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2018 Microchip Technology Inc. DS20006081A-page 1
MIC2874
Features
• Up to 1.2A Flash LED Driving Current
• Highly Efficient Synchronous Boost Driver
• Control through Single-Wire Serial Interface or
External Control Pin
• Input Voltage Range: 2.7V to 5.5V
• True Load Disconnect
• Configurable Safety Time-Out Protection
• Output Overvoltage Protection (OVP)
• LED Short Detection and Protection
• 1 µA Shutdown Current
• Available in 9-Bump 1.30 mm x 1.30 mm WLCSP
Package
Applications
• Camera Phones/Mobile Handsets
• Cell Phones/Smartphones
• LED Light for Image Capture/Auto-Focus/
White Balance
• Handset Video Light (Torch Light)
• Digital Cameras
• Portable Applications
General Description
The MIC2874 is a high-current, high-efficiency Flash
LED driver. The LED driver current is generated by an
integrated inductive boost converter with a 4 MHz switch-
ing frequency, which allows for the use of a very small
inductor and output capacitor. These features make the
MIC2874 an ideal solution for high-resolution camera
phone LED Flash light driver applications.
MIC2874 operates in either Flash or Torch mode that can
be controlled through the single-wire serial interface
and/or external control pin. A robust single-wire serial
interface allows the host processor to control the LED
current and brightness. The MIC2874 is available in a
9-bump 1.30 mm x 1.30 mm WLCSP package.
1.2A High-Brightness Flash LED Driver with
Single-Wire Serial Interface
MIC2874
DS20006081A-page 2 2018 Microchip Technology Inc.
Package Type
Typical Application Schematic
LED
A
B
C
DC OUT
LGND SWFEN
AGND V
IN
PGND
1 2 3
MIC2874
9-Bump 1.30 mm x 1.30 mm WLCSP (CS)
(Top View)
Note: WLCSP Bump A1 identifier = “•”.
DC
LED
FEN
VIN SW OUT
V
BAT
AGND
FLASH ENABLE
SINGLE-WIRE SERIAL I/F
PGND
LGND
2018 Microchip Technology Inc. DS20006081A-page 3
MIC2874
Functional Block Diagram
SW
SYSTEM
CONTROL
LOGIC +
ANTI-CROSS
CONDUCTION
DC
FEN
VIN
AGND
LED
OUT
PGND
LGND
SINGLE-
WIRE
SERIAL
INTERFACE
LED SCP
UVLO
BODY
SWITCH
OTP
155°C/
140°C
LBVD
SAFETY
TIMER
DIE TEMP
2.53V/
2.35V
OUT
LED 1.7V
VIN
AGND
PGND
Z Z
4 MHz
OSCILLATOR
V/I
OUT
SAFETY
TIMER
SAFETY
TIMER
DECODER
4-BIT
MIC2874
DS20006081A-page 4 2018 Microchip Technology Inc.
1.0 ELECTRICAL CHARACTERISTICS
Absolute Maximum Ratings†
Input Voltage (VIN)......................................................................................................................................-0.3V to +6.0V
General I/O Voltage (VFEN) ............................................................................................................................ -0.3V to V
IN
VOUT and VLED Voltage.............................................................................................................................. -0.3V to +6.0V
Single-Wire I/O Voltage (VDC) ........................................................................................................................ -0.3V to V
IN
VSW Voltage ...............................................................................................................................................-0.3V to +6.0V
ESD Rating( )1
HBM .......................................................................................................................................................................2 kV
MM ........................................................................................................................................................................200V
Note 1: Devices are ESD-sensitive. Handling precautions are recommended. Human body model, 1.5 k in series
with 100 pF.
Operating Ratings( )1
Input Voltage (VIN)..................................................................................................................................... +2.7V to +5.5V
Enable Input Voltage (VFEN)............................................................................................................................... 0V to V
IN
Single-Wire I/O Voltage (VDC) ............................................................................................................................ 0V to V
IN
Power Dissipation (PD)....................................................................................................................... Internally Limited
( )2
Note 1: The device is not ensured to function outside the operating range.
2: The maximum allowable power dissipation at any T
A (ambient temperature) is PD(max) = (TJ(max) – TA)/JA.
