Datasheet MCP1643 Datasheet

MCP1643

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

SWV

OUT

* Includes Exposed Thermal Pad (EP), see Table 3-1.

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

• Maximum Output Voltage:

-5.0V

- Overvoltage Protection

• Low Reference Voltage:

-V

= 120 mV

FB

- Minimal Power Loss on Sense Resistor

• Pulse-Width Modulation Mode Operation (1 MHz)

• Internal Synchronous Rectifi er

• Internal Compensat ion

• 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

LED

<5.0V

Applications

• One and Two Cell Alkaline and NiMH/NiCd
Portable LED Lighting Products

• LED Flashlight and Head Lamps

• Rechargeable Flashlights

• Wall LED Lamp s with Motion Detectors

• LED supply for backlights

• General LED constant current applications

Description

MCP1643 is a compact, high-efficiency, fixed
frequency , sy nchronous st ep-up converte r optimized to
drive one LED with consta nt current, that operate s from
one and two-cell alkaline and NiMH/NiCd batteries.
The device can also drive two red/green/yellow series
connection LEDs.

Low-voltage tec hnolo gy allo ws the regula tor to sta rt up
without high-output v olt age a nd load -curren t overs hoot
from a low 0.65V input. High ef ficiency is acco mplished
by integrating the low resistance N-Channel Boost
switch and synchronous P-Channel switch. All
compensation and protection circuitry a re i nte grated to
minimize external components.

The internal feedba ck (V
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 ou tput volt age to 5.0V typ ical, in ca se the
LED fails or output load is disconnected.

The LED will either be turned OFF or turned ON using
the enable input. A T rue Outpu t Load Disconne ct 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.

) voltage is set to 120mV for

FB

Package Types

 2013 Microchip Technology Inc. DS20005208A-page 1

10

100

1000

0.1

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

TA = +25oC

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

+

-

ALKALINE

ON

OFF

MCP1643

I

LED

=25mA

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

+

-

NIMH 1.2V

ON/OFF

MCP1643

I

LED

=360mA

R

SET

+

-

NIMH 1.2V

1M

R

EN

I

LED

0.12V

R

SET

---------------- -=

R

SET

Minimum and Maximum Limits for I

LED

in Regulation, with ±6% Tolerance

WHITE LED

I

LED MAX

I

LED MIN

MCP1643

Typical Applications

DS20005208A-page 2  2013 Microchip Technology Inc.

MCP1643

1.0 ELECTRICAL

CHARACTERISTICS

Absolute Maximum Ratings †

EN, FB, V

EN, FB .........< m ax im um V

Output Short Circuit Current.......................Continuous

IN, VSW

, V

- GND...........................+6.5V

OUT

or VIN>(GND–0.3V)

OUT

† 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 tho se or any oth er conditions ab ove those
indicated in the operational sections of this
specification is not intended. Exposure to maximum
rating conditions for extended periods may affect

device reliability.

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

Electrica l Characteristics: Unless otherwise indicated, VIN= EN = 1.2V, C

I

=25mA, TA=+25°C. Boldface specifications apply over the TA range of -40°C to +85°C.

LED

Parameters Sym Min Typ Max Units Conditions

Input Characteristics

Minimum Input Voltage

V

IN

—0.5 — VNote 1, Note 3

After Start-Up
Start-Up Voltage V
Output Overvoltage

V

OUT_OVP

IN

—0.65 0.8 VNote 2, Note 1
—5.0 — VNote 3

Protection
Shutdown

I

QSHDN

—1.2 — µAEN= GND;

Quiescent Current

Feedback Voltage V
Feedback Input

I

VFB

FB

105 120 135 mV

—60 —pA

Bias Current
NMOS Switch Leakage I

PMOS Switch Leakage I

NMOS Switch

R

NLK

PLK

DS(ON)N

—0.4 —µAV

—0.25 — µAVIN=VSW= GND;

—0.2 —  I

ON Resistance
PMOS Switch

R

DS(ON)P

—0.4 —  I

ON Resistance
NMOS Peak

I

N(MAX)

—1.6 — ANote 3

Switch Current Limit
Maximum Duty Cycle DC
Minimum Duty Cycle DC
Switching Frequency f
EN Input Logic High V
EN Input Logic Low V

Note 1: For V

2: V

OUT

IN <VOUT

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

, I

remains in regulation up to V

LED

MAX

MIN

SW

IH
IL

—90 —%Note 3
—5 —%Note 3

0.85 1.0 1.15 MHz
75 — — %of VINI
—— 20%of VINI

IN =VLED

minus a headroom @ LED typical VF and IF.

the minimum possible voltage.

3: Determined by characterization, not production tested.

=20µF, CIN= 10 µF, L = 4.7µH,

OUT

includes N-Channel and
P-Channel Switch Leakage

IN=VSW

V

OUT

V

EN=VFB

V

OUT

LED

LED

LED
LED

=4.0V

=4.5V

=GND

=4.5V

= 250 mA, Note 3

= 250 mA, Note 3

=25mA

=25mA

 2013 Microchip Technology Inc. DS20005208A-page 3

MCP1643

DC CHARACTERISTICS (CONTINUED)

Electrica l Characteristics: Unless otherwise indicated, VIN= EN = 1.2V, C

I

=25mA, TA=+25°C. Boldface specifications apply over the TA range of -40°C to +85°C.

