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 < VLED <5.0V
• Maximum Output Voltage:
-5.0V
- Overvolt a ge Prote cti on
• Low Reference Voltage:
-V
FB = 120 mV
- Minimal Power Loss on Sense Resistor
• Pulse-Width Modulation Mode Operation (1 MHz)
• Intern al Syn chr ono us Rectifi er
• Intern al Com pen sation
• 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
frequenc y , sync hronous step-u p converter opti mized to
drive one LED with const ant 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-vo lta ge techn olo gy allows the regula tor to sta rt up
withou t high- output v olt age a nd load -curren t overs hoot
from a low 0.6 5V input. High efficienc y is accomplis hed
by integrating the low resistance N-Channel Boost
switch and synchronous P-Channel switch. All
compen sa tio n a nd protect ion ci rcu itry a re i nte grated to
minimize external components.
The inter nal feedback (VFB) 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 limi ts the ou tput volt age to 5.0 V typical, i n case the
LED fails or output load is disconnected.
The LED will either be turned OFF or turned ON using
the enabl e 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.
Package Types
MCP1643
2x3 DFN*
NC
VFB
VOUT
SGND
PGND
1
2
3
4
8
7
6
5SW
VIN
EN
EP
9
6
1
2
3
8VIN
PGND
EN
VFB
NC
7SGND
MCP1643
MSOP-8
5
4SWVOUT
* Includes Exposed Thermal Pad (EP), see Table 3-1.
1 MHz Low Start-up Voltage Synchronous Boost
LED Constant Current Regulator
MCP1643
DS20005208A-page 2 2013 Microchip Technology Inc.
Typical Applications
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)
RSET for ILED MIN
ILED MIN
ILED MAX
RSET for ILED MAX
TA = +25oC
VIN
GND
VFB
COUT
4.7 µF
CIN
4.7...10 µF
L1
4.7 µH
SW
LED
4.7
EN
VOUT
+
-
ALKALINE
ON
OFF
MCP1643
ILED =25mA
RSET
VIN
GND
VFB
COUT
20 µF
CIN
4.7...10 µF
L1
4.7 µH
SW
WHITE LED
0.33
EN
VOUT
+
-
NIMH 1.2V
ON/OFF
MCP1643
ILED =360mA
RSET
+
-
NIMH 1.2V
1M
REN
ILED 0.12V
RSET
-----------------=
RSET Minimum and Maximum Limits for ILED in Regulation, with ±6% Tolerance
WHITE LED
ILED MAX
ILED MIN
2013 Microchip Technology Inc. DS20005208A-page 3
MCP1643
1.0 ELECTRICAL
CHARACTERISTICS
Absolute Maximum Ratings †
EN, FB, VIN, VSW, VOUT - GND.......................... .+6 .5V
EN, FB .........< m axim um VOUT or VIN >(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: S tresses above those listed under “Maximum
Ratings” may cause permanent damage to the device.
This is a stress rating only and functional operation of
the devi ce at those or any other c onditions 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.
DC CHARACTERISTICS
Electrical Characteris tics: Unless otherwise indicated, VIN = EN = 1.2V, COUT =20µF, C
IN = 10 µF, L = 4.7 µH,
ILED =25mA, T
A=+25°C. Boldface specifications apply over the TA range of -40°C to +85°C.
