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User's Guide
SNVA015C–February 2000–Revised April 2013
AN–1143 LM2651_3.3V_EVAL 1.5A High Efficiency
Synchronous Switching Regulator Evaluation Board
1 Introduction
The LM2651 switching regulator provides high efficiency power conversion over a 100:1 load range (1.5A
to 15 mA). This feature makes the LM2651 an ideal fit in battery powered applications.
Synchronous rectification and 75 mΩ internal switches provide 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 15 mA load.
A shutdown pin is available to disable the LM2651 and reduce the supply current to 7 µA. The IC contains
patented current sensing circuitry for current mode control. This feature eliminates the external current
sensing required by other current mode DC to DC converters. The IC has a 300 kHz fixed frequency
internal oscillator. The high oscillator frequency allows the use of extremely small, low profile components.
The evaluation board can be obtained by ordering part number LM2651_3.3V_EVAL from your local TI
sales office, or TI's website at www.ti.com.
2 Evaluation Board Design
The evaluation board is designed to supply 3.3 V at 15 mA up to 1.5A. The input voltage range is 4 V to
14 V. Components were selected based on the design procedure in the LM2651 datasheet. PCB layout is
critical to reduce noise and ensure specified performance for any power supply design. To minimize the
parasitic inductance in the loop of input capacitors and the internal MOSFETs, connect the capacitors to
V
IN
and PGND pins with short and wide traces. This is important because the rapidly switching current,
together with wiring inductance can generate large voltage spikes that may cause noise problems. The
feedback trace from the output to the feedback pin should be wide, short and kept away from the flux field
of the inductor. The artwork for the evaluation board is shown at the end of this application report and the
schematic shown in Figure 1. The parts list is given in Table 1. The pictorial representations of top, bottom
and silkscreen layers are shown at the end of this document.
When an undervoltage situation occurs, the output voltage can be pulled below ground as the inductor
current is reversed through the synchronous FET. For applications that need to be protected from a
negative voltage, a clamping diode D2 is recommended. When used, D2 should be connected cathode to
V
OUT
and anode to ground. A diode rated for a minimum of 2A is recommended.
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SNVA015C–February 2000–Revised April 2013 AN–1143 LM2651_3.3V_EVAL 1.5A High Efficiency Synchronous Switching
Regulator Evaluation Board
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Verzeichnis
- ・ Blockdiagramm on Seite 2
- ・ Anwendungsbereich on Seite 4
