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MIC3203/MIC3203-1
High-Brightness LED Driver Controller with High-Side Current Sense
General Description
The MIC3203 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 MIC3203 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 MIC3203 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 MIC3203 offers frequency dither feature for EMI control. The MIC3203 operates over a junction temperature from -40C to +125C and is available in an 8-pin SOIC package. A dither disabled version MIC3203-1 is also available in the same package as the MIC3203. Datasheets and support documentation can be found on Micrel's web site at: www.micrel.com.
Features
* * * * * * * * * * * * 4.5V to 42V input voltage range High efficiency (>90%) 5% LED current accuracy MIC3203: Dither enabled for low EMI MIC3203-1: Dither disabled 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 -40C to +125C 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
MIC3203 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
March 2010
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Micrel, Inc.
MIC3203
Ordering Information (1)
Part Number MIC3203YM MIC3203-1YM
Note: 1. YM is a GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
(R)
Marking MIC3203YM MIC3203-1YM
Junction Temperature Range -40C to +125C -40C to +125C
Package 8-Pin SOIC 8-Pin SOIC
PWM Dither Non-Dither
Pin Configuration
8-Pin SOIC MIC3203/MIC3203-1
Pin Description
Pin Number 1 Pin Name VCC Pin Function Voltage Regulator Output. The VCC pin supplies the power to the internal circuitry. The VCC in the output of a linear regulator which is powered from VIN. A 1F 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. Current-Sense Input. The CS pin provides the high-side current sense to set the LED current with an external sense resistor. 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 10F 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. Ground pin for analog circuitry. Internal signal ground for all low power sections. 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 1A). 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. 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. 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. 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.
2
CS
3 4
VIN AGND
5
EN
6
DIM
7
PGND
8
DRV
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Absolute Maximum Ratings (1)
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 ................................................ 150C Storage Temperature Range .................... -60C to +150C Lead Temperature (Soldering, 10sec) ....................... 260C ESD Ratings (3) HBM ...................................................................... 1.5kV MM .........................................................................200V
Operating Ratings (2)
Supply Voltage (VIN).......................................... 4.5V to 42V Enable Voltage (VEN) .............................................. 0V to VIN Dimming Voltage (VDIM)................................................................. 0V to VIN Junction Temperature (TJ) ........................ -40C to +125C Junction Thermal Resistance SOIC (JA) .......................................................98.9C/W SOIC (JC).......................................................48.8C/W
Electrical Characteristics (4)
VIN = VEN = VDIM = 12V; CVCC = 1.0F; TJ = 25C, bold values indicate -40C TJ +125C; unless noted.
Symbol VIN IS ISD UVLO UVLOHYS VCC Parameter Input Voltage Range (VIN) Supply Current Shutdown Current VIN UVLO Threshold VIN UVLO Hysteresis VCC Output Voltage VIN = 12V, ICC = 10mA 4.5 201.4 199 168 165 DRV = open VEN = 0V VIN rinsing 3.2 4 500 5 212 212 177 177 35 VCS Rising VCS Falling VIN - VCS = 220mV 50 70 0.5 10 1.5 6 % of Switching Frequency 12 5.5 222.6 225 186 189 Condition Min. 4.5 1 Typ. Max. 42 3 1 4.5 Units V mA A V mV V mV mV mV mV mV ns ns A MHz mV % Input Supply
VCC Supply Current Limit VCS(MAX) VCS(MIN) VCSHYS Current Sense Upper Threshold Sense Voltage Threshold Low VCS Hysteresis Current Sense Response Time CS Input Current Frequency FMAX VDITH FDITHER Switching Frequency VCS Hysteresis Dithering Range(5) Frequency Dithering Range
(5)
VCS(MAX ) = VIN - VCS VCS(MIN ) = VIN - VCS
Dithering (MIC3203)
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Electrical Characteristics (4) (Continued)
VIN = VEN = VDIM = 12V; CVCC = 1.0F; TJ = 25C, bold values indicate -40C TJ +125C; unless noted.
