SSL5021BTS datasheet(4/20 Pages) NXP

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SSL5021BTS

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Product data sheet

Rev. 2 — 11 March 2015

4 of 20

NXP Semiconductors

SSL5021BTS

Compact low-ripple buck LED driver IC

7.2 Pin description

Functional description

8.1 Converter operation

The SSL5021BTS is a power MOSFET and bipolar compatible controller. The converter in

the SSL5021BTS is a source/emitter switch, Boundary Conduction Mode (BCM), on-time

controlled system. Figure 3 shows the basic application diagram for MOSFET. Figure 4

shows the basic application diagram for bipolar.

The integrated switch is used to save IC supply current. It enables the use a single

external resistor as supply even in switching mode. This converter operates at the

boundary between Continuous Conduction Mode (CCM) and Discontinuous Conduction

Mode (DCM). Figure 5 shows the waveforms.

When the internal switch is switched on at t0, the inductor current IL builds up from zero in

proportional with VIN -VOUT during the switch on-time (t0 to t1). Energy is stored in the

inductor.

When the internal switch switches off at t1, IL drops proportionally to the value of VOUT.

The current flows through the freewheeling diode and the output capacitor (t2 to t3). When

IL reaches zero, after a short delay (t3 to t00), a new switching cycle starts.

Table 3.

Pin description

Symbol

Description

ISNS

current sense input

VCC

supply voltage

internal switch drain

DEMOVP

input from LED output for demagnetization timing, valley detection,

temperature foldback, and OVP

GND

ground

COMP

loop compensation to provide a stable response

Fig 3.

SSL5021BTS basic application diagram for MOSFET

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