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What is LM25085A?

This electronic component, produced by the manufacturer "National Semiconductor", performs the same function as "42V Constant On-Time PFET Buck Switching Controller".


LM25085A Datasheet PDF - National Semiconductor

Part Number LM25085A
Description 42V Constant On-Time PFET Buck Switching Controller
Manufacturers National Semiconductor 
Logo National Semiconductor Logo 


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LM25085A
March 16, 2009
42V Constant On-Time PFET Buck Switching Controller
with 0.9V Reference
General Description
The LM25085A is a functional variant of the LM25085 COT
PFET Buck Switching Controller. The functional differences
of the LM25085A are: The feedback reference voltage is
0.9V, the forced off-time after current limit detection is longer,
and the soft-start time is shorter (1.8 ms).
The LM25085A is a high efficiency PFET switching regulator
controller that can be used to quickly and easily develop a
small, efficient buck regulator for a wide range of applications.
This high voltage controller contains a PFET gate driver and
a high voltage bias regulator which operates over a wide 4.5V
to 42V input range. The constant on-time regulation principle
requires no loop compensation, simplifies circuit implemen-
tation, and results in ultra-fast load transient response. The
operating frequency remains nearly constant with line and
load variations due to the inverse relationship between the
input voltage and the on-time. The PFET architecture allows
100% duty cycle operation for a low dropout voltage. Either
the RDS(ON) of the PFET or an external sense resistor can be
used to sense current for over-current detection.
Features
Wide 4.5V to 42V input voltage range
Adjustable current limit using RDS(ON) or a current sense
resistor
Programmable switching frequency to 1MHz
No loop compensation required
Ultra-Fast transient response
Nearly constant operating frequency with line and load
variations
Adjustable output voltage from 0.9V
Precision ±2% feedback reference
Capable of 100% duty cycle operation
Internal soft-start timer
Integrated high voltage bias regulator
Thermal shutdown
Package
MSOP-8EP
MSOP-8
LLP-8 (3 mm x 3 mm)
Typical Application, Basic Step Down Controller
© 2009 National Semiconductor Corporation 300852
30085201
www.national.com

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LM25085A equivalent
Symbol
Parameter
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Conditions
tOFF(CL1)
Off-time (current limit) (Note 7) VIN = 12V, VFB = 0V
tOFF(CL2)
VIN = 12V, VFB = 0.75V
tOFF(CL3)
VIN = 24V, VFB = 0V
tOFF(CL4)
VIN = 24V, VFB = 0.75V
Regulation and Over-Voltage Comparators (FB Pin)
VREF
FB regulation threshold
VOV FB over-voltage threshold
IFB FB bias current
Soft-Start Function
Measured with respect to VREF
tSS Soft-start time
Thermal Shutdown
TSD Junction shutdown temperature
THYS
Junction shutdown hysteresis
Thermal Resistance
Junction temperature rising
θJA Junction to ambient, 0 LFPM air MSOP-8 package
flow (Note 5)
MSOP-8EP package
LLP-8 package
θJC Junction to case, 0 LFPM air flow MSOP-8 package
(Note 5)
MSOP-8EP package
LLP-8 package
Min Typ Max Units
5.56
2.59
9.03
4.29
8 10.96
3.7 5.16
13.2 18.1
6 8.54
µs
µs
µs
µs
0.882
0.9 0.918 V
350 mV
10 nA
1.16 1.8 3.15 ms
170 °C
20 °C
126 °C/W
46
54
29 °C/W
5.5
9.1
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 100 pF capacitor discharged through a 1.5 kresistor into each pin.
Note 3: VCC provides self bias for the internal gate drive.
Note 4: For detailed information on soldering plastic MSOP and LLP packages refer to the Packaging Data Book available from National Semiconductor
Corporation.
Note 5: Tested on a 4 layer JEDEC board. Four vias provided under the exposed pad. See JEDEC standards JESD51-5 and JESD51-7.
Note 6: Operating current and shutdown current do not include the current in the RT resistor.
Note 7: The tolerance of the minimum on-time (tON-4) and the current limit off-times (tOFF(CL1) through (tOFF(CL4)) track each other over process and temperature
variations. A device which has an on-time at the high end of the range will have an off-time that is at the high end of its range.
5 www.national.com


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