Parameters Sym Min Typ Max Units Conditions
Input Characteristics
Minimum Input Voltage
After Start-Up VIN —0.5 — VNote 1, Note 3
Start-Up Voltage VIN —0.65 0.8 VNote 2, Note 1
Output Ov erv ol t age
Protection VOUT_OVP —5.0 — VNote 3
Shutdown
Quiescent Current IQSHDN —1.2 —µAEN= GND;
includes N-Channel and
P-Channel Switch Leakage
Feedbac k Voltage VFB 105 120 135 mV
Feedbac k Inpu t
Bias Current IVFB —60 —pA
NMOS Switch Leakage INLK —0.4 —µAV
IN =V
SW =4.0V
VOUT =4.5V
VEN =V
FB =GND
PMOS Switch Leakage IPLK —0.25 — µAV
IN =VS
W= GND;
VOUT =4.5V
NMOS Switch
ON Resista nce RDS(ON)N —0.2 — ILED = 250 mA, Note 3
PMOS Switch
ON Resista nce RDS(ON)P —0.4 — ILED = 250 mA, Note 3
NMOS Peak
Switch Current Limit IN(MAX) —1.6 — ANote 3
Maximu m Duty Cycle DCMAX —90 —%Note 3
Minimu m Duty Cycle DCMIN —5 —%Note 3
Switching Frequency fSW 0.85 1.0 1.15 MHz
EN Input Logic High VIH 75 — — %of VIN ILED=25mA
EN Input Logic Low VIL —— 20%of V
IN ILED =25mA
Note 1: For VIN <V
OUT, ILED remains in regulation up to VIN =V
LED minus a headroom @ LED typical VF and IF.
2: VOUT 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.
MCP1643
DS20005208A-page 4 2013 Microchip Technology Inc.
EN Input Leakage Current IENLK —0.9 —µAV
EN =1.2V
Soft Start Time tSS — 240 — µs EN Lo w-to-High,
90% of VOUT;
ILED =25mA, Note 3
— 270 — µs EN Low-to- Hig h,
90% of VOUT;
ILED =300mA, Note 3
Thermal Shutdown
Die Temperature TSD —150 — CI
LED=25mA
Die Temperature
Hysteresis TSDHYS —25 —C
DC CHARACTERISTICS (CONTINUE D)
Electrical Characteris tics: Unless otherwise indicated, VIN = EN = 1.2V, COUT =20µF, C
IN = 10 µF, L = 4.7 µH,
ILED =25mA, T
A=+25°C. Boldface specifications apply over the TA range of -40°C to +85°C.
Parameters Sym Min Typ Max Units Conditions
Note 1: For VIN <V
OUT, ILED remains in regulation up to VIN =V
LED minus a headroom @ LED typical VF and IF.
2: VOUT 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 Characteris tics: Unless otherwise indicated, VIN = EN = 1.2V, COUT =20µF, C
IN = 10 µF, L = 4.7 µH,
ILED =25mA, T
A=+25°C. Boldface specifications apply over the TA range of -40°C to +85°C.
Parameters Sym Min Typ Max Units Conditions
Temperature Ranges
Operating Ambient Temperature Range TA-40 — +85 °C Steady State
Storage Temperature Range TA-65 — +150 °C
Maximum Junction Tempe rature TJ— — +150 °C Transient
Package Thermal Resistances
Thermal Resistance, 8L-2x3 DFN JA —68 —°C/W
Thermal Resistance, 8L-MSOP JA —211 —°C/W
2013 Microchip Technology Inc. DS20005208A-page 5
MCP1643
2.0 TYPICAL PERFORMANCE CURVES
Note: Unless otherwise indicated, VIN =EN=1.2V, C
OUT =20µF, C
IN = 10 µF, L = 4.7 µH, ILED =25mA, T
A=+25°C,
MSOP-8 package.
FIGURE 2-1: One Whit e LED ILED vs. VIN.
FIGURE 2-2: One Red LED ILED vs. VIN.
FIGURE 2-3: Two Series Connection Red
LEDs ILED vs. VIN.
FIGURE 2-4: One White LED Efficiency
vs. ILED.
FIGURE 2-5: One Red LED Efficiency vs.
ILED.
FIGURE 2-6: T wo Red LEDs Efficiency (in
Series Connection) vs. ILED.
