MCP1643 Data Sheet

MCP1643
1 MHz Low Start-up Voltage Synchronous Boost
LED Constant Current Regulator
Features
Description
• 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
- Overvoltage Protection
• Low Reference Voltage:
- VFB = 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
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.
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
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 (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 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
MSOP-8
EN 1
VFB 2
NC 3
VOUT 4
MCP1643
2x3 DFN*
8 VIN
EN 1
7 SGND VFB 2
NC 3
6 PGND
VOUT 4
5 SW
8 VIN
EP
9
7 SGND
6 PGND
5 SW
* Includes Exposed Thermal Pad (EP), see Table 3-1.
 2013 Microchip Technology Inc.
DS20005208A-page 1
MCP1643
Typical Applications
L1
4.7 µH
I
CIN
4.7...10 µF
LED
ILED = 25 mA
SW
VOUT
VIN
0.12V
= ----------------R SET
LED
COUT
4.7 µF
MCP1643
ALKALINE
+
VFB
EN
-
RSET
4.7
GND
ON
L1
4.7 µH
OFF
CIN
4.7...10 µF
SW
VOUT
VIN
REN
1 M
NIMH 1.2V
+
WHITE LED
ILED = 360 mA
COUT
20 µF
MCP1643
VFB
EN
-
RSET
0.33
GND
ON/OFF
NIMH 1.2V
+
-
RSET Minimum and Maximum Limits for ILED in Regulation, with ±6% Tolerance
10
1000
ILED MAX
ILED MAX
1
100
RSET for ILED MAX
ILED MIN
ILED
MIN
WHITE LED
TA = +25oC
0.1
0.6
0.9
1.2
1.5
1.8
2.1
2.4
2.7
LED Current (mA)
RSET (Ω)
RSET for ILED MIN
10
3
Input Voltage (V)
DS20005208A-page 2
 2013 Microchip Technology Inc.
MCP1643
1.0
ELECTRICAL
CHARACTERISTICS
† Notice: Stresses above those listed under “Maximum
Ratings” may cause permanent damage to the device.
This is a stress rating only and functional operation of
the device at those or any other conditions above those
indicated in the operational sections of this
specification is not intended. Exposure to maximum
rating conditions for extended periods may affect
device reliability.
Absolute Maximum Ratings †
EN, FB, VIN, VSW, VOUT - GND ........................... +6.5V
EN, FB ......... < maximum 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
DC CHARACTERISTICS
Electrical Characteristics: Unless otherwise indicated, VIN = EN = 1.2V, COUT = 20 µF, CIN = 10 µF, L = 4.7 µH,
ILED = 25 mA, TA = +25°C. Boldface specifications apply over the TA range of -40°C to +85°C.
Parameters
Sym
Min
Typ
Max
Units
Conditions
Minimum Input Voltage
After Start-Up
VIN
—
0.5
—
V
Note 1, Note 3
Start-Up Voltage
VIN
—
0.65
0.8
V
Note 2, Note 1
Output Overvoltage
Protection
VOUT_OVP
—
5.0
—
V
Note 3
Shutdown
Quiescent Current
IQSHDN
—
1.2
—
µA
EN = GND;
includes N-Channel and
P-Channel Switch Leakage
Feedback Voltage
VFB
105
120
135
mV
Feedback Input
Bias Current
IVFB
—
60
—
pA
NMOS Switch Leakage
INLK
—
0.4
—
µA
VIN = VSW = 4.0V
VOUT = 4.5V
VEN = VFB = GND
PMOS Switch Leakage
IPLK
—
0.25
—
µA
VIN = VSW = GND;
VOUT = 4.5V
NMOS Switch
ON Resistance
RDS(ON)N
—
0.2
—

ILED = 250 mA, Note 3
PMOS Switch
ON Resistance
RDS(ON)P
—
0.4
—

ILED = 250 mA, Note 3
NMOS Peak
Switch Current Limit
IN(MAX)
—
1.6
—
A
Note 3
Maximum Duty Cycle
DCMAX
—
90
—
%
Note 3
Minimum Duty Cycle
DCMIN
—
5
—
%
Note 3
Switching Frequency
fSW
0.85
1.0
1.15
EN Input Logic High
VIH
75
—
—
EN Input Logic Low
VIL
—
—
20
Input Characteristics
Note 1:
2:
3:
MHz
%of VIN ILED= 25 mA
%of VIN ILED = 25 mA
For VIN < VOUT, ILED remains in regulation up to VIN = VLED minus a headroom @ LED typical VF and IF.
