TI LM3561

LM3561
LM3561 Synchronous Boost Converter with 600mA High Side LED Driver and I 2
C-Compatible Interface
Literature Number: SNOSB44B
LM3561
Synchronous Boost Converter with 600mA High Side LED
Driver and I2C-Compatible Interface
General Description
The LM3561 is a 2 MHz fixed-frequency, current mode synchronous boost converter. The device is designed to operate
as a single 600mA constant current driver for high-current
white LEDs. The high side current source allows for grounded
cathode LED operation while the 250mV regulated headroom
voltage ensures that the LED current is well regulated and
efficiency remains high.
The main features of the LM3561 include: an I2C-compatible
interface for controlling the LED current, a hardware Flash
enable input for direct triggering of the Flash pulse, dual TX
inputs (TX1 and TX2) which force the Flash pulse into a lowcurrent Torch mode during high battery current instances, an
active high hardware enable (HWEN) allowing for fast hardware shutdown during system software failures, a dual mode
pin which serves as either an indicator LED driver at up to
18mA or as a dedicated comparator input with an internal 1V
reference, designed to monitor the voltage across a negative
temperature coefficient thermistor (NTC), and a programmable input voltage monitor which monitors IN and can
reduce the flash current or shutdown the device during low
battery conditions.
Seven fault flags are available for read back over the I2Ccompatible bus. These include: a flash timeout flag indicating
the flash pulse has reached the end of the programmable
timeout duration, a thermal shutdown flag indicating the
LM3561's die temperature has exceeded 150°C, an LED fault
flag indicating the output voltage has tripped the over-voltage
threshold, or the LED has become shorted, TX1 and TX2 interrupt flags indicating if either of the TX inputs have been
triggered, an NTC flag indicating the LED has experienced an
over temperature condition, and a VIN Monitor flag indicating
the input voltage has fallen below the VIN Monitor threshold.
The LM3561 is available in a tiny (1.215mm × 1.615mm ×
0.6mm) 12-bump micro SMD and operates over the -40°C to
+85°C temperature range.
Features
■ High Side Current Source allowing for Grounded LED
■
■
■
■
■
■
■
■
■
■
■
■
■
Cathode
Up to 90% Efficient
Ultra-Small Solution Size: < 16mm2
Three Operating Modes: Torch, Flash, and LED Indicator
Accurate and Programmable LED Current from 18mA to
600mA
Hardware Flash and Torch Enable
LED Thermal Sensing and Current Scaleback
Software Selectable Input Voltage Monitor
Programmable Flash Timeout
Dual Synchronization Inputs for RF Power Amplifier Pulse
Events
Open and Short LED Detection
Active High Hardware Enable for Protection Against
System Faults
400kHz I2C-compatible Interface
12-Bump (1.215mm × 1.615mm × 0.6mm) micro SMD
Applications
■ Camera Phone LED Flash Controller
■ LED Current Source Biasing
Typical Application Circuits
30113902
30113901
© 2011 National Semiconductor Corporation
301139
Example Layout
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LM3561 Synchronous Boost Converter with 600mA High Side LED Driver and I2C-Compatible
Interface
June 21, 2011
LM3561
Application Circuit Component List
Component
Manufacturer
Value
Part Number
Size (mm)
Rating
L
TDK
1µH
MLP2520-1R0
2x2.5x1.2
1.5A
COUT
Murata
10µF
GRM188R60J106M
1.6×0.8×0.8 (0603)
6.3V
1.6×0.8×0.8 (0603)
6.3V
CIN
Murata
10µF
GRM188R60J106M
LEDs
Lumiled
[email protected]
LXCL-PWF4
1.5A
Connection Diagram
30113903
Pin Descriptions
Pin
Name
A1
GND
A2
IN
A3
HWEN
B1
B2
B3
SW
STROBE
Function
Ground
Input Voltage Connection. Connect IN to the input supply and bypass to GND with a minimum
10µF ceramic capacitor.
Active Low Hardware Reset Input. This input is high impedance and cannot be left floating.
Typically this would be tied to a pullup resistor and to a logic high voltage, or VIN, in order to enable
the LM3561.
Drain Connection for Internal NMOS and Synchronous PMOS Switches
Active High Hardware Flash Enable. Drive STROBE high to turn on the Flash pulse. STROBE has
an internal 300kΩ pulldown to GND.
SCL
Serial Clock Input.
C1
OUT
Step-Up DC/DC Converter Output. Bypass OUT to GND with a 10µF Ceramic Capacitor.
C2
TX1/TORCH/
GPIO
C3
SDA
Serial Data Input/Output.
D1
LED
High Side Current Source Output for Flash LED.
D2
LEDI/NTC
Configurable as a High Side Current Source Output for Indicator LEDs or as a Threshold Detector
for LED Temperature Sensing.
D3
TX2/GPIO2/INT
Configurable as a Flash Interrupt Input, a Programmable General Purpose Logic Input/Output, or
as an Interrupt output for fault notification. This pin has an internal 300kΩ pulldown to GND.
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Configurable as a Flash Interrupt Input, a Hardware Torch Enable, or a Programmable General
Purpose Logic Input/Output. This pin has an internal 300kΩ pulldown to GND.
2
LM3561
Ordering Information
Package
Top Marking
2 Lines: First line XY, where X is the
single digit date code and Y is the die
run code, Second line has the letters
DV
LM3561TME
TMD12AAA
XY
250 units, Tape-and-Reel
LM3561TMX
TMD12AAA
XY
3000 units, Tape-and-Reel
Order Number
3
Supplied As
No-Lead
YES (NOPB)
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LM3561
Absolute Maximum Ratings (Note 1, Note
Operating Ratings
VIN
Junction Temperature (TJ)
Ambient Temperature (TA)
(Note 5)
2)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
VIN, VSW, VOUT
VSCL, VSDA, VHWEN, VSTROBE, VTX1,
VTX2, VLED, VLEDI/NTC
-0.3V to 6V
-0.3V to (VIN
+0.3V) w/ 6.0V
max
Internally Limited
+150°C
-65°C to +150°C
Continuous Power Dissipation(Note 3)
Junction Temperature (TJ-MAX)
Storage Temperature Range
Maximum Lead Temperature
(Soldering)
(Note 1, Note 2)
2.5V to 5.5V
-40°C to +125°C
-40°C to +85°C
Thermal Properties
Junction-to-Ambient Thermal
Resistance (θJA), TMD12
Package(Note 6)
68°C/W
(Note 4)
ESD Caution Notice
National Semiconductor recommends that all integrated circuits be handled with appropriate
ESD precautions. Failure to observe proper ESD handling techniques can result in damage to the device.
