NSC LM3478MWC, LM3478MMX, LM3478MM, LM3478MDC, LM3478EVAL Datasheet
LM3478
High Efficiency Low-Side N-Channel Controller for
Switching Regulator
General Description
The LM3478 is a versatile Low-Side N-FET switching regulator controller. It is suitable for use in topologies requiring
low side FET, such as boost, flyback, SEPIC, etc. Moreover,
the LM3478 can be operated at extremely high switching
frequency in order to reduce the overall solution size. The
switching frequency of LM3478 can be adjusted to any value
between 100kHz and 1MHz by using a single external resistor. Current mode control provides superior bandwidth and
transient response, besides cycle-by-cycle current limiting.
Output current can be programmed with a single external
resistor.
The LM3478 has built in features such as thermal shutdown,
short-circuit protection, over voltage protection, etc. Power
saving shutdown mode reduces the total supply current to
5µA and allows power supply sequencing. Internal soft-start
limits the inrush current at start-up.
Key Specifications
n Wide supply voltage range of 2.97V to 40V
n 100kHz to 1MHz Adjustable clock frequency
n
±
2.5% (over temperature) internal reference
n 10µA shutdown current (over temperature)
Features
n 8-lead Mini-SO8 (MSOP-8) package
n Internal push-pull driver with 1A peak current capability
n Current limit and thermal shutdown
n Frequency compensation optimized with a capacitor and
a resistor
n Internal softstart
n Current Mode Operation
n Undervoltage Lockout with hysteresis
Applications
n Distributed Power Systems
n Battery Chargers
n Offline Power Supplies
n Telecom Power Supplies
n Automotive Power Systems
Typical Application Circuit
10135501
Typical High Efficiency Step-Up (Boost) Converter
May 2003
LM3478 High Efficiency Low-Side N-Channel Controller for Switching Regulator
© 2003 National Semiconductor Corporation DS101355 www.national.com
Connection Diagram
10135502
8 Lead Mini SO8 Package (MSOP-8 Package)
Package Marking and Ordering Information
Order Number Package Type Package Marking Supplied As:
LM3478MM MSOP-8 S14B 1000 units on Tape and
Reel
LM3478MMX MSOP-8 S14B 3500 units on Tape and
Reel
Pin Description
Pin Name Pin Number Description
I
SEN
1 Current sense input pin. Voltage generated across an external
sense resistor is fed into this pin.
COMP 2 Compensation pin. A resistor, capacitor combination connected to
this pin provides compensation for the control loop.
FB 3 Feedback pin. The output voltage should be adjusted using a
resistor divider to provide 1.26V at this pin.
AGND 4 Analog ground pin.
PGND 5 Power ground pin.
DR 6 Drive pin of the IC. The gate of the external MOSFET should be
connected to this pin.
FA/SD 7 Frequency adjust and Shutdown pin. A resistor connected to this
pin sets the oscillator frequency. A high level on this pin for ≥ 30µs
will turn the device off. The device will then draw less than 10µA
from the supply.
V
IN
8 Power Supply Input pin.
LM3478
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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.
Input Voltage 45V
FB Pin Voltage -0.4V
<
V
FB
<
7V
FA/SD Pin Voltage
-0.4V<V
FA/SD
<
7V
Peak Driver Output Current (
<
10µs) 1.0A
Power Dissipation Internally Limited
Storage Temperature Range −65˚C to +150˚C
Junction Temperature +150˚C
ESD Susceptibilty
Human Body Model (Note 2) 2kV
Lead Temperature
MM Package
Vapor Phase (60 sec.)
Infared (15 sec.)
215˚C
220˚C
DR Pin Voltage −0.4V ≤ VDR ≤ 8V
I
SEN
Pin Voltage 500mV
Operating Ratings (Note 1)
Supply Voltage 2.97V ≤ V
IN
≤ 40V
Junction
Temperature Range −40˚C ≤ TJ≤ +125˚C
Switching Frequency 100kHz ≤ F
SW
≤ 1MHz
Electrical Characteristics
Specifications in Standard type face are for TJ= 25˚C, and in bold type face apply over the full Operating Temperature
Range. Unless otherwise specified, V
IN
= 12V, RFA= 40kΩ
Symbol Parameter Conditions Typical Limit Units
V
FB
Feedback Voltage V
COMP
= 1.4V,
2.97 ≤ V
IN
≤ 40V
1.26
1.2416/1.228
1.2843/1.292
V
V(min)
V(max)
∆V
LINE
Feedback Voltage
Line Regulation
2.97 ≤ VIN≤ 40V 0.001 %/V
∆V
LOAD
Output Voltage Load
Regulation
I
EAO
Source/Sink
±
0.5 %/V (max)
V
UVLO
Input Undervoltage
Lock-out
2.85
2.97
V
V(max)
V
UV(HYS)
Input Undervoltage
Lock-out Hysteresis
170
130
210
mV
mV (min)
mV (max)
F
nom
Nominal Switching
Frequency
RFA= 40KΩ 400
360
430
kHz
kHz(min)
kHz(max)
R
DS1 (ON)
Driver Switch On
Resistance (top)
IDR= 0.2A, VIN=5V 16 Ω
R
DS2 (ON)
Driver Switch On
Resistance (bottom)
IDR= 0.2A 4.5 Ω
V
DR (max)
Maximum Drive
Voltage Swing(Note 6)
V
IN
<
7.2V V
IN
V
V
IN
≥ 7.2V 7.2
D
max
Maximum Duty
Cycle(Note 7)
100 %
T
min
(on) Minimum On Time 325
210
600
nsec
nsec(min)
nsec(max)
I
SUPPLY
Supply Current