VOUT completely discharged. If the output capacitor remains partially charged, the device will start-up at
the minimum possible voltage.
Determined by characterization, not production tested.
 2013 Microchip Technology Inc.
DS20005208A-page 3
MCP1643
DC CHARACTERISTICS (CONTINUED)
Electrical Characteristics: Unless otherwise indicated, VIN = EN = 1.2V, COUT = 20 µF, CIN = 10 µF, L = 4.7 µH,
ILED = 25 mA, TA = +25°C. Boldface specifications apply over the TA range of -40°C to +85°C.
Parameters
Sym
Min
Typ
Max
Units
EN Input Leakage Current
IENLK
—
0.9
—
µA
VEN = 1.2V
tSS
—
240
—
µs
EN Low-to-High,
90% of VOUT;
ILED = 25 mA, Note 3
—
270
—
µs
EN Low-to-High,
90% of VOUT;
ILED = 300 mA, Note 3
TSD
—
150
—
C
ILED= 25 mA
TSDHYS
—
25
—
C
Soft Start Time
Thermal Shutdown
Die Temperature
Die Temperature
Hysteresis
Note 1:
2:
3:
Conditions
For VIN < VOUT, ILED remains in regulation up to VIN = VLED minus a headroom @ LED typical VF and IF.
VOUT completely discharged. If the output capacitor remains partially charged, the device will start-up at
the minimum possible voltage.
Determined by characterization, not production tested.
TEMPERATURE SPECIFICATIONS
Electrical Characteristics: Unless otherwise indicated, VIN = EN = 1.2V, COUT = 20 µF, CIN = 10 µF, L = 4.7 µH,
ILED = 25 mA, TA = +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
Storage Temperature Range
TA
-65
—
+150
°C
Maximum Junction Temperature
TJ
—
—
+150
°C
Thermal Resistance, 8L-2x3 DFN
JA
—
68
—
°C/W
Thermal Resistance, 8L-MSOP
JA
—
211
—
°C/W
Steady State
Transient
Package Thermal Resistances
DS20005208A-page 4
 2013 Microchip Technology Inc.
MCP1643
2.0
TYPICAL PERFORMANCE CURVES
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.
Note: Unless otherwise indicated, VIN = EN = 1.2V, COUT = 20 µF, CIN = 10 µF, L = 4.7 µH, ILED = 25 mA, TA = +25°C,
MSOP-8 package.
LED Current (mA)
450
100
LED VF = 3.5V @ IF = 700 mA
95
RSET = 0.25ȍ
400
Efficiency (%)
500
350
RSET = 0.41ȍ
300
250
200
RSET = 0.82ȍ
150
100
50
0.9
FIGURE 2-1:
RSET = 5ȍ
65
1.2
1.5
1.8
Input Voltage (V)
2.1
2.4
One White LED ILED vs. VIN.
10
FIGURE 2-4:
vs. ILED.
100
ILED (mA)
1000
One White LED Efficiency
100
LED VF = 2.5V @ IF = 350 mA
95
200
175
Efficiency (%)
LED Current (mA)
VIN = 1.8V
VIN = 1.2V
75
70
RSET = 0.82ȍ
150
125
RSET = 1.2ȍ
100
75
50
RSET = 5ȍ
25
90
VIN = 2.4V
VIN = 1.8V
85
VIN = 1.2V
80
75
0
70
0.6
0.7
0.8
0.9
1
1.1 1.2
Input Voltage (V)
1.3
1.4
1.5
One Red LED ILED vs. VIN.
FIGURE 2-2:
10
FIGURE 2-5:
ILED.
350
100
ILED (mA)
1000
One Red LED Efficiency vs.
100
LED VF = 2.5V @ IF = 350 mA
300
95
RSET = 0.41ȍ
90
Efficiency (%)
LEDs Current (mA)
80
60
0.6
225
VIN = 2.4V
85
RSET = 1.2ȍ
0
250
90
250
200
RSET = 0.82ȍ
150
RSET = 1.2ȍ
100
VIN = 3.6V
85
80
75
VIN = 2.4V
VIN = 3.0V
70
65
60
50
RSET = 5ȍ
55
0
50
0.6
0.9
1.2
1.5
1.8
Input Voltage (V)
2.1
2.4
FIGURE 2-3:
Two Series Connection Red
LEDs ILED vs. VIN.
