LM25007
42V, 0.5A Step-Down Switching Regulator
General Description
The LM25007 is a monolithic step-down switching regulator
featuring all of the functions needed to implement a low cost,
efficient, power supply. Capable of driving a 0.5Amp load
over a 9V-42V input voltage range, this device is easy to
apply and is provided in the small MSOP-8 and the thermally
enhanced LLP-8 packages. Ultra-fast transient response is
achieved through the use of a constant on-time architecture
with Vin feed forward. This feature provides an almost con-
stant operating frequency over load and input voltage varia-
tions. The operating frequency can be adjusted with a single
resistor. This architecture is easy to use and tolerant of
component selection. An intelligent current limit is imple-
mented in the LM25007 with forced off time that is inversely
proportional to Vout thus ensuring recovery from fault con-
ditions. The output voltage may be set from 2.5V to
>
30V. To
improve efficiency in light load applications, the Vcc pin can
be connected to an external voltage source to eliminate the
drop through the internal regulator. Additional features in-
clude: thermal shutdown, Vcc under-voltage lockout, gate
drive under-voltage lockout, and max duty cycle limiter.
Features
n
Integrated 0.74 ohm N-Channel MOSFET switch
n
Guaranteed 0.5Amp output current
n
Ultra-Fast Transient Response
n
Up to 800kHz operation
n
No control loop compensation required
n
Vin feed forward provides constant operating frequency
n
2% accurate 2.5V feedback from -40C to 125C
n
Highly efficient operation
n
Intelligent current limit protection
n
External shutdown control
n
Thermal shutdown
n
MSOP-8 and thermally enhanced LLP packages
Typical Applications
n
12VDC and 24VDC distributed rail systems
n
24VAC systems
n
Automotive body electronics and telematics
n
Industrial systems
n
HB-LED constant current source
Package
n
MSOP - 8
n
LLP - 8 (4mm x 4mm)
Basic Step-Down Regulator
20165513
February 2006
LM25007
42V
,
0.5A
Step-Down
Switching
Regulator
2006 National Semiconductor Corporation
DS201655
www.national.com
Connection Diagram
20165502
8-Lead MSOP, LLP
Ordering Information
Order Number
Package Type
NSC Package Drawing
Supplied As
LM25007MM
MSOP-8
MUA08A
1000 Units on Tape and Reel
LM25007MMX
MSOP-8
MUA08A
3500 Units on Tape and Reel
LM25007SD
LLP-8
SDC08A
1000 Units on Tape and Reel
LM25007SDX
LLP-8
SDC08A
4500 Units on Tape and Reel
Typical Application Circuit and Block Diagram
20165501
LM25007
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2
Pin Descriptions
Pin
Name
Description
Application Information
1
SW
Switching Node
Power switching node. Connect to the inductor,
bootstrap capacitor, and free-wheeling diode.
2
BST
Boost Bootstrap capacitor input
An external capacitor is required between the BST
and the SW pins. A 0.01F ceramic capacitor is
recommended.
3
RCL
Current Limit OFF time programming pin
A resistor between this pin and RTN sets the
off-time when current limit is detected. The off-time
is preset to 17 s if FB = 0V .
4
RTN
Circuit Ground
5
FB
Feedback Signal from Regulated Output
This pin is connected to the inverting input of the
internal regulation comparator. The regulation
threshold is 2.5V.
6
RON/SD
On-time set pin
A resistor between this pin and VIN sets the switch
on-time as a function of Vin. The minimum
recommended on-time is 300ns at the maximum
input voltage.
7
VCC
Output from the internal high voltage bias
regulator.
If an auxiliary voltage is available to raise the
voltage on this pin above the regulation setpoint
(7V), the internal series pass regulator will
shutdown, reducing the IC power dissipation. Do not
exceed 14V. This output provides gate drive power
for the internal Buck switch. An internal diode is
provided between this pin and the BST pin. A local
0.1uF decoupling capacitor is recommended.
8
VIN
Input supply voltage
Recommended operating range: 9V to 42V.
-
EP
Exposed pad, underside of the LLP package
option
Exposed metal pad on the LLP package underside.
It is recommended to connect this pad to the PC
board ground plane to aid in heat dissipation.
