LM25010 42V, 1.0A Step-Down Switching Regulator
February 2006
LM25010
42V, 1.0A Step-Down Switching Regulator
General Description
The LM25010 features all the functions needed to implement
a low cost, efficient, buck regulator capable of supplying in
excess of 1A load current. This high voltage regulator inte-
grates an N-Channel Buck Switch, and is available in ther-
mally enhanced LLP-10 and TSSOP-14EP packages. The
constant on-time regulation scheme requires no loop com-
pensation resulting in fast load transient response and sim-
plified circuit implementation. The operating frequency re-
mains 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. Addi-
tional features include: VCC under-voltage lock-out, thermal
shutdown, gate drive under-voltage lock-out, and maximum
duty cycle limiter.
Features
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Wide 6V to 42V Input Voltage Range
Valley Current Limiting At 1.25A
Programmable Switching Frequency Up To 1 MHz
Integrated N-Channel Buck Switch
Integrated High Voltage Bias Regulator
No Loop Compensation Required
Ultra-Fast Transient Response
Nearly Constant Operating Frequency With Line and
Load Variations
Adjustable Output Voltage
2.5V,
±
2% Feedback Reference
Programmable Soft-Start
Thermal shutdown
Typical Applications
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Non-Isolated Telecommunications Regulator
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Secondary Side Post Regulator
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Power SUpply for Automotive Electronics
Package
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LLP-10 (4 mm x 4 mm)
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TSSOP-14EP
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Both Packages Have Exposed Thermal Pad For
Improved Heat Dissipation
Basic Step-Down Regulator
20172743
© 2006 National Semiconductor Corporation
DS201727
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LM25010
Connection Diagrams
20172702
20172703
Ordering Information
Order Number
LM25010SD
LM25010SDX
LM25010MH
LM25010MHX
Package Type
LLP-10 (4x4)
LLP-10 (4x4)
TSSOP-14EP
TSSOP-14EP
NSC Package
Drawing
SDC10A
SDC10A
MXA14A
MXA14A
Junction Temperature
Range
−40˚C to + 125˚C
−40˚C to + 125˚C
−40˚C to + 125˚C
−40˚C to + 125˚C
Supplied As
1000 Units on Tape and Reel
4500 Units on Tape and Reel
94 Units in Rail
2500 Units on Tape and Reel
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2
LM25010
Pin Descriptions
Pin Number
LLP-10
1
TSSOP-14
2
Name
SW
Description
Switching Node
Application Information
Internally connected to the buck switch source.
Connect to the inductor, free-wheeling diode, and
bootstrap capacitor.
Connect a capacitor from SW to the BST pin. The
capacitor is charged from VCC via an internal diode
during the buck switch off-time.
During the buck switch off-time, the inductor current
flows through the internal sense resistor, and out of
the ISEN pin to the free-wheeling diode. The current
limit comparator keeps the buck switch off if the
ISEN current exceeds 1.25A (typical).
Re-circulating current flows into this pin to the
current sense resistor.
Ground return for all internal circuitry other than the
current sense resistor.
Input to both the regulation and over-voltage
comparators. The FB pin regulation level is 2.5V.
An internal 11.5 µA current source charges the SS
pin capacitor to 2.5V to soft-start the reference input
of the regulation comparator.
An external resistor from VIN to the RON/SD pin
sets the buck switch on-time. Grounding this pin
shuts down the regulator.
The voltage at VCC is nominally equal to V
IN
for V
IN
<
8.9V, and regulated at 7V for V
IN
>
8.9V.
Connect a 0.47 µF, or larger capacitor from VCC to
ground, as close as possible to the pins. An external
voltage can be applied to this pin to reduce internal
dissipation if V
IN
is greater than 8.9V. MOSFET
body diodes clamp VCC to VIN if V
CC
>
V
IN
.
Nominal input range is 6V to 42V. Input bypass
capacitors should be located as close as possible to
the VIN pin and RTN pins.
No internal connection. Can be connected to ground
plane to improve heat dissipation.
Exposed metal pad on the underside of the device.
It is recommended to connect this pad to the PC
board ground plane to aid in heat dissipation.
2
3
BST
Boost pin for bootstrap capacitor
3
4
ISEN
Current sense
4
5
6
7
5
6
9
10
SGND
RTN
FB
SS
Current Sense Ground
Circuit Ground
Voltage feedback input from the
regulated output
Softstart
8
11
RON/SD
On-time control and shutdown
9
12
VCC
Output of the bias regulator
10
13
VIN
Input supply voltage
1,7,8,14
NC
EP
No connection.