LED

Parameters Sym Min Typ Max Units Conditions

EN Input Leakage Current I
Soft Start Time t

ENLK

SS

—0.9 —µAVEN=1.2V
— 240 — µs EN Low-to-H igh,

— 270 — µs EN Low-to-H igh,

Thermal Shutdown

T

SD

—150 — CI

Die Temperature
Die Temperature

T

SDHYS

—25 —C

Hysteresis

Note 1: For V

2: V

OUT

IN <VOUT

remains in regulation up to V

LED

IN =VLED

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

minus a headroom @ LED typical VF and IF.

, I

the minimum possible voltage.

3: Determined by characterization, not production tested.

=20µF, CIN= 10 µF, L = 4.7µH,

OUT

90% of V
I

LED

90% of V
I

LED
LED

OUT

=25mA, Note 3

OUT

=300mA, Note 3

=25mA

;

;

TEMPERATURE SPECIFICATIONS

Electrica l Characteristics: Unless otherwise indicated, VIN= EN = 1.2V, C

=25mA, TA=+25°C. Boldface specifications apply over the TA range of -40°C to +85°C.

I

LED

Parameters Sym Min Typ Max Units Conditions

Temperature Ranges

Operating Ambient Temperature Range T
Storage Temperature Range T
Maximum Junction Temperature T

A
A

J

-40 — +85 °C Steady State

-65 — +150 °C
— — +150 °C Transient

Package Thermal Resistances

Thermal Resistance, 8L-2x3 DFN 
Thermal Resistance, 8L-MSOP 

JA
JA

—68 —°C/W
—211 —°C/W

=20µF, CIN= 10 µF, L = 4.7µH,

OUT

DS20005208A-page 4  2013 Microchip Technology Inc.

MCP1643

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

R

SET

= 5ȍ

R

SET

= 1.2ȍ

R

SET

= 0.82ȍ

R

SET

= 0.41ȍ

R

SET

= 0.25ȍ

LED VF= 3.5V @ IF= 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)

R

SET

= 5ȍ

LED VF= 2.5V @ IF= 350 mA

R

SET

= 1.2ȍ

R

SET

= 0.82ȍ

0

50

100

150

200

250

300

350

0.6 0.9 1.2 1.5 1.8 2.1 2.4

R

SET

= 5ȍ

R

SET

= 1.2ȍ

R

SET

= 0.82ȍ

R

SET

= 0.41ȍ

LED VF= 2.5V @ IF= 350 mA

60

65

70

75

80

85

90

95

100

10 100 1000

Efficiency (%)

VIN= 1.2V

VIN= 1.8V

VIN= 2.4V

70

75

80

85

90

95

100

10 100 1000

VIN= 1.2V

VIN= 1.8V

VIN= 2.4V

50

55

60

65

70

75

80

85

90

95

100

10 100 1000

Efficiency (%)

VIN= 3.0V

VIN= 2.4V

VIN= 3.6V

2.0 TYPICAL PERFORMANCE CURVES

Note: The graphs and table s pro vi ded follo w ing this note ar e a st a tis tic al sum ma ry ba sed 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, VIN=EN=1.2V, C
MSOP-8 package.

LED Current (mA)

Input Voltage (V)

FIGURE 2-1: One White LED I

LED

vs. VIN.

=20µF, CIN= 10 µF, L = 4.7 µH, I

OUT

FIGURE 2-4: One White LED Efficiency
vs. I

LED

Efficiency (%)

.

=25mA, TA=+25°C,

LED

I

(mA)

LED

FIGURE 2-2: One Red LED I

LEDs Current (mA)

FIGURE 2-3: Two Series Connection Red
LEDs I

 2013 Microchip Technology Inc. DS20005208A-page 5

LED

vs. VIN.

Input Voltage (V)

Input Voltage (V)

LED

vs. VIN.

I

(mA)

LED

FIGURE 2-5: One Red LED Efficiency vs.

.

I

LED

I

(mA)

LED

FIGURE 2-6: Two Red LEDs Efficiency (in
Series Connection) vs. I

LED

.

MCP1643

0

50

100

150

200

250

300

350

-40 -25 -10 5 20 35 50 65 80

R

SET

= 5ȍ

R

SET

= 1.2ȍ

R

SET

= 0.82ȍ

R

SET

= 0.41ȍ

VIN= 1.5V

0

25

50

75

100

125

150

0 102030405060708090100

R

SET

= 0.82ȍ

VIN= 1.5V

fEN= 400 Hz

fEN= 1 kHz

34

35

36

37

38

39

40

-40 -25 -10 5 20 35 50 65 80

Duty Cycle (%)

R

SET

= 1.2ȍ

(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

TA= +85oC

TA= +25oC

TA= 0oC

980

985

990

995

1000

1005

1010

-40 -25 -10 5 20 35 50 65 80

Switching Frequency (kHz)

I

LED

= 100 mA

117

118

119

120

121

122

123

-40 -25 -10 5 20 35 50 65 80

I

LED

= 100 mA

Note: Unless otherwise indicated, VIN=EN=1.2V, C
MSOP-8 package.

LED Current (mA)

Ambient Temperature (°C)

FIGURE 2-7: One White I

vs. Ambient

LED

Temperature.

=20µF, CIN= 10 µF, L = 4.7 µH, I

OUT

LED Current (mA)

FIGURE 2-10: Maximum I

=25mA, TA=+25°C,

LED

Input Voltage (V)

LED

vs. VIN.

LED Current (mA)

Duty Cycle (%)

FIGURE 2-8: I

vs. VEN Duty Cycle.

LED

Ambient Temperature (°C)

FIGURE 2-9: Duty Cycle vs. Ambient Temperature.

Ambient Temperature (°C)

FIGURE 2-11: f
Temperature.