Electrical Characteristics
Limits in standard typeface are for TA = +25°C. Limits in boldface type apply over the full operating ambient temperature range
(-40°C ≤ TA ≤ +85ºC). Unless otherwise specified, VIN = 3.6V, VHWEN = VIN. (Note 2, Note 7)
Symbol
Parameter
Conditions
Min
Typ
Max
-40C ≤ TA ≤
+85C
-5%
600
+6%
TA = +25C
-3%
600
+6%
-10%
18
+10%
Units
Current Source Specifications
600mA Flash LED
Setting, VOUT = 4.5V,
ILED
Current Source Accuracy
3V ≤ VIN ≤ 4.2V
18mA Torch Current Setting, VOUT = 4.5V,
3V ≤ VIN ≤ 4.2V
VHR
Current Source Regulation
600mA setting, VOUT = 4.5V
Voltage (VOUT - VLED)
240
mA
mV
Step-Up DC/DC Converter Specifications
VOVP
Output Over-Voltage
Protection Trip Point(Note
8)
On Threshold
4.90
5
Off Threshold
4.88
5.05
V
RPMOS
PMOS Switch OnResistance
IPMOS = 500mA
270
mΩ
RNMOS
NMOS Switch OnResistance
INMOS = 500mA
250
mΩ
ICL
Switch Current Limit(Note
9)
IOUT_SC
Output Short Circuit
Current Limit
ILED/NTC
Indicator Current
VTRIP
fSW
Comparator Trip Threshold
Switching Frequency
tTIMEOUT(Note
Timeout Duration
10), (Note 11)
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3.0V ≤ VIN ≤ 4.2V
Flash Duration
Register Bit [5] =
0
0.88
Flash Duration
Register Bit [5] =
'1'
1.35
1
1.12
A
VOUT < 2.3V
1.5
1.65
200
Indicator Register = 0xFF, VLEDI/NTC = 2V,
mA
16
18
20
mA
≤ VIN ≤ 4.2V
0.97
1
1.03
V
2.7V ≤ VIN ≤ 5.5V
1.8
2
2.2
MHz
2.7V ≤ VIN ≤ 5.5V
-10
+10
%
2.7V ≤ VIN ≤ 4.2V
Configuration Register 1 Bit [4] = '1', 3.0V
4
Parameter
IQ
Quiescent Supply Current
into IN
Conditions
Min
Typ
Device Not Switching
676
Device Switching
1140
Indicate Mode, Indicator Register = 0x07
560
Max
Units
µA
ISHDN
Shutdown Supply Current
2.7V ≤ VIN ≤ 5.5V, HWEN = GND
0.02
1
µA
ISTBY
Standby Supply Current
2.7V ≤ VIN ≤ 5.5V, HWEN = IN, Enable
Register bit [1:0] = 00
1.1
2.3
µA
Flash-to-Torch LED
Current Settling Time
TX_ Low-to-High, ILED = 600mA to
93.2mA
2
Torch-to-Flash LED
Current Settling Time
TX_ Low-to-High, ILED = 93.2mA to
600mA
80
VIN Monitor Trip Threshold
VIN Falling, VIN Monitor Register = 0x01
(Enabled with VIN_TH = 2.9V)
tTX
VIN_TH
µs
2.84
2.90
2.95
V
HWEN, STROBE, TX1/TORCH/GPIO1, TX2/INT/GPIO2 Voltage Specifications
VIL
Input Logic Low
2.7V ≤ VIN ≤ 5.5V
0
0.4
V
VIH
Input Logic High
2.7V ≤ VIN ≤ 5.5V
1.2
VIN
V
VOL
Output Logic Low
(GPIO1,GPIO2, INT)
ILOAD = 3mA, 2.7V ≤ VIN ≤ 5.5V
0.4
V
RTX1
Internal Pulldown
Resistance at TX1/
TORCH/GPIO1
300
kΩ
RTX2
Internal Pulldown
Resistance at TX2/GPIO2
300
kΩ
Internal Pulldown
Resistance at STROBE
300
kΩ
RSTROBE
I2C-Compatible Voltage Specifications (SCL, SDA)
VIL
Input Logic Low
2.7V ≤ VIN ≤ 5.5V
0
0.4
V
VIH
Input Logic High
2.7V ≤ VIN ≤ 5.5V
1.3
VIN
V
VOL
Output Logic Low (SDA)
ILOAD = 3mA, 2.7V ≤ VIN ≤ 5.5V
400
mV
I2C-Compatible Timing Specifications (SCL, SDA) (Note 10) see Figure 1
fSCL
0
400
kHz
Rise Time of Both SDA and
tRISE(Note 12)
SCL
20 + 0.1 ×
CBUS
300
ns
Fall Time of Both SDA and
SCL
20 + 0.1 ×
CBUS
300
ns
tFALL(Note 12)
SCL(Clock Frequency)
tLOW
Low Period of SCL Clock
1.3
µs
tHIGH
High Period of SCL Clock
600
ns
tHD;STA
Hold Time for Start (or
Repeated Start) Condition
600
ns
tSU;STA
Set-up Time for a Repeated
Start
600
ns
tHD;DAT
Data Hold Time
0
ns
tSU;DAT
Data Setup Time
100
ns
tSU;STO
Set-up Time for Stop
Condition
600
ns
tVD;DAT
Data Valid Time
900
ns
tVD;ACK
Data Valid Acknowledge
Time
900
ns
tBUF
Bus Free Time Between a
Start and a Stop Condition
1.3
5
µs
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LM3561
Symbol
LM3561
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of
the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see
the Electrical Characteristics table.
Note 2: All voltages are with respect to the potential at the GND pin.
Note 3: Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ=150ºC (typ.) and disengages at
TJ=135ºC (typ.).
Note 4: For detailed soldering specifications and information, please refer to National Semiconductor Application Note 1112: Micro SMD Wafer Level chip Scale
Package (AN-1112)
Note 5: 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 = +125ºC), 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 (θJA), as given by the
following equation: TA-MAX = TJ-MAX-OP – (θJA × PD-MAX).
Note 6: Junction-to-ambient thermal resistance (θJA) is taken from a thermal modeling result, performed under the conditions and guidelines set forth in the
JEDEC standard JESD51-7. The test board is a 4-layer FR-4 board measuring 102mm x 76mm x 1.6mm with a 2x1 array of thermal via's. The ground plane on
the board is 50mm x 50mm. Thickness of copper layers are 36µm/18µm/18µm/36µm (1.5oz/1oz/1oz/1.5oz). Ambient temperature in simulation is 22°C, still air.
Power dissipation is 1W.
Note 7: Min and Max limits are guaranteed by design, test, or statistical analysis. Typical (Typ) numbers are not guaranteed, but do represent the most likely
norm. Unless otherwise specified, conditions for typical specifications are: VIN = 3.6V and TA = +25°C.
Note 8: The typical curve for Over-Voltage Protection (OVP) is measured in closed loop using the typical application circuit . The OVP value is found by forcing
an open circuit in the LED current path and recording the peak value of VOUT. The value given in the Electrical Table is found in an open loop configuration by
ramping the voltage at OUT until the OVP comparator trips. The closed loop data can appear higher due to the stored energy in the inductor being dumped into
the output capacitor after the OVP comparator trips. This results in an open circuit condition where the output voltage can continue to rise after the OVP comparator
trips by approximately IIN×sqrt(L/COUT).
Note 9: The typical curve for Current Limit is measured in closed loop using the typical application circuit by increasing IOUT until the peak inductor current stops
increasing. The value given in the Electrical Table is measured open loop and is found by forcing current into SW until the current limit comparator threshold is
reached. Closed loop data appears higher due to the delay between the comparator trip point and the NFET turning off. This delay allows the closed loop inductor
current to ramp higher after the trip point by approximately 40ns × VIN/L
Note 10: Guaranteed by design. Not production tested.
Note 11: The timeout duration period is a divided down representation of the 2MHz clock and thus the accuracy spec. is the same as the switching frequency.
This accuracy spec. applies to all settings in Table 8.
Note 12: Min rise and fall times on SDA and SCL can typically be less than 20ns.
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6
LM3561
I2C Timing
301139119
FIGURE 1. I2C Timing
7
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LM3561
Typical Performance Characteristics VIN = 3.6V, LEDs are Lumiled PWF-4, COUT = 10µF, CIN = 10µF,
L = MLP2520-1R0 (1µH, RL = 0.085Ω), TA = +25°C unless otherwise specified.
