MAQ3203YM Evaluation Board User Guide

MAQ3203
High-Brightness LED Driver Controller
with High-Side Current Sense
General Description
The MAQ3203 is a hysteretic, step-down, constantcurrent, High-Brightness LED (HB LED) driver. It provides
an ideal solution for interior/exterior lighting, architectural
and ambient lighting, LED bulbs, and other general
illumination applications.
The MAQ3203 is well suited for lighting applications
requiring a wide-input voltage range. The hysteretic control
gives good supply rejection and fast response during load
transients and PWM dimming. The high-side current
sensing and on-chip current-sense amplifier delivers LED
current with ±5% accuracy. An external high-side currentsense resistor is used to set the output current.
The MAQ3203 offers a dedicated PWM input (DIM) which
enables a wide range of pulsed dimming. A high-frequency
switching operation up to 1.5MHz allows the use of smaller
external components minimizing space and cost. The
MAQ3203 offers frequency dither feature for EMI control.
The MAQ3203 operates over a junction temperature from
−40°C to +125°C and is available in an 8-pin SOIC
package. The MAQ3203 is AEC-Q100 qualified for
automotive applications.
Datasheets and support documentation are available on
Micrel’s web site at: www.micrel.com.
Features
•
•
•
•
•
•
•
•
•
•
•
•
AEC-Q100 qualified
4.5V to 42V input voltage range
High efficiency (>90%)
±5% LED current accuracy
Dither enabled for low EMI
High-side current sense
Dedicated dimming control input
Hysteretic control (no compensation!)
Up to 1.5MHz switching frequency
Adjustable constant LED current
Over-temperature protection
−40°C to +125°C junction temperature range
Applications
• Automotive lighting
• Industrial lighting
Typical Application
MAQ3203 Step-Down LED Driver
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
April 20, 2015
Revision 1.2
Micrel, Inc.
MAQ3203
Ordering Information
(1)
Part Number
Marking
Junction Temperature Range
Package
PWM
MAQ3203YM
MAQ3203YM
−40°C to +125°C
8-Pin SOIC
Dither
Note:
1. YM is a GREEN RoHS-compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
Pin Configuration
8-Pin SOIC (M)
(Top View)
Pin Description
Pin Number
Pin Name
Pin Function
1
VCC
Voltage Regulator Output. The VCC pin supplies the power to the internal circuitry. The VCC is the
output of a linear regulator which is powered from VIN. A 1µF ceramic capacitor is recommended for
bypassing and should be placed as close as possible to the VCC and AGND pins. Do not connect to
an external load.
2
CS
Current-Sense Input. The CS pin provides the high-side current sense to set the LED current with an
external sense resistor.
3
VIN
Input Power Supply. VIN is the input supply pin to the internal circuitry and the positive input to the
current sense comparator. Due to the high frequency switching noise, a 10µF ceramic capacitor is
recommended to be placed as close as possible to VIN and the power ground (PGND) pin for
bypassing. Please refer to layout recommendations.
4
AGND
Ground pin for analog circuitry. Internal signal ground for all low power sections.
5
EN
Enable Input. The EN pin provides a logic level control of the output and the voltage has to be 2.0V or
higher to enable the current regulator. The output stage is gated by the DIM pin. When the EN pin is
pulled low, the regulator goes to off state and the supply current of the device is greatly reduced
(below 1µA). In the off state, during this period the output drive is placed in a "tri-stated" condition,
where MOSFET is in an “off” or non-conducting state. Do not drive the EN pin above the supply
voltage.
6
DIM
PWM Dimming Input. The DIM pin provides the control for brightness of the LED. A PWM input can
be used to control the brightness of LED. DIM high enables the output and its voltage has to be at
least 2.0V or higher. DIM low disables the output, regardless of EN “high” state.
7
PGND
Power Ground Pin for Power FET. Power Ground (PGND) is for the high-current switching with
hysteretic mode. The current loop for the power ground should be as small as possible and separate
from the Analog ground (AGND) loop. Refer to the layout considerations for more details.
DRV
Gate-Drive Output. Connect to the gate of an external N-channel MOSFET. The drain of the external
MOSFET connects directly to the inductor and provides the switching current necessary to operate in
hysteretic mode. Due to the high frequency switching and high voltage associated with this pin, the
switch node should be routed away from sensitive nodes.
8
April 20, 2015
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Revision 1.2
Micrel, Inc.