Symbol ENHI ENLO Parameter EN Logic Level High EN Logic Level Low EN Bias Current Start-Up Time Dimming Input DIMHI DIMLO DIM Logic Level High DIM Logic Level Low DIM Bias Current DIM Delay Time FDIM Maximum Dimming Frequency Pull Up, ISOURCE = 10mA Pull Down, ISINK = -10mA Rise Time, CLOAD = 1000pF Fall Time, CLOAD = 1000pF TJ Rising 2 1.5 13 7 160 20 20 VDIM = 0V From DIM Pin going high to DRV going high 450 20 2.0 0.4 50 1 V V A ns kHz VEN = 12V VEN = 0V From EN Pin going high to DRV going high 30 Condition Min. 2.0 0.4 60 1 Typ. Max. Units V V A A s Enable Input
External FET Driver DRV On-Resistance DRV Transition Time Thermal Protection TLIM TLIMHYS
Notes: 1. Exceeding the absolute maximum rating may damage the device. 2. The device is not guaranteed to function outside its operating rating. 3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF. 4. Specification for packaged product only. 5. Guaranteed by design.
ns
Over-Temperature Shutdown Over-Temperature Shutdown Hysteresis
C
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Typical Characteristics
Efficiency vs. Input Voltage
100
Efficiency vs Input Voltage
100
NORMALIZED LED CURRENTS (A)
1.03
Normalized LED Currents vs. Input Voltage
L=150H ILED=1A 1.02
90
90 EFFICIENCY (%)
1.01 1LED 1 2LED 4LED 6LED
10LED 8LED
EFFICIENCY (%)
80 4LED 6LED 8LED 70 10LED
80
4LED 6LED
0.99
70
8LED 10LED L=68H ILED=1A
0.98
L=150H ILED=1A 60 0 5 10 15 20 25 30 35 40 45
60 0 5 10 15 20 25 30 INPUT VOLTAGE (V) 35 40 45
0.97 0 5 10 15 20 25 30 35 40 45
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Normalized LED Currents vs Input Voltage
1.03
Frequency vs. Input Voltage
350
L=68H ILED=1A
Frequency vs Input Voltage
700 L = 68H ILED = 1A
NORMALIZED LED CURRENTS (A)
L=150H ILED=1A
1.02
300
600
1.01
FREQUENCY (kHz)
250 4LED 200
FREQUENCY (kHz)
500
4LED
400 2LED 300 1LED
1 1LED 0.99 2LED 0.98 4LED
150
2LED
100 50
1LED 10LED 8LED 6LED 0 5 10 15 20 25 30 35 40 45
200 100
6LED
8LED
10LED
0.97 0 5 10 15 20 25 30 35 40 45
6LED 0 0 5 10 15 20 25
8LED 30 35
10LED 40 45
0
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Duty Cycle vs. Input Voltage
100 100
Duty Cycle vs Input Voltage
1.4
Supply Current vs. Input Voltage
SUPPLY CURRENT (mA)
1.2 1.0 0.8 0.6 0.4 0.2 0.0 TA = 25C ILED = 0A
75
75
DUTY CYCLE (%)
50
1LED 2LED 4LED
DUTY CYCLE (%)
50
1LED 2LED 4LED
25 6LED 8LED 0 0 5 10 15 20 25 30 35 40 45 L=150H ILED=1A
25
6LED 8LED L=68H ILED=1A 10 15 20 25 30 35
10LED
0 0 5
10LED 40 45
0
5
10
15
20
25
30
35
40
45
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
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Typical Characteristics (Continued)
VCC vs. Input Voltage
6.0 5.0 4.0 TA = 25C ILED = 0A ICC = 0A 1.8
Enable Threshold vs. Input Voltage
ENABLE THRESHOLD (V)
1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 TA = 25C ILED = 0A ICC = 0A
250
Current-Sense Voltage vs. Input Voltage
