Micrel MIC3202YME High-brightness led driver with integrated mosfet and high-side current sense Datasheet

MIC3202/MIC3202-1
High-Brightness LED Driver with
Integrated MOSFET and High-Side
Current Sense
General Description
Features
The MIC3202 is a hysteretic, step-down, constant-current,
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 MIC3202 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 MIC3202 offers a dedicated PWM input (DIM) which
enables a wide range of pulsed dimming. High-frequency
switching operation of up to 1MHz allows the use of
smaller external components, minimizing space and cost.
The MIC3202 offers a frequency dither feature for low-EMI
applications.
The MIC3202 operates over a junction temperature from
−40°C to +125°C and is available in an 8-pin e-PAD SOIC
package.
A dither disabled version MIC3202-1 is also available in
the same package as the MIC3202.
•
•
•
•
•
•
•
•
•
•
•
•
Datasheets and support documentation can be found on
Micrel’s web site at: www.micrel.com.
6V to 37V input voltage range
High efficiency (>90%)
±5% LED current accuracy
MIC3202: Dither enabled for low EMI
MIC3202-1: Dither disabled
High-side current sense (up to 1A)
Dedicated dimming control input
Hysteretic control (no compensation required)
Up to 1MHz switching frequency
Adjustable constant LED current
Over-temperature protection
−40°C to +125°C junction temperature range
Applications
•
•
•
•
•
•
Architectural, industrial, and ambient lighting
LED bulbs
Indicators and emergency lighting
Street lighting
Channel letters
12V lighting systems (MR-16 bulbs, under-cabinet
lighting, garden/pathway lighting)
_________________________________________________________________________________________________________________________
Typical Application
Efficiency
vs. Input Voltage
100
6LED
8LED
EFFICIENCY (% )
4LED
95
2LED
90
85
ILED = 1A
L = 47uH
80
6
14
22
30
38
INPUT VOLTAGE (V)
MIC3202 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
September 2010
M9999-091710-A
Micrel, Inc.
MIC3202/MIC3202-1
Ordering Information (1)
Part Number
Marking
Junction Temperature Range
Package
PWM
MIC3202YME
MIC3202YME
−40°C to +125°C
8-Pin SOIC
Dither
MIC3202-1YME
−40°C to +125°C
8-Pin SOIC
Non-Dither
MIC3202-1YME
Note:
1.
®
YM is a GREEN RoHS-compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
Pin Configuration
8-Pin ePAD SOIC
MIC3202/MIC3202-1
Pin Description
Pin
Number
Pin Name
1
VCC
2
CS
Current-Sense Input. The CS pin provides the high-side current sense to set the LED current using an
external sense resistor.
3
VIN
Input Power Supply. The VIN pin 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 1µF ceramic capacitor is
recommended to be placed as close as possible to VIN pin and the power ground (PGND) pin for
bypassing. Please refer to layout recommendations.
4
AGND
Pin Function
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.
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. The voltage has to be 2.0V or higher
to enable the current regulator. The output stage is also gated by the DIM input. 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).
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 Internal Power FET. Power Ground (PGND) is the ground path for the high current.
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.
8
LX
Drain of Internal Power MOSFET. The LX pin 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.
EP
GND
September 2010
Connect to PGND.
2
M9999-091710-A
Micrel, Inc.
