June 2, 2008
36V, 3A PowerWise® Synchronous Buck Regulator with
The LM20333 is a full featured synchronous buck regulator
capable of delivering up to 3A of load current. The current
mode control loop is externally compensated with only two
components, offering both high performance and ease of use.
The device is optimized to work over the input voltage range
of 4.5V to 36V making it well suited for high voltage systems.
The device features internal Over Voltage Protection (OVP)
and Over Current Protection (OCP) circuits for increased sys-
tem reliability. A precision Enable pin and integrated UVLO
allows the turn on of the device to be tightly controlled and
sequenced. Startup inrush currents are limited by both an in-
ternally fixed and externally adjustable soft-start circuit. Fault
detection and supply sequencing are possible with the inte-
grated power good (PGOOD) circuit.
The LM20333 is designed to work well in multi-rail power
supply architectures. The output voltage of the device can be
configured to track a higher voltage rail using the SS/TRK pin.
If the output of the LM20333 is pre-biased at startup it will not
sink current to pull the output low until the internal soft-start
ramp exceeds the voltage at the feedback pin.
The switching frequency of the LM20333 can be synchro-
nized to an external clock by use of the SYNC pin. The SYNC
pin is capable of synchronizing to input signals ranging from
250 kHz to 1.5 MHz.
The LM20333 is offered in an exposed pad 20-pin eTSSOP
package that can be soldered to the PCB, eliminating the
need for bulky heatsinks.
■ 4.5V to 36V input voltage range
■ 3A output current, 5.2A peak current
■ 130 mΩ/110 mΩ integrated power MOSFETs
■ 94% peak efficiency with synchronous rectification
■ 1.5% feedback voltage accuracy
■ Current mode control, selectable compensation
■ Oscillator synchronization from 250kHz to 1.5MHz
■ Adjustable output voltage down to 0.8V
■ Compatible with pre-biased loads
■ Programmable soft-start with external capacitor
■ Precision enable pin with hysteresis
■ OVP, UVLO inputs and PGOOD output
■ Internally protected with peak current limit, thermal
shutdown and restart
■ Accurate current limit minimizes inductor size
■ Non-linear current mode slope compensation
■ eTSSOP-20 exposed pad package
■ Simple to design, high efficiency point of load regulation
from a 4.5V to 36V bus
■ High Performance DSPs, FPGAs, ASICs and
■ Communications Infrastructure, Automotive
Simplified Application Circuit
PowerWise® is a registered trademark of National Semiconductor Corporation.
© 2008 National Semiconductor Corporation 300516
NSC Package Drawing
73 Units per Rail
250 Units per Tape and Reel
2500 Units per Tape and Reel
SS/TRK Soft-Start or Tracking control input
An internal 4.5 µA current source charges an external capacitor to set
the soft-start rate. The PWM can track to an external voltage ramp with
a low impedance source. If left open, an internal 1 ms SS ramp is
FB Feedback input to the error amplifier This pin is connected to the inverting input of the internal
from the regulated output
transconductance error amplifier. An 800 mV reference is internally
connected to the non-inverting input of the error amplifier.
PGOOD Power good output signal
Open drain output indicating the output voltage is regulating within
tolerance. A pull-up resistor of 10 kΩ to 100 kΩ is recommended if this
function is used.
COMP Output of the internal error amplifier and The loop compensation network should be connected between the
input to the Pulse Width Modulator
COMP pin and the AGND pin.
VIN Input supply voltage
Nominal operating range: 4.5V to 36V.
SW Switch pin
The drain terminal of the internal Synchronous Rectifier power
NMOSFET and the source terminal of the internal Control power
Internal reference for the power MOSFETs.
AGND Analog ground
Internal reference for the regulator control functions.
BOOT Boost input for bootstrap capacitor
An internal diode from VCC to BOOT charges an external capacitor
required from SW to BOOT to power the Control MOSFET gate driver.
Output of the high voltage linear
VCC tracks VIN up to about 7.2V. Above VIN = 7.2V, VCC is regulated
regulator. The VCC voltage is regulated to approximately 5.5 Volts. A 0.1 µF to 1 µF ceramic decoupling
to approximately 5.5V.
capacitor is required. The VCC pin is an output only.
EN Enable or UVLO input
An external voltage divider can be used to set the line undervoltage
lockout threshold. If the EN pin is left unconnected, a 2 µA pull-up
current source pulls the EN pin high to enable the regulator.
SYNC Frequency synchronization input
An external clock connected to this pin will set the switching frequency.
If left open the device will operate at approximately 200 kHz.
Exposed Exposed pad
Exposed metal pad on the underside of the package with a weak
electrical connection to GND. Connect this pad to the PC board ground
plane in order to improve heat dissipation.
wwAwb.DsatoaSlhueette4UM.coamximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
VCC to GND
Human Body Model (Note 2)
-0.3V to +8V
-65°C to 150°C
VIN to GND
BOOT to GND
BOOT to SW
SW to GND
SW to GND (Transient)
FB, EN, SS/TRK, COMP,
SYNC, PGOOD to GND
-0.3V to +38V
-0.3V to +43V
-0.3V to +7V
-0.5V to +38V
-1.5V (< 20 ns)
-0.3V to +6V
VIN to GND
+4.5V to +36V
−40°C to + 125°C
Electrical Characteristics Unless otherwise stated, the following conditions apply: VVIN = 12V. Limits in standard
type are for TJ = 25°C only, limits in bold face type apply over the junction temperature (TJ) range of -40°C to +125°C. Minimum
and maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely
parametric norm at TJ = 25°C, and are provided for reference purposes only.
Min Typ Max Units
Feedback Pin Voltage
High-Side MOSFET On-Resistance
Low-Side MOSFET On-Resistance
Operating Quiescent Current
Shutdown Quiescent Current
VIN Under Voltage Lockout
VIN Under Voltage Lockout Hysteresis
Soft-Start Pin Source Current
Soft-Start/Track Pin Accuracy
BOOT Diode Leakage
BOOT Diode Forward Voltage
VVIN = 4.5V to 36V
ISW = 3A
ISW = 3A
VVIN = 4.5V to 36V
VEN = 0V
IVCC = -5 mA, VEN = 5V
VSS = 0V
VSS = 0.4V
VBOOT = 4V
IBOOT = -100 mA
Over Voltage Protection Rising Threshold
Over Voltage Protection Hysteresis
PGOOD Threshold, VOUT Rising
PGOOD Low Sink Current
PGOOD High Leakage Current
VFB(OVP) / VFB
ΔVFB(OVP) / VFB
VFB(PG) / VFB
ΔVFB(PG) / VFB
VPGOOD = 0.5V
VPGOOD = 5V
107 110 112 %
93 95 97 %
5 200 nA
Maximum SYNC Frequency
Minimum SYNC Frequency
VIH_SYNC SYNC pin Logic High
VIL_SYNC SYNC pin Logic Low
SYNC pin input leakage
Minimum Off Time
VSYNC = 0V
VSYNC = 5V
ILOAD = 3A
160 200 240 kHz
Feedback Pin Bias Current
COMP Output Source Current
ICOMP(SNK) COMP Output Sink Current
VFB = 1V
VFB = 0V
VCOMP = 0V
VFB = 1.6V
VCOMP = 1.6V
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