MIC2297
40V PWM Boost Regulator
White LED Driver
General Description
The MIC2297 is a 600KHz PWM boost-switching regulator
that is optimized for driving 6-10 series white LEDs. With
its internal 40V switch and a guaranteed switch current of
1.2A, the MIC2297 easily drives a string of 10 white LEDs
in series at 20mA, ensuring a high level of brightness and
eliminating several ballast resistors.
The MIC2297 implements constant frequency 600KHz
PWM control. The high frequency PWM operation saves
board space by reducing external component sizes. The
added benefit of the constant frequency PWM operation is
much lower noise and input ripple injected back to the
battery source than with variable frequency topologies.
To optimize efficiency, the feedback voltage is set to
200mV. This reduced voltage reduces the power
dissipation in the current set resistor, and allows the lowest
total output voltage, hence minimal current draw from the
battery.
The MIC2297 is available with output over-voltage
protection that protects the IC and external components in
case of open LED conditions.
The MIC2297 is available in low profile small size 10-pin
2.5mm x 2.5mm MLF
®
package. The MIC2297 has a
junction temperature range of –40°C to +125°C.
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
•
2.5V to 10V input voltage range
Output voltage up to 40V
1.2A switch current
600KHz PWM operation
Trimmed 200mV feedback voltage
Output over voltage protection (fixed or adjustable)
PWM Brightness Control
DAC Brightness Control
<1% line regulation
1µA shutdown current
Over temperature protection
UVLO
10-pin 2.5mm x 2.5mm MLF
®
package
–40
o
C to +125
o
C junction temperature range
Applications
•
•
•
•
•
•
•
PDAs
GPS systems
Smart phones
Mini PCs
Digital cameras
IP phones
LED flashlights
___________________________________________________________________________________________________________
Typical Applications
6.8µH-22µH
6.8µH-22µH
VIN
SW
OVP
1-Cell
Li I on
3V to 4.2V
1µF
EN
MIC2297
BRT
-42BM
L
REF
FB
0.47µF
/50V 1-Ce ll
Li I on
3V to 4.2V
VIN
SW
OVP
1µF
PWM
EN
MIC2297
BRT
-42BM
L
REF
FB
0.47µF
/50V
1µF
AGN PGND COMP
D
0.1µF
10
1µF
AGND PGND COMP
0.1µF
10
10 Series LED Driver with Output OVP
MLF and
MicroLeadFrame
is a trademark of Amkor Technology, Inc.
10 Series LED Driver with PWM Brightness Control
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 2008
M9999-032708
Micrel, Inc.
MIC2297
Ordering Information
Part Number
MIC2297-15YML
MIC2297-42YML
*(
Mark Code*
S115
S142
Output Over
Voltage Protection
15V
42V
Junction
Temp. Range
–40°C to 125°C
–40°C to 125°C
Package
10-Pin 2.5 x2.5 MLF
10-Pin 2.5 x2.5 MLF
®
®
Lead Finish
Pb-Free
Pb-Free
) Top bar symbol after PI indicator identifying Pb-Free may not be to scale.
Pin Configuration
PGND 1
OVP 2
VIN 3
EN 4
COMP 5
10 SW
9
8
7
6
FB
REF
BRT
AGND
Pin Description
Pin Number
1
2
3
4
5
6
Pin Name
PGND
OVP
VIN
EN
COMP
AGND
Pin Function
Ground (Return).
Over Voltage Protection (Input): Connect to the output to
clamp the maximum output voltage. A resistor divider from
this pin to ground could be used to raise the OVP level of
the 15V OVP option.
Supply (Input): Input voltage.
Enable (Input): Logic high enables regulator. Logic low shuts
down regulator.
Compensation Pin.
Analog Ground.
Brightness Control (Input): Either an analog (DAC) or filtered
PWM signal can be used. The gain equation is: VFB =
VBRT / 5. This pin should be left open if the brightness
function is not used. In that case, the FB will be set to its
default value of 200mV.