Note: The gra phs and table s pro vi ded follo wing this note are a st atistical summary ba sed on a limi ted nu mb er 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
0.6 0.9 1.2 1.5 1.8 2.1 2.4
LED Current (mA)
Input Voltage (V)
RSET = 5ȍ
RSET = 1.2ȍ
RSET = 0.82ȍ
RSET = 0.41ȍ
RSET = 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)
Input Voltage (V)
RSET = 5ȍ
LED VF= 2.5V @ IF= 350 mA
RSET = 1.2ȍ
RSET = 0.82ȍ
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)
RSET = 5ȍ
RSET = 1.2ȍ
RSET = 0.82ȍ
RSET = 0.41ȍ
LED VF= 2.5V @ IF= 350 mA
60
65
70
75
80
85
90
95
100
10 100 1000
Efficiency (%)
ILED (mA)
VIN = 1.2V
VIN = 1.8V
VIN = 2.4V
70
75
80
85
90
95
100
10 100 1000
Efficiency (%)
ILED (mA)
VIN = 1.2V
VIN = 1.8V
VIN = 2.4V
50
55
60
65
70
75
80
85
90
95
100
10 100 1000
Efficiency (%)
ILED (mA)
VIN = 3.0V
VIN = 2.4V
VIN = 3.6V
MCP1643
DS20005208A-page 6 2013 Microchip Technology Inc.
Note: Unless otherwise indicated, VIN =EN=1.2V, C
OUT =20µF, C
IN = 10 µF, L = 4.7 µH, ILED =25mA, T
A=+25°C,
MSOP-8 package.
FIGURE 2-7: One White ILED vs. Ambient
Temperature.
FIGURE 2-8: ILED vs. VEN Duty Cycle.
FIGURE 2-9: Duty Cycle vs. Ambient
Temperature.
FIGURE 2-10: Maximum ILED vs. VIN.
FIGURE 2-11: fSW vs. Ambient
Temperature.
FIGURE 2-12: VFB 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)
RSET = 5ȍ
RSET = 1.2ȍ
RSET = 0.82ȍ
RSET = 0.41ȍ
VIN = 1.5V
0
25
50
75
100
125
0 102030405060708090100
LED Current (mA)
Duty Cycle (%)
RSET = 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 (%)
Ambient Temperature (°C)
RSET = 1.2ȍ
(ILED = 100 mA)
0
100
200
300
400
500
600
0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3
LED Current (mA)
Input Voltage (V)
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)
Ambient Temperature (°C)
ILED = 100 mA
117
118
119
120
121
122
123
-40 -25 -10 5 20 35 50 65 80
Feadback Voltage (mV)
Ambient Temperature (°C)
ILED = 100 mA
2013 Microchip Technology Inc. DS20005208A-page 7
MCP1643
Note: Unless otherwise indicated, VIN =EN=1.2V, C
OUT =20µF, C
IN = 10 µF, L = 4.7 µH, ILED =25mA, 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 VIN =V
EN.
FIGURE 2-17: 400 Hz PWM Dimming,
15% Duty Cycle.
FIGURE 2-18: Open Load Response.
VEN
80 us/div
1 V/div
VIN
ILED
20 mA/div
20 mV/div, AC Coupled
VOUT
1 V/div
VSW
ILED
100 mA/div
1us/div
ILED
50 mA/div
1 V/div
VSW
1 V/div
VEN 400 us/div
80 us/div
500 mA/div
IL
1 V/div
VIN
ILED
20 mA/div
ILED
50 mA/div
1 V/div
VSW
1 V/div
VEN
400 us/div
ILED
10 ms/div
2 V/div
Step from ILED = 100 mA to Open Load
2 V/div 100 mA/div
VOUT
VSW
2V
5V
MCP1643
DS20005208A-page 8 2013 Microchip Technology Inc.
NOTES:
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 VIN) will
enable the regulator output. A logic low (<20% of VIN)
will ensu re that the regulat or is disa bled.
3.2 Feedback Voltage Pin (VFB)
The VFB pin i s used to reg ula te t he vo ltage ac ros s the
RSET sense resis tor 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 (VOUT)
High current flows through the integrated P-Channel
and out o f this pin to the output cap acitor , LED load and
RSET 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 so urce are internall y connected at th e SW node.
3.6 Power Ground (PGND) and Signal
Ground Pins (SGND)
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
integra ted VFB and error amplifier.
The length of the trace from input cap return, output
cap return and PGND and SGND should be made as
short as po ssible to minimize noi se on the grou nd pins.
The SGND and PGND pins are connecte d exte rnal ly.
3.7 Power Supply Input Volt age Pin
(VIN)
Connect the input voltage source to VIN. The input
source should be decoupled to GND with a 4.7 µF
minimum cap ac itor.