Exceeding the maximum allowable power dissipation will result in excessive die temperature and the regulator
will go into thermal shutdown.
† Notice: Stresses above those listed under “Maximum Ratings” may cause permanent damage to the device. This
is a stress rating only and functional operation of the device at those or any other conditions above those indi-
cated in the operational sections of this specification is not intended. Exposure to maximum rating conditions for
extended periods may affect device reliability.
2018 Microchip Technology Inc. DS20006081A-page 5
MIC2874
TABLE 1-1: ELECTRICAL CHARACTERISTICS(Note 1)
Electrical Specifications:
unless otherwise specified, V
IN
= 3.6V; L = 0.47 µH; C
OUT
= 4.7 µF; I
OUT
= 100 mA;
TA = TJ = +25°C. Boldface values indicate -40°C T
J+125°C.
Parameter Symbol Min. Typ. Max. Units Test Conditions
Power Supply
Supply Voltage Range VIN 2.7 —5.5 V —
UVLO Threshold (rising) VUVLO_R 2.41 2.53 2.68 V —
UVLO Hysteresis VUVLO_HYS — 180 — mV —
Standby Current
ISTB 150 185 220 µA
VDC = 3.6V, VFEN = 0V, boost
regulator and LED current
driver are both off
Shutdown Current ISD — 1 2 µA VDC = 0V
Maximum Duty Cycle DMAX 82 86 90 % —
Minimum Duty Cycle DMIN — 6.4 — % —
Switch Current Limit ISW — 4.1 — A VIN = VOUT = 2.7V
Switch-On Resistance RDS(ON)_P —125 —mISW
= 100 mA
RDS(ON)_N — — ISW
= 100 mA
Switch Leakage Current I
SW_LK — 0.01 1 µA VDC = 0V, VSW = 5.5V
Oscillator Frequency F
SW 3.6 44.4 MHz —
Overtemperature Shutdown
Threshold TSD — 155 — °C —
Overtemperature Shutdown
Hysteresis TSD_HYS — 15 — °C —
Safety Time-out Shutdown TTO — 1.25 — s Default timer setting
Safety Timer Current
Threshold ITO — 250 — mA Default current threshold set-
ting
Low-Battery Voltage
Detection Threshold VLBVD — 3.0 — V Default LBVD threshold set-
ting
Low-Battery Voltage
Detection Threshold
Accuracy
— — 50 — mV
All low-battery voltage detec-
tion threshold settings
LED Short-Circuit Detection
Voltage Threshold VSHORT 1.55 1.7 1.85 V VOUT
– VLED
LED Short-Circuit Detection
Test Current ITEST 1.6 2 2.7 mA —
Current Sink Channel
Channel Current Accuracy — -6 — 6 %VOUT
= 4.2V, I LED
= 0.20A
-8 — 8 VOUT
= 4.2V, I LED
= 1.0A
Current Sink Voltage
Dropout VLED — 250 — mV Boost mode
FEN Control Pin
FEN High-Level Voltage V
FEN_H 1.3 — — VFlash is on
FEN Low-Level Voltage VFEN_L — — 0.6 Flash is off
FEN Pull-Down Current IFEN_PD — 51.3 µA VFEN = 5.5V
Note 1: Specification for packaged product only.
MIC2874
DS20006081A-page 6 2018 Microchip Technology Inc.
TABLE 1-2: ELECTRICAL CHARACTERISTICS – SINGLE-WIRE INTERFACE
(ENSURED BY DESIGN)
Electrical Specifications:
unless otherwise specified, V
IN
= 3.6V; L = 0.47 µH; C
OUT
= 4.7 µF; I
OUT
= 100 mA;
TA = TJ = +25°C. Boldface values indicate -40°C T
J+125°C.
Parameter Symbol Min. Typ. Max. Units Test Conditions
Low-Level Input Voltage VL— — 0.4 V—
High-Level Input Voltage VH1.3 — — —
DC Pull-Down Current IDC_PD — 2.8 5 µA VDC = 5.5V
On Time TON 0.1 —72 µs —
Off Time TOFF 0.1 —72 µs —
Latch Time T
LAT 97 324— µs —
End Time TEND 405 — — µs —
MIC2874
DS20006081A-page 8 2018 Microchip Technology Inc.