Exposed Pad
3
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LM25010
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
BST to RTN
SW to RTN (Steady State)
BST to VCC
BST to SW
VCC to RTN
SGND to RTN
SS to RTN
-0.3V to 45V
-0.3V to 59V
-1.5V
45V
14V
-0.3V to 14V
-0.3V to +0.3V
-0.3V to 4V
VIN to SW
All Other Inputs to RTN
ESD Rating (Note 2)
Human Body Model
Storage Temperature Range
Lead Temperature (Soldering 4 sec) (Note 4)
45V
-0.3V to 7V
2kV
-65˚C to +150˚C
260˚C
Operating Ratings
(Note 1)
VIN Voltage
Junction Temperature
LM25010
−40˚C to + 125˚C
6.0V to 42V
Specifications with standard type are for T
J
= 25˚C only; limits in boldface type ap-
ply over the full Operating Junction Temperature (T
J
) range. Minimum and Maximum limits are guaranteed through test, de-
sign, or statistical correlation. Typical values represent the most likely parametric norm at T
J
= 25˚C, and are provided for ref-
erence purposes only. Unless otherwise stated the following conditions apply: V
IN
= 24V, R
ON
= 200kΩ. See (Note 5).
Symbol
V
CC
Regulator
V
CC
Reg
V
CC
regulated output
V
IN
- V
CC
V
CC
Bypass Threshold
V
CC
Bypass Hysteresis
V
CC
output impedance
(0 mA
≤
I
CC
≤
5 mA)
V
CC
current limit (Note 3)
UVLOVcc
V
CC
under-voltage lock-out
threshold
UVLO
VCC
hysteresis
UVLO
VCC
filter delay
I
IN
operating current
I
IN
shutdown current
Switch Characteristics
R
DS(on)
UVLO
GD
Buck Switch R
DS(on)
Gate Drive UVLO
UVLO
GD
hysteresis
SOFT-START Pin
I
SS
Current Limit
I
LIM
Threshold
Resistance from ISEN to
SGND
Response time
On Timer, RON/SD Pin
t
ON
- 1
t
ON
- 2
On-time
On-time
Shutdown threshold
Threshold hysteresis
V
IN
= 10V, R
ON
= 200 kΩ
V
IN
= 42V, R
ON
= 200 kΩ
Voltage at RON/SD rising
2.1
500
0.30
2.75
695
0.7
40
3.4
890
1.05
µs
ns
V
mV
Current out of I
SEN
1
1.25
130
150
1.5
A
mΩ
ns
Internal current source
8.0
11.5
15
µA
I
SW
= 200mA
V
BST
- V
SW
Increasing
1.7
0.35
3.0
400
0.80
4.0
Ω
V
mV
I
CC
= 0 mA, F
S
≤
200 kHz, 6.0V
≤
V
IN
≤
8.5V
V
IN
Increasing
V
IN
Decreasing
V
IN
= 6.0V
V
IN
= 8.0V
V
IN
= 24V
V
IN
= 24V, V
CC
= 0V
V
CC
Increasing
V
CC
Decreasing
100 mV overdrive
Non-switching, FB = 3V
RON/SD = 0V
6.6
7
100
8.9
260
55
50
0.21
15
5.25
180
3
645
90
920
170
mA
V
mV
µs
µA
µA
7.4
Volts
mV
V
mV
Ω
Parameter
Conditions
Min
Typ
Max
Units
Electrical Charateristics
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LM25010
Electrical Charateristics
Specifications with standard type are for T
J
= 25˚C only; limits in boldface type apply
over the full Operating Junction Temperature (T
J
) range. Minimum and Maximum limits are guaranteed through test, design,
or statistical correlation. Typical values represent the most likely parametric norm at T
J
= 25˚C, and are provided for reference
purposes only. Unless otherwise stated the following conditions apply: V
IN
= 24V, R
ON
= 200kΩ. See (Note 5). (Continued)
Symbol
Off Timer
t
OFF
V
REF
Minimum Off-time
FB regulation threshold
FB over-voltage threshold
FB bias current
Thermal Shutdown
T
SD
Thermal shutdown temperature
Thermal shutdown hysteresis
Thermal Resistance
θ
JA
θ
JC
Junction to Ambient, 0 LFPM
Air Flow
Junction to Case
SDC Package
MXA Package
SDC Package
MXA Package
40
40
5.2
5.2
˚C/W
˚C/W
175
20
˚C
˚C
2.445
260
2.50
2.9
1
2.550
ns
V
V
nA
Regulation and Over-Voltage Comparators (FB Pin)
Parameter
Conditions
Min
Typ
Max
Units
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:
V
CC
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.
5
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