Sample &
Buy
Product
Folder
Support &
Community
Tools &
Software
Technical
Documents
LM3646
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
LM3646 1.5-A Synchronous Boost Converter With Dual High-Side Current Sources
and I2C-Compatible Interface
1 Features
3 Description
•
The LM3646 utilizes a 4-MHz fixed-frequency
synchronous boost converter to provide power to dual
1.5-A constant current LED sources. The high-side
current sources allow for grounded cathode LED
operation providing flash current up to 1.5 A total. An
adaptive headroom regulation scheme ensures the
LED currents remain in regulation and maximizes
efficiency. The combination of dual LED driving
capability, high LED current, small solution size and
high level of adjustability make the LM3646 perfect
for camera phone LED flash and torch applications.
1
•
•
•
•
•
•
•
•
•
•
•
•
•
•
High-Side Current Sources Allowing for Grounded
LED Cathode for Improved Thermal Management
> 85% Efficiency in Torch and Flash Modes
Small Solution Size < 20 mm2
Accurate and Programmable Flash LED Current
from 24 mA to 1.5 A in 11.7-mA Steps
Accurate and Programmable Torch LED Current
from 2.5 mA to 187 mA in 1.5-mA Steps
Dual 1.5-A High-Side Current Sources for Dual
LED Drive
Hardware Flash and Torch Enables
Hardware Enable Pin
Soft-Start Operation for Battery Protection
LED Thermal Sensing and Current Scale-Back
Synchronization Input for RF Power Amplifier
Pulse Events
VIN Flash Monitor Optimization
1-MHz I²C-Compatible Interface
I²C-Programmable NTC Trip Point
0.4-mm Pitch, 20-Bump DSBGA
2 Applications
Camera Phone LED Flash and Torch
The LM3646 is controlled through an I2C-compatible
interface. The main features of the LM3646 include: a
hardware flash enable (STROBE) input for direct
triggering of the flash pulse, a hardware Torch enable
(TORCH) for movie mode or flashlight functions, a TX
input which forces the flash pulse into a low-current
torch mode allowing for synchronization to RF power
amplifier events or other high-current conditions, an
integrated comparator designed to monitor an NTC
thermistor and provide an interrupt to the LED
current, and a programmable input voltage monitor
which monitors the battery voltage and can reduce
the flash current during low battery conditions. A
hardware enable (ENABLE) input provides a
hardware shutdown during system software failures.
The 4-MHz switching frequency, overvoltage
protection, and adjustable current limit allow for the
use of tiny, low-profile inductors and (10-μF) ceramic
capacitors. The device is available in a small 20bump DSBGA package and operates over the –40°C
to 85°C temperature range.
Device Information(1)
PART NUMBER
LM3646
PACKAGE
BODY SIZE (NOM)
DSBGA (20)
2.015 mm x 1.615 mm
(1) For all available packages, see the orderable addendum at
the end of the datasheet.
Typical Application Circuit
System Performance
1 PH
2800
TA = +25ºC
2600
10 PF
OUT
LM3646
LED1
ENABLE
LED2
STROBE
TORCH
TEMP
TX
SDA
SCL
GND
TA = -40ºC
TA = +85ºC
2400
10 PF
2200
IIN (mA)
IN
2.7V to 5.5V
SW
ILED = 1.5A, VLED = 3.7V
2000
1800
1600
1400
1200
2.8
3
3.2
3.4
3.6
3.8
4
VIN (V)
4.2
4.4
4.6
4.8
5
C032
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LM3646
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
www.ti.com
Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
6.1
6.2
6.3
6.4
6.5
6.6
6.7
4
4
4
4
5
6
7
Absolute Maximum Ratings ......................................
Handling Ratings.......................................................
Recommended Operating Conditions ......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Timing Requirements ................................................
Typical Characteristics ..............................................
Detailed Description ............................................ 12
7.1 Overview ................................................................. 12
7.2 Functional Block Diagram ....................................... 13
7.3 Feature Description................................................. 13
7.4 Device Functional Modes........................................ 14
7.5 Programming........................................................... 17
7.6 Register Map........................................................... 19
8
Application and Implementation ........................ 24
8.1 Application Information............................................ 24
8.2 Typical Application .................................................. 24
9 Power Supply Recommendations...................... 32
10 Layout................................................................... 32
10.1 Layout Guidelines ................................................. 32
10.2 Layout Example .................................................... 33
11 Device and Documentation Support ................. 34
11.1
11.2
11.3
11.4
11.5
Device Support......................................................
Documentation Support ........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
34
34
34
34
34
12 Mechanical, Packaging, and Orderable
Information ........................................................... 34
4 Revision History
Changes from Original (December 2013) to Revision A
Page
•
Added Device Information and Handling Rating tables, Feature Description, Device Functional Modes, Application
and Implementation, Power Supply Recommendations, Layout, Device and Documentation Support, and
Mechanical, Packaging, and Orderable Information sections; moved some curves to Application Curves section .............. 1
•
Deleted "TX interrupt" .......................................................................................................................................................... 12
•
Changed reference to "Max LED Control Register (0x05)" to "Enable Register (0x01)" .................................................... 14
•
Added Control Truth table ................................................................................................................................................... 17
2
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
LM3646
www.ti.com
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
5 Pin Configuration and Functions
DSBGA Package
20 Pins
4
4
3
3
2
2
1
1
A
B
C
D
E
Top View
E
D
C
B
A
Bottom View
Pin Functions
PIN
TYPE
DESCRIPTION
NUMBER
COUNT
NAME
A1, B1
2
GND
-
Ground.
A2, B2
2
SW
O
Drain Connection for Internal NMOS and Synchronous PMOS Switches.
A3, B3, C3
3
OUT
O
Step-Up DC/DC Converter Output. Connect a 10-µF ceramic capacitor between this pin and
GND.
A4,B4
2
LED1
O
High-Side Current Source Output for Flash LED. Both bumps must be connected for proper
operation.
C1
1
AGND
-
Analog Ground.
C2
1
TORCH
I
Active High Hardware Torch Enable. Drive TORCH high to turn on Torch/Movie Mode. Used
for External PWM mode. Has an internal pull-down resistor of 200 kΩ between TORCH and
GND.
C4, D4
2
LED2
O
High-Side Current Source Output for Flash LED. Both bumps must be connected for proper
operation.
D1
1
IN
I
Input Voltage Connection. Connect IN to the input supply, and bypass to GND with a 10-µF or
larger ceramic capacitor.
D2
1
SCL
I
Serial Clock Input.
D3
1
ENABLE
I
Active High Enable Pin. High = Standby, Low = Shutdown/Reset. Has an internal pull-down
resistor of 200 kΩ between ENABLE and GND.
E1
1
TEMP
O
Threshold Detector for LED Temperature Sensing and Current Scale Back.
E2
1
SDA
I/O
Serial Data Input/Output.
E3
1
STROBE
I
Active High Hardware Flash Enable. Drive STROBE high to turn on Flash LEDs. STROBE
overrides TORCH. Has an internal pull-down resistor of 200 kΩ between STROBE and GND.
E4
1
TX
I
Configurable Dual Polarity Power Amplifier Synchronization Input. Has an internal pull-down
resistor of 200 kΩ between TX and GND.
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
3
LM3646
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
www.ti.com
6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1) (2)
SCL, SDA, ENABLE, STROBE, TX, TORCH, LED1, LED2, TEMP
IN, SW, OUT
MIN
MAX
UNIT
−0.3
the lesser of
(VIN+0.3) w/ 6 max
V
−0.3
6
V
150
°C
Internally
Limited
Continuous power dissipation (3)
Junction temperature (TJ-MAX)
See (4)
Maximum lead temperature (soldering)
(1)
(2)
(3)
(4)
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, and functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating
Conditions is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
All voltages are with respect to the potential at the GND pin.
Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 135°C (typ.).
Thermal shutdown is verified by design.
For detailed soldering specifications and information, please refer to Texas Instruments Application Note 1112: DSBGA Wafer Level
Chip Scale Package (SNVA009).
6.2 Handling Ratings
Tstg
V(ESD)
(1)
(2)
MIN
MAX
UNIT
–65
150
°C
Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all
pins (1)
–2500
2500
Charged device model (CDM), per JEDEC specification
JESD22-C101, all pins (2)
–1500
1500
Storage temperature range
Electrostatic discharge
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted) (1) (2)
VIN
Junction temperature (TJ)
Ambient temperature (TA)
(1)
(2)
(3)
(3)
MIN
MAX
2.7
5.5
UNIT
V
−40
125
°C
−40
85
°C
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, and functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating
Conditions is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
All voltages are with respect to the potential at the GND pin.
In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may
have to be derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP
= 125°C), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to-ambient thermal resistance of the
part/package in the application (RθJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (RθJA × PD-MAX).