Reference Voltage (Output): This node is equal to the
voltage on the FB pin. A capacitor from REF to ground
should be used to filter the BRT voltage if PWM dimming is
implemented. A capacitor from REF to ground can also be
used to implement a soft-start function. This pin can be left
open if not used.
Feedback (Input): Output voltage sense node. Default value
is 200mV. Connect the cathode of the LED chain to this pin.
Connect current set resistor from this pin to ground.
Switch Node (Output): Internal power BIPOLAR collector.
Ground (Return): Backside pad.
2
M9999-032708
7
BRT
8
REF
9
10
EPad
Mach 2008
FB
SW
GND
Micrel, Inc.
MIC2297
Absolute Maximum Rating
(1)
Supply voltage (V
IN
)........................................................12V
Switch voltage (V
SW
) ........................................ -0.3V to 50V
Enable pin voltage (V
EN
)....................................... -0.3 to V
IN
FB Voltage (V
FB
)...............................................................6V
V
BRT
..................................................................................6V
Switch Current (I
SW
) .........................................................3A
Ambient Storage Temperature (T
S
)............-65°C to +150°C
ESD Rating
(3)
................................................................ 2KV
Operating Range
(2)
Supply Voltage (V
IN
).......................................... 2.5V to 10V
Maximum Output Voltage (V
OUT
)....................................40V
Junction Temperature Range (T
J
)..............-40°C to +125°C
Package Thermal Impedance
MLF
®
-10 (θ
JA
).....................................................65°C/W
Electrical Characteristics
T
A
=25
o
C, V
IN
=V
EN
= 3.6V, V
OUT
= 30V, I
OUT
= 20mA, unless otherwise noted.
Bold
values indicate -40°C
≤
T
J
≤
125°C.
Symbol
V
IN
V
UVLO
I
VIN
I
SD
V
FB
I
FB
Parameter
Supply Voltage Range
Under-Voltage Lockout
Quiescent Current
Shutdown Current
Feedback Voltage
Feedback Input Current
Line Regulation
(5)
Load Regulation
D
MAX
I
SW
V
SW
I
SW
V
EN
I
EN
V
REF
f
SW
V
OVP
T
J
(5)
Condition
Min
2.5
1.8
Typ
2.1
4
0.1
200
-450
0.5
0.5
Max
10
2.4
7
1
210
213
Units
V
V
mA
µA
mV
nA
V
FB
= 200mV (not switching)
V
EN
= 0V
(4)
(+/-5%)
(+/±6.5%) (Over Temp)
V
FB
= 200mV
2.5V
≤
V
IN
≤
4.5V
5mA
≤
I
OUT
≤
20mA
93
V
IN
2.5V
V
IN
= 2.5V, I
SW
= 0.5A
V
EN
= 0V, V
IN
= 10V
TURN ON
TURN OFF
V
EN
= 10V
V
BRT
= 0V
V
BRT
= 1V
V
BRT
= 5V
V
BRT
= OPEN
MIC2297-42BML (nominal voltage)
MIC2297-15BML (nominal voltage)
Hysteresis
1.2
190
187
1
%
%
%
Maximum Duty Cycle
Switch Current Limit
Switch Saturation Voltage
Switch Leakage Current
Enable Threshold
Enable Pin Current
Brightness Control Accuracy
Oscillator Frequency
Over Voltage protection
Over-Temperature Threshold
Shutdown
1.7
220
0.01
2.5
1
0.4
40
0.015
0.215
1.05
0.21
675
47
18
A
mV
µA
V
µA
V
1.5
20
0.185
0.93
0.19
525
40.5
15
0.2
1.0
0.2
600
42
16
150
10
KHz
V
°C
°C
Notes:
1.
2.
3.
4.
5.
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.
This device is not guaranteed to operate beyond its specified operating rating.
