National Semiconductor LM3224 Technical data
LM3224
615kHz/1.25MHz Step-up PWM DC/DC Converter
LM3224 615kHz/1.25MHz Step-up PWM DC/DC Converter
December 2004
General Description
The LM3224 is a step-up DC/DC converter with a 0.15Ω
(typ.), 2.45A (typ.) internal switch and pin selectable operating frequency. With the ability to convert 3.3V to multiple
outputs of 8V, -8V, and 23V, the LM3224 is an ideal part for
biasing TFT displays. With the high current switch it is also
ideal for driving high current white LEDs for flash applications. The LM3224 can be operated at switching frequencies
of 615kHz and 1.25MHz allowing for easy filtering and low
noise. An external compensation pin gives the user flexibility
in setting frequency compensation, which makes possible
the use of small, low ESR ceramic capacitors at the output.
An external soft-start pin allows the user to control the
amount of inrush current during start up. The LM3224 is
available in a low profile 8-lead MSOP package.
Typical Application Circuit
Features
n Operating voltage range of 2.7V to 7V
n 615kHz/1.25MHz pin selectable frequency operation
n Over temperature protection
n Optional soft-start function
n 8-Lead MSOP package
Applications
n TFT Bias Supplies
n Handheld Devices
n Portable Applications
n GSM/CDMA Phones
n Digital Cameras
n White LED Flash/Torch Applications
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© 2004 National Semiconductor Corporation DS200976 www.national.com
Connection Diagram
LM3224
Top View
8-Lead Plastic MSOP
NS Package Number MUA08A
20097604
Ordering Information
Order Number Spec. Package
Type
LM3224MM-ADJ MSOP-8 MUA08A 1000 Units, Tape and
LM3224MMX-ADJ MSOP-8 MUA08A 3500 Units, Tape and
LM3224MM-ADJ NOPB MSOP-8 MUA08A 1000 Units, Tape and
LM3224MMX-ADJ NOPB MSOP-8 MUA08A 3500 Units, Tape and
NSC Package
Drawing
Supplied As Package Top Mark
Reel
Reel
Reel
Reel
Pin Description
Pin Name Function
1V
2 FB Output voltage feedback input.
3 SHDN
4 GND Analog and power ground.
5 SW Power switch input. Switch connected between SW pin and GND pin.
6V
7 FSLCT Switching frequency select input. V
8 SS Soft-start Pin.
C
IN
Compensation network connection. Connected to the output of the voltage error amplifier.
Shutdown control input, active low. This pin has an internal pulldown resistor so the
default condition is off. The pin must be pulled high to turn on the device.
Analog power input.
= 1.25MHz. Ground = 615kHz.
IN
SEKB
SEKB
SEKB
SEKB
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Block Diagram
LM3224
General Description
The LM3224 utilizes a PWM control scheme to regulate the
output voltage over all load conditions. The operation can
best be understood referring to the block diagram and Figure
1 of the Operation section. At the start of each cycle, the
oscillator sets the driver logic and turns on the NMOS power
device conducting current through the inductor, cycle 1 of
Figure 1 (a). During this cycle, the voltage at the V
controls the peak inductor current. The V
voltage will in-
C
crease with larger loads and decrease with smaller. This
voltage is compared with the summation of the SW voltage
and the ramp compensation. The ramp compensation is
used in PWM architectures to eliminate the sub-harmonic
oscillations that occur during duty cycles greater than 50%.
Once the summation of the ramp compensation and switch
voltage equals the V
voltage, the PWM comparator resets
C
the driver logic turning off the NMOS power device. The
pin
C
20097603
inductor current then flows through the schottky diode to the
load and output capacitor, cycle 2 of Figure 1 (b). The NMOS
power device is then set by the oscillator at the end of the
period and current flows through the NMOS power device
once again.
The LM3224 has dedicated protection circuitry running during normal operation to protect the IC. The Thermal Shutdown circuitry turns off the NMOS power device when the
die temperature reaches excessive levels. The UVP comparator protects the NMOS power device during supply
power startup and shutdown to prevent operation at voltages
less than the minimum input voltage. The OVP comparator is
used to prevent the output voltage from rising at no loads
allowing full PWM operation over all load conditions. The
LM3224 also features a shutdown mode decreasing the
supply current to 0.1µA (typ.).