6.4 Thermal Information
LM3646
THERMAL METRIC
(1)
YFQ
UNIT
20 PINS
RθJA
(1)
4
Junction-to-ambient thermal resistance
53.4
°C/W
For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
LM3646
www.ti.com
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
6.5 Electrical Characteristics
Typical (TYP) limits apply for TA = 25°C. Minimum (MIN) and maximum (MAX) limits apply over the full operating ambient
temperature range (−40°C ≤ TA ≤ 85°C). Unless otherwise specified, VIN = 3.6 V. (1) (2)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
1.5A Flash, VOUT = 4 V, LED1 or LED2
Active
1.395
(−7%)
1.5
1.605
(7%)
A
93.4 mA Torch, VOUT = 3.6 V, LED1 or
LED2 Active
84.06
(−10%)
93.4
102.74
(10%)
mA
250
280
(12%)
mV
150
172.5
(15%)
−15%
1
15%
−10%
3.1
10%
CURRENT SOURCE SPECIFICATIONS
ILED1/2
VOUT VLED1/2
Current source accuracy
ILED = 1.5A
Flash
ILED = 93.4 mA
Torch
Current source regulation
STEP-UP DC/DC CONVERTER SPECIFICATIONS
ICL
Switch current limit
VOVP
Output overvoltage protection trip
point
ON threshold
4.85
5.0
5.15
OFF threshold
4.65
4.8
4.95
RPMOS
RPMOS switch on-resistance
IPMOS = 1A
RNMOS
NMOS switch on-resistance
INMOS = 1A
UVLO
Undervoltage lockout threshold
Falling VIN
VNTC-Trip
85
A
V
mΩ
65
2.74
2.8
2.85
V
NTC comparator trip threshold
−6%
600
6%
mV
INTC
NTC Current
−6%
50
6%
µA
VNTC-Open
NTC open trip threshold
2.2
2.3
2.4
V
VNTC-Short
NTC short trip threshold
75
100
125
mV
VIVFM
Input voltage flash monitor trip
threshold
−5%
2.9
5%
V
fSW
Switching frequency
2.8 V ≤ VIN ≤ 4.8 V
4
4.28
MHz
ISD
Shutdown supply current
Device disabled, EN = 0 V
2.8 V ≤ VIN ≤ 4.8 V
0.1
1.3
µA
ISB
Standby supply current
Device disabled, EN = 1.8 V
2.8 V ≤ VIN ≤ 4.8 V
2.5
10
µA
0
0.4
V
1.2
VIN
3.72
ENABLE, STROBE, TORCH, TX VOLTAGE SPECIFICATIONS
VIL
Input logic low
VIH
Input logic high
2.8 V ≤ VIN ≤ 4.2 V
I2C-COMPATIBLE INTERFACE SPECIFICATIONS (SCL, SDA)
VIL
Input logic low
VIH
Input logic high
VOL
Output logic low
tSCL
SCL clock period
(1)
(2)
2.8 V ≤ VIN ≤ 4.2 V
0
0.4
1.2
VIN
ILOAD = 1.5 mA
300
1
V
mV
µs
All voltages are with respect to the potential at the GND pin.
Min and Max limits are 100% production tested at an ambient temperature (TA) of 25°C. Limits over the operating temperature range are
specified through correlation using Statistical Quality Control (SQC) methods.
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
5
LM3646
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
www.ti.com
6.6 Timing Requirements
DELAY
EXPLANATION
TIME
ta
Time for the LED current to start ramping up after an I2C Write command.
560 µs
tb
Time for the LED current to start ramping down after an I2C Stop command.
120 µs
tc
Time for the LED current to start ramping up after the STROBE pin is raised high.
560 µs
td
Time for the LED current to start ramping down after the STROBE pin is pulled low.
te
Time for the LED current to start ramping up after the TORCH pin is raised high.
tf
Time for the LED current to start ramping down after the TORCH pin is pulled low.
8 µs
tg
Time for the LED current to start ramping down after the TX pin is pulled high.
3 µs
th
Time for the LED current to start ramping up after the TX pin is pulled low, provided the part has not timed
out in flash mode.
2 µs
Strobe Controlled Flash Start and
Stop Delay Times
I2C Controlled Flash Start and Stop
Delay Times
I2C
Bus
I2C Flash
8 µs
560 µs
STROBE
I2C Stop
ILED
ILED
tb
ta
External Indicator Start and Stop
Delay Times
Using Torch Pin
TX event ± Start and Stop
Delay Times
TORCH
TX
ILED
EDGE TRIG
STROBE
te
td
tc
tf
ILED
tg
th
Flash time-out
Figure 1. Control Logic Delays
6
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
LM3646
www.ti.com
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
6.7 Typical Characteristics
Unless otherwise specified: TA= 25°C; VIN = 3.6 V; VEN = VIN; CIN = 10 µF; COUT = 10 µF; L = 1 µH.
1600
1400
1200
1000
1530
1520
800
600
1510
1500
1490
1480
400
1470
200
1460
0
1450
0
2.8
8 16 24 32 40 48 56 64 72 80 88 96 104112120128
LED1 Code (#)
3
3.2
3.4
3.6
Figure 2. Flash LED Current vs. Brightness Code
200
4.2
4.4
4.6
4.8
5
C001
D1, +25ºC
D1, -40ºC
D1, +85ºC
D2, +25ºC
D2, -40ºC
D2, +85ºC
180
160
140
ILED (mA)
760
4
Figure 3. Flash LED Current Line Regulation, ILED = 1.5A
D1, +25ºC
D1, -40ºC
D1, +85ºC
D2, +25ºC
D2, -40ºC
D2, +85ºC
770
3.8
VIN (V)
C004
780
ILED (mA)
D1, +25ºC
D1, -40ºC
D1, +85ºC
D2, +25ºC
D2, -40ºC
D2, +85ºC
1540
ILED (mA)
ILED (mA)
1550
D1, +25ºC
D1, -40ºC
D1, +85ºC
D2, +25ºC
D2, -40ºC
D2, +85ºC
750
120
100
740
80
60
40
730
20
0
720
2.8
3
3.2
3.4
3.6
3.8
4
4.2
4.4
4.6
4.8
VIN (V)
0
5
LED1 Code (#)
196
194
192
TA = +25ºC
1.7
TA = -40ºC
1.6
TA = +85ºC
1.5
ICL (A)
ILED (mA)
1.8
D1, +25ºC
D1, -40ºC
D1, +85ºC
D2, +25ºC
D2, -40ºC
D2, +85ºC
198
C005
Figure 5. Torch LED Current vs. Brightness Code
Figure 4. Flash LED Current Line Regulation,
ILED1 = ILED2 = 0.75A
200
8 16 24 32 40 48 56 64 72 80 88 96 104112120128
C002
190
188
1.4
1.3
186
ILED = 1.5A, VLED = 4.5V
1.2
184
1.1
182
180
1
2.8
3
3.2
3.4
3.6
3.8
4
4.2
4.4
4.6
4.8
VIN (V)
5
2.5
Figure 6. Torch LED Current Line Regulation,
ILED = 187.1 mA
2.8
3.1
3.4
3.7
4
4.3
4.6
4.9
5.2
VIN (V)
C003
5.5
C009
Figure 7. Inductor Current vs. Input Voltage, CL= 1 A
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
7
LM3646
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
www.ti.com
Typical Characteristics (continued)
Unless otherwise specified: TA= 25°C; VIN = 3.6 V; VEN = VIN; CIN = 10 µF; COUT = 10 µF; L = 1 µH.
2
2
TA = +25ºC
1.9
TA = -40ºC
1.8
TA = +85ºC
ILED = 1.5A, VLED = 4.5V
ILED = 1.5A, VLED = 4.5V
1.9
1.8
ICL (A)
ICL (A)
1.7
1.6
1.5
1.7
1.6
1.4
TA = +25ºC
1.5
1.3
1.2
TA = -40ºC
TA = +85ºC
1.4
2.5
2.8
3.1
3.4
3.7
4
4.3
4.6
4.9
5.2
VIN (V)
5.5
2.5
2.8
3.1
3.4
3.7
Figure 8. Inductor Current vs. Input Voltage, CL = 1.3 A
4
4.3
4.6
4.9
5.2
VIN (V)
C010
5.5
C011
Figure 9. Inductor Current vs. Input Voltage, CL = 1.6 A
2.3
2.6
2.2
ILED = 1.5A, VLED = 4.5V
ILED = 1.5A, VLED = 4.5V
2.4
2.1
2.2
ICL (A)
ICL (A)
2
1.9
1.8
1.7
1.8
1.6
TA = +25ºC
1.5
TA = -40ºC
TA = +25ºC
1.6
TA = +85ºC
1.4
2.5
2.8
3.1
3.4
4
4.3
4.6
4.9
5.2
5.5
TA = +85ºC
2.5
2.8
3.1
3.4
3.7
4
4.3
4.6
4.9
5.2
VIN (V)
C012
Figure 10. Inductor Current vs. Input Voltage, CL = 1.9 A
5.5
C013
Figure 11. Inductor Current vs. Input Voltage, CL = 2.2 A
3
3.4
2.8
ILED = 1.5A, VLED = 4.5V
3.2
ILED = 1.5A, VLED = 4.5V
3
2.6
2.8
ICL (A)
2.4
ICL (A)
TA = -40ºC
1.4
3.7
VIN (V)
2.2
2.6
2.4
2.2
2
2
1.8
1.6
TA = +25ºC
1.8
TA = -40ºC
1.6
TA = +85ºC
1.4
2.5
2.8
3.1
3.4
TA = +25ºC
TA = -40ºC
TA = +85ºC
1.4
3.7
4
VIN (V)
4.3
4.6
4.9
5.2
5.5
2.5
2.8
3.1
3.4
3.7
4
VIN (V)
C014
Figure 12. Inductor Current vs. Input Voltage, CL = 2.5 A
8
2
4.3
4.6
4.9
5.2
5.5
C015
Figure 13. Inductor Current vs. Input Voltage, CL = 2.8 A
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
LM3646
www.ti.com
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
Typical Characteristics (continued)
Unless otherwise specified: TA= 25°C; VIN = 3.6 V; VEN = VIN; CIN = 10 µF; COUT = 10 µF; L = 1 µH.
