NSC LM3103MH, LM3103 Datasheet

October 2007

LM3103
SIMPLE SWITCHER® Synchronous 1MHz 0.75A
Step-Down Voltage Regulator

General Description

The LM3103 Synchronously Rectified Buck Converter fea­tures all required functions to implement a highly efficient and
cost effective buck regulator. It is capable of supplying 0.75A
to loads with an output voltage as low as 0.6V. Dual N-Chan­nel synchronous MOSFET switches allow a low component
count, thus reducing complexity and minimizing board size.

Different from most other COT regulators, the LM3103 does
not rely on output capacitor ESR for stability, and is designed
to work exceptionally well with ceramic and other very low
ESR output capacitors. It requires no loop compensation, re­sults in a fast load transient response and simple circuit
implementation. The operating frequency remains nearly con­stant with line variations due to the inverse relationship be­tween the input voltage and the on-time. The operating
frequency can be externally programmed up to 1 MHz. Pro­tection features include VCC under-voltage lock-out, output
over-voltage protection, thermal shutdown, and gate drive
under-voltage lock-out. The LM3103 is available in the ther­mally enhanced eTSSOP-16 package.

Key Specifications

■

Input voltage range 4.5V-42V

■

0.75A output current

■

0.6V, ±2% reference

■

Integrated dual N-Channel main and synchronous
MOSFETs

■

Thermally enhanced eTSSOP-16 package

Features

■

Low component count and small solution size

■

Stable with ceramic and other low ESR capacitors

■

No loop compensation required

■

High efficiency at a light load by DCM operation

■

Pre-bias startup

■

Ultra-fast transient response

■

Programmable soft-start

■

Programmable switching frequency up to 1 MHz

■

Valley current limit

■

Thermal shutdown

■

Output over-voltage protection

■

Precision internal reference for an adjustable output
voltage down to 0.6V

Typical Applications

■

5VDC, 12VDC, 24VDC, 12VAC, and 24VAC systems

■

Embedded Systems

■

Industrial Control

■

Automotive Telematics and Body Electronics

■

Point of Load Regulators

■

Storage Systems

■

Broadband Infrastructure

■

Direct Conversion from 2/3/4 Cell Lithium Batteries
Systems

Typical Application

30029701

SIMPLE SWITCHER® is a registered trademark of National Semiconductor Corporation

© 2007 National Semiconductor Corporation 300297 www.national.com

LM3103 SIMPLE SWITCHER® Synchronous 1MHz 0.75A Step-Down Voltage Regulator

Connection Diagram

30029702

16-Lead Plastic eTSSOP

NS Package Number MXA16A

Ordering Information

Order Number Package Type NSC Package Drawing Supplied As

LM3103MH Exposed Pad TSSOP-16 MXA16A 92 units per Anti-Static Tube

LM3103MHX 2500 Units on Tape and Reel

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LM3103

Pin Descriptions

Pin Name Description Application Information

1, 2 VIN Input supply voltage Supply pin to the device. Nominal input range is 4.5V to 42V.

3, 4 SW Switch Node Internally connected to the source of the main MOSFET and the drain of the

synchronous MOSFET. Connect to the output inductor.

5 BST Connection for

bootstrap capacitor

Connect a 33 nF capacitor from the SW pin to this pin. This capacitor is charged through
an internal diode during the main MOSFET off-time.

6 AGND Analog Ground Ground for all internal circuitry other than the PGND pin.

7 SS Soft-start A 70 µA internal current source charges an external capacitor of larger than 22 nF to

provide the soft-start function.

8 NC No Connection This pin should be left unconnected.

9, 10 GND Ground Must be connected to the AGND pin for normal operation. The GND and AGND pins

are not internally connected.

11 FB Feedback Internally connected to the regulation and over-voltage comparators. The regulation

setting is 0.6V at this pin. Connect to feedback resistors.

