MIC3202 Просмотр технического описания (PDF) - Micrel

Номер в каталоге

Компоненты Описание

производитель

MIC3202

High-Brightness LED Driver with Integrated MOSFET and High-Side Current Sense

Micrel 

Micrel, Inc.

MIC3202

Application Information

The internal block diagram of the MIC3202 is shown in

Figure 1. The MIC3202 is composed of a current-sense

comparator, voltage and current reference, 5V regulator

and MOSFET. Hysteretic mode control, also called

bang-bang control, is a topology that does not employ an

error amplifier, using an error comparator instead.

The inductor current is controlled within a hysteretic

window. If the inductor current is too small, the power

MOSFET is turned on; if the inductor current is large

enough, the power MOSFET is turned off. It is a simple

control scheme with no oscillator and no loop

compensation. Since the control scheme does not need

loop compensation, it simplifies design and avoids

problems of instability.

Transient response to load and line variation is very fast

and only depends on propagation delay. This makes the

control scheme very popular to achieve low dimming

duty cycles.

LED Current and RCS

The main function of the MIC3202 is to control the LED

current accurately within ±5% of the set current. A high-

side RCS resistor sets LED current. The following

equation gives the RCS value:

RCS

=

1

2

x( VCS(MAX) + VCS(MIN)

ILED

)

RCS (Ω)

1.33

0.56

0.4

0.28

0.2

ILED (A)

0.15

0.35

0.5

0.7

1.0

I2R (W)

0.03

0.07

0.1

0.137

0.2

Size (SMD)

0603

0805

0805

0805

1206

Table 1. RCS Values for Various LED Currents

For VCS(MAX) and VCS(MIN), refer to the Electrical

Characteristic table.

Frequency of Operation

To calculate the frequency spread across input supply:

VL

=L

ΔIL

Δt

L is the inductance, ∆IL is fixed (the value of the hysteresis):

ΔIL

=

VCS(MAX) - VCS(MIN)

RCS

VL is the voltage across inductor L which varies by supply.

For current rising (MOSFET is ON):

tr

=L

ΔIL

VL _ RISE

where:

VL_RISE = VIN − ILED × RCS − VLED.

For current falling (MOSFET is OFF):

tf

= L ΔIL

VL _ FALL

where:

VL_FALL = VD + ILED × RCS + VLED

T = tr + tf ,

f SW

=

1

T

fSW

=

(VD

+ILED×RCS+ VLED)×(VIN-ILED×RCS-

L×ΔIL ×(VD + VIN)

VLED)

where:

VD is Schottky diode forward drop.

VLED is total LEDs voltage drop.

VIN is input voltage.

ILED is average LED current.

September 2010

10

M9999-091710-A

Share Link: