7

LP5524

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SNVS500C – JULY 2007 – REVISED NOVEMBER 2016

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7 Detailed Description

7.1 Overview

The LP5524 is an easy-to-use high side current source capable of driving 4 indicator LEDs with up to 25 mA per

LED. The device operates over the 2.7-V to 5.5-V input voltage range. The output current is user-programmable

via the optional external ISET resistor.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 LED

Forward voltage of LED must be less than minimum input voltage minus minimum headroom voltage (VHR). For

example with 2.7-V input voltage and 20-mA LED current the maximum LED forward voltage is 2.7 V – 100 mV =

2.6 V.

7.3.2 LED Headroom Voltage

A single current source is connected internally between VIN and DX outputs (D1A, D2A, D1B and D2B). The

voltage across the current source, (VIN – VDX), is referred to as headroom voltage (VHR). The current source

requires a sufficient amount of headroom voltage to be present across it in order to regulate properly.

Figure 4 shows how output current of the LP5524 varies with respect to headroom voltage. On the flat part of the

graph, the current is regulated properly as there is sufficient headroom voltage for regulation. On the sloping part

of the graph the headroom voltage is too small, the current source is squeezed, and the current drive capability is

limited. Thus, operating the LP5524 with insufficient headroom voltage across the current source must be

avoided.