MCP1643
1 MHz Low Start-up Voltage Synchronous Boost
LED Constant Current Regulator
Features
• 1.6A Typical Peak Input Current Limit
• Up to 550 mA LED Load Current
• Low Start-up Voltage: 0.65V (typical, 25 mA LED
Current)
• Low Operating Input Voltage: down to 0.5V
• Maximum Input Voltage < V
LED
< 5.0V
• Maximum Output Voltage:
- 5.0V
- Overvoltage Protection
• Low Reference Voltage:
- V
FB
= 120 mV
- Minimal Power Loss on Sense Resistor
• Pulse-Width Modulation Mode Operation (1 MHz)
• Internal Synchronous Rectifier
• Internal Compensation
• Inrush Current Limiting
• Internal Soft-Start (240 µs typical)
• Shutdown (EN = GND):
- True Load Disconnect
- Dimming Control by Variable Duty Cycle
• Shutdown Current: 1.2 µA (typical)
• Overtemperature protection
• Packages:
- MSOP-8
- 2x3 DFN-8
Description
MCP1643 is a compact, high-efficiency, fixed
frequency, synchronous step-up converter optimized to
drive one LED with constant current, that operates from
one and two-cell alkaline and NiMH/NiCd batteries.
The device can also drive two red/green/yellow series
connection LEDs.
Low-voltage technology allows the regulator to start up
without high-output voltage and load-current overshoot
from a low 0.65V input. High efficiency is accomplished
by integrating the low resistance N-Channel Boost
switch and synchronous P-Channel switch. All
compensation and protection circuitry are integrated to
minimize external components.
The internal feedback (V
FB
) voltage is set to 120 mV for
low power dissipation when sensing and regulating
LED current. A single resistor sets the constant current
output that drives the LED load.
The device features an output overvoltage protection
that limits the output voltage to 5.0V typical, in case the
LED fails or output load is disconnected.
The LED will either be turned OFF or turned ON using
the enable input. A True Output Load Disconnect mode
provides input-to-output isolation while Shutdown
(EN = GND) by removing the normal boost regulator
diode path from input to output. Shutdown state
consumes 1.2 µA from input at room temperature.
The LED can be turned on and off with a variable duty
cycle pulse-width modulation (PWM) signal applied to
the EN pin for dimming applications.
The device also features a thermal shutdown at
+150°C, with +25°C hysteresis.
Two package options, MSOP-8 and 2x3 DFN-8, are
available.
Applications
• One and Two Cell Alkaline and NiMH/NiCd
Portable LED Lighting Products
• LED Flashlight and Head Lamps
• Rechargeable Flashlights
• Wall LED Lamps with Motion Detectors
• LED supply for backlights
• General LED constant current applications
Package Types
MCP1643
MSOP-8
EN 1
V
FB
2
NC 3
V
OUT
4
8 V
IN
EN 1
EP
9
MCP1643
2x3 DFN*
8 V
IN
7 S
GND
6 P
GND
5 SW
7 S
GND
V
FB
2
NC 3
6 P
GND
V
OUT
4
5 SW
* Includes Exposed Thermal Pad (EP), see
Table 3-1.
2013 Microchip Technology Inc.
DS20005208A-page 1
MCP1643
Typical Applications
L
1
4.7 µH
I
LED
0.12V
= ----------------
-
R SET
C
IN
4.7...10 µF
V
IN
+
ALKALINE
SW
V
OUT
I
LED
= 25 mA
LED
C
OUT
4.7 µF
R
SET
4.7
MCP1643
V
FB
EN
ON
OFF
-
GND
L
1
4.7 µH
WHITE LED
I
LED
= 360 mA
C
IN
4.7...10 µF
V
IN
+
NIMH 1.2V
SW
V
OUT
R
EN
1 M
MCP1643
V
FB
EN
R
SET
0.33
C
OUT
20 µF
-
GND
ON/OFF
+
NIMH 1.2V
-
R
SET
Minimum and Maximum Limits for I
LED
in Regulation, with ±6% Tolerance
10
R
SET
for I
LED MIN
I
LED MAX
1000
I
LED MAX
1
R
SET
for I
LED MAX
100
I
LED MIN
I
LED MIN
WHITE LED
0.1
0.6
0.9
1.2
1.5
1.8
2.1
Input Voltage (V)
T
A
= +25
o
C
10
3
2.4
2.7
DS20005208A-page 2
2013 Microchip Technology Inc.
LED Current (mA
)
R
SET
(Ω)
MCP1643
1.0
ELECTRICAL
CHARACTERISTICS
† Notice:
Stresses above those listed under “Maximum
Ratings” may cause permanent damage to the device.