Feadback Voltage (mV)

Ambient Temperature (°C)

FIGURE 2-12: V
Temperature.

vs. Ambient

SW

vs. Ambient

FB

DS20005208A-page 6  2013 Microchip Technology Inc.

MCP1643

VEN

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

1us/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

IL

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

Note: Unless otherwise indicated, VIN=EN=1.2V, C

MSOP-8 package.

FIGURE 2-13: Start-up After Enable.

=20µF, CIN= 10 µF, L = 4.7 µH, I

OUT

FIGURE 2-16: Start-up when VIN=VEN.

=25mA, TA=+25°C,

LED

FIGURE 2-14: 100 mA PWM Operation.

FIGURE 2-15: 400 Hz PWM Dimming,

85% Duty Cycle.

 2013 Microchip Technology Inc. DS20005208A-page 7

FIGURE 2-17: 400 Hz PWM Dimming, 15% Duty Cycle.

FIGURE 2-18: Open Load Response.

MCP1643

NOTES:

DS20005208A-page 8  2013 Microchip Technology Inc.

MCP1643

3.0 PIN DESCRIPTIONS

The descriptions of the pins are listed in Table 3-1.

TABLE 3-1: PIN FUNCTION TABLE

MCP1643

2x3 DFN

1 1 EN Enable pin. The logic high enables the operation. Do not allow this pin to

22V

3 3 NC Unconnected pin
44V

5 5 SW Boost and Rectifier Switch Input pin. Connect the boost inductor between

66P
77S
88VINInput Sup ply Voltage pin. A local bypass capacitor is required.
9 — EP Exposed Thermal Pad, must be connected to V

MCP1643

MSOP

Symbol Description

float.

FB

OUT

GND
GND

Reference Voltage pin. Connect to the VFB pin, the R
resistor), and the cathode of the LED load.

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

SW and V
Power Ground Reference pin
Signal Ground Reference pin

.

IN

SS

(LED current set

SET

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 VIN) will
enable the regulator output. A logic low (<20% of V
will ensure that the regulator is disabled.

IN

3.2 Feedback Voltage Pin (VFB)

The VFB pin is used to r egu lat e the vo ltage acr oss t he
R

sense resistor to 120 mV , to keep the outp ut LED

SET

current in regulation.

3.3 Unconnected Pin (NC)

This pin is unconnected.

3.4 Output Voltage Power Pin (V

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

sense resistor. The output voltage must be

R

SET

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

OUT

)

3.5 Switch Node Pin (SW)

3.6 Power Ground (P
Ground Pins (S

The power gr ound pins are used as a r eturn for the
high-current N-Channel switch.

)

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

The length of the trace from input cap return, output
cap return and P
short as possible to min imize noi se on the grou nd pins.

The S

GND

and error amplifier.

FB

and S

GND

and P

pins are connected externally.

GND

GND

) and Signal

GND

)

GND

should be made as

3.7 Power Supply Input Voltage Pin
(V

)

IN

Connect the input voltage source to VIN. The input
source should be decoupled to GND with a 4.7 µF
minimum capac itor.

3.8 Exposed Thermal Pad (EP)

There is no internal electrical connection between the
Exposed Thermal Pad (EP) and the P
pins. They must be conn ected to the same poten tia l on
the Printed Circuit Board (PCB).

GND

and S

GND

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 intern ally connect ed at the SW node.

 2013 Microchip Technology Inc. DS20005208A-page 9

MCP1643

NOTES:

DS20005208A-page 10  2013 Microchip Technology Inc.

MCP1643

Gate Drive

and

Shutdown

Control

Logic

V

IN

EN

V

OUT

P

GND

I

SENSE

I

ZERO

I

LIMIT

SOFT-START

Direction

Control

Oscillator

Slope

Compensation

S

PWM/PFM

Logic

120 mV

Internal

BIAS

SW

V

FB

EA

S

GND

4.0 DETAILED DESCRIPTION

4.1 Device Overview

The MCP1643 is capable of starting up with a low volt­age, while achieving high efficiency to drive one or
more LEDs with constant current.

The MCP1643 is a fixed frequency, synchronous
step-up converter, with a low voltage reference of
120 mV, optimized to keep the output current constant
by regulating the voltage across the feedback resistor
(R

).

SET

The normal boost converter with a high voltage
reference has a high voltage drop across the current
sense resistor. The power dissipated in the sense
resistor reduces the efficiency of a LED driver solution.
Therefore, the voltage drop on the sense resistor used
to regulate the LED cur rent mu st be low, in this c ase by
a low V

The device can operate from one or two-cell alkaline
and NiMH/NiCd batteries. The maximum input voltage
is 5.0V. The dev ic e f eatu res an O ve rvol tage Protection

value of 120 mV.

FB

that protects the device if the output voltage (V
higher than 5.0V. This usually happens if the LED is
disconnected. Whi le VIN<V
remains in regulation until V

Typical Applications and Figures 2-1 to 2-3).

A True Output Load Disconnect mode provides input­to-output isolation while in Shutdown (EN= GND). In
this state, the MCP1643 LED driver drains 1.2 µA cur­rent from the battery at room temperature.

A high level of integration lowers the total system cost,
eases the implementation and reduces board area.
The device also features internal compensation, low
noise, soft start and thermal shutdown.

, the load current (I

OUT

is close to V

IN

LED

OUT

(see

) is

LED

4.2 Function al Description

The MCP1643 is a compact, high-efficiency, fixed
frequency, step-up DC-DC converter that operates as a
constant current gen erat or for appl icati ons powe red by
either one or two-cell, alkaline, NiCd, or NiMH
batteries.

