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LMR12007 Datasheet(PDF) 7 Page - Texas Instruments |
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LMR12007 Datasheet(HTML) 7 Page - Texas Instruments |
7 / 30 page L R1 R2 D 1 D2 BOOST Output Control Logic Current Limit Thermal Shutdown Under Voltage Lockout Corrective Ramp Reset Pulse PWM Comparator Current-Sense Amplifier RSENSE + + Internal Regulator and Enable Circuit Oscillator Driver 0.3: Switch Internal Compensation SW EN FB GND Error Amplifier - + VREF 1.25V COUT ON OFF VBOOST VSW + - CBOOST VOUT CIN VIN VIN ISENSE + - + - 1.375V OVP Comparator Error Signal - + IL LMR12007 www.ti.com SNVS982 – SEPTEMBER 2013 Block Diagram Figure 19. APPLICATION INFORMATION THEORY OF OPERATION The LMR12007 is a constant frequency PWM buck regulator IC that delivers a 750mA load current. The regulator has a preset switching frequency of either 550kHz (LMR12007Y) or 1.6MHz (LMR12007X). These high frequencies allow the LMR12007 to operate with small surface mount capacitors and inductors, resulting in DC/DC converters that require a minimum amount of board space. The LMR12007 is internally compensated, so it is simple to use, and requires few external components. The LMR12007 uses current-mode control to regulate the output voltage. The following operating description of the LMR12007 will refer to the Simplified Block Diagram (Figure 19) and to the waveforms in Figure 20. The LMR12007 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) swings up to approximately VIN, 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 sense 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 Schottky diode D1, which forces the SW pin to swing below ground by the forward voltage (VD) of the catch diode. The regulator loop adjusts the duty cycle (D) to maintain a constant output voltage. Copyright © 2013, Texas Instruments Incorporated Submit Documentation Feedback 7 Product Folder Links: LMR12007 |
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