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MIC3201
High Brightness LED Driver with High-Side Current Sense
General Description
The MIC3201 is a hysteretic step-down, constant-current, High-Brightness LED (HB LED) driver capable of driving up to four, 1A LEDs. It provides an ideal solution for interior/exterior lighting, architectural and ambient lighting, LED bulbs, and other general illumination applications. The MIC3201 operates with an input voltage range from 6V to 20V. 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 current sense resistor is used to set the output current. The MIC3201 offers a dedicated PWM input (DIM) which enables a wide range of pulsed dimming. A high switching frequency operation up to 1MHz allows the use of smaller external components minimizing space and cost. The MIC3201 operates from -40C to 85C and is available in an 8-pin epad SOIC package. Datasheets and support documentation can be found on Micrel's web site at: www.micrel.com.
Features
* * * * * * * * * * * * * 6.0V to 20V input voltage range High efficiency (>90%) 5% LED current accuracy High-side current sense Dedicated dimming control input Hysteretic control (no compensation!) 1A internal power switch Up to 1MHz switching frequency Adjustable constant LED current 5V on board regulator Over temperature protection -40C to +125C junction temperature range Available in an 8-Pin ePad SOIC package
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
MIC3201 Step-down LED Driver Circuit
Micrel Inc. * 2180 Fortune Drive * San Jose, CA 95131 * USA * tel +1 (408) 944-0800 * fax + 1 (408) 474-1000 * http://www.micrel.com
January 2010
M9999-011210-B
Micrel, Inc.
MIC3201
Ordering Information(1)
Part Number MIC3201YME
Note: 1. YME is a GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
(R)
Marking MIC3201YME
Junction Temp. Range -40C to +125C
Package 8-Pin ePAD SOIC
Lead Finish Pb-Free
Pin Configuration
8-Pin ePAD SOIC (ME)
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, 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 the ground path for the high current 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. 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. Connect to PGND.
2 3
CS VIN
4 5
AGND EN
6
DIM
7
PGND
8
LX
ePAD
GND
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Absolute Maximum Ratings(1)
VIN, VCS to PGND/AGND ................................ -0.3V to +22V VDIM, VEN to PGND/AGND ..................................-0.3V to VIN VLX to PGND/AGND ................................. -0.3V to VIN+1.0V VCC to PGND/AGND ..................................... -0.3V to +7.0V VCS to VIN ...................................................................... 0.3V Storage Temperature (Ts).........................-60C to +150C Lead Temperature (Soldering, 10sec) ....................... 260C ESD Ratings (HBM)(3) ...... ...........................................2kV (MM)(3)......................... ...........................100V
Operating Ratings(2)
Supply Voltage (VIN).......................................... 6.0V to 20V Junction Temperature (TJ) .........................-40C to +125C Junction Thermal Resistance SOIC (JA) ..........................................................41C/W SOIC (JC).......................................................14.7C/W
Electrical Characteristics(4)
VIN = 12V, VDIM = VEN = VIN, CVCC = 1F, bold values indicate -40C TA +85C, unless noted. Typical values are at TA = +25C.
Symbol VIN IS ISD VCS(MAX) VCS(MIN) VHYS Parameter Operating Input Voltage Range Supply Current Shut Down Supply Current Sense Voltage Threshold High Sense Voltage Threshold Low Current Sense Hysteresis Current Sense Response Time CS Pin Input Current RDSON FMAX VCC ENHI ENLO Internal Switch RON Maximum Switching Frequency VCC Regulator EN Input Voltage High EN Input Voltage Low EN Input Current High EN Input Leakage Low DIMHI DIMLO DIM Input Voltage High DIM Input Voltage Low DIM Input Current High DIM Input Leakage Low FDIM TLIM TLIMHYS Maximum DIM Frequency LX Pin Leakage Current Over-Temperature Shutdown Over-Temperature Shutdown Hysteresis Start-up Time
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.