MAQ3203
Absolute Maximum Ratings(2)
Operating Ratings(3)
VIN to PGND .................................................. −0.3V to +45V
VCC to PGND ................................................ −0.3V to +6.0V
CS to PGND ........................................ −0.3V to (VIN + 0.3V)
EN to AGND ........................................ −0.3V to (VIN + 0.3V)
DIM to AGND ...................................... −0.3V to (VIN + 0.3V)
DRV to PGND .................................... −0.3V to (VCC + 0.3V)
PGND to AGND........................................... −0.3V to + 0.3V
Junction Temperature ................................................ 150°C
Storage Temperature Range .................... −60°C to +150°C
Lead Temperature (soldering, 10s) ............................ 260°C
(4)
ESD Ratings
HBM ...................................................................... 1.5kV
MM ......................................................................... 200V
Supply Voltage (VIN) .......................................... 4.5V to 42V
Enable Voltage (VEN) .............................................. 0V to VIN
Dimming Voltage (VDIM) ................................................................. 0V to VIN
Junction Temperature (TJ) ........................ −40°C to +125°C
Junction Thermal Resistance
SOIC (θJA) ....................................................... 98.9°C/W
SOIC (θJC) ....................................................... 48.8°C/W
Electrical Characteristics(5)
VIN = VEN = VDIM = 12V; CVCC = 1.0µF; TJ = 25°C, bold values indicate −40°C ≤ TA ≤ +125°C; unless noted.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Units
42
V
3
mA
1
µA
4.5
V
Input Supply
4.5
VIN
Input Voltage Range (VIN)
IS
Supply Current
DRV = open
ISD
Shutdown Current
VEN = 0V
UVLO
VIN UVLO Threshold
VIN rinsing
UVLOHYS
VIN UVLO Hysteresis
1
3.2
4
500
mV
VCC Supply
VCC
VCC Output Voltage
VIN = 12V, ICC = 10mA
4.5
5
5.5
201.4
212
222.6
199
212
225
168
177
186
165
177
189
V
Current Limit
VCS(MAX)
Current Sense Upper Threshold
VCS(MAX ) = VIN − VCS
VCS(MIN)
Sense Voltage Threshold Low
VCS(MIN ) = VIN − VCS
VCSHYS
VCS Hysteresis
Current Sense Response Time
CS Input Current
35
VCS Rising
50
VCS Falling
70
VIN − VCS = 220mV
0.5
mV
mV
mV
ns
10
µA
Notes:
2. Exceeding the absolute maximum ratings may damage the device.
3. The device is not guaranteed to function outside its operating ratings.
4. Devices are ESD sensitive. Handling precautions are recommended. Human body model, 1.5kΩ in series with 100pF.
5. Specification for packaged product only.
April 20, 2015
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Revision 1.2
Micrel, Inc.
MAQ3203
Electrical Characteristics(5) (Continued)
VIN = VEN = VDIM = 12V; CVCC = 1.0µF; TJ = 25°C, bold values indicate −40°C ≤ TA ≤ +125°C; unless noted.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Units
1.5
MHz
Frequency
FMAX
Switching Frequency
Dithering
VDITH
FDITHER
VCS Hysteresis Dithering Range
Frequency Dithering Range
(6)
(6)
% of switching frequency
±6
mV
±12
%
Enable Input
ENHI
EN Logic Level High
ENLO
EN Logic Level Low
EN Bias Current
Start-Up Time
2.0
V
0.4
V
VEN = 12V
60
µA
VEN = 0V
1
µA
From EN going high to DRV going high
30
µs
Dimming Input
DIMHI
DIM Logic Level High
DIMLO
DIM Logic Level Low
DIM Bias Current
DIM Delay Time
FDIM
2.0
V
0.4
20
VDIM = 0V
50
1
From DIM going high to DRV going
high
450
Maximum Dimming Frequency
V
µA
ns
20
kHz
External FET Driver
DRV On-Resistance
DRV Transition Time
Pull Up, ISOURCE = 10mA
2
Pull Down, ISINK = -10mA
1.5
Rise Time, CLOAD = 1000pF
13
Fall Time, CLOAD = 1000pF
7
Ω
ns
Thermal Protection
TLIM
Over-Temperature Shutdown
TLIMHYS
Over-Temperature Shutdown Hysteresis
TJ Rising
160
20
°C
Note:
6. Guaranteed by design.
April 20, 2015
4
Revision 1.2
Micrel, Inc.