Figure 4-1 depicts the functional block diagram of the

MCP1643 device.

)

FIGURE 4-1: MCP1643 Block Diagram.

 2013 Microchip Technology Inc. DS20005208A-page 11

MCP1643

4.2.1 LOW-VOLTAGE START-UP

The MCP1643 LE D Constant Current D river is c ap able
of starting from a lo w-i np ut v oltag e. Start-up v oltag e is
typically 0.65V for a 25 mA LED load.
For applications in which the device turns on and off
fast, the start-up voltage is lower than 0.65V, because
the output capacitor remains partially charged. After
start-up, the device operates down to 0.5V input.
There is no Undervoltage-Lockout feature for the
MCP1643 LED Constant Current Driver. The device
will start up at the low est possible vol tage and run down
to the lowest possible voltage.
When enabled, the internal start-up logic turns the
rectifying P-Channel switch on until the output
capacitor is charged to a value close to the input
voltage. The r ectifying s witch is cur rent limite d during
this time. After charging the output capacitor to the
input voltage, the device starts switching in open loop,
because the LED is turned off and the feedback input
voltage is zero. On ce V
forward voltage (V

) of the LED , the device en ters in

F

close loop and regulates the voltage across the R

is equal to the minimum

OUT

SET

resistor , which i s connected b etween VFB pin and GND.

4.2.2 PWM MODE OPERATION

The MCP1643 LED Constant Current Driver operates
as a fixed frequency, synchronous boost converter . The
switching frequency is internally maintained with a
precision oscillator typically set to 1 MHz. Because the
LEDs require high currents, the device will work in
PWM Continuous mode. At very low LED currents, the
MCP1643 might run in PWM Discontinuous mode. As
it features an anti -ringin g c ontro l, the switc hing noise is
low. The P-Channel switch acts as a synchronous
rectifier, by turning off to prevent reverse current flow
from the output cap back to the input in order to keep
efficiency high.

Lossless current sensing converts the peak current
signal to a voltage to sum with the internal slope
compensation. Thi s su mm ed s ign al is compared to th e
voltage error amplifier output to provide a peak current
control command for the PWM signal. The slope
compensation is adaptive to the input and output
voltage. Therefore, the converter provides the proper
amount of slope com pensation to ensure stability , but is
not excessive, which causes a loss of phase margin.
The peak current limit is set to 1.6 A typical.

4.2.3 ADJUSTABLE OUTPUT LED
CURRENT

The MCP1643 LED’s current is adjustable with an
external resistor , c alled R

, connected to VFB pin and

SET

GND.
The device regulates the voltage on the R

SET

and
provides a constant current trough LED while
VIN V

(minus a 300 – 400 mV headroom in case

OUT

of low LED currents) (see Figures 2-1 and 2-2).
The internal V

applied when the R

voltage is 120 mV. There are limits

REF

value is calculated over the

SET

input voltages (see Typical Applications).

4.2.4 ENABLE

The enable pin is used to turn the boost converter on
and off. The enable threshold voltage varies with input
voltage. To enable the boost converter, the EN voltage
level must be greater than 75% of the V

voltage. To

IN

disable the boost converter, the EN voltage must be
less than 20% of the VIN voltage.

4.2.4.1 True Output Disconnect

The MCP1643 device incorporates a true output
disconnect feature. With the EN pin pulled low, the
output of the MCP1643 is isolated or disconnected
from the input by turning off the integrated P-Channel
switch and removing the switc h bulk diode connection.
This removes the DC path, typical in boost converters,
which allows the output to be disconnected from the
input. During this mode, 1.2µA (typical) of current is
consumed from the input (battery). True output
disconnect does no t disc harge th e outpu t; this allow s a
faster start-up in dimming or load step applications.

4.2.4.2 PWM Dim min g

The MCP1643 allows dimming by turning the LED on
and off with a variable duty cycle PWM signal applied
to the EN pin. The maximum frequency for dimming is
limited by the internal soft-start of 240µs (typical). By
varying the duty cy cle of the PWM signal app lied on EN
input, the LED current is changing linearly (see

Figure 2-8).

4.2.5 INTERNAL BIAS

The MCP1643 LED Constant Current Driver gets its
start-up bias from V
input, bias comes from the output. Therefore, once
started, the operation is completely independent of

. The operation is only limited by the output power

V

IN

level and the input source series resistance. Once
started, the output will remain in regulation, down to

0.5V typical with 25 mA LED current for low-source
impedance inputs.

. Once the output exceeds the

IN

DS20005208A-page 12  2013 Microchip Technology Inc.

4.2.6 INTERNAL COMPENSATION

The error am plifier, with its associat ed compensation
network, completes the closed loop system by
comparing the voltage from the sense resistor to a
120 mV reference at the input of the error amplifier
and feeding the amplified and inverted signal to the
control input of the inner current loop. The
compensation network provides phase leads and lags
at appropriate frequencies to cancel excessive phase
lags and leads of the power circuit. All necessary
compensation components and slope compensation
are integrated.

4.2.7 SHORT CIRCUIT PROTECTION

Unlike most boost converters, the MCP1643 LED
Constant Current Driver allows its output to be shorted
during normal operation. The internal current limit and
overtemperature protection limit excessive stress and
protect the device during periods of short circuit,
overcurrent and overtemp erature.