MIC3202
Absolute Maximum Ratings (1, 2)
Operating Ratings (3)
VIN to PGND .................................................. −0.3V to +42V
VLX to PGND........................................ −0.3V to (VIN + 0.6V)
VCS to PGND ....................................... −0.3V to (VIN + 0.3V)
VEN to AGND ....................................... −0.3V to (VIN + 0.3V)
VDIM to AGND ...................................... −0.3V to (VIN + 0.3V)
VCC to PGND ................................................ −0.3V to +6.0V
PGND to AGND .......................................... −0.3V to + 0.3V
Junction Temperature ................................................ 150°C
Storage Temperature Range .................... −60°C to +150°C
Lead Temperature (Soldering, 10sec) ....................... 260°C
Supply Voltage (VIN).......................................... 6.0V to 37V
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) ..........................................................41°C/W
SOIC (θJC).......................................................14.7°C/W
Electrical Characteristics (4)
VIN = VEN = VDIM = 12V; CVCC = 1.0µF; TJ = 25°C, bold values indicate −40°C ≤ TJ ≤ +125°C; unless noted.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Units
Input Supply
6.0
VIN
Input Voltage Range (VIN)
IS
Supply Current
LX Pin = open
ISD
Shut Down Current
VEN = 0V; TJ = from -40ºC to 85ºC
UVLO
VIN UVLO Threshold
UVLOHYS
VIN UVLO Hysteresis
VIN Rinsing
37.0
V
1.75
mA
0.05
5
µA
4
4.5
1.2
3.2
500
V
mV
VCC Supply
VCC
VCC Output Voltage
VCS = VIN = 12V, ICC = 10mA
4.5
5
5.5
V
Current Limit
VCS(MAX)
Current-Sense Upper Threshold
VCS(MAX ) = VIN − VCS
199
212
225
mV
VCS(MIN)
Current-Sense Lower Threshold
VCS(MIN ) = VIN − VCS
165
177
189
mV
VCS Hysteresis
VCSHYS
35
Current-Sense Response Time
Current-Sense Input Current
VCS Rising
60
VCS Falling
40
VIN - VCS = 200mV
mV
ns
3
µA
1
MHz
Frequency
FMAX
Maximum Switching Frequency
Dithering (MIC3202)
VDITH
FDITHER
VCS Hysteresis Dithering Range(5)
Frequency Dithering Range
(5)
% of Switching Frequency
±6
mV
±12
%
Enable Input
ENHI
2.0
EN Logic Level High
V
0.4
EN Logic Level Low
ENLO
EN Bias Current
Start-up Time
September 2010
VEN = 12V
30
60
VEN = 0V
0.1
1
From EN Pin going high to LX
going low
30
3
V
µA
µs
M9999-091710-A
Micrel, Inc.
MIC3202
Electrical Characteristics (4)
VIN = VEN = VDIM = 12V; CVCC = 1.0µF; TJ = 25°C, bold values indicate −40°C ≤ TJ ≤ +125°C; unless noted.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Units
Dimming Input
DIMHI
2.0
DIM Logic Level High
V
0.4
DIM Logic Level Low
DIMLO
fDIM
DIM Bias Current
VDIM = 12V
20
35
VDIM = 0V
0.1
1
Maximum Dimming Frequency
V
µA
20
kHz
275
625
mΩ
5
50
µA
Internal MOSFET
RDS(ON)
MOSFET RDS(ON)
ILX = 200mA
LX Leakage Current
VEN = 0V; VIN = VLX = 37V
Thermal Protection
TLIM
Over-Temperature Shutdown
TLIMHYS
Over-Temperature Shutdown Hysteresis
TJ Rising
160
20
°C
Notes:
1.
Exceeding the absolute maximum rating may damage the device.
2.
Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF.
3.
The device is not guaranteed to function outside its operating rating.
4.
Specification for packaged product only.
5.
Guaranteed by design.
September 2010
4
M9999-091710-A
Micrel, Inc.
MIC3202
Typical Characteristics
Efficiency
vs. Input Voltage
LED Current Normalized
vs. Input Voltage
100
95
2LED
90
1LED
85
80
ILED = 1A
L = 47uH
75
ILED = 1A
L = 47uH
ILED = 1A
L = 47uH
1.01
2LED
4LED
0.99
1LED
14
22
30
6
14
22
100%
30
38
500
1LED
250
6LED
22
14
50%
1LED
25%
30
ILED = 1A
L = 47uH
0%
38
30
38
2.5
2.0
1.5
1.0
VOUT = OPEN
0.5
VCC = 5V
NO-SWITCHING
0.0
6
14
INPUT VOLTAGE (V)
22
30
6
38
VIN Shutdown Current
vs. Input Voltage
14
22
30
38
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
VCC Voltage
vs. Input Voltage
0.5
22
3.0
8LED
75%
8LED
0
8LED
1LED
6
SUPPLY CURRENT (mA)
DUTY CYCLE (%)
750
6LED
INPUT VOLTAGE (V)
2LED
4LED
4LED
VIN Supply Current
vs. Input Voltage
6LED
4LED
ILED = 1A
L = 47uH
14
-1.0%
Duty Cycle
vs. Input Voltage
1000
2LED
2LED
0.0%
INPUT VOLTAGE (V)
Switching Frequency
vs. Input Voltage
6
1.0%
-2.0%
38
INPUT VOLTAGE (V)
CS Voltage
vs. Input Voltage
5.050
250
VLED =3.5V
ILED =1A
0.3
0.2
0.1
5.025
CS VOLTAGE (mV)
V CC VOLTAGE (V)
0.4
5.000
4.975
4.950
14
22
30
38
Enable Bias Current
vs. Enable Voltage
125
14
22
30
38
6
DIMMING BIAS CURRENT (µA)
100
75
50
VIN = VEN
VLED =OPEN
ILED = 0A
14
22
30
ENABLE VOLTAGE (V)
September 2010
38
22
30
INPUT VOLTAGE (V)
Dimming Bias Current
vs. Dimming Voltage
Switch RDSON
vs. Input Voltage
38
425
75
50
VIN = VDIM
25
375
325
275
VLED =OPEN
VLED = 3.5V
ILED = 0A
ILED = 1A
225
0
0
14
INPUT VOLTAGE (V)
100
6
VCS MIN
175
150
6
INPUT VOLTAGE (V)
25
200
ILED = 0A
0.0
6
VCS MAX
225
VLED = OPEN
V EN = 0V
SWITCH RDSON (mΩ)
SWITCHING FREQUENCY (kHz)
8LED
0.98
6
SHUTDOWN CURRENT (µA)
6LED
1.00
LED CURRENT (%)
8LED
LED CURRENT NORM (A)
EFFICIENCY (% )
2.0%
1.02
6LED
4LED
ENABLE BIAS CURRENT (µA)
LED Current Accuracy
vs. Input Voltage
6
14
22
30
DIMMING VOLTAGE (V)
5
38
6
14
22
30
38
INPUT VOLTAGE (V)
M9999-091710-A
Micrel, Inc.
