MIC2282
Single-Cell Ultra Low EMI
Boost LED Driver
General Description
The MIC2282 is a boost LED driver optimized for single
cell operation from alkaline, nickel-metal-hydride, or lithium
ion batteries. The MIC2282 operates with an input voltage
between 0.9V to 15V, driving a string of series LEDs up to
33V. The combination of a low feedback voltage of 220mV
and an operating current of 120μA provides a high
efficiency solution that prolongs battery life.
The MIC2282 requires only five external components
(diode, inductor, sense resistor, input capacitor and output
capacitor) to implement a low cost LED boost regulator. It
is available in a compact 8-pin MSOP package with an
operating range from –40°C to +125°.
Data sheets and support documentation can be found on
Micrel’s web site at: www.micrel.com.
Features
•
•
•
•
•
•
•
•
•
Operates from a single-cell supply (V
IN
= 0.9V to 15V)
Ultra Low EMI
120µA typical quiescent current
Adjustable output voltages
220mV sense voltage
20kHz switching frequency
Over temperature protection
8-pin MSOP package
Low component count solution
Applications
•
LED flashlight and head lamps
•
LCD bias generator
•
Battery-powered, hand-held instruments
•
Palmtop computers
•
Remote controls
•
Detectors
___________________________________________________________________________________________________________
Typical Application
L1
220µH
8
D1
MBR0530
V
OUT
= 3V
8
L1
220µH
D1
MBR0530
V
OUT
= 9V
IN
1V to1.5V
1 Cell
C1
47µF
16V
SW
MIC2282
GND
7
1
IN
100µF
SNS
SNS
6
1V to1.5V
1 Cell
C1
47µF
16V
SW
MIC2282
GND
7
1
SNS
6
100µF
SNS
GND
2
GND
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
October 2009
M9999-102309
Micrel, Inc.
MIC2282
Ordering Information
Part Number
MIC2282YMM
Marking
Code
2282
Output
Voltage
ADJ
Temperature Range
–40° to +125°C
Package
8-pin MSOP
Lead Finish
Pb-Free
Pin Configuration
SW 1
GND 2
NC 3
NC 4
8
7
6
5
VIN
GND
SNS
NC
Top View
8-Pin MSOP (MM)
Pin Description
Pin Number
1
2,7
3,4,5
6
8
Pin Name
SW
GND
NC
SNS
VIN
Pin Function
Switch: NPN output switch collector.
Power Ground: NPN output switch emitter.
Not internally connected.
Sense (Input): Connect a sense resistor or external voltage divider network.
Supply (Input): Positive supply voltage input.
October 2009
2
M9999-102309
Micrel, Inc.
Absolute Maximum Ratings
(1)
Supply Voltage (V
IN
)................................................ 18V
Switch Voltage (V
SW
)............................................... 36V
Storage Temperature (T
A
).................. –65°C to +150°C
MSOP Power Dissipation (P
D
).......................... 250mW
ESD Rating
(3)
.………………………………………..2KV
MIC2282
Operating Ratings
(2)
Supply Voltage (V
IN
) .............................. +0.9V to +15V
Ambient Operating Temperature (T
A
).... –40°C to +85°C
Junction Temperature (T
J
)................... –40°C to +125°C
MSOP Thermal Resistance (θ
JA
)..................... 160°C/W
Electrical Characteristics
(4)
V
IN
= 1.5V; T
A
= 25°C,
bold
indicates –40°C
≤
T
J
≤
125°C; unless noted
Parameter
Supply Voltage Range
Quiescent Current
Sense Voltage
Comparator Hysteresis
Feedback Current
Switch Saturation Voltage
Switch Leakage Crrent
Maximum Output Voltage
Switch On Time
Current Limit
Duty Cycle
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, T
J(MAX)
, the
junction-to-ambient thermal resistance,
θ
JA
, and the ambient temperature, T
A
. 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.
Condition
Startup guaranteed, I
SW
= 100mA
Output switch off
I
SW
= 100mA
V
SNS
= 0V
V
IN
= 1.0V, I
SW
= 200mA
V
IN
= 1.2V, I
SW
= 600mA
V
IN
= 1.5V, I
SW
= 800mA
Output switch off, V
SW
= 36V
Min
0.9
Typ
120
Max
15
Units
V
μA
mV
mV
nA
mV
μA
V
μs
A
%
200
220
6
25
200
400
500
1
35
35
236
V
IN
= 3.6V
V
SNS
< 200mV, I
SW
= 100mA
1.1
67
October 2009
3
M9999-102309
Micrel, Inc.