4.2.8 OUTPUT OVERVOLTAGE
PROTECTION

Overvoltage Protection is designed to protect the
MCP1643 if the output v ol t age (V
than 5.0V. Because the device is a step-up converter
that runs as a constant current generator, if the load is
disconnected, the output increases up to dangerous
voltages. This happens when the L ED fails. The dev ice
stops switching and the V
periodically if it is higher than 5.0V (see Figure 2-18).

This feature does not protect the LED. An optional
Zener diode is added between V
clamp the output voltage and protects the LED against
excessive voltag e and cu rrent.

) becomes higher

OUT

value is verified

OUT

and VFB pins to

OUT

MCP1643

4.2.9 OVERTEMPERATURE
PROTECTION

Overtemperature protection circuitry is integrated in the
MCP1643 LED Constant Current Driver. This circuitry
monitors the device juncti on temperature and sh uts the
device off if the junction temperature exceeds the
typical +150°C thres hol d. If this threshold is exceede d,
the device will automatically restart once the junction
temperature drops by 25°C.

 2013 Microchip Technology Inc. DS20005208A-page 13

MCP1643

NOTES:

DS20005208A-page 14  2013 Microchip Technology Inc.

MCP1643

I

LED

V

FB

R

SET

----------- -=

5.0 APPLICATION INFORMATION

5.1 Typical Applications

The MCP1643 synchronous boost regulator operates
at 0.5V input. The maximum output voltage range is
limited by overvoltage protection at 5.0V. LED current

 V

stays in regulation while V

IN

400 mV headroom. The power eff iciency con version is
high when driving LED currents up to hundreds of mA.
Output current capability is limited by the 1.6A typical
peak input current l imit. Typical c haracterizati on curve s
in this data sheet are presented to display the typical
output current capability.

5.2 LED Brightness Cont rol

5.2.1 ADJUSTABLE CONSTANT

CURRENT CALCULATIONS

T o c alculate the re sistor value s for the MCP1643’ s LED
current, use Equation 5-1, where R

and GND. The reference voltage (VFB) is 120 mV.

V

FB

EQUATION 5-1:

EXAMPLE 1:

V

= 120 mV

FB

I

=25mA

LED

R

=4.8with a standard value of 4.7

SET

EXAMPLE 2:

V

FB

I

LED

R

SET

Power dissipated on the R
equal with V
power dissipate d on sense resistor is only 12 mW, and
the efficiency of the conversion is high.

Equation 5-1 applies for one or even two LEDs in

series connection. The Typical Applications graphic
shows the maximum a nd minimum limits for R
the input voltage range that ensures current regulation
for a white LED.

I

is 25.53 mA)

LED

= 120 mV
= 100 mA
=1.2

FB*ILED

resistor is very low and

SET

. For 100 mA LED current, the

minus a 300 –

OUT

is connected to

SET

SET

over

5.2.2 PWM DIMMING

LED’s brightness can also be controlled by setting a
maximum current allowed for LED (using Equation 5-1)
and lowering it in s ma ll ste p s w ith a v ari abl e du ty cy cl e
PWM signal applied to the EN pin. The maximum
frequency for dimmin g is li mi ted by the sof t st art, whic h
varies with the LED current. By varying the duty cycle
of the signal applied on the EN pin (from 0 to 100%),
the LED current is changing linearly (see Figure 2-8).

5.3 Input Capacitor Selection

The boost input current is smoothed by the boost
inductor, reducing the amount of filtering necessary at
the input. Some capacitance is recommended to
provide decoupling from the source. Low ESR X5R or
X7R are well suited, since they have a low temperature
coefficient and small size. For most applications,

4.7 µF of capacitance is suf ficient at the input. For hig h­power applications that have high-source impedance
or long lead s, conn ecting th e batt ery to 10 µF ca paci­tance is recommended. Additional input capacitance
can be added to provide a stable input voltage.

5.4 Output Capacitor Selection

The output capacitor helps provide a stable output
voltage and smooth load current during sudden load
transients, as is the PWM dimming. Cer amic cap acitors
are well suited for this application (X5R and X7R). The
range of the output capacitor vary from 4.7 µF (in case
of light loads and static applications) up to 20 µF (for
hundreds of milliamp LED currents and PWM dimming
applications).

5.5 Connecting More LEDs to Output

White LEDs have a typical 2.7 to 3.2V forward voltage

), which depends on the power dissip ated accordin g

(V

F

to its V
to 5.0V maximum to output, two white LEDs in series
connection are not possible.

Two or more white LEDs can be connected in parallel
to output, as shown in Figure 6-1. Current sensing is
necessary only for one LED. Each LED of the string is
passed by the calculated current according to

Equation 5-1. A protection circuit formed by a Zener

and general purpose diodes will protect the rest of
LEDs, if the LED in the sense loop fails.

Two red, green or yellow LEDs can be connected in
series to the output of MCP1643 (see application
example on Figure 6-2). Red LEDs ha ve a typical V
between 1.8V and 2.2V (it depends on the real color),
yellow LEDs have the V
for green options, consider values from 2.0V to 2.4V.

characteristic. Because M CP1643 allows up

F/IF

between 2.1V and 2.2V, while

F

F

 2013 Microchip Technology Inc. DS20005208A-page 15

MCP1643

V

OUTIOUT



Efficienc y

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





V

OUTIOUT



– P

Dis

=

5.6 Induct or Se lection

The MCP1643 device is desi gned to be used with smal l
surface mount inductors. An inductance value of

4.7 µH is recommended to achieve a good balance
between the inductor size, converter load transient
response and minimized noise.