CURRENT-SENSE VOLTAGE (mV)
200 VCS_MIN VCS_MAX L = 100H ILED = 1A
VCC (V)
150
3.0 2.0 1.0 0.0 0 5 10 15 20 25 30 35 40 45
100
50
0 0 5 10 15 20 25 30 35 40 45 0 5 10 15 20 25 30 35 40 45
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Shutdown Current vs. Input Voltage
40
160
Enable Current vs. Enable Voltage
200 180 160 140 120 100 80 60 TA = 25C 40 20 0
ICC Limit vs. Input Voltage
SHUTDOWN CURRENT (A)
35 30 25 20 15 10 5 0 -5 0 5 10 15 20 25 30 35 40 45 TA = 25C ILED = 0A
ENABLE CURRENT (A)
ICC LIMIT (mA)
140 120 100 80 60 40 20 0 TA = 25C VCC = 4.2V ILED = 0A
0
5
10
15
20
25
30
35
40
45
0
5
10
15
20
25
30
35
40
45
INPUT VOLTAGE (V)
ENABLE VOTLAGE (V)
INPUT VOLTAGE (V)
Supply Current vs. Temperature
1.2 6.0 5.0 4.0
VCC vs. Temperature
ENABLE THRESHOLD (V)
2.0 1.8
Enable Threshold vs. Temperature
SUPPLY CURRENT (mA)
1.0 0.8
1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 OFF
ON
0.6 0.4 0.2 0.0 -40 -20
VCC (V)
VIN = 12V ILED = 0A
VIN = 12V ICC = 0A
3.0 2.0 1.0 0.0
0.0 -40 -20 0 20 40 60 80 100 120 -40 -20 0 20 40 60 80 100 120
0
20
40
60
80
100
120
TEMPERATURE (C)
TEMPERATURE (C)
TEMPERATURE (C)
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Typical Characteristics (Continued)
Shutdown Current vs. Temperature
3.5 50 45
Enable Current vs. Temperature
CURRENT-SENSE VOLTAGE (mV)
250
Current-Sense Voltage vs. Temperature
SHUTDOWN CURRENT (uA)
ENABLE CURRENT (uA)
3.0 2.5 2.0 1.5 1.0 0.5 0.0 -40 -20 0 20 40 60 80 100 120
40 35 30 25 20 15 10 5 0 -40 -20 0 20 40 60 80 100 120 VIN = 12V EN = VIN
200
VCS_MAX
150
VCS_MIN
VIN = 12V EN = 0V
100
_VCS ILED ILED = 1A
50
0 -40 -20 0 20 40 60 80 100 120
TEMPERATURE (C)
TEMPERATURE (C)
TEMPERATURE (C)
Switching Frequency vs. Temperature
160
4.5 4.0
UVLO Threshold vs. Temperature
ON
180
Thermal Shutdown vs. Input Voltage
OFF
SWITCHING FREQUENCY (kHz)
140
120 100 80 60 40 20 0 -40 -20 0 20 40 60 80 100 120 VIN = 12V 1ILED ILED = 1A L = 100H
3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -40 -20 0 20 40 60 80 100 120 OFF
THERMAL SHUTDOWN (C)
160 140 120 100 80 60 40 20 0 0 5 10 15 20 25 30 35 40 45 ON
TEMPERATURE (C)
UVLO THRESHOLD (V)
TEMPERATURE (C)
INPUT VOLTAGE (V)
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Functional Characteristics
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Functional Characteristics (Continued)
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Functional Diagram
Figure 1. MIC3203/MIC3203-1 Block Diagram
Functional Description
The MIC3203 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.
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 MIC3203 has an on board 5V regulator which is for internal use only. Connect a 1F capacitor on VCC pin to analog ground. The MIC3203 has an EN pin which gives the flexibility to enable and disable the output with logic high and low signals. The MIC3203 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%.
