Threshold

IPK

'I

IOCL

IO

Load Current

Increases

Normal Operation

Current Limited

13

LM5010

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SNVS307G – SEPTEMBER 2004 – REVISED APRIL 2016

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Feature Description (continued)

Figure 10. Inductor Current, Current Limit Operation

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

external resistor typically is less than 1

Ω, and its calculation is explained in Application and Implementation.

The peak current out of SW and ISEN must not exceed 3.5 A. The average current out of SW must be less than

3 A, and the average current out of ISEN must be less than 2 A.

7.3.7 Soft Start

The soft-start feature allows the converter to gradually reach a steady-state operating point, thereby reducing

start-up stresses and current surges. Upon turnon, after VCC reaches the undervoltage threshold (t1 in Figure 7),

an internal 11.5-µA current source charges the external capacitor at the soft-start pin to 2.5 V (t2 in Figure 7).

The ramping voltage at SS (and at the non-inverting input of the regulation comparator) ramps up the output

voltage in a controlled manner. This feature keeps the load current from going to current limit during start-up,

thereby reducing inrush currents.

An internal switch grounds the soft-start pin if VCC is below the undervoltage lockout threshold, if a thermal

shutdown occurs, or if the circuit is shutdown using the RON/SD pin.

7.3.8 N-Channel Buck Switch and Driver

The LM5010 integrates an N-Channel buck switch and associated floating high voltage gate driver. The peak

current through the buck switch must not be allowed to exceed 3.5 A, and the average current must be less than

3 A. The gate driver circuit is powered by the external bootstrap capacitor between BST and SW (C4). During

each OFF-time, the SW pin is at approximately –1 V, and C4 is recharged from VCC through the internal high

voltage diode. The minimum OFF-time of 265 ns ensures a minimum time each cycle to recharge the bootstrap

capacitor. TI recommends a 0.022-µF ceramic capacitor for C4.

7.3.9 Thermal Shutdown

The LM5010 should be operated so the junction temperature does not exceed 125°C. If the junction temperature

increases above that, an internal Thermal Shutdown circuit activates (typically) at 175°C, taking the controller to

a low-power reset state by disabling the buck switch and the ON timer, and grounding the soft-start pin. This

feature helps prevent catastrophic failures from accidental device overheating. When the junction temperature

reduces below 155°C (typical hysteresis = 20°C), the softstart pin is released and normal operation resumes.