TABLE 5-1: MCP1643 RECOMMENDED

INDUCTORS

Part Number

®

Group

Wurth

744025004 4.7 0.100 1.7 2.8x2.8x2.8
744042004 4.7 0.082 1.65 4.8x4.8x1.8

Coilcraft

ME3220 4.7 0.190 1.5 2.5x3.2x2.0
LPS4018 4.7 0.125 1.8 4x4x1.8
XFL4020 4.7 0.052 2. 0 4x4x2.1

TDK Corporation

B82462 G4472M 4.7 0.04 1.8 6x6x3
B82462 A4472M 4.7 0.08 2.8 6x6x3
SLF6028-

4R7M1R6

Value

(µH)

4.7 0.028 1.6 6x6x2.8

DCR

(– typ)

I

SAT

(A)

Several parameters are used to select the correct
inductor:

• maximum-rated current

• saturation current

• copper resistance (ESR)
For boost converters, t he induct or current c an be much

higher than the output current. The lower the inductor
ESR, the higher the efficiency of the converter, a
common trad e-off in size versus efficiency.

The saturation current typically specifies a point at
which the induc tance has rolled off a percentage of the
rated value. This can range from a 20% to 40%
reduction in induct ance. As th e induc tan ce rol ls off, the
inductor ripple current increases, as does the peak
switch current. It is important to keep the inductance
from rolling off too much, causing switch current to
reach the peak limit.

Size

WxLxH

(mm)

5.7 Thermal Calcul ations

The MCP1643 is available in two different packages:
MSOP-8 and 2 x 3 DFN-8. By calculating the power
dissipation and applying the package thermal resis­tance (

), the junction temperature is estimated. The

JA

maximum continuous ambient temperature rating for
the MCP1643 family of devices is +85°C.

To quickly estimate the internal power dissipation for
the switching boost regulator, an empirical calculation
using measured efficiency can be used. Given the
measured efficiency, the internal power dissipation is
estimated by Equation 5-2:

EQUATION 5-2:

The difference b etw ee n the firs t term , i npu t p ower, an d
the second term, power delivered, is the internal
MCP1643’s power dissipation. This is an estimate
assuming that most of the power lost is internal to the
MCP1643 device and not CIN, C
There is some percentage of power lost in the boost
inductor, with very little loss in the input and output
capacitors. For a more accurate estimation of the
internal power dissipation, subtract the I
power dissipation.

and the inductor.

OUT

INRMS

2

xL

DCR

5.8 PCB Layout Information

Good printed circuit board layout techniques are
important to any switching circuitry, and switching
power supplies are no different. When wiring the
switching high current paths, short and wide traces
should be used. For the MCP1643, these paths are
from V
R

pin to the V

IN

sense resistor, and S

SET

input capacitor. Therefore, it is important that the input
and output capa citors be place d as close a s possible to
the MCP1643, to minimize the loop area.

The feedback track should be routed away from the
switching node and clos e to the V
connected as clos e as po ssible t o the V
regulation issues appears. When possible, ground
planes and traces should be used to help shield the
feedback signal and minimize noise and magnetic
interference.

output capacitor, LED load,

OUT,

GND

and P

pin. R

FB

pins to the

GND

SET

pin, unless

FB

must be

DS20005208A-page 16  2013 Microchip Technology Inc.

MCP1643

C

OUT

L

C

IN

+V

IN

GND

+V

OUT

MCP1643

Enable

LED

R

SET

GND

Wired on Bottom
Plane

1

A

K

SW

FIGURE 5-1: MCP1643 LED Constant Current Driver MSOP8 Recommended Layout. Apply the same guidance for 8-DFN package.

 2013 Microchip Technology Inc. DS20005208A-page 17

MCP1643

NOTES:

DS20005208A-page 18  2013 Microchip Technology Inc.

6.0 TYPICAL APPLICATION CIRCUITS

Note: DZ and D group protects WLED2 and WLED3 from excessive voltage and current, if WLED1

fails. The MCP1643 input quiescent current in Shutdown (EN = GND) is typically 1.2 µA. High­load currents require additional output capacitance.

V

IN

GND

V

FB

C

OUT

10...20 µF

C

IN

4.7...10 µF

L

1

4.7 µH

SW

WLED1

2.4

EN

V

OUT

ON

OFF

I

LED1

=50mA

R

SET

WLED2

2.4

R

2

WLED3

2.4

R

3

I

LED2

=50mA

I

LED3

=50mA
Battery input
(One or Two Cells)

D

Z

VZ=2.4V

D

MCP1643

I

LED

0.12V
R

SET

--------------=

From PIC® MCU I/O

V

IN

GND

V

FB

C

OUT

20 µF

C

IN

4.7 – 10 µF

L1

4.7 µH

SW

LED1 - RED

0.82

EN

V

OUT

I

LED

=150mA

R

SET

Battery input
(One or Two Cells)

LED2 - RED

PWM signal, f = 400 Hz,
Duty Cycle variable

I

LED

0.12V
R

SET

--------------=

MCP1643

MCP1643

FIGURE 6-1: Three White LEDs Application Powered from One or Two Cells.

FIGURE 6-2: 150 mA Two Power Red LEDs Driver with PWM Dimming Control from PIC

Microcontroller.

 2013 Microchip Technology Inc. DS20005208A-page 19

®

MCP1643

NOTES:

DS20005208A-page 20  2013 Microchip Technology Inc.

