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MIC4043
Micrel
MIC4043
Low-Voltage Secondary-Side Shunt Regulator Final Information
General Description
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.
Features
* 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 VIN MIC4043 Low-Side Feedback Control
COMPENSATION
VOUT
1 7
R1 R2
2
6
MIC38HC43BN
1 2 3 4
COMP FB ISNS RT/CT
VREF VDD VOUT GND
8 4 7 6 5
SECONDARY SIDE
Return
3
R2 VOUT = 1.245V + 1 R1
PRIMARY SIDE
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
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MIC4043
MIC4043
Micrel
Ordering Information
Part Number Marking Voltage Tolerance Configuration Temperature Range Package Lead-Finish
MIC4043BM4 MIC4043YM4
RB1D RB1D
1.245V 1.245V
1% 1%
Open Collector Open Collector
-40C to +85C -40C to +85C
SOT-143 SOT-143
Leaded Pb-Free
Pin Configuration
FB 4 GND 3
Part Identification
RBxx
1 IN 2 SNK
MIC4043
Pin Description
Pin Number 1 2 3 4 Pin Name IN SNK GND FB Pin Function Input: Supply voltage input. Sink (Output): NPN open collector output. Ground Feedback (Input): Feedback input from external voltage-divider network.
Absolute Maximum Ratings (Note 1)
Input Voltage (VIN) ...................................................... +15V Output Voltage (VSNK) ................................................ +15V Storage Temperature (TS) ....................... -65C to +150C ESD Rating, Note 3 human body model .................................................... 2kV machine model ........................................................ 200V
Operating Ratings (Note 2)
Input Voltage (VIN) ...................................................... +10V Output Voltage (VSNK) ................................................ +10V Maximum Output Current (ISNK) ................................ 15mA Temperature Range (TA) ........................... -40C to +85C
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Electrical Characteristics
TA = 25C, bold values indicate -40C TA +85C; unless noted Parameter Reference Voltage, Note 4 Reference Voltage Tolerance Supply Current Transconductance ISINK/VIN Output Transistor Saturation Voltage Output Leakage
Note 1. Note 2. Note 3. Note 4.
Condition
Min
Typ 1.245
Max 1
Units V
2
ISNK = 0mA 1mA < ISNK < 15mA ISNK = 15mA VSNK = 5V, output transistor off 3.5 2 35 150 160 250 400 0.5 1 65 70
% % A A S S mV mV A A
Exceeding the absolute maximum rating may damage the device. The device is not guaranteed to function outside its operating rating. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF. Machine model, 200pF. Reference voltage is not referenced to ground. The reference is between pins IN and FB.
Test Circuits
Floating Bench Supply
OUT RETURN 1k
R A
MIC4043 IN SNK GND FB
R1 Analyzer R R2 33k
R R
Do Not Ground!
R3 C1* 50
OUTPUT A
* Compensation element A VOUT 1.8V 2.5V 3.3V R1 72k 33k 20k R2 33k 33k 33k R3 20k 40k 150k C1 0.001F 0.001F 0.001F
A
Test Circuit 1. Compensation (Bode Plot) Circuit
Supply OUT RETURN 1k
MIC4043 IN SNK GND FB
R1
R2 33k R3 C1 * Compensation components
Test Circuit 2. Transient Response Circuit
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Transient Response 1a. 1.8V Output
Turn On Transient Response 1b. 1.8V Output
6.0V
VIN
5.0V AC Coupled
VIN
Overshoot 25mV
VOUT VREG 1.8V AC Coupled VOUT
VREG 1.8V
Transient Response 2a. 1.8V Output
Turn On Transient Response 2b. 1.8V Output
6.0V
VIN
5.0V AC Coupled
VIN
Overshoot 56mV VOUT VREG 2.5V AC Coupled VOUT
VREG 2.5V
Transient Response 2a. 1.8V Output
Turn On Transient Response 3b. 1.8V Output
6.0V
VIN
5.0V AC Coupled
VIN
Overshoot 64mV VOUT VREG 3.3V AC Coupled VOUT
VREG 3.3V
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Functional Diagram
IN VREF 1.245V SNK
FB MIC4043 GND
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.