MIC3202
Typical Characteristics (Continued)`
SHUTDOWN CURRENT (µA)
ILED = 0A
1.0
0.5
0.3
0.2
0.1
-20
10
40
70
100
130
-50
-20
10
40
70
100
TEMPERATURE (°C)
TEMPERATURE (°C)
Switching Frequency
vs. Temperature
Enable Bias Current
vs. Temperature
40
ENABLE BIAS CURRENT (µA)
340
VIN = 12V
VLED = 3.5V
330
ILED = 1A
L = 47uH
320
310
300
-20
10
40
70
100
130
ILED = 1A
L = 47uH
-20
10
40
70
100
VCC Voltage
vs. Temperature
5.20
ILED = 0A
35
30
25
5.10
5.00
4.90
VIN = 12V
VLED = OPEN
ILED = 0A
4.80
-20
10
40
70
100
130
-50
-20
10
40
70
100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
CS Voltage
vs. Temperature
Switch RDSON
vs. Temperature
Case Temperature
vs. Input Voltage
CASE TEMPERATURE (º C)
SWITCH RDSON (Ω)
VCS MAX
VIN = 12V
200
VLED = 3.5V
ILED = 1A
L = 47uH
VCS MIN
175
350
300
VIN = 12V
250
150
200
10
40
70
100
-20
10
Switch Voltage
vs. Switch Current
40
70
100
130
SWITCH RDSON (mΩ)
250
200
150
100
VLED = 3.5V
270
0.8
SWITCH CURRENT (A)
September 2010
1.0
0.0
0.3
0.5
0.8
SWITCH CURRENT (A)
6
30
38
300
275
VIN = 12V
22
Switch Voltage
vs. Switch Current
280
VLED = 3.5V
14
INPUT VOLTAGE (V)
285
VIN = 12V
0
0.5
VLED = 3.5V
ILED = 1A
L = 47uH
1oz/3.5 Sq Inch
6
Switch RDSON
vs. Switch Current
290
300
0.3
30
TEMPERATURE (°C)
TEMPERATURE (°C)
50
40
20
-50
130
SWITCH VOLTAGE (mV)
-20
130
50
400
225
130
TEMPERATURE (°C)
ISW = 0.2A
SWITCH VOLTAGE (mV)
VLED = 3.5V
VLED = OPEN
450
0.0
VIN = 12V
Falling
-50
VIN =VEN = 12V
-50
250
-50
3.5
130
20
-50
Rising
4.0
3.0
0
-50
SWITCHING FREQUENCY (kHz)
VIN = 12V
VEN = 0V
V CC VOLTAGE (V)
0.0
CS VOLTAGE (mV)
4.5
0.4
VIN =VIN = 12V
VLED = OPEN
1.5
VIN UVLO Threshold
vs. Temperature
VIN UVLO THRESHOLD (V)
2.0
VIN SUPPLY CURRENT (mA)
Shutdown Current
vs. Temperature
VIN Supply Current
vs. Temperature
1.0
250
200
150
100
VLED = 3.5V
50
VIN = 12V
0
0.0
0.3
0.5
0.8
1.0
SWITCH CURRENT (A)
M9999-091710-A
Micrel, Inc.
MIC3202
Functional Characteristics
September 2010
7
M9999-091710-A
Micrel, Inc.
