MIC2282

Single-Cell Ultra Low EMI

Boost LED Driver

General Description Features

The MIC2282 is a boost LED driver optimized for single • Operates from a single-cell supply (VIN = 0.9V to 15V)
cell operation from alkaline, nickel-metal-hydride, or lithium • Ultra Low EMI
ion batteries. The MIC2282 operates with an input voltage
• 120µA typical quiescent current
between 0.9V to 15V, driving a string of series LEDs up to
33V. The combination of a low feedback voltage of 220mV • Adjustable output voltages
and an operating current of 120μA provides a high • 220mV sense voltage
efficiency solution that prolongs battery life. • 20kHz switching frequency
The MIC2282 requires only five external components • Over temperature protection
(diode, inductor, sense resistor, input capacitor and output • 8-pin MSOP package
capacitor) to implement a low cost LED boost regulator. It
is available in a compact 8-pin MSOP package with an • Low component count solution
operating range from –40°C to +125°.
Data sheets and support documentation can be found on Applications
Micrel’s web site at: www.micrel.com.
• LED flashlight and head lamps
• LCD bias generator
• Battery-powered, hand-held instruments
• Palmtop computers
• Remote controls
• Detectors
___________________________________________________________________________________________________________

Typical Application
L1 D1 L1 D1
220µH MBR0530 220µH MBR0530
VOUT = 3V VOUT = 9V
8 8
IN IN
1 1
SW SW
C1 C1
1V to1.5V 47µF MIC2282 100µF 1V to1.5V 47µF MIC2282 100µF
6 6
1 Cell 16V SNS 1 Cell 16V SNS

GND GND SNS GND GND SNS

7 2 7 2

Single-Cell to 3V DC-to-DC Converter Triple-Cell to 9V DC-to-DC Converter

Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com

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Ordering Information
Part Number Marking Output Temperature Range Package Lead Finish
Code Voltage
MIC2282YMM 2282 ADJ –40° to +125°C 8-pin MSOP Pb-Free

Pin Configuration
SW 1 8 VIN
GND 2 7 GND
NC 3 6 SNS
NC 4 5 NC

Top View
8-Pin MSOP (MM)

Pin Description

Pin Number Pin Name Pin Function

1 SW Switch: NPN output switch collector.
2,7 GND Power Ground: NPN output switch emitter.
3,4,5 NC Not internally connected.
6 SNS Sense (Input): Connect a sense resistor or external voltage divider network.
8 VIN Supply (Input): Positive supply voltage input.

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Absolute Maximum Ratings(1) Operating Ratings(2)

Supply Voltage (VIN)................................................ 18V Supply Voltage (VIN) .............................. +0.9V to +15V
Switch Voltage (VSW)............................................... 36V Ambient Operating Temperature (TA).... –40°C to +85°C
Storage Temperature (TA).................. –65°C to +150°C Junction Temperature (TJ)................... –40°C to +125°C
MSOP Power Dissipation (PD).......................... 250mW MSOP Thermal Resistance (θJA)..................... 160°C/W
ESD Rating(3).………………………………………..2KV

Electrical Characteristics(4)
VIN = 1.5V; TA = 25°C, bold indicates –40°C ≤ TJ ≤ 125°C; unless noted
Parameter Condition Min Typ Max Units
Supply Voltage Range Startup guaranteed, ISW = 100mA 0.9 15 V
Quiescent Current Output switch off 120 μA
Sense Voltage ISW = 100mA 200 220 236 mV
Comparator Hysteresis 6 mV
Feedback Current VSNS = 0V 25 nA
VIN = 1.0V, ISW = 200mA 200
Switch Saturation Voltage VIN = 1.2V, ISW = 600mA 400 mV
VIN = 1.5V, ISW = 800mA 500
Switch Leakage Crrent Output switch off, VSW = 36V 1 μA
Maximum Output Voltage 35 V
Switch On Time 35 μs
Current Limit VIN = 3.6V 1.1 A
Duty Cycle VSNS < 200mV, ISW = 100mA 67 %

Notes:
1. Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when operating
the device outside of its operating ratings. The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(MAX), the
junction-to-ambient thermal resistance, θJA , and the ambient temperature, TA. The maximum allowable power dissipation will result in excessive die
temperature, and the regulator will go into thermal shutdown.
2. The device is not guaranteed to function outside its operating rating.
3. Devices are ESD sensitive. Handling precautious recommended. Human body model, 1.5kΩ in series with 100pF.
4. Specification for packaged product only.

