MIC4043 Micrel MIC4043 Low-Voltage Secondary-Side Shunt Regulator 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 COMPENSATION OPTICAL ISOLATION MIC4043 MIC4043 Low-Side Feedback Control VIN IN SNK GND FB 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 May 2000 1 MIC4043 MIC4043 Micrel Ordering Information Part Number Marking Voltage Tolerance Configuration Temperature Range Package MIC4043BM4 RBAD 1.245V 1% Open Collector –40°C to +85°C SOT-143 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): 1.245V 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 May 2000 MIC4043 Micrel Electrical Characteristics TA = 25°C, bold values indicate –40°C ≤ TA ≤ +85°C; unless noted Parameter Condition Min Reference Voltage Typ Max Units 1.245 Reference Voltage Tolerance Supply Current ISNK = 0mA Transconductance ∆ISINK/∆VIN 1mA < ISNK < 15mA Output Transistor Saturation Voltage ISNK = 15mA Output Leakage VSNK = 5V, output transistor off 35 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. Test Circuits Floating Bench Supply R1 MIC4043 IN SNK 1k OUT RETURN R GND FB A Analyzer R CFB 2700pF Do Not Ground! R2 33k R R * Compensation element 50Ω OUTPUT A VOUT R1 R2 1.8V 72k 33k 2.5V 33k 33k 3.3V 20k 33k A A Test Circuit 1. Compensation (Bode Plot) Circuit Supply OUT RETURN 1k MIC4043 IN SNK R3 2k R1 C2* 2700pF R2 33k GND FB C1* 1000pF * Compensation components Test Circuit 2. Transient Response Circuit May 2000 3 MIC4043 MIC4043 Micrel Transient Response 1b. 1.8V Output With Compensation VOUT VOUT VREG VREG VIN VIN Transient Response 1a. 1.8V Output Without Compensation Transient Response 2b. 2.5V Output With Compensation VOUT VOUT VREG VREG VIN VIN Transient Response 2a. 2.5V Output Without Compensation Transient Response 3b. 3.3V Output With Compensation VOUT VOUT VREG VREG VIN VIN Transient Response 3a. 3.3V Output Without Compensation MIC4043 4 May 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. May 2000 5 MIC4043 MIC4043 Micrel Applications Information Voltage Detector 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 effectively puts the regulator reference voltage in parallel with the LED and drives the LED with a single, series NPN transistor. The headroom required by this transistor is its saturation voltage of 400mV over it’s operating temperature range, reducing the overall headroom requirement to 1.4V + 0.4V = 1.8V. 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 small value of capacitance is necessary between the FB pin and SNK 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 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. MIC4043 R2 VTRIP = 1.245V + 1 R1 VOUT (FROM POWER SUPPLY) MIC4043 IN SNK R1 RPULL-UP 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 R1 33k GND FB R2 33k 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 May 2000 MIC4043 Micrel Off-Line 1.8V/2A Power Supply U2b 2501 85 to 264Vac 50/60Hz BR1 DBR1 F1 Hot L1 Ground C14 R10 3000pF 72k 50V 1% 1A C1 