MIC4043 Micrel MIC4043 Low-Voltage Secondary-Side Shunt Regulator Final Information General Description Features The MIC4043 is a shunt regulator optimized for secondaryside regulation in low-voltage power supplies. Featuring an output stage guaranteed to swing within 400mV of ground, the MIC4043 can be used in power supplies operating down to 1.8V, even with optoisolators requiring greater than 1.2V of headroom. In power supply applications, the MIC4043 normally drives the LED of an optically isolated feedback circuit. The MIC4043 monitors a resistively-divided output voltage and sinks error current through the optoisolator’s LED (secondary side); the optoisolator’s transistor (primary side) provides this signal to the controller’s feedback input. The MIC4043 is also practical for other voltage-monitoring applications requiring an opencollector output. The MIC4043 replaces conventional ’431-type shunt regulators to allow low-voltage applications where there is inadequate headroom for a 2.5V regulator in series with an optoisolator. Replacing ’431-type devices requires only a minor change to the way that the resistive-divider values are calculated. • Ideal for 1.8V switching converters • Low-voltage operation 400mV maximum saturation over operating temperature range • Easy to use voltage in, current out • 2% voltage tolerance over operating temperature range Applications • Optically isolated low-volage power supplies • Low-voltage discrete regulator control Typical Application OPTICAL ISOLATION MIC4043 IN SNK GND FB MIC4043 Low-Side Feedback Control VIN COMPENSATION VOUT 1 7 R1 R2 2 6 MIC38HC43BN COMP VREF 8 2 FB VDD 7 3 ISNS VOUT 6 GND 5 RT/CT 3 R2 VOUT = 1.245V + 1 R1 PRIMARY SIDE 4 Return 4 SECONDARY SIDE 1 200kHz DC-DC Flyback Converter Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com November 2000 1 MIC4043 MIC4043 Micrel Ordering Information Part Number Marking Voltage MIC4043BM4 MIC4043YM4 RB1D RB1D 1.245V 1.245V Tolerance 1% 1% Configuration Open Collector Open Collector Temperature Range Package –40°C to +85°C –40°C to +85°C Lead-Finish SOT-143 SOT-143 Leaded Pb-Free Pin Configuration FB 4 GND 3 Part Identification RBxx 1 2 SNK IN MIC4043 Pin Description Pin Number Pin Name Pin Function 1 IN 2 SNK Sink (Output): NPN open collector output. 3 GND Ground 4 FB Input: Supply voltage input. Feedback (Input): Feedback input from external voltage-divider network. Absolute Maximum Ratings (Note 1) Operating Ratings (Note 2) Input Voltage (VIN) ...................................................... +15V Output Voltage (VSNK) ................................................ +15V Storage Temperature (TS) ....................... –65°C to +150°C ESD Rating, Note 3 human body model .................................................... 2kV machine model ........................................................ 200V Input Voltage (VIN) ...................................................... +10V Output Voltage (VSNK) ................................................ +10V Maximum Output Current (ISNK) ................................ 