AN63

A Product Line of
Diodes Incorporated
AN63
Designing with Shunt Regulators - ZXRE060 low
voltage regulator
Peter Abiodun A. Bode, Snr. Applications Engineer, Diodes Zetex Ltd
Introduction
More and more there is a trend towards lower operating voltages for electronic circuits in order
to both increase speed and keep power consumption down. This is especially the case with
microprocessor applications.
Many applications are now required to operate at voltages as low as 1V and less. Until recently
the lowest reference devices with a reference voltage of 1.2V will not do in these applications. The
ZXRE060, a 0.6V reference, is designed to fill this gap.
With a normal reference, the power to drive its internal functions is normally derived from the
voltage dropped across its cathode (K) and anode (A) terminals. Because the minimum 0.6V
terminal voltage at which this device works is too low for this, provision is made for the device to
be separately powered via two pins. This makes the 0.6V reference a 5-terminal device as
illustrated in Figure 1 below.
ZXRE060
OUT
V IN
FB
GND
PGND
Figure 1 ZXRE060 - 0.6V reference
The extra two power pins are shown labelled VIN and GND respectively. These pins require a
minimum supply of 2.2V for the ZXRE060 to function correctly.
An interesting point is that VIN can be connected to the OUT pin and GND connect to the PGND
pin. This effectively turns the ZXRE060 into a 3-terminal device. The FB pins still controls at 0.6
but the regulated voltage across the device can not be less than 2.2V.
In its 3-terminal configuration, the ZXRE060 can technically be used in all the example circuits for
a standard 3-terminal reference. However, using it for some of the circuits in the 5-terminal mode
to take advantage of its 0.6V operation requires modified configurations. Primarily, this device is
targeted at applications that need to operate below 1.24V and only this aspect is covered in this
document.
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AN63
I OUT
I R3 R3
Vin
1k
ZXRE060
3
C1
2
OUT
3
C1
FB
4
IN
2
GND
FB
4
GND
GND
GND
C2 0.47μF
PGND 1
C2
0.47μF
PGND 1
R1
10k
5
U1
0.1uF
R2
15k
GND
GND
Figure 2
0.6V shunt regulator
Figure 3
1.0V shunt regulator
VOUT = VREF
R1 ⎞
⎛
VOUT = VREF ⎜1 +
⎟
R2 ⎠
⎝
R3 =
IO
Q1
Vcc
ZXTN25020CFH
R3
I R3
Vin
Vout
IKA
ZXRE060
5
IN
U1
0.1uF
1k
IKA
OUT
I OUT
I R3
R3
Vin
Vout
1k
ZXTN25020CFH
1k ZXRE060
IN
0.1μF
2
FB
4
0.47μF
GND
PGND 1
R2
15k
C2
0.47μF
PGND 1
GND
GND
C2
5
U1
C1
FB
4
U1
C1
0.1μF 2
GND
IN
R1
10k
IKA
OUT
3
5
Vout
IB
I R3
R3
Vin
IKA
OUT
IO
Q1
Vcc
Vout
IB
ZXRE060
3
VIN − VOUT
IR3
GND
GND
Figure 4
0.6V series LDO regulator
Figure 5
1.0V series LDO regulator
VOUT = VREF
R1 ⎞
⎛
VOUT = VREF ⎜1 +
⎟
R2 ⎠
⎝
Design guides
1. Determine IOUT and choose a suitable transistor taking power dissipation into consideration.
2. Determine IB from
IB =
I OUT (max)
(hFE (min) + 1)
3. Determine IR3 from I R 3 ≥ I B + I KA(min) . The design of the ZXRE060 effectively means there is
no IKA(min) limitation as in conventional references. There is only an output leakage current
which is a maximum of 1µA. Nevertheless, it is necessary to determine an IKA(min) to ensure
that the device operates within its linear range at all times. IKA(min) ⱖ 10µA should be adequate
for this.
4. Determine R3 from
R3 =
VIN − (VOUT + VBE )
I R3
5. Although unlikely to be a problem, ensure that IR3 ⱕ 20 mA.
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AN63
Refer to the Appendix in AN57 for information on calculating output error.
