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MIC4043
Micrel
MIC4043
Low-Voltage Secondary-Side Shunt Regulator
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
COMPENSATION
MIC4043 VIN MIC4043 Low-Side Feedback Control IN SNK GND FB 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
Return
3
R2 VOUT = 1.245V + 1 R1
SECONDARY SIDE 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
May 2000
1
MIC4043
MIC4043
Micrel
Ordering Information
Part Number MIC4043BM4 Marking RBAD Voltage 1.245V Tolerance 1% Configuration Open Collector Temperature Range -40C to +85C Package SOT-143
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): 1.245V 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
MIC4043
2
May 2000
MIC4043
Micrel
Electrical Characteristics
TA = 25C, bold values indicate -40C TA +85C; unless noted Parameter Reference Voltage Reference Voltage Tolerance Supply Current Transconductance ISINK/VIN Output Transistor Saturation Voltage Output Leakage
Note 1. Note 2. Note 3.
Condition
Min
Typ 1.245
Max 1 65 70
Units V
2
ISNK = 0mA 1mA < ISNK < 15mA ISNK = 15mA VSNK = 5V, output transistor off 3.5 2 35 150 160
% % A A S S
250 400 0.5 1
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.
Test Circuits
Floating Bench Supply
OUT RETURN 1k
R A
MIC4043 IN SNK GND FB CFB 2700pF
R1 Analyzer R R2 33k
R R
Do Not Ground!
* Compensation element VOUT 1.8V 2.5V 3.3V R1 72k 33k 20k R2 33k 33k 33k 50
OUTPUT A
A
A
Test Circuit 1. Compensation (Bode Plot) Circuit
Supply OUT RETURN 1k
MIC4043 IN SNK GND FB
R3 2k
R1
C2* 2700pF
R2 33k
C1* 1000pF
* Compensation components
Test Circuit 2. Transient Response Circuit
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MIC4043
MIC4043
Micrel
Transient Response 1a. 1.8V Output Without Compensation
Transient Response 1b. 1.8V Output With Compensation
VIN
VREG
VOUT
VOUT
VREG
VIN
Transient Response 2a. 2.5V Output Without Compensation
Transient Response 2b. 2.5V Output With Compensation
VIN
VOUT
VREG
Transient Response 3a. 3.3V Output Without Compensation
VOUT
VREG
VIN
Transient Response 3b. 3.3V Output With Compensation
VIN
VREG
MIC4043
VOUT
4
VOUT
VREG
VIN
May 2000
MIC4043
Micrel
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.
May 2000
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MIC4043
MIC4043
Micrel
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 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.
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
R1 33k 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).
MIC4043
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May 2000
MIC4043
Off-Line 1.8V/2A Power Supply
U2b 2501 F1 L1 Ground Neutral 20mH C2 2200pF 400V C3 2200pF 400V 1A C1 0.1F 250V BR1 DBR1 U3 MIC4043 IN SNK GND FB
Micrel
85 to 264Vac 50/60Hz Hot
C14 R10 3000pF 72k 50V 1% R15 47.5k 1% C13 1000pF 50/63V R11 33k 1% L2 5H C11 1200F 10V C12 220F 10V R14 200 1% Return R12 90
C4 47F 400V
D4 12CTQ045 R2 332k 1% R3 332k 1%
8 7 6 5 1 7
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