3.6
3.6
3.4
ILED = 1.5A, VLED = 4.5V
3.3
3.2
CL = 1.0A
CL = 1.3A
CL = 1.6A
CL = 1.9A
CL = 2.2A
CL = 2.5A
CL = 2.8A
CL = 3.1A
ILED = 1.5A, VLED = 4.5V
3
3
2.7
ICL (A)
ICL (A)
2.8
2.6
2.4
2.2
2.4
2.1
1.8
2
1.8
1.6
TA = +25ºC
1.5
TA = -40ºC
1.2
TA = +85ºC
1.4
2.5
2.8
3.1
3.4
0.9
3.7
4
4.3
4.6
4.9
5.2
2.5
5.5
VIN (V)
2.8
3.1
3.4
3.7
4
4.3
4.6
4.9
5.2
5.5
VIN (V)
C016
C008
Figure 15. Inductor Current Limit vs. Input Voltage
Figure 14. Inductor Current vs. Input Voltage, CL = 3.1 A
3400
1600
3200
1400
ILED = 1.5A, ICL = 3.1A, VLED = 4V
3000
2800
2600
CL = 1.0A
CL = 1.3A
CL = 1.6A
CL = 1.9A
CL = 2.2A
CL = 2.5A
CL = 2.8A
CL = 3.1A
1000
800
600
ILED = 1.5A, VLED = 4V
400
2.5
2.8
3.1
3.4
IIN (mA)
ILED (mA)
1200
3.7
4
4.3
4.6
4.9
5.2
2400
2200
2000
1800
TA = +25ºC
1600
TA = -40ºC
1400
TA = +85ºC
1200
2.5
5.5
VIN (V)
2.8
3.1
3.4
3.7
4
4.3
4.6
4.9
5.2
5.5
VIN (V)
C017
C018
Figure 17. Input Current vs. Input Voltage
Figure 16. Flash LED Current vs. Input Voltage in Current
Limit
1.0000
0.3
0.29
ILED = 1.5A, VLED = 4V
0.1000
0.28
ISD (µA)
VFB (V)
0.27
0.26
0.0100
0.25
0.24
TA = +25ºC
0.23
TA = -40ºC
0.0010
TA = -40ºC
TA = +85ºC
0.22
2.8
3
3.2
3.4
3.6
3.8
4
VIN (V)
4.2
4.4
TA = +25ºC
TA = +85ºC
0.0001
4.6
2.5
3.1
3.4
3.7
4
4.3
4.6
4.9
5.2
VIN (V)
C029
Figure 18. Current Source Headroom vs. Input Voltage
2.8
5.5
C020
Figure 19. Shutdown Current vs. Input Voltage
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
9
LM3646
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
www.ti.com
Typical Characteristics (continued)
Unless otherwise specified: TA= 25°C; VIN = 3.6 V; VEN = VIN; CIN = 10 µF; COUT = 10 µF; L = 1 µH.
14
2
TA = +25ºC
12
10
TA = +25ºC
TA = -40ºC
1.8
TA = -40ºC
TA = +85ºC
1.6
TA = +85ºC
ISB (µA)
ISB (µA)
1.4
8
6
1.2
1
4
0.8
2
0.6
0
0.4
2.5
2.8
3.1
3.4
3.7
4
4.3
4.6
4.9
5.2
2.5
5.5
VIN (V)
ILED = 0
4.6
700
650
4.9
5.2
5.5
C022
TA = +25ºC
TA = -40ºC
TA = +85ºC
4.15
fSW (MHz)
IQ (µA)
4.3
4.2
TA = +85ºC
600
4.1
4.05
4
3.95
550
3.9
500
3.85
450
3.8
2.5
2.8
3.1
3.4
3.7
4
4.3
4.6
4.9
5.2
5.5
VIN (V)
2.7
2.9
3.1
3.3
3.5
3.7
3.9
4.1
4.3
4.5
4.7
VIN (V)
C023
Figure 22. Input Current vs. Input Voltage in Pass Mode
C019
Figure 23. Frequency vs. Input Voltage
50.0
0.65
VNTC = 1.0V
0.64
49.5
0.63
0.62
VNTC (V)
49.0
INTC (µA)
4
4.25
750
48.5
48.0
0.61
0.6
0.59
0.58
TA = +25ºC
47.5
2.8
3.1
3.4
3.7
4
4.3
4.6
4.9
5.2
VIN (V)
TA = -40ºC
0.56
TA = +85ºC
2.5
TA = +25ºC
0.57
TA = -40ºC
47.0
TA = +85ºC
0.55
5.5
2.5
2.8
3.1
3.4
3.7
4
VIN (V)
C024
Figure 24. NTC Bias Current vs. Input Voltage
10
3.7
4.3
TA = -40ºC
800
3.4
Figure 21. Standby Current vs. Input Voltage, VEN = VIN
TA = +25ºC
850
3.1
VIN (V)
Figure 20. Standby Current vs. Input Voltage, VEN = 1.8 V
900
2.8
C021
4.3
4.6
4.9
5.2
5.5
C026
Figure 25. NTC Threshold vs. Input Voltage, VNTC = 0.6 V
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
LM3646
www.ti.com
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
Typical Characteristics (continued)
Unless otherwise specified: TA= 25°C; VIN = 3.6 V; VEN = VIN; CIN = 10 µF; COUT = 10 µF; L = 1 µH.
51
2.35
50
2.33
49
2.31
TA = +25ºC
VNTC (V)
INTC (µA)
TA = -40ºC
48
TA = +85ºC
2.29
VNTC = 0.5V
VNTC = 1.0V
47
2.27
VNTC = 1.5V
VNTC = 2.0V
46
2.5
2.8
3.1
3.4
3.7
4
4.3
4.6
VIN (V)
4.9
5.2
2.25
5.5
2.5
Figure 26. NTC Bias Current vs. Input Voltage at Different
VNTC
2.8
3.1
3.4
3.7
4
4.3
4.6
4.9
5.2
5.5
VIN (V)
C025
C027
Figure 27. NTC Open Threshold vs. Input Voltage
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
11
LM3646
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
www.ti.com
7 Detailed Description
7.1 Overview
The LM3646 is a high-power white LED flash driver capable of delivering up to 1.5 A (total LED current) into two
parallel LEDs. The device incorporates a 4-MHz constant frequency, synchronous Current-Mode PWM boost
converter, and two high-side current sources to regulate the LED current over the 2.7 V to 5.5 V input voltage
range.
The LM3646 PWM converter switches and maintains at least VHR across the current sources (LED1 and LED2).
This minimum headroom voltage ensures that the current source remains in regulation. If the input voltage is
above the LED voltage + current source headroom voltage, the device does not switch and turns the PFET on
continuously (Pass Mode). In Pass Mode the difference between (VIN - ILED x RPMOS) and the voltage across the
LED is dropped across the current sources.
The LM3646 has three logic inputs including a hardware Flash Enable (STROBE), a hardware Torch Enable
(TORCH) used for external Torch Mode control, and a Flash Interrupt input (TX) designed to interrupt the flash
pulse during high battery current conditions. All three logic inputs have internal 200 kΩ (typ.) pull-down resistors
to GND.
Additional features of the LM3646 include an internal comparator for LED thermal sensing via an external NTC
thermistor and an input voltage monitor that can reduce the Flash current (during low VIN conditions).
Control of the LM3646 is done via an I2C-compatible interface. This includes adjustment of the Flash and Torch
current levels, current source selection, changing the Flash Timeout Duration, changing the switch current limit,
and enabling the NTC block. Additionally, there are flag and status bits that indicate flash current time-out, LED
over-temperature condition, LED failure (open/short), device thermal shutdown and VIN undervoltage conditions.
12
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
LM3646
www.ti.com
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
7.2 Functional Block Diagram
SW
Over Voltage
Comparator
VREF
4 MHz
Oscillator
+
-
IN
85 m:
Input Voltage
Flash Monitor
UVLO
ILED1
VOVP
OUT
ILED2
+
-
+
-
PWM
Control
65 m:
INTC
Thermal
Shutdown
+150oC
TEMP
+
-
LED1
Error
Amplifier
FB
SELECT
LED2
+
-
+
-
OUT-VHR
Current Sense/
Current Limit
NTC VTRIP
Slope
Compensation
SDA
Control
Logic/
Registers
2
SCL
I C
Interface
ENABLE
Soft-Start
TORCH
STROBE
TX
GND
7.3 Feature Description
7.3.1 Flash Mode
In Flash Mode, the LED current sources (LED1/2) provide 128 target current levels from 0 mA to 1500 mA. The
Flash currents are adjusted via bits[3:0] of the Max LED Current Control Register (0x05) and bits[6:0] of the
LED1 Flash Current Control Register (0x06). Flash Mode is activated by the Enable Register (0x01), or by pulling
the STROBE pin HIGH. Once the Flash sequence is activated the current source (LED) will ramp up to the
programmed Flash current by stepping through all current steps until the programmed current is reached.