LED Efficiency vs VIN
Flash Brightness Codes (1111 - 1100)
(Typical Application Circuit)
LED Efficiency vs VIN
Flash Brightness Codes (1011 - 1000)
(Typical Application Circuit)
30113954
30113953
LED Efficiency vs VIN
Flash Brightness Codes (0111 - 0100)
(Typical Application Circuit)
LED Efficiency vs VIN
Flash Brightness Codes (0011 - 0000)
(Typical Application Circuit)
30113952
30113951
LED Current vs VIN
Flash Brightness Codes (1111 - 1100)
LED Current vs VIN
Flash Brightness Codes (1011 - 1000)
30113950
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30113949
8
LM3561
LED Current vs VIN
Flash Brightness Codes (0111 - 0100)
LED Current vs VIN
Flash Brightness Codes (0011 - 0000)
30113948
30113947
Shutdown Current vs VIN
( VHWEN = GND)
Shutdown Current vs VIN
( VHWEN = VIN)
30113957
30113958
Indicator Current vs Headroom Voltage (VIN - VLED)
Indicator Brightness Codes (111 - 100)
Indicator Current vs Headroom Voltage (VIN - VLED)
Indicator Brightness Codes (011 - 000)
30113956
30113955
9
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LM3561
Startup into Flash Mode
Max Flash Setting
Torch Mode to Flash Mode Transition
Torch Brightness Code (100)
Flash Brightness Code (111)
30113961
30113963
TX Interrupt Operation
Torch Brightness Code (100)
Flash Brightness Code (111)
Line Transient
Flash Brightness Code (111)
30113962
30113960
HWEN Operation
NTC Mode Response
Flash Brightness Code (111)
Circuit of Figure 15
(R(T) = 10kΩ (@+25°C), RBIAS = 1.3kΩ, VBIAS = 1.2V)
30113959
30113965
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10
LM3561
VIN Monitor Response
Flash Brightness Code (111)
3.0V Setting
30113964
11
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LM3561
Block Diagram
30113905
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12
OVERVIEW
The LM3561 is a high power white LED flash driver capable
of delivering up to 600mA of LED current into a single white
LED. The device incorporates a 2MHz constant frequency,
synchronous boost converter, and a high side current source
to regulate the LED current over the 2.5V to 5.5V input voltage
range.
When the LM3561 is enabled and the output voltage is greater
than VIN – 150mV, the PWM converter switches and maintains at least 250mV (VHR) across the current source (VOUT VLED). This minimum headroom voltage ensures that the
current sinks remain in regulation. When the input voltage is
above VLED + VHR the device operates in pass mode with the
device not switching and the PFET on continuously. In pass
mode the difference between (VIN - ILED×RON_P) and VLED is
dropped across the current source. If the device is operating
in pass mode and VIN drops to a point that forces the device
into switching, the LM3561 will make a one-time decision to
jump into switching mode. The LM3561 remains in switching
mode until the device is shutdown and re-enabled. This is true
even if VIN were to rise back above VLED + 250mV during the
active Flash or Torch cycle. This prevents the LED current
from oscillating back and forth between pass and boost mode
when VIN is close to VOUT.
The main features of the LM3561 include: dual TX inputs (TX1
and TX2) for forcing the device into a lower current state during high battery current conditions, a hardware flash enable
input (STROBE), an active low shutdown input (HWEN), an
input voltage monitor for detecting low battery voltage conditions, and a dual function pin that can be configured as a low
power indicator LED current source or as a comparator input
for LED thermal sensing via an external NTC thermistor.
Control of the LM3561 is done via an I2C-compatible interface. This includes: adjustment of the LED current in TORCH
and FLASH mode, adjustment of the indicator LED current,
programming the flash LED current timeout duration, and
programming of the switch current limit. Additionally, there are
7 flag bits that can be read back indicating that the programmed flash current timeout has expired, a device over
temperature condition has happened, an LED failure (open or
short), an LED thermal failure (tripping of the internal NTC
comparator), an input under voltage fault (VIN Monitor), and
a separate flag for each TX input.
OVER-VOLTAGE PROTECTION
The output voltage is limited to typically 5V (4.9V min). In situations such as the current source open, the LM3561 will
raise the output voltage in order to try and keep the LED current at its target value. When VOUT reaches 5V, the overvoltage comparator will trip and turn off both the internal NFET
and PFET switches. When VOUT falls below 4.8V (typical) the
LM3561 will begin switching again.
CURRENT LIMIT
The LM3561 features 2 selectable current limits — 1A and
1.5A. These are selectable through the I2C-compatible interface via bit [5] of the Flash Duration Register. When the
current limit is reached the LM3561 stops switching for the
remainder 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 situations where there could potentially be
large load currents at OUT, and the LM3561 is operating in
Pass mode, the load current must be limited to 1.5A. In Boost
mode or Pass mode if VOUT falls below approximately 2.3V
the part stops switching and the PFET operates as a current
source limiting the current to typically 200mA. This prevents
damage to the LM3561 and excessive current draw from the
battery during output short circuit conditions.
THERMAL SHUTDOWN
The LM3561 features a thermal shutdown threshold of typically +150°C. When the die temperature reaches +150°C, the
active current source (LED) will shutdown, and the TSD flag
in the Flags register is written high. The device cannot be
started up again until the Flags register is read back. Once
the Flags register is read back the current source can be reenabled into Torch, or Flash Mode. The thermal shutdown
(TSD) circuitry has an internal 250µs de-glitch timer which
helps prevent unwanted noise from falsely triggering a TSD
event. However, when the LM3561 is in boost mode at higher
flash currents, the de-glitch timer can get reset by the high
currents in the LM3561's GND. As a result the thermal
shutdown's internal de-glitch timer can get reset before the
TSD event can get latched in. This causes a TSD event to not
get triggered until the LM3561's flash pulse reaches the end
of the flash duration, when the noisy currents have dropped
to a lower level. However, once the noise is lower and a TSD
event is triggered, the next flash pulse is not allowed until the
flags register is read back. In pass mode the boost switcher
is off and the lower noise environment allows the devices TSD
circuitry to shutdown immediately when the die temperature
reaches +150°C.
STARTUP
Turn on of the LM3561 via the I2C-compatible interface is
done through bits [1:0] of the Enable Register. The device can
be enabled in either Indicate mode, Torch mode, or Flash
mode (see Table 2). On startup in Flash or Torch mode, when
VOUT is less than VIN, the internal synchronous PFET turns on
as a current source and delivers typically 200mA to the output
capacitor. During this time the flash LED current source (LED)
is off. When the voltage across the output capacitor reaches
2.3V the current source can turn on. At turn-on, the current
source steps through each FLASH and TORCH level until the
target LED current is reached (32µs/step). This gives the device a controlled turn-on and limits inrush current from the
VIN supply.
FLASH MODE
In Flash mode the LED current source (LED) provides 16 different current levels from typically 36mA to 600mA. The Flash
currents are set by writing to bits [3:0] of the Flash Brightness
Resister. Flash mode is activated by either writing a (1, 1) to
bits [1:0] of the Enable Register, 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
PASS MODE
On turn on, when the output voltage charges up to ( VIN – 150
mV), the LM3561 will decide if the part operates in Pass Mode
or Boost mode. If the voltage difference between VOUT and
VLED is less than 250mV, the device will transition into Boost
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LM3561
Mode. If the difference between VOUT and VLED is greater than
250mV, the device will operate in Pass Mode. In Pass Mode
the boost converter stops switching and the synchronous
PFET turns fully on, bringing VOUT up to (VIN – IIN×RPMOS)
where (RPMOS = 240mΩ). In Pass Mode the inductor current
is not limited by the peak current limit. In this situation the
output current must be limited to 1.5A.
Circuit Description
LM3561
by stepping through all Torch and Flash levels (32µs/step)
until the programmed current is reached.