MIC3202
Functional Characteristics (Continued)
September 2010
8
M9999-091710-A
Micrel, Inc.
MIC3202
Functional Diagram
Figure 1. MIC3202/MIC3202-1 Functional Block Diagram
Functional Description
The MIC3202 is a hysteretic step-down driver which
regulates the LED current over wide input voltage range
and capable of driving up to eight 1A LEDs in series.
The device operates from a 6V to 37V input. When the
input voltage reaches 6V, the internal 5V VCC is
regulated and the LX pin is pulled low if the EN pin and
DIM pin are high. The inductor current builds up linearly.
When the CS pin voltage hits 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.
September 2010
The frequency of operation depends upon the input voltage,
total LED voltage drop, LED current and temperature. The
calculation for frequency of operation is given in the
Application Information section.
The MIC3202 has an EN pin which gives the flexibility to
enable and disable the output with logic high and low
signals.
The MIC3202 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 pin
from 1% to 99%.
9
M9999-091710-A
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 highside RCS resistor sets LED current. The following
equation gives the RCS value:
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):
RCS =
1
x(
2
VCS(MAX ) + VCS(MIN)
ILED
)
tf = L
RCS (Ω)
ILED (A)
I2R (W)
Size (SMD)
1.33
0.15
0.03
0603
0.56
0.35
0.07
0805
0.4
0.5
0.1
0805
0.28
0.7
0.137
0805
0.2
1.0
0.2
1206
ΔI L
VL _ FALL
where:
VL_FALL = VD + ILED × RCS + VLED
1
T = t r + t f , f SW =
T
(V + I
×R + V
) × (V - I
×R - V
)
fSW = D LED CS LED IN LED CS LED
L × ΔIL × (VD + VIN)
Table 1. RCS Values for Various LED Currents
For VCS(MAX) and VCS(MIN), refer to the Electrical
Characteristic table.
September 2010
where:
VD is Schottky diode forward drop.
VLED is total LEDs voltage drop.
VIN is input voltage.
ILED is average LED current.
10
M9999-091710-A
Micrel, Inc.
MIC3202
Inductor
According to the above equation, choose the inductor to
make the operating frequency no higher than 1.0MHz.
Tables 2, 3, and 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 the efficiency of
the regular will be reduced.
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
Table 2. Inductor for VIN = 12V, 1 LED
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
where:
IL is inductor average current.
Select an inductor with saturation current rating at least 30%
higher than the peak current.
Free-Wheeling Diode
The free-wheeling diode should have the reverse voltage
rating to accommodate the maximum input voltage. The
forward voltage drop should be small to get the lowest
conduction dissipation for high efficiency. The forward current
rating has to be at least equal to LED current. A Schottky
diode is recommended for highest efficiency.
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:
ICIN(RMS) = ILED × D × (1 - D)
The power loss in the input capacitor is:
2
PLOSS(CIN) = I
Table 3. Inductor for VIN = 24V, 4 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
Table 4. Inductor for VIN = 36V, 8 LEDs
Given an inductor value, the size of the inductor can be
determined by its RMS and peak current rating.
VCS(MAX ) - VCS(MIN)
ΔIL
= 2×
= 0.18
IL
VCS(MAX ) + VCS(MIN)
IL(RMS ) = IL2 +
IL(PK ) = IL +
September 2010
1 2
ΔI ≈ I
12 L L
1
ΔI = 1.09IL
2 L
CIN(RMS)
× CIN
ESR
The input capacitor current rating can be considered as
ILED/2 under the worst condition D = 50%.
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 MIC3202 is designed to reduce EMI by dithering the
switching frequency ±12% in order to spread the noise
spectrum over a wider range. This lowers the EMI noise
peaks generated by the switching regulator.
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 MIC3202
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.
11
M9999-091710-A
Micrel, Inc.
MIC3202
PCB Layout Guidelines
Warning!!! To minimize EMI and output noise, follow
these layout recommendations.
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.
The following guidelines should be followed to insure
proper operation of the MIC3202 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.
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.
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.
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.
RC Snubber
Place the RC snubber on the same side of the board and as
close to the Schottky diode as possible. Also the snubber
closest to LX pin and PGND pin.
RCS (Current-Sense Resistor)
Make a Kelvin connection to the VIN and CS pins
respectively for current sensing.
Trace Routing Recommendation
Keep the power traces as short and wide as possible. One
current flowing loop is during the internal MOSFET ON time,
the traces connecting the input capacitor CIN, RCS, LEDs,
Inductor, the LX pin, PGND and back to CIN. The other
current flowing loop is during the internal MOSFET OFF
time, the traces connecting RCS, LED, inductor, free wheeling
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 (LX Pin)
short.