0.1µF 250V Neutral 20mH C3 2200pF 400V C2 2200pF 400V U3 MIC4043 C4 47µF 400V IN SNK GND FB 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 Q1 IRFIBE30G R8 1.9Ω 1/4W 1% R11 33k 1% C11 1200µF 10V 6 D1 1N4448 C8 22µF 25V C13 1000pF 50/63V VOUT +1.8V/2A 5µH 3T 2 R4 34Ω 1% R12 90Ω L2 7 80T 4 7 R13 R1 1 R2 332k 1% R15 47.5k 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 3a. 1.8V/1A Bode Plot (θ margin = 69°) May 2000 Figure 3b. 1.8V/2A Bode Plot (θ margin = 79°) 7 MIC4043 MIC4043 Micrel Off-Line 2.5V/2A Power Supply U2b 2501 85 to 264Vac 50/60Hz BR1 DBR1 F1 Hot L1 Ground C14 R10 3000pF 33k 50V 1% C1 0.1µF 250V 1A Neutral 20mH C2 2200pF 400V C3 2200pF 400V U3 MIC4043 C4 47µF 400V IN SNK GND FB D4 12CTQ045 C10 U2a 0.1µF 50/63V 2501 U1 MIC38HC43BN R5 1 VREF COMP 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 Q1 IRFIBE30G R8 1.2Ω 1/4W 1% R11 33k 1% C11 1200µF 10V 6 D1 1N4448 C8 22µF 25V C13 1000pF 50/63V VOUT +2.5V/2A 5µH 3T 2 R4 34Ω 1% R12 90Ω L2 7 75T 4 7 R13 R1 1 R2 332k 1% R15 47.5k 1% C12 220µF 10V R14 200Ω 1% Return T1 9T 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 = 73°) MIC4043 Figure 4b. 2.5V/2A Bode Plot (θ margin = 65°) 8 May 2000 MIC4043 Micrel Off-Line 3.3V/2A Power Supply BR1 DBR1 F1 Hot L1 Ground C1 0.1µF 250V 1A Neutral 20mH C2 2200pF 400V C3 2200pF 400V C14 R10 3000pF 20k 50V 1% U2b 2501 85 to 264Vac 50/60Hz U3 MIC4043 C4 47µF 400V IN SNK GND FB D4 12CTQ045 C10 U2a 0.1µF 50/63V 2501 U1 MIC38HC43BN R5 1 VREF COMP 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 3T 2 R4 34Ω 1% C5 0.1µF 50/ 63V 6 D1 1N4448 C8 22µF 25V Q1 IRFIBE30G R12 90Ω C13 1000pF 50/63V R11 33k 1% VOUT +3.3V/2A L2 5µH 7 77T 4 7 R13 R1 1 R2 332k 1% R15 47.5k 1% C11 1200µF 10V C12 220µF 10V R14 200Ω 1% Return T1 10T R2 VTRIP = 1.245V + 1 R1 3 C9 100pF 1kV R8 1.0Ω 1/4W 1% R9 470Ω 1/2W D3 UF4005 Figure 5. Off-Line 3.3V/2A Power Supply Figure 5a. 3.3V/1A Bode Plot (θ margin = 76°) May 2000 Figure 5b. 3.3V/2A Bode Plot (θ margin = 74°) 9 MIC4043 MIC4043 Micrel Off-Line 5V/2A Power Supply BR1 DBR1 F1 Hot L1 Ground C1 0.1µF 250V 1A Neutral 20mH C2 2200pF 400V C3 2200pF 400V C14 R10 3000pF 11k 50V 1% U2b 2501 85 to 264Vac 50/60Hz U3 MIC4043 C4 47µF 400V IN SNK GND FB 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 R13 R1 C5 0.1µF 50/ 63V Q1 IRFIBE30G 6T R11 33k 1% C11 1200µF 10V 6 D1 1N4448 C8 22µF 25V C13 1000pF 50/63V VOUT +5V/2A 5µH 3T 2 R4 34Ω 1% R12 90Ω L2 7 45T 4 7 10Ω 1% C7 1k 1% 470pF 63V 1 R2 332k 1% R15 47.5k 1% C12 220µF 10V R14 200Ω 1% Return T1 Coiltronics 561-241-7876 R2 VTRIP = 1.245V + 1 R1 3 C9 100pF 1kV R8 0.68Ω 1/4W 1% R9 470Ω 1/2W D3 UF4005 Figure 6. Off-Line 5V/2A Power Supply Figure 6a. Off-Line 12V Input, 5V/2A Output Bode Plot (θ margin = 83°) MIC4043 10 May 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) May 2000 11 MIC4043 MIC4043 Micrel MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 TEL + 1 (408) 944-0800 FAX + 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 May 2000