MIC38C42A/43A/44A/45A Micrel, Inc. MIC38C42A/43A/44A/45A BiCMOS Current-Mode PWM Controllers General Description Features The MIC38C4xA are fixed frequency, high performance, current-mode PWM controllers. Micrel’s BiCMOS devices are pin compatible with 384x bipolar devices but feature several improvements. Undervoltage lockout circuitry allows the ’42 and ’44 versions to start up at 14.5V and operate down to 9V, and the ’43 and ’45 versions start at 8.4V with operation down to 7.6V. All versions operate up to 20V. When compared to bipolar 384x devices operating from a 15V supply, start-up current has been reduced to 50µA typical and operating current has been reduced to 4.0mA typical. Decreased output rise and fall times drive larger MOSFETs, and rail-to-rail output capability increases efficiency, especially at lower supply voltages. The MIC38C4xA also features a trimmed oscillator discharge current and bandgap reference. The MIC38C4xA family is available in 8-pin SOIC and MSOP8 (MM8) package options • Fast 40ns output rise and 30ns output fall times • –40°C to +85°C temperature range meets UC284x specifications • High-performance, low-power BiCMOS Process • Ultralow start-up current (100µA typical) • Low operating current (4mA typical) • CMOS outputs with rail-to-rail swing • ≥ 500kHz current-mode operation • Trimmed 5V bandgap reference • Pin-for-pin compatible with UC3842/3843/3844/3845 • Trimmed oscillator discharge current • UVLO with hysteresis • Low cross-conduction currents Applications • • • • • • • For fast rise and fall times and higher output drive, refer to the MIC38HC4x. Current-mode, off-line, switched-mode power supplies Current-mode, dc-to-dc converters. Step-down “buck” regulators Step-up “boost” regulators Flyback, isolated regulators Forward converters Synchronous FET converters Functional Diagram VDD 7 5V Reference VREF 8 UVLO † Oscillator RT/CT OUT 4 6 FB T Q S R Q ‡ 2R 2 2.5V † ‡ R COMP GND ISNS 1 5 3 MIC38C42A, MIC38C43A (96% max. duty cycle) versions only MIC38C44A, MIC38C45A (50% max. duty cycle) versions only MM8 is a trademark of Micrel, Inc. Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com April 2005 1 M9999-042205 MIC38C42A/43A/44A/45A Micrel, Inc. Ordering Information Standard Part Number Pb-Free Temperature Range Package MIC38C42ABM MIC38C42AYM –40°C to +85°C 8-pin SOIC MIC38C43ABM MIC38C43AYM –40°C to +85°C 8-pin SOIC MIC38C44ABM MIC38C44AYM –40°C to +85°C 8-pin SOIC MIC38C45ABM MIC38C45AYM –40°C to +85°C 8-pin SOIC MIC38C42ABMM MIC38C42AYMM –40°C to +85°C 8-pin MM8™ MIC38C43ABMM MIC38C43AYMM –40°C to +85°C 8-pin MM8™ MIC38C44ABMM MIC38C44AYMM –40°C to +85°C 8-pin MM8™ MIC38C45ABMM MIC38C45AYMM –40°C to +85°C 8-pin MM8™ Refer to the Part Number Cross Reference for a listings of Micrel devices equivalent to UC284x and UC384x devices. Selection Guide UVLO Thresholds M9999-042205 Duty Cycle Startup 8.4V Minimum Operating 7.6V Startup 14.5V Minimum Operating 9V 0% to 96% MIC38C43A MIC38C42A 0% to 50% MIC38C45A MIC38C44A 2 April 2005 MIC38C42A/43A/44A/45A Micrel, Inc. Pin Configuration MIC38C4xA COMP 1 8 VREF FB 2 7 VDD ISNS 3 6 OUT RT/CT 4 5 GND 8-Lead SOIC (M) 8-Lead MM8™ (MM) Pin Description Pin Number Pin Name 1 COMP Compensation: Connect external compensation network to modify the error amplifier output. 2 FB Feedback (Input): Error amplifier input. Feedback is 2.5V at desired output voltage. 3 ISNS Current Sense (Input): Current sense comparator input. Connect to current sensing resistor or current transformer. 4 RT/CT 5 GND Ground: Combined analog and power ground. 6 OUT Power Output: Totem-pole output. 