3.8 Exposed Thermal Pad (EP)
There is no internal electrical connection between the
Exposed Thermal Pad (EP) and the PGND and SGND
pins. T hey m ust be conn ected to the same poten tial o n
the Printed Circuit Board (PCB).
TABLE 3-1: PIN FUNCTION TABLE
MCP1643
2x3 DFN MCP1643
MSOP Symbol Description
1 1 EN Enable pin. The logic high enables the operation. Do not allow this pin to
float.
22V
FB Reference Voltage pin. Connect to the VFB pin, the RSET (LED current set
resistor), and the cathode of the LED load.
3 3 NC Unconnected pin
44V
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 VIN.
66P
GND Power Ground Reference pin
77S
GND Signal Ground Reference pin
88V
IN Input Supply Voltage pin. A local bypass capacitor is r equired.
9 — EP Exposed Thermal Pad, must be connected to VSS
MCP1643
DS20005208A-page 10 2013 Microchip Technology Inc.
NOTES:
2013 Microchip Technology Inc. DS20005208A-page 11
MCP1643
4.0 DETAILED DESCRIPTION
4.1 Device Overview
The MCP1643 is capable of starting up with a low volt-
age, 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
(RSET).
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 regula te the LE D current mu st be low, in this case b y
a low VFB value of 120 mV.
The device can operate from one or two-cell alkaline
and NiMH/NiCd batteries. The maximum input voltage
is 5.0V. The de v ic e f eatu r es an O vervo l t ag e Pro t ection
that protects the device if the output voltage (VOUT) is
higher than 5.0V. This usually happens if the LED is
discon nected. While V IN <V
OUT, the load cu rrent (ILED)
remains in regulation until VIN is close to VLED (see
Typical Applications and Figures 2-1 to 2-3).
A True Output Load Disconnect mode provides input-
to-output isolation while in Shutdown (EN = GND). In
this state, the MCP1643 LED driver drains 1.2 µA cur-
rent 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.
4.2 Functional Description
The MCP1643 is a compact, high-efficiency, fixed
frequency , step-up DC-DC converter that operates as a
const ant cu rrent gen erat or for appl ications 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.
Gate Drive
and
Shutdown
Control
Logic
VIN
EN
VOUT
PGND
ISENSE
IZERO
ILIMIT
SOFT-START
Direction
Control
Oscillator Slope
Compensation S
PWM/PFM
Logic
120 mV
Internal
BIAS
SW
VFB
EA
SGND
MCP1643
DS20005208A-page 12 2013 Microchip Technology Inc.
4.2.1 LOW-VOLTAGE START-UP
The MC P1643 LED Constant Current D river is cap abl e
of star ti ng f rom a l ow -in put vol tage . 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 lowest pos sible voltage 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 rectifying switch is current limited 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. Once VOUT is equal to the minimum
forward voltage (VF) of the LED, the device enters in
close loop and regulates the voltage across the RSET
resistor , which is connected b etween VFB pin and GND.
4.2.2 PWM MODE OP ER AT IO N
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 f eatures 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
effi ci enc y hig h.
Lossless current sensing converts the peak current
signal to a voltage to sum with the internal slope
compen sa tion. Thi s su mm ed s ign al is com pared to the
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 compensati on to ensure sta bility , 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 RSET, connec ted to VFB pin and
GND.
The device regulates the voltage on the RSET and
provides a constant current trough LED while
VIN VOUT (minus a 300 – 400 mV headroom in case
of low LED currents) (see Figures 2-1 and 2-2).
The internal VREF voltage is 120 mV. There are limits
applied when the RSET value is calculated over the
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 VIN voltage. To
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 remo vi ng the sw itc h bul k di ode conn ec tio n.
This removes the DC path, typical in boost converters,
which allows the output to be disconnected from the
input. During this mode, 1.2 µA (typical) of current is
consumed from the input (battery). True output
discon nect d oes no t disc harge th e outpu t; this allows a
faster start-up in dimming or load step applications.
4.2.4.2 PW M 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 240 µs (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 VIN. Once the output exceeds the
input, bias comes from the output. Therefore, once
started, the operation is completely independent of
VIN. The operation is only limited by the output power
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.