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
LM3224
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
V
IN
SW Voltage 21V
7.5V
Vapor Phase (60 sec.) 215˚C
Infrared (15 sec.) 220˚C
ESD Susceptibility
(Note 5)
Human Body Model 2kV
Machine Model 200V
FB Voltage (Note 2) 7V
V
Voltage (Note 3) 1.26V±0.3V
C
SHDN Voltage
7.5V
FSLCT 7.5V
Maximum Junction
150˚C
Temperature
Power Dissipation(Note 4) Internally Limited
Lead Temperature 300˚C
Operating Conditions
Operating Junction
Temperature Range (Note 6) −40˚C to +125˚C
Storage Temperature −65˚C to +150˚C
Supply Voltage 2.7V to 7V
Maximum Output Voltage 20V
Electrical Characteristics
Specifications in standard type face are for TJ= 25˚C and those with boldface type apply over the full Operating Temperature Range (T
Symbol Parameter Conditions
I
Q
V
FB
I
(Note 8) Switch Current Limit VIN= 2.7V (Note 9) 2.45
CL
%V
/∆VINFeedback Voltage Line
FB
I
B
I
SS
V
SS
V
IN
g
m
A
V
D
MAX
f
S
I
SHDN
I
L
R
DSON
Th
SHDN
UVP On Threshold 2.3 2.5 V
Note 1: Absolute maximum ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions for which the device is intended to
be functional, but device parameter specifications may not be guaranteed. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: The FB pin should never exceed V
Note 3: Under normal operation the V
however the V
Note 4: The maximum allowable power dissipation is a function of the maximum junction temperature, T
and the ambient temperature, T
Exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown.
= −40˚C to +125˚C). VIN= 2.7V, FSLCT = SHDN = VIN, and IL= 0A, unless otherwise specified.
J
Min
(Note 6)
Typ
(Note 7)
Max
(Note 6)
Quiescent Current FB = 2V (Not Switching) 1.3 2.0 mA
V
= 0V 0.1 2.0 µA
SHDN
Feedback Voltage 1.2285 1.26 1.2915 V
Regulation
FB Pin Bias Current (Note
10)
= 3V, V
IN
V
= 3V, V
IN
2.7V ≤ VIN≤ 7V
= 8V 2.1
OUT
= 5V 2.2
OUT
0.085 0.15 %/V
35 250 nA
SS Pin Current 7.5 11 13 µA
SS Pin Voltage 1.2090 1.2430 1.2622
Input Voltage Range 2.7 7 V
Error Amp Transconductance ∆I = 5µA 40 87 135 µmho
Error Amp Voltage Gain 78 V/V
Maximum Duty Cycle 85 92.5 %
Switching Frequency FSLCT = Ground 450 615 750 kHz
Shutdown Pin Current V
FSLCT = V
SHDN
V
SHDN
IN
= 2.7V 2.4 5.0 µA
= 0.3V 0.3 1.2
0.9 1.25 1.5 MHz
Switch Leakage Current VSW= 20V 0.2 8.0 µA
Switch R
DSON
VIN= 2.7V, ISW= 1A 0.15 0.4 Ω
Shutdown Threshold Output High 1.2 0.8 V
Output Low 0.8 0.3 V
Off Threshold 2.6 2.7 V
.
IN
pin may go to voltages above this value. This maximum rating is for the possibility of a voltage being applied to the pin,
pin should never have a voltage directly applied to it.
C
C
(MAX), the junction-to-ambient thermal resistance, θJA,
. The maximum allowable power dissipation at any ambient temperature is calculated using: PD(MAX) = (T
A
J
J(MAX)−TA
Units
AV
)/θJA.
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Electrical Characteristics (Continued)
Note 5: The human body model is a 100 pF capacitor discharged through a 1.5kΩ resistor into each pin. The machine model is a 200pF capacitor discharged
directly into each pin.
Note 6: All limits guaranteed at room temperature (standard typeface) and at temperature extremes (bold typeface). All room temperature limits are 100%
production 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 7: Typical numbers are at 25˚C and represent the most likely norm.
Note 8: Duty cycle affects current limit due to ramp generator.
Note 9: Current limit at 0% duty cycle. See TYPICAL PERFORMANCE section for Switch Current Limit vs. V
Note 10: Bias current flows into FB pin.
IN
Typical Performance Characteristics
SHDN Pin Current vs. SHDN Pin Voltage SS Pin Current vs. Temperature
LM3224
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FSLCT Pin Current vs. FSLCT Pin Voltage FB Pin Current vs. Temperature
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Typical Performance Characteristics (Continued)
LM3224
NMOS R
vs. Input Voltage 615kHz Non-switching IQvs. Input Voltage
DSON
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1.25MHz Non-switching IQvs. Input Voltage 615kHz Switching IQvs. Input Voltage
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1.25MHz Switching IQvs. Input Voltage 615kHz Switching IQvs. Temperature
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