 2013 Microchip Technology Inc.
10
100
ILED (mA)
1000
FIGURE 2-6:
Two Red LEDs Efficiency (in
Series Connection) vs. ILED.
DS20005208A-page 5
MCP1643
Note: Unless otherwise indicated, VIN = EN = 1.2V, COUT = 20 µF, CIN = 10 µF, L = 4.7 µH, ILED = 25 mA, TA = +25°C,
MSOP-8 package.
700
350
TA = +85oC
VIN = 1.5V
250
200
RSET = 0.82ȍ
150
RSET = 1.2ȍ
100
50
400
TA = 0oC
300
200
0
-40
-25
-10
5
20
35
50
65
Ambient Temperature (°C)
FIGURE 2-7:
Temperature.
0.6
80
One White ILED vs. Ambient
150
0.9
1.2
1.5 1.8 2.1
Input Voltage (V)
2.4
2.7
3
Maximum ILED vs. VIN.
FIGURE 2-10:
1010
VIN = 1.5V
RSET = 0.82ȍ
125
Switching Frequency (kHz)
LED Current (mA)
500
100
RSET = 5ȍ
0
1005
100
1000
75
50
fEN = 400 Hz
fEN = 1 kHz
25
0
995
990
985
ILED = 100 mA
980
0
10
20
30 40 50 60
Duty Cycle (%)
FIGURE 2-8:
70
80
90 100
ILED vs. VEN Duty Cycle.
-40
-25
-10
5
20
35
50
65
Ambient Temperature (°C)
FIGURE 2-11:
Temperature.
40
80
fSW vs. Ambient
123
RSET = 1.2ȍ
(ILED = 100 mA)
122
Feadback Voltage (mV)
39
Duty Cycle (%)
TA = +25oC
600
RSET = 0.41ȍ
LED Current (mA)
LED Current (mA)
300
38
37
36
35
121
120
119
118
ILED = 100 mA
117
34
-40
-25
-10
5
20
35
50
65
Ambient Temperature (°C)
FIGURE 2-9:
Temperature.
DS20005208A-page 6
80
Duty Cycle vs. Ambient
-40
-25
FIGURE 2-12:
Temperature.
-10
5
20
35
50
65
Ambient Temperature (°C)
80
VFB vs. Ambient
 2013 Microchip Technology Inc.
MCP1643
Note: Unless otherwise indicated, VIN = EN = 1.2V, COUT = 20 µF, CIN = 10 µF, L = 4.7 µH, ILED = 25 mA, TA = +25°C,
MSOP-8 package.
ILED
20 mA/div
ILED
20 mA/div
VIN
1 V/div
VIN
1 V/div
VEN
80 us/div
FIGURE 2-13:
Start-up After Enable.
IL
500 mA/div
80 us/div
FIGURE 2-16:
Start-up when VIN = VEN.
VOUT
20 mV/div, AC Coupled
ILED
50 mA/div
VSW
1 V/div
VSW 1 V/div
ILED
100 mA/div
VEN
1 V/div
400 us/div
1 us/div
FIGURE 2-14:
100 mA PWM Operation.
ILED
50 mA/div
FIGURE 2-17:
15% Duty Cycle.
400 Hz PWM Dimming,
VOUT
5V
2 V/div
VSW
1 V/div
2V
Step from ILED = 100 mA to Open Load
ILED
100 mA/div
VSW
2 V/div
VEN
1 V/div
FIGURE 2-15:
85% Duty Cycle.
10 ms/div
400 us/div
400 Hz PWM Dimming,
 2013 Microchip Technology Inc.
FIGURE 2-18:
Open Load Response.
DS20005208A-page 7
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
2 x 3 DFN
MCP1643
MSOP
Symbol
1
1
EN
Enable pin. The logic high enables the operation. Do not allow this pin to
float.
2
2
VFB
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
4
4
VOUT
5
5
SW
6
6
PGND
Power Ground Reference pin
7
7
SGND
Signal Ground Reference pin
8
8
VIN
Input Supply Voltage pin. A local bypass capacitor is required.
