Microchip MIC3231 Handleiding

Microchip Niet gecategoriseerd MIC3231

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Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
July 2009 M9999-071609-A
(408) 944-0800
General Description
The MIC3230/1 are constant current boost switching
controllers specifically designed to power one or more
strings of high power LEDs. The MIC3230/1 have an input
voltage range from 6V to 45V and are ideal for a variety of
applications.
The MIC3230/1 utilizes an external power device which
offers a cost conscious solution for driving high power LED
applications. Power consumption has been minimized
through the implementation of a 250mV feedback voltage
reference providing an accuracy of ±3%. The MIC3230/1
are dimmable via a PWM input signal and also features an
enable pin for low power shutdown.
The LED current is regulated by keeping the voltage drop
across the current sense resistor (R7) constant. The LED
current can be set by selecting the value of R7. In this
version of the eval board, the output current is limited to
750mA.
Multiple MIC3230 ICs can be synchronized to a common
operating frequency by connecting the ICs together
through the SYNC pin. This feature is only good on the
MIC3230. The clocks of these synchronized devices can
be used together which help reduce noise and errors in a
system.
The MIC3231 offers a dither feature to assist in the
reduction of EMI. This is particularly useful in sensitive
EMI applications, and provides for a reduction in emissions
by approximately 10dB.
Table 1 provides a summary of the eval board
specifications. The evaluation board schematic is shown in
Figure 1 and the parts list is shown in the Bill of Materials
table.
The switching frequency is determined by the selection of
R1. The chart in Figure 2 can be used to select the
desired frequency. The board is set at approximately
500kHz.
Requirements
1. Voltage source capable of supplying 50 Watts
2. Load: LED, resistive or electronic load
3. Scope
4. Voltage meter
5. (Optional) Function generator for PWM Dimming
Precautions
The evaluation board does not have input reverse polarity
protection. Applying a negative voltage at the VIN terminal
may damage the board. When the controller is off there is
a current path through the inductor and the flyback diode
to the output. No current limit exists for this current path so
care must be taken not to short circuit the output.
How it works
The MIC3230/1 evaluation board is set to operate as a
boost converter, which requires the output voltage to be
greater than the input voltage. It is important to have the
series LED forward voltage drops be greater than the input
voltage because when the converter is off the input is
connected to the output through the inductor (L1) and
diode (D1). VIN is effectively applied across the LEDs and
will turn on if the series sum of their forward voltage drop is
not greater than VIN. For 100% duty cycle, simply pull
PWMD high or leave open. For a different LED current
change R7 using the following equation. When R7 is
0.62Ω, the LED current is equal to 0.4A. The evaluation
board is currently set to this output current value.
7R
V
IREF
LED = Where VREF = 0.25V
PWM Dimming
A PWM signal applied to the PWMD pin turns the current
to the load LEDs on and off. When PWMD is high the
MIC3230/1 is enabled and the boost converter regulates
the LED current by keeping the voltage drop across R7
constant. When PWMD is low the converter turns off and
the LED current discharges the output caps and LED
current stops.
Ordering Information
Part Number Description
MIC3230ML
BOOST EV
Boost evaluation board for the
MIC3230YML IC
MIC3231ML
BOOST EV
Boost evaluation board for the
MIC3231YML IC
Micrel, Inc. MIC3230/1 Evaluation Board
July 2009 2 M9999-071609-A
(408) 944-0800
Quick-Start Guide
1. Connect a load (LED series string or resistive load)
between VOUT and LED RTN (this is not the same as
ground).
2. Connect 12V (or other input voltage) to VIN and
GND.
3. Use a current probe to measure the load current.
and Monitor the Switch node with a scope to view
the switch waveform
4. PWM Dimming:
a. For no PWM dimming, leave the PWMD
terminal open
b. For PWM DIMMING connect a function
generator to the PWM DIM input and GND
(not LED RTN). Set the output at 0-5V
square wave pulse at 300Hz. Make sure the
pulse goes all the way to 0V.
RSET – Current Limit Sensing
The MIC3230/1 features current limit sensing. Current
limit is set by an external resistor by the following
equation:
IS=0.5V = R6×IQ1
Where, IQ1 is the peak FET current that will trigger the
current limit, the Default setting for the evaluation board
is R6 = 75mΩ with the current limit set at 6.7A.
OVP – Setting the over voltage protection
OVP is set with R9 according to this equation;
(
)
( )
9R8R
V9R
V245.1OVP MAX,O
+
×
==
On the evaluation board, these values have been set to:
R9 = 2kΩ and R8 = 100kΩ and VO,MAX = 64V.
VFB=0.25V
R7
R9
R8
R1
100k
R2
R3
C5
10uF/10V
C4
10nF
L1
4.7µH
R6
0.075
1/2W
R4
1
/2W
R5
C2
4.7µF
50V
C1
4.7µF
50V
D1
SS5P10-E3
1
1
1
1
1
J1
+VIN
J3
EN
J4
PWM Dim
J5
SYNCH
J2
GND
J7
LED RTN
1J6
+VOUT LED
8
4
1
7
6
2
3
5
Q1
SI7148DP
COMP
4
PWMD
3
VDD GND
EPAD
12 10
IS 8
OVP 9
DRV 11
VIN
1
EN
2
IADJ 5
SYNC
7
FS
6
U1
MIC3230-YML
C3
100pF /100V
C6
2.2µF
100V
C7
2.2µF
100V R10
TBD/OPEN
1
1
Figure 1. Schematic Diagram
Micrel, Inc. MIC3230/1 Evaluation Board
July 2009 3 M9999-071609-A
(408) 944-0800
Evaluation Board Design Specifications
MIN TYP MAX
VIN 6V 12-24 45V
Output Voltage Vin 12-20 Series
LEDs
70V
LED Current 0 0.2-0.5 1A
Power Out 0 20W 70W
Efficiency 90%
Switching Frequency 100kHz 400kHz 1MHz
PWM Dim Frequency 0 300Hz 500Hz
Line Regulation <3%
Load Regulation <3%
Ambient Temperature –40°C +25°C +85°C
*Evaluation Board parts are rated to 75V
Table 1. Evaluation Board Design Specifications
LED current selection
R7 (Ω) I_LED
5 50mA
2 125mA
1 250mA
0.62 404mA
0.5 500mA
0.4 625mA
.25 1A
Table 2. LED current selection
Figure 2. Frequency selection

Product specificaties

Merk: Microchip
Categorie: Niet gecategoriseerd
Model: MIC3231

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