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LM5010MHX Datasheet(PDF) 8 Page - Texas Instruments |
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LM5010MHX Datasheet(HTML) 8 Page - Texas Instruments |
8 / 24 page FB SW L1 C2 R3 LM5010 R1 R2 V OUT2 FS = VOUT 2 x L1 x 1.4 x 1020 RL x (RON) 2 DC = tON tON + tOFF VOUT VIN = FS = VOUT 1.18 x 10 -10 x R ON LM5010 SNVS307F – SEPTEMBER 2004 – REVISED FEBRUARY 2013 www.ti.com Hysteretic Control Circuit Overview The LM5010 buck DC-DC regulator employs a control scheme based on a comparator and a one-shot on-timer, with the output voltage feedback (FB) compared to an internal reference (2.5V). If the FB voltage is below the reference the buck switch is turned on for a time period determined by the input voltage and a programming resistor (RON). Following the on-time the switch remains off for 265 ns, or until the FB voltage falls below the reference, whichever is longer. The buck switch then turns on for another on-time period. Typically when the load current increases suddenly, the off-times are temporarily at the minimum of 265 ns. Once regulation is established, the off-time resumes its normal value. The output voltage is set by two external resistors (R1, R2). The regulated output voltage is calculated as follows: VOUT = 2.5V x (R1 + R2) / R2 (1) Output voltage regulation is based on ripple voltage at the feedback input, requiring a minimum amount of ESR for the output capacitor C2. The LM5010 requires a minimum of 25 mV of ripple voltage at the FB pin. In cases where the capacitor’s ESR is insufficient additional series resistance may be required (R3 in Typical Application Circuit and Block Diagram). When in regulation, the LM5010 operates in continuous conduction mode at heavy load currents and discontinuous conduction mode at light load currents. In continuous conduction mode current always flows through the inductor, never reaching zero during the off-time. In this mode the operating frequency remains relatively constant with load and line variations. The minimum load current for continuous conduction mode is one-half the inductor’s ripple current amplitude. The approximate operating frequency is calculated as follows: (2) The buck switch duty cycle is approximately equal to: (3) At low load current, the circuit operates in discontinuous conduction mode, during which the inductor current ramps up from zero to a peak during the on-time, then ramps back to zero before the end of the off-time. The next on-time period starts when the voltage at FB falls below the reference - until then the inductor current remains zero, and the load current is supplied by the output capacitor (C2). In this mode the operating frequency is lower than in continuous conduction mode, and varies with load current. Conversion efficiency is maintained at light loads since the switching losses reduce with the reduction in load and frequency. The approximate discontinuous operating frequency can be calculated as follows: (4) where RL = the load resistance. For applications where lower output voltage ripple is required the output can be taken directly from a low ESR output capacitor as shown in Figure 9. However, R3 slightly degrades the load regulation. Figure 9. Low Ripple Output Configuration 8 Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated Product Folder Links: LM5010 |
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