2.0 TYPICAL CHARACTERISTIC CURVES
FIGURE 2-1: Shutdown Current vs.
Temperature.
FIGURE 2-2: Standby Current vs.
Temperature.
FIGURE 2-3: UVLO Thresholds vs.
Temperature.
FIGURE 2-4: Switching Frequency vs.
Temperature.
FIGURE 2-5: Maximum Duty Cycle vs.
Temperature.
FIGURE 2-6: LED Short Threshold
Voltage vs. Temperature.
Note: The graphs and tables provided following this note are a statistical summary based on a limited number of
samples and are provided for informational purposes only. The performance characteristics listed herein
are not tested or guaranteed. In some graphs or tables, the data presented may be outside the specified
operating range (e.g., outside specified power supply range) and therefore outside the warranted range.
MIC2874
DS20006081A-page 10 2018 Microchip Technology Inc.
FIGURE 2-13: Flash Mode Turn-On
Sequence (Boost Mode).
FIGURE 2-14: Flash Mode Turn-On
Sequence (Linear Mode).
FIGURE 2-15: Torch Mode Turn-On
Sequence (Boost Mode).
FIGURE 2-16: Torch Mode Turn-On
Sequence (Linear Mode).
FIGURE 2-17: Flash Safety Timer at
1250 ms.
FIGURE 2-18: Flash Safety Timer at
156 ms.
I
LED
= 1.2A
V
IN
= 3.0V
L
= 0.47μH
Time (100μs/div)
I
LED
(500mA/div)
V
OUT
(2V/div)
V
FEN
(5V/div)
V
LED
(2V/div)
V
OUT
-V
LED
(2V/div)
ILED
= 1.2A
VIN = 4.5V
L = 0.47μH
Time (100μs/div)
ILED
(500mA/div)
VOUT
(2V/div)
VFEN
(5V/div)
VLED
(2V/div)
V
OUT -VLED
(2V/div)
ILED
= 300mA
VIN
= 3.0V
L = 0.47μH
Time (200μs/div)
ILED
(200mA/div)
VOUT
(2V/div)
VDC
(5V/div)
VLED
(2V/div)
VOUT -VLED
(2V/div)
ILED = 300mA
VIN = 4.0V
L = 0.47μH
Time (200μs/div)
ILED
(200mA/div)
VOUT
(2V/div)
VDC
(5V/div)
VLED
(2V/div)
V
OUT -V LED
(2V/div)
ILED = 1.2A
VIN = 4.2V
L = 0.47μH
Time (200ms/div)
ILED
(500mA/div)
VOUT
(2V/div)
VDC
(5V/div)
VLED
(2V/div)
ILED = 1.2A
VIN = 4.2V
L = 0.47μH
Time (200ms/div)
ILED
(500mA/div)
VOUT
(2V/div)
VDC
(5V/div)
VLED
(2V/div)
2018 Microchip Technology Inc. DS20006081A-page 11
MIC2874
FIGURE 2-19: LED Short-Circuit Protection
(LED is Shorted by 0
).
FIGURE 2-20: LED Short-Circuit Protection
(LED is Shorted by 620
).
FIGURE 2-21: Load Disconnect at
Shutdown (VIN = 2.7V).
FIGURE 2-22: Load Disconnect at
Shutdown (VIN = 5.0V).
FIGURE 2-23: VOUT Overvoltage
Protection (Overvoltage during Start-up).
FIGURE 2-24: VOUT Overvoltage
Protection (Overvoltage after Start-up).