7 VDD Analog Supply (Input): Controller circuitry supply input. Return to analog ground (AGND). 8 VREF 5V Reference (Output): Connect external RC network. April 2005 Pin Function Timing Resistor/Timing Capacitor: Connect external RC network to select switching frequency. 3 M9999-042205 MIC38C42A/43A/44A/45A Micrel, Inc. Absolute Maximum Ratings Operating Ratings Supply Voltage (VDD) .................................................... 20V Switch Supply Voltage (VD) .......................................... 20V Current Sense Voltage (VISNS) ..................... –0.3V to 5.5V Feedback Voltage (VFB) ................................ –0.3V to 5.5V Output Current (IOUT) ................................................... 0.5A Storage Temperature (TA) ....................... –65°C to +150°C Junction Temperature (TJ) ........................................ 150°C Package Thermal Resistance 8-Pin MM8™ (θJA) ............................................. 250°C/W 8-Pin SOIC (θJA) ............................................... 170°C/W Electrical Characteristics(Note 6) VDD = 15V, Note 4; RT = 11.0k; CT = 3.3nF; –40°C ≤ TA ≤ 85°C; unless noted Parameter Test Conditions Min Typ Max Units Output Voltage TA = 25°C, IO = 1mA 4.90 5.00 5.10 V Line Regulation 12V ≤ VDD ≤ 18V, IO = 5µA 2 20 mV Load Regulation 1 ≤ IO ≤ 20mA 1 25 mV Temp. Stability Note 1 Total Output Variation Line, Load, Temp., Note 1 Output Noise Voltage 10Hz ≤ f ≤ 10kHz, TA = 25°C, Note 1 50 Long Term Stability TA = 125°C, 1000 hrs., Note 1 5 25 mV –30 –80 –180 mA 47 53 59 kHz 1.0 % Reference Section 0.2 4.82 Output Short Circuit mV/°C 5.18 V µV Oscillator Section Initial Accuracy TA = 25°C, Note 5 Voltage Stability 12 ≤ VDD ≤ 18V 0.2 Temp. Stability TMIN ≤ TA ≤ TMAX, Note 1 0.04 Clock Ramp Reset Current TA = 25°C, VRT/CT = 2V, Note 1 Amplitude VRT/CT peak to peak 7.7 8.4 %/°C 9.0 1.9 mA Vp-p Error Amp Section Input Voltage VCOMP = 2.5V Input Bias Current VFB = 5.0V AVOL 2 ≤ VO ≤ 4V 65 90 dB Unity Gain Bandwidth Note 1 0.7 1.0 MHz PSRR 12 ≤ VDD ≤ 18V 60 Output Sink Current VFB = 2.7V, VCOMP = 1.1V 2 14 mA Output Source Current VFB = 2.3V, VCOMP = 5V –0.3 –1 mA VOUT High VFB = 2.3V, RL = 15k to ground 5 6.8 V VOUT Low VFB = 2.7V, RL = 15k to VREF M9999-042205 2.4 2.50 2.58 V –0.1 –2 µA dB 0.1 4 1.1 V April 2005 MIC38C42A/43A/44A/45A Parameter Micrel, Inc. Test Conditions Min Typ Max Units Gain Notes 2, 3 2.85 3.0 3.15 V/V MaximumThreshold VCOMP = 5V, Note 2 0.9 1 1.1 V PSRR 12 ≤ VDD ≤ 18V, Note 2 Current Sense 70 dB Input Bias Current –0.1 –2 µA Delay to Output 120 250 ns Output RDS(ON) High RDS(ON) Low ISOURCE = 200mA ISINK = 200mA 20 11 Rise Time TA = 25°C, CL = 1nF 40 80 ns Fall Time TA = 25°C, CL = 1nF 30 60 ns Ω Ω Undervoltage Lockout Start Threshold Minimum Operating Voltage MIC38C42A/4A 13.5 14.5 15.5 V MIC38C43A/5A 7.8 8.4 9.0 V MIC38C42A/4A 8 9 10 V MIC38C43A/5A 7.0 7.6 8.2 V MIC38C42A/3A 94 96 % MIC38C44A/5A 46 50 % Pulse Width Modulator Maximum Duty Cycle Minimum Duty Cycle 0 % Total Standby Current Start-Up Current VDD = 13V for MIC38C42A/44A VDD = 7.5V for MIC38C43A/45A 100 230 µA Operating Supply Current VFB = VISNS = 0V 4.0 6.0 mA Note 1: These parameters, although guaranteed, are not 100% tested in production. Note 2: Parameter measured at trip point of latch with VEA = 0. Note 3: Gain defined as: A = ∆ VPIN1 ; 0 ≤ VTH (ISNS ) ≤ 0.8V VTH (ISNS ) Note 4: Adjust VDD above the start threshold before setting at 15V. Note 5: Output frequency equals oscillator frequency for the MIC38C42 and MIC38C43. Output frequency for the MIC38C44A, and MIC38C45A equals one half the oscillator frequency. Note 6: Specification for packaged