DN545 - Monolithic Converter Delivers High Output Voltages

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Monolithic Converter Delivers High Output Voltages
Design Note 545
Jesus Rosales
Introduction
Industrial, telecom, medical and automotive applications use a wide variety of regulated voltages to
operate effectively, including high voltage and negative rails. When the designer is faced with producing
industrial power supplies, the job can be simplified by
minimizing the parts count, as well as the number of
required controller ICs. The LT®8331 achieves both of
these goals with an integrated 140V, 500mA switch,
programmable frequency, ultra-quiescent current and
light load Burst Mode ® operation.
A high voltage negative output rail can easily be
attained by configuring the converter as shown in
Figure 2. This converter allows full switch voltage
utilization to produce a negative output, by adding a
capacitor and a diode. A coupling capacitor, C5, adds
input to output disconnect during shutdown, similar
to a CUK converter.
Figure 3 shows a CUK converter using the LT8331, and
Figure 4 shows the efficiency curve for this inverter
with a 12V input. Efficiency for this converter peaks
at 84%. Burst Mode operation kicks in when the load
drops to about 40mA, which allows the converter to
maintain a respectable efficiency level of 73% even
with a 1mA load.
High voltage applications are easily accomplished
using a simple boost converter, as shown in Figure 1.
This application can output 120V at 25mA to 80mA
in a straight boost configuration or 240V at 12mA
to 35mA as a two stage boost by adding a few components, as shown inside the dotted line. The load
can be taken entirely from VOUT2, or a combination
of VOUT1 and VOUT2.
D1, D2, D3 : BAV21W
L1: CDRH8D43RT125NP-331
C1
10µF
D2
0.1µF
L1
VIN
10V to 48V
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are
registered trademarks of Linear Technology Corporation. All other trademarks
are the property of their respective owners.
VIN
BIAS
EN/UVLO
R3
215k
SS GND
C4
0.22µF
***
R2
2M
SW
LT8331
R5
154k
FBX
SYNC/MODE
RT
1µF
D1
330µH
R1
1M
D3
100Ω
1/4W
R4
13.3k
VOUT2
240V
12mA to 35mA
VOUT2
VOUT1
120V
C7
4.7pF
C2
2µF
INTVCC
C3
1µF
***
R2: USE 1M VALUE AND TIE TO VOUT1 FOR SINGLE STAGE BOOST
R2: USE 2M VALUE, AND TIE TO VOUT2 FOR DUAL STAGE BOOST
R2: MAY REQUIRE MILTIPLE SERIES RESISTORS TO COMPLY
WITH VOLTAGE RATING
Figure 1. 120V or 240V Output Boost Converter
12/15/545
The LT8331 has very low quiescent current. It features
an operation mode where the switching frequency
is allowed to decrease progressively when a light
load is detected. This mode enables the converter to
maintain both high efficiency and low output ripple at
light loads. The input current is just 29µA when the
output is unloaded and about 11µA comes from the
FBX resistor divider. If the converter is turned off by
pulling the EN pin to ground, the input current drops
to about 1µA for a 5V input, or 2µA with a 12V input.
A good portion of the shutdown current is drawn by
the EN/UVLO resistor divider.
input to output DC path, a desirable characteristic in
applications where the output must be disconnected
from the input. This has the added benefit of removing
the current drawn by the FBX resistor divider. The
switch voltage in these converters equals the sum
of the input and output voltages.
Conclusion
The LT8331 simplifies the design of high output
voltage and wide input voltage applications by reducing the number of external components. Its 140V,
500mA internal switch, 100V input, programmable
frequency, ultra-low quiescent current and light load
Burst Mode operation make it ideal for a broad range
of applications.
The LT8331’s 4.5V to 100V input range and its 140V
rated switch make it an ideal candidate for SEPIC and
CUK converters. Coupling capacitor, C5, breaks the
C5
1µF
VIN
10V to
48V
100Ω
D1
1/4W
VOUT
–120V
25mA
to 65mA
330µH
VIN
D2
SW
1M
4.7pF
BIAS
10µF
1M
LT8331
FBX
EN/UVLO SYNC/MODE
215k
SS GND
0.22µF
1µF
x2
6.7k
RT INTVCC
1µF
154k
D1, D2 : BAV21W
L1: CDRH8D43RT125NP-331
Figure 2. –120V Inverting Converter
95
1M
4.7µF
VIN
SW
4.7µF
120µH
D2
1M 10pF
VOUT
–12V
90mA
to 180mA
BIAS
LT8331
FBX
71.5k
22µF
90
85
EFFICIENCY (%)
C5
120µH
VIN
5V
to 80V
80
75
70
EN/UVLO
SYNC/MODE
SS GND
RT INTVCC
60
1µF
55
665k
0.22µF
63.4k
65
50
1
20
40
60
80
100 120 140 160
LOAD (mA)
Figure 3. –12V Output CUK Converter
Data Sheet Download
www.linear.com/LT8331
Linear Technology Corporation
Figure 4. Efficiency Curve for Figure 3 (with a 12V Input)
For applications help,
call (408) 432-1900
DN545f LT/AP 1215 111K • PRINTED IN THE USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2015
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