While both LED1 and LED2 are capable of delivering 1.5A to the LED, the sum total of the LED current will not
exceed the value stored in the Max LED Current Control Register. LED1 will receive the current value stored in
the LED1 Flash Current Control Register, and LED2 will receive the difference of the value stored in the MAX
LED Current Control Register and LED1 Flash Current Control Register.
If LED1 and LED2 Active:
LED1 = LED1 Flash Current Control Value
LED2 = MAX Flash Current Control Value - LED1 Flash Current Control Value
If MAX Flash Current Control Value < LED1 Flash Current Control Value
LED1 = MAX Flash Current Control Value
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
13
LM3646
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
www.ti.com
Feature Description (continued)
LED2 = Off
If the LED1 Current Control Value is set to a level that is higher than the MAX Flash LED Current Control Value,
LED1 receives the MAX Flash LED Current Control value, and LED2 is disabled.
When the part is enabled in Flash Mode through the Enable Register or the STROBE pin, all mode bits in the
Enable Register are cleared after completion of the flash event. Before the device can be enabled again, the
mode bits need to be set.
7.3.2 Torch Mode
In Torch Mode, the LED current sources (LED1/2) provide 128 target current levels from 0 mA to 187.5 mA. The
Torch currents are adjusted via bits[6:4] of the Max LED Current Control Register (0x05) and bits[6:0] of the
LED1 Torch Current Control Register (0x07). Torch Mode is activated by the Enable Register (0x01), or by
pulling the TORCH pin HIGH. Once the TORCH sequence is activated the current source (LED) will ramp up to
the programmed Torch current by stepping through all current steps until the programmed current is reached.
LED1 receives the current value stored in the LED1 Torch Current Control Register, and LED2 receives the
difference of the value stored in the MAX LED Current Control Register and LED1 Torch Current Control
Register.
If LED1 and LED2 Active:
LED1 = LED1 Torch Current Control Value
LED2 = MAX Torch Current Control Value - LED1 Torch Current Control Value
If MAX Torch Current Control Value < LED1 Torch Current Control Value
LED1 = MAX Torch Current Control Value
LED2 = Off
If the LED1 Torch Current Control Value is set to a level that is higher than the MAX Torch LED Current Control
Value, LED1 receives the MAX Torch LED Current Control value, and LED2 is disabled. Torch Mode is not
affected by Flash Timeout.
7.4 Device Functional Modes
7.4.1 Start-Up (Enabling the Device)
Turn on of the LM3646 Torch and Flash Modes can be done through the Enable Register (0x01). On start-up,
when VOUT is less than VIN, the internal synchronous PFET turns on as a current source and delivers 200 mA
(typ.) to the output capacitor. During this time the current source (LED) is off. When the voltage across the output
capacitor reaches 2.2 V (typ.) the current source turns on. At turnon the current source steps through each
FLASH or TORCH level until the target LED current is reached. This gives the device a controlled turn-on and
limits inrush current from the VIN supply.
7.4.2 Pass Mode
The LM3646 starts up in Pass Mode and stays there until Boost Mode is needed to maintain regulation. In Pass
Mode the boost converter does not switch and the synchronous PFET turns fully on bringing VOUT up to VIN (ILED x RPMOS). In Pass Mode the inductor current is not limited by the peak current limit. In this situation the
output current must be limited to 2A. If the voltage difference between VOUT and VLED falls below VHR, the device
switches to Boost Mode.
7.4.3 Power Amplifier Synchronization (TX)
The TX pin is a Power Amplifier Synchronization input. This is designed to reduce the flash LED current and thus
limit the battery current during high battery current conditions such as PA transmit events. When the LM3646 is
engaged in a Flash event and the TX pin is pulled high, the LED current is forced into Torch Mode at the
programmed Torch current setting. If the TX pin is then pulled low before the Flash pulse terminates, the LED
current will return to the previous Flash current level. At the end of the Flash time-out, whether the TX pin is high
or low, the LED current will turn off. The TX input can be disabled by setting bit TX Pin Enable to a ‘0’ in the
Enable Register (0x01).
14
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
LM3646
www.ti.com
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
Device Functional Modes (continued)
7.4.4 Input Voltage Flash Monitor (IVFM)
The LM3646 has the ability to adjust the flash current based upon the voltage level present at the IN pin utilizing
an Input Voltage Flash Monitor. The IVFM block has an adjustable threshold (IVM-D) ranging from 2.9 V to 3.2 V
in 100-mV steps as well as adjustable hysteresis. The IVFM threshold and hysteresis are controlled by bits[4:3]
and bits[2:1] respectively, in the IVFM Mode Register (0x02). Flags Register1 (0x08) has the IVFM flag (bit[3])
set when the input voltage crosses the IVFM value. The IVFM threshold sets the input voltage boundary that
forces the LM3646 to stop ramping the flash current during startup in Stop and Hold Mode, or to actively adjust
the LED current lower in Down Adjust Mode, or to continuously adjust the LED current up and down in Up &
Down mode.
Stop and Hold Mode (Figure 28): Stops Current Ramp and Holds the level for the remaining flash if VIN crosses
IVM-D Line. Sets IVFM Flag (bit[3] in Flags Register1) upon crossing IVM-D Line.
Down Mode (Figure 29): Adjusts current down if VIN crosses IVM-D Line and stops decreasing once VIN rises
above the IVM-D line + the IVFM hysteresis setting. The LM3646 will decrease the current throughout the flash
pulse anytime the input voltage falls below the IVM-D line, not just once. The flash current will not increase again
until the next flash. Sets IVFM Flag (bit[3] in Flags Register1) upon crossing IVM-D Line.
Up and Down Mode (Figure 30): Adjusts current down if VIN crosses IVM-D Line and adjusts current up if VIN
rises above the IVM-D line + the IVFM hystersis setting. In this mode, the current will continually adjust with the
rising and falling of the input voltage throughout the entire flash pulse. Sets IVFM Flag (bit[3] in Flags Register1)
upon crossing IVM-D Line.
IFLASH
ILED
0 mA
IVM-U
VIN
IVM-D
tfilter
tfilter
t
Figure 28. IVFM Stop and Hold Mode
IFLASH
ILED
0 mA
VIN IVM-U
IVM-D
t
tfilter
Figure 29. IVFM Down Mode
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
15
LM3646
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
www.ti.com
Device Functional Modes (continued)
IFLASH
ILED
0 mA
VIN IVM-U
IVM-D
t
tfilter
tfilter
tfilter
Figure 30. IVFM Up and Down Mode
7.4.5 Fault/Protections
7.4.5.1 Fault Operation
Upon entering a fault condition, the LM3646 sets the appropriate flag in the Flags Register1 (0x08) or Flags
Register2 (0x09), and place the part into standby by clearing and locking the Torch Enable bit (bit[7] in LED1
Torch Current Control Register (0x07)) and Mode Bits (M1, M0) in the Enable Register (0x01), until the Flags
Register1 or Flags Register2 is read back via I2C.
7.4.5.2 Flash Time-Out
The Flash Time-Out period sets the amount of time that the Flash Current is being sourced from the current
source (LED). The LM3646 has 8 timeout levels ranging 50 ms to 400 ms in 50 ms steps. The Flash Time-Out
period is controlled by bits[2:0] in the Flash Timing Register (0x04). Flash Time-Out only applies to the Flash
Mode operation. The mode bits are cleared and bit[0] is set in the Flags Register1 (0x08) upon a Flash Timeout.
7.4.5.3 Overvoltage Protection (OVP)
The output voltage is limited to typically 5 V (see VOVP Spec). In situations such as an open LED, the LM3646
raises the output voltage in order to try to keep the LED current at its target value. When VOUT reaches 5 V (typ.)
the overvoltage comparator trips and turns off the internal NFET. When VOUT falls below the “VOVP Off
Threshold”, the LM3646 begins switching again. The mode bits are cleared, and the OVP flag is set (bit[7] in
Flags Register1 (0x08)) when an OVP condition is present for 512 microseconds, preventing momentary OVP
events from forcing the part to shut down.
7.4.5.4 Current Limit
The LM3646 features 8 selectable inductor current limits ranging from 1 A to 3.1 A in 300-mA steps. The current
limit is programmable through bits[7:5] of the Enable Register (0x01) of the I2C-compatible interface. When the
inductor current limit is reached, the LM3646 terminates the charging phase of the switching cycle.