Condition LX open VEN = 0V VIN - VCS VIN - VCS VCS Rising VCS Falling VIN - VCS = 200mV TA = 25C
Min 6.0
Typ 1.2
Max 20.0 1.75 1 224 189
Units V mA A mV mV mV ns ns
206 171 35 100 60
3 300 6 2.0 0.4 550 1.0
A m MHz V V V A A V V A A kHz A C C s
VEN =12V VEN = 0V 2.0
30
50 1 0.4
VDIM =12V VDIM= 0V VIN - VCS 250mV VLX=VIN
22
30 1 20
5 165 20
From EN Pin going high, DIM = 12V, CVCC = 1F
300
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Typical Characteristics
1 LED Efficiency vs. Input Voltage
1A
90 80 70 EFFICIENCY (%)
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0
2 LED Efficiency vs. Input Voltage
1A
1200 1000
1 LED Current vs. Input Voltage
1A
50 40 30 20 10 0 5 10
ILED (mA)
60
350mA
350mA
800 600 400 200 0
350mA
15
20
5
10
15
20
5
10
15
20
INPUT VOTLAGE (V)
INPUT VOTLAGE (V)
INPUT VOTLAGE (V)
1200 1000
2 LED Current vs. Input Voltage
1.4 SUPPLY CURRENT (mA) 1.2 1.0 0.8 0.6 0.4 0.2 0.0 5 10 15 20 5
Supply Current vs. Input Voltage
0.050 SHUTDOWN CURRENT (uA) 0.045 0.040 0.035 0.030 0.025 0.020 0.015 0.010 0.005 0.000
10 15 20
Shutdown Current vs. Input Voltage
1A
ILED (mA)
800 600 400 200 0 INPUT VOTLAGE (V)
350mA
TA = 25C
TA = 25C
5
10
15
20
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Switching Frequency vs. Input Voltage
SWITCHING FREQUENCY (kHz) 800
Enable Threshold vs. Input Voltage
1.6 ENABLE THRESHOLD (V) 1.4 1.2 VCC (V) 1.0 0.8 0.6 0.4 0.2 0.0 5 10 15 20 INPUT VOLTAGE (V)
TA = 25C
VCC vs. Input Voltage
7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 5 10 15 20 INPUT VOLTAGE (V)
TA = 25C
700 600 500 400 300 200 100 0 5 10 15 20 INPUT VOLTAGE (V)
RCS = 0.2 L = 22H TA = 25C
Current Sense Voltage vs. Input Voltage
250
VCS(Max)
VCC vs. ICC
7.0 SWITCH VOLTAGE (mV) 6.0 5.0 VCC (V) 350 300 250 200 150 100 50 0 0
Switch Voltage vs. Switch Current
CURRENT SENSE (mV)
200 150 100 50 0 5 10 15 20 INPUT VOLTAGE (V)
VCS(Min)
4.0 3.0 2.0 1.0 0.0 0 5 10 ICC (mA) 15 20
TA = 25C
TA = 25C
0.25
0.5
0.75
1
SWITCH CURRENT (A)
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RDSON vs. Input Voltage
THERMAL SHUTDOWN (C)
MIC3201
Thermal Shutdown vs. Input Voltage
ON
400 350 300 RDS(ON) (m) 250 200 150 100 50 0 5
180 160 140 120 100 80 60 40 20 0 5
6.0
ON
UVLO Threshold vs. Temperature
UVLO THRESHOLD (V)
5.0 4.0 3.0 2.0 1.0 0.0
OFF
OFF
IOUT = 1A @ 25C
10
15
20
10
15
20
-40 -20
0
20 40 60 80 100 120
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
TEMPERATURE (C)
60 50 40 30 20 10 0 5
T CASE @ 1.0A vs. Input Voltage
SUPPLY CURRENT (mA)
Supply Current vs. Temperature
2.0 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -40 -20 0 20 40 60 80 100 120
1.6 ENABLE THRESHOLD (V) 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -40 -20
Enable Threshold vs. Temperature
ON
1.8 VIN = 12V
1 LED
TCASE (C)
OFF
10
15
20
0
20
40
60
80 100 120
INPUT VOTLAGE (V)
TEMPERATURE (C)
TEMPERATURE (C)
Shutdown Current vs. Temperature
SWITCHING FREQUENCY (kHz)
35 SHUTDOWN CURRENT (uA) 30 25 20 15 10 5 0 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C)
VIN = 12V
Switching Frequency vs. Temperature
800 700 600 500 400 300 200 100 0 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C)
12V Input RCS = 0.2 L = 22H
500 450 400 RDS(ON) (m) 350 300 250 200 150 100 50 0
Low-Side MOSFET RDS(ON) vs. Temperature
VIN = 12V
-40 -20
0
20
40 60 80 100 120
TEMPERATURE (C)
VCC vs. Temperature
7.0 CURRENT SENSE (mV) 6.0 5.0 VCC (V) 4.0 3.0 2.0 1.0 0.0 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C)
VIN = 12V
250 200 150 100 50
Current Sense Voltage vs. Temperature
VC(Max)
VCS(Min)
VHYS
0 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C)
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MIC3201
Functional Characteristics
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Functional Diagram
Figure 1. MIC3201 Block Diagram
Functional Description
The MIC3201 is a hysteretic step-down regulator which regulates the LED current over wide input voltage range and capable of driving up to four, 1A LEDs in series. The device operates from a 6V to 20V input voltage range, and includes an integrated 1.0A power switch. When the input voltage approaches 6V, the internal 5V VCC is regulated and the integrated MOSFET is turned on 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 internal 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 internal 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 MIC3201 has an on board 5V regulator which is for internal use only. Connect a 1F capacitor on VCC pin to analog ground. The MIC3201 has an EN pin which gives the flexibility to enable and disable the output with logic high and low signals. The MIC3201 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 from 1% to 99%.