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Typical Characteristics
1 LED Efficiency 2 LED in Series Efficiency 3 LED in Series Efficiency
85 90 90
50mA 50mA 100mA
50mA
80 85 100mA 85
80 10mA 80 10mA
EFFICIENCY (%)

EFFICIENCY (%)

EFFICIENCY (%)
75 10mA
25mA 75 75
70
70 70
65
65 65
60
60 60
55 55 55
50 50 50
0 0.5 1 1.5 2 2.5 3 3.5 0 1 2 3 4 5 0 1 2 3 4 5 6
INPUT VOLTAGE (V) INPUT VOLTAGE (V) INPUT VOLTAGE (V)

Oscillator Frequency Oscillator Duty Cycle Quiescent Current

vs. Temperature vs. Temperature vs. Temperature
30 75 200
VIN = 1.5V VIN = 1.5V VIN = 1.5V

QUIESCENT CURRENT (µA)

OSC. FREQUENCY (kHz)

ISW = 100mA 70 ISW = 100mA 175

DUTY CYCLE (%)

25 150
65
125
60
20 100

55 75

15 50 50
5

5
-40
-25
-10

20
35
50
65
80
95
110
125

-40
-25
-10

20
35
50
65
80
95
110
125

-40
-25
-10

20
35
50
65
80
95
110
125
TEMPERATURE (¡C) TEMPERATURE (°C) TEMPERATURE (°C)

Quiescent Current Current Limit Output Current Limit

vs. Supply Volage vs. Input Voltage vs. Temperature
200 1.6 1.75
QUIESCENT CURRENT (µA)

175 –40°C
1.4 1.50
+25°C
CURRENT LIMIT (A)

CURRENT LIMIT (A)

150
1.2 1.25
125
+85°C 1 1.00
100
0.8 0.75
75
0.6 0.50
50
0.4 0.25
25
0 0.2 0
5

3 3.5 4 4.5 5 5.5 6

-40
-25
-10

20
35
50
65
80
95
110
125
0 2 4 6 8 10
INPUT VOLTAGE (V)
SUPPLY VOLTAGE (V) TEMPERATURE (°C)

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Functional Diagram
VBATT VOUT

VIN
MIC2282

Oscillator
0.22V
Reference
Driver SW

SNS GND

Adjustable Voltage with External Components

Functional Description approximately 3 times larger than the input voltage.

Other output voltages are also easily generated with a
The MIC2282 boost LED driver has a gated oscillator slight drop in efficiency. The fixed oscillator frequency is
architecture designed to operate from a single cell input set to 20kHz.
voltage as low as 0.9V and provide a high-efficiency
adjustable regulated output voltage. One advantage of
this architecture is that the output switch is disabled Current Limit
whenever the output voltage is above the feedback
Current limit for the MIC2282 functions by modifying the
comparator threshold thereby greatly reducing quiescent
oscillator duty cycle and frequency. When current
current and improving efficiency, especially at low output
exceeds 1.1A, the duty cycle is reduced (switch on-time
currents.
is reduced, off-time is unaffected) and the corresponding
The comparator senses the output voltage through an frequency is increased. In this way less time is available
external resistor and compares it to the internal for the inductor current to build up while maintaining the
reference voltage. When the voltage at the inverting same discharge time. The onset of current limit is soft
input of the comparator is below 0.22V, the comparator rather than abrupt but sufficient to protect the inductor
output is high and the output of the oscillator is allowed and output switch from damage. Certain combinations of
to pass through the AND gate to the output driver and input voltage, output voltage and load current can cause
output switch. The output switch then turns on and off the inductor to go into a continuous mode of operation.
storing energy in the inductor. When the output switch is This is what happens when the inductor current can not
on (low) energy is stored in the inductor; when the switch fall to zero and occurs when:
is off (high) the stored energy is dumped into the output
VOUT + VDIODE − VIN
capacitor which causes the output voltage to rise. duty cycle ≤
When the output voltage is high enough to cause the VOUT + VDIODE − VSAT
comparator output to be low (inverting input voltage is
above 0.22V) the AND gate is disabled and the output
switch remains off (high). The output switch remains
disabled until the output voltage falls low enough to
cause the comparator output to go high.

