Inverting Application for the LMZ14203 SIMPLE SWITCHER Power

Inverting Application for the LMZ14203 SIMPLE SWITCHER Power
Application Report
SNVA425A – March 2010 – Revised May 2013
AN-2027 Inverting Application for the LMZ14203 SIMPLE
SWITCHER® Power Module
Alan Martin
.....................................................................................................................................
ABSTRACT
This application report illustrates how to apply the LMZ14203 integrated buck module into the buck-boost
configuration such that a positive input voltage can be used to create a regulated negative output voltage.
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2
3
4
5
Contents
Introduction ..................................................................................................................
Enable Options ..............................................................................................................
External Enable Logic Level Shifters .....................................................................................
Typical Performance Characteristics .....................................................................................
References ...................................................................................................................
2
4
5
6
7
List of Figures
1
2
3
4
5
..............................................................
Inverting Application Schematic for Simple Enable and –5VOUT ......................................................
PNP Level Shifter ...........................................................................................................
P-ch MOSFET Level Shifter ...............................................................................................
Adjustable Shunt Reference-Based Precision UVLO Circuits ........................................................
Evaluation Board Connections for Inverting Application
3
4
5
5
5
SIMPLE SWITCHER is a registered trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
SNVA425A – March 2010 – Revised May 2013
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AN-2027 Inverting Application for the LMZ14203 SIMPLE SWITCHER®
Power Module
Copyright © 2010–2013, Texas Instruments Incorporated
1
Introduction
1
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Introduction
This application report shows how the conventional non-inverting demonstration and evaluation boards for
the device can be connected into the inverting configuration without the need to acquire a new PCB to
evaluate the application. For detailed descriptions on the PCB assemblies in the conventional buck
topology, see the AN-2024 LMZ1420x / LMZ1200x Evaluation Board User's Guide (SNVA422), the AN2031 LMZ12003 3A Demo Board SIMPLE SWITCHER® Power Module Quick Start Guide User's Guide
(SNVA427), and the AN-2032 LMZ14202 / LMZ14203 Demo Board SIMPLE SWITCHER® Power Module
Quick Start Guide User's Guide (SNVA428).
Figure 1 illustrates the method of reassigning the terminals of the evaluation board (or demo board) for the
inverting application. Careful labeling of leads is suggested to avoid confusion since the terminals formerly
at ground potential are now connected to –VOUT, and the connection formerly assigned to +Vout is now
connected to ground. The three connections to the power path are straightforward. But there may be
additional circuitry required for the enable signal to function as desired in the target system as the
precision enable reference voltage is referred to ground while disabled and to –VOUT once enabled. This
adds a large and possibly undesirable amount of hysteresis to the simplest form of enable. To alleviate
this situation several level shift methods are discussed in the following text.
It should also be noted that the maximum output current obtained from the module is decreased from that
obtained in the conventional buck configuration (see the graphs in Section 4). Further, since the ground
terminal of the module is connected to –VOUT the maximum positive input voltage into the inverting
application is decreased by the amplitude of the output voltage.Thus for a –5V output application the
maximum input voltage will be 37V.
This configuration can be applied to the whole family of LMZ1420x and LMZ1200x modules so long as the
input voltage and output current limits are observed. Be aware that efficiency is lower in the inverting
configuration resulting in higher dissipation for a given output power and that thermal derating may need
to be observed when operating at maximum output current.
2
AN-2027 Inverting Application for the LMZ14203 SIMPLE SWITCHER®
Power Module
Copyright © 2010–2013, Texas Instruments Incorporated
SNVA425A – March 2010 – Revised May 2013
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Introduction
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-VOUT
EN
(See Text)
+VIN
Figure 1. Evaluation Board Connections for Inverting Application
SNVA425A – March 2010 – Revised May 2013
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AN-2027 Inverting Application for the LMZ14203 SIMPLE SWITCHER®
Power Module
Copyright © 2010–2013, Texas Instruments Incorporated
3
Enable Options
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LMZ14203
U1
EP
NOTE: EP IS
CONNECTED
TO -VOUT
11V to 37V
Vin
VOUT
FB
SS
GND
EN
RON
VIN
Cin2 **
10 PF
7
6
5
4
3
2
1
Rent *
93.1k
Ron *
100k
Cff
0.022 PF
Rfbt *
ON @ 10.5Vin
Renb
11.8k
OFF @ 5.5Vin
Cin1
10 PF
50V
5.62k
Css
0.022 PF
Rfbb Co1
1.07k 1 PF
Co2
100 PF
-5 Vout
* Value differs from stock evaluation board
** Optional
A
For the Bill of Materials (BOM), see the AN-2024 LMZ1420x / LMZ1200x Evaluation Board User's Guide (SNVA422).
Figure 2. Inverting Application Schematic for Simple Enable and –5VOUT
2
Enable Options
Essentially there are three methods for enabling the module in the inverting application. The first is the
precision threshold shown in Figure 2. Under-voltage lock-out (UVLO) is determined by the values of
RENT and RENB in the same manner as described in the device-specific data sheet. Once the module is
enabled –VOUT goes from its initial ground potential to the regulated negative VOUT level at a rate
determined by the soft-start capacitor. Since RENB is also tied to –VOUT a reinforcing action occurs that
increases the 90 mV hysteresis level substantially such that the total hysteresis is essentially the
magnitude of VOUT. As previously suggested, a hysteresis level this large may be undesirable in certain
system situations so two other methods are described as alternatives.
