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11

LM3409, LM3409-Q1, LM3409HV, LM3409HV-Q1

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SNVS602L – MARCH 2009 – REVISED JUNE 2016

Product Folder Links: LM3409 LM3409-Q1 LM3409HV LM3409HV-Q1

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8.3 Feature Description

8.3.1 Buck Current Regulators

The buck regulator is unique among non-isolated topologies due to the direct connection of the inductor to the

load during the entire switching cycle. An inductor will control the rate of change of current that flows through it,

therefore a direct connection to the load is excellent for current regulation. A buck current regulator, using the

LM3409/09HV, is shown in the Application and Implementation section. During the time that the PFET (Q1) is

diode (D1) becomes forward biased and L1 discharges. During both intervals, the current is supplied to the load

operating in CCM.

efficiency (

η):

(1)

8.3.2 Controlled Off-Time (COFT) Architecture

which vary depending on the operating point. This creates a variable switching frequency over the entire

operating range. This type of hysteretic control eliminates the need for control loop compensation necessary in

many switching regulators, simplifying the design process and providing fast transient response.

8.3.2.1 Adjustable Peak Current Control

At the beginning of a switching period, PFET Q1 is turned on and inductor current increases. Once peak current

is detected, Q1 is turned off, the diode D1 forward biases, and inductor current decreases. Figure 20 shows how

peak current detection is accomplished using the differential voltage signal created as current flows through the