7.0 PACKAGING INFORMATION

8-Lead MSOP Example

1643I

312256

8-Lead DFN (2 x 3 x 0.9 mm)

Example

AKF

312

25

Part Number Code

MCP1643-I/MC AKF
MCP1643T-I/MC AKF

Legend: XX...X Customer-specific information

Y Year code (last digit of calendar year)
YY Year code (last 2 digits of calendar year)
WW Week code (week of January 1 is week ‘01’)
NNN Alphanumeric traceability code
RoHS Compliant JEDEC designator for Matte Tin (Sn)
* This package is RoHS Compliant. The RoHS Compliant

JEDEC designator ( ) can be found on the outer packaging
for this package.

Note: In the event the full Microchip part num ber can not be ma rke d on one li ne, it will

be carried over to the next line, thus limiting the number of available
characters for customer-specific information.

3

e

Part Number Code

MCP1643-I/MS 1643I
MCP1643T-I/MS 1643I

7.1 Package Marking Information

MCP1643

 2013 Microchip Technology Inc. DS20005208A-page 21

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2

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D2

K

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b

A3 A1

A

NOTE 2

BOTTOM VIEW

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DS20005208A-page 22  2013 Microchip Technology Inc.

Note: For the most current package drawings, please see the Microchip Packaging Specification located at

http://www.microchip.com/packaging

MCP1643

 2013 Microchip Technology Inc. DS20005208A-page 23

MCP1643

Note: For the most current package drawings, please see the Microchip Packaging Specification located at

http://www.microchip.com/packaging

DS20005208A-page 24  2013 Microchip Technology Inc.

Note: For the most current package drawings, please see the Microchip Packaging Specification located at

http://www.microchip.com/packaging

MCP1643

 2013 Microchip Technology Inc. DS20005208A-page 25

MCP1643

Note: For the most current package drawings, please see the Microchip Packaging Specification located at

http://www.microchip.com/packaging

DS20005208A-page 26  2013 Microchip Technology Inc.

APPENDIX A: REVISION HISTORY

Revision A (August 2013)

• Original Release of this Document .

MCP1643

 2013 Microchip Technology Inc. DS20005208A-page 27

MCP1643

NOTES:

DS20005208A-page 28  2013 Microchip Technology Inc.

PRODUCT IDENTIFICATION SYSTEM

Device: MCP1643: LED Constant Current Regulator

MCP1643T: LED Constant Current Regulator

(Tape and Reel)

Temperature Range: I= -40C to +85C (Industrial)

Package: MC = Plastic Dual Flat, No Lead Package -

2x3x0.9 mm Body (DFN)

MS = Plastic Micro Small Outline Package (MSOP)

Examples:

a) MCP1643-I/MC: Industrial Temperature,

8LD 2x3 DFN package

b) MCP1643T-I/MC: Tape and Reel,

Industrial Temperature,
8LD 2x3 DFN package

c) MCP1643-I/MS: Industrial Temperature,

8LD MSOP package

d) MCP1643T-I/MS: Tape and Reel,

Industrial Temperature,
8LD MSOP package

PART NO. X /XX

PackageTemperature

Range

Device

To order or obtain information, e.g., on pricing or delivery , refer to the factory or the listed sales office.

MCP1643

 2013 Microchip Technology Inc. DS20005208A-page 29

MCP1643

NOTES:

DS20005208A-page 30  2013 Microchip Technology Inc.

Note the following details of the code protection feature on Microchip devices:

YSTEM

CERTIFIED BY DNV

== ISO/TS 16949 ==

• Microchip products meet the specification contained in their particular Microchip Data Sheet.

• Microchip believes that its family of products is one of the most secure families of its kind on the market today , when used in the
intended manner and under normal conditions.

• There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our
knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data
Sheets. Most likely, the person doing so is engaged in theft of intellectual property.

• Microchip is willing to work with the customer who is concerned about the integrity of their code.

• Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not
mean that we are guaranteeing the product as “unbreakable.”

Code protection is constantly evolving. We at Microchip are com mitted to continuously improving the c ode prot ection f eatures of our
products. Attempts to break Microchip’s code protection feature may be a violation of t he Digit al Mill ennium Copyright Act. If such act s
allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act.

Information contained in this publication regarding device
applications and t he lik e is provided only f or your convenience
and may be su perseded by updates. It is you r r es ponsibility to
ensure that your application meets with your specifications.
MICROCHIP MAKES NO REPRESENTATIONS OR
WARRANTIES OF ANY KIND WHETHER EXPRESS OR
IMPLIED, WRITTEN OR ORAL, STATUTORY OR
OTHERWISE, RELATED TO THE INFORMATION,
INCLUDING BUT NOT LIMITED TO ITS CONDITION,
QUALITY, PERFORMANCE, MERCHANTABILITY OR
FITNESS FOR PURPOSE. Microchip disclaims all liability
arising from this information and its use. Use of Microchip
devices in life supp ort and/or safety ap plications is entir ely at
the buyer’s risk, and the buyer agrees to defend, indemnify and
hold harmless M icrochip from any and all dama ges, claims,
suits, or expenses re sulting from such use. No licens es are
conveyed, implicitly or otherwise, under any Microchip
intellectual property rights.

Trademarks

The Microchip name and logo, the Microchip logo, dsPIC,
FlashFlex, K
PICSTART, PIC
and UNI/O are registered trademarks of Microchip T echnology
Incorporated in the U.S.A. and other countries.

FilterLab, Hampshire, HI-TECH C, Linear Active Thermistor,
MTP, SEEVAL and The Embedded Control Solutions
Company are registered trademarks of Microchip Technology
Incorporated in the U.S.A.

Silicon Storage Technology is a registered trademark of
Microchip Technology Inc. in other countries.

