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LM20242 Datasheet

2A PowerWise Adjustable Frequency Synchronous Buck Regulator

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November 1, 2007
LM20242
36V, 2A PowerWise® Adjustable Frequency Synchronous
Buck Regulator
General Description
The LM20242 is a full featured 1MHz capable synchronous
buck regulator capable of delivering up to 2A of load current.
The current mode control loop is externally compensated with
only two external components, offering both high perfor-
mance 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 PGOOD circuit.
The LM20242 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 LM20242 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 LM20242 is offered in an exposed pad 20 pin TSSOP
package that can be soldered to the PCB, eliminating the
need for bulky heatsinks.
Features
2A Output Current, 3.7A peak current
130 m/110 mintegrated power MOSFETs
1.5% output voltage accuracy
Current Mode Control, selectable compensation
Resistor programmed, 1MHz capable oscillator
Synchronous rectifier with diode emulation
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 with frequency foldback
Non-linear current mode slope compensation
eTSSOP-20 exposed pad package
Applications
Simple to design, high efficiency point of load regulation
from a 4.5V to 36V bus
High Performance DSPs, FPGAs, ASICs and
Microprocessors
Communications Infrastructure, Automotive
Simplified Application Circuit
PowerWise® is a registered trademark of National Semiconductor Corporation.
© 2007 National Semiconductor Corporation 300314
30031401
www.national.com


National Semiconductor Electronic Components Datasheet

LM20242 Datasheet

2A PowerWise Adjustable Frequency Synchronous Buck Regulator

No Preview Available !

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Connection Diagram
Ordering Information
Order Number
LM20242MH
LM20242MHE
LM20242MHX
Package Type
eTSSOP-20
Top View
30031402
eTSSOP-20 Package
NSC Package Drawing
MXA20A
Package Marking
20242MH
Supplied As
73 Units per Rail
250 Units per Tape and Reel
2500 Units per Tape and Reel
Pin Descriptions
Pin(s)
1
2
3
4
5,6,15,16
7,8,13,14
9,10,11
12
17
18
19
20
EP
Name Description
Application Information
SS/TRK Soft-Start or Tracking control input
An internal 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 activated.
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 kto 100 kis 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
NMOSFET.
GND Ground
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.
VCC
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.
RT Internal oscillator frequency adjust input Normally biased at 550 mV. An external resistor connected between
RT and AGND sets the internal oscillator frequency.
Exposed Exposed pad
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.
www.national.com
2


Part Number LM20242
Description 2A PowerWise Adjustable Frequency Synchronous Buck Regulator
Maker National Semiconductor
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LM20242 Datasheet PDF






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