Hardware Torch Mode
With Configuration Register 1 Bit [7] = '1', TX1/TORCH/
GPIO1 is configured as a hardware Torch mode enable. In
this mode (TORCH mode), a high at TORCH turns on the LED
current at the programmed Torch current setting. The
STROBE input and I2C Enabled flash take precedence over
TORCH mode. In hardware torch mode, both the LED current
source will turn off after a flash event and Configuration Register 1 Bit [7] will be reset to '0'. In this situation, to re-enter
torch mode via hardware torch, the hardware torch enable bit
(Configuration Register 1 Bit [7] must be reset to '1'). , , and
detail the functionality of the TX1/TORCH input.
FLASH TERMINATION
Bit [2] of the Enable Register determines how the Flash pulse
terminates. With this bit = '1' the Flash current pulse will only
terminate by reaching the end of the Flash timeout period (see
Figure 6). With STR = '0', Flash mode can be terminated by
pulling STROBE low, programming bits [1:0] of the Enable
Register with (0,0), or by allowing the Flash timeout period to
elapse (see Figure 5). If STR = '0' and STROBE is toggled
before the end of the Flash timeout period, the timeout period
resets on the rising edge of STROBE. See LM3561 Timing
Diagrams regarding the Flash pulse termination for the different STR bit settings.
After the Flash pulse terminates, either by a flash timeout,
pulling STROBE low, or disabling it via the I2C-compatible interface, the current source (LED) turns completely off. This
happens even when Torch is enabled via the I2C-compatible
interface and the Flash pulse is turned on by toggling
STROBE. After a Flash event ends (bits [1:0] of the Enable
Register are automatically re-written with (0, 0).
GPIO1 Mode
With GPIO Register bit[0] = '1', the TX1/TORCH/GPIO1 pin is
configured as a general purpose I/O. In GPIO1 mode this pin
can be either a logic input or a logic output depending on the
bit settings in bits [2:1] of the GPIO Register (see Table 4).
FLASH PULSE INTERRUPT (TX2), GENERAL PURPOSE
I/O (GPIO2), AND INTERRUPT OUTPUT (INT)
The TX2/GPIO2/INT pin has a triple function: either a flash
interrupt input (TX2), a general purpose I/O (GPIO2), or as an
interrupt output (INT).
FLASH TIMEOUT
The Flash timeout period sets the maximum duration of the
flash current pulse. Bits [4:0] of the Flash Duration Register
programs the 32 different Flash timeout levels in steps of
32ms, giving a Flash timeout range of 32ms to 1024ms (see
Table 8).
Flash Interrupt (TX2 Mode)
In TX2 mode (default), TX2 is a flash pulse interrupt input.
This is designed to force the flash pulse into a lower current
state in order to reduce the current pulled from the battery
during high battery current situations. For example, when the
LM3561 is engaged in a Flash event, and TX2 is pulled high
(active high polarity, the current source (LED) is forced into
torch mode at the programmed Torch current setting. If TX2
is then pulled low before the flash pulse terminates, the LED
current will step back to the previous flash current level. At the
end of the flash timeout, whether the TX2 pin is high or low,
the LED current will turn off. In addition to forcing torch mode
with a TX2 event, the TX2 input can be set to force shutdown.
Configuration Register 2 bit[0] sets this mode (see Table
11). In TX2 shutdown mode, a TX2 event will shut down the
flash pulse. Once shut down, the flash pulse must be re-enabled via STROBE or the flash enable bits in the Enable
Register.
TORCH MODE
In Torch mode the current source (LED) provides 8 different
current levels (see Table 6). The Torch currents are adjusted
by writing to bits [2:0] of the Torch Brightness Register. Torch
mode is activated by setting Enable Register bits [1:0] to (1,
0). Once the Torch mode is enabled the current sources will
ramp up to the programmed Torch current level by stepping
through all of the Torch currents at (32µs/step) until the programmed Torch current level is reached.
FLASH PULSE INTERRUPT (TX1), HARDWARE TORCH
INPUT (TORCH) AND GENERAL PURPOSE I/O (GPIO1)
The TX1/TORCH/GPIO1 input has a triple function; either as
a flash pulse interrupt (TX1), a hardware torch mode enable
(TORCH), or as a general purpose I/O (GPIO1).
TX2 Forcing Shutdown
TX2 also has the capability to force shutdown (see Figure 7).
When bit [0] of Configuration Register 2 is set to a '1', TX2 will
force shutdown when active. For example, if TX2 is configured for TX2 mode with active high polarity, and bit [0] of
Configuration Register 2 is set to '1' then when TX2 is driven
high, (LED) will be forced into shutdown. Once the current
source is forced into shutdown by activating TX2, the current
source can only be re-enabled in flash mode if TX2 is pulled
low, and the Flags register is read back. If only the Flags register is read back and TX2 is kept high, the device will be reenabled into torch mode and not shutdown. This occurs
because the TX2 shutdown feature is an edge-triggered
event. With active high polarity the TX2 shutdown requires a
rising edge at TX2 in order to force the current source back
into shutdown. Once shut down, it takes a read back of the
flags Register and another rising edge at TX2 to force shut
down again.
Flash Interrupt (TX1)
With Configuration Register 1 Bit [7] = '0' (default), TX1/
TORCH/GPIO1 is a flash pulse interrupt input. This is designed to force the flash pulse into a lower current state in
order to reduce the current pulled from the battery during high
battery current situations. For example, when the LM3561 is
engaged in a Flash event and TX1 is pulled high (active high
polarity) the current source (LED) is forced into Torch mode
at the programmed Torch current setting. If TX1 is then pulled
low before the Flash pulse terminates, the LED current will
ramp back to the previous Flash current level. At the end of
the Flash timeout, whether TX1 is high or low, the LED current
will turn off.
TX1 Polarity
In TX1 mode, TX1 can be programmed as an active low TX1
input where pulling TX1 to GND will cause a TX1 event. TX1
polarity inversion is done via Configuration Register 1 bit [5].
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TX2 Polarity
In TX2 mode (default), TX2 is a flash pulse interrupt input.
This is designed to force the flash pulse into a lower current
state in order to reduce the current pulled from the battery
14
VTRIP. With Configuration Register 2 bit [1] = '1' the device will
shut down the current source (LED) when VLEDI/NTC falls below VTRIP. When the LM3561 is forced from Flash to Torch,
normal LED operation (during the same Flash pulse) can only
be re-started by reading from the Flags Register and ensuring
the voltage at VLEDI/NTC is above VTRIP. When VLEDI/NTC falls
below VTRIP and the Flags register is cleared, the LM3561 will
go through a 250µs deglitch time before the flash current falls
to either torch mode or goes into shutdown. This deglitch time
prevents noise from inadvertently tripping the NTC comparator. For a more detailed description of this mode and designing the NTC circuit (see NTC THERMISTOR SELECTION
section in the Applications Information section of this
datasheet).
In NTC mode the NTC flag (see Flags Register and Fault Indicators section) can be output on the TX2/GPIO2/INT pin.
This is accomplished by making the TX2/GPIO2/INT an interrupt output (see Interrupt Output Mode section).
GPIO2 Mode
The TX2/GPIO2/INT pin is configured as a general purpose
logic input/output by setting GPIO Register bit[3] = '1'. In
GPIO2 mode this pin can be either a logic input or output depending on the bit settings for GPIO Register bit [4] (see Table
4).
ALTERNATE EXTERNAL TORCH (AET MODE)
With Configuration Register 2 bit [2] set to '1' the operation of
TX1/TORCH becomes dependent on its occurrence relative
to STROBE. In this mode if TX1/TORCH goes high first, followed by STROBE going high, the LEDs are forced into torch
mode with no timeout. In this mode if TX1/TORCH goes high
after STROBE has gone high, then the TX1/TORCH pin operates as a normal flash interrupt, and the LEDs will turn off
at the end of the timeout duration. (See LM3561 Timing Diagrams: Figure 9 and Figure 10). AET mode is can only be
used with STROBE configured as a level sensitive input.