This is a stress rating only and functional operation of
the device at those or any other conditions above those
indicated in the operational sections of this
specification is not intended. Exposure to maximum
rating conditions for extended periods may affect
device reliability.
Absolute Maximum Ratings †
EN, FB, V
IN,
V
SW
, V
OUT
- GND ........................... +6.5V
EN, FB ......... < maximum V
OUT
or V
IN
> (GND – 0.3V)
Output Short Circuit Current....................... Continuous
Power Dissipation ............................ Internally Limited
Storage Temperature ......................... -65°C to +150°C
Ambient Temp. with Power Applied...... -40°C to +85°C
Operating Junction Temperature........ -40°C to +125°C
ESD Protection On All Pins:
HBM .............................................................. 4 kV
MM................................................................ 300V
DC CHARACTERISTICS
Electrical Characteristics:
Unless otherwise indicated, V
IN
= EN = 1.2V, C
OUT
= 20 µF, C
IN
= 10 µF, L = 4.7 µH,
I
LED
= 25 mA, T
A
= +25°C.
Boldface
specifications apply over the T
A
range of -40°C to +85°C.
Parameters
Input Characteristics
Minimum Input Voltage
After Start-Up
Start-Up Voltage
Output Overvoltage
Protection
Shutdown
Quiescent Current
Feedback Voltage
Feedback Input
Bias Current
NMOS Switch Leakage
V
IN
V
IN
V
OUT_OVP
I
QSHDN
—
—
—
—
0.5
0.65
5.0
1.2
—
0.8
—
—
V
V
V
µA
Note 1, Note 3
Note 2, Note 1
Note 3
EN = GND;
includes N-Channel and
P-Channel Switch Leakage
Sym
Min
Typ
Max
Units
Conditions
V
FB
I
VFB
I
NLK
105
—
—
120
60
0.4
135
—
—
mV
pA
µA
V
IN
= V
SW
= 4.0V
V
OUT
= 4.5V
V
EN
= V
FB
= GND
V
IN
= VS
W
= GND;
V
OUT
= 4.5V
I
LED
= 250 mA,
Note 3
I
LED
= 250 mA,
Note 3
Note 3
Note 3
Note 3
PMOS Switch Leakage
NMOS Switch
ON Resistance
PMOS Switch
ON Resistance
NMOS Peak
Switch Current Limit
Maximum Duty Cycle
Minimum Duty Cycle
Switching Frequency
EN Input Logic High
EN Input Logic Low
Note 1:
2:
3:
I
PLK
R
DS(ON)N
R
DS(ON)P
I
N(MAX)
DC
MAX
DC
MIN
f
SW
V
IH
V
IL
—
—
—
—
—
—
0.85
75
—
0.25
0.2
0.4
1.6
90
5
1.0
—
—
—
—
—
—
—
—
1.15
—
20
µA
A
%
%
MHz
%of V
IN
I
LED
= 25 mA
%of V
IN
I
LED
= 25 mA
For V
IN
< V
OUT
, I
LED
remains in regulation up to V
IN
= V
LED
minus a headroom @ LED typical V
F
and I
F
.
V
OUT
completely discharged. If the output capacitor remains partially charged, the device will start-up at
the minimum possible voltage.
Determined by characterization, not production tested.
2013 Microchip Technology Inc.
DS20005208A-page 3
MCP1643
DC CHARACTERISTICS (CONTINUED)
Electrical Characteristics:
Unless otherwise indicated, V
IN
= EN = 1.2V, C
OUT
= 20 µF, C
IN
= 10 µF, L = 4.7 µH,
I
LED
= 25 mA, T
A
= +25°C.
Boldface
specifications apply over the T
A
range of -40°C to +85°C.