15mA Temperature Range (TA) ........................... –40°C to +85°C MIC4043 2 November 2000 MIC4043 Micrel Electrical Characteristics TA = 25°C, bold values indicate –40°C ≤ TA ≤ +85°C; unless noted Parameter Condition Min Reference Voltage, Note 4 Typ Max Units 1.245 Reference Voltage Tolerance Supply Current ISNK = 0mA 35 Transconductance ∆ISINK/∆VIN 1mA < ISNK < 15mA Output Transistor Saturation Voltage ISNK = 15mA Output Leakage VSNK = 5V, output transistor off 3.5 2 V ±2 ±1 % % 65 70 µA µA 150 160 S S 250 400 mV mV 0.5 1 µA µA Note 1. Exceeding the absolute maximum rating may damage the device. Note 2. The device is not guaranteed to function outside its operating rating. Note 3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF. Machine model, 200pF. Note 4. Reference voltage is not referenced to ground. The reference is between pins IN and FB. Test Circuits Floating Bench Supply OUT R1 MIC4043 IN SNK 1k RETURN R Analyzer R GND FB A R2 33k Do Not Ground! C1* R3 R R 50Ω OUTPUT A * Compensation element A VOUT R1 R2 R3 1.8V 72k 33k 20k 0.001µF 2.5V 33k 33k 40k 0.001µF 3.3V 20k 33k 150k 0.001µF C1 A Test Circuit 1. Compensation (Bode Plot) Circuit Supply OUT 1k RETURN MIC4043 R1 IN SNK GND FB R2 33k C1 R3 * Compensation components Test Circuit 2. Transient Response Circuit November 2000 3 MIC4043 MIC4043 Micrel Turn On Transient Response 1b. 1.8V Output Transient Response 1a. 1.8V Output 6.0V 5.0V AC Coupled VIN VIN Overshoot 25mV VREG 1.8V AC Coupled VOUT VREG 1.8V VOUT Transient Response 2a. 1.8V Output Turn On Transient Response 2b. 1.8V Output 6.0V 5.0V AC Coupled VIN VIN Overshoot 56mV VREG 2.5V AC Coupled VOUT VREG 2.5V VOUT Transient Response 2a. 1.8V Output Turn On Transient Response 3b. 1.8V Output 6.0V 5.0V AC Coupled VIN VIN Overshoot 64mV VOUT MIC4043 VREG 3.3V AC Coupled VOUT 4 VREG 3.3V November 2000 MIC4043 Micrel Functional Diagram IN VREF 1.245V SNK FB MIC4043 GND Reference The MIC4043 uses a high-side reference. External voltage dividers providing feedback to the MIC4043 will be inverted when compared to those used with ’431-equivalent devices. Behavior The external feedback voltage is compared to the internal high-side 1.245V reference. If the feedback voltage, VFB, is less than VIN – VREF, the amplifier provides no drive to the sink transistor. If the feedback voltages is greater than VIN – VREF, the amplifier drives the pass transistor which sinks current to ground. Functional Description The MIC4043 combines a Gm amplifier, precision 1.245V reference, and a pass transistor in a single package. The operation of the MIC4043 is similar to conventional shunt regulators such as the industry standard ’431. In a closed loop system, the MIC4043 maintains the desired feedback voltage at the FB pin by sinking current onto the SNK pin proportional to the error voltage at the FB pin. The ratio of sink current to error voltage is the transconductance of the device. November 2000 5 MIC4043 MIC4043 Micrel response, if a network analyzer is not available, is to step load the output of the systems from 10% to 100% of nominal load. The resultant small signal response at the output of the systems will provide an idea of which direction to go based on the overshoot and settling time of VOUT. Applications