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
n
Wide 6V to 42V Input Voltage Range
n
Valley Current Limiting At 1.25A
n
Programmable Switching Frequency Up To 1 MHz
n
Integrated N-Channel Buck Switch
n
Integrated High Voltage Bias Regulator
n
No Loop Compensation Required
n
Ultra-Fast Transient Response
n
Nearly Constant Operating Frequency With Line and
Load Variations
n
Adjustable Output Voltage
n
2.5V,
2% Feedback Reference
n
Programmable Soft-Start
n
Thermal shutdown
Typical Applications
n
Non-Isolated Telecommunications Regulator
n
Secondary Side Post Regulator
n
Power SUpply for Automotive Electronics
Package
n
LLP-10 (4 mm x 4 mm)
n
TSSOP-14EP
n
Both Packages Have Exposed Thermal Pad For
Improved Heat Dissipation
Basic Step-Down Regulator
20172743
February 2006
LM25010
42V
,
1.0A
Step-Down
Switching
Regulator
2006 National Semiconductor Corporation
DS201727
www.national.com
Connection Diagrams
20172702
20172703
Ordering Information
Order Number
Package Type
NSC Package
Drawing
Junction Temperature
Range
Supplied As
LM25010SD
LLP-10 (4x4)
SDC10A
-40C to + 125C
1000 Units on Tape and Reel
LM25010SDX
LLP-10 (4x4)
SDC10A
-40C to + 125C
4500 Units on Tape and Reel
LM25010MH
TSSOP-14EP
MXA14A
-40C to + 125C
94 Units in Rail
LM25010MHX
TSSOP-14EP
MXA14A
-40C to + 125C
2500 Units on Tape and Reel
LM25010
www.national.com
2
Pin Descriptions
Pin Number
Name
Description
Application Information
LLP-10
TSSOP-14
1
2
SW
Switching Node
Internally connected to the buck switch source.
Connect to the inductor, free-wheeling diode, and
bootstrap capacitor.
2
3
BST
Boost pin for 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.
3
4
ISEN
Current sense
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).
4
5
SGND
Current Sense Ground
Re-circulating current flows into this pin to the
current sense resistor.
5
6
RTN
Circuit Ground
Ground return for all internal circuitry other than the
current sense resistor.
6
9
FB
Voltage feedback input from the
regulated output
Input to both the regulation and over-voltage
comparators. The FB pin regulation level is 2.5V.
7
10
SS
Softstart
An internal 11.5 A current source charges the SS
pin capacitor to 2.5V to soft-start the reference input
of the regulation comparator.
8
11
RON/SD
On-time control and shutdown
An external resistor from VIN to the RON/SD pin
sets the buck switch on-time. Grounding this pin
shuts down the regulator.
9
12
VCC
Output of the bias 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 F, 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
.
10
13
VIN
Input supply voltage
Nominal input range is 6V to 42V. Input bypass
capacitors should be located as close as possible to
the VIN pin and RTN pins.
1,7,8,14
NC
No connection.
No internal connection. Can be connected to ground
plane to improve heat dissipation.
EP
Exposed Pad
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.
LM25010
www.national.com
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
-0.3V to 45V
BST to RTN
-0.3V to 59V
SW to RTN (Steady State)
-1.5V
BST to VCC
45V
BST to SW
14V
VCC to RTN
-0.3V to 14V
SGND to RTN
-0.3V to +0.3V
SS to RTN
-0.3V to 4V
VIN to SW
45V
All Other Inputs to RTN
-0.3V to 7V
ESD Rating (Note 2)
Human Body Model
2kV
Storage Temperature Range
-65C to +150C
Lead Temperature (Soldering 4 sec) (Note 4)
260C
Operating Ratings
(Note 1)
VIN Voltage
6.0V to 42V
Junction Temperature
LM25010
-40C to + 125C
Electrical Charateristics
Specifications with standard type are for T
J
= 25C 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
= 25C, and are provided for ref-
erence purposes only. Unless otherwise stated the following conditions apply: V
IN
= 24V, R
ON
= 200k
. See (Note 5).
Symbol
Parameter
Conditions
Min
Typ
Max
Units
V
CC
Regulator
V
CC
Reg
V
CC
regulated output
6.6
7
7.4
Volts
V
IN
- V
CC
I
CC
= 0 mA, F
S
200 kHz, 6.0V V
IN
8.5V
100
mV
V
CC
Bypass Threshold
V
IN
Increasing
8.9
V
V
CC
Bypass Hysteresis
V
IN
Decreasing
260
mV
V
CC
output impedance
(0 mA
I
CC
5 mA)
V
IN
= 6.0V
55
V
IN
= 8.0V
50
V
IN
= 24V
0.21
V
CC
current limit (Note 3)
V
IN
= 24V, V
CC
= 0V
15
mA
UVLOVcc
V
CC
under-voltage lock-out
threshold
V
CC
Increasing
5.25
V
UVLO
VCC
hysteresis
V
CC
Decreasing
180
mV
UVLO
VCC
filter delay
100 mV overdrive
3
s
I
IN
operating current
Non-switching, FB = 3V
645
920
A
I
IN
shutdown current
RON/SD = 0V
90
170
A
Switch Characteristics
R
DS(on)
Buck Switch R
DS(on)
I
SW
= 200mA
0.35
0.80
UVLO
GD
Gate Drive UVLO
V
BST
- V
SW
Increasing
1.7
3.0
4.0
V
UVLO
GD
hysteresis
400
mV
SOFT-START Pin
I
SS
Internal current source
8.0
11.5
15
A
Current Limit
I
LIM
Threshold
Current out of I
SEN
1
1.25
1.5
A
Resistance from ISEN to
SGND
130
m
Response time
150
ns
On Timer, RON/SD Pin
t
ON
- 1
On-time
V
IN
= 10V, R
ON
= 200 k
2.1
2.75
3.4
s
t
ON
- 2
On-time
V
IN
= 42V, R
ON
= 200 k
500
695
890
ns
Shutdown threshold
Voltage at RON/SD rising
0.30
0.7
1.05
V
Threshold hysteresis
40
mV
LM25010
www.national.com
4
Electrical Charateristics
Specifications with standard type are for T
J
= 25C 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
= 25C, and are provided for reference
purposes only. Unless otherwise stated the following conditions apply: V
IN
= 24V, R
ON
= 200k
. See (Note 5). (Continued)
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Off Timer
t
OFF
Minimum Off-time
260
ns
Regulation and Over-Voltage Comparators (FB Pin)
V
REF
FB regulation threshold
2.445
2.50
2.550
V
FB over-voltage threshold
2.9
V
FB bias current
1
nA
Thermal Shutdown
T
SD
Thermal shutdown temperature
175
C
Thermal shutdown hysteresis
20
C
Thermal Resistance
JA
Junction to Ambient, 0 LFPM
Air Flow
SDC Package
MXA Package
40
40
C/W
JC
Junction to Case
SDC Package
MXA Package
5.2
5.2
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: The human body model is a 100pF capacitor discharged through a 1.5k
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 25C operation.
LM25010
www.national.com
5
PDF 
ZIP