MICREL MIC4043YM4

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