Configuring STROBE for edge sensitive operation (STR bit =
1), will force TX1 to act as a simple flash interrupt.
Interrupt Output Mode
The TX2/GPIO2/INT pin is configured as an interrupt output
by setting the TX2/GPIO2/INT as a GPIO output and setting
bit [6] of the GPIO register to '1'. When in INT mode, the TX2/
GPIO2/INT pin will pull low when either of the following occur:
1. The LM3561 is in NTC Mode, the LED current source is
enabled, and VNTC falls below VTRIP.
2. The LM3561's Input Voltage Monitor is enabled and VIN
falls below VIN_TH.
INDICATOR LED/THERMISTOR (LEDI/NTC)
The LEDI/NTC pin serves a dual function, either as an LED
indicator driver or as a threshold detector for a negative temperature coefficient (NTC) thermistor circuit.
INPUT VOLTAGE MONITOR
The LM3561 has an internal comparator that monitors the
voltage at IN and can force the LED current into torch mode
or into shutdown if VIN falls below the programmable VIN
Monitor Threshold (VIN_TH). Bit [0] in the VIN Monitor register
enables or disables this feature. When enabled, Bits [2:1]
program the 4 adjustable thresholds of 2.9V, 3V, 3.1V, and
3.2V. Bit [3] in Configuration Register 2 selects whether an
under-voltage event forces Torch mode or forces the LED
current source off. (See Table 5 and Table 11.)
When the VIN Monitor is active and VIN falls below the programmed threshold (VIN_TH) the LEDs will either turn off or
their current will be reduced to the programmed Torch current
setting. To reset the LED current to its previous level, two
things must occur. First, VIN must go above VIN_TH, and the
Flags register must be read back.
In VIN Monitor mode the VIN Monitor Flag (see Flags Register
and Fault Indicators section) can be output on the TX2/
GPIO2/INT pin. This is accomplished by making the TX2/
GPIO2/INT an interrupt output (see Interrupt Output Mode
section).
Led Indicator Mode (LEDI)
LEDI/NTC is configured as an LED indicator driver by setting
Configuration Register 1 bit [4] = '0' (default). The indicator
current source is enabled by setting Enable Register bits [1:0]
= '01'. In Indicator mode there are 8 different current levels
available (2.25mA - 18mA) which are programmed through
the Indicator Register (see Table 3).
Led Thermal Comparator (NTC Mode)
Writing a '1' to Configuration Register 1 bit [4] disables the
indicator current source and configures LEDI/NTC as a comparator input for monitoring an NTC thermistor circuit. In this
mode LEDI/NTC becomes the negative input of an internal
comparator, with the positive input internally connected to an
internal reference (VTRIP = 1V). Additionally, Configuration
Register 2 bit [1] determines the action NTC Mode takes if the
voltage at LEDI/NTC falls below VTRIP . With Configuration
register 2 bit [1] = '0', the LED current source will be forced
into Torch mode when the voltage at LEDI/NTC falls below
15
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LM3561
during high battery current situations. For example, when the
LM3561 is engaged in a Flash event and TX2 is pulled high
(active high polarity) the current source (LED) is forced into
torch mode at the programmed Torch current setting. If TX2
is then pulled low before the flash pulse terminates, the LED
current will step back to the previous flash current level. At the
end of the flash timeout, whether the TX2 pin is high or low,
the LED current will turn off. In addition to forcing torch mode
with a TX2 event, the TX2 input can be set to force shutdown.
Configuration Register 2 bit[0] sets this mode (see Figure 8).
In TX2 shutdown mode, a TX2 event will shutdown the flash
pulse. Once shut down, the flash pulse must be re-enabled
via STROBE or the flash enable bits in the Enable Register.
LM3561
LM3561 Timing Diagrams
30113937
FIGURE 2. Torch to Flash Operation
30113938
FIGURE 3. TX Event During a Flash Pulse (TX1/TORCH is an Active High TX Input)
30113939
FIGURE 4. TX Event Before and After a Flash Event (TX1/TORCH is an Active High TX Input)
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LM3561
30113940
FIGURE 5. STROBE Input is Level Sensitive (Enable Register Bit [2] = '0')
30113941
FIGURE 6. STROBE Input is Edge Sensitive (Enable Register Bit [2] = '1')
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LM3561
30113942
FIGURE 7. TX2 Configured as an Active High Flash Interrupt and Set to Force Shutdown
30113943
FIGURE 8. TX2 Configured as an Active Low TX Input and Set to Force Torch Mode
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LM3561
30113944
FIGURE 9. Alternate External Torch Mode
(TX1/TORCH Turns on Before STROBE; when TX1/TORCH goes low, Flash mode is initiated)
30113945
FIGURE 10. Alternative External Torch Mode
(STROBE Goes High Before TX1/TORCH, Same as Normal TX1 Operation)
30113946
FIGURE 11. TX1/TORCH Pin is Configured as a Hardware Torch Input
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LM3561
LED short threshold of 500mV (typical) to when the fault flag
is valid. There is a 2µs delay from when the LEDF flag is valid
on an LED open. This delay is the time between when the
OVP threshold is triggered and when the fault flag is valid.
The LEDF flag can only be reset to (0) by pulling HWEN low,
removing power to the LM3561, or reading the Flags Register.
Flags Register and Fault Indicators
The Flags Register contains the Interrupt and Fault indicators.
Seven flags are available in the Flags Register. These include
a Flash Timeout flag (TO), a Thermal Shutdown flag (TSD) ,
an LED Failure flag (LEDF) , an LED Thermal flag (NTC), and
a VIN Monitor flag. Additionally, two interrupt flag bits TX1
interrupt and TX2 interrupt indicate a change of state of the
TX1/TORCH pin (TX1 mode) and TX2/GPIO2/INT pin (TX2
mode) . Reading back a '1' indicates the TX lines have
changed state since the last read of the Flags Register. A read
of the Flags Register resets the flag bits.
LED THERMAL FAULT
The NTC flag (bit [5] of the Flags Register) reads back a '1' if
the LM3561 is active in Flash or Torch mode, the device is in
NTC mode, and the voltage at LEDI/NTC has fallen below
VTRIP (1V typical). When this has happened and the LM3561
has been forced into Torch or LED shutdown, depending on
the state of Configuration Register 2 bit [1], the voltage at LEDI/NTC must rise above the VTRIP threshold and the Flags
Register must be read in order to place the device back in
normal operation. (see Led Thermal Comparator (NTC
Mode) section for more details).
FLASH TIMEOUT
The Flash Timeout Flag (TO), (bit [0] of the Flags Register)
reads back a '1' if the LM3561 is active in Flash Mode and the
timeout period expires before the flash pulse is terminated.
The flash pulse can be terminated before the timeout period
expires by pulling the STROBE pin low (with STR bit '0'), or
by writing a ‘0’ to bits [1:0] of the Enable Register. The TO flag
is reset to (0) by pulling HWEN low, removing power to the
LM3561, reading the Flags Register, or when the next Flash
pulse is triggered.
INPUT VOLTAGE MONITOR FAULT
The VIN Monitor Flag (bit [7] of the Flags Register) reads back
a '1' when the Input Voltage Monitor is enabled and VIN falls
below the programmed (VIN_TH). The input voltage must rise
above VIN_TH and the Flags register must be read back in order to resume normal operation after the LED current has
been forced to Torch mode or turned off due to a VIN Monitor
event.
THERMAL SHUTDOWN
When the LM3561’s die temperature reaches +150°C the
boost converter shuts down and the NFET and PFET turn off.
Additionally, both current sources (LED and LEDI/NTC) turn
off. When the thermal shutdown threshold is tripped a '1' gets
written to bit [1] of the Flag Register (Thermal Shutdown bit).