LM25007
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3
Absolute Maximum Ratings
(Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
VIN to RTN
45V
BST to RTN
59V
SW to RTN (Steady State)
-1V
ESD Rating (Note 5)
Human Body Model
2kV
BST to V
CC
45V
BST to SW
14V
VCC to RTN
14V
All Other Inputs to RTN
-0.3 to 7V
Storage Temperature Range
-65C to +150C
Operating Ratings
(Note 1)
V
IN
9V to 42V
Junction Temperature
-40C to + 125C
Electrical Characteristics
Specifications with standard type are for T
J
= 25C only; limits in boldface type apply over the full Operating Junction Tempera-
ture (T
J
) range. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values rep-
resent the most likely parametric norm at T
J
= 25C, and are provided for reference purposes only. Unless otherwise stated the
following conditions apply: V
IN
= 24V, R
ON
= 200k
. (Note 3).
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Startup Regulator
V
CC
Reg
V
CC
Regulator Output
6.6
7
7.4
V
V
CC
Current Limit
(Note 4)
11
mA
V
CC
Supply
V
CC
undervoltage Lockout
Voltage (V
CC
increasing)
6.3
V
V
CC
Undervoltage Hysteresis
206
mV
V
CC
UVLO Delay (filter)
3
s
Operating Current (I
CC
)
Non-Switching, FB = 3V
500
675
A
Shutdown/Standby Current
RON/SD = 0V
70
150
A
Switch Characteristics
Buck Switch Rds(on)
I
TEST
= 200mA,
VBST -VSW = 6.3V
(Note 6)
0.74
1.34
Gate Drive UVLO (VBST
VSW)
Rising
3.4
4.5
5.5
V
Gate Drive UVLO Hysteresis
400
mV
Current Limit
Current Limit Threshold
535
725
900
mA
Current Limit Response Time
I
switch
Overdrive = 0.1A
Time to Switch Off
225
ns
OFF time generator (test 1)
FB=0V, RCL = 100K
17
s
OFF time generator (test 2)
FB=2.3V, RCL = 100K
2.65
s
On Time Generator
TON -1
Vin = 10V
Ron = 200K
2.15
2.77
3.5
s
TON -2
Vin = 40V
Ron = 200K
450
615
810
ns
Remote Shutdown Threshold
Rising
0.45
0.7
1.1
V
Remote Shutdown Hysteresis
40
mV
LM25007
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4
Electrical Characteristics
(Continued)
Specifications with standard type are for T
J
= 25C only; limits in boldface type apply over the full Operating Junction Tempera-
ture (T
J
) range. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values rep-
resent the most likely parametric norm at T
J
= 25C, and are provided for reference purposes only. Unless otherwise stated the
following conditions apply: V
IN
= 24V, R
ON
= 200k
. (Note 3).
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Minimum Off Time
Minimum Off Timer
FB = 0V
300
ns
Regulation and OV Comparators
FB Reference Threshold
Internal reference
Trip point for switch ON
2.445
2.5
2.550
V
FB Over-Voltage Threshold
Trip point for switch OFF
2.875
V
FB Bias Current
100
nA
Thermal Shutdown
Tsd
Thermal Shutdown Temp.
165
C
Thermal Shutdown Hysteresis
25
C
Thermal Resistance
JA
Junction to Ambient
MUA Package
200
C/W
SDC Package
40
C/W
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: For detailed information on soldering plastic MSOP and LLP packages, refer to the Packaging Data Book available from National Semiconductor
Corporation.
Note 3: All limits are guaranteed. All electrical characteristics having room temperature limits are tested during production with T
A
= T
J
= 25C. All hot and cold limits
are guaranteed by correlating the electrical characteristics to process and temperature variations and applying statistical process control.
Note 4: The V
CC
output is intended as a self bias for the internal gate drive power and control circuits. Device thermal limitations limit external loading.
Note 5: The human body model is a 100pF capacitor discharge through a 1.5k
resistor into each pin. The human body ESD compliance level for Pin 7 and 8 is
1000V.
Note 6: For devices procurred in the LLP-8 package the Rds(on) limits are guaranteed by design characterization data only.
LM25007
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