MIC2282
Typical Characteristics
1 LED Efficiency
85
80
EFFICIENCY (%)
EFFICIENCY (%)
75
70
65
60
55
50
0
0.5
1 1.5 2 2.5 3
INPUT VOLTAGE (V)
3.5
10mA
25mA
50mA
90
85
80
75
70
65
60
55
50
0
1
2
3
4
INPUT VOLTAGE (V)
5
100mA
EFFICIENCY (%)
10mA
2 LED in Series Efficiency
50mA
90
85
80
75
70
65
60
55
50
0
3 LED in Series Efficiency
50mA
100mA
10mA
1
2
3
4
5
INPUT VOLTAGE (V)
6
30
OSC. FREQUENCY (kHz)
Oscillator Frequency
vs. Temperature
V
IN
= 1.5V
I
SW
= 100mA
75
70
65
60
55
50
Oscillator Duty Cycle
vs. Temperature
QUIESCENT CURRENT (µA)
V
IN
= 1.5V
I
SW
= 100mA
200
175
150
125
100
75
Quiescent Current
vs. Temperature
V
IN
= 1.5V
25
20
-40
-25
-10
5
20
35
50
65
80
95
110
125
-40
-25
-10
5
20
35
50
65
80
95
110
125
TEMPERATURE (¡C)
TEMPERATURE (°C)
200
QUIESCENT CURRENT (µA)
175
150
125
100
75
50
25
0
0
Quiescent Current
vs. Supply Volage
1.6
Current Limit
vs. Input Voltage
1.75
1.50
CURRENT LIMIT (A)
1.25
1.00
0.75
0.50
0.25
–40°C
CURRENT LIMIT (A)
1.4
+25°C
+85°C
1.2
1
0.8
0.6
0.4
2
4
6
8
SUPPLY VOLTAGE (V)
10
3.5
4
4.5
5
5.5
INPUT VOLTAGE (V)
6
October 2009
4
-40
-25
-10
5
20
35
50
65
80
95
110
125
TEMPERATURE (°C)
0.2
3
0
-40
-25
-10
5
20
35
50
65
80
95
110
125
TEMPERATURE (°C)
15
DUTY CYCLE (%)
50
Output Current Limit
vs. Temperature
M9999-102309
Micrel, Inc.
MIC2282
Functional Diagram
V
BATT
VIN
MIC2282
Oscillator
0.22V
Reference
Driver
SW
V
OUT
SNS
GND
Adjustable Voltage with External Components
Functional Description
The MIC2282 boost LED driver has a gated oscillator
architecture designed to operate from a single cell input
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
whenever the output voltage is above the feedback
comparator threshold thereby greatly reducing quiescent
current and improving efficiency, especially at low output
currents.
The comparator senses the output voltage through an
external resistor and compares it to the internal
reference voltage. When the voltage at the inverting
input of the comparator is below 0.22V, the comparator
output is high and the output of the oscillator is allowed
to pass through the AND gate to the output driver and
output switch. The output switch then turns on and off
storing energy in the inductor. When the output switch is
on (low) energy is stored in the inductor; when the switch
is off (high) the stored energy is dumped into the output
capacitor which causes the output voltage to rise.
When the output voltage is high enough to cause the
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.
approximately 3 times larger than the input voltage.
Other output voltages are also easily generated with a
slight drop in efficiency. The fixed oscillator frequency is
set to 20kHz.
Current Limit
Current limit for the MIC2282 functions by modifying the
oscillator duty cycle and frequency. When current
exceeds 1.1A, the duty cycle is reduced (switch on-time
is reduced, off-time is unaffected) and the corresponding
frequency is increased. In this way less time is available
for the inductor current to build up while maintaining the
same discharge time. The onset of current limit is soft
rather than abrupt but sufficient to protect the inductor
and output switch from damage. Certain combinations of
input voltage, output voltage and load current can cause
the inductor to go into a continuous mode of operation.
This is what happens when the inductor current can not
fall to zero and occurs when:
duty cycle
≤
V
OUT
+
V
DIODE
−
V
IN
V
OUT
+
V
DIODE
−
V
SAT
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
October 2009
5
M9999-102309
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