VIN = 3.6V
L = 0.47μH
LED IS SHORTED
BY 0ȍ
Time (40μs/div)
IL
(100mA/div)
VOUT
(2V/div)
VFEN
(5V/div)
VOUT-VLED
(2V/div)
VLED
(2V/div)
VIN = 3.6V
L = 0.47μH
LED IS SHORTED
BY 620ȍ
Time (40μs/div)
IL
(100mA/div)
VOUT
(2V/div)
VFEN
(5V/div)
VOUT -VLED
(2V/div)
VLED
(2V/div)
ILED = 1.2A
VIN
= 2.7V
L = 0.47μH
VFEN = 0V
Time (200ms/div)
ILED
(500mA/div)
VDC
(5V/div)
VOUT
(2V/div)
VLED
(2V/div)
ILED
= 1.2A
VIN
= 5.0V
L = 0.47μH
VFEN
= 3.6V
Time (200ms/div)
ILED
(500mA/div)
VLED
(2V/div)
VDC
(5V/div)
VOUT
(2V/div)
VIN = 3.6V
L = 0.47μH
Time (40μs/div)
IL
(1A/div)
V
SW
(2V/div)
VLED
(2V/div)
VOUT
(2V/div)
ILED = 1.2A
VIN = 3.6V
L = 0.47μH
Time (2μs/div)
IL
(1A/div)
V
SW
(2V/div)
VLED
(2V/div)
VOUT
(2V/div)
2018 Microchip Technology Inc. DS20006081A-page 13
MIC2874
3.0 PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 3-1.
TABLE 3-1: PIN FUNCTION TABLE
MIC2874
Pin Number Pin Name Pin Function
A1 LED LED Current Sink Pin: Connect the LED anode to OUT and the cathode to this pin.
A2 DC Single-Wire Interface: Serial control input.
A3 OUT Boost Converter Output Pin: To be connected to the anode of the LED. Connect a
low-ESR ceramic capacitor of at least 4.7 µF at this pin to PGND.
B1 LGND Linear Ground: LED current return path.
B2 FEN Flash Mode Enable Pin: Asserting this pin high enables the MIC2874 to enter Flash
mode. If this pin is left floating, it is pulled down internally by a built-in 1 µA current
source when the device is enabled.
B3 SW Inductor Connection Pin: It is connected to the internal power MOSFETs.
C1 AGND Analog Ground.
C2 VIN Supply Input Pin: Connect a low-ESR ceramic capacitor of at least 4.7 µF at this pin to
AGND.
C3 PGND Power Ground: Inductor current return path.
MIC2874
DS20006081A-page 14 2018 Microchip Technology Inc.
4.0 FUNCTIONAL DESCRIPTION
4.1 VIN
The input supply provides power to the internal
MOSFETs’ gate drive and controls circuitry for the
Switch mode regulator. The operating input voltage
range is from 2.7V to 5.5V. A 4.7 µF low-ESR ceramic
input capacitor should be connected from V
IN to AGND,
as close to MIC2874 as possible, to ensure a clean
supply voltage for the device. The minimum voltage
rating of 10V is recommended for the input capacitor.
4.2 SW
The MIC2874 has internal low-side and synchronous
MOSFET switches. The switch node (SW) between the
internal MOSFET switches connects directly to one end
of the inductor and provides the current paths during
switching cycles.
The other end of the inductor is connected to the input
supply voltage. Due to the high-speed switching on this
pin, the switch node should be routed away from
sensitive nodes wherever possible.
4.3 LGND
This is the ground path of the LED current sink. It should
be connected to the AGND on the PCB. The current loop
of the Analog Ground should be separated from that of
the Power Ground (PGND). LGND and AGND should be
connected to PGND at a single point.
4.4 AGND
This is the ground path for the internal biasing and con-
trol circuitry. AGND should be connected to the LGND
directly. The current loop of the Analog Ground should
be separated from that of the Power Ground (PGND).
The AGND and LGND should be connected to PGND at
a single point.
4.5 PGND
The Power Ground pin is the ground path for the high
current in the boost switch. The current loop for the
Power Ground should be as small as possible and
separate from the Analog Ground (AGND) loop as
applicable.
4.6 OUT
This is the boost converter output pin, which is con-
nected to the anode of the LED. A low-ESR ceramic
capacitor of 4.7 µF or larger should be connected from
OUT to PGND, as close as possible to the MIC2874.
The minimum voltage rating of 10V is recommended for
the output capacitor.
4.7 LED
This is the current sink pin for the LED. The LED anode
is connected to the OUT pin and the LED cathode is
connected to this pin.
4.8 DC
The DC is a single multiplexed device enable and serial
data control pin used for functional control, and com-
munication in GPIO limited applications. When the DC
pin is used as a hardware device enable pin, a logic
high signal on the DC pin enables the device and a
logic low signal on the DC pin disables the device.