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MIC3203 Frequency of Operation To calculate the frequency spread across input supply:
IL t
Application Information
The internal block diagram of the MIC3203 is shown in Figure 1. The MIC3203 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. 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. 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. LED Current and RCS The main feature in MIC3203 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. The following equation gives the RCS value:
VL = L
L is the inductance, IL is fixed (the value of the hysteresis): VCS(MAX ) - VCS(MIN) RCS
IL =
VL is the voltage across inductor L which varies by supply. For current rising (MOSFET is ON):
IL VL _ RISE
tr = L
where: VL_RISE = VIN - ILED x RCS - VLED For current falling (MOSFET is OFF):
I L VL _ FALL
RCS =
1 VCS(MAX) + VCS(MIN) x( ) 2 ILED where:
tf = L
RCS () 1.33 0.56 0.4 0.28 0.2 0.13 0.1 0.08 0.068
Table 1. RCS for LED Current ILED (A) I2R (W) Size (SMD) 0.15 0.35 0.5 0.7 1.0 1.5 2.0 2.5 3.0 0.03 0.07 0.1 0.137 0.2 0.3 0.4 0.5 0.6 0603 0805 0805 0805 1206 1206 2010 2010 2010
VL_FALL = VD + ILED x RCS + VLED
T = t r + t f , FSW =
FSW =
1 T
(VD +ILEDxRCS + VLED) x(VIN - ILEDxRCS - VLED) L x IL x(VD + VIN)
where :
* * * *
VD is Schottky diode forward drop VLED is total LEDs voltage drop VIN is input voltage ILED is average LED current
For VCS(MAX) and VCS(MIN), refer to the Electrical Characteristic table.
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Inductor According to the above equation, choose the inductor to make the operating frequency no higher than 1.5MHz. The following Tables 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 regular will be reduced.
MIC3203 Given an inductor value, the size of the inductor can be determined by its RMS and peak current rating.
VCS(MAX ) - VCS(MIN) IL = 2x = 0.18 IL VCS(MAX ) + VCS(MIN) 12 I I 12 L L
2 IL(RMS ) = IL +
Table 2. Inductor for VIN = 12V, 1 LED L (H) FSW (kHz) RCS () ILED (A) 1.33 0.56 0.4 0.28 0.2 0.13 0.1 0.08 0.068 0.15 0.35 0.5 0.7 1.0 1.5 2.0 2.5 3.0 220 100 68 47 33 22 15 12 10 474 439 461 467 475 463 522 522 533
IL(PK ) = IL +
1 I = 1.09IL 2L
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. 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. 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:
2 PLOSS( CON) = IRMS(FET ) x RDSON
Table 3. Inductor for VIN = 24V, 4 LEDs L (H) FSW (kHz) RCS () ILED (A) 1.33 0.56 0.4 0.28 0.2 0.13 0.1 0.08 0.068 0.15 0.35 0.5 0.7 1.0 1.5 2.0 2.5 3.0 470 220 150 100 68 47 33 27 22 474 426 447 470 493 463 507 496 517
IRMS(FET ) = ILED x D D= VTOTAL _ LED VIN
Table 4. Inductor for VIN = 36V, 8 LEDs L (H) FSW (kHz) RCS () ILED (A) 1.33 0.56 0.4 0.28 0.2 0.13 0.1 0.08 0.068 0.15 0.35 0.5 0.7 1.0 1.5 2.0 2.5 3.0 470 220 150 100 68 47 33 27 22 495 446 467 490 515 485 530 519 541
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V xI xF PLOSS( TRAN) = IN LED SW x (Qgs2 + Qgd ) IDRV IDRV = VDRV RGATE
MIC3203
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 4.7F/50V ceramic capacitor across LED. Frequency Dithering The MIC3203 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 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 MIC3203 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.
where: RGATE is total MOSFET resistance, Qgs2 and Qgd can be found in a MOSFET manufacturer datasheet. The total power loss is:
PLOSS( TOT ) = PLOSS( CON) + PLOSS( TRAN)
The MOSFET junction temperature is given by:
TJ = PLOSS( TOT ) x R JA + TA The TJ must not exceed maximum junction temperature under any conditions.