Information Replacement of ’431-Type Devices Since the MIC4043 uses a high-side reference, external voltage dividers providing the feedback voltage will be inverted when compared to those used with ’431-equivalent devices. The industry-standard ’431 is also typically used in series with an opto-isolator LED. This configuration has a voltage drop of at least 2.5V for the ’431 plus 1.4V for the LED (3.9V). More recent lower-voltage shunt regulators require at least 1.25V of headroom in addition to the 1.4V for the opto isolator, for a total of 2.65V. The MIC4043 removes the need to place the shunt reference in parallel with the opto-isolator. The MIC4043 combines a 1.245V reference in conjunction with an error amplifier that drives an NPN output transistor. The NPN transistor is connected in series with the opto-isolator and regulates the drive current in the opto-isolator. Unlike conventional shunt regulators, the MIC4043 does not have to connect the shunt reference in series with the opto-isolator. Only the NPN output stage is in series with the opto-isolator, so the voltage drop is just the saturation voltage or one transistor, typucally 160mV at full load Compensation The noninverting side of the error amplifier is connected to the high-side reference; the reference is connected to the IN pin. The inverting side of the error amplifier is brought out to the FB pin. For some applications, no compensation is needed, but for most, some resistor capacitor network is necessary between the FB pin and GND pin. The value of the feedback capacitance is application specific, but for most applications 100pF to 3000pF is all that is needed. Changing the feedback capacitor changes the loop response; that is, phase and gain margin. An empirical way to check overall system loop MIC4043 Voltage Detector R2 VTRIP = 1.245V + 1 R1 VOUT (FROM POWER SUPPLY) MIC4043 R1 RPULL-UP IN SNK Logic Output GND FB R2 33k DISABLED ENABLED Figure 1. Voltage Detector Figure 1 shows a simple voltage threshold detector with a logic output. High-Current Regulator VIN IBIAS ≥500µA VOUT = 2.5V RBIAS MIC4043 IN SNK Q1 R2 VOUT = 1.245V + 1 R1 ∴ R1 = 33k, R2 = 33k GND FB R2 33k 40Ω 1000pF Figure 2. High-Current Regulator For the high-current regulator shown in Figure 2, headroom is equal to the saturation voltage of Q1 plus the saturation voltage of the MIC4043 (VSAT(min) = 200mV). 6 November 2000 MIC4043 Micrel Off-Line 1.8V/2A Power Supply U2b 2501 R10 72k 1% 85 to 264Vac 50/60Hz BR1 DBR1 F1 Hot L1 Ground 1A C1 0.1µF 250V Neutral IN SNK 20mH C3 2200pF 400V C2 2200pF 400V U3 MIC4043 C4 47µF 400V GND FB 1000pF 249Ω D4 12CTQ045 C10 U2a 0.1µF 50/63V 2501 U1 MIC38HC43BN R5 1 COMP VREF 1.21k 1% 2 FB VDD R6 3 1.21k ISNS VOUT 1% 4 R7 14k 1% C6 470pF 63V RT/CT GND R3 332k 1% 8 D2 18V 6 5 10Ω 1% C7 1k 1% 470pF 63V C5 0.1µF 50/ 63V 5µH 3T 2 R4 34Ω 1% C11 1200µF 10V 6 D1 1N4448 C8 22µF 25V Q1 IRFIBE30G R8 1.9Ω 1/4W 1% VOUT +1.8V/2A L2 7 80T 4 7 R13 R1 1 R2 332k 1% R11 33k 1% C12 220µF 10V R14 200Ω 1% Return T1 10T R2 VTRIP = 1.245V + 1 R1 3 C9 100pF 1kV R9 470Ω 1/2W D3 UF4005 Figure 3. Off-Line 1.8V/2A Power Supply Figure 3b. 1.8V/2A Bode Plot (θ margin = 87°) Figure 3a. 1.8V/1A