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.
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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. Voltage Detector
VOUT
(FROM POWER SUPPLY)
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
R2 VTRIP = 1.245V + 1 R1 MIC4043 IN SNK GND FB R2 33k R1 RPULL-UP Logic Output
DISABLED ENABLED
Figure 1. Voltage Detector Figure 1 shows a simple voltage threshold detector with a logic output. High-Current Regulator
VIN IBIAS 500A RBIAS Q1 VOUT = 2.5V
MIC4043 IN SNK GND FB
R2 VOUT = 1.245V + 1 R1 R1 = 33k, R2 = 33k
R2 33k 40 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).
MIC4043
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MIC4043
Off-Line 1.8V/2A Power Supply
U2b 2501
Micrel
R10 72k 1%
85 to 264Vac 50/60Hz Hot Ground Neutral 20mH C2 2200pF 400V C3 2200pF 400V F1 L1 1A C1 0.1F 250V BR1 DBR1 U3 MIC4043 IN SNK C4 47F 400V 249 GND FB 1000pF R11 33k 1%
D4 12CTQ045 R2 332k 1% R3 332k 1%
8 7 6 5 1 7
L2 5H C11 1200F 10V C12 220F 10V
VOUT +1.8V/2A
C10 U2a 0.1F 50/63V 2501 U1 MIC38HC43BN R5 1 COMP VREF 1.21k 1% 2 FB VDD R6 3 1.21k ISNS VOUT 1%
4
80T
2
3T
6
R4 34 1% C5 0.1F 50/ 63V C8 22F 25V
D1 1N4448
4
R14 200 1% Return
T1
D2 18V
10T
3
RT/CT
GND
R2 VTRIP = 1.245V + 1 R1
R7 14k 1% C6 470pF 63V
R13 R1 C7 1k 1% 470pF 63V 10 1%
Q1 IRFIBE30G R8 1.9 1/4W 1%
C9 100pF 1kV R9 470 1/2W D3 UF4005
Figure 3. Off-Line 1.8V/2A Power Supply
Figure 3a. 1.8V/1A Bode Plot ( margin = 102)
Figure 3b. 1.8V/2A Bode Plot ( margin = 87)
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MIC4043
MIC4043
Off-Line 2.5V/2A Power Supply
U2b 2501
Micrel
R10 72k 1%
85 to 264Vac 50/60Hz Hot Ground Neutral 20mH C2 2200pF 400V C3 2200pF 400V F1 L1 1A C1 0.1F 250V BR1 DBR1 U3 MIC4043 IN SNK C4 47F 400V 249 GND FB 1000pF R11 33k 1%
D4 12CTQ045 R2 332k 1% R3 332k 1%
8 7 6 5 1 7
L2 5H C11 1200F 10V C12 220F 10V
VOUT +2.5V/2A
C10 U2a 0.1F 50/63V 2501 U1 MIC38HC43BN R5 1 COMP VREF 1.21k 1% 2 FB VDD R6 3 1.21k ISNS VOUT 1%
4
80T
2
3T
6
R4 34 1% C5 0.1F 50/ 63V C8 22F 25V
D1 1N4448
4
R14 200 1% Return
T1
D2 18V
10T
3
RT/CT
GND
R2 VTRIP = 1.245V + 1 R1
R7 14k 1% C6 470pF 63V
R13 R1 C7 1k 1% 470pF 63V 10 1%
Q1 IRFIBE30G R8 1.9 1/4W 1%
C9 100pF 1kV R9 470 1/2W D3 UF4005
Figure 4. Off-Line 2.5V/2A Power Supply
Figure 4a. 2.5V/1A Bode Plot ( margin = 83)
Figure 4b. 2.5V/2A Bode Plot ( margin = 83)
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MIC4043