When the DC pin is used as the single-wire serial
interface Digital Control pin, a combination of bit edges
and the period between edges is used to communicate
a variable length data word across the single wire.
Each word is transmitted as a series of pulses, with
each pulse incrementing an internal data counter. A stop
sequence, consisting of an inactive period, is used to
latch the data word internally. Two data words in series
received are then used to set a specific register with a
specific value for controlling a specific function. The
MIC2874 supports five writable registers for controlling
Flash mode, Torch mode, safety timer duration, safety
timer threshold current and low-battery threshold.
An address/data frame is used to improve protection
against erroneous writes where communications are in
error. When the DC is in a low state, and no data is
detected for longer than 405 µs, the MIC2874 will
automatically go into a low-power Shutdown state,
simultaneously resetting all internal registers to their
default states.
4.9 FEN
FEN is the hardware enable pin for Flash mode. A logic
low-to-high transition on the FEN pin can initiate the
MIC2874 in Flash mode. If FEN is left floating, it is pulled
down internally by a built-in 1 µA current source when
the device is enabled. Flash mode is terminated when
FEN is pulled low or left floating and the Flash register is
cleared.
2018 Microchip Technology Inc. DS20006081A-page 15
MIC2874
5.0 APPLICATION INFORMATION
The MIC2874 can drive a high-current Flash WLED in
either Flash mode or Torch mode.
5.1 Boost Converter
The internal boost converter is turned on/off automatically
when the LED driver is activated/deactivated without any
exception.
The boost converter is an internally compensated Current
mode PWM boost converter running at 4 MHz. It is for
stepping up the supply voltage to a high enough value at
the OUT pin to drive the LED current. If the supply voltage
is high enough, the synchronous switch of the converter
is then fully turned on. In this case, all the excessive
voltage is dropped over the linear LED driver.
5.2 Flash Mode
The maximum and default current levels in the Flash
mode are 1.2A and 1A, respectively. The Flash mode cur-
rent can be initiated by asserting the FEN pin high or by
setting the Flash Control register (Address 1) for the
desired Flash duration, subjected to the safety time-out
setting. The Flash mode current is terminated when the
FEN pin is brought low and the Flash register is cleared or
when the configurable safety timer expires.
Flash mode current can be adjusted to a fraction of the
maximum Flash mode current level by selecting the
desired value in the Flash Control register through the
single-wire serial interface.
5.3 Torch Mode
By default, the maximum Torch mode level is 300 mA.
The Torch mode operation is activated by setting the
Torch Control register (Address 2) for the desired dura-
tion. The Torch mode current is terminated when the
Torch register is cleared or when the configurable safety
timer expires.
Like the Flash mode current, the Torch mode current can
be set to a fraction of the maximum Torch mode current
level by selecting the desired torch current in the Torch
Control register (Address 2) via the single-wire serial
interface.
5.4 Configurable Safety Timer
The Flash safety time-out feature automatically shuts
down the LED current, after the safety timer duration is
expired, if the programmed LED current exceeds a certain
current threshold. Both the current threshold and the timer
duration are programmable via the Safety Timer registers
(Addresses 3 and 5).
5.5 Low-Battery Voltage Detection
(LBVD)
When the VIN voltage drops below the LBVD threshold
(default = 3.0V) in Flash or Torch mode, the LED current
driver is disabled. The LED driver can be resumed by rais-
ing the VIN above the LBVD threshold and toggling the
corresponding Flash or torch command. The LBVD
threshold is adjustable through the LBVD Control register
(Address 4).
5.6 Overvoltage Protection
When the output voltage rises above an internal overvolt-
age protection (OVP) threshold, MIC2874 is latched off
automatically to avoid permanent damage to the IC. To
clear the latched off condition, either power cycle the
MIC2874 or assert the DC pin low.
5.7 Short-Circuit Detection
Each time, before enabling the LED driver, the
MIC2874 performs the short-circuit test by driving the
Flash LED with a small (2 mA typical) current for
200 µs. If (VOUT – VLED) is less than 1.7V at the end of
the short-circuit test, then the LED is considered to be
shorted and MIC2874 will ignore the Flash and/or Torch
mode command. Note that the short-circuit test is
carried out every time, prior to Flash and Torch mode,
but the result is not latched.