12 EN Enable pin Internal pull-up. Connect to a voltage higher than 1.6V to enable the device.

13 RON On-time Control An external resistor from the VIN pin to this pin sets the main MOSFET on-time.

14 VCC Startup regulator

Output

Nominally regulated to 6V. Connect a capacitor of larger than 1 µF between the VCC
and AGND pins for stable operation.

15, 16 PGND Power Ground Synchronous MOSFET source connection. Tie to a ground plane.

DAP EP Exposed Pad Thermal connection pad. Connect to the ground plane.

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LM3103

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

VIN, RON to AGND -0.3V to 43.5V
SW to AGND -0.3V to 43.5V
SW to AGND (Transient) -2V (< 100ns)
VIN to SW -0.3V to 43.5V
BST to SW -0.3V to 7V
VCC to AGND -0.3V to 7V
FB to AGND -0.3V to 5V

All Other Inputs to AGND -0.3V to 7V
ESD Rating (Note 2)
Human Body Model ±2kV
Storage Temperature Range -65°C to +150°C
Junction Temperature (TJ) 150°C

Operating Ratings (Note 1)

Supply Voltage Range (VIN) 4.5V to 42V
Junction Temperature Range (TJ)

−40°C to +125°C

Thermal Resistance (θJA) (Note 3)

35°C/W

Electrical Characteristics Specifications with standard type are for T

J

= 25°C only; limits in boldface type apply
over the full Operating Junction Temperature (TJ) range. 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. Unless otherwise stated the following conditions apply: VIN = 18V, V

OUT

= 3.3V.

Symbol Parameter Conditions Min Typ Max Units

Start-Up Regulator, V

CC

V

CC

VCC output voltage C

VCC

= 1 µF, no load 5.6 6.0 6.2 V

VIN - V

CC

V

IN

- VCC dropout voltage (Note 4) ICC = 2mA 55 150 mV

ICC = 10mA 235 500

V

CC-UVLO

VCC under-voltage lockout threshold
(UVLO)

VIN increasing 3.5 3.7 4.1 V

V

CC-UVLO-HYS

VCC UVLO hysteresis VIN decreasing 275 mV

I

IN

IIN operating current No switching, VFB = 1V 1.0 1.25 mA

I

IN-SD

IIN operating current, Device shutdown VEN = 0V 20 40 µA

I

VCC

VCC current limit VCC = 0V 20 33 42 mA

Switching Characteristics

R

DS-UP-ON

Main MOSFET R

DS(on)

0.370 0.7

Ω

R

DS- DN-ON

Syn. MOSFET R

DS(on)

0.220 0.4

Ω

Soft-start

I

SS

SS pin source current VSS = 0V 45 70 95 µA

Current Limit

I

CL

Syn. MOSFET current limit threshold 0.9 A

ON/OFF Timer

t

on

ON timer pulse width

VIN = 10V, RON = 33 kΩ

0.350 µs

VIN = 18V, RON = 33 kΩ

0.170

t

on-MIN

ON timer minimum pulse width 100 ns

t

off

OFF timer pulse width 240 ns

Enable Input

V

EN

EN Pin input threshold VEN rising 1.6 1.85 V

V

EN-HYS

Enable threshold hysteresis VEN falling 230 mV

I

EN

Enable Pull-up Current VEN = 0V 1 µA

Regulation and Over-Voltage Comparator

V

FB

In-regulation feedback voltage TJ = −40°C to +125°C 0.588 0.6 0.612 V

V

FB-OV

Feedback over-voltage threshold 0.655 0.680 0.705 V

I

FB

1 nA

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LM3103

Symbol Parameter Conditions Min Typ Max Units

Thermal Shutdown

T

SD

Thermal shutdown temperature TJ rising 165 °C

T

SD-HYS

Thermal shutdown temperature
hysteresis

TJ falling 20 °C

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 100pF capacitor discharged through a 1.5kΩ resistor into each pin.

Note 3: θJA measurements were performed in general accordance with JEDEC Standards JESD51-1 to JESD51-11.

Note 4: VCC provides self bias for the internal gate drive and control circuits. Device thermal limitations limit external loading.

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LM3103