MAQ3203
Typical Characteristics
Efficiency
vs Input Voltage
Efficiency
vs Input Voltage
100
100
90
90
Normalized LED Currents
vs Input Voltage
1.03
4LED
6LED
80
8LED
10LED
70
4LED
6LED
80
8LED
10LED
70
L=150µH
ILED=1A
5
10
15
20
25
30
35
40
45
0
5
10
INPUT VOLTAGE (V)
20
25
30
35
40
1
1LED
0.99
6LED
0.98
10LED
8LED
15
20
25
30
35
40
4LED
200
2LED
150
100
1LED
50
45
0
5
10
15
20
25
30
35
40
25
INPUT VOLTAGE (V)
April 20, 2015
5
35
40
45
10
15
20
25
30
35
40
45
35
40
45
Supply Current
vs. Input Voltage
75
8LED
1LED
2LED
4LED
6LED
50
25
0
30
10LED
INPUT VOLTAGE (V)
L=68µH
ILED=1A
0
8LED
1.4
L=150µH
ILED=1A
25
1LED
200
0
SUPPLY CURRENT (mA)
DUTY CYCLE (%)
4LED
6LED
20
2LED
300
45
10LED
8LED
15
45
400
6LED
10LED
75
10
40
100
8LED
100
5
35
4LED
Duty Cycle
vs Input Voltage
100
0
500
INPUT VOLTAGE (V)
50
30
0
Duty Cycle
vs. Input Voltage
1LED
25
L=68µH
ILED=1A
600
250
INPUT VOLTAGE (V)
2LED
20
Frequency
vs. Input Voltage
0
10
15
10LED
0.97
5
10
700
6LED
0
5
INPUT VOLTAGE (V)
FREQUENCY (kHz)
1.01
4LED
L=150µH
ILED=1A
0
45
L=150µH
ILED=1A
300
FREQUENCY (kHz)
LED CURRENTS (A)
15
350
L=68µH
ILED=1A
8LED
0.99
Frequency
vs. Input Voltage
1.03
2LED
1LED
6LED
1
INPUT VOLTAGE (V)
Normalized LED Currents
vs. Input Voltage
1.02
4LED
2LED
0.97
60
0
10LED
1.01
0.98
L=68µH
ILED=1A
60
DUTY CYCLE (%)
LED CURRENTS (A)
EFFICIENCY (%)
EFFICIENCY (%)
1.02
1.2
1.0
TA = 25°C
ILED = 0A
0.8
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
INPUT VOLTAGE (V)
5
35
40
45
0
5
10
15
20
25
30
INPUT VOLTAGE (V)
Revision 1.2
Micrel, Inc.
MAQ3203
Typical Characteristics (Continued)
VCC vs. Input Voltage
Enable Threshold
vs. Input Voltage
Current-Sense Voltage
vs. Input Voltage
6.0
250
1.8
3.0
2.0
1.0
0.0
1.6
200
1.4
1.2
5
10
15
20
25
30
35
40
1.0
0.8
100
0.6
TA=25°C
1LED
ILED=1A
0.4
0.2
L=100µA
ILED=1A
50
0
45
0
5
INPUT VOLTAGE (V)
10
15
20
25
30
35
40
45
0
5
10
INPUT VOLTAGE (V)
15
20
25
30
35
40
45
40
45
100
120
INPUT VOLTAGE (V)
Enable Current
vs. Enable Voltage
Shutdown Current
vs. Input Voltage
ICC Limit
vs. Input Voltage
160
40
200
140
30
25
20
15
10
TA=25°C
ILED=0A
5
0
180
160
120
ICC LIMIT (mA)
35
ENABLE CURRENT (µA)
SHUTDOWN CURRENT (µA)
VCS_MIN
150
0.0
0
VCS_MAX
CURRENT SENSE VOLTAGE
(mV)
TA = 25°C
ILED = 0A
ICC = 0A
4.0
VCC (V)
ENABLE THRESHOLD (V)
5.0
100
80
60
40
0
5
10
15
20
25
30
35
40
100
80
60
TA=25°C
VCC=4.2V
ILED=0A
40
20
0
0
45
120
TA=25°C
20
-5
140
0
5
INPUT VOLTAGE (V)
10
15
20
25
30
35
40
0
45
5
10
ENABLE VOLTAGE (V)
Supply Current
vs. Temperature
15
20
25
30
35
INPUT VOLTAGE (V)
VCC
vs. Temperature
Enable Threshold
vs. Temperature
2.0
1.2
6.0
1.0
5.0
ENABLE THRESHOLD (V)
0.8
4.0
VCC (V)
SUPPLY CURRENT (mA)
1.8
0.6
0.4
3.0
2.0
VIN=12V
ILED=0A
0.2
VIN=12V
ILED=0A
ICC=0A
1.0
0.0
-20
0
20
40
60
80
TEMPERATURE (°C)
April 20, 2015
100
120
ON
1.4
1.2
OFF
1.0
0.8
0.6
1LED
ILED=1A
0.4
0.2
0.0
-40
1.6
0.0
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
6
100
120
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
Revision 1.2
Micrel, Inc.
