LM3075
High Efficiency, Synchronous Current Mode Buck
Controller
General Description
The LM3075 is a current mode control, synchronous buck
controller IC. Use of synchronous rectification and pulse-
skipping operation at light load achieves high efficiency over
a wide load range. Fixed frequency operation can be ob-
tained by disabling the pulse-skipping mode. Current mode
control assures excellent line and load regulation and a wide
loop bandwidth for fast response to load transients.
Current mode control can be achieved by either sensing
across the high side NFET or a sense resistor. The switching
frequency can be selected as either 200 kHz or 300 kHz
from an internal clock.
The LM3075 is available with an adjustable output in a
TSSOP-20 package.
Features
n
Input voltage range of 4.5V-36V
n
Current Mode Control
n
Skip mode operation available
n
Cycle by cycle current limit
n
1.24V
2% Reference
Applications
n
Automotive Power Supplies
n
Distributed Power Systems
Typical Application Circuit
20162301
September 2005
LM3075
High
Efficiency
,
Synchronous
Current
Mode
Buck
Controller
2005 National Semiconductor Corporation
DS201623
www.national.com
Connection Diagram
TOP VIEW
20162302
20-Lead TSSOP (MTC)
Ordering Information
Order Number
Package Type
NSC Package Drawing
Supplied As
LM3075MTC
TSSOP-20
MTC-20
73 Units per Anti-Static Tube
LM3075MTCX
TSSOP-20
MTC-20
2500 Units on Tape and Reel
Pin Descriptions
LM3075 Pin #
Name
Function
1
VLIN5
5V linear regulator output
2
VIN
Input voltage supply
3
EXT
External power connection for VLIN5
4
FS
Frequency select
5
EN
Enable pin
6
FB
Feedback pin
7
FPWM
Forced PWM selection
8
COMP
Compensation pin
9
SS
Output enable / soft-start pin
10
AGND
Analog ground
11
PGND
Power ground
12
LDRV
Low side gate drive
13
VDD
Low side gate drive supply
14
CBOOT
Bootstrap capacitor connection
15
HDRV
High side gate drive
16
SW
Switch node
17
CSL
Current sense low
18
CSH
Current sense high
19
ILIM
Current limit threshold adjustment
20
PGOOD
Power good flag
LM3075
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2
Absolute Maximum Ratings
(Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Voltages from the indicated pins to GND:
VIN, ILIM, CSH
-0.3V to 38V
SW, CSL
-0.3 to (V
IN
+ 0.3V)
PGOOD, FB, VDD, EXT, EN
-0.3V to +7V
COMP, SS, FPWM, FS
-0.3V to (V
LIN5
+0.3)V
CBOOT
-0.3V to +43V
CBOOT to SW
-0.3V to 7V
LDRV
-0.3V to (V
DD
+0.3V)
HDRV to SW
-0.3V
HDRV to CBOOT
+0.3V
Storage Temperature Range
-65C to +150C
Junction Temperature
150C
Lead Temperature (Soldering, 10
sec)
260C
ESD Rating (Note 2)
1.5kV
Operating Ratings
(Note 1)
Junction Temperature
-40C to +125C
VIN to GND
4.5V to 36V
EXT
6V Max
Electrical Characteristics
Limits in standard type are for T
J
= 25C only, and limits in boldface type apply
over the junction temperature T
J
range of -40C to +125C. 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 specified V
IN
= 12V.
