LM5005
High Voltage 2.5 Amp Buck Regulator
General Description
The LM5005 high voltage switching regulator features all of
the functions necessary to implement an efficient high volt-
age buck regulator using a minimum of external compo-
nents. This easy to use regulator includes a 75V N-Channel
buck switch 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 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 LM5005 regulators to self-synchronize or to be syn-
chronized to an external clock. Additional protection features
include: current limit, thermal shutdown and remote shut-
down 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 75V, 2.5A N-Channel Buck Switch
n
Ultra-wide input voltage range from 7V to 75V
n
Internal high voltage 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
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TSSOP-20EP (Exposed Pad)
Simplified Application Schematic
20161901
September 2005
LM5005
High
V
oltage
2.5
Amp
Buck
Regulator
2005 National Semiconductor Corporation
DS201619
www.national.com
Pin Descriptions
Pin(S)
Name
Description
Application Information
1
VCC
Output of the bias regulator
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.
2
SD
Shutdown or UVLO input
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 5A pull-up current source
configures the regulator fully operational.
3, 4
Vin
Input supply voltage
Nominal operating range: 7V to 75V
5
SYNC
Oscillator synchronization input or
output
The internal oscillator can be synchronized to an external
clock with an external pull-down device. Multiple LM5005
devices can be synchronized together by connection of
their SYNC pins.
6
COMP
Output of the internal error amplifier
The loop compensation network should be connected
between this pin and the FB pin.
7
FB
Feedback signal from the regulated
output
This pin is connected to the inverting input of the internal
error amplifier. The regulation threshold is 1.225V.
8
RT
Internal oscillator frequency set input
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.
9
RAMP
Ramp control signal
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.
10
AGND
Analog ground
Internal reference for the regulator control functions
11
SS
Soft-start
An external capacitor and an internal 10A 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.
12
OUT
Output voltage connection
Connect directly to the regulated output voltage.
13, 14
PGND
Power ground
Low side reference for the PRE switch and the IS sense
resistor.
15, 16
IS
Current sense
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.
17, 18
SW
Switching node
The source terminal of the internal buck switch. The SW
pin should be connected to the external Schottky diode
and to the buck inductor.
19
PRE
Pre-charge assist for the bootstrap
capacitor
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 LM5005 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.
LM5005
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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.
V
IN
to GND
76V
BST to GND
90V
PRE to GND
76V
SW to GND (Steady State)
-1.5V
BST to V
CC
76V
V
CC
to GND
14V
BST to SW
14V
OUT to GND
Limited to Vin
SD, SYNC, SS, FB to GND
8V
ESD Rating (Note 2)
Human Body Model
2kV
Storage Temperature Range
-65C to +150C
Operating Ratings
(Note 1)
V
IN
7V to 75V
Operation Junction Temperature
-40C to + 125C
Electrical Characteristics
Specifications with standard typeface are for T
J
= 25C, and those with boldface
type apply over full Operating Junction Temperature range. V
IN
= 48V, R
T
= 32.4k
unless otherwise stated .
Symbol
Parameter
Conditions
Min
Typ
Max
Units
STARTUP REGULATOR
VccReg
Vcc Regulator Output
6.85
7.15
7.45
V
Vcc LDO Mode turn-off
9
V
Vcc Current Limit
Vcc = 0V
20
mA
VCC SUPPLY
Vcc UVLO Threshold
(Vcc increasing)
5.95
6.35
6.75
V
Vcc Undervoltage Hysteresis
1
V
Bias Current (Iin)
FB = 1.3V
5
mA
Shutdown Current (Iin)
SD = 0V
60
100
A
SHUTDOWN THRESHOLDS
Shutdown Threshold
0.5
0.7
0.9
V
Shutdown Hysteresis
0.1
V
Standby Threshold
1.18
1.225
1.27
V
Standby Hysteresis
0.1
V
SD Pull-up Current Source
5
A
SWITCH CHARACTERSICS
Buck Switch Rds(on)
160
320
m
BOOST UVLO
3.8
V
BOOST UVLO Hysteresis
0.56
V
Pre-charge Switch Rds(on)
75
Pre-charge Switch on-time
275
ns
CURRENT LIMIT
Cycle by Cycle Current Limit
RAMP = 0V
3
3.5
4.25
A
Cycle by Cycle Current Limit Delay
RAMP = 2.5V
100
ns
SOFT-START
SS Current Source
7
10
13
A
OSCILLATOR
Frequency1
180
200
220
KHz
Frequency2
RT = 11k
425
485
525
KHz
SYNC Source Impedance
10
k
SYNC Sink Impedance
160
SYNC Threshold (falling)
1.4
V
SYNC Frequency Range
550
KHz
SYNC Pulse Width Minimum
15
ns
LM5005
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