MAQ3203
Typical Characteristics (Continued)
VIN Shutdown Current
vs. Temperature
0.3
250
50
EN = 0V
VIN = 12V
0.2
0.15
0.1
0.05
200
40
35
25
-25
0
25
50
75
TEMPERATURE (°C)
April 20, 2015
100
125
1LED
ILED=1A
100
20
15
10
D_VCS
50
VIN=12V
VEN=VIN
0
-50
VCS_MIN
150
30
5
0
VCS_MAX
CURRENT SENSE VOLTAGE
(mV)
45
0.25
ENABLE CURRENT (uA)
VIN SHUTDOWN CURRENT (uA)
Current-Sense Voltage
vs. Temperature
Enable Current
vs. Temperature
0
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
7
100
120
-40
-20
0
20
40
60
80
100
120
TEMPERATURE (°C)
Revision 1.2
Micrel, Inc.
MAQ3203
Functional Characteristics
April 20, 2015
8
Revision 1.2
Micrel, Inc.
MAQ3203
Functional Characteristic (Continued)
April 20, 2015
9
Revision 1.2
Micrel, Inc.
MAQ3203
Functional Diagram
Functional Description
The frequency of operation depends upon input voltage,
total LEDs voltage drop, LED current and temperature.
The calculation for frequency of operation is given in
application section.
The MAQ3203 is a hysteretic step-down driver which
regulates the LED current over wide input voltage range.
The device operates from a 4.5V to 42V input MOSFET
voltage range and provides up to 0.5A source and 1A
sink drive capability. When the input voltage reaches
4.5V, the internal 5V VCC is regulated and the DRV pin is
pulled high to turn on an external MOSFET if EN pin and
DIM pin are high. The inductor current builds up linearly.
When the CS pin voltage hits the VCS(MAX) with respect to
VIN, the MOSFET turns off and the Schottky diode takes
over and returns the current to VIN. Then the current
through inductor and LEDs starts decreasing. When CS
pin hits VCS(MIN), the MOSFET turns on and the cycle
repeats.
April 20, 2015
The MAQ3203 has an on board 5V regulator which is
for internal use only. Connect a 1µF capacitor on VCC
pin to analog ground.
The MAQ3203 has an EN pin which gives the flexibility to
enable and disable the output with logic high and low
signals.
The MAQ3203 also has a DIM pin which can turn on and
off the LEDs if EN is in HIGH state. This DIM pin controls
the brightness of the LED by varying the duty cycle of
DIM from 1% to 99%.
10
Revision 1.2
Micrel, Inc.
MAQ3203
Frequency of Operation
Refer to Equation 2 to calculate the frequency spread
across input supply.
Application Information
The internal block diagram of the MAQ3203 is shown in
the Functional Diagram. The MAQ3203 is composed of a
current-sense comparator, voltage and current reference,
5V regulator and MOSFET driver. Hysteretic mode
control – also called bang-bang control – is a topology
that does not employ an error amplifier, using an error
comparator instead.
VL = L
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 makes a design easy, and avoids
problems of instability.
Eq. 2
L is the inductance; ∆IL is fixed (the value of the
hysteresis):
∆IL =
Transient response to load and line variation is very fast
and only depends on propagation delay. This makes the
control scheme very popular for certain applications.
VCS(MAX ) - VCS(MIN)
R CS
Eq. 3
VL is the voltage across inductor L which varies by
supply.
LED Current and RCS
The main feature in MAQ3203 is to control the LED
current accurately within ±5% of set current. Choosing a
high-side RCS resistor helps for setting constant LED
current irrespective of wide input voltage range. Equation
1 gives the RCS value:
RCS
ΔI L
Δt
For current rising (MOSFET is ON):
tr = L
∆IL
VL _ RISE
Eq. 4
where:
1 VCS(MAX ) + VCS(MIN)
= x(
)
2
ILED
Eq. 1
VL_RISE = VIN − ILED × RCS − VLED
For current falling (MOSFET is OFF):
Table 1. RCS for LED Current
∆IL
RCS (Ω)
ILED (A)
I R (W)
Size (SMD)
1.33
0.15
0.03
0603
0.56
0.35
0.07
0805
0.4
0.5
0.1
0805
where:
0.28
0.7
0.137
0805
VL_FALL = VD + ILED × RCS + VLED
0.2
1.0
0.2
1206
0.13
1.5
0.3
1206
0.1
2.0
0.4
2010
0.08
2.5
0.5
2010
0.068
3.0
0.6
2010
2
For VCS(MAX) and VCS(MIN), refer
Characteristics section.
