LM2735XMFSLASHNOPB datasheet(8/58 Pages) TI1

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1.6 MHz

VIN

ThermalSHDN

ILIMIT

NMOS

UVLO = 2.3V

ISENSE-AMP

Internal

Compensation

Soft-Start

Corrective - Ramp

Oscillator

Control Logic

VREF = 1.255V

GND

LM2735

SNVS485F – JUNE 2007 – REVISED APRIL 2013

www.ti.com

Simplified Internal Block Diagram

Figure 18. Simplified Block Diagram

APPLICATION INFORMATION

THEORY OF OPERATION

The LM2735 is a constant frequency PWM boost regulator IC that delivers a minimum of 2.1A peak switch

current. The regulator has a preset switching frequency of either 520 kHz or 1.60 MHz. This high frequency

allows the LM2735 to operate with small surface mount capacitors and inductors, resulting in a DC/DC converter

that requires a minimum amount of board space. The LM2735 is internally compensated, so it is simple to use,

and requires few external components. The LM2735 uses current-mode control to regulate the output voltage.

The following operating description of the LM2735 will refer to the Simplified Internal Block Diagram (Figure 18)

the simplified schematic (Figure 19), and its associated waveforms (Figure 20). The LM2735 supplies a regulated

output voltage by switching the internal NMOS control switch at constant 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 control logic turns on the internal NMOS control switch. During this on-time, the SW pin

voltage (VSW) decreases to approximately GND, and the inductor current (IL) increases with a linear slope. IL is

measured by the current sense amplifier, which generates an output proportional to the switch current. The

sensed signal is summed with the regulator’s corrective ramp and compared to the error amplifier’s output, which

is proportional to the difference between the feedback voltage and VREF. When the PWM comparator output goes

high, the output switch turns off until the next switching cycle begins. During the switch off-time, inductor current

discharges through diode D1, which forces the SW pin to swing to the output voltage plus the forward voltage

(VD) of the diode. The regulator loop adjusts the duty cycle (D) to maintain a constant output voltage .

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LM2735XMF/NOPB 데이터시트(PDF) 8 Page - Texas Instruments