The LM3561 will start up again when the die temperature falls
to below +135°C, the Flags Register is read back, and the
device is re-enabled.
TX1 AND TX2 INTERRUPT FLAGS
The TX1 and TX2 interrupt flags (bits [3] and [4] of the Flags
register) indicate a TX event on the TX1 or TX2 pins. Bit 3 will
read back a '1' if TX1/TORCH is in TX1 mode and the pin has
changed from low to high since the last read of the Flags
Register. Bit [4] will read back a '1' if TX2 is in TX2 mode and
the pin has had a TX event since the last read of the Flags
Register. A read of the Flags Register automatically resets
these bits.
A TX event can be either a high to low transition or a low to
high transition depending on the setting of the TX1 or TX2
polarity bits (see Table 10).
LED FAULT
The LED Fault flag (bit 2 of the Flags Register) reads back a
'1' if the part is active in Flash or Torch mode and the current
source (LED) experiences an open or short condition. An LED
open condition is signaled if the OVP threshold is crossed at
OUT. An LED short condition is signaled if the voltage at LED
goes below 500mV.
There is a delay of 250µs before the LEDF flag is valid on a
LED short. This is the time from when VLED falls below the
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20
LM3561
I2C-Compatible Interface
START AND STOP CONDITIONS
The LM3561 is controlled via an I2C-compatible interface.
START and STOP conditions classify the beginning and end
of the I2C session. A START condition is defined as SDA
transitioning from HIGH to LOW while SCL is HIGH. A STOP
condition is defined as SDA transitioning from LOW to HIGH
while SCL is HIGH. The I2C master always generates the
START and STOP conditions.
30113918
FIGURE 12. Start and Stop Sequences
The I2C bus is considered busy after a START condition and
free after a STOP condition. During data transmission the
I2C master can generate repeated START conditions. A
START and a repeated START condition are equivalent function-wise. The data on SDA must be stable during the HIGH
period of the clock signal (SCL). In other words, the state of
SDA can only be changed when SCL is LOW. Figure 1 and
Figure 13 show the SDA and SCL signal timing for the I2Ccompatible Bus. See the Electrical Characteristics Table for
timing values.
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LM3561
301139119
FIGURE 13. I2C-Compatible Timing
I2C-COMPATIBLE CHIP ADDRESS
The 7 bit I2C-compatible device address for the LM3561 is
1010011 (53). After the START condition, the I2C master
sends the 7-bit address followed by an eighth bit, read or write
(R/W). R/W = 0 indicates a WRITE (0xA6) and R/W = '1' in-
dicates a READ (0xA7). 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.
30113920
FIGURE 14. Device Address
TRANSFERRING DATA
Every byte on the SDA line must be eight bits long with the
most significant bit (MSB) transferred first. Each byte of data
must be followed by an acknowledge bit (ACK). The acknowledge related clock pulse (9th clock pulse) is generated by the
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master. The master releases SDA (HIGH) during the 9th clock
pulse (write mode). The LM3561 pulls down SDA during the
9th clock pulse, signifying an acknowledge. An acknowledge
is generated after each byte has been received.
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LM3561
Register Descriptions
TABLE 1. LM3561 Internal Registers
Register Name
Internal Hex Address
Power On or Reset Value
Enable Register
0x10
0xF8
Indicator Brightness Register
0x12
0xF8
GPIO Register
0x20
0x80
VIN Monitor Register
0x80
0xF8
Torch Brightness Register
0xA0
0xFA
Flash Brightness Register
0xB0
0xFD
Flash Duration Register
0xC0
0xEF
Flags Register
0xD0
0x00
Configuration Register 1
0xE0
0x6A
Configuration Register 2
0xF0
0xF0
ENABLE REGISTER (ADDRESS 0x10)
The Enable Register contains the enable bits that turn on the device in Indicate Mode, Torch Mode, or Flash Mode (bits[1:0]).
These bits are always reset at the end of a flash pulse. Bit [2] sets the STROBE level or edge control.
TABLE 2. Enable Register Bit Settings
Bits[7:3]
Not Used
N/A
Bit 2
(Strobe Level or Edge, STR bit)
0 = STROBE Input set for Level. Flash current
turns on when STROBE input is high and turns
off when STROBE either goes low or the
Timeout Duration expires (default)
1 = STROBE Input set for edge triggered. Flash
current turns on when STROBE sees a rising
edge. Flash pulse turns off when timeout
duration expires
Bits [1:0]
Enable Bits
Enable Bits
00 = Shutdown (default)
01 = Indicator Mode
10 = Torch Mode
11 = Flash Mode (bits reset at timeout)
INDICATOR BRIGHTNESS REGISTER (ADDRESS 0x12)
The Indicator Register contains the bits to set the indicator current level in indicate mode.
TABLE 3. Indicator Brightness Register Bit Settings
Bits [7:3]
Not Used
Bits [2:0]
Indicate Current Settings
N/A
000 = 2.25mA (default)
001 = 4.5mA
010 = 6.75mA
011 = 9mA
100 = 11.25mA
101 = 13.5mA
110 = 15.75mA
111 = 18mA
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LM3561
GPIO REGISTER (ADDRESS 0x20)
The GPIO register contains the control bits which change the state of the TX1/TORCH/GPIO1 pin and the TX2/GPIO2 pin to general
purpose I/O’s (GPIO’s).
TABLE 4. GPIO Register Bit Settings
Bit 7
Not Used
Bit 6
TX2/GPIO2/
INT Interrupt
Output
Bit 5
TX2/GPIO2
data
Bit 4
TX2/GPIO2
data direction
Bit 3
TX2/GPIO2
Control
Bit 2
TX1/GPIO1
data
Bit 1
TX1/GPIO1
data direction
Bit 0
TX1/GPIO1
Control
N/A
0 = INT mode
is disabled
(default)
1 = When TX2/
GPIO2 is
configured as
a GPIO output
TX2/GPIO2/
INT is set for
INT mode and
will pull low
when either
the LED
Thermal Fault
Flag is set or
the VIN
Monitor Flag is
set
This bit is the
read or write
data for TX2/
GPIO2 in
GPIO mode
(default is 0)
0 = TX2/
GPIO2 is a
GPIO Input
(default)
1 = TX2/
GPIO2 is a
GPIO Output
0 = TX2/
GPIO2 is a
flash interrupt
input (default)
1 = TX2/
GPIO2 is
configured as
a GPIO
This bit is the
read or write
data for TX1/
GPIO1 in
GPIO mode
(default is 0)
0 = TX1/
GPIO1 is a
GPIO input
(default)
1 = TX1/
GPIO1 is a
GPIO output
0 = TX1/
GPIO1 is
configured as
flash interrupt
input(default)
1 = TX1/
GPIO1 is
configured as
a GPIO
VIN MONITOR REGISTER (ADDRESS 0X80)
The VIN Monitor Register controls the on/off state of the VIN Monitor comparator as well as selects the 4 programmable thresholds.
TABLE 5. VIN Monitor Register Bit Settings
Bits [7:3]
Not Used
Bits [2:1]
VIN Monitor Threshold Settings
N/A
00 = 2.9V threshold (VIN falling)
Default
01=3.0V threshold (VIN falling)
10 = 3.1V threshold (VIN falling)
11 = 3.2V threshold (VIN falling)
TORCH BRIGHTNESS REGISTER (0XA0)
The Torch Brightness Register contains the bits to program the LED current in Torch Mode.
TABLE 6. Torch Brightness Register Bit Settings
Bits [7:3]
Not Used
Bits [2:0]
Torch Current Settings
N/A
000 = 18mA
001 = 36.8mA
010 = 55.6mA (default)
011 = 74.4mA
100 = 93.2mA
101 = 112mA
110 = 130.8mA
111 = 149.6mA
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24
Bit 0
VIN Monitor Enable
0 = VIN Monitor Comparator is
disabled (default)
1 = VIN Monitor Comparator is
enabled.