Many systems have ground referred control or supervisory logic signals that need to be level shifted for
compatibility with the enable input of the LMZ14203 which in this application is referenced to –VOUT. The
level shift is quite straight forward and can be accomplished with a single transistor. The transistor type
can either be small signal PNP or low level P-channel mosfet. The transistor terminal connections are
essentially identical. These circuits are shown in Figure 3 and Figure 4.
For applications where precision UVLO is needed with a small and controllable amount of hysteresis, then
an adjustable shunt reference can be configured as a precision comparator to meet the requirements.
Suggested circuitry is detailed in Figure 5. The first is based on the common LMV431 type device with a
PNP inverter output section. The other circuit uses the similar LM4041 that differs in that it has high side
feedback reference and the inversion is not required. Either circuit is both low cost and compact.
4
AN-2027 Inverting Application for the LMZ14203 SIMPLE SWITCHER®
Power Module
Copyright © 2010–2013, Texas Instruments Incorporated
SNVA425A – March 2010 – Revised May 2013
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External Enable Logic Level Shifters
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3
External Enable Logic Level Shifters
Q1
CMPT3906
CMOS LOGIC ENABLE
V IH = 2.3V
VIL = 0.5V
RIB
10.0k
RENT
10.0k
LMZ14203 ENABLE
GND
RENB
10.0k
-VOUT
Figure 3. PNP Level Shifter
Q2
CMOS LOGIC ENABLE
S
D
G
RENT
10.0k
GND
LMZ14203 ENABLE
RENB
10.0k
-VOUT
Figure 4. P-ch MOSFET Level Shifter
9.5V PRECISION GROUND REFERENCED UVLO
9.5V PRECISION HIGH-SIDE REFERENCED UVLO
RENTA = (V(UVLO) - 1.24 ) x 10 k:
RENBC || RENHB = (V(UVLO) - 1.225 ) x 10 k:
VIN FOR INVERTING POWER STAGE
VIN FOR INVERTING POWER STAGE
RENTD = (V(UVLO)-1.1V-1.18V ) x 0.85 x10 k:
RENTA
82.5k
RRPU
10.0k
RENTC
12.1k
RBB
10.0k
RIB
82.5k
Q1
CMPT3906
1.225V
U2
LM4041-ADJ
RENHA
2.2M
RENHA
ADJUSTS
HYSTERESIS
1.24V
RENBA
12.4k
U1
LMV431
RENTB
75.0k
RENTB = 0.90 x RENTA
RENBC
100k
RENHB
ADJUSTS
HYSTERESIS
LMZ14203 ENABLE
RENBB
11.8k
GND
-VOUT
RENHB
470k
GND
RENTD
61.9k
LMZ14203 ENABLE
RENBD
11.8k
-VOUT
Figure 5. Adjustable Shunt Reference-Based Precision UVLO Circuits
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AN-2027 Inverting Application for the LMZ14203 SIMPLE SWITCHER®
Power Module
Copyright © 2010–2013, Texas Instruments Incorporated
5
Typical Performance Characteristics
4
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Typical Performance Characteristics
Max IOUT
vs
Input Voltage
3
3
I L = 3A
MAXIMUM OUTPUT CURRENT(A)
MAXIMUM OUTPUT CURRENT(A)
VOUT = -3.3V
2.5
2
1.5
1
0.5
25°C
0
V OUT = -5.0V
11
16
21
26
31
2
1.5
1
0.5
25°C
36
6
11
Efficiency at Max IOUT
VOUT = -3.3V
90
90
85
85
80
75
70
65
60
31
36
Efficiency at Max IOUT
VOUT = -5.0V
IL = 3A
80
75
70
65
55
25°C
6
11
16
21
26
31
36
50
25°C
6
INPUT VOLTAGE (V)
6
26
60
55
50
21
95
EFFICIENCY (%)
EFFICIENCY (%)
100
I L = 3A
95
16
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
100
I L = 3A
2.5
0
6
Max IOUT
vs
Input Voltage
AN-2027 Inverting Application for the LMZ14203 SIMPLE SWITCHER®
Power Module
Copyright © 2010–2013, Texas Instruments Incorporated
11
16
21
26
31
36
INPUT VOLTAGE (V)
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References
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Dissipation at Max IOUT
3
IL = 3A
V OUT = -3.3V
Dissipation at Max IOUT
4
3.5
2.5
VOUT = -5.0V
IL = 3A
DISSIPATION (W)
DISSIPATION (W)
3
2
1.5
1
2.5
2
1.5
1
0.5
0.5
25°C
0
6
25°C
11
16
21
26
31
36
0
6
11
16
21
26
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Output Ripple
Output Ripple
VOUT = -3.3V
31
36
I OUT = 2.2A
20 mV/Div
2 Ps/Div
25°C
Startup
CSS = 0.022 PF
Startup
1 ms/Div
CSS = 0.022 PF
VIN = 12V
VIN = 12V
ENABLE
ENABLE
1 ms/Div
VOUT = -3.3V @ 2.2A
25°C
5
25°C
V OUT = -5.0V @ 1.9A
References
•
•
•
AN-2024 LMZ1420x / LMZ1200x Evaluation Board User's Guide (SNVA422)
AN-2031 LMZ12003 3A Demo Board SIMPLE SWITCHER® Power Module Quick Start Guide User's
Guide (SNVA427)
AN-2032 LMZ14202 / LMZ14203 Demo Board SIMPLE SWITCHER® Power Module Quick Start
Guide User's Guide (SNVA428)
SNVA425A – March 2010 – Revised May 2013
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AN-2027 Inverting Application for the LMZ14203 SIMPLE SWITCHER®
Power Module
Copyright © 2010–2013, Texas Instruments Incorporated
7
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