Texas Instruments AN-2027 Inverting Application for the LMZ14203 SIMPLE SWITCHER Power Module (Rev. A) Application notes
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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.
Contents
1 Introduction .................................................................................................................. 2
2 Enable Options .............................................................................................................. 4
3 External Enable Logic Level Shifters ..................................................................................... 5
4 Typical Performance Characteristics ..................................................................................... 6
5 References ................................................................................................................... 7
List of Figures
1 Evaluation Board Connections for Inverting Application .............................................................. 3
2 Inverting Application Schematic for Simple Enable and –5V
OUT
...................................................... 4
3 PNP Level Shifter........................................................................................................... 5
4 P-ch MOSFET Level Shifter............................................................................................... 5
5 Adjustable Shunt Reference-Based Precision UVLO Circuits ........................................................ 5
SIMPLE SWITCHER is a registered trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
1
SNVA425A–March 2010–Revised May 2013 AN-2027 Inverting Application for the LMZ14203 SIMPLE SWITCHER
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Introduction
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1 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 AN-
2031 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 –V
OUT
, 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 –V
OUT
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 –V
OUT
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
®
SNVA425A–March 2010–Revised May 2013
Power Module
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-V
OUT
+V
IN
EN
(See Text)
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Introduction
Figure 1. Evaluation Board Connections for Inverting Application
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SNVA425A–March 2010–Revised May 2013 AN-2027 Inverting Application for the LMZ14203 SIMPLE SWITCHER
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50V
Cin1
ON @ 10.5Vin
Cff
Css
93.1k
Rent *
11.8k
Renb
100k
Ron *
5.62k
Rfbt *
1.07k
Rfbb
Vin
-5 Vout
GND
4
SS
5
FB
6
VOUT
7
EN
3
RON
2
VIN
1
EP
U1
LMZ14203
11V to 37V
100 PF
Co2Co1
Cin2 **
OFF @ 5.5Vin
NOTE: EP IS
CONNECTED
TO -VOUT
* Value differs from stock evaluation board
** Optional
1 PF
10 PF
0.022 PF
10 PF
0.022 PF
Enable Options
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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 –5V
OUT
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 –V
OUT
goes from its initial ground potential to the regulated negative V
OUT
level at a rate
determined by the soft-start capacitor. Since RENB is also tied to –V
OUT
a reinforcing action occurs that
increases the 90 mV hysteresis level substantially such that the total hysteresis is essentially the
magnitude of V
OUT
. 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 –V
OUT
. 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
®
SNVA425A–March 2010–Revised May 2013
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9.5V PRECISION HIGH-SIDE REFERENCED UVLO
RENTD = (V(UVLO)-1.1V-1.18V ) x 0.85 x10 k:
U1
LMV431
12.4k
RENBA
82.5k
RENTA
10.0k
RRPU
Q1
CMPT3906
82.5k
RIB
2.2M
RENHA
GND
75.0k
RENTB
-VOUT
LMZ14203 ENABLE
9.5V PRECISION GROUND REFERENCED UVLO
11.8k
RENBB
1.24V
RENTA = (V(UVLO) - 1.24 ) x 10 k:
RENTB = 0.90 x RENTA
VIN FOR INVERTING POWER STAGE
U2
LM4041-ADJ
12.1k
RENTC
100k
RENBC
61.9k
RENTD
11.8k
RENBD
GND
VIN FOR INVERTING POWER STAGE
LMZ14203 ENABLE
-VOUT
470k
RENHB
RENHA
ADJUSTS
HYSTERESIS
RENHB
ADJUSTS
HYSTERESIS
RENBC || RENHB = (V(UVLO) - 1.225 ) x 10 k:
1.225V
10.0k
RBB
LMZ14203 ENABLE
-VOUT
GND
10.0k
RENB
10.0k
RENT
CMOS LOGIC ENABLE
D
G
S
Q2
Q1
CMPT3906
-VOUT
LMZ14203 ENABLE
GND
10.0k
RIB
10.0k
RENB
10.0k
RENT
CMOS LOGIC ENABLE
V
IH
= 2. 3V
V
IL
= 0.5V
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External Enable Logic Level Shifters
3 External Enable Logic Level Shifters
Figure 3. PNP Level Shifter
Figure 4. P-ch MOSFET Level Shifter
Figure 5. Adjustable Shunt Reference-Based Precision UVLO Circuits
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SNVA425A–March 2010–Revised May 2013 AN-2027 Inverting Application for the LMZ14203 SIMPLE SWITCHER
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50
55
60
65
70
75
80
85
90
95
100
6 11 16 21 26 31 36
INPUT VOLTAGE (V)
EFFICIENCY (%)
V
OUT
= -3.3V I
L
= 3A
25°C
50
55
60
65
70
75
80
85
90
95
100
6 11 16 21 26 31 36
INPUT VOLTAGE (V)
EFFICIENCY (%)
V
OUT
= -5.0V I
L
= 3A
25°C
0
0.5
1
1.5
2
2.5
3
6 11 16 21 26 31 36
INPUT VOLTAGE (V)
MAXIMUM OUTPUT CURRENT(A)
V
OUT
= -3.3V
25°C
I
L
= 3A
0
0.5
1
1.5
2
2.5
3
6 11 16 21 26 31 36
INPUT VOLTAGE (V)
MAXIMUM OUTPUT CURRENT(A)
V
OUT
= -5.0V I
L
= 3A
25°C
Typical Performance Characteristics
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4 Typical Performance Characteristics
Max I
OUT
Max I
OUT
vs vs
Input Voltage Input Voltage
Efficiency at Max I
OUT
Efficiency at Max I
OUT
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AN-2027 Inverting Application for the LMZ14203 SIMPLE SWITCHER
®
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VOUT = -3.3V @ 2.2A
ENABLE
C
SS
= 0.022 PF
25°C
1 ms/Div
V
IN
= 12V
V
OUT
= -5.0V @ 1.9A
25°C
C
SS
= 0.022 PF
ENABLE
1 ms/Div
V
IN
= 12V
V
OUT
= -3.3V I
OUT
= 2.2A
20 mV/Div 2 Ps/Div
25°C
0
0.5
1
1.5
2
2.5
3
6 11 16 21 26 31 36
INPUT VOLTAGE (V)
DISSIPATION (W)
V
OUT
= -3.3V
I
L
= 3A
25°C
0
0.5
1
1.5
2
2.5
3
3.5
4
6 11 16 21 26 31 36
INPUT VOLTAGE (V)
DISSIPATION (W)
V
OUT
= -5.0V I
L
= 3A
25°C
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References
Dissipation at Max I
OUT
Dissipation at Max I
OUT
Output Ripple Output Ripple
Startup Startup
5 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)
7
SNVA425A–March 2010–Revised May 2013 AN-2027 Inverting Application for the LMZ14203 SIMPLE SWITCHER
®
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Copyright © 2010–2013, Texas Instruments Incorporated
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Texas Instruments AN-2027 Inverting Application for the LMZ14203 SIMPLE SWITCHER Power Module (Rev. A) Application notes
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