5.8 Thermal Shutdown
When the internal die temperature of MIC2874 reaches
155°C, the LED driver is disabled until the die tempera-
ture falls below 140°C and either the FEN pin, FEN
register, TEN register or VIN is toggled.
5.9 Single-Wire Interface
The single-wire interface allows the use of a single
multiplexed enable and data pin (DC) for control and
communication in GPIO limited applications. The inter-
face is implemented using a simple mechanism, allowing
any open-drain or directly driven GPIO to control the
MIC2874.
The MIC2874 uses the single-wire interface for simple
command and control functions. The interface provides
fast access to write-only registers with protection features
to avoid potentially erroneous data writes and improve
robustness. When the DC is in a low state and no data is
detected for longer than 405 µs, the MIC2874 will
automatically go into a low-power Shutdown state, simul-
taneously resetting the internal registers to their default
states.
2018 Microchip Technology Inc. DS20006081A-page 17
MIC2874
After receiving the stop sequence, the internal registers’
decode and update cycle is started, with the Shadow
register values being transferred to the decoder.
Figure 5-3 shows an example of entering a write of Data 5
to Address 3.
FIGURE 5-3: Communication Timing
Example of Entering Write for Data 5 to Address 3.
Only a correctly formatted address/data combination will
be treated as a valid frame and processed by the
MIC2874. Any other input, such as a single data word
followed by TEND or three successive data words, will be
discarded by the target hardware as an erroneous entry.
Additionally, any register write to either an invalid register
or with invalid register data will also be discarded.
5.13 MIC2874 Registers
The MIC2874 supports five writable registers for
controlling the Torch and the Flash modes of operation, as
shown in Table 5-2. Note that register addressing starts
at 1. Writing any value above the maximum value shown
for each register will cause an invalid data error and the
frame will be discarded.
TABLE 5-2: FIVE WRITABLE REGISTERS
OF MIC2874
5.13.1 FLASH CURRENT REGISTER
(FEN/FCUR: DEFAULT 4)
The Flash Current register enables and sets the Flash
mode current level. Valid values are 0 to 31. Values 0-15
will set the Flash current without enabling the Flash (such
that it can be triggered externally). Values 16-31 will set
the Flash current and enable the Flash. The Flash current
register maps into the internal FEN and FCUR registers,
as shown in the following table below. Table 5-3 describes
the relationship between the Flash current and the FCUR
register setting.
TABLE 5-3: FLASH CURRENT REGISTER
MAPPING INTO INTERNAL
FEN/FCUR REGISTERS AND
RELATIONSHIP BETWEEN
FLASH CURRENT AND FCUR
REGISTER SETTING
Address Name Max.
Value Description
1 FEN/FCUR 31 Flash Enable/Current
2 TEN/TCUR 31 Torch Enable/Current
3 STDUR 7 Safety Timer Duration
4 LB_TH 9 Low-Battery Voltage
Detection Threshold
5 ST_TH 5 Safety Timer Threshold
T
LAT
< T END
0123
START
012345
END
REGISTER
WRITE
STARTLATCH
> T END
LATCH
TLAT
ADDRESS/DATA FRAME
FEN/FCUR<4:0> Value
IFLASH (A)
Dec. Binary FEN<4> FCUR<3:0>
000000 0 0000 1.200
100001 0 0001 1.150
200010 0 0010 1.100
300011 0 0011 1.050
400100 0 0100 1.000
500101 0 0101 0.950
600110 0 0110 0.900
700111 0 0111 0.850
801000 0 1000 0.800
901001 0 1001 0.750
10 0.70001010 0 1010
11 01011 0 1011 0.650
12 0.60001100 0 1100
13 0.55001101 0 1101
14 0.40001110 0 1110
15 0.25001111 0 1111
16 1.20010000 1 0000
17 1.15010001 1 0001
18 1.10010010 1 0010
19 1.05010011 1 0011
20 1.00010100 1 0100
21 0.95010101 1 0101
22 0.90010110 1 0110
23 0.85010111 1 0111
24 0.80011000 1 1000
25 0.75011001 1 1001
26 0.70011010 1 1010
27 0.65011011 1 1011
28 0.60011100 1 1100
29 0.55011101 1 1101
30 0.40011110 1 1110
31 0.25011111 1 1111
MIC2874
DS20006081A-page 18 2018 Microchip Technology Inc.
