LM5010ASD datasheet(10/25 Pages) TI

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'I =

(VIN - VOUT) x tON

VIN

STOP

RUN

RON

Input

Voltage

LM5010A

RON/SD

tON(min) =

VOUT x 300 ns

(VIN(min) ± VOUT)

LM5010A

LM5010A-Q1

SNVS376E – OCTOBER 2005 – REVISED FEBRUARY 2013

www.ti.com

(8)

Shutdown

The LM5010A can be remotely shut down by forcing the RON/SD pin below 0.7V with a switch or open drain

device. See Figure 9. In the shutdown mode the SS pin is internally grounded, the on-time one-shot is disabled,

the input current at VIN is reduced, and the VCC bypass switch is turned off. The VCC regulator is not disabled in

the shutdown mode. Releasing the RON/SD pin allows normal operation to resume. The nominal voltage at

RON/SD is shown in the Typical Performance Characteristics. When switching the RON/SD pin, the transition

time should be faster than one to two cycles of the regulator’s nominal switching frequency.

Figure 9. Shutdown Implementation

Current Limit

Current limit detection occurs during the off-time by monitoring the recirculating current through the internal

current sense resistor (RSENSE). The detection threshold is 1.25A, ±0.25A. Referring to the Block Diagram, if the

current into SGND during the off-time exceeds the threshold level the current limit comparator delays the start of

the next on-time period. The next on-time starts when the current into SGND is below the threshold and the

voltage at FB is below 2.5V. Figure 10 illustrates the inductor current waveform during normal operation and

during current limit. The output current IO is the average of the inductor ripple current waveform. The Low Load

Current waveform illustrates continuous conduction mode operation with peak and valley inductor currents below

the current limit threshold. When the load current is increased (High Load Current), the ripple waveform

maintains the same amplitude and frequency since the current falls below the current limit threshold at the valley

of the ripple waveform. Note the average current in the High Load Current portion of Figure 10 is above the

current limit threshold. Since the current reduces below the threshold in the normal off-time each cycle, the start

of each on-time is not delayed, and the circuit’s output voltage is regulated at the correct value. When the load

current is further increased such that the lower peak would be above the threshold, the off-time is lengthened to

allow the current to decrease to the threshold before the next on-time begins (Current Limited portion of

Figure 10). Both VOUT and the switching frequency are reduced as the circuit operates in a constant current

mode. The load current (IOCL) is equal to the current limit threshold plus half the ripple current (ΔI/2). The ripple

amplitude (

ΔI) is calculated from:

(9)

The current limit threshold can be increased by connecting an external resistor (RCL) between SGND and ISEN.

RCL typically is less than 1Ω, and the calculation of its value is explained in Applications Information. If the

current limit threshold is increased by adding RCL, the maximum continuous load current should not exceed 1.5A,

and the peak current out of the SW pin should not exceed 2A.

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