product only. April 2005 5 M9999-042205 MIC38C42A/43A/44A/45A Micrel, Inc. 200pF 470pF 1nF 10 1.8nF 4.7nF 10nF 100 OUTPUT DEAD TIME (%) RT RESISTANCE (kΩ) 100 MIC38C42/43 Output Dead Time vs. Oscillator Frequency VDD = 15V 1.2 1.0 125°C 0.8 0.6 25°C 0.4 -50°C 0 2 4 6 8 ERROR AMPLIFIER OUTPUT (V) M9999-042205 10 200pF 10nF 470pF 1nF 1 1x104 VREF SHORT CURCUIT CURRENT (mA) CURRENT SENSE AMP THRESHOLD (V) Current Sense Amplifier vs. Error Amplifier Output 0.0 4.7nF 18nF 1 1x104 1x105 5x105 OSCILLATOR FREQUENCY (Hz) 0.2 VDD = 15V 1x105 FREQUENCY (Hz) 1x106 Oscillator Discharge Current vs. Temperature 9.0 8.8 8.6 8.4 8.2 8.0 7.8 7.6 7.4 VDD = 15V VOSC = 2V 7.2 7.0 -60 -30 0 30 60 90 120 150 TEMPERATURE (°C) Short-Circuit Reference Current vs. Temperature MIC38C4x Output Waveform 120 25 100 80 60 40 20 VDD = 15V 0 -60 -30 0 30 60 90 120 150 TEMPERATURE (°C) 6 OUTPUT VOLTAGE (V) Oscillator Frequency Configuration OSC. DISCHARGE CURRENT (mA) Typical Characteristics 20 15 10 5 0 -5 -10 -15 0.0 VD = 15V CL = 1nF 0.2 0.4 0.6 TIME (µs) 0.8 1.0 April 2005 MIC38C42A/43A/44A/45A Micrel, Inc. mended. When designing high-frequency converters, avoid capacitive and inductive coupling of the switching waveform into highimpedance circuitry such as the error amplifier, oscillator, and current sense amplifier. Avoid long printed-circuit traces and component leads. Locate oscillator and compensation circuitry near the IC. Use high frequency decoupling capacitors on VREF, and if necessary, on VDD. Return high di/dt currents directly to their source and use large area ground planes. Buck Converter Refer to figure 1. When at least 26V is applied to the input, C5 is charged through R2 until the voltage VDD is greater than 14.5V (the undervoltage lockout value of the MIC38C42). Output switching begins when Q1 is turned on by the gate drive transformer T1, charging the output filter capacitor C3 through L1. D5 supplies a regulated +12V to VDD once the circuit is running. Current sense transformer CT1 provides current feedback to ISNS for current-mode operation and cycle-by-cycle current limiting. This is more efficient than a high-power sense resistor and provides the required ground-referenced level shift. When Q1 turns off, current flow continues from ground through D1 and L1 until Q1 is turned on again. The 100V Schottky diode D1 reduces the forward voltage drop in the main current path, resulting in higher efficiency than could be accomplished using an ultra-fast-recovery diode. R1 and C2 suppress parasitic oscillations from D1. Using a high-value inductance for L1 and a low-ESR capacitor for C3 permits small capacitance with minimum output ripple. This inductance value also improves circuit efficiency by reducing the flux swing in L1. Application Information Familiarity with 384x converter designs is assumed. MIC38C4x Advantages Start-up Current Start-up current has been reduced to an ultra-low 50µA (typical) permitting higher-valued, lower-wattage, start-up resistors (powers controller during power supply start-up). The reduced resistor wattage reduces cost and printed circuit space. Operating Current Operating current has been reduced to 4mA compared to 11mA for a typical bipolar controller. The controller runs cooler and the VDD hold-up capacitance required during start-up may be reduced. Output Driver Complementary internal P- and N-channel MOSFETs produce rail-to-rail output voltages for better performance driving external power MOSFETs. The driver transistor’s low onresistance and high peak current capability can drive gate capacitances of greater than 1000pF. The value of output