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LM25005 Datasheet
STEP-DOWN SWITCHING REGULATOR

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February 2006
LM25005
42V, 2.5A Step-Down Switching Regulator
General Description
The LM25005 switching regulator features all of the func-
tions necessary to implement an efficient, high voltage buck
regulator using a minimum of external components. This
easy to use regulator includes a 42V, 160m, N-channel
MOSFET, with an output current capability of 2.5 Amps. The
regulator control method is based upon current mode control
utilizing an emulated current ramp. Current mode control
provides inherent line voltage feed-forward, cycle-by-cycle
current limiting and ease of loop compensation. The use of
an emulated control ramp reduces noise sensitivity of the
pulse-width modulation circuit, allowing reliable control of
very small duty cycles necessary in high input voltage appli-
cations. The operating frequency is programmable from
50kHz to 500kHz. An oscillator synchronization pin allows
multiple LM25005 regulators to self-synchronize or to be
synchronized to an external clock. Additional protection fea-
tures include: current limit, thermal shutdown and remote
shutdown capability. The device is available in a power
enhanced TSSOP-20 package featuring an exposed die
attach pad to aid thermal dissipation.
Features
n Integrated 42V, 160mN-channel MOSFET
n Ultra-wide input voltage range from 7V to 42V
n Internal bias regulator
n Adjustable output voltage from 1.225V
n 1.5% feedback reference accuracy
n Current mode control with emulated inductor current
ramp
n Single resistor oscillator frequency setting
n Oscillator synchronization input
n Programmable soft-start
n Shutdown / Standby input
n Wide bandwidth error amplifier
n Thermal Shutdown
Package
n TSSOP-20EP (Exposed Pad)
Simplified Application Schematic
© 2006 National Semiconductor Corporation DS201700
20170001
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LM25005 Datasheet
STEP-DOWN SWITCHING REGULATOR

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Connection Diagram
20170002
Top View
20-Lead TSSOP
Ordering Information
Order Number
LM25005MH
LM25005MHX
Package Type
Exposed Pad TSSOP-20
Exposed Pad TSSOP-20
NSC Package Drawing
MXA20A
MXA20A
Supplied As
73 Units in Rail
2500 Units on Tape and Reel
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STEP-DOWN SWITCHING REGULATOR

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Pin Descriptions
Pin(S)
1
Name
VCC
Description
Output of the bias regulator
2 SD Shutdown or UVLO input
3, 4 Vin Input supply voltage
5 SYNC Oscillator synchronization input or
output
6 COMP Output of the internal error amplifier
7 FB Feedback signal from the regulated
output
8 RT Internal oscillator frequency set input
9 RAMP Ramp control signal
10 AGND Analog ground
11 SS Soft-start
12
13, 14
15, 16
OUT
PGND
Output voltage connection
Power ground
IS Current sense
17, 18
SW Switching node
19
PRE
Pre-charge assist for the bootstrap
capacitor
Application Information
Vcc tracks Vin up to 9V. Beyond 9V, Vcc is regulated to
7 Volts. A 0.1uF to 1uF ceramic decoupling capacitor is
required. An external voltage (7.5V – 14V) can be
applied to this pin to reduce internal power dissipation.
If the SD pin voltage is below 0.7V the regulator will be in
a low power state. If the SD pin voltage is between 0.7V
and 1.225V the regulator will be in standby mode. If the
SD pin voltage is above 1.225V the regulator will be
operational. An external voltage divider can be used to
set a line undervoltage shutdown threshold. If the SD pin
is left open circuit, a 5µA pull-up current source
configures the regulator fully operational.
Nominal operating range: 7V to 42V
The internal oscillator can be synchronized to an external
clock with an external pull-down device. Multiple
LM25005 devices can be synchronized together by
connection of their SYNC pins.
The loop compensation network should be connected
between this pin and the FB pin.
This pin is connected to the inverting input of the internal
error amplifier. The regulation threshold is 1.225V.
The internal oscillator is set with a single resistor,
connected between this pin and the AGND pin. The
recommended frequency range is 50KHz to 500KHz.
An external capacitor connected between this pin and the
AGND pin sets the ramp slope used for current mode
control. Recommended capacitor range 50pF to 2000pF.
Internal reference for the regulator control functions
An external capacitor and an internal 10µA current
source set the time constant for the rise of the error amp
reference. The SS pin is held low during standby, Vcc
UVLO and thermal shutdown.
Connect directly to the regulated output voltage.
Low side reference for the PRE switch and the IS sense
resistor.
Current measurement connection for the re-circulating
diode. An internal sense resistor and a sample/hold
circuit sense the diode current near the conclusion of the
off-time. This current measurement provides the DC level
of the emulated current ramp.
The source terminal of the internal buck switch. The SW
pin should be connected to the external Schottky diode
and to the buck inductor.
This open drain output can be connected to SW pin to
aid charging the bootstrap capacitor during very light load
conditions or in applications where the output may be
pre-charged before the LM25005 is enabled. An internal
pre-charge MOSFET is turned on for 250ns each cycle
just prior to the on-time interval of the buck switch.
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STEP-DOWN SWITCHING REGULATOR