(switching)
(Note 9)
2.0
3.0
mA
mA (max)
I
Q
Quiescent Current in
Shutdown Mode
V
FA/SYNC/SD
= 5V (Note
10), V
IN
=5V
5
10
µA
µA (max)
V
SENSE
Current Sense
Threshold Voltage
VIN= 5V 165
140/ 135
195/ 200
mV
mV (min)
mV (max)
LM3478
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Electrical Characteristics (Continued)
Specifications in Standard type face are for TJ= 25˚C, and in bold type face apply over the full Operating Temperature
Range. Unless otherwise specified, V
IN
= 12V, RFA= 40kΩ
Symbol Parameter Conditions Typical Limit Units
V
SC
Short-Circuit Current
Limit Sense Voltage
VIN= 5V 325
235
395
mV
mV (min)
mV (max)
V
SL
Internal Compensation
Ramp Voltage
VIN=5V 92
52
132
mV
mV(min)
mV(max)
V
OVP
Output Over-voltage
Protection (with
respect to feedback
voltage) (Note 8)
V
COMP
= 1.4V 50
32/ 25
78/ 85
mV
mV(min)
mV(max)
V
OVP(HYS)
Output Over-Voltage
Protection
Hysteresis(Note 8)
V
COMP
= 1.4V 60
20
110
mV
mV(min)
mV(max)
Gm Error Ampifier
Transconductance
V
COMP
= 1.4V
I
EAO
= 100µA
(Source/Sink)
800
600/ 365
1000/ 1265
µmho
µmho (min)
µmho (max)
A
VOL
Error Amplifier Voltage
Gain
V
COMP
= 1.4V
I
EAO
= 100µA
(Source/Sink)
38
26
44
V/V
V/V (min)
V/V (max)
I
EAO
Error Amplifier Output
Current (Source/ Sink)
Source, V
COMP
= 1.4V,
V
FB
=0V
110
80/ 50
140/ 180
µA
µA (min)
µA (max)
Sink, V
COMP
= 1.4V, V
FB
= 1.4V
−140
−100/ −85
−180/ −185
µA
µA (min)
µA (max)
V
EAO
Error Amplifier Output
Voltage Swing
Upper Limit
V
FB
=0V
COMP Pin = Floating
2.2
1.8
2.4
V
V(min)
V(max)
Lower Limit
V
FB
= 1.4V
0.56
0.2
1.0
V
V(min)
V(max)
T
SS
Internal Soft-Start
Delay
VFB= 1.2V, V
COMP
=
Floating
4 msec
T
r
Drive Pin Rise Time Cgs = 3000pf, VDR=0to
3V
25 ns
T
f
Drive Pin Fall Time Cgs = 3000pf, VDR=0to
3V
25 ns
VSD Shutdown threshold
(Note 5)
Output = High 1.27
1.35
V
V (max)
Output = Low 0.65
0.35
V
V (min)
I
SD
Shutdown Pin Current VSD=5V −1 µA
V
SD
=0V +1
TSD Thermal Shutdown 165 ˚C
T
sh
Thermal Shutdown
Hysteresis
10 ˚C
θ
JA
Thermal Resistance MM Package 200 ˚C/W
LM3478
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Electrical Characteristics (Continued)
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 100 pF capacitor discharged through a 1.5kΩ resistor into each pin.
Note 3: All limits are guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100%
tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate
Average Outgoing Quality Level (AOQL).
Note 4: Typical numbers are at 25˚C and represent the most likely norm.
Note 5: The FA/SD pin should be pulled to V
IN
through a resistor to turn the regulator off. The voltage on the FA/SD pin must be above the maximum limit for Output
= High to keep the regulator off and must be below the limit for Output = Low to keep the regulator on.
Note 6: The voltage on the drive pin, V
DR
is equal to the input voltage when input voltage is less than 7.2V. VDRis equal to 7.2V when the input voltage is greater
than or equal to 7.2V.
Note 7: The limits for the maximum duty cycle can not be specified since the part does not permit less than 100% maximum duty cycle operation.
Note 8: The over-voltage protection is specified with respect to the feedback voltage. This is because the over-voltage protection tracks the feedback voltage. The
overvoltage protection threshold is given by adding the feedback voltage, V
FB
to the over-voltage protection specification.
Note 9: For this test, the FA/SD pin is pulled to ground using a 40K resistor.
Note 10: For this test, the FA/SD pin is pulled to 5V using a 40K resistor.
Typical Performance Characteristics Unless otherwise specified, V
IN
= 12V, TJ= 25˚C.
I
Q
vs Input Voltage (Shutdown) I
Supply
vs Input Voltage (Non-Switching)
10135503
10135534
I
Supply
vs VIN(Switching) Switching Frequency vs R
FA
10135535
10135504
LM3478
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Typical Performance Characteristics Unless otherwise specified, V
IN
= 12V, TJ= 25˚C. (Continued)
Frequency vs Temperature Drive Voltage vs Input Voltage
10135554
10135505
Current Sense Threshold vs Input Voltage COMP Pin Voltage vs Load Current
10135545
10135562
Efficiency vs Load Current (3.3V In and 12V Out) Efficiency vs Load Current (5V In and 12V Out)
10135559 10135558
LM3478
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Typical Performance Characteristics Unless otherwise specified, V
IN
= 12V, TJ= 25˚C. (Continued)
Efficiency vs Load Current (9V In and 12V Out) Efficiency vs Load Current (3.3V In and 5V Out
10135560
10135553
Error Amplifier Gain Error Amplifier Phase
10135555 10135556
COMP Pin Source Current vs Temperature Short Circuit Sense Voltage vs Input Voltage
10135536
10135557
LM3478
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