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Application Information
The MIC3201 is a hysteretic step-down constant-current High-Brightness LED (HB LED) driver. The internal block diagram is shown in Figure 1. The MIC3201 is composed of a current sense comparator, voltage and current reference, 5V regulator, MOSFET driver, and a MOSFET. Hysteretic mode control, also called bangbang control, is the topology that does not employ an error amplifier, and instead uses an error comparator. 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 MIC3201 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: Frequency of Operation To calculate the frequency spread across input supply:
VL = L
dI dt
L is the inductance, dI is fixed (the value of the hysteresis)
dI =
VCS ( MAX ) - VCS ( MIN ) RCS
VL voltage across inductor L which varies by supply. For current rising (MOSFET is ON):
tr = L
where:
dI VL _ RISE
VL_RISE = VIN - ILED*RCS - VLED
For current falling (MOSFET is OFF):
tf = L
where:
dI V L _ FALL
+ VCS ( MIN ) 1V RCS = ( CS ( MAX ) ) I LED 2
RCS () ILED (A) I2R (W) Size (SMD)
VL_FALL = VD + ILED*RCS + VLED 1 T = t r + t f , FSW = T
FSW = (VD + I LED RCS + VLED ) * (VIN - I LED RCS - VLED ) L dI (VD + VIN )
2.00 1.00 0.63 0.56 0.50 0.40 0.33 0.28 0.24 0.22 0.20
0.1 0.2 0.3 0.35 0.4 0.5 0.6 0.7 0.8 0.9 1.0
0.0200 0.0400 0.0567 0.0691 0.0800 0.1000 0.1188 0.1372 0.1536 0.1782 0.2000
0402 0402 0402 0603 0603 0805 0805 0805 0805 0805 1206
where
VD is Schottky diode forward drop VLED is total LEDs voltage drop VIN is input voltage ILED is average LED current: According to the above equation, choose the inductor to make the operating frequency not beyond 1MHz. 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. LED Ripple Current The LED current is the same as inductor current. If LED ripple current needs to be reduced then place a 10F capacitor across LED.
Table 1. Selecting RCS for LED Current
For VCS(MAX) and VCS(MIN) refer to electrical characteristic table.
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MIC3201 Output Capacitor If LED ripple current needs to be reduced then place a 10F 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 IC LX pin 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 MIC3201 LX and PGND pin 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 LX pin and its connecting traces.
PCB Layout Guideline
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 MIC3201 regulator. IC Use fat traces to route the input and output power lines. The exposed pad (EP) on the bottom of the IC must be connected to the ground. Use 4 via to connect the EP to the ground plane. 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 connections short. 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 (LX) 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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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, C2 Part Number 12103D106KAT2A GRM32DR71E106KA12L C3225X7R1E106M 08053D105KAT2A C3 GRM216R61E105KA12D C2012X7R1E105K C4 D1 L1 R1 R2, R3 R4 U1 08055A271JAT2A GQM2195C1H271JB01D SS24-TP SS24 CDRH8D43NP-220NC CSR 1/2 0.2 1% I CRCW08051003FKEA CRCW08052R20FKEA MIC3201YME Manufacturer AVX
(1) (2)
Description 10F/25V, Ceramic Capacitor, X5R, Size 0805 10F/25V, Ceramic Capacitor, X7R, Size 0805 10F/25V, Ceramic Capacitor, X7R, Size 0805 1F/25V, Ceramic Capacitor, X5R, Size 0805 1F/25V, Ceramic Capacitor, X5R, Size 0805 1F/25V, Ceramic Capacitor, X7R, Size 0805 270pF/50V, Ceramic Capacitor NPO, Size 0805 40V, 2A, SMA, Schottky Diode 22H, 2.6A, SMT, Power Inductor
(7)
Qty. 2
Murata
TDK(3) AVX(1) Murata TDK
(2) (3)
1
AVX(1) Murata(2) MCC(4) Fairchild(5) SUMIDA(6) Stackpole Electronics Inc Vishay
(8)
1 1 1 1 2 1 1
0.2 Resistor, 1/2W, 1%, Size 1206 100k Resistor, 1% , Size 0805 2.2 Ohms Resistor, 1%, Size 0805 High-Brightness LED Driver with High-Side Current Sense
Vishay(8) Micrel, Inc.(9)
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. Sumida Tel: www.sumida.com 7. Stackpole Electronics: www.seielect.com 8. Vishay: www.vishay.com 9. Micrel, Inc.: www.micrel.com
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PCB Layout Recommendations
Top Assembly
Top Layer
Bottom Layer
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Package Information
8-Pin ePAD SOIC (ME)
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Recommended Landing Pattern
8-Pin ePAD 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) 2009 Micrel, Incorporated.
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