April 20, 2015
to
the
tf = L
VL _ FALL
T = t r + t f , FSW =
FSW =
Eq. 5
1
T
( VD + ILED × RCS + VLED ) × ( VIN - ILED × RCS - VLED )
L × ΔIL × ( VD + VIN )
where :
Electrical
•
•
•
•
11
VD is Schottky diode forward drop
VLED is total LEDs voltage drop
VIN is input voltage
ILED is average LED current
Revision 1.2
Micrel, Inc.
MAQ3203
Given an inductor value, the size of the inductor can be
determined by its RMS and peak current rating.
Inductor
According to the above equation, choose the inductor to
make the operating frequency no higher than 1.5MHz.
Table 2, Table 3, and Table 4 give a reference inductor
value and corresponding frequency for a given LED
current. For space-sensitive applications, smaller inductor
with higher switching frequency could be used but
efficiency of the regulator will be reduced.
VCS(MAX ) - VCS(MIN)
∆IL
= 2×
= 0.18
IL
VCS(MAX ) + VCS(MIN)
IL(RMS) = IL2 +
Table 2. Inductor for VIN = 12V, 1 LED
RCS (Ω)
ILED (A)
L (µH)
FSW (kHz)
1.33
0.15
220
474
0.56
0.35
100
439
0.4
0.5
68
461
0.28
0.7
47
467
0.2
1.0
33
475
0.13
1.5
22
463
0.1
2.0
15
522
0.08
2.5
12
522
0.068
3.0
10
533
IL(PK ) = IL +
1 2
∆I ≈ IL
12 L
1
∆IL = 1.09IL
2
where:
IL is inductor average current.
Select an inductor with saturation current rating at least
30% higher than the peak current.
MOSFET
MOSFET selection depends upon the maximum input
voltage, output LED current and switching frequency.
The selected MOSFET should have 30% margin on
maximum voltage rating for high reliability requirements.
Table 3. Inductor for VIN = 24V, 4 LEDs
The MOSFET channel resistance RDSON is selected such
that it helps to get the required efficiency at the required
LED currents as well as meets the cost requirement.
RCS (Ω)
ILED (A)
L (µH)
FSW (kHz)
1.33
0.15
470
474
0.56
0.35
220
426
0.4
0.5
150
447
0.28
0.7
100
470
0.2
1.0
68
493
0.13
1.5
47
463
0.1
2.0
33
507
0.08
2.5
27
496
2
PLOSS(CON) = IRMS
× R DSON
(FET )
0.068
3.0
22
517
IRMS(FET ) = ILED × D
Logic level MOSFETs are preferred as the drive voltage
is limited to 5V.
The MOSFET power loss has to be calculated for proper
operation. The power loss consists of conduction loss
and switching loss. The conduction loss can be found by:
D=
Table 4. Inductor for VIN = 36V, 8 LEDs
RCS (Ω)
ILED (A)
L (µH)
FSW (kHz)
1.33
0.15
470
495
0.56
0.35
220
446
0.4
0.5
150
467
0.28
0.7
100
490
0.2
1.0
68
515
0.13
1.5
47
485
0.1
2.0
33
530
0.08
2.5
27
519
0.068
3.0
22
541
April 20, 2015
Eq. 6
12
Eq. 7
VTOTAL _ LED
VIN
Revision 1.2
Micrel, Inc.
MAQ3203
The switching loss occurs during the MOSFET turn-on
and turn-off transition and can be found by:
V ×I
×F
PLOSS( TRAN) = IN LED SW × (Qgs2 + Qgd )
IDRV
IDRV =
VDRV
RGATE
Proper snubber design requires the parasitic inductance
and capacitance be known. A method of determining
these values and calculating the damping resistor value
is outlined below:
1. Measure the ringing frequency at the switch node
which is determined by parasitic LP and CP. Define
this frequency as f1.
Eq. 8
2. Add a capacitor CS (normally at least 3 times as big
as the COSS of the diode) across the diode and
measure the new ringing frequency. Define this new
(lower) frequency as f2. LP and CP can now be solved
using the values of f1, f2 and CS.
where:
RGATE is total MOSFET resistance, Qgs2 and Qgd can be
found in a MOSFET manufacturer datasheet.
3. Add a resistor RS in series with CS to generate critical
damping. If the snubber resistance is equal to the
characteristic impedance of the resonant circuit
(1/sqrt(LPCP)), the resonant circuit will be critically
damped and have no ringing.
