'I

Normal

Operation

Load Current

Decreases

Current

Limited

Load

Current

Increases

Normal

Operation

Current Limit

Threshold

2.5V

2

LM34914

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SNVS453B – MAY 2006 – REVISED MARCH 2013

Figure 10. Inductor Current - Normal and Current Limit Operation

N - Channel Buck Switch and Driver

The LM34914 integrates an N-Channel buck switch and associated floating high voltage gate driver. The gate

driver circuit works in conjunction with an external bootstrap capacitor and an internal high voltage diode. A 0.022

µF capacitor (C4) connected between BST and SW provides the voltage to the driver during the on-time. During

internal diode. The minimum off-time ensures a minimum time each cycle to recharge the bootstrap capacitor.

Softstart

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

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

controlled manner.

grounded.

Thermal Shutdown

The LM34914 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. This feature helps prevent

catastrophic failures from accidental device overheating. When the junction temperature reduces below 155°C

(typical hysteresis = 20°C), normal operation resumes.

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