compensation capacitor C3 to achieve the desired phase margin. For applications with typical inductor values, setting the compensation zero, f Z1, below one quarter of the crossover frequency provides sufficient phase margin. The C3 capacitor value can be determined using the following inequality: C3 > 4 2πR3 fC 3. Determine if the second compensation capacitor, C6, is needed. It is needed if the ESR zero (fZ2) of the output capacitor (C2) is located at less than half of the switching frequency as expressed in the following inequality: 9 TF6002 / TF6002A fS 1 > 2 2πC 2 ESRC 2 If the above inequality is valid, add the second compensation capacitor, C6, to set the third pole, fP3, at the location of the ESR zero, fZ2. The C6 capacitor value can be determined using the following equation: C6 = C 2 ESRC 2 R3 External Bootstrap Diode: To improve the efficiency of the regulator, an external bootstrap diode may be added when any or combination of the following conditions occur in the regulator circuit: • The system has a 5V or 3.3V fixed input • The power supply generates a 5V or 3.3V output • The regulator operates with high duty cycle (>65%) • The output voltage is above 12V (VOUT > 12V) The optimized application circuit is shown in Figure 10. The diode D2 can be a low cost diode such as BAT54 or IN4148. Figure 10. TF6002 Application Circuit with Optional Diodes March 15, 2011 10 TF6002 / TF6002A Package Dimensions (SOIC-8(N)) Important Notice Telefunken Semiconductors does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and Telefunken Semiconductors reserves the right to change said circuitry and specifications at any time without notice. If Military/Aerospace or Automotive specified devices are required, please contact the Telefunken Semiconductors Sales Office or Distributors for availability and specifications. LIFE SUPPORT POLICY TELEFUNKEN SEMICONDUCTORS’ PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE CEO OF TELEFUNKEN SEMICONDUCTORS. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component in any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. 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