The total power loss is:
PLOSS( TOT ) = PLOSS(CON) + PLOSS( TRAN)
Eq. 9
Step 1: First measure the ringing frequency on the switch
node voltage when the high-side MOSFET turns on. This
ringing is characterized by the equation:
The MOSFET junction temperature is given by:
TJ = PLOSS( TOT ) × R θJA + TA
Eq. 10
1
f1 =
The TJ must not exceed maximum junction temperature
under any conditions.
2π LP × CP
Eq. 11
where:
Snubber
A RC voltage snubber is used to damp out highfrequency ringing on the switch node caused by parasitic
inductance and capacitance. The capacitor is used to
slow down the switch node rise and fall time and the
resistor damps the ringing. Excessive ringing can cause
the MAQ3203 to operate erratically by prematurely
tripping its current limit comparator circuitry.
CP and LP are the parasitic capacitance and inductance.
Step 2: Add a capacitor, CS, in parallel with the Schottky
diode. The capacitor value should be approximately 3
times the COSS of D1. Measure the frequency of the
switch node ringing, f2.
The snubber is connected across the Schottky diode as
shown in the evaluation board schematic. Capacitor CS
(C4) is used to block the DC voltage across the resistor,
minimizing the power dissipation in the resistor. This
capacitor value should be between two to five times the
parasitic capacitance of the MOSFET COSS and the
Schottky diode junction capacitance Cj. A capacitor that is
too small will have high impedance and prevent the
resistor from damping the ringing. A capacitor that is too
large causes unnecessary power dissipation in the
resistor, which lowers efficiency.
f2 =
1
2π LP × (C S + CP )
Eq. 12
Define f’ as:
f' =
f1
f2
Eq. 13
The snubber components should be placed as close as
possible to the Schottky diode. Placing the snubber too
far from the diode or using an etch that is too long or too
thin adds inductance to the snubber and diminishes its
effectiveness.
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MAQ3203
Freewheeling Diode
The diode provides a conduction path for the inductor
current during the switch off time. The reverse voltage
rating of the diode should be at least 1.2 times the
maximum input voltage. A Schottky diode is recommend
for highest efficiency.
Combining the equations for f1, f2 and f’ to derive CP, the
parasitic capacitance:


CS
 CP =

, 2


2
×
(f
)
−
1


Eq. 14
The Schottky diode can be the major source of power
loss, especially at the maximum input voltage. The
current through the diode is equal to the LED current with
a duty cycle of (VIN – VLED)/VIN.
LP is solved by re-arranging the equation for f1:
The diode dissipation is given by:
LP =
1
(2π )2 × CP × (f1 )2
Eq. 15
PD = ILED ×
(VIN − VLED )
× Vf
VIN
Eq. 18
Step 3: Calculate the damping resistor. Critical damping
occurs at Q = 1:
Q=
1
RS
LP
=1
C S + CP
Vf is the forward voltage of the diode at ILED. A Schottky
diode forward voltage is typically 0.6V at its full rated
current. It is normal design practice to use a diode rated
at 1.5 to 2 times output current to maintain efficiency.
This derating allows Vf to drop to approximately 0.5V.
When calculating the “worst case” power dissipation, use
the maximum input voltage and the actual diode forward
voltage drop at the maximum operating temperature;
otherwise the calculated power dissipation will be
artificially high. The forward voltage drop of a diode
decrease as ambient temperature is increased, at a rate
of −1.0mV/°C.
Eq. 16
Solving for RS:
RS =
LP
C S + CP
Eq. 17
Input Capacitor
The ceramic input capacitor is selected by voltage rating
and ripple current rating. To determine the input current
ripple rating, the RMS value of the input capacitor can be
found by:
The snubber capacitor, CS, is charged and discharged
each switching cycle. The energy stored in CS is
dissipated by the snubber resistor, RS, two times per
switching period. This power is calculated in the equation
below:
PSNUBBER = fS × C S × VIN 2
ICIN(RMS) = ILED × D × (1 − D )
Eq. 19
Eq. 18
The power loss in the input capacitor is:
where:
PLOSS(CIN) = I2 CIN(RMS) × CINESR
fS is the switching frequency for each phase. VIN is the
DC input voltage.
An alternate method to reduce the switch node ringing is
to place a 2.2Ω resistor in series with the n-channel
MOSFETs gate pin. This will slow down both the rising
and falling edge of the switch node waveform.
April 20, 2015
Eq. 20
The input capacitor current rating can be considered as
ILED/2 under the worst condition D = 50%.
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MAQ3203
LED Ripple Current
The LED current is the same as inductor current. If LED
ripple current needs to be reduced then place a 4.7µF/50V
ceramic capacitor across LED.