IC devices are inherently ESD sensitive. Handling precautions required. Human body model.
I
SD
= I
VIN
.
Guaranteed by design.
Mach 2008
3
M9999-032708
Micrel
MIC2297
Typical Characteristics
6
5.5
5
4.5
4
3.5
3
2
3
Not Switching
V
FB
= 1V
4 5 6 7 8 9
INPUT VOLTAGE (V)
10
97
96
95
2
500
Supply Current
vs. Input Voltage
100
99
98
Max Duty Cycle
vs. Input Voltage
800
Frequency
vs. Input Voltage
700
600
3
4 5 6 7 8 9
INPUT VOLTAGE (V)
10
400
2
3
4 5 6 7 8 9
INPUT VOLTAGE (V)
10
1200
1000
800
600
400
200
Switch Current
vs. Switch Voltage
220
215
210
205
200
195
Switch Voltage
vs. Input Voltage
20
18
16
14
12
LED Current
vs. Input Voltage
V
IN
= 3.6V
0
0
500
1000
1500
SWITCH CURRENT (mA)
190
2
I
FSWITCH
= 0.5A
3
4 5 6 7 8 9
INPUT VOLTAGE (V)
10
10
2
3
4 5 6 7 8 9
INPUT VOLTAGE (V)
10
1.5
1.4
1.3
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
2
3
BRT Voltage
vs. Input Voltage
300
280
260
240
220
200
180
160
140
120
100
2
FB Voltage
vs. Input Voltage
30
25
20
15
10
5
LED Current
vs. BRT Voltage
4 5 6 7 8 9
INPUT VOLTAGE (V)
10
3
4 5 6 7 8 9
INPUT VOLTAGE (V)
10
0
R
SENSE
10001200
BRT VOLTAGE (mV)
300
250
200
150
100
50
0
FB Voltage
vs. BRT Voltage
Efficiency for 10 LEDs @ 20mA
vs. Input Voltage
80
78
76
74
72
L = 6.8µH
70
2
80
75
70
65
60
55
50
45
Efficiency for 10 LEDs
vs. LED Current
V
IN
= 4.2V
V
IN
= 3.6V
V
IN
= 3.2V
L = 6.8µH
5
10 15 20 25 30
LED CURRENT (mA)
35
10001200
BRT VOLTAGE (mV)
3
4 5 6 7 8 9
INPUT VOLTAGE (V)
10
40
0
Mach 2008
4
M9999-032708
Micrel
MIC2297
Typical Characteristics (continued)
85
80
75
70
65
60
55
50
45
40
35
0
Efficiency for 10 LEDs
vs. LED Current
V
IN
= 4.2V
V
IN
= 3.2V V
IN
= 3.6V
80
75
70
65
60
55
50
Efficiency for 9 LEDs
vs. LED Current
V
IN
= 4.2V
V
IN
= 3.2V
V
IN
= 3.6V
85
80
75
70
65
60
55
50
45
Efficiency for 9 LEDs
vs. LED Current
V
IN
= 4.2V
V
IN
= 3.2V
V
IN
= 3.6V
L = 15µH
10
20
30
LED CURRENT (mA)
40
45
40
0
5
L = 6.8µH
10 15 20 25 30
LED CURRENT (mA)
35
40
35
0
5
L = 15µH
10 15 20 25 30 35 40
LED CURRENT (mA)
35
30
25
20
15
10
5
0
0
20
LED Current
vs. Duty Cycle
4V
5V
3V
2V
C1
1µF, 16V
L1 = Murata LQH32CN100K11
L1
VIN
SW
MIC2297BML
C2
0.47µF, 50V
2V peak PWM
C3
0.22µF, 10V
PWM
EN
REF
BRT
OVP
C4
0.1µF, 10V
COMP
AGND
PGND
FB
PWM = 20kHz
R
SENSE
40
60
80
DUTY CYCLE (%)
100
Mach 2008
5
M9999-032708
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