Off-Line 3.3V/2A Power Supply
U2b 2501
Micrel
R10 72k 1%
85 to 264Vac 50/60Hz Hot Ground Neutral 20mH C2 2200pF 400V C3 2200pF 400V F1 L1 1A C1 0.1F 250V BR1 DBR1 U3 MIC4043 IN SNK C4 47F 400V 249 GND FB 1000pF R11 33k 1%
D4 12CTQ045 R2 332k 1% R3 332k 1%
8 7 6 5 1 7
L2 5H C11 1200F 10V C12 220F 10V
VOUT +3.3V/2A
C10 U2a 0.1F 50/63V 2501 U1 MIC38HC43BN R5 1 COMP VREF 1.21k 1% 2 FB VDD R6 3 1.21k ISNS VOUT 1%
4
80T
2
3T
6
R4 34 1% C5 0.1F 50/ 63V C8 22F 25V
D1 1N4448
4
R14 200 1% Return
T1
D2 18V
10T
3
RT/CT
GND
R2 VTRIP = 1.245V + 1 R1
R7 14k 1% C6 470pF 63V
R13 R1 C7 1k 1% 470pF 63V 10 1%
Q1 IRFIBE30G R8 1.9 1/4W 1%
C9 100pF 1kV R9 470 1/2W D3 UF4005
Figure 5. Off-Line 3.3V/2A Power Supply
Figure 5a. 3.3V/1A Bode Plot ( margin = 82)
Figure 5b. 3.3V/2A Bode Plot ( margin = 80)
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MIC4043
MIC4043
Off-Line 5V/2A Power Supply
U2b 2501
Micrel
R10 72k 1%
85 to 264Vac 50/60Hz Hot Ground Neutral 20mH C2 2200pF 400V C3 2200pF 400V F1 L1 1A C1 0.1F 250V BR1 DBR1 U3 MIC4043 IN SNK C4 47F 400V 249 GND FB 1000pF R11 33k 1%
D4 12CTQ045 R2 332k 1% R3 332k 1%
8 7 6 5 1 7
L2 5H C11 1200F 10V C12 220F 10V
VOUT +5.0V/2A
C10 U2a 0.1F 50/63V 2501 U1 MIC38HC43BN R5 1 COMP VREF 1.21k 1% 2 FB VDD R6 3 1.21k ISNS VOUT 1%
4
80T
2
3T
6
R4 34 1% C5 0.1F 50/ 63V C8 22F 25V
D1 1N4448
4
R14 200 1% Return
T1
D2 18V
10T
3
RT/CT
GND
R2 VTRIP = 1.245V + 1 R1
R7 14k 1% C6 470pF 63V
R13 R1 C7 1k 1% 470pF 63V 10 1%
Q1 IRFIBE30G R8 1.9 1/4W 1%
C9 100pF 1kV R9 470 1/2W D3 UF4005
Figure 6. Off-Line 5V/2A Power Supply
Figure 6a. 5V/1A Output Bode Plot ( margin = 67)
Figure 6b. 5V/2A Output Bode Plot ( margin = 61)
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Micrel
Package Information
0.950 (0.0374) TYP
C L
1.40 (0.055) 2.50 (0.098) 1.20 (0.047) 2.10 (0.083) C L 1.12 (0.044) 0.81 (0.032)
DIMENSIONS: MM (INCH) 0.150 (0.0059) 0.089 (0.0035)
3.05 (0.120) 2.67 (0.105)
8 0
0.800 (0.031) TYP 0.400 (0.016) TYP 3 PLACES
0.10 (0.004) 0.013 (0.0005)
0.41 (0.016) 0.13 (0.005)
SOT-143 (M4)
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MIC4043
MIC4043
Micrel
MICREL INC. 1849 FORTUNE DRIVE
TEL
SAN JOSE, CA 95131
WEB
USA
+ 1 (408) 944-0800
FAX
+ 1 (408) 944-0970
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. (c) 2000 Micrel Incorporated
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November 2000

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