Frequency Dithering
The MAQ3203 is designed to reduce EMI by dithering the
switching frequency ±12% in order to spread the
frequency spectrum over a wider range. This lowers the
EMI noise peaks (see Figure 1) generated by the
switching regulator.
Output Voltage Frequency
Spectrum with Dither
100
90
Amplitude (dBµV)
80
70
60
50
40
30
20
10
0
100
1000
10000
Frequency (kHz)
Figure 1. Output Voltage Frequency Spectrum
with Dither
Switching regulators generate noise by their nature and
they are the main EMI source to interference with nearby
circuits. If the switching frequency of a regulator is
modulated via frequency dithering, the energy of the EMI is
spread among many frequencies instead of concentrated
at fundamental switching frequency and its harmonics. The
MAQ3203 modulates the VCS(MAX) with amplitude ±6mV by
a pseudo random generator to generate the ±12% of the
switching frequency dithering to reduce the EMI noise
peaks.
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Micrel, Inc.
MAQ3203
PCB Layout Guidelines
Warning!!! To minimize EMI and output noise, follow
these layout recommendations.
Output Capacitor
• If LED ripple current needs to be reduced then place a
4.7µF/50V capacitor across LED. The capacitor must
be placed as close to the LED as possible.
PCB layout is critical to achieve reliable, stable and
efficient performance. A ground plane is required to
control EMI and minimize the inductance in power, signal
and return paths.
MOSFET
• Place the MOSTET as close as possible to the
MAQ3203 to avoid the trace inductance. Provide
sufficient copper area on MOSFET ground to dissipate
the heat.
The following guidelines should be followed to insure
proper operation of the MAQ3203 regulator:
IC
• Use thick traces to route the input and output power
lines.
• Signal and power grounds should be kept separate
and connected at only one location.
Diode
• Place the Schottky diode on the same side of the
board as the IC and input capacitor.
• The connection from the Schottky diode’s Anode to the
switching node must be as short as possible.
• The diode’s Cathode connection to the RCS must be
keep as short as possible.
Input Capacitor
• Place the input capacitors on the same side of the
board and as close to the IC as possible.
• Keep both the VIN and PGND traces as short as
possible.
• Place several vias to the ground plane close to the
input capacitor ground terminal, but not between the
input capacitors and IC pins.
• Use either X7R or X5R dielectric input capacitors. Do
not use Y5V or Z5U type capacitors.
• Do not replace the ceramic input capacitor with any
other type of capacitor. Any type of capacitor can be
placed in parallel with the input capacitor.
• If a Tantalum input capacitor is placed in parallel with
the input capacitor, it must be recommended for
switching regulator applications and the operating
voltage must be derated by 50%.
• In “Hot-Plug” applications, a Tantalum or Electrolytic
bypass capacitor must be placed in parallel to ceramic
capacitor to limit the over-voltage spike seen on the
input supply with power is suddenly applied. In this
case an additional Tantalum or Electrolytic bypass
input capacitor of 22µF or higher is required at the
input power connection if necessary.
RC Snubber
• If a RC snubber is needed, place the RC snubber on
the same side of the board and as close to the
Schottky diode as possible.
RCS (Current-Sense Resistor)
• VIN and CS pin must be as close as possible to RCS.
Make a Kelvin connection to the VIN and CS pin
respectively for current sensing.
Trace Routing Recommendation
• Keep the power traces as short and wide as possible.
One current flowing loop is during the MOSFET ON
time, the traces connecting the input capacitor CIN,
RCS, LEDs, Inductor, the MOSFET and back to CIN.
The other current flowing loop is during the MOSFET
OFF time, the traces connecting RCS, LED, inductor,
freewheeling diode and back to RCS. These two loop
areas should kept as small as possible to minimize the
noise interference,
• Keep all analog signal traces away from the switching
node and its connecting traces.
Inductor
• Keep the inductor connection to the switch node
(MOSFET drain) short.
• Do not route any digital lines underneath or close to
the inductor.
• To minimize noise, place a ground plane underneath
the inductor.
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Micrel, Inc.
MAQ3203
Ripple Measurements
To properly measure ripple on either input or output of a
switching regulator, a proper ring in tip measurement is
required. Standard oscilloscope probes come with a
grounding clip, or a long wire with an alligator clip.
Unfortunately, for high-frequency measurements, this
ground clip can pick-up high-frequency noise and
erroneously inject it into the measured output ripple.
The standard evaluation board accommodates a
homemade version by providing probe points for both the
input and output supplies and their respective grounds.