capacitance which can be driven is determined only by the rise/fall time requirements. Within the restrictions of output capacity and controller power dissipation, maximum switching frequency can approach 500kHz. Design Precautions When operating near 20V, circuit transients can easily exceed the 20V absolute maximum rating, permanently damaging the controller’s CMOS construction. To reduce transients, use a 0.1µF low-ESR capacitor to next to the controller’s supply VDD (or VD for ‘-1’ versions) and ground connections. Film type capacitors, such as Wima MKS2, are recom- VIN 26V to 40V R2 68k D4 1N765B 0.1µF* D2 M17Z105 1/4W MKS2 C5 4.7µF 4.7Ω R1 10 1/2W C2 1000pF L1 48µH 31DQ10 D1 C3 3.3µF C4 0.1µF 0.1µF 6.8k 100k 1 D3 MBR030 VOUT 12V, 2A Q1 IRF820 CT1 0.22µF 2 3 R4 18 MIC38C42A COMP VREF FB VDD ISNS OUT 4 8 5 R5 16k 1N4001 T1 6 RT/CT GND C7 200pF D5 7 C8 0.1µF 6.19k 1% 1.62k 1% *Locate near MIC38C42 supply pins 0.1µF Figure 1. 500kHz, 25W, Buck Converter April 2005 7 M9999-042205 MIC38C42A/43A/44A/45A Micrel, Inc. Magnetic components are carefully chosen for minimal loss at 500kHz. CT1 and T1 are wound on Magnetics, Inc. P-type material toroids. L1 is wound on a Siemens N49 EFD core. Test Conditions Line Regulation VIN = 26V to 80V, IO = 2A Load Regulation VIN = 48V, IO = 0.2A to 2A Efficiency VIN = 48V, IO = 2A Output Ripple Symbol Custom Coil1 ETS2 0.5% CT1 4923 ETS 92420 0.6% T1 4924 ETS 92419 90% L1 4925 ETS 92421 Results VIN = 48V, IO = 2A (20MHz BW) 1. Custom Coils, Alcester, SD tel: (605) 934-2460 2. Energy Transformation Systems, Inc. tel: (415) 324-4949. 100mV Synchronous Buck Converter Refer to figure 2. This MIC38C43 synchronous buck converter uses an MIC5022 half-bridge driver to alternately drive the PWM switch MOSFET (driven by GATEH, or high-side output) and a MOSFET which functions as a synchronous rectifier (driven by the GATEL, or low-side output). The low-side MOSFET turns on when the high-side MOSFET is off, allowing current to return from ground. Current flows through the low-side MOSFET in the source to drain direction. The on-state voltage drop of the low-side MOSFET is lower than the forward voltage drop of an equivalent Schottky rectifier. This lower voltage drop results in higher efficiency. A sense resistor (5mΩ) is connected to the driver’s high-side current sense inputs to provide overcurrent protection. Refer to the MIC5020, MIC5021, and MIC5022 data sheets for more information. +12V VDD 0.1µF 6.8k 300k 4.7nF MIC38C43A COMP VREF 4.3k FB 47k 2200 pF 3.3k 0.1µF MIC5022 0.15µF 10k VDD NC FLT VB NC EN GATEL 470µF 25V NC ISNS VOUT RT/CT GND GATEH IN SH+ CT SH– 0.1µF* MKS2 SMP60N06-14 5mΩ 35µH VOUT 5V, 8A 1000µF Low ESR SL+ GND 10k SL– *Locate near the MIC38C43 supply pins. Figure 2. 100kHz, Synchronous Buck Converter M9999-042205 8 April 2005 MIC38C42A/43A/44A/45A Micrel, Inc. Package Information 0.026 (0.65) MAX) PIN 1 0.157 (3.99) 0.150 (3.81) DIMENSIONS: INCHES (MM) 0.020 (0.51) 0.013 (0.33) 0.050 (1.27) TYP 0.064 (1.63) 0.045 (1.14) 45° 0.0098 (0.249) 0.0040 (0.102) 0°–8° 0.197 (5.0) 0.189 (4.8) 0.010 (0.25) 0.007 (0.18) 0.050 (1.27) 0.016 (0.40) SEATING PLANE 0.244 (6.20) 0.228 (5.79) 8-Pin SOP (M) 0.199 (5.05) 0.187 (4.74) 0.122 (3.10) 0.112 (2.84) DIMENSIONS: INCH (MM) 0.120 (3.05) 0.116 (2.95) 0.036 (0.90) 0.032 (0.81) 0.043 (1.09) 0.038 (0.97) 0.012 (0.30) R 0.012 (0.03) 0.0256 (0.65) TYP 0.008 (0.20) 0.004 (0.10) 5° MAX 0° MIN 0.007 (0.18) 0.005 (0.13) 0.012 (0.03) R 0.039 (0.99) 0.035 (0.89) 0.021 (0.53) 8-Pin MSOP (MM) MICREL INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2002 Micrel Incorporated April 2005 9 M9999-042205