Since the current limit is sensed in the NMOS switch, there is no mechanism to limit the current when the device
operates in Pass Mode. In Boost Mode or Pass Mode if VOUT falls below 2.3 V, the part stops switching, and the
PFET operates as a current source limiting the current to 200 mA. This prevents damage to the LM3646 and
excessive current draw from the battery during output short-circuit conditions. The mode bits are not cleared
upon a Current Limit event, but the OCP flag (bit[4]) in Flags Register1 (0x08) is set.
16
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
LM3646
www.ti.com
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
Device Functional Modes (continued)
7.4.5.5 NTC Thermistor Input (TEMP)
The TEMP pin serves as a threshold detector for negative temperature coefficient (NTC) thermistors. It interrupts
the LED current and sets the NTC TRIP flag bit[6] in Flags Register1 (0x08) when the voltage at TEMP goes
below the programmed threshold. The NTC threshold voltage is adjustable from 200 mV to 900 mV in 100 mV
steps via the NTC and Torch Ramp Register (0x03). The NTC current is set to 50 µA. When an over-temperature
event is detected, the LM3646 is forced into shutdown. The NTC detection circuitry can be enabled or disabled
via bit[4] of the Enable Register (0x01). If Enabled, the NTC block will turn on and off during the start and stop of
a Flash/Torch event. The mode bits are cleared upon an NTC event.
Additionally, the NTC input looks for an open NTC connection and a short NTC connection. If the NTC input falls
below 100 mV, the NTC short flag is set (bit[1] in Flags Register2 (0x09)), and the part is disabled. If the NTC
input rises above 2.3 V, the NTC Open flag is set (bit[0] in Flags Register2), and the part is disabled. These fault
detections can be individually disabled/enabled via the NTC Open Detect Enable bit in IVFM Mode Register
(0x02) and the NTC Short Fault Enable bit in Flags Register2.
7.4.5.6 Undervoltage Lockout (UVLO)
The LM3646 has an internal comparator that monitors the voltage at IN and forces the LM3646 into shutdown if
the input voltage drops to 2.8 V. If the UVLO monitor threshold is tripped, the UVLO flag bit is set in Flags
Register1 (0x08). If the input voltage rises above 2.8 V, the LM3646 is not available for operation until there is an
I2C read command initiated for the Flags Register1. Upon a read, Flags Register1 is cleared, and normal
operation can resume if the input voltage is greater than 2.8 V. This feature can be disabled by writing a ‘0’ to the
UVLO Enable bit in the IVFM Mode Register (0x02). The mode bits are cleared upon a UVLO event.
7.4.5.7 Thermal Shutdown (TSD)
When the LM3646’s die temperature reaches 135°C the boost converter shuts down, and the NFET and PFET
turn off, as does the current source (LED). When the thermal shutdown threshold is tripped, a '1' gets written to
bit[5] of Flags Register1 (0x08) (Thermal Shutdown bit), and the LM3646 will go into standby. The LM3646 is
allowed to restart only after Flags Register1 is read, clearing the fault flag. Upon restart, if the die temperature is
still above 135°C, the LM3646 resets the Fault flag and re-enters standby. The mode bits are cleared upon a
TSD.
7.4.5.8 LED and/or VOUT Short Fault
The LED Fault flags (bit[2] or bit[3]) in Flags Register2 (0x09) read back a '1' if the part is active in Flash or Torch
Mode and either LED output experiences a short condition. The Output Short Fault flag (bit[1] in Flags Register1
(0x08)) reads back a '1' if the part is active in Flash or Torch Mode and the boost output experiences a short
condition. An LED short condition is determined if the voltage at LED goes below 500 mV (typ.); VOUT short
condition occurs if the voltage at OUT goes below 2.1 V (typ.) while the device is in Torch or Flash Mode. There
is a delay of 256 μs deglitch time before the LED flag is valid and 2.048 ms before the VOUT flag is valid. This
delay is the time between when the Flash or Torch current is triggered, and when the LED voltage and the output
voltage are sampled. The LED and VOUT short flags can only be reset to '0' by removing power to the LM3646,
or by reading back the Flags Register1 or Flags Register2. The mode bits are cleared upon an LED and/or
VOUT short fault.
7.5 Programming
7.5.1 Control Truth Table
Table 1. Control Truth Table
MODE1
MODE0
STROBE EN
TORCH EN
STROBE PIN
TORCH PIN
0
X
X
0
X
X
ACTION
Standby
0
X
X
1
X
pos edge
Ext Torch
1
1
1
X
pos edge
X
Ext Flash
1
0
X
0
X
X
Int Torch
1
1
0
X
X
X
Int Flash
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
17
LM3646
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
www.ti.com
7.5.2 I2C-Compatible Interface
7.5.2.1 Data Validity
The data on SDA line must be stable during the HIGH period of the clock signal (SCL). In other words, state of
the data line can only be changed when SCL is LOW.
SCL
SDA
data
change
allowed
data
valid
data
change
allowed
data
valid
data
change
allowed
Figure 31. Data Validity Diagram
A pull-up resistor between the controller's VIO line and SDA must be greater than [(VIO-VOL) / 3mA] to meet the
VOL requirement on SDA. Using a larger pullup resistor results in lower switching current with slower edges, while
using a smaller pullup results in higher switching currents with faster edges.
7.5.2.2 START and STOP Conditions
START and STOP conditions classify the beginning and the end of the I2C session. A START condition is
defined as the SDA signal transitioning from HIGH to LOW while SCL line is HIGH. A STOP condition is defined
as the SDA transitioning from LOW to HIGH while SCL is HIGH. The I2C-compatible master always generates
START and STOP conditions. The I2C-compatible bus is considered to be busy after a START condition and free
after a STOP condition. During data transmission, the I2C-compatible master can generate repeated START
conditions. First START and repeated START conditions are equivalent, function-wise.
SDA
SCL
S
P
Start Condition
Stop Condition
Figure 32. Start and Stop Conditions
7.5.2.3 Transferring Data
Every byte put on the SDA line must be eight bits long, with the most significant bit (MSB) transferred first. Each
byte of data has to be followed by an acknowledge bit. The acknowledge related clock pulse is generated by the
master. The master releases the SDA line (HIGH) during the acknowledge clock pulse. The LM3646 pulls down
the SDA line during the 9th clock pulse, signifying an acknowledge. The LM3646 generates an acknowledge
after each byte is received. There is no acknowledge created after data is read from the LM3646.
After the START condition, the I2C master sends a chip address. This address is seven bits long followed by an
eighth bit which is a data direction bit (R/W). The LM3646 7-bit address is 0x67 (Figure 33). For the eighth bit, a
'0' indicates a WRITE, and a '1' indicates a READ. The second byte selects the register to which the data will be
written. The third byte contains data to write to the selected register.
18
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
LM3646
www.ti.com
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
ack from slave
ack from slave
start
msb Chip Address lsb
w
ack
msb Register Add lsb
ack
start
Id = 67h
w
ack
addr = 01h
ack
ack from slave
msb
DATA
lsb
ack
stop
ack
stop
SCL
SDA
Data = 03h
w = write (SDA = "0") , r = read (SDA = "1") , ack = acknowledge (SDA pulled down by either master or slave), id =
chip address, 67h for LM3646
Figure 33. Write Cycle for the LM3646
7.5.2.4 I2C-Compatible Chip Address
The device address for the LM3646 is 1100111 (67). After the START condition, the I2C-compatible master
sends the 7-bit address followed by an eighth read or write bit (R/W). R/W = 0 indicates a WRITE and R/W = 1
indicates a READ. The second byte following the device address selects the register address to which the data
will be written. The third byte contains the data for the selected register.
MSB
1
Bit 7
LSB
1
Bit 6
0
Bit 5
0
Bit 4
1
Bit 3
1
Bit 2
1
Bit 1
R/W
Bit 0
2
I C Slave Address (chip address)
Figure 34. I2C-Compatible Device Address for LM3646
7.6 Register Map
Table 2. LM3646 Internal Registers
Internal Hex Address
Power On/RESET Value (1)
SILICON REVISION REGISTER
0x00
0x11
ENABLE REGISTER
0x01
0xE0
IVFM MODE REGISTER
0x02
0xA4
NTC AND TORCH RAMP REGISTER
0x03
0x20
FLASH TIMING REGISTER
0x04
0x42
MAX LED CURRENT CONTROL REGISTER
0x05
0x7F
LED1 FLASH CURRENT CONTROL REGISTER
0x06
0x7F
LED1 TORCH CURRENT CONTROL REGISTER
0x07
0x7F
FLAGS REGISTER1
0x08
0x00
FLAGS REGISTER2
0x09
0x30
Register Name
(1)
All unused bits are internally pulled HIGH.
