20005208A.book

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 2013 Microchip Technology Inc.

DS20005208A-page 1

MCP1643

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

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

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.

Package Types

MCP1643 

2x3 DFN*

NC

V

FB

V

OUT

S

GND

P

GND

1

2

3

4

8

7

6

5 SW

V

IN

EN

EP

9

6

1

2

3

8 V

IN

P

GND

EN

V

FB

NC

7 S

GND

MCP1643 

MSOP-8

5

4

SW

V

OUT

* Includes Exposed Thermal Pad (EP), see 

Table 3-1

.

1 MHz Low Start-up Voltage Synchronous Boost 

LED Constant Current Regulator

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MCP1643

DS20005208A-page 2

 2013 Microchip Technology Inc.

Typical Applications

10 

100 

1000 

0.1 

10 

0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7  3 

LED Current (mA

R

SET

 (

Ω

Input Voltage (V) 

R

SET 

for I

LED

 

MIN

 

 

 
 

I

LED MIN

 

 

 

 
 

I

LED MAX

 

 

 
 

R

SET 

for I

LED

 

MAX

 

 

 
 

T

A

 = +25

o

C  

V

IN

GND

V

FB

C

OUT

4.7 µF

C

IN

4.7...10 µF

L

1

4.7 µH

SW

LED 

4.7

EN

V

OUT

+

-

A

L

KA

L

INE

ON

OFF

MCP1643

I

LED

= 25 mA

R

SET

V

IN

GND

V

FB

C

OUT

20 µF

C

IN

4.7...10 µF

L

1

4.7 µH

SW

WHITE LED 

0.33

EN

V

OUT

+

-

NI

M

H

 1.

2V

ON/OFF

MCP1643

I

LED

= 360 mA

R

SET

+

-

NI

M

H

 1.

2V

1 M

R

EN

I

L ED

0.12 V

R

SET

-----------------

=

R

SET

 Minimum and Maximum Limits for I

LED

 in Regulation, with ±6% Tolerance 

WHITE LED

I

LED MAX

I

LED MIN

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 2013 Microchip Technology Inc.

DS20005208A-page 3

MCP1643

1.0

ELECTRICAL 
CHARACTERISTICS

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

† 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.

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

Sym

Min

Typ

Max

Units

Conditions

Input Characteristics

Minimum Input Voltage 
After Start-Up

V

IN

0.5

V

Note 1

Note 3

Start-Up Voltage

V

IN

0.65

0.8

V

Note 2

Note 1

Output Overvoltage 
Protection

V

OUT_OVP

5.0

V

Note 3

Shutdown 
Quiescent Current

I

QSHDN

1.2

µA

EN =  GND; 
includes N-Channel and 
P-Channel Switch Leakage

Feedback Voltage

V

FB

105

120

135

mV

Feedback Input 
Bias Current

I

VFB

60

pA

NMOS Switch Leakage

I

NLK

0.4

µA

V

IN

= V

SW

= 4.0V 

V

OUT

= 4.5V

V

EN

= V

FB

= GND

PMOS Switch Leakage

I

PLK

0.25

µA

V

IN

= VS

W

= GND; 

V

OUT

= 4.5V

NMOS Switch 
ON Resistance

R

DS(ON)N

0.2

I

LED

= 250 mA, 

Note 3

PMOS Switch 
ON Resistance

R

DS(ON)P

0.4

I

LED

= 250 mA, 

Note 3

NMOS Peak 
Switch Current Limit

I

N(MAX)

1.6

A

Note 3

Maximum Duty Cycle

DC

MAX

90

%

Note 3

Minimum Duty Cycle

DC

MIN

5

%

Note 3

Switching Frequency

f

SW

0.85

1.0

1.15

MHz

EN Input Logic High

V

IH

75

%of V

IN

I

LED

= 25 mA

EN Input Logic Low

V

IL

20

%of  V

IN

I

LED

= 25 mA

Note 1:

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

2:

V

OUT 

completely discharged. If the output capacitor remains partially charged, the device will start-up at 

the minimum possible voltage. 

3:

Determined by characterization, not production tested.

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MCP1643

DS20005208A-page 4

 2013 Microchip Technology Inc.

EN Input Leakage Current

I

ENLK

0.9

µA

V

EN

= 1.2V

Soft Start Time

t

SS

240

µs

EN Low-to-High, 
90% of V

OUT

I

LED

= 25 mA, 

Note 3

270

µs

EN Low-to-High, 
90% of V

OUT

I

LED

= 300 mA, 

Note 3

Thermal Shutdown 
Die Temperature

T

SD

150

C

I

LED

= 25 mA

Die Temperature 
Hysteresis

T

SDHYS

25

C

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

Sym

Min

Typ

Max

Units

Conditions

Note 1:

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

2:

V

OUT 

completely discharged. If the output capacitor remains partially charged, the device will start-up at 

the minimum possible voltage. 