I R3
R3
Vin
I OUT
I R4
R4
IB
ZXRE060
OUT
3
Vout
IC
R1
10k
Q1
R1 ⎞
⎛
VOUT = VREF ⎜1 +
⎟
R2 ⎠
⎝
5
IN
FB
4
U1
C1
0.1uF 2
GND
C2
(VOUT ≥ 0.2V + VBE )
R2
15k
PGND 1
0.47μF
GND
R3 =
VIN − VOUT
IR3
GND
Figure 6
1V Current-boosted shunt regulator
Design guides
1. Determine IOUT and choose a suitable transistor taking power dissipation into consideration.
2. Determine IB from
IB =
I OUT (max)
(hFE (min) + 1)
3. Determine IR3 from
I R 3 = I OUT (max)
4. Determine R3 from
R3 =
VIN − VOUT
I R3
5. It is best to let the ZXRE060 supply as much current as it can before bringing Q1 into
conduction. Not only does this minimise the strain on Q1, it also guarantees the most stable
operation. Choose a nominal value between 15mA and 20mA for this current, IR4. Calculate R4
from
VBE
R4 =
I R4
I R3
R3
Vin
Monitored supply, Vm
LED1
OUT
C1
0.1uF
IN
5
FB
4
U1
2
GND
PGND 1
GND
R1 ⎞
⎛
VM > VREF ⎜1 +
⎟
R2 ⎠
⎝
Vout
ZXRE060
3
VOUT goes low and LED is lit when
monitored supply
R1
10k
R3 =
R2
11k
VIN − (VF + 0.2)
IR3
I F (max) ≥ I R 3 ≤ 20mA
VF and IF are forward voltage drop and
current of LED1 respectively.
GND
Figure 7
1.15V over-voltage indicator
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AN63
U2
I R3
R3
Vin
To controller
1k
OUT
3
IN
2
ZXRE060
OUT
C1
FB
4
GND
PGND 1
GND
To controller
Regulated supply (Vout)
5
U1
0.1μF
To controller
1k
Regulated supply (Vout)
ZXRE060
C1
U2
I R3
R3
Vin
To controller
3
2
FB
4
GND
C2
GND
PGND 1
GND
R1
10k
5
U1
0.1μF
C2
0.47μF
IN
0.47μF
R2
15k
GND
Figure 8
Opto-isolated 0.6V shunt regulator
Figure 9
Opto-isolated 1.0V shunt regulator
VOUT = VREF
R1 ⎞
⎛
VOUT = VREF ⎜1 +
⎟
R2 ⎠
⎝
R3 =
VIN − (VOUT (SAT ) + VF )
IR3
20mA ≥ I R 3 ≤ I F ( MAX )
VF and IF are forward voltage drop and current for the opto-coupler LED respectively.
Stability considerations
The physical position of C2 and its value is critical to maintaining good stability. C2 should be
located in close physical proximity to the ZXRE060 and connected to its pins with the shorted and
widest possible copper track. The value of C2 required to ensure stability generally ranges from
about 0.1µF up to 10 µF depending on application and environment with higher gain applications
generally requiring smaller values.
Conclusion
The above circuits are only representative of what could be done with the ZXRE060 and are by no
means exhaustive. They provide examples of basic considerations and calculations that are
needed by the designer. These calculations can either be applied to, or be adapted for, use in
similar designs.
Recommended further reading
AN58 - Designing with Shunt Regulators - Shunt Regulation
AN59- Designing with Shunt Regulators - Series Regulation
AN60 - Designing with Shunt Regulators - Fixed Regulators and Opto-Isolation
AN61- Designing with Shunt Regulators - Extending the operating voltage range
AN62 - Designing with Shunt Regulators - Other Applications
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The circuits in this design/application note are offered as design ideas. It is the responsibility of the user to ensure that the circuit is fit for
the user’s application and meets with the user’s requirements. No representation or warranty is given and no liability whatsoever is
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written approval of the Chief Executive Officer of Diodes Incorporated. As used herein:
A. Life support devices or systems are devices or systems which:
1. are intended to implant into the body
or
2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the
labeling can be reasonably expected to result in significant injury to the user.
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cause the failure of the life support device or to affect its safety or effectiveness.
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To ensure quality of service and products we strongly advise the purchase of parts directly from Diodes Inc. or one of our regionally
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of damage can vary from immediate functional or parametric malfunction to degradation of function or performance in use over time.
Devices suspected of being affected should be replaced.
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Future device intended for production at some point. Samples may be available
“Active”
Product status recommended for new designs
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“Not recommended for new designs” Device is still in production to support existing designs and production
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This term denotes a very early datasheet version and contains highly provisional information, which
may change in any manner without notice.
“Provisional version”
This term denotes a pre-release datasheet. It provides a clear indication of anticipated performance.
However, changes to the test conditions and specifications may occur, at any time and without notice.
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© 2008 Published by Diodes Incorporated
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