9
—
EP
Exposed Thermal Pad, must be connected to VSS
3.1
Description
Boost Converter Output pin. Connect to this pin the anode of the LED load.
An output filter capacitor is required.
Boost and Rectifier Switch Input pin. Connect the boost inductor between
SW and VIN.
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 ensure that the regulator is disabled.
3.2
Feedback Voltage Pin (VFB)
The VFB pin is used to regulate the voltage across the
RSET sense resistor to 120 mV, to keep the output LED
current in regulation.
3.3
Output Voltage Power Pin (VOUT)
High current flows through the integrated P-Channel
and out of this pin to the output capacitor, 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
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
integrated 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 possible to minimize noise on the ground pins.
The SGND and PGND pins are connected externally.
3.7
Unconnected Pin (NC)
This pin is unconnected.
3.4
3.6
Power Supply Input Voltage Pin
(VIN)
Connect the input voltage source to VIN. 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 PGND and SGND
pins. They must be connected to the same potential on
the Printed Circuit Board (PCB).
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.
 2013 Microchip Technology Inc.
DS20005208A-page 9
MCP1643
NOTES:
DS20005208A-page 10
 2013 Microchip Technology Inc.
MCP1643
4.0
DETAILED DESCRIPTION
4.1
Device Overview
that protects the device if the output voltage (VOUT) is
higher than 5.0V. This usually happens if the LED is
disconnected. While VIN < VOUT, the load current (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 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 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
(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 regulate the LED current must be low, in this case by
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 device features an Overvoltage Protection
4.2
Functional Description
The MCP1643 is a compact, high-efficiency, fixed
frequency, step-up DC-DC converter that operates as a
constant current generator for applications powered by
either one or two-cell, alkaline, NiCd, or NiMH
batteries.
Figure 4-1 depicts the functional block diagram of the
MCP1643 device.
VOUT
Internal
BIAS
VIN
IZERO
Direction
Control
SOFT-START
SW
Gate Drive
and
Shutdown
Control
Logic
EN
PGND
Oscillator
ILIMIT
ISENSE
Slope
Compensation
S
SGND
PWM/PFM
Logic
120 mV
VFB
EA
FIGURE 4-1:
MCP1643 Block Diagram.
 2013 Microchip Technology Inc.
DS20005208A-page 11
MCP1643
4.2.1
LOW-VOLTAGE START-UP
The MCP1643 LED Constant Current Driver is capable
of starting from a low-input voltage. Start-up voltage 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 possible 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 between 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-ringing control, the switching 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. This summed signal is compared 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 compensation 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.
DS20005208A-page 12
4.2.3
ADJUSTABLE OUTPUT LED
CURRENT
The MCP1643 LED’s current is adjustable with an
external resistor, called RSET, connected 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 removing the switch 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, 1.2 µA (typical) of current is
consumed from the input (battery). True output
disconnect does not discharge the output; this allows a
faster start-up in dimming or load step applications.
4.2.4.2
PWM Dimming
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 cycle of the PWM signal applied 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.
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 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 overtemperature.
4.2.8
OUTPUT OVERVOLTAGE
PROTECTION
Overvoltage Protection is designed to protect the
MCP1643 if the output voltage (VOUT) becomes higher
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 LED 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
excessive voltage and current.
4.2.9
OVERTEMPERATURE
PROTECTION
Overtemperature protection circuitry is integrated in the
MCP1643 LED Constant Current Driver. This circuitry
monitors the device junction temperature and shuts the
device off if the junction temperature exceeds the
typical +150°C threshold. If this threshold is exceeded,
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
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
stays in regulation while VIN  VOUT minus a 300 –
400 mV headroom. The power efficiency conversion is
high when driving LED currents up to hundreds of mA.
Output current capability is limited by the 1.6A typical
peak input current limit. Typical characterization curves
in this data sheet are presented to display the typical
output current capability.
5.2
5.2.1
LED Brightness Control
ADJUSTABLE CONSTANT
CURRENT CALCULATIONS
To calculate the resistor values for the MCP1643’s LED
current, use Equation 5-1, where RSET is connected to
VFB and GND. The reference voltage (VFB) is 120 mV.