This requires the removing of the oscilloscope probe
sheath and ground clip from a standard oscilloscope
probe and wrapping a non-shielded bus wire around the
oscilloscope probe. If there does not happen to be any
non-shielded bus wire immediately available, the leads
from axial resistors will work. By maintaining the shortest
possible ground lengths on the oscilloscope probe, true
ripple measurements can be obtained.
Figure 2. Low-Noise Measurement
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Micrel, Inc.
MAQ3203
Evaluation Board Schematic
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Micrel, Inc.
MAQ3203
Bill of Materials
Item
C1, C5
Part Number
12105C475KAZ2A
GRM32ER71H475KA88L
12105C475KAZ2A
C2
GRM32ER71H475KA88L
C3225X7S1H475M
08053D105KAT2A
C3
C4
D1
GRM21BR71E105KA99L
Manufacturer
AVX
Murata
(8)
Murata
TDK
AVX
Murata
(Open) 08055A271JAT2A
AVX
(Open) GRM2165C2A271JA01D
Murata
SK36-TP
MCC
L1
SLF10145T-680M1R2
M1
FDS5672
R1
CSR 1/2 0.2 1% I
4.7µF/50V, Ceramic Capacitor, X7R, Size 1210
2
4.7µF/50V, Ceramic Capacitor, X5R, Size 1210
1
1µF/25V, Ceramic Capacitor, X5R, Size 0805
1
1µF/25V, Ceramic Capacitor, X7R, Size 0805
1
270pF/50V, Ceramic Capacitor NPO, Size 0805
1
60V, 3A, SMC, Schottky Diode
1
68µH, 1.2A, 0.14Ω, SMT, Power Inductor
1
MOSFET, N-CH, 60V, 12A, SO-8
1
0.2Ω Resistor, 1/2W, 1%, Size 1206
1
100kΩ Resistor, 1% , Size 0805
2
(9)
TDK
SK36-7-F
Qty.
AVX
C2012X7R1E105K
SK36
Description
(7)
(10)
Fairchild
(11)
Semiconductor
Diodes, Inc.
(12)
TDK
Fairchild
Semiconductor
Stackpole
Electronics,
(13)
Inc.
(14)
R2, R3
CRCW08051003FKEA
R4
CRCW08050000FKEA
Vishay
0Ω Resistor, 1%, Size 0805
1
R5
(Open) CRCW08052R20FKEA
Vishay
2.2Ω Resistor, 1%, Size 0805
1
R6
CRCW08051002FKEA
Vishay
10kΩ Resistor, 1% , Size 0805
1
High-Brightness LED Driver Controller with HighSide Current Sense
1
U1
MAQ3203YM
Vishay
(15)
Micrel, Inc.
Notes:
7. AVX: www.avx.com.
8. Murata: www.murata.com.
9. TDK: www.tdk.com.
10. MCC: www.mcc.com.
11. Fairchild Semiconductor: www.fairchildsemi.com.
12. Diodes, Inc.: www.diodes.com.
13. Stackpole Electronics, Inc.: www.seielect.com.
14. Vishay: www.vishay.com.
15. Micrel, Inc.: www.micrel.com.
April 20, 2015
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Micrel, Inc.
MAQ3203
PCB Layout Recommendations
Top Assembly
Top Layer
April 20, 2015
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Micrel, Inc.
MAQ3203
PCB Layout Recommendations (Continued)
Bottom Layer
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Micrel, Inc.
MAQ3203
Package Information and Recommended Landing Pattern(16)
8-Pin SOIC (M)
Note:
16. Package information is correct as of the publication date. For updates and most current information, go to www.micrel.com.
April 20, 2015
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Micrel, Inc.
MAQ3203
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
Micrel, Inc. is a leading global manufacturer of IC solutions for the worldwide high performance linear and power, LAN, and timing & communications
markets. The Company’s products include advanced mixed-signal, analog & power semiconductors; high-performance communication, clock
management, MEMs-based clock oscillators & crystal-less clock generators, Ethernet switches, and physical layer transceiver ICs. Company
customers include leading manufacturers of enterprise, consumer, industrial, mobile, telecommunications, automotive, and computer products.
Corporation headquarters and state-of-the-art wafer fabrication facilities are located in San Jose, CA, with regional sales and support offices and
advanced technology design centers situated throughout the Americas, Europe, and Asia. Additionally, the Company maintains an extensive network
of distributors and reps worldwide.
Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this datasheet. This
information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry,
specifications and descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual
property rights is granted by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no liability
whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties
relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright, or other intellectual property right.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product
can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical
implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A
Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully
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© 2011 Micrel, Incorporated.
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