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 = 69)
Figure 3b. 1.8V/2A Bode Plot ( margin = 79)
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MIC4043
MIC4043
Off-Line 2.5V/2A Power Supply
U2b 2501 F1 L1 Ground Neutral 20mH C2 2200pF 400V C3 2200pF 400V 1A C1 0.1F 250V BR1 DBR1 U3 MIC4043 IN SNK GND FB C14 R10 3000pF 33k 50V 1% R15 47.5k 1% C13 1000pF 50/63V R11 33k 1% L2 5H C11 1200F 10V C12 220F 10V R14 200 1% Return R12 90
Micrel
85 to 264Vac 50/60Hz Hot
C4 47F 400V
D4 12CTQ045 R2 332k 1% R3 332k 1%
8 7 6 5 1 7
VOUT +2.5V/2A
C10 U2a 0.1F 50/63V 2501 U1 MIC38HC43BN R5 1 VREF COMP 1.21k 1% 2 FB VDD R6 3 1.21k ISNS VOUT 1%
4
75T
2
3T
6
R4 34 1% C5 0.1F 50/ 63V C8 22F 25V
D1 1N4448
4
T1 R2 VTRIP = 1.245V + 1 R1
D2 18V
9T
3
RT/CT
GND
R7 14k 1% C6 470pF 63V
R13 R1 C7 1k 1% 470pF 63V 10 1%
Q1 IRFIBE30G R8 1.2 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 = 73)
Figure 4b. 2.5V/2A Bode Plot ( margin = 65)
MIC4043
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May 2000
MIC4043
Off-Line 3.3V/2A Power Supply
U2b 2501 C14 R10 3000pF 20k 50V 1% R15 47.5k 1% C13 1000pF 50/63V R11 33k 1% L2 5H C11 1200F 10V C12 220F 10V R14 200 1% Return R12 90
Micrel
85 to 264Vac 50/60Hz Hot Ground Neutral 20mH C2 2200pF 400V C3 2200pF 400V F1 L1 1A C1 0.1F 250V BR1 DBR1
C4 47F 400V
U3 MIC4043 IN SNK GND FB
D4 12CTQ045 R2 332k 1% R3 332k 1%
8 7 6 5 1 7
VOUT +3.3V/2A
C10 U2a 0.1F 50/63V 2501 U1 MIC38HC43BN R5 1 VREF COMP 1.21k 1% 2 FB VDD R6 3 1.21k ISNS VOUT 1%
4
77T
2
3T
6
R4 34 1% C5 0.1F 50/ 63V C8 22F 25V
D1 1N4448
4
T1 R2 VTRIP = 1.245V + 1 R1
D2 18V
10T
3
RT/CT
GND
R7 14k 1% C6 470pF 63V
R13 R1 C7 1k 1% 470pF 63V 10 1%
Q1 IRFIBE30G R8 1.0 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 = 76)
Figure 5b. 3.3V/2A Bode Plot ( margin = 74)
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9
MIC4043
MIC4043
Off-Line 5V/2A Power Supply
85 to 264Vac 50/60Hz Hot Ground Neutral 20mH C2 2200pF 400V C3 2200pF 400V F1 L1 1A C1 0.1F 250V BR1 DBR1 U2b 2501 C14 R10 3000pF 11k 50V 1% R15 47.5k 1% C13 1000pF 50/63V R11 33k 1% L2 5H C11 1200F 10V C12 220F 10V R14 200 1% Return R12 90
Micrel
C4 47F 400V
U3 MIC4043 IN SNK GND FB
D4 12CTQ045 R2 332k 1% R3 332k 1%
8 7 6 5 1 7
VOUT +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
45T
2
3T
6
R4 34 1% C5 0.1F 50/ 63V C8 22F 25V
D1 1N4448
4
D2 18V
6T
3
T1 Coiltronics 561-241-7876 R2 VTRIP = 1.245V + 1 R1
RT/CT
GND
R7 14k 1% C6 470pF 63V
R13 R1 C7 1k 1% 470pF 63V 10 1%
Q1 IRFIBE30G R8 0.68 1/4W 1%
C9 100pF 1kV R9 470 1/2W D3 UF4005
Figure 6. Off-Line 5V/2A Power Supply
Figure 6a. Off-Line 12V Input, 5V/2A Output Bode Plot ( margin = 83)
MIC4043
10
May 2000
MIC4043
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)
May 2000
11
MIC4043
MIC4043
Micrel
MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131
TEL
USA
+ 1 (408) 944-0800
FAX
+ 1 (408) 944-0970
WEB
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
MIC4043
12
May 2000

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