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
19
LM3646
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
www.ti.com
7.6.1 Silicon Revision Register (0x00)
Bit 7
Bit 6
Bit 5
RFU
Bit 4
Bit 3
Chip ID Current Value = '010'
Bit 2
Bit 1
Bit 0
Silicon Revision Current Value = '001'
7.6.2 Enable Register (0x01)
Bit 7
Bit 6
Bit 5
Inductor Current Limit
000 = 1.0A
001 = 1.3A
010 = 1.6A
011 = 1.9A
100 = 2.2A
101 = 2.5A
110 = 2.8A
111 = 3.1A (default)
NTC Enable
TX Pin EN
Soft-Start EN
Bit 4
NTC Enable
0 = Disabled
(default)
1 = Enabled
Bit 3
TX Pin Enable
0 = Disabled
(default)
1 = Enabled
Bit 2
Soft-Start Enable
Enable 0 = Disabled
(default)
1 = Enabled
Bit 1
Bit 0
LED Mode Bits: M1, M0
00 = Standby (default)
01 = Standby
10 = Torch
11 = Flash
Enables or Disables the NTC detection block when the LM3646 is enabled
Enables the TX pin and TX current reduction function
Enables the Pass-Mode startup sequence
LED Mode Bits (M1, M0)
00–Standby
Off
01–Standby
Off
10–Torch
Sets Torch Mode. If Torch EN = 0, Torch will start after I²C-compatible command.
11–Flash
Sets Flash Mode. If Strobe EN = 0, Flash will start after I²C-compatible command.
7.6.3 IVFM Mode Register (0x02)
Bit 7
UVLO
Enable(2.8 V)
0 = Disabled
1 = Enabled
(default)
Bit 6
IVFM Filter
Bit 5
IVFM Enable
Bit 4
Bit 3
IVFM Level Adjust Threshold
Bit 2
Bit 1
IVFM Mode/Hysteresis
0 = 4 µs
(default)
1 = 256 µs
0 = Disabled
1 = Enabled
(default)
00 = 2.9V (default)
01 = 3.0V
10 = 3.1V
11 = 3.2V
00 = Ramp and Hold
01 = 0mV Hyst
10 = 50 mV Hyst (default)
11 = 100 mV Hyst
Bit 0
NTC Open
Fault Enable
0 = Disabled
(default)
1 = Enabled
7.6.4 NTC and Torch Ramp Register (0x03)
Bit 7
Bit 6
Boost Mode
00 = Automatic (default)
01 = Force Pass-Mode
10 = Force Boost-Mode
11 = Automatic
20
Bit 5
Bit 4
NTC Trip Thresholds
000 = 200 mV
001 = 300 mV
010 = 400 mV
011 = 500 mV
100 = 600 mV (default)
101 = 700 mV
110 = 800 mV
111 = 900 mV
Bit 3
Submit Documentation Feedback
Bit 2
Bit 1
Bit 0
Torch Current Ramp Times
000 = Ramp Disabled (default)
001 = 16 ms
010 = 32 ms
011 = 64 ms
100 = 128 ms
101 = 256 ms
110 = 512 ms
111 = 1024 ms
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
LM3646
www.ti.com
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
VIN
NTC Control Block
INTC
TEMP
VTRIP
NTC
+
Control
Logic
Figure 35. NTC Control Block
The TEMP node is connected to an NTC resistor as shown in Figure 35. A constant current source from the
input is connected to this node. Any change in the voltage because of a change in the resistance of the NTC
resistor is compared to a set VTRIP. The trip thresholds are selected by Bits[5:3] of the NTC and Torch Ramp
Register.
7.6.5 Flash Timing Register (0x04)
Bit 7
IVFM Modulation
0 = Down Adjust
(default)
1 = Up/Down
Adjust
Bit 6
Strobe Usage
0 = Level
1 = Edge
(default)
Bit 5
Bit 4
Bit 3
Flash Ramp Time
000 = 256 µs (default)
001 = 512 µs
010 = 1.024 ms
011 = 2.048 ms
100 = 4.096 ms
101 = 8.192 ms
110 = 16.384 ms
111 = 32.768 ms
Bit 2
Bit 1
Flash Time-Out Time
000 = 50 ms
001 = 100 ms
010 = 150 ms (default)
011 = 200 ms
100 = 250 ms
101 = 300 ms
110 = 350 ms
111 = 400 ms
Bit 0
7.6.6 Max LED Current Control Register (0x05)
Bit 7
LED Short Fault
Enable
0 = Down Adjust
(default)
1 = Up/Down Adjust
Bit 6
Bit 5
Max Torch Current
Bit 4
Bit 3
000 = 23.04 mA
001 = 46.48 mA
010 = 69.91 mA
011 = 93.35 mA
100 = 116.79 mA
101 = 140.23 mA
110 = 163.66 mA
111 = 187.10 mA (default)
Bit 2
Bit 1
Max Flash Current
Bit 0
0000 = 93.35 mA
0001 = 187.10 mA
0010 = 280.85 mA
0011 = 374.60 mA
0100 = 468.35 mA
0101 = 562.10 mA
0110 = 655.85 mA
0111 = 749.60 mA
1000 = 843.35 mA
1001 = 937.10 mA
1010 = 1030.85 mA
1011 = 1124.60 mA
1100 = 1218.35 mA
1101 = 1312.10 mA
1110 = 1405.85 mA
1111 = 1499.60 mA (default)
If LED1 and LED2 Active:
LED2 = MAX Current Control Value - LED1 Current Control Value
If MAX Current Control Value < LED1 Current Control Value
LED1 = MAX Current Control Value
LED2 = Off
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
21
LM3646
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
www.ti.com
7.6.7 LED1 Flash Current Control Register (0x06)
Bit 7
Strobe Pin Enable
Bit
0 = Disabled
(default)
1 = Enabled
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
LED1 Flash Current Level
Bit 1
Bit 0
Bit 1
Bit 0
0x00= 0 mA, LED1 Disabled, LED2 = Max Flash Current
0x01 = 23.04 mA
0x02 = 34.76 mA
0x03 = 46.48 mA
0x04 = 58.19 mA
...
0x7D = 1476.16 mA
0x7E = 1487.88 mA
0x7F = 1499.60 mA, LED2 Disabled (default)
7.6.8 LED1 Torch Current Control Register (0x07)
LED1 TORCH CURRENT CONTROL REGISTER (0x07)
Bit 7
Torch Pin Enable
Bit
0 = Disabled
(default)
1 = Enabled
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
LED1 Torch Current Level
0x00= 0 mA, LED1 Disabled, LED2 = Max Torch Current
0x01 = 2.53 mA
0x02 = 3.99 mA
0x03 = 5.46 mA
0x04 = 6.92 mA
...
0x7D = 184.17 mA
0x7E = 185.64 mA
0x7F = 187.10 mA, LED2 Disabled (default)
7.6.9 Flags Register1 (0x08)
Bit 7
OVP
0 = Default
Bit 6
NTC TRIP
0 = Default
Bit 5
THERMAL
SHUTDOWN
0 = Default
OVP Fault
NTC Trip Fault
Thermal Shutdown Fault
Over-Current Protection Event Flag
IVFM Flag
UVLO Fault
VOUT Short Fault
Time-Out Flag
Bit 4
OCP
0 = Default
Bit 3
IVFM
0 = Default
Bit 2
UVLO
0 = Default
Bit 1
VOUT SHORT
FAULT
0 = Default
Bit 0
FLASH
TIMEOUT
0 = Default
Over-Voltage Protection tripped. Open Output capacitor or open LED.
NTC Threshold crossed.
LM3646 Die temperature reached thermal shutdown value.
Inductor Current limit value was reached.
IVFM block adjusted LED current.
UVLO Threshold crossed.
VOUT Short detected.
Flash Time-Out detected.
Note: Faults require an I2C read-back of the “Flags Register” to resume operation. Flags report an event occurred, but do not
inhibit future functionality. A read-back of the Flags Register will only get updated again if the fault or flag is still present upon a
restart.
7.6.10 Flags Register2 (0x09)
Bit 7
RFU
Bit 6
SOFTWARE
RESET Bit
0 = Normal
Operation
(Default)
1 = RESET
22
Bit 5
Fault
Shutdown
Enable
0 = Disabled
1 = Enabled
(default)
Bit 4
NTC Short
Fault Enable
Bit 3
LED2 Short
Fault
Bit 2
LED1 Short
Fault
Bit 1
NTC Short
Flag
Bit 0
NTC Open Flag
0 = Disabled
1 = Enabled
(default)
0 = Default
0 = Default
0 = Default
0 = Default
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
LM3646
www.ti.com
Software Reset Bit
Fault Shutdown Enable
NTC Short Fault Enable
LED2 Short Fault
LED1 Short Fault
NTC Short Fault
NTC Open Fault
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
Writing to this bit resets the LM3646 to the default power up conditions. This bit self-clears upon assertion.
When Enabled, faults will force the LM3646 to shutdown. When disabled, faults will not force the LM3646 to
shutdown. The LM3646 protection mechanisms will remain active until the part is manually disabled via the I2C
bus.
When enabled, NTC Short faults will be detected and reported. When disabled, NTC Short faults will not be
detected or reported.
Set to a '1' if LED2 is shorted.
Set to a '1' if LED1 is shorted.
The NTC Short Flag is set if the NTC pin voltage crosses below 100 mV during operation.
The NTC Open Flag is set if the NTC pin voltage crosses above 2.3V during operation.
Note: An I2C readback of the Flags Register2 will clear both the NTC Open and NTC Short Flags.
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
23
LM3646
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
www.ti.com
8 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
The LM3646 can drive two flash LED at currents up to 1.5 A total. The 4-MHz DC/DC boost regulator allows for
the use of small value discrete external components.