EQUATION 5-1:
I LED
VFB
= -----------R SET
EXAMPLE 1:
VFB = 120 mV
ILED = 25 mA
RSET = 4.8with a standard value of 4.7
ILED is 25.53 mA)
5.2.2
LED’s brightness can also be controlled by setting a
maximum current allowed for LED (using Equation 5-1)
and lowering it in small steps with a variable duty cycle
PWM signal applied to the EN pin. The maximum
frequency for dimming is limited by the soft start, which
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
VFB = 120 mV
ILED = 100 mA
RSET = 1.2
Power dissipated on the RSET resistor is very low and
equal with VFB*ILED. For 100 mA LED current, the
power dissipated 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 and minimum limits for RSET over
the input voltage range that ensures current regulation
for a white LED.
 2013 Microchip Technology Inc.
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 highpower applications that have high-source impedance
or long leads, connecting the battery to 10 µF capacitance 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. 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
EXAMPLE 2:
PWM DIMMING
Connecting More LEDs to Output
White LEDs have a typical 2.7 to 3.2V forward voltage
(VF), which depends on the power dissipated according
to its VF/IF characteristic. Because MCP1643 allows 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 LEDs have the VF between 2.1V and 2.2V, while
for green options, consider values from 2.0V to 2.4V.
DS20005208A-page 15
MCP1643
5.6
Inductor Selection
5.7
The MCP1643 device is designed to be used with small
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:
Part Number
MCP1643 RECOMMENDED
INDUCTORS
Value
DCR
(µH) (– typ)
ISAT
(A)
Size
WxLxH
(mm)
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 resistance (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
estimated by Equation 5-2:
Wurth® Group
744025004
4.7
0.100
1.7
2.8x2.8x2.8
744042004
4.7
0.082
1.65
4.8x4.8x1.8
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
B82462 G4472M
4.7
0.04
1.8
6x6x3
B82462 A4472M
4.7
0.08
2.8
6x6x3
SLF60284R7M1R6
4.7
0.028
1.6
6x6x2.8
EQUATION 5-2:
V
I
OUT OUT
 ------------------------------------– V
I
 = P
Dis
 Efficiency 
OUT OUT
Coilcraft
TDK Corporation
Several parameters are used to select the correct
inductor:
• maximum-rated current
• saturation current
• copper resistance (ESR)
For boost converters, the inductor current can be much
higher than the output current. The lower the inductor
ESR, the higher the efficiency of the converter, a
common trade-off in size versus efficiency.
The saturation current typically specifies a point at
which the inductance has rolled off a percentage of the
rated value. This can range from a 20% to 40%
reduction in inductance. As the inductance 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.
DS20005208A-page 16
The difference between the first term, input power, 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 IINRMS2 x LDCR
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 output capacitors be placed as close as possible to
the MCP1643, to minimize the loop area.
The feedback track should be routed away from the
switching node and close to the VFB pin. RSET must be
connected as close as possible 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.
 2013 Microchip Technology Inc.
MCP1643
L
+VIN
SW
CIN
GND
GND
MCP1643
COUT
Enable
1
RSET
Wired on Bottom
Plane
+VOUT
LED
K
A
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.
MCP1643
6.0
TYPICAL APPLICATION CIRCUITS
L1
4.7 µH
ILED1 = 50 mA
CIN
Battery input
4.7...10
µF
(One or Two Cells)
VZ = 2.4V
SW
EN
VOUT
MCP1643
VIN
WLED1
DZ
ILED2 = 50 mA ILED3 = 50 mA
WLED2
WLED3
COUT
10...20 µF
D
VFB
RSET
2.4
R2
2.4
R3
2.4
GND
ON
OFF
Note:
0.12V
I LED = -------------R SET
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.
FIGURE 6-1:
Three White LEDs Application Powered from One or Two Cells.
L1
4.7 µH
SW
CIN
4.7 – 10 µF
VIN
EN
PWM signal, f = 400 Hz,
Duty Cycle variable
From PIC® MCU I/O
FIGURE 6-2:
Microcontroller.