LM3561
FLASH BRIGHTNESS REGISTER (ADDRESS 0XB0)
The Flash Brightness Register contains the bits to program the LED current in flash mode.
TABLE 7. Flash Brightness Register Bit Settings
Bits [7:4]
Not Used
Bits [3:0]
Flash Current Settings
N/A
0000 = 36mA
0001 = 73.6mA
0010 = 111.2mA
0011 = 148.8mA
0100 = 186.4mA
0101 = 224mA
0110 = 261.6mA
0111 = 299.2mA
1000 = 336.8mA
1001 = 374.4mA
1010 = 412mA
1011 = 449.6mA
1100 = 487.2mA
1101 = 524.8mA Default
1110 = 562.4mA
1111 = 600mA
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LM3561
FLASH DURATION REGISTER (ADDRESS 0XC0)
Bits [4:0] of the Flash Duration Register set the Flash timeout duration. Bit [5] sets the switch current limit.
TABLE 8. Flash Timeout Duration Register Bit Settings
Bit [7:6]
Not Used
N/A
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Bit 5
Current Limit
Select
0 = 1A Peak
Current Limit
1 = 1.5A Peak
Current Limit
(default)
Bits [4:0]
Flash Timeout Duration Settings
00000 = 32ms timeout
00001 = 64ms timeout
00010 = 96ms timeout
00011 = 128ms timeout
00100 = 160ms timeout
00101 = 192ms timeout
00110 = 224ms timeout
00111 = 256ms timeout
01000 = 288ms timeout
01001 = 320ms timeout
01010 = 352ms timeout
01011 = 384ms timeout
01100 = 416ms timeout
01101 = 448ms timeout
01110 = 480ms timeout
01111 = 512ms timeout (default)
10000 = 544ms timeout
10001 = 576ms timeout
10010 = 608ms timeout
10011 = 640ms timeout
10100 = 672ms timeout
10101 = 704ms timeout
10110 = 736ms timeout
10111 = 768ms timeout
11000 = 800ms timeout
11001 = 832ms timeout
11010 = 864ms timeout
11011 = 896ms timeout
11100 = 928ms timeout
11101 = 960ms timeout
11110 = 992ms timeout
11111 = 1024ms timeout
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The Flags Register holds the status of the flag bits indicating LED Failure, Over-Temperature, the Flash Timeout expiring, VIN
Monitor Fault, LED over temperature (NTC), and a TX1 or TX2 interrupt.
TABLE 9. Flags Register Bit Settings
Bit 7
VIN Monitor
Flag
Bit 6
Not Used
0 = No Fault at N/A
VIN (default)
1 = Input
Voltage
Monitor is
enabled and
VIN has fallen
below (VIN_TH)
Bit 5
LED Thermal
Fault
(NTC)
Bit 4
TX2 Interrupt
Bit 3
TX1 Interrupt
Bit 2
Led Fault
(LEDF)
Bit 1
Thermal
Shutdown
(TSD)
Bit 0
Flash Timeout
(TO)
0 =LEDI/NTC
pin is above
VTRIP (default)
1=LEDI/NTC
has fallen
below VTRIP
(NTC mode
only)
0=TX2 has not
changed state
(default)
1=TX2 has
changed state
(TX2 mode
only)
0=TX1/
TORCH has
not changed
state (default)
1=TX1/
TORCH pin
has changed
state (TX1
mode only)
0 = Proper
LED Operation
(default)
1 = LED Failed
(Open or
Short)
0 = Die
Temperature
below Thermal
Shutdown
Limit (default)
1 = Die
Temperature
has crossed
the Thermal
Shutdown
Threshold of
+150°C
0 = Flash
timeout did not
expire
(default)
1 = Flash
timeout
Expired
CONFIGURATION REGISTER 1 (ADDRESS 0XE0)
Configuration Register 1 contains the STROBE enable/disable bit, the STROBE polarity bit, the NTC enable bit, the polarity selection for TX1 and TX2 flash interrupts, and the hardware torch mode enable for TX1/TORCH.
TABLE 10. Configuration Register 1 Bit Settings
Bit 7
Hardware
Torch Mode
Enable
Bit 6
TX2 Polarity
Bit 5
TX1 Polarity
Bit 4
NTC Mode
Enable
Bit 3
STROBE
Polarity
Bit 2
Bit 1
STROBE Input Not Used
Enable
Bit 0
Not Used
0 = TX1/
TORCH is a
TX1 flash
interrupt input
(default)
1 = TX1/
TORCH pin is
a hardware
TORCH
enable. This
bit is reset to 0
after a flash
event.
0 = TX2 is set
for active low
polarity
1 = TX2 is set
for active high
polarity
(default)
0 = TX1 is set
for active low
polarity
1 = TX1 is set
for active high
polarity
(default)
0 = LEDI/NTC
is a Indicator
Current
Source Output
(default)
1 = LEDI/NTC
is a
Comparator
Input for LED
Temperature
Sensing
0 = STROBE
set for active
low polarity
1 = STROBE
set for active
high polarity
(default)
0 = STROBE N/A
Input Disabled
(default)
1 = STROBE
Input Enabled
N/A
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LM3561
FLAGS REGISTER (ADDRESS 0XD0)
LM3561
CONFIGURATION REGISTER 2 (ADDRESS 0XF0)
Configuration Register 2 contains the TX2 shutdown bit, the NTC shutdown bit, the Alternate External Torch Enable bit, and the
VIN Monitor Shutdown bit.
TABLE 11. Configuration Register 2 Bit Settings
Bits [7:4]
Not Used
N/A
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Bit 3
VIN Monitor
Shutdown
Bit 2
AET mode
0 = If IN drops
below VIN_TH
and the VIN
Monitor
feature is
enabled, the
LEDs are
forced into
Torch mode
(default)
1 = If IN drops
below VIN_TH
and the VIN
Monitor
feature is
enabled, the
LEDs turn off
0 = Normal
operation for
TX1/TORCH
high before
STROBE (TX1
mode only)
default
1 = Alternate
External Torch
Mode. TX1/
TORCH high
before
STROBE
forces Torch
mode with no
timeout (TX1
mode only)
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Bit 1
NTC
Shutdown
0 = LEDI/NTC
pin going
below VTRIP
forces the
LEDs into
Torch mode
(NTC mode
only) default
1 = LEDI/NTC
pin going
below VTRIP
forces the
LEDs into
shutdown
(NTC mode
only)
Bit 0
TX2 Shutdown
0 = TX2
interrupt event
forces the
flash LED into
Torch mode
(TX2 mode
only) default
1 = TX2
interrupt event
forces the
flash LED into
shutdown
(TX2 mode
only)
OUTPUT CAPACITOR SELECTION
The LM3561 is designed to operate with a at least a 10µF
ceramic output capacitor. When the boost converter is running the output capacitor supplies the load current during the
boost converters 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 offtime. 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 LED operation the output capacitor must be at
least a 10µF ceramic. Larger capacitors such as 22µF 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 capacitors ESR
(ΔVESR) use the following equations:
For continuous conduction mode, the output voltage ripple
due to the capacitor discharge is:
In ceramic capacitors the ESR is very low so assume that 80%
of the output voltage ripple is due to capacitor discharge and
20% from ESR. Table 12 lists different manufacturers for various output capacitors and their case sizes suitable for use
with the LM3561.