Parameters
EN Input Leakage Current
Soft Start Time
Sym
I
ENLK
t
SS
Min
—
—
Typ
0.9
240
Max
—
—
Units
µA
µs
Conditions
V
EN
= 1.2V
EN Low-to-High,
90% of V
OUT
;
I
LED
= 25 mA,
Note 3
EN Low-to-High,
90% of V
OUT
;
I
LED
= 300 mA,
Note 3
I
LED
= 25 mA
—
270
—
µs
Thermal Shutdown
Die Temperature
Die Temperature
Hysteresis
Note 1:
2:
3:
T
SD
T
SDHYS
—
—
150
25
—
—
C
C
For V
IN
< V
OUT
, I
LED
remains in regulation up to V
IN
= V
LED
minus a headroom @ LED typical V
F
and I
F
.
V
OUT
completely discharged. If the output capacitor remains partially charged, the device will start-up at
the minimum possible voltage.
Determined by characterization, not production tested.
TEMPERATURE SPECIFICATIONS
Electrical Characteristics:
Unless otherwise indicated, V
IN
= EN = 1.2V, C
OUT
= 20 µF, C
IN
= 10 µF, L = 4.7 µH,
I
LED
= 25 mA, T
A
= +25°C.
Boldface
specifications apply over the T
A
range of -40°C to +85°C.
Parameters
Temperature Ranges
Operating Ambient Temperature Range
Storage Temperature Range
Maximum Junction Temperature
Package Thermal Resistances
Thermal Resistance, 8L-2x3 DFN
Thermal Resistance, 8L-MSOP
JA
JA
—
—
68
211
—
—
°C/W
°C/W
T
A
T
A
T
J
-40
-65
—
—
—
—
+85
+150
+150
°C
°C
°C
Transient
Steady State
Sym
Min
Typ
Max
Units
Conditions
DS20005208A-page 4
2013 Microchip Technology Inc.
MCP1643
2.0
Note:
TYPICAL PERFORMANCE CURVES
The graphs and tables provided following this note are a statistical summary based on a limited number of
samples and are provided for informational purposes only. The performance characteristics listed herein
are not tested or guaranteed. In some graphs or tables, the data presented may be outside the specified
operating range (e.g., outside specified power supply range) and therefore outside the warranted range.
Note:
Unless otherwise indicated, V
IN
= EN = 1.2V, C
OUT
= 20 µF, C
IN
= 10 µF, L = 4.7 µH, I
LED
= 25 mA, T
A
= +25°C,
MSOP-8 package.
500
450
LED Current (mA)
400
350
300
250
200
150
100
50
0
0.6
0.9
1.2
1.5
1.8
Input Voltage (V)
2.1
2.4
R
SET
= 0.82
R
SET
= 1.2
R
SET
= 5
R
SET
= 0.41
LED V
F
= 3.5V @ I
F
= 700 mA
R
SET
= 0.25
100
95
Efficiency (%)
90
85
80
75
70
65
60
10
100
I
LED
(mA)
1000
V
IN
= 1.2V
V
IN
= 2.4V
V
IN
= 1.8V
FIGURE 2-1:
One White LED I
LED
vs. V
IN
.
FIGURE 2-4:
vs. I
LED
.
100
95
One White LED Efficiency
250
225
LED Current (mA)
200
175
150
125
100
75
50
25
0
LED V
F
= 2.5V @ I
F
= 350 mA
R
SET
= 0.82
Efficiency (%)
90
85
V
IN
= 2.4V
V
IN
= 1.8V
V
IN
= 1.2V
R
SET
= 1.2
80
75
70
R
SET
= 5
0.6
0.7
0.8
0.9
1
1.1 1.2
Input Voltage (V)
1.3
1.4
1.5
10
100
I
LED
(mA)
1000
FIGURE 2-2:
One Red LED I
LED
vs. V
IN
.
FIGURE 2-5:
I
LED
.
100
One Red LED Efficiency vs.
350
LED V
F
= 2.5V @ I
F
= 350 mA
LEDs Current (mA)
300
250
200
150
100
50
0
0.6
0.9
95
R
SET
= 0.41
90
Efficiency (%)
85
80
75
70
65
60
55
50
2.1
2.4
10
100
I
LED
(mA)
V
IN
= 3.0V
V
IN
= 3.6V
R
SET
= 0.82
R
SET
= 1.2
V
IN
= 2.4V
R
SET
= 5
1.2
1.5
1.8
Input Voltage (V)
1000
FIGURE 2-3:
Two Series Connection Red
LEDs I
LED
vs. V
IN
.
FIGURE 2-6:
Two Red LEDs Efficiency (in
Series Connection) vs. I
LED
.
2013 Microchip Technology Inc.
DS20005208A-page 5
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