Freewheeling 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 x D x (1 - D)
The power loss in the input capacitor is:
PLOSS(CIN) = I
2 CIN(RMS)
x CIN
ESR
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MIC3203 placed as close to the LED as possible.
MOSFET Place the MOSTET as close as possible to the MIC3203 to avoid the trace inductance. Provide sufficient copper area on MOSFET ground to dissipate the heat. 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 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 pin 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, 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.
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 MIC3203 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 22F or higher is required at the input power connection if necessary. 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. Output Capacitor If LED ripple current needs to be reduced then place a 4.7F/50V capacitor across LED. The capacitor must be
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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.
Figure 2. Low Noise Measurement
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Evaluation Board Schematic
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Bill of Materials
Item C1, C5 Part Number 12105C475KAZ2A GRM32ER71H475KA88L 12105C475KAZ2A C2 GRM32ER71H475KA88L C3225X7S1H475M 08053D105KAT2A C3 GRM21BR71E105KA99L C2012X7R1E105K C4 (Open) 08055A271JAT2A (Open) GRM2165C2A271JA01D SK36-TP D1 L1 M1 R1 R2, R3 R4 R5 R6 U1 SK36 SK36-7-F SLF10145T-680M1R2 FDS5672 CSR 1/2 0.2 1% I CRCW08051003FKEA CRCW08050000FKEA (Open) CRCW08052R20FKEA CRCW08051002FKEA MIC3203YM Manufacturer AVX
(1)
Description 4.7F/50V, Ceramic Capacitor, X7R, Size 1210
Qty. 2
Murata(2) AVX(1) Murata TDK
(2)
4.7F/50V, Ceramic Capacitor, X5R, Size 1210 1F/25V, Ceramic Capacitor, X5R, Size 0805 1F/25V, Ceramic Capacitor, X7R, Size 0805 270pF/50V, Ceramic Capacitor NPO, Size 0805
1 1 1 1
(3)
AVX(1) Murata(2) TDK(3) AVX(1) Murata(2) MCC(4) Fairchild(5) Diodes, Inc. TDK(3) Fairchild
(7) (6)
60V, 3A, SMC, Schottky Diode 68H, 1.2A, 0.14, SMT, Power Inductor MOSFET, N-CH, 60V, 12A, SO-8 0.2 Resistor, 1/2W, 1%, Size 1206 100k Resistor, 1% , Size 0805 0 Resistor, 1%, Size 0805 2.2 Resistor, 1%, Size 0805 10k Resistor, 1% , Size 0805 High Brightness LED Driver Controller with High-Side Current Sense
1 1 1 1 2 1 1 1 1
Stackpole Electronics, Inc(8) Vishay(9) Vishay Vishay
(9)
Vishay(9)
(9)
Micrel, Inc.(10)
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. Fairchild : www.Fairchildsemi.com. 8. Stackpole Electronics: www.seielect.com. 9. Vishay: www.vishay.com. 10. Diodes Inc. : www.diodes.com. 11. Micrel, Inc.: www.micrel.com.
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M9999-032910-A
Micrel, Inc.
MIC3203
PCB Layout Recommendation
Top Assembly
Top Layer
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M9999-032910-A
Micrel, Inc.
MIC3203
PCB Layout Recommendation (Continued)
Bottom Layer
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M9999-032910-A
Micrel, Inc.
MIC3203
Package Information
8-Pin SOIC
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M9999-032910-A
Micrel, Inc.
MIC3203
Recommended Landing Pattern
8-Pin SOIC
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
The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. 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. (c) 2010 Micrel, Incorporated.
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M9999-032910-A

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