Document
LM2651 1.5A High Efficiency Synchronous Switching Regulator
February 2000
LM2651 1.5A High Efficiency Synchronous Switching Regulator
General Description
The LM2651 switching regulator provides high efficiency power conversion over a 100:1 load range (1.5A to 15mA). This feature makes the LM2651 an ideal fit in battery-powered applications that demand long battery life in both run and standby modes. Synchronous rectification is used to achieve up to 97% efficiency. At light loads, the LM2651 enters a low power hysteretic or “sleep” mode to keep the efficiency high. In many applications, the efficiency still exceeds 80% at 15mA load. A shutdown pin is available to disable the LM2651 and reduce the supply current to less than 10µA. The LM2651 contains a patented current sensing circuitry for current mode control. This feature eliminates the external current sensing resistor required by other current-mode DC-DC converters. The LM2651 has a 300 kHz fixed frequency internal oscillator. The high oscillator frequency allows the use of extremely small, low profile components. A programmable soft-start feature limits current surges from the input power supply at start up and provides a simple means of sequencing multiple power supplies. Other protection features include input undervoltage lockout, current limiting, and thermal shutdown.
Features
n n n n n n n n n n n n Ultra high efficiency up to 97% High efficiency over a 1.5A to milliamperes load range 4V to 14V input voltage range 1.8V, 2.5V, 3.3V, or ADJ output voltage Internal MOSFET switch with low RDS(on) of 75mΩ 300kHz fixed frequency internal oscillator 7µA shutdown current Patented current sensing for current mode control Input undervoltage lockout Adjustable soft-start Current limit and thermal shutdown 16-pin TSSOP package
Applications
n n n n n Personal digital assistants (PDAs) Computer peripherals Battery-powered devices Handheld scanners High efficiency 5V conversion
Typical Application
DS100925-1 DS100925-15
Efficiency vs Load Current (VIN = 5V, VOUT = 3.3V)
© 2000 National Semiconductor Corporation
DS100925
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LM2651
Connection Diagram
16-Lead TSSOP (MTC)
DS100925-2
Ordering Information
Part Number VOUT 1.8 2.5 3.3 ADJ Supplied as 94 Units, Rail LM2651MTC-1.8 LM2651MTC-2.5 LM2651MTC-3.3 LM2651MTC-ADJ Supplied as 2.5k Units, Tape and Reel LM2651MTCX-1.8 LM2651MTCX-2.5 LM2651MTCX-3.3 LM2651MTCX-ADJ TSSOP-16 MTC16 Package Type NSC Package Drawing
Pin Description
Pin 1, 2 3-5 6 7 8 9 10 11 12-13 14-16 Name SW VIN VCB AVIN SD(SS) FB COMP NC AGND PGND Function Switched-node connection, which is connected with the source of the internal high-side MOSFET. Main power supply pin. Bootstrap capacitor connection for high-side gate drive. Input supply voltage for control and driver circuits. Shutdown control input, active low. This pin can also function as soft-start control pin. A capacitor connected from this pin to ground sets the ramp time to full current output. Output voltage feedback input. Connected to the output voltage. Compensation network connection. Connected to the output of the voltage error amplifier. No internal connection. Low-noise analog ground. Power ground.
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LM2651
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 Feedback Pin Voltage Power Dissipation (TA = 25˚C), (Note 2) Junction Temperature Range 15V −0.4V ≤ VFB ≤ 5V 893 mW −40˚C ≤ TJ ≤ +125˚C
Storage Temperature Range ESD Susceptibility Human Body Model (Note 3)
−65˚C to +150˚C 1kV
Operating Ratings (Note 1)
Supply Voltage 4V ≤ VIN ≤ 14V
Electrical Characteristics
Specifications in standard type face are for TJ = 25˚C and those with boldface type apply over full operating junction temperature range. VIN = 10V unless otherwise specified.
LM2651-1.8 System Parameters
Symbol VOUT Parameter Output Voltage Conditions ILOAD = 900 mA Typical 1.8 Limit 1.761/1.719 1.836/1.854 Units V V(min) V(max) % % % mV
VOUT VOUT VOUT VHYST
Output Voltage Line Regulation Output Voltage Load Regulation Output Voltage Load Regulation Sleep Mode Output Voltage Hysteresis
VIN = 4V to 14V ILOAD = 900 mA ILOAD = 10 mA to 1.5A VIN = 5V ILOAD = 200 mA to 1.5A VIN = 5V
0.2 1.3 0.3 35
LM2651-2.5 System Parameters
Symbol VOUT Parameter Output Voltage Conditions ILOAD = 900 mA Typical 2.5 Limit 2.43/2.388 2.574/2.575 Units V V(min) V(max) % % % mV
VOUT VOUT VOUT VHYST
Output Voltage Line Regulation Output Voltage Load Regulation Output Voltage Load Regulation Sleep Mode Output Voltage Hysteresis
VIN = 4V to 12V ILOAD = 900 mA ILOAD = 10 mA to 1.5A VIN = 5V ILOAD = 200 mA to 1.5A VIN = 5V
0.2 1.3 0.3 48
LM2651-3.3 System Parameters
Symbol VOUT Parameter Output Voltage Conditions ILOAD = 900 mA Typical 3.3 Limit 3.265/3.201 3.379/3.399 Units V V(min) V(max) % % %
VOUT VOUT VOUT
Output Voltage Line.