下载
t
on
=
V
IN
- 0.5V
1.25 x 10
-10
x (R1 + 500:)
+ 30 ns
User's Guide
SNVA434A–February 2011–Revised April 2013
AN-2050 LM5006 Evaluation Board
1 Introduction
The LM5006EVAL evaluation board provides the design engineer with a fully functional buck regulator,
employing the constant on-time (COT) operating principle. This evaluation board provides a 5V output
over an input range of 6V to 75V. The circuit delivers load currents to 500 mA, with current limit set at a
nominal 1 Amp.
The board’s specification are:
• Input Voltage: 6V to 75V
• Output Voltage: 5V
• Maximum load current: 500 mA
• Minimum load current: 0A
• Current Limit: 1 Amp (nominal)
• Measured Efficiency: 94.75% (V
IN
= 6V, I
OUT
= 100 mA)
• Nominal Switching Frequency: 200 kHz
• Size: 2.6 in. × 1.6 in.
2 Theory of Operation
Refer to the evaluation board schematic in Figure 1. When the circuit is in regulation, the buck switch is on
each cycle for a time determined by R1 and VIN according to the equation:
(1)
The on-time of this evaluation board ranges from ≊4.38 µs at VIN = 6V, to ≊351 ns at VIN = 75V. The on-
time varies inversely with VIN to maintain a nearly constant switching frequency. At the end of each on-
time the Minimum Off-Timer ensures the buck switch is off for at least 260 ns. In normal operation, the off-
time is much longer. During the off-time, the load current is supplied by the output capacitor (C2). When
the output voltage falls sufficiently that the voltage at FB is below 2.5V, the regulation comparator initiates
a new on-time period. For stable, fixed frequency operation, a minimum of 25 mV of ripple is required at
FB to switch the regulation comparator. Refer to the LM5006 data sheet for a more detailed block
diagram, and a complete description of the various functional blocks.
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1
SNVA434A–February 2011–Revised April 2013 AN-2050 LM5006 Evaluation Board
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