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PDF LM5010 Data sheet ( Hoja de datos )
| Número de pieza | LM5010 | |
| Descripción | High Voltage 1A Step Down Switching Regulator | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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October 2004
LM5010
High Voltage 1A Step Down Switching Regulator
General Description
The LM5010 Step Down Switching Regulator features all the
functions needed to implement a low cost, efficient, buck
bias regulator capable of supplying in excess of 1A load
current. This high voltage regulator contains an N-Channel
Buck Switch, and is available in thermally enhanced LLP-10
and TSSOP-14EP packages. The hysteretic regulation
scheme requires no loop compensation, results in fast load
transient response, and simplifies circuit implementation.
The operating frequency remains constant with line and load
variations due to the inverse relationship between the input
voltage and the on-time. The valley current limit detection is
set at 1.25A. Additional features include: VCC under-voltage
lockout, thermal shutdown, gate drive under-voltage lockout,
and maximum duty cycle limiter.
Features
n Input Voltage Range: 8V to 75V
n Valley Current Limit At 1.25A
n Switching Frequency Can Exceed 1 MHz
n Integrated N-Channel Buck Switch
n Integrated Startup Regulator
n No Loop Compensation Required
n Ultra-Fast Transient Response
n Operating Frequency Remains Constant With Load and
Line Variations
n Maximum Duty Cycle Limited During Startup
n Adjustable Output Voltage
n Precision 2.5V Feedback Reference
n Thermal shutdown
Typical Applications
n High Efficiency Point-Of-Load (POL) Regulator
n Non-Isolated Telecommunications Buck Regulator
n Secondary High Voltage Post Regulator
n Automotive Systems
Package
n LLP-10 (4 mm x 4 mm)
n TSSOP-14EP
n Both Packages Have Exposed Thermal Pad For
Improved Heat Dissipation
Basic Stepdown Regulator
20119943
© 2004 National Semiconductor Corporation DS201199
www.national.com
1 page  
Electrical Charateristics (Continued)
Specifications with standard typeface are for TJ = 25˚C, and those with boldface type apply over full Operating Junction
Temperature range. VIN = 48V, RON = 200kΩ, unless otherwise stated (Note 5) and (Note 6).
Symbol
Parameter
Conditions
Min Typ Max
Units
Regulation and Over-Voltage Comparators (FB Pin)
VREF
FB regulation threshold
FB over-voltage threshold
SS pin = steady state
2.445
2.5
2.9
2.550
V
V
FB bias current
1 nA
Thermal Shutdown
TSD Thermal shutdown
temperature
175 ˚C
Thermal shutdown hysteresis
20 ˚C
Thermal Resistance
θJA
Junction to Ambient
SDC Package
MXA Package
40
˚C/W
40
Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device
is intended to be functional. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin.
Note 3: VCC provides bias for the internal gate drive and control circuits. Device thermal limitations limit external loading.
Note 4: For detailed information on soldering plastic TSSOP and LLP packages refer to the Packaging Data Book available from National Semiconductor
Corporation.
Note 5: Typical specifications represent the most likely parametric norm at 25˚C operation.
Note 6: All limits are guaranteed. All electrical characteristics having room temperature limits are tested during production with TA = 25˚C. All hot and cold limits are
guaranteed by correlating the electrical characteristics to process and temperature variations and applying statistical process control.
5 www.national.com
5 Page 
Start-up Regulator (VCC) (Continued)
FIGURE 10. Self Biased Configuration
20119916
Regulation Comparator
The feedback voltage at FB is compared to the voltage at the
Softstart pin (2.5V, ±2%). In normal operation (the output
voltage is regulated) an on-time period is initiated when the
voltage at FB falls below 2.5V. The buck switch stays on for
the on-time causing the FB voltage to rise above 2.5V. After
the on-time period the buck switch stays off until the FB
voltage falls below 2.5V. Bias current at the FB pin is less
than 5 nA over temperature.
Over-Voltage Comparator
The feedback voltage at FB is compared to an internal 2.9V
reference. If the voltage at FB rises above 2.9V the on-time
is immediately terminated. This condition can occur if the
input voltage, or the output load, change suddenly. The buck
switch will not turn on again until the voltage at FB falls below
2.5V.
ON-Time Control
The on-time of the internal switch (see Figure 5) is deter-
mined by the RON resistor and the input voltage (VIN), cal-
culated from the following:
(5)
The inverse relationship of tON vs. VIN results in a nearly
constant frequency as VIN is varied. If the application re-
quires a high frequency the minimum value for tON, and
consequently RON, is limited by the off-time (265 ns, ±15%)
which limits the maximum duty cycle at minimum VIN. The
tolerance for Equation 5 is ±25%. Frequencies in excess of
1 MHz are possible with the LM5010.
Shutdown
The LM5010 can be remotely shut down by taking the
RON/SD pin below 0.65V. See Figure 11. In this mode the
softstart pin is internally grounded, the on-timer is disabled,
and the input current at VIN is reduced (Figure 7). Releasing
the RON/SD pin allows normal operation to resume. When
the switch is open, the nominal voltage at RON/SD is shown
in Figure 6.
20119918
FIGURE 11. Shutdown Implementation
11
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| Páginas | Total 19 Páginas | |
| PDF Descargar | [ Datasheet LM5010.PDF ] | |
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