Analog-for-the-Digital Age, Application Maestro, BodyCom,
chipKIT, chipKIT logo, CodeGuard, dsPICDEM,
dsPICDEM.net, dsPICworks, dsSPEAK, ECAN,
ECONOMONITOR, FanSense, HI-TIDE, In-Circuit Serial
Programming, ICSP, Mindi, MiWi, MPASM, MPF, MPLAB
Certified logo, MPLIB, MPLINK, mTouch, Omniscient Code
Generation, PICC, PICC-18, PICDEM, PICDEM.net, PICkit,
PICtail, REAL ICE, rfLAB, Select Mode, SQI, Serial Quad I/O,
Total Endurance, TSHARC, UniWinDriver , WiperLock, ZENA
and Z-Scale are trademarks of Microchip Technology
Incorporated in the U.S.A. and other countries.

SQTP is a service mark of Microchip T echnology Incorporated
in the U.S.A.

GestIC and ULPP are registered trademarks of Microchip
Technology Germany II GmbH & Co. KG, a subsidiary of
Microchip T echnology Inc., in other countries.

All other trademarks mentioned herein are property of their
respective companies.

© 2013, Microchip Technology Incorporated, Printed in the
U.S.A., All Rights Reserved.

Printed on recycled paper.

ISBN: 978-1-62077-402-1

EELOQ, KEELOQ logo, MPLAB, PIC, PICmicro,

32

logo, rfPIC, SST, SST Logo, SuperFlash

QUALITY MANAGEMENT S

 2013 Microchip Technology Inc. DS20005208A-page 31

Microchip received ISO/TS-16949:2009 certification for its worldwide
headquarters, design and wafer fabrication facilities in Chandler and
Tempe, Arizona; Gresham, Oregon and design centers in California
and India. The Company’s quality system processes and procedures
are for its PIC
devices, Serial EEPROMs, microperipherals, nonvolatile memory and
analog products. In addition, Microchip’s quality system for the design
and manufacture of development systems is ISO 9001:2000 certified.

®

MCUs and dsPIC® DSCs, KEELOQ

®

code hopping

Worldwide Sales and Service

AMERICAS

Corporate Office

2355 West Chandler Blvd.
Chandler, AZ 85224-6199
Tel: [phone]
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Technical Support:

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Tel: [phone]
Fax: [phone]

Indianapolis

Noblesville, IN
Tel: [phone]
Fax: [phone]

Los Angeles

Mission Viejo, CA
Tel: [phone]
Fax: [phone]

Santa Clara

Santa Clara, CA
Tel: [phone]
Fax: [phone]

Toronto

Mississauga, Ontario,
Canada
Tel: [phone]
Fax: [phone]

ASIA/PACIFIC

Asia Pacific Office

Suites 3707-14, 37th Floor
Tower 6, The Gateway
Harbour City, Kowloon
Hong Kong
Tel: [phone]
Fax: [phone]

Australia - Sydney

Tel: [phone]
Fax: [phone]

China - Beijing

Tel: [phone]
Fax: [phone]

China - Chengdu

Tel: [phone]
Fax: [phone]

China - Chongqing

Tel: [phone]
Fax: [phone]

China - Hangzhou

Tel: [phone]
Fax: [phone]

China - Hong Kong SAR

Tel: [phone]
Fax: [phone]

China - Nanjing

Tel: [phone]
Fax: [phone]

China - Qingdao

Tel: [phone]
Fax: [phone]

China - Shanghai

Tel: [phone]
Fax: [phone]

China - Shenyang

Tel: [phone]
Fax: [phone]

China - Shenzhen

Tel: [phone]
Fax: [phone]

China - Wuhan

Tel: [phone]
Fax: [phone]

China - Xian

Tel: [phone]
Fax: [phone]

China - Xiamen

Tel: [phone]
Fax: [phone]

China - Zhuhai

Tel: [phone]
Fax: [phone]

ASIA/PACIFIC

India - Bangalore

Tel: [phone]
Fax: [phone]

India - New Delhi

Tel: [phone]
Fax: [phone]

India - Pune

Tel: [phone]
Fax: [phone]

Japan - Osaka

Tel: [phone]
Fax: [phone]

Japan - Tokyo

Tel: [phone]
Fax: [phone]

Korea - Daegu

Tel: [phone]
Fax: [phone]

Korea - Seoul

Tel: [phone]
Fax: [phone] or
82-2-558-5934

Malaysia - Kuala Lumpur

Tel: [phone]
Fax: [phone]

Malaysia - Penang

Tel: [phone]
Fax: [phone]

Philippines - Manila

Tel: [phone]
Fax: [phone]

Singapore

Tel: [phone]
Fax: [phone]

Tai wan - Hsin Chu

Tel: [phone]
Fax: [phone]

Taiwan - Kaohsiung

Tel: [phone]
Fax: [phone]

Taiwan - Taipei

Tel: [phone]
Fax: [phone]

Thailand - Bangkok

Tel: [phone]
Fax: [phone]

EUROPE

Austria - Wels

Tel: [phone]
Fax: [phone]

Denmark - Copenhagen

Tel: [phone]
Fax: [phone]

France - Paris

Tel: [phone]
Fax: [phone]

Germany - Munich

Tel: [phone]
Fax: [phone]

Italy - Milan

Tel: [phone]
Fax: [phone]

Netherlands - Drunen

Tel: [phone]
Fax: [phone]

Spain - Madrid

Tel: [phone]
Fax: [phone]

UK - Wokingham

Tel: [phone]
Fax: [phone]

11/29/12

DS20005208A-page 32  2013 Microchip Technology Inc.