3:

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

Sym

Min

Typ

Max

Units

Conditions

Temperature Ranges

Operating Ambient Temperature Range

T

A

-40

+85

°C

Steady State

Storage Temperature Range

T

A

-65

+150

°C

Maximum Junction Temperature

T

J

+150

°C

Transient

Package Thermal Resistances

Thermal Resistance, 8L-2x3 DFN

JA

68

°C/W

Thermal Resistance, 8L-MSOP

JA

211

°C/W

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 2013 Microchip Technology Inc.

DS20005208A-page 5

MCP1643

2.0

TYPICAL PERFORMANCE CURVES

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.

FIGURE 2-1:

One White LED I

LED

 vs. V

IN

.

FIGURE 2-2:

One Red LED I

LED

 vs. V

IN

.

FIGURE 2-3:

Two Series Connection Red 

LEDs I

LED

 vs. V

IN

.

FIGURE 2-4:

One White LED Efficiency 

vs. I

LED

.

FIGURE 2-5:

One Red LED Efficiency vs. 

I

LED

.

FIGURE 2-6:

Two Red LEDs Efficiency (in 

Series Connection) vs. I

LED

.

Note:

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.

0

50

100

150

200

250

300

350

400

450

500

0.6

0.9

1.2

1.5

1.8

2.1

2.4

LED Current (mA)

Input Voltage (V)

R

SET

= 5

ȍ

 

R

SET

= 1.2

ȍ

 

R

SET

= 0.82

ȍ

 

R

SET

= 0.41

ȍ

 

R

SET

= 0.25

ȍ

 

LED V

F

= 3.5V @ I

F

= 700 mA

0

25

50

75

100

125

150

175

200

225

250

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

LED Current (mA)

Input Voltage (V)

R

SET

= 5

ȍ

 

LED V

F

= 2.5V @ I

F

= 350 mA

R

SET

= 1.2

ȍ

 

R

SET

= 0.82

ȍ

 

0

50

100

150

200

250

300

350

0.6

0.9

1.2

1.5

1.8

2.1

2.4

LEDs Current (mA)

Input Voltage (V)

R

SET

= 5

ȍ

 

R

SET

= 1.2

ȍ

 

R

SET

= 0.82

ȍ

 

R

SET

= 0.41

ȍ

 

LED V

F

= 2.5V @ I

F

= 350 mA

60

65

70

75

80

85

90

95

100

10

100

1000

Efficiency

 (%

)

I

LED

(mA)

V

IN

= 1.2V

V

IN

= 1.8V

V

IN

= 2.4V

70

75

80

85

90

95

100

10

100

1000

Efficiency

 (%

)

I

LED

(mA)

V

IN

= 1.2V

V

IN

= 1.8V

V

IN

= 2.4V

50

55

60

65

70

75

80

85

90

95

100

10

100

1000

Efficiency

 (%

)

I

LED

(mA)

V

IN

= 3.0V

V

IN

= 2.4V

V

IN

= 3.6V

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MCP1643

DS20005208A-page 6

 2013 Microchip Technology Inc.

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.

FIGURE 2-7:

One White I

LED

 vs. Ambient 

Temperature.

FIGURE 2-8:

I

LED

 vs. V

EN

 Duty Cycle.

FIGURE 2-9:

Duty Cycle vs. Ambient 

Temperature.

FIGURE 2-10:

Maximum I

LED

 vs. V

IN

.

FIGURE 2-11:

f

SW

 vs. Ambient 

Temperature.

FIGURE 2-12:

V

FB

 vs. Ambient 

Temperature.

0

50

100

150

200

250

300

350

-40

-25

-10

5

20

35

50

65

80

LED Current (mA)

Ambient Temperature (°C)

R

SET

= 5

ȍ

 

R

SET

= 1.2

ȍ

 

R

SET

= 0.82

ȍ

 

R

SET

= 0.41

ȍ

 

V

IN

= 1.5V

0

25

50

75

100

125

150

0

10

20

30

40

50

60

70

80

90 100

LED Current (mA)

Duty Cycle (%)

R

SET

= 0.82

ȍ

 

V

IN

= 1.5V

f

EN

= 400 Hz

 

f

EN

= 1 kHz

 

34

35

36

37

38

39

40

-40

-25

-10

5

20

35

50

65

80

Duty

 Cy

cle (%

)

Ambient Temperature (°C)

R

SET

= 1.2

ȍ

 

(I

LED

= 100 mA)

 

0

100

200

300

400

500

600

700

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

3

LED Current (mA)

Input Voltage (V)

T

A

= +85

o

T

A

= +25

o

T

A

= 0

o

980

985

990

995

1000

1005

1010

-40

-25

-10

5

20

35

50

65

80

Sw

itching Frequency

 (kHz)

Ambient Temperature (°C)

I

LED

= 100 mA

 

117

118

119

120

121

122

123

-40

-25

-10

5

20

35

50

65

80

Feadback V

o

ltage (mV)

Ambient Temperature (°C)

I

LED

= 100 mA

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DS20005208A-page 7

MCP1643

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.