8.2 Typical Application
L1
1 µH
VIN
VBATT
C1
2.7V ± 5.5V
10 µF
LM3646
ENABLE
SW
OUT
C2
10 µF
STROBE
µC/µP
TORCH
LED1
TX
LED2
SCL
D2
D1
SDA
TEMP
GND
Figure 36. Typical Application Circuit
24
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
LM3646
www.ti.com
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
Typical Application (continued)
8.2.1 Design Requirements
Example requirements based on default register values:
DESIGN PARAMETER
EXAMPLE VALUE
Input voltage range
2.5 V to 5.5 V
Brightness control
I2C Register
Inductor
1-µH, 3.1-A saturation Current
LED configuration
2 Flash LEDs
Maximum flash brightness
1.5 A
Flash brightness
1.5 A on LED1, LED2 Disabled
8.2.2 Detailed Design Procedure
8.2.2.1 Output Capacitor Selection
The LM3646 is designed to operate with at least a 10-µF ceramic output capacitor. When the boost converter is
running, the output capacitor supplies the load current during the boost converter's on-time. When the NMOS
switch turns off, the inductor energy is discharged through the internal PMOS switch, supplying power to the load
and restoring charge to the output capacitor. This causes a sag in the output voltage during the on-time and a
rise in the output voltage during the off-time. The output capacitor is therefore chosen to limit the output ripple to
an acceptable level depending on load current and input/output voltage differentials and also to ensure the
converter remains stable.
For proper operation the output capacitor must be at least a 10-µF ceramic. Larger capacitors such as a 22-µF or
capacitors in parallel can be used if lower output voltage ripple is desired. To estimate the output voltage ripple
considering the ripple due to capacitor discharge (ΔVQ) and the ripple due to the capacitor's ESR (ΔVESR), use
the following equations:
For continuous conduction mode, the output voltage ripple due to the capacitor discharge is:
ILED x (VOUT - VIN)
'VQ =
fSW x VOUT x COUT
(1)
The output voltage ripple due to the output capacitor's ESR is found by:
'VESR = R ESR x §
©
where
'IL =
I LED x VOUT
VIN
+ 'I L·
¹
VIN x (VOUT - VIN )
2 x f SW x L x VOUT
(2)
In ceramic capacitors the ESR is very low so a close approximation is to assume that 80% of the output voltage
ripple is due to capacitor discharge and 20% from ESR. Table 3 lists different manufacturers for various output
capacitors and their case sizes suitable for use with the LM3646.
8.2.2.2 Input Capacitor Selection
Choosing the correct size and type of input capacitor helps minimize the voltage ripple caused by the switching
of the LM3646 device’s boost converter, and reduces noise on the boost converter's input pin that can feed
through and disrupt internal analog signals. In the Figure 36 a 10-µF ceramic input capacitor works well. It is
important to place the input capacitor as close as possible to the LM3646’s input (IN) pin. This reduces the series
resistance and inductance that can inject noise into the device due to the input switching currents. Table 3 lists
various input capacitors that are recommended for use with the LM3646.
Table 3. Recommended Input/Output Capacitors (X5R Dielectric)
MANUFACTURER
PART NUMBER
VALUE
CASE SIZE
VOLTAGE RATING
TDK Corporation
C1608JB0J106M
10 µF
0603 (1.6 mm × 0.8 mm × 0.8 mm)
6.3V
TDK Corporation
C2012JB1A106M
10 µF
0805 (2.0 mm × 1.25 mm × 1.25 mm)
10V
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
25
LM3646
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
www.ti.com
Table 3. Recommended Input/Output Capacitors (X5R Dielectric) (continued)
MANUFACTURER
PART NUMBER
VALUE
CASE SIZE
VOLTAGE RATING
TDK Corporation
C2012JB0J226M
22 µF
0805 (2.0 mm × 1.25 mm ×1.25 mm)
6.3V
Murata
GRM21BR61A106KE19
10 µF
0805 (2.0 mm × 1.25 mm × 1.25 mm)
10V
Murata
GRM21BR60J226ME39L
22 µF
0805 (2.0 mm × 1.25 mm × 1.25 mm)
6.3V
8.2.2.3 Inductor Selection
The LM3646 is designed to use a 1 µH or 2.2 µH inductor. Table 4 lists various inductors and their
manufacturers that can work well with the LM3646. When the device is boosting (VOUT > VIN) the inductor will
typically be the largest area of efficiency loss in the circuit. Therefore, choosing an inductor with the lowest
possible series resistance is important. Additionally, the saturation rating of the inductor should be greater than
the maximum operating peak current of the LM3646. This prevents excess efficiency loss that can occur with
inductors that operate in saturation and prevents over-heating of the inductor and further efficiency loss. For
proper inductor operation and circuit performance ensure that the inductor saturation and the peak current limit
setting of the LM3646 is greater than IPEAK in the following calculation:
I LOAD VOUT
VIN x (VOUT - VIN)
IPEAK =
K
x
VIN
+ 'IL where 'IL =
2 x f SW x L x VOUT
(3)
where ƒSW = 4 MHz, and efficiency can be found in the Typical Characteristics plots.
Table 4. Recommended Inductors
MANUFACTURER
VALUE
PART NUMBER
DIMENSIONS (L×W×H)
ISAT
RDC
TOKO
1 µH
1286AS-H-1R0N
2.0 mm × 1.6 mm × 1.2 mm
3.1A
68 mΩ
TOKO
1 µH
1285AS-H-1R0M
2.0 mm × 1.6 mm × 1.0 mm
2.7A
80 mΩ
TDK
1 µH
TFM201610G-1R0M-T05
2.0 mm × 1.6 mm × 1.0 mm
2.9A
60 mΩ
8.2.2.4 NTC Thermistor Selection
The TEMP pin is a comparator input for flash LED thermal sensing. NTC Mode is intended to monitor an external
thermistor which monitors LED temperature and prevents LED overheating. An internal comparator checks the
voltage on the TEMP pin against the trip point programmed in the NTC and Torch Ramp Register (0x03). The
thermistor is driven by an internally regulated current source, and the voltage on the TEMP pin is related to the
source current and the NTC resistance. NTC thermistors have a temperature to resistance relationship of:
E
R(T) = R25°C x e
§ 1 - 1·
©T °C+ 273 298¹
(4)
where β is given in the thermistor datasheet and R25°C is the thermistor's value at 125°C.
Table 5. Application Circuit Component List
COMPONENT MANUFACTURER
26
VALUE
PART NUMBER
SIZE
CURRENT/VOLTAGE
RATING (RESISTANCE)
L
TOKO
1 µH
1286AS-H-1R0N
2.0 mm x 1.6 mm x 1.2 mm
ISAT = 3.1 A (68 mΩ)
COUT1,2
Murata
10 µF
GRM188R60J106M
1.6 mm x 0.8 mm x 0.8 mm (0603)
6.3 V
CIN1,2
Murata
10 µF
GRM188R60J106M
1.6 mm x 0.8 mm x 0.8 mm (0603)
6.3 V
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
LM3646
www.ti.com
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
8.2.3 Application Curves
Unless otherwise specified: TA= 25°C; VIN = 3.6 V; VEN = VIN; CIN = 10 µF; COUT = 10 µF; L = 1 µH.
100
100
ILED = 750mA, VLED = 3.5V
90
90
80
80
³LED (%)
³LED (%)
ILED = 1.5A, VLED = 4V
70
TA = +25ºC
60
70
TA = +25ºC
60
TA = -40ºC
TA = -40ºC
TA = +85ºC
50
2.8
3
3.2
3.4
3.6
3.8
4
4.2
4.4
4.6
4.8
VIN (V)
TA = +85ºC
50
2.8
5
3
3.2
3.4
3.6
3.8
Figure 37. Flash LED Efficiency vs. Input Voltage
4.2
4.4
4.6
4.8
5
C028
Figure 38. Flash LED Efficiency vs. Input Voltage
100
100
ILED = 187.5mA, VLED = 3.2V
VIN = 3.7V
90
90
80
80
³LED (%)
³LED (%)
4
VIN (V)
C006
70
TA = +25ºC
60
70
TA = +25ºC
60
TA = -40ºC
TA = -40ºC
TA = +85ºC
50
100
300
500
700
900
1100
1300
ILED (mA)
TA = +85ºC
50
1500
2.8
3.2
3.4
3.6
3.8
4
4.2
4.4
4.6
4.8
VIN (V)
C031
Figure 39. Flash LED Efficiency vs. LED Current
3
5
C007
Figure 40. Torch LED Efficiency vs. Input Voltage
VOUT = 2 V/div
VOUT = 2 V/div
VLED = 2 V/div
VLED = 2 V/div
IIN = 1 A/div
ILED = 1 A/div
IIN = 1 A/div
ILED = 1 A/div
t ± Time Base ± 100 µs/div
t ± Time Base ± 100 µs/div
Figure 42. Flash Ramp-Down
Figure 41. Flash Ramp-Up
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
27
LM3646
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
www.ti.com
Unless otherwise specified: TA= 25°C; VIN = 3.6 V; VEN = VIN; CIN = 10 µF; COUT = 10 µF; L = 1 µH.