2013 Microchip Technology Inc. DS20005208A-page 13
MCP1643
4.2.6 INTERNAL COMPENSATION
The error amplifier, with its associated 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 inte grated.
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 overte mp erat ure.
4.2.8 OUTPUT OV ERV O LTAG E
PROTECTION
Overvoltage Protection is designed to protect the
MCP1643 i f the output v ol t age (V OUT) becomes h igher
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
volt ages. This happe ns when the L ED fails. The device
stops switching and the VOUT value is verified
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 VOUT and VFB pins to
clamp the output voltage and protects the LED against
excessi ve v o lt ag e and current.
4.2.9 OVERTEMPERATURE
PROTECTION
Overtemperature protection circuitry is integrated in the
MCP1643 LED Constant Current Driver. This circuitry
monitor s the devic e junction tempe rature and shut s the
device off if the junction temperature exceeds the
typica l +1 50°C th res hol d. If this thr esh ol d is ex ce ede d,
the device will automatically restart once the junction
temperature drop s by 25°C.
MCP1643
DS20005208A-page 14 2013 Microchip Technology Inc.
NOTES:
2013 Microchip Technology Inc. DS20005208A-page 15
MCP1643
5.0 APPLICATION INFORMATION
5.1 Typical Application s
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
stays in regulation while VIN VOUT minus a 300 –
400 mV headroom. Th e 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 i nput curre nt limit. Typical characteriz ation cu rves
in this data sheet are presented to display the typical
output current capability.
5.2 LED Brightness Control
5.2.1 ADJUSTABLE CONSTANT
CURRENT CALCULATIONS
To calc ulate the resi stor values fo r the MCP1643’s LED
current, us e Equation 5-1, where RSET is conne cte d to
VFB and GND. The reference voltage (VFB) is 120 mV.
EQUATION 5-1:
EXAMPL E 1:
EXAMPL E 2:
Power dissipated on the RSET resistor is very low and
equal with VFB*ILED. For 100 mA LED current, the
power di ss ipated on sense r esi st or is onl y 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 maxim um a nd minimum l im it s fo r RSET ov er
the input voltage range that ensures current regulation
for a white LED.
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 low eri ng it i n 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
frequenc y for di mmin g is li mited 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 sufficient at the input. For hig h-
power applications that have high-source impedance
or lo ng lead s, connec ting th e batter y to 10 µF capaci -
tance 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
transien ts, as is the PWM dimming. Ceramic capacitors
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
(VF), which depends on the power dissip ated according
to it s VF/IF c haracteristic. Bec ause MCP1643 all ows up
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 have a typical VF
between 1.8V and 2.2V (it depends on the real color),
yellow LED s have the VF betw een 2.1V and 2.2V, while
for green options, consider values from 2.0V to 2.4V.
VFB = 120 mV
ILED =25mA
RSET =4.8with a standard value of 4.7
ILED is 25.53 mA)
VFB = 120 mV
ILED = 100 mA
RSET =1.2
ILED VFB
RSET
------------=
MCP1643
DS20005208A-page 16 2013 Microchip Technology Inc.
5.6 Inductor Selection
The MCP1643 device is designed 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.
Several parameters are used to select the correct
inductor:
• maximum-rated current
• saturati on current
• copper resistance (ESR)
For boos t converte rs, the ind uctor curre nt can be muc h
higher than the output current. The lower the inductor
ESR, the higher the efficiency of the converter, a
comm on trade-off in size vers us efficiency.
The saturation current typically specifies a point at
which th e ind uc tance ha s roll ed off a percentage o f th e
rated value. This can range from a 20% to 40%
reductio n in indu cta nce. As th e induc tan ce rolls 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.
5.7 Thermal Calculations
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 resis-
tance (JA), the junction temperature is estimated. The
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
estima ted by Equation 5-2:
EQUATION 5-2:
The differenc e b etween the first term, inpu t p ow er, and
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, COUT and the inductor.
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 IINRMS2xL
DCR
power dissipation.