FIGURE 2-13:

Start-up After Enable.

FIGURE 2-14:

100 mA PWM Operation.

FIGURE 2-15:

400 Hz PWM Dimming, 

85% Duty Cycle.

FIGURE 2-16:

Start-up when V

IN

= V

EN

.

FIGURE 2-17:

400 Hz PWM Dimming, 

15% Duty Cycle.

FIGURE 2-18:

Open Load Response.

V

EN

 

80 us/div

1 V/div

V

IN

 

I

LED

20 mA/div

20 mV/div, AC Coupled

V

OUT

 

1 V/div

V

SW

 

I

LED

100 mA/div

1 us/div

I

LED

50 mA/div

1 V/div

V

SW

 

1 V/div

V

EN

 

400 us/div

80 us/div

500 mA/div

I

L

 

1 V/div

V

IN

 

I

LED

20 mA/div

I

LED

50 mA/div

1 V/div

V

SW

 

1 V/div

V

EN

 

400 us/div

I

LED

10 ms/div

2 V/div

Step from I

LED

= 100 mA to Open Load

2 V/div

100 mA/div

V

OUT

 

V

SW

 

2V

5V

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MCP1643

DS20005208A-page 8

 2013 Microchip Technology Inc.

NOTES:

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 2013 Microchip Technology Inc.

DS20005208A-page 9

MCP1643

3.0

PIN DESCRIPTIONS

The descriptions of the pins are listed in 

Table 3-1

.

3.1

Enable Pin (EN)

The EN pin is a logic-level input used to enable or
disable device switching. Device has low quiescent
current while disabled. A logic high (>75%

 

of V

IN

) will

enable the regulator output. A logic low (<20% of V

IN

)

will ensure that the regulator is disabled.

3.2

Feedback Voltage Pin (V

FB

)

The V

FB

 pin is used to regulate the voltage across the

R

SET

 sense resistor to 120 mV, to keep the output LED

current in regulation.

3.3

Unconnected Pin (NC)

This pin is unconnected.

3.4

Output Voltage Power Pin (V

OUT

)

High current flows through the integrated P-Channel
and out of this pin to the output capacitor, LED load and
R

SET

 sense resistor. The output voltage must be

filtered using a 4.7 to 20 µF X7R or X5R ceramic
capacitor. The value of the output capacitor depends
on the load current.

3.5

Switch Node Pin (SW)

Connect the inductor from the input voltage to the SW
pin. The SW pin carries inductor current and can be as
high as 1.6 A typical peak value. The integrated
N-Channel switch drain and integrated P-Channel
switch source are internally connected at the SW node.

3.6

Power Ground (P

GND

) and Signal 

Ground Pins (S

GND

)

The power ground pins are used as a return for the
high-current N-Channel switch.

The signal ground pin is used as a return for the
integrated V

FB

 and error amplifier.

The length of the trace from input cap return, output
cap return and P

GND

 and S

GND

 should be made as

short as possible to minimize noise on the ground pins.

The S

GND

 and P

GND

 pins are connected externally.

3.7

Power Supply Input Voltage Pin 
(V

IN

)

Connect the input voltage source to V

IN

. The input

source should be decoupled to GND with a 4.7 µF
minimum capacitor.

3.8

Exposed Thermal Pad (EP)

There is no internal electrical connection between the
Exposed Thermal Pad (EP) and the P

GND

 and S

GND

pins. They must be connected to the same potential on
the Printed Circuit Board (PCB).

TABLE 3-1:

PIN FUNCTION TABLE

MCP1643

2 x 3  DFN

MCP1643

MSOP

Symbol

Description

1

1

EN

Enable pin. The logic high enables the operation. Do not allow this pin to 
float.

2

2

V

FB

Reference Voltage pin. Connect to the V

FB

 pin, the 

R

SET

 (LED current set 

resistor), and the cathode of the LED load.

3

3

NC

Unconnected pin

4

4

V

OUT

Boost Converter Output pin. Connect to this pin the anode of the LED load. 
An output filter capacitor is required.

5

5

SW

Boost and Rectifier Switch Input pin. Connect the boost inductor between 
SW and V

IN

.

6

6

P

GND

Power Ground Reference pin

7

7

S

GND

Signal Ground Reference pin

8

8

V

IN

Input Supply Voltage pin. A local bypass capacitor is required.

9

EP

Exposed Thermal Pad, must be connected to V

SS

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MCP1643

DS20005208A-page 10

 2013 Microchip Technology Inc.

NOTES:

Maker
Microchip Technology Inc.
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