VIN = 200 mV/div
VIN = 500 mV/div
VOUT = 200 mV/div
VOUT = 500 mV/div
ILED = 100 mA/div
ILED = 200 mA/div
t ± Time Base ± 40 µs/div
t ± Time Base ± 40 µs/div
Figure 43. Line-step (200 mV) During Flash
Figure 44. Line-step (400 mV) During Flash
VOUT = 200 mV/div
VOUT = 200 mV/div
VIN = 3.3V
VIN = 3.6V
ILED = 1.5A
VLED = 200 mV/div
ILED = 1.5A
VLED = 200 mV/div
IIN = 20 mA/div
IIN = 20 mA/div
ILED = 10 mA/div
ILED = 10 mA/div
t ± Time Base ± 200 ns/div
t ± Time Base ± 200 ns/div
Figure 46. LED Current Ripple
Figure 45. LED Current Ripple
VOUT = 200 mV/div
VOUT = 2 V/div
VIN = 3.3V
ILED = 1 A/div
ILED = 750mA
VLED = 200 mV/div
IFLASH = 1.5A
ITORCH = 187mA
VLED = 2 V/div
IIN = 20 mA/div
IIN = 1 A/div
ILED = 10 mA/div
t ± Time Base ± 200 ns/div
t ± Time Base ± 1 ms/div
Figure 47. LED Current Ripple
28
Figure 48. TX-Mask Event, Default Settings
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
LM3646
www.ti.com
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
Unless otherwise specified: TA= 25°C; VIN = 3.6 V; VEN = VIN; CIN = 10 µF; COUT = 10 µF; L = 1 µH.
VTX = 5 V/div
VTX = 5 V/div
IFLASH = 1.5A
IFLASH = 1.5A
ILED = 1 A/div
ITORCH = 0A
ILED = 1 A/div
ITORCH = 100A
IIN = 1 A/div
IIN = 1 A/div
t ± Time Base ± 1 µs/div
t ± Time Base ± 1 µs/div
Figure 49. TX Signal Low-to-High Transition
Figure 50. TX Signal Low-to-High Transition
VTX = 5 V/div
VIN = 200 mV/div
tFILTER = ¼*t UVLO
IFLASH = 1.5A
tRAMP = 256µs
IIN = 1 A/div
ILED = 500 mA/div
ITORCH = 100A
ILED = 500 mA/div
IIN = 1 A/div
t ± Time Base ± 40 µs/div
t ± Time Base ± 100 µs/div
Figure 51. TX Signal High-to-Low Transition
Figure 52. Input Voltage Flash Monitor, Stop & Hold Mode,
Default settings
VIN = 200 mV/div
VIN = 200 mV/div
tFILTER = ¼*t UVLO
tFILTER = ¼*t UVLO
tRAMP = 256µs
tRAMP = 256µs
VHYST = 50mV
IIN = 1 A/div
IIN = 1 A/div
VHYST = 50mV
ILED = 500 mA/div
ILED = 500 mA/div
t ± Time Base ± 100 µs/div
t ± Time Base ± 100 µs/div
Figure 53. Input Voltage Flash Monitor, Down Mode,
Default Settings
Figure 54. Input Voltage Flash Monitor, Up & Down Mode,
Default Settings
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
29
LM3646
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
www.ti.com
Unless otherwise specified: TA= 25°C; VIN = 3.6 V; VEN = VIN; CIN = 10 µF; COUT = 10 µF; L = 1 µH.
VIN = 200 mV/div
VIN = 200 mV/div
tFILTER = ¼*t UVLO
tFILTER = ¼*t UVLO
IIN = 1 A/div
tRAMP = 256µs
VHYST = 0mV
tRAMP = 256µs
IIN = 1 A/div
VHYST = 100mV
ILED = 500 mA/div
ILED = 500 mA/div
t ± Time Base ± 100 µs/div
t ± Time Base ± 100 µs/div
Figure 55. Input Voltage Flash Monitor, Up & Down Mode,
Figure 56. Input Voltage Flash Monitor, Up & Down Mode,
VIN = 200 mV/div
VIN = 200 mV/div
tFILTER = 256µs
tFILTER = ¼*t UVLO
tRAMP = 256µs
IIN = 1 A/div
VHYST = 50mV
tRAMP = 512µs
VHYST = 50mV
IIN = 1 A/div
ILED = 500 mA/div
ILED = 500 mA/div
t ± Time Base ± 200 µs/div
t ± Time Base ± 100 µs/div
Figure 57. Input Voltage Flash Monitor, Up & Down Mode
Figure 58. Input Voltage Flash Monitor, Up & Down Mode
VTX = 5 V/div
tFILTER = ¼*t UVLO
tRAMP = 256µs
VHYST = 50mV
VIN = 200 mV/div
VSTROBE = 2 V/div
IIN = 1 A/div
ILED = 1 A/div
ILED = 500 mA/div
t ± Time Base ± 400 µs/div
30
t ± Time Base ± 20 ms/div
Figure 59. Input Voltage Flash Monitor, Up & Down Mode
with TX Event
Figure 60. Edge-Sensitive Strobe
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
LM3646
www.ti.com
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
Unless otherwise specified: TA= 25°C; VIN = 3.6 V; VEN = VIN; CIN = 10 µF; COUT = 10 µF; L = 1 µH.
VSTROBE = 2 V/div
VSTROBE = 2 V/div
ILED = 500 mA/div
ILED = 500 mA/div
t ± Time Base ± 20 ms/div
t ± Time Base ± 20 ms/div
Figure 61. Level-Sensitive Strobe without Timeout
Figure 62. Level-Sensitive Strobe with Timeout
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
31
LM3646
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
www.ti.com
9 Power Supply Recommendations
The LM3646 is designed to operate from an input voltage supply range between 2.5 V and 5.5 V. This input
supply must be well regulated and capable to supply the required input current. If the input supply is located far
from the LM3646 additional bulk capacitance may be required in addition to the ceramic bypass capacitors.
10 Layout
10.1 Layout Guidelines
The high switching frequency and large switching currents of the LM3646 make the choice of layout important.
The following steps should be used as a reference to ensure the device is stable and maintains proper LED
current regulation across its intended operating voltage and current range.
1. Place CIN on the top layer (same layer as the LM3646) and as close to the device as possible. The input
capacitor conducts the driver currents during the low-side MOSFET turn-on and turn-off and can see current
spikes over 1 A in amplitude. Connecting the input capacitor through short, wide traces to both the IN and
GND pins will reduce the inductive voltage spikes that occur during switching and which can corrupt the VIN
line.
2. Place COUT on the top layer (same layer as the LM3646) and as close as possible to the OUT and GND pins.
The returns for both CIN and COUT should come together at one point, as close to the GND pin as possible.
Connecting COUT through short, wide traces will reduce the series inductance on the OUT and GND pins that
can corrupt the OUT and GND lines and cause excessive noise in the device and surrounding circuitry.
3. Connect the inductor on the top layer close to the SW pin. There should be a low-impedance connection
from the inductor to SW due to the large DC inductor current, and at the same time, the area occupied by the
SW node should be small to reduce the capacitive coupling of the high dV/dt present at SW that can couple
into nearby traces.
4. Avoid routing logic traces near the SW node to avoid any capacitively coupled voltages from SW onto any
high impedance logic lines such as TORCH, STROBE, ENABLE, TEMP, TX, SDA and SCL. A good
approach is to insert an inner layer GND plane underneath the SW node and between any nearby routed
traces. This creates a shield from the electric field generated at SW.
5. Terminate the Flash LED cathodes directly to the GND pin of the LM3646. If possible, route the LED returns
with a dedicated path to keep the high amplitude LED currents out of the GND plane. For Flash LEDs that
are routed relatively far away from the LM3646, a good approach is to sandwich the forward and return
current paths over the top of each other on two layers. This will help in reducing the inductance of the LED
current paths.
32
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
LM3646
www.ti.com
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
10.2 Layout Example
1 P+
SW
10 PF
VIAs to GND Plane
OUT
IN
GND
SW
OUT
LED1
LED1
GND
SW
OUT
LED1
AGND
TORCH
OUT
LED2
LED2
10 PF
IN
SCL
EN
LED2
TEMP
SDA
STROBE
TX
TEMP
SDA
STROBE
TX
Figure 63. LM3646 Layout
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
33
LM3646
SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014
www.ti.com
11 Device and Documentation Support
11.1 Device Support
11.1.1 Third-Party Products Disclaimer
TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT
CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES
OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER
ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.
11.2 Documentation Support
11.2.1 Related Documentation
For related documentation, see the following:
Texas Instruments Application Note 1112: DSBGA Wafer Level Chip Scale Package (SNVA009).
11.3 Trademarks
All trademarks are the property of their respective owners.
11.4 Electrostatic Discharge Caution
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
11.5 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
34
Submit Documentation Feedback
Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: LM3646
PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LM3646YFQR
ACTIVE
DSBGA
YFQ
20
3000
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-40 to 85
3646
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
工商网监
湘ICP备2023018690号