Symbol
Parameter
Conditions
Min
Typ
Max
Unit
V
FB
Feedback pin voltage
V
IN
= 4.5V to 36V
1.213
1.238
1.259
V
Load Regulation
V
COMP
= 0.5V to 1.5V
0.04
%
Line Regulation
V
IN
= 4.5V to 36V
0.04
%
I
Q
Operating Quiescent current V
IN
= 4.5V to 36V
1.0
2
mA
I
SD
Shutdown Quiescent current V
EN
= 0V
60
100
A
V
LIN5
V
LIN5
Output Voltage
I
VLIN5
= 0 to 25mA
V
V
IN
= 5.5V to 36V
4.7
5
5.3
V
UVLO
V
LIN5
Under Voltage
Lockout
3.7
3.9
4.1
V
V
UVLO_HYS
V
LIN5
Under Voltage
Lockout Hysteresis
0.2
V
V
CL_OS
Current Limit Comparator
Offset
(V
ILIM
V
CSL
)
0.2
mV
I
ILIM
I
LIM
sink current
8.3
10
11.3
A
I
SS_SRC
Soft-Start Pin Source
Current
V
SS
= 1.2V
1
2
3
A
I
SS_SNK
Soft-Start Pin Sink Current
V
SS
= 2V
4
A
V
SS_TO
Soft-Start Timeout
Threshold
2
V
V
OVP
Over Voltage Protection
Rising Threshold
With respect to V
FB
105
111
117
%
V
OVP_HYS
Over Voltage Protection
Hysteresis
With respect to V
FB
2.8
%
POWERGOOD
V
PWR_GOOD
PGOOD Rising Threshold
92.5
95.5
98.5
%
V
PWR_BAD
PGOOD Falling Threshold
87
90.5
95
%
T
PGOOD
PGOOD delay
PGOOD pin de-asserting
10
s
I
OL
PGOOD Low Sink Current
V
PGOOD
= 0.4V
0.6
1
mA
I
OH
PGOOD High Leakage
Current
V
PGOOD
= 5V
5
200
nA
GATE DRIVE
LM3075
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Electrical Characteristics
Limits in standard type are for T
J
= 25C only, and limits in boldface type apply
over the junction temperature T
J
range of -40C to +125C. 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 specified V
IN
= 12V. (Continued)
Symbol
Parameter
Conditions
Min
Typ
Max
Unit
I
CBOOT
C
BOOT
Leakage Current
V
CBOOT
= 7V
10
nA
R
ds_on 1
HDRV FET driver pull-up
On resistance
2.9
R
ds_on 2
HDRV FET driver pull-down
On resistance
1.7
R
ds_on 3
LDRV FET driver pull-up On
resistance
2.4
R
ds_on 4
LDRV FET driver pull-down
On resistance
0.8
OSCILLATOR
f
OSC
Oscillator Frequency
V
FS
= 5V
255
300
330
kHz
V
FS
= 0V
165
200
215
D
MAX
Maximum Dutycycle
V
FB
= 1V
95.5
98
%
T
ON_MIN
Minimum On Time
180
260
ns
ERROR AMPLIFIER
I
FB
Feedback pin bias current
V
FB
= 1.5V
50
nA
I
COMP_SRC
COMP Output Source
Current
V
FB
= 1V
V
COMP
= 1V
120
A
I
COMP_SNK
COMP Output Sink Current
V
FB
= 1.5V
V
COMP
= 0.5V
110
A
Gm
Error Amplifier
Transconductance
620
mho
A
VOL
Error Amplifier Voltage Gain
1250
V/V
V
SL
Slope Compensation
(referred to the internal
summing node)
V
FS
= 0V
0.051
V/s
V
FS
= 5V
0.076
A
CS
Current Sense Amplifier
Gain
V
COMP
= 1.25V
4
5
6
V/V
LOGIC
V
IL
FS, /FPWM Pin Maximum
Low Level Input Level
0.8
V
V
IH
FS, /FPWM Pin Minimum
High Level Input Level
2
V
THERMAL SHUTDOWN
T
SD
Thermal Shutdown
160
C
T
SD_HYS
Thermal Shutdown
Hysteresis
10
C
EXT
R
EXT
EXT pin on resistance
V
EXT
= 5V
I
VLIN5
= 50 mA
4
TH
EXT
VLIN5 to EXT Switch Over
Rising Threshold
4.6
V
LM3075
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Electrical Characteristics
Limits in standard type are for T
J
= 25C only, and limits in boldface type apply
over the junction temperature T
J
range of -40C to +125C. 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 specified V
IN
= 12V. (Continued)
Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Operating Range indicates conditions for which the device is
intended to be functional, but does not guarantee specfic performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics.
The guaranteed specifications apply only for the test conditions. Some performance characteristics may degrade when the device is not operated under the listed
test conditions.
Note 2: For testing purposes, ESD was applied using the human-body model, a 100pF capacitor discharged through a 1.5k
resistor.
LM3075
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