INPUT CAPACITOR SELECTION
Choosing the correct size and type of input capacitor helps
minimize the voltage ripple caused by the switching of the
LM3561’s boost converter and reduces noise on the devices
input terminal that can feed through and disrupt internal analog signals. In the Typical Application Circuit a 10µF ceramic
input capacitor works well. It is important to place the input
capacitor as close as possible to the LM3561’s input (IN) terminals. This reduces the series resistance and inductance
that can inject noise into the device due to the input switching
currents. Table 12 lists various input capacitors recommended for use with the LM3561.
TABLE 12. Recommended Input/Output Capacitors (X5R Dielectric)
Manufacturer
Part Number
Value
Case Size
Voltage Rating
TDK Corporation
C1608JB0J106M
10µF
0603(1.6mm×0.8mm×0.8mm)
6.3V
TDK Corporation
C2012JB1A106M
10µF
0805(2mm×1.25mm×1.25mm)
10V
TDK Corporation
C2012JB0J226M
22µF
0805(2mm×1.25mm×1.25mm)
6.3V
Murata
GRM21BR61A106KE19
10µF
0805(2mm×1.25mm×1.25mm)
10V
Murata
GRM21BR60J226ME39L
22µF
0805(2mm×1.25mm×1.25mm)
6.3V
mance ensure that the inductor saturation and the peak current limit setting of the LM3561 is greater than IPEAK. This can
be calculated by:
INDUCTOR SELECTION
The LM3561 is designed to use a 1µH to 2.2µH inductor.
Table 13 lists various inductors that can work well with the
LM3561. When the device is boosting (VOUT > VIN) the inductor will typically be the biggest 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 LM3561. This prevents excess
efficiency loss that can occur with inductors that operate in
saturation. For proper inductor operation and circuit perfor-
ƒSW = 2MHz, and η can be found in the Typical Performance
Characteristics plots.
TABLE 13. Recommended Inductors
Manufacturer
L
Part Number
Dimensions (L×W×H)
RDC
ISAT
Coilcraft
1µH
XPL2010-102ML
2mm×1.9mm×1mm
81mΩ
1.6A
TDK
1µH
VLS252012T-1R0N
2mm×2.5mm×1.2mm
73mΩ
2.7A
TDK
1µH
VLS2010-1R0N
2mm x 2mm x 1mm
90mΩ
1.65A
TDK
1µH
VLS2012ET-1R0N
2mm x 2mm x 1.2mm
71mΩ
1.65A
TDK
1µH
VLS20160ET-1R0N
2mm x 1.6mm x 0.95mm
100mΩ
1.5A
TDK
1µH
VLS252010ET-1R0N
2.5mm x 2mm x 1mm
70mΩ
1.9A
a comparator input for flash LED thermal sensing. The thermal sensing circuit consists of a negative temperature coef-
NTC THERMISTOR SELECTION
Programming bit [4] of Configuration Register 1 with a (1) selects Thermal Comparator mode, making the LEDI/NTC pin
29
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LM3561
The output voltage ripple due to the output capacitors ESR is
found by:
Applications Information
LM3561
ficient (NTC) thermistor and a series resistor which forms a
resistive divider (see Figure 15).
30113966
FIGURE 15. NTC Circuit
The NTC thermistor senses the LEDs temperature via conducting the LEDs heat into the NTC thermistor. Heat conduction is improved with a galvanic connection at GND (LED
cathode and NTC thermistor GND terminal) and by placing
the thermistor in very close proximity to the flash LED.
NTC thermistors have a temperature to resistance relationship of:
where R(T)TRIP is the thermistor's value at the temperature
trip point, VBIAS is the bias voltage for the thermistor circuit,
and VTRIP = 1V (typical). Choosing RBIAS here gives a more
linear response around the temperature trip voltage. For example with VBIAS = 1.8V and a thermistor whose nominal
value at +25°C is 10kΩ and a β = 3380K, the trip point is chosen to be +93°C. The value of R(T) at 93°C is:
where β is given in the thermistor datasheet and R25C is the
thermistor's value at +25°C. RBIAS is chosen so that it is equal
to:
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Figure 16 shows the linearity of the thermistor resistive divider
of the previous example.
30
LM3561
VLEDI/NTC vs Temp (VBIAS = 1.8V, THERMISTOR = 10kΩ @+25C, β = 3380, RBIAS =972Ω)
30113934
FIGURE 16. Thermistor Resistive Divider Response vs Temperature
Another useful equation for the thermistor resistive divider is
developed by combining the equations for RBIAS, and R(T)
and solving for temperature. This gives the following relationship.
for practical values of thermistors, series resistors (R3), or
reference voltages VBIAS.
NTC THERMISTOR PLACEMENT
The termination of the thermistor must be done directly to the
cathode of the Flash LED in order to adequately couple the
heat from the LED into the thermistor. Consequentially, the
noisy environment generated from the switching of the
LM3561's boost converter can introduce noise from GND into
the thermistor sensing input. To filter out this noise it is necessary to place a 0.1µF or larger ceramic capacitor close to
the LEDI/NTC pin. The filter capacitor's return must also connect with a low-impedance trace, as close as possible to the
GND pin of the LM3561.
Using a spreadsheet such as Excel, different curves for the
temperature trip point T(°C) can be created vs RBIAS, Beta, or
VBIAS in order to help better choose the thermal components
31
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LM3561
4.
Layout Recommendations
The high frequency and relatively large switching currents of
the LM3561 make the choice of layout important. The following steps should be used as a reference to ensure the device
is stable and maintains proper voltage and current regulation
across its intended operating voltage and current range.
1. Place CIN on the top layer (same layer as the LM3561)
and as close to the device as possible. The input
capacitor conducts the driver currents during the lowside MOSFET turn-on and turn-off and can see current
spikes over 500mA in amplitude. Connecting the input
capacitor through short wide traces on both the IN and
GND terminals 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 LM3561)
and as close as possible to the OUT and GND terminal.
The returns for both CIN and COUT should come together
at one point, and as close to the GND pin as possible.
Connecting COUT through short wide traces will reduce
the series inductance on the OUT and GND terminals
that can corrupt the VOUT and GND line 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 so as to reduce the capacitive coupling
of the fast dV/dt present at SW that can couple into
nearby traces.
www.national.com
5.
6.
32
Avoid routing logic traces near the SW node so as to
avoid any capacitively coupled voltages from SW onto
any high impedance logic lines such as TX1/TORCH/
GPIO1, TX2/GPIO2/INT, HWEN, LEDI/NTC (NTC
mode), 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.
Terminate the Flash LED cathode directly to the GND pin
of the LM3561. If possible, route the LED return with a
dedicated path so as to keep the high amplitude LED
current out of the GND plane. For a Flash LED that is
routed relatively far away from the LM3561, a good
approach is to sandwich the forward and return current
paths over the top of each other on two adjacent layers.
This will help in reducing the inductance of the LED
current paths.
The NTC Thermistor is intended to have its return path
connected to the LED's cathode. This allows the
thermistor resistive divider voltage (VNTC) to trip the
comparators threshold as VNTC is falling. Additionally, the
thermistor to LED cathode junction can have low thermal
resistivity since both the LED and the thermistor are
electrically connected at GND. The draw back is that the
thermistor's return will see the switching currents from
the LM3561's boost converter. Because of this, it is
necessary to have a filter capacitor at the NTC pin which
terminates close to the GND of the LM3561 and which
can conduct the switched currents to GND.
LM3561
Physical Dimensions inches (millimeters) unless otherwise noted
12 Bump micro SMD (0.4mm pitch)
For Ordering, Refer to Ordering Information Table
NS Package Number TMD12AAA
X1 = 1.215mm (±0.03mm), X2 = 1.615mm (±0.03mm), X3 = 0.6mm(±0.075mm)
33
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LM3561 Synchronous Boost Converter with 600mA High Side LED Driver and I2C-Compatible
Interface
Notes
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