Bode Plot (θ margin = 102°) November 2000 7 MIC4043 MIC4043 Micrel Off-Line 2.5V/2A Power Supply U2b 2501 R10 72k 1% 85 to 264Vac 50/60Hz BR1 DBR1 F1 Hot L1 Ground 1A C1 0.1µF 250V Neutral IN SNK 20mH C3 2200pF 400V C2 2200pF 400V U3 MIC4043 C4 47µF 400V GND FB 1000pF 249Ω D4 12CTQ045 C10 U2a 0.1µF 50/63V 2501 U1 MIC38HC43BN R5 1 COMP VREF 1.21k 1% 2 FB VDD R6 3 1.21k ISNS VOUT 1% 4 R7 14k 1% C6 470pF 63V RT/CT GND R3 332k 1% 8 D2 18V 6 5 10Ω 1% C7 1k 1% 470pF 63V C5 0.1µF 50/ 63V 5µH 3T 2 R4 34Ω 1% C11 1200µF 10V 6 D1 1N4448 C8 22µF 25V Q1 IRFIBE30G R8 1.9Ω 1/4W 1% VOUT +2.5V/2A L2 7 80T 4 7 R13 R1 1 R2 332k 1% R11 33k 1% C12 220µF 10V R14 200Ω 1% Return T1 10T R2 VTRIP = 1.245V + 1 R1 3 C9 100pF 1kV R9 470Ω 1/2W D3 UF4005 Figure 4. Off-Line 2.5V/2A Power Supply Figure 4a. 2.5V/1A Bode Plot (θ margin = 83°) MIC4043 Figure 4b. 2.5V/2A Bode Plot (θ margin = 83°) 8 November 2000 MIC4043 Micrel Off-Line 3.3V/2A Power Supply U2b 2501 R10 72k 1% 85 to 264Vac 50/60Hz BR1 DBR1 F1 Hot L1 Ground 1A C1 0.1µF 250V Neutral IN SNK 20mH C3 2200pF 400V C2 2200pF 400V U3 MIC4043 C4 47µF 400V GND FB 1000pF 249Ω D4 12CTQ045 C10 U2a 0.1µF 50/63V 2501 U1 MIC38HC43BN R5 1 COMP VREF 1.21k 1% 2 FB VDD R6 3 1.21k ISNS VOUT 1% 4 R7 14k 1% C6 470pF 63V RT/CT GND R3 332k 1% 8 D2 18V 6 5 10Ω 1% C7 1k 1% 470pF 63V C5 0.1µF 50/ 63V 5µH 3T 2 R4 34Ω 1% C11 1200µF 10V 6 D1 1N4448 C8 22µF 25V Q1 IRFIBE30G R8 1.9Ω 1/4W 1% VOUT +3.3V/2A L2 7 80T 4 7 R13 R1 1 R2 332k 1% R11 33k 1% C12 220µF 10V R14 200Ω 1% Return T1 10T R2 VTRIP = 1.245V + 1 R1 3 C9 100pF 1kV R9 470Ω 1/2W D3 UF4005 Figure 5. Off-Line 3.3V/2A Power Supply Figure 5b. 3.3V/2A Bode Plot (θ margin = 80°) Figure 5a. 3.3V/1A Bode Plot (θ margin = 82°) November 2000 9 MIC4043 MIC4043 Micrel Off-Line 5V/2A Power Supply U2b 2501 R10 72k 1% 85 to 264Vac 50/60Hz BR1 DBR1 F1 Hot L1 Ground 1A C1 0.1µF 250V Neutral IN SNK 20mH C3 2200pF 400V C2 2200pF 400V U3 MIC4043 C4 47µF 400V GND FB 249Ω 1000pF D4 12CTQ045 C10 U2a 0.1µF 50/63V 2501 U1 MIC38HC43BN R5 1 COMP VREF 1.21k 1% 2 FB VDD R6 3 1.21k ISNS VOUT 1% 4 R7 14k 1% C6 470pF 63V RT/CT GND R3 332k 1% 8 6 D2 18V 5 10Ω 1% C7 1k 1% 470pF 63V C5 0.1µF 50/ 63V 5µH 3T 2 R4 34Ω 1% 6 D1 1N4448 C8 22µF 25V Q1 IRFIBE30G R8 1.9Ω 1/4W 1% VOUT +5.0V/2A L2 7 80T 4 7 R13 R1 1 R2 332k 1% R11 33k 1% C11 1200µF 10V C12 220µF 10V R14 200Ω 1% Return T1 10T R2 VTRIP = 1.245V + 1 R1 3 C9 100pF 1kV R9 470Ω 1/2W D3 UF4005 Figure 6. Off-Line 5V/2A Power Supply Figure 6b. 5V/2A Output Bode Plot (θ margin = 61°) Figure 6a. 5V/1A Output Bode Plot (θ margin = 67°) MIC4043 10 November 2000 MIC4043 Micrel Package Information 0.950 (0.0374) TYP 1.40 (0.055) 2.50 (0.098) 1.20 (0.047) 2.10 (0.083) CL CL 3.05 (0.120) 2.67 (0.105) 0.800 (0.031) TYP 0.400 (0.016) TYP 3 PLACES DIMENSIONS: MM (INCH) 1.12 (0.044) 0.81 (0.032) 0.10 (0.004) 0.013 (0.0005) 8° 0° 0.150 (0.0059) 0.089 (0.0035) 0.41 (0.016) 0.13 (0.005) SOT-143 (M4) November 2000 11 MIC4043 MIC4043 Micrel MICREL INC. 1849 FORTUNE DRIVE TEL + 1 (408) 944-0800 FAX SAN JOSE, CA 95131 + 1 (408) 944-0970 WEB USA http://www.micrel.com This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc. © 2000 Micrel Incorporated MIC4043 12 November 2000