VOUT
LED1 - RED
MCP1643
Battery input
(One or Two Cells)
0.12V
I LED = -------------RSET
GND
COUT
20 µF
LED2 - RED
VFB
RSET
0.82
ILED = 150 mA
150 mA Two Power Red LEDs Driver with PWM Dimming Control from PIC®
 2013 Microchip Technology Inc.
DS20005208A-page 19
MCP1643
NOTES:
DS20005208A-page 20
 2013 Microchip Technology Inc.
MCP1643
7.0
PACKAGING INFORMATION
7.1
Package Marking Information
8-Lead DFN (2 x 3 x 0.9 mm)
Part Number
Example
Code
MCP1643-I/MC
AKF
MCP1643T-I/MC
AKF
8-Lead MSOP
Example
Part Number
Legend: XX...X
Y
YY
WW
NNN
e3
*
Note:
AKF
312
25
Code
MCP1643-I/MS
1643I
MCP1643T-I/MS
1643I
1643I
312256
Customer-specific information
Year code (last digit of calendar year)
Year code (last 2 digits of calendar year)
Week code (week of January 1 is week ‘01’)
Alphanumeric traceability code
RoHS Compliant JEDEC designator for Matte Tin (Sn)
This package is RoHS Compliant. The RoHS Compliant
JEDEC designator ( e3 ) can be found on the outer packaging
for this package.
In the event the full Microchip part number cannot be marked on one line, it will
be carried over to the next line, thus limiting the number of available
characters for customer-specific information.
 2013 Microchip Technology Inc.
DS20005208A-page 21
MCP1643
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EXPOSED PAD
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0LFURFKLS 7HFKQRORJ\ 'UDZLQJ &&
DS20005208A-page 22
 2013 Microchip Technology Inc.
MCP1643
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 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.
MCP1643
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
DS20005208A-page 26
 2013 Microchip Technology Inc.
MCP1643
APPENDIX A:
REVISION HISTORY
Revision A (August 2013)
• Original Release of this Document.
 2013 Microchip Technology Inc.
DS20005208A-page 27
MCP1643
NOTES:
DS20005208A-page 28
 2013 Microchip Technology Inc.
MCP1643
PRODUCT IDENTIFICATION SYSTEM
To order or obtain information, e.g., on pricing or delivery, refer to the factory or the listed sales office.
PART NO.
X
/XX
Device
Temperature
Range
Package
Device:
MCP1643:
MCP1643T:
LED Constant Current Regulator
LED Constant Current Regulator
(Tape and Reel)
Temperature Range:
I
= -40C to
Package:
MC
=
MS
=
 2013 Microchip Technology Inc.
Examples:
+85C
(Industrial)
a)
MCP1643-I/MC:
b)
MCP1643T-I/MC:
c)
MCP1643-I/MS:
d)
MCP1643T-I/MS:
Industrial Temperature,
8LD 2x3 DFN package
Tape and Reel,
Industrial Temperature,
8LD 2x3 DFN package
Industrial Temperature,
8LD MSOP package
Tape and Reel,
Industrial Temperature,
8LD MSOP package
Plastic Dual Flat, No Lead Package 2x3x0.9 mm Body (DFN)
Plastic Micro Small Outline Package (MSOP)
DS20005208A-page 29
MCP1643
NOTES:
DS20005208A-page 30
 2013 Microchip Technology Inc.
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.
•
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 committed to continuously improving the code protection features of our
products. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts
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 the like is provided only for your convenience
and may be superseded by updates. It is your responsibility 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, PIC32 logo, rfPIC, SST, SST Logo, SuperFlash
and UNI/O are registered trademarks of Microchip Technology
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 Technology Incorporated
in the U.S.A.
GestIC and ULPP are registered trademarks of Microchip
Technology Germany II GmbH & 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, Printed in the
U.S.A., All Rights Reserved.
Printed on recycled paper.
ISBN: 978-1-62077-402-1
QUALITY MANAGEMENT SYSTEM
CERTIFIED BY DNV
== ISO/TS 16949 ==
 2013 Microchip Technology Inc.
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® MCUs and dsPIC® DSCs, KEELOQ® code hopping
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.
DS20005208A-page 31
Worldwide Sales and Service
AMERICAS
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EUROPE
Corporate Office
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Technical Support:
http://www.microchip.com/
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Web Address:
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Tel: 39-0331-742611
Fax: 39-0331-466781
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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
China - Xiamen
Tel: 86-592-2388138
Fax: 86-592-2388130
China - Zhuhai
Tel: 86-756-3210040
Fax: 86-756-3210049
DS20005208A-page 32
Japan - Tokyo
Tel: 81-3-6880- 3770
Fax: 81-3-6880-3771
11/29/12
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