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Pin Descriptions (Continued)
Pin(S)
20
Name
BST
Description
Boost input for bootstrap capacitor
NA EP Exposed Pad
Application Information
An external capacitor is required between the BST and
the SW pins. A 0.022µF ceramic capacitor is
recommended. The capacitor is charged from Vcc via an
internal diode during the off-time of the buck switch.
Exposed metal pad on the underside of the device. It is
recommended to connect this pad to the PWB ground
plane, in order to aid in heat dissipation.
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STEP-DOWN SWITCHING REGULATOR

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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 GND
BST to GND
PRE to GND
SW to GND (Steady State)
BST to VCC
VCC to GND
BST to SW
45V
60V
45V
-1.5V
45V
14V
14V
OUT to GND
SD, SYNC, SS, FB to GND
ESD Rating (Note 2)
Human Body Model
Storage Temperature Range
Limited to Vin
7V
2kV
-65˚C to +150˚C
Operating Ratings (Note 1)
VIN
Operation Junction Temperature
7V to 42V
−40˚C to + 125˚C
Electrical Characteristics Specifications with standard typeface are for TJ = 25˚C, and those with boldface
type apply over full Operating Junction Temperature range. VIN = 24V, RT = 32.4kunless otherwise stated. (Note 3)
Symbol
Parameter
STARTUP REGULATOR
VccReg Vcc Regulator Output
Vcc LDO Mode turn-off
Vcc Current Limit
VCC SUPPLY
Vcc UVLO Threshold
Vcc Undervoltage Hysteresis
Bias Current (Iin)
Shutdown Current (Iin)
SHUTDOWN THRESHOLDS
Shutdown Threshold
Shutdown Hysteresis
Standby Threshold
Standby Hysteresis
SD Pull-up Current Source
SWITCH CHARACTERSICS
Buck Switch Rds(on)
BOOST UVLO
BOOST UVLO Hysteresis
Pre-charge Switch Rds(on)
Pre-charge Switch on-time
CURRENT LIMIT
Cycle by Cycle Current Limit
Cycle by Cycle Current Limit Delay
SOFT-START
SS Current Source
OSCILLATOR
Frequency1
Frequency2
SYNC Source Impedance
SYNC Sink Impedance
SYNC Threshold (falling)
Upper SYNC Frequency
SYNC Pulse Width Minimum
Conditions
Vcc = 0V
(Vcc increasing)
FB = 1.3V
SD = 0V
(SD Increasing)
(Standby Increasing)
RAMP = 0V
RAMP = 2.5V
RT = 11k
Min Typ
6.85
7.15
9
20
5.95
6.35
1
3
50
0.5
1.18
0.7
0.1
1.225
0.1
5
160
3.8
0.56
75
275
3 3.5
100
7 10
180 200
425 485
10
160
1.4
15
Max
7.45
6.75
4.5
85
0.9
1.27
320
4.25
14
220
525
550
Units
V
V
mA
V
V
mA
µA
V
V
V
V
µA
m
V
V
ns
A
ns
µA
KHz
KHz
k
V
KHz
ns
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LM25005 datasheets pdf
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