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 VIN pin to the VOUT, output capacitor, LED load,
RSET sense resistor, and SGND and PGND pins to the
input capacitor. Therefore, it is important that the input
and outp ut capaci tors be place d as close as p ossible to
the MCP1643, to minimize the loop area.
The feedback track should be routed away from the
switch ing nod e and clos e to the VFB pin . RSET must be
conne cted a s clos e as po ssibl e to the VFB pin, unless
regulation issues appears. When possible, ground
planes and traces should be used to help shield the
feedback signal and minimize noise and magnetic
interference.
TABLE 5-1: MCP1643 RECOMMENDED
INDUCTORS
Par t Number Value
(µH) DCR
(– typ) ISAT
(A)
Size
WxLxH
(mm)
Wurth® Group
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 6x 6x3
SLF6028-
4R7M1R6 4.7 0.028 1.6 6x6x2.8
VOUT IOUT
Efficiency
-------------------------------------


VOUT IOUT
–PDis
=
2013 Microchip Technology Inc. DS20005208A-page 17
MCP1643
FIGURE 5-1: MCP1643 LED Constant Current Driver MSOP8 Recommended Layout. Apply the
same guidance for 8-DFN package.
COUT
L
CIN
+VIN
GND
+VOUT
MCP1643
Enable
LED
RSET
GND
Wired on Bottom
Plane
1
A
K
SW
MCP1643
DS20005208A-page 18 2013 Microchip Technology Inc.
NOTES:
2013 Microchip Technology Inc. DS20005208A-page 19
MCP1643
6.0 TYPICAL APPLICATION CIRCUITS
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.
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. High-
load currents require additional output capacitance.
VIN
GND
VFB
COUT
10...20 µF
CIN
4.7...10 µF
L1
4.7 µH
SW
WLED1
2.4
EN
VOUT
ON
OFF
ILED1 =50mA
RSET
WLED2
2.4
R2
WLED3
2.4
R3
ILED2 =50mA ILED3 =50mA
Battery input
(On e or Two Cells) DZ
VZ=2.4V
D
MCP1643
ILED 0.12V
RSET
--------------=
From PIC® MCU I/O
VIN
GND VFB
COUT
20 µF
CIN
4.7 – 10 µF
L1
4.7 µH
SW
LED1 - RED
0.82
EN
VOUT
ILED =150mA
RSET
Battery input
(One or Two Cells)
LED2 - RED
PWM signal, f = 400 Hz,
Duty Cycle variable
ILED 0.12V
RSET
--------------=
MCP1643
MCP1643
DS20005208A-page 20 2013 Microchip Technology Inc.
NOTES:
2013 Microchip Technology Inc. DS20005208A-page 21
MCP1643
7.0 PACKAGING INFORMATION
7.1 Package Marking 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 pac kage.
Note: In the eve nt the full Micro chip p art num ber can not be ma rked on on e line, it will
be carried over to the next line, thus limiting the number of available
characters for customer-specific information.
3
e
3
e
Part Number Code
MCP1643-I/MS 1643I
MCP1643T-I/MS 1643I
MCP1643
DS20005208A-page 22 2013 Microchip Technology Inc.
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12
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NOTE 1
21
D2
K
L
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e
b
A3 A1
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BOTTOM VIEW
TOP VIEW
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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
MCP1643
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
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
MCP1643
DS20005208A-page 26 2013 Microchip Technology Inc.
Note: For the most current package drawings, please see the Microchip Packaging Specification located at
http://www.microchip.com/packaging
2013 Microchip Technology Inc. DS20005208A-page 27
MCP1643
APPENDIX A: REVISION HISTORY
Revision A (August 2013)
• Original Release of this Document.
MCP1643
DS20005208A-page 28 2013 Microchip Technology Inc.
NOTES:
2013 Microchip Technology Inc. DS20005208A-page 29
MCP1643
PRODUCT IDENTIFICATION SYSTEM
To order or obtain information, e.g., on pricing or delivery, refer to the factory or the listed sales office.