5.13.2 TORCH CURRENT REGISTER
(TEN/TCUR: DEFAULT 4)
The Torch Current register enables and sets the Torch
mode current level. Valid values are 0 to 31. Values 0-15
will set the torch current without enabling the torch (such
that it can be triggered by setting the internal TEN register
value to 1). Values 16-31 will set the torch current and
enable the torch. A value of 0 at the internal TEN register
will disable the torch. The Torch Current register maps
into the internal TEN and TCUR registers, as shown in
Table 5-4. The table also describes the relationship
between the torch current and the TCUR register setting.
TABLE 5-4: TORCH CURRENT REGISTER
MAPPING INTO INTERNAL
TEN/TCUR REGISTERS AND
RELATIONSHIP BETWEEN
TORCH CURRENT AND TCUR
REGISTER SETTING
5.13.3 SAFETY TIMER DURATION
REGISTER (STDUR: DEFAULT 7)
The Safety Timer Duration register sets the duration of the
Flash and Torch mode when the LED current exceeds the
programmed threshold current. Valid values are 0 for the
minimum timer duration to 7 for the maximum duration.
TABLE 5-5: SAFETY TIMER DURATION
REGISTER SETTING AND
SAFETY TIMER DURATION
5.13.4 LOW-BATTERY THRESHOLD
REGISTER (LB_TH: DEFAULT 1)
The LB_TH register sets the supply threshold voltage,
below which the internal low-battery flag is asserted and
the LED current driver is disabled. Table 5-6 shows the
threshold values that correspond to the register settings.
Setting 0 is reserved for disabling the function, and
settings between 1 and 9 inclusively enable and set the
LB_TH value, between 3.0V and 3.8V, with 100 mV
resolution.
TABLE 5-6: LOW-BATTERY THRESHOLD
REGISTER SETTING AND
SUPPLY THRESHOLD
VOLTAGE
TEN/TCUR<4:0> Value ITORCH (mA)
Dec. Binary TEN<4> TCUR<3:0>
000000 0 0000 300.0
100001 0 0001 287.5
200010 0 0010 275.0
300011 0 0011 262.5
400100 0 0100 250.0
500101 0 0101 237.5
600110 0 0110 225.0
700111 0 0111 212.5
801000 0 1000 200.0
901001 0 1001 187.5
10 01010 0 1010 175.0
11 01011 0 1011 162.5
12 01100 0 1100 150.0
13 01101 0 1101 137.5
14 01110 0 1110 100.0
15 01111 0 1111 62.5
16 10000 1 0000 300.0
17 10001 1 0001 287.5
18 10010 1 0010 275.0
19 10011 1 0011 262.5
20 10100 1 0100 250.0
21 10101 1 0101 237.5
22 10110 1 0110 225.0
23 10111 1 0111 212.5
24 11000 1 1000 200.0
25 11001 1 1001 187.5
26 11010 1 1010 175.0
27 11011 1 1011 162.5
28 11100 1 1100 150.0
29 11101 1 1101 137.5
30 11110 1 1110 100.0
31 11111 1 1111 62.5
Value STDUR<2:0>
(Binary) Time-out (ms)
Dec. Binary
0000 000 156.25
1001 001 312.5
2010 010 468.75
3011 011 625
4100 100 781.25
5101 101 937.5
6110 110 1093.75
7111 111 1250
Value
LB_TH<3:0> VBAT Threshold (V)
Dec. Binary
00000 0000 Disabled
10001 0001 3.0
20010 0010 3.1
30011 0011 3.2
40100 0100 3.3
50101 0101 3.4
60110 0110 3.5
TEN/TCUR<4:0> Value ITORCH (mA)
Dec. Binary TEN<4> TCUR<3:0>
2018 Microchip Technology Inc. DS20006081A-page 19
MIC2874
5.13.5 SAFETY TIMER THRESHOLD
CURRENT REGISTER
(ST_TH: DEFAULT 4)
The Safety Timer Threshold Current register determines
the amount of LED current flowing through the external
LED before the internal LED safety timer is activated. Set-
ting ST_TH to 0 disables the safety timer function, and
setting the register to Values 1-5 sets the safety timer
threshold current to 100 mA to 300 mA in 50 mA steps.