Application Information
Oscillator Duty Cycle and Frequency
The oscillator duty cycle is set to 67% which is optimized
to provide maximum load current for output voltages

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2b has a lower saturation threshold. Another

consideration in the selection of inductors is the radiated
energy. In general, toroids have the best radiation
Current "ratchet"
without current limit characteristics while bobbins have the worst. Some
bobbins have caps or enclosures which significantly
reduce stray radiation.
Inductor Current

Current limit threshold

The last electrical characteristic of the inductor that must
Continuous current be considered is ESR (equivalent series resistance).
Figure 2c shows the current waveform when ESR is
excessive. The normal symptom of excessive ESR is
reduced power transfer efficiency. Note that inductor
Discontinuous current
ESR can be used to the designers advantage as reverse
battery protection (current limit) for the case of relatively
Time low output power one-cell designs. The potential for very
large and destructive currents exits if a battery in a one-
Figure 1. Current Limit Behavior
cell application is inserted backwards into the circuit. In
Figure 1 shows an example of inductor current in the some applications it is possible to limit the current to a
continuous mode with its associated change in oscillator nondestructive (but still battery draining) level by
frequency and duty cycle. This situation is most likely to choosing a relatively high inductor ESR value which
occur with relatively small inductor values, large input does not affect normal circuit performance.
voltage variations and output voltages which are less
than ~3× the input voltage. Selection of an inductor with Capacitors
a saturation threshold above 1.1A will insure that the It is important to select high-quality, low ESR, filter
system can withstand these conditions. capacitors for the output of the regulator circuit. High
ESR in the output capacitor causes excessive ripple due
Inductors, Capacitors and Diodes
to the voltage drop across the ESR. A triangular current
The importance of choosing correct inductors, capacitors pulse with a peak of 500mA into a 200mΩ ESR can
and diodes can not be ignored. Poor choices for these cause 100mV of ripple at the output due the capacitor
components can cause problems as severe as circuit only. Acceptable values of ESR are typically in the
failure or as subtle as poorer than expected efficiency. 50mΩ range. Inexpensive aluminum electrolytic
capacitors usually are the worst choice while tantalum
capacitors are typically better. Figure 4 demonstrates the
a.
effect of capacitor ESR on output ripple voltage.
Inductor Current

5.25
OUTPUT VOLTAGE (V)

b.

5.00
c.

Time
4.75
Figure 2. Inductor Current: a. Normal, 0 500 1000 1500
b. Saturating and c. Excessive ESR TIME (µs)

Inductors Figure 3. Output Ripple

Inductors must be selected such that they do not
Output Diode
saturate under maximum current conditions. When an
inductor saturates, its effective inductance decreases Finally, the output diode must be selected to have
rapidly and the current can suddenly jump to very high adequate reverse breakdown voltage and low forward
values. voltage at the application current. Schottky diodes
typically meet these requirements.
Figure 2 compares inductors with currents that are
correct and unacceptable due to core saturation. The Standard silicon diodes have forward voltages which are
inductors have the same nominal inductance but Figure too large except in extremely low power applications.