Device: M CP1643: LED Constant Current Regulator
MCP 1643T: LED Constant C urrent Regulato r
(Tape and Reel)
Temperature Range: I= -40C to +85C (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,
Indus trial Tem per atu re ,
8LD MSOP package
PART NO. X/XX
PackageTemperature
Range
Device
MCP1643
DS20005208A-page 30 2013 Microchip Technology Inc.
NOTES:
2013 Microchip Technology Inc. DS20005208A-page 31
Information contained in this publication regarding device
applications a nd the lik e is p ro vided on ly for yo ur con ve nien ce
and may be supers eded by updates . I t is you r r es ponsibil it y 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 support and/or safety applications is entirely at
the buyer’s risk, and the buyer agrees to defend, indemnify and
hold harmless Microchip from any and all damages, claims,
suits, or expenses resulting from such use. No licenses are
conveyed, implicitly or otherwise, under any Microchip
intellectual property rights.
Trademarks
The Microchip name and logo, the Microchip logo, dsPIC,
FlashFlex, KEELOQ, KEELOQ logo, MPLAB, PIC, PICmicro,
PICSTART, PI C 32 logo, rfPIC, SST, SST Logo, SuperFlash
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 I nc. in other countries.
Analog-for-the-Digital Age, Application Maestro, BodyCom,
chipKIT, chipKIT logo, CodeGuard, dsPICDEM ,
dsPICDEM.net, dsPICworks, dsSPEAK, ECAN,
ECONOMONIT OR, FanSense, HI-TIDE , In - Circuit Serial
Programm ing, 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 Germ any II Gm bH & Co. KG, a subsidiary of
Microchip Technology Inc., in other countries.
All other trademarks mentioned herein are property of their
respective companies.
© 2013, Microchip Technology Incorporated, Pr inted in the
U.S.A., All Rights Reserved.
Printed on recycled paper.
ISBN: 978-1-62077-402-1
Note the following details of the code protection feature on Microchip devices:
• 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.
• Neit her 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 c onstantly evolving. We a t Microc hip are co m mitted to continuously improving the code prot ect ion featur es of our
products. Attempts to break Microchip’ s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts
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QUALITY MANAGEMENT S
YSTEM
CERTIFIED BY DNV
== ISO/TS 16949 ==
DS20005208A-page 32 2013 Microchip Technology Inc.
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Japan - Tokyo
Tel: 81-3-6880- 3770
Fax: 81-3-6880-3771
Korea - Daegu
Tel: 82-53-744-4301
Fax: 82-53-744-4302
Korea - Seoul
Tel: 82-2-554-7200
Fax: 82-2-558-5932 or
82-2-558-5934
Malaysia - Kuala Lumpur
Tel: 60-3-6201-9857
Fax: 60-3-6201-9859
Malaysia - Penang
Tel: 60-4-227-8870
Fax: 60-4-227-4068
Philippines - Manila
Tel: 63-2-634-9065
Fax: 63-2-634-9069
Singapore
Tel: 65-6334-8870
Fax: 65-6334-8850
Taiwan - Hsin Chu
Tel: 886-3-5778-366
Fax: 886-3-5770-955
Taiwan - Kaohsiung
Tel: 886-7-213-7828
Fax: 886-7-330-9305
Taiwan - Taipei
Tel: 886-2-2508-8600
Fax: 886-2-2508-0102
Thailand - Bangkok
Tel: 66-2-694-1351
Fax: 66-2-694-1350
EUROPE
Austria - Wels
Tel: 43-7242-2244-39
Fax: 43-7242-2244-393
Denmark - Cop e nha gen
Tel: 45-4450-2828
Fax: 45-4485-2829
France - Paris
Tel: 33-1-69-53 -63-20
Fax: 33-1-69-30-90-79
Germany - Munich
Tel: 49-89-627-144-0
Fax: 49-89-627-14 4-44
Italy - Milan
Tel: 39-0331-742611
Fax: 39-0331-466781
Netherlands - Drunen
Tel: 31-416-690399
Fax: 31-416-690340
Spain - Madrid
Tel: 34-91-708-08-90
Fax: 34-91-708-08 -91
UK - Wokingham
Tel: 44-118-921-5869
Fax: 44-118-921-5820
Worldwide Sales and Service
11/29/12