TABLE 5-7: SAFETY TIMER THRESHOLD
CURRENT REGISTER
SETTING AND SAFETY TIMER
THRESHOLD CURRENT
70111 0111 3.6
81000 1000 3.7
91001 1001 3.8
Value
LB_TH<3:0> VBAT Threshold (V)
Dec. Binary
Value
ST_TH<2:0>
Safety Timer
Threshold Current
(mA)
Dec. Binary
0000 000 Disabled
1001 001 100
2010 010 150
3011 011 200
4100 100 250
5101 101 300
MIC2874
DS20006081A-page 20 2018 Microchip Technology Inc.
6.0 COMPONENT SELECTION
6.1 Inductor
Inductor selection should strike a balance between
efficiency, stability, cost, size, and rated current. Because
the boost converter is compensated internally, the recom-
mended inductance of L is limited from 0.47 µH to 1 µH to
ensure system stability, and a 0.47 µH inductor is typically
recommended. It is usually a good balance between
these considerations.
A large inductance value reduces the peak-to-peak
inductor ripple current, hence the output ripple voltage
and the LED ripple current. This also reduces both the
DC loss and the transition loss at the same inductor’s
DC Resistance (DCR). However, the DCR of an inductor
usually increases with the inductance in the same pack-
age size. This is due to the longer windings required for
an increase in inductance. Because the majority of the
input current passes through the inductor, the higher the
DCR, the lower the efficiency is, and more significantly,
at higher load currents. On the other hand, an inductor
with a smaller DCR, but the same inductance, usually
has a larger size. The saturation current rating of the
selected inductor must be higher than the maximum
peak inductor current to be encountered and should be
at least 20% to 30% higher than the average inductor
current at maximum output current.
6.2 Input Capacitor
A ceramic capacitor of 4.7 µF or larger with low-ESR is
recommended to reduce the input voltage ripple to
ensure a clean supply voltage for the device. The input
capacitor should be placed as close as possible to the
MIC2874 VIN pin with a short trace for good noise
performance. X5R or X7R type ceramic capacitors are
recommended for better tolerance over temperature.
The Y5V and Z5U type temperature rating ceramic
capacitors are not recommended due to their large
reduction in capacitance over temperature and
increased resistance at high frequencies. These reduce
their ability to filter out high-frequency noise. The rated
voltage of the input capacitor should be at least 20%
higher than the maximum operating input voltage over
the operating temperature range.
6.3 Output Capacitor
Output capacitor selection is also a trade-off between
performance, size and cost. Increasing output
capacitance will lead to an improved transient
response; however, the size and cost also increase.
The output capacitor’s preferable range of 2.2 µF to
10 µF with ESR from 10 m to 50 m, and a 4.7 µF
ceramic capacitor is typically recommended. X5R or
X7R type ceramic capacitors are recommended for
better tolerance over temperature. The Y5V and Z5U
type ceramic capacitors are not recommended due to
their wide variation in capacitance over temperature
and increased resistance at high frequencies. The
rated voltage of the output capacitor should be at least
20% higher than the maximum operating output
voltage over the operating temperature range.
7.0 POWER DISSIPATION
CONSIDERATION
As with all power devices, the ultimate current rating of the
output is limited by the thermal properties of the device
package and the PCB on which the device is mounted.
There is a simple Ohm’s law type relationship between
thermal resistance, power dissipation and temperature,
which are analogous to an electrical circuit:
FIGURE 7-1: Series Electrical Resistance
Circuit.
From this simple circuit, we can calculate VX if we know
ISOURCE, VZ and the resistor values, R
XY and RYZ, using
Equation 7-1:
EQUATION 7-1: CALCULATING VX
VX
VYVZ
VZ
RXY RYZ
ISOURCE
+
VX = ISOURCE (RXY + RYZ) = VZ
2018