LMZ14203_2 [NSC]
Inverting Application for the SIMPLE SWITCHER? Power Module; 反相申请的SIMPLE SWITCHER ？电源模块
| 型号： | LMZ14203_2 |
| 厂家： | 
National Semiconductor |
| 描述： | Inverting Application for the SIMPLE SWITCHER? Power Module |
| 文件： | 总6页 (文件大小：1087K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
National Semiconductor
Application Note 2027
Alan Martin
Inverting Application for the
LMZ14203 SIMPLE
SWITCHER® Power Module
March 24, 2010
is referred to ground while disabled and to –VOUT once en-
abled. This adds a large and possibly undesirable amount of
hysteresis to the simplest form of enable. To alleviate this sit-
uation several level shift methods are discussed in the fol-
lowing text.
Introduction
This application note 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. It is also shown 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 eval-
uate the application. Refer to AN-2024, AN-2031, and
AN-2032 for detailed descriptions on the PCB assemblies in
the conventional buck topology.
It should also be noted that the maximum output current ob-
tained from the module is decreased from that obtained in the
conventional buck configuration. (See graphs) 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.
Figure 1 illustrates the method of reassigning the terminals of
the evaluation board (or demo board) for the inverting appli-
cation. Careful labeling of leads is suggested to avoid confu-
sion 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 3 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
This configuration can be applied to the whole family of
LMZ1420x and LMZ1200x modules so long as the input volt-
age 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 maxi-
mum output current.
30113401
FIGURE 1. Evaluation board connections for inverting application
© 2010 National Semiconductor Corporation
301134
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30113406
FIGURE 2. Inverting application schematic for simple enable and –5VOUT. For BOM refer to AN-2024.
the enable input of the LMZ14203 which in this application is
Enable Options
referenced to –VOUT. The level shift is quite straight forward
and can be accomplished with a single transistor. The tran-
sistor 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 Figures 3
and 4.
Essentially there are three methods for enabling the module
in the inverting application. The first is the precision threshold
shown in figure 2. UVLO (Under Voltage Lock Out) is deter-
mined by the values of RENT and RENB in the same manner
as described in the 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 ca-
pacitor. 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.
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 de-
vice 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.
Many systems have ground referred control or supervisory
logic signals that need to be level shifted for compatibility with
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2
External Enable Logic Level Shifters
30113402
FIGURE 3. PNP Level Shifter
30113403
FIGURE 4. P-ch MOSFET Level Shifter
30113407
FIGURE 5. Adjustable Shunt Reference Based Precision UVLO Circuits
3
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Typical Performance Characteristics
Max IOUT vs Input Voltage
Max IOUT vs Input Voltage
Efficiency at Max IOUT
Dissipation at Max IOUT
30113416
30113413
Efficiency at Max IOUT
30113414
30113417
Dissipation at Max IOUT
30113418
30113415
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4
Output Ripple
Output Ripple
30113419
30113420
Startup
Startup
30113421
30113422
5
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Notes
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