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They can also be very slow, especially those suited to To select an inductor for a particular application, the
power rectification such as the 1N400x series, which worst case input and output conditions must be
affects efficiency. determined. Based on the worst case output current we
can estimate efficiency and therefore the required input
Inductor Behavior current. Remember that this is power conversion, so the
The inductor is an energy storage and transfer device. worst case average input current will occur at maximum
Its behavior (neglecting series resistance) is described output current, one minimum input voltage.
by the following equation: VOUT × IOUT(max)
V Average IIN(max) =
I= ×t VIN(min) × Efficency
L
Referring to Figure 1, it can be seen the peak input
where:
current will be twice the average input current.
V = inductor voltage (V) Rearranging the inductor equation to solve for L:
L = inductor value (H) V
t = time (s) L= × t1
I
I = inductor current (A) VIN(min)
If a voltage is applied across an inductor (initial current is L= × t1
zero) for a known time, the current flowing through the 2 × Average IIN(max)
inductor is a linear ramp starting at zero, reaching a duty cycle 0.67
maximum value at the end of the period. When the where t 1 = =
f OSC 20kHz
output switch is on, the voltage across the inductor is:
V1 = VIN – VSAT To illustrate the use of these equations a design
example will be given:
When the output switch turns off, the voltage across the
inductor changes sign and flies high in an attempt to Assume:
maintain a constant current. The inductor voltage will VOUT = 3.0V
eventually be clamped to a diode drop above VOUT. IOUT(max) =10mA
Therefore, when the output switch is off, the voltage
VIN(min) = 1.0V
across the inductor is:
V2 = VOUT + VDIODE – VIN efficiency = 75%
For normal operation the inductor current is a triangular 5V × 5mA
Average IIN(max) = = 33.3mA
waveform which returns to zero current (discontinuous 1.0V × 0.75
mode) at each cycle. At the threshold between 1.0V × 0.7
continuous and discontinuous operation we can use the L=
fact that I1 = I2 to get: 2 × 33.3mA × 20kHz
V1 × t1 = V2 × t2 3.0 × 10mA
IIN(max) = = 40mA
V1 t 1.0 × .75
= 2
V2 t1 1 . 0 V × 0. 7
L= = 438µH
This relationship is useful for finding the desired 2 × 40 × 20kHz
oscillator duty cycle based on input and output voltages. L = 438µH
Since input voltages typically vary widely over the life of Use the next lowest standard value of inductor and verify
the battery, care must be taken to consider the worst that it does not saturate at a current below about 75mA
case voltage for each parameter. For example, the worst (< 2 ⋅ 33.3mA).
case for t1 is when VIN is at its minimum value and the
worst case for t2 is when VIN is at its maximum value
(assuming that VOUT, VDIODE and VSAT do not change
much).

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Typical Application Circuit

Bill of Materials
Item Part Number Manufacturer Description Qty.
C1 TAJE107K035RNJ AVX Capacitor,100μF ,20V , TANT 1
C2 TAJE476K035RNJ AVX Capacitor ,47μF ,25V , TANT 1
D1 MBR0530 Fairchild 500mA, 30V Schottky Rectifier 1
D2, OVS5WBCR4 OPTEK Technology,Inc 100mA, White LED 3
D3, D4
L1 DR127-221-R Coil Tronics Inductor, 200μH, 2.43A 1
R2 CRCW06032R20FKE Vishay Dale Resistor,2.2 Ohms , 0603 , 1% , 1/16W 1
A
U1 MIC2282YMM Micrel, Inc.(6) Single-Cell Boost LED Driver 1
Notes:
1. AVX: www.AVX.com.
2. Fairchild Semi: www.fairchildsemi.com.
3. OPTEK Technology: www.optekinc.com.
4. Coil Tronics: www.cooperbussman.com.
5. Vishay Tel: www.vishay.com.
6. Micrel, Inc.: www.micrel.com.

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PCB Layout

TOP LAYER

BOTTOM LAYER

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Package Information

8-Pin MSOP (MM)

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.

© 2009 Micrel, Incorporated.

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