LM2734ZEVAL National Semiconductor, LM2734ZEVAL Datasheet - Page 5

• Manufacturer Part Number: LM2734ZEVAL
• Description: BOARD EVALUATION LM2734Z
• Manufacturer: National Semiconductor

Specifications of LM2734ZEVAL

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 1.8V
• Current - Output: 1A
• Voltage - Input: 3 ~ 20V
• Regulator Topology: Buck
• Frequency - Switching: 3MHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM2734
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Power - Output: -

Block Diagram
Application Information
THEORY OF OPERATION
The LM2734Z is a constant frequency PWM buck regulator
IC that delivers a 1A load current. The regulator has a preset
switching frequency of 3MHz. This high frequency allows the
LM2734Z to operate with small surface mount capacitors and
inductors, resulting in a DC/DC converter that requires a min-
imum amount of board space. The LM2734Z is internally
compensated, so it is simple to use, and requires few external
components. The LM2734Z uses current-mode control to reg-
ulate the output voltage.
The following operating description of the LM2734Z will refer
to the Simplified Block Diagram (Figure 1) and to the wave-
forms in Figure 2. The LM2734Z supplies a regulated output
voltage by switching the internal NMOS control switch at con-
stant frequency and variable duty cycle. A switching cycle
begins at the falling edge of the reset pulse generated by the
internal oscillator. When this pulse goes low, the output con-
trol logic turns on the internal NMOS control switch. During
this on-time, the SW pin voltage (V
mately V
slope. I
generates an output proportional to the switch current. The
sense signal is summed with the regulator’s corrective ramp
and compared to the error amplifier’s output, which is propor-
tional to the difference between the feedback voltage and
V
put switch turns off until the next switching cycle begins.
REF
. When the PWM comparator output goes high, the out-
L
IN
is measured by the current-sense amplifier, which
, and the inductor current (I
SW
L
) increases with a linear
) swings up to approxi-
FIGURE 1.
5
During the switch off-time, inductor current discharges
through Schottky diode D1, which forces the SW pin to swing
below ground by the forward voltage (V
The regulator loop adjusts the duty cycle (D) to maintain a
constant output voltage.
FIGURE 2. LM2734Z Waveforms of SW Pin Voltage and
Inductor Current
D
) of the catch diode.
20130306
www.national.com
20130307