Do not route any digital lines underneath or close to the
inductor.
To minimize noise, place a ground plane underneath the
inductor.
September 2010
12
M9999-091710-A
Micrel, Inc.
MIC3202
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 home
made 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.
September 2010
Figure 2. Low-Noise Measurement
13
M9999-091710-A
Micrel, Inc.
MIC3202
Evaluation Board Schematic
Figure 3. MIC3202 Application Circuit
(R9 is for test purposes only)
September 2010
14
M9999-091710-A
Micrel, Inc.
MIC3202
Bill of Materials
Item
C1, C2,
C8
Part Number
12105C475KAZ2A
GRM32ER71H475KA88L
08053D105KAT2A
C3, C9
C4, C7
GRM21BR71E105KA99L
D1
AVX
(2)
Murata
AVX(1)
Murata
(3)
06035C271KAT2A
AVX(1)
GRM188R71H104KA93D
(2)
Murata
4.7µF/50V, Ceramic Capacitor, X7R, Size 1210
2
1µF/25V, Ceramic Capacitor, X5R, Size 0805
1
1µF/25V, Ceramic Capacitor, X7R, Size 0805
1
270pF/50V, Ceramic Capacitor NPO, Size 0603
2
0.1µF/50V, Ceramic Capacitor, X7R, Size 0603
2
60V, 2A, SMA, Schottky Diode
1
AVX(1)
Murata(2)
C1608X7R1H104K
TDK(3)
SS24-TP
MCC(4)
SS24
Qty.
(2)
TDK
GRM188R71H271KA01D
Description
(1)
C2012X7R1E105K
06035C104MAT
C5, C6
Manufacturer
Fairchild(5)
D2, D3
B0530WS-TP
MCC(4)
30V, 200mA, Schottky diode, SOD-323
2
L1
SLF10145T-470M1R4
TDK(3)
47µH, 1.4A, SMT, Power Inductor
1
R1
CSR 1/2 0.2 1% I
0.2Ω Resistor, 1/2W, 1%, Size 1206
1
R2, R3
CRCW06031003FKEA
Vishay(8)
100kΩ Resistor, 1%, Size 0603
2
R4
CRCW08052R20FKEA
(8)
Vishay
2.2Ω Resistor, 1%, Size 0805
1
R5
CRCW080510R0FKEA
Vishay(8)
10Ω Resistor, 1%, Size 0805
1
R6
CRCW060310K0FKEA
Vishay(8)
10kΩ Resistor, 1%, Size 0603
1
R7, R8
CRCW06030000FKEA
(8)
Vishay
0Ω Resistor, 1%, Size 0603
2
R9
CRCW060349R9FKEA
Vishay(8)
49.9Ω Resistor, 1%, Size 0603
1
RV1
U1
U2
3386P-1-104TLF
MIC3202YM
MIC1557YM5
Stackpole
Electronics,
Inc(7)
(9)
POT 100kΩ 3/8" SQ CERM SL ST
1
Micrel, Inc.
(10)
High Brightness LED Driver with High-Side Current Sense
1
Micrel, Inc.
(10)
RC Time/Oscillator (SOT-23-5)
1
Bourns
Notes:
1. AVX: www.avx.com.
2. Murata: www.murata.com.
3. TDK: www.tdk.com.
4. MCC: www.mccsemi.com.
5. Fairchild: www.fairchildsemi.com.
6. Diodes Inc. : www.diodes.com.
7. Stackpole Electronics: www.seielect.com.
8. Vishay: www.vishay.com.
9. Bourns Inc : www.bourns.com.
10. Micrel, Inc.: www.micrel.com.
September 2010
15
M9999-091710-A
Micrel, Inc.
MIC3202
PCB Layout Recommendation
Top Assembly
Top Layer
September 2010
16
M9999-091710-A
Micrel, Inc.
MIC3202
PCB Layout Recommendation (Continued)
Bottom Layer
September 2010
17
M9999-091710-A
Micrel, Inc.
MIC3202
Package Information
8-Pin ePAD SOIC (ME)
September 2010
18
M9999-091710-A
Micrel, Inc.
MIC3202
Recommended Landing Pattern
8-Pin ePAD SOIC (ME)
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 makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. 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 indemnify
Micrel for any damages resulting from such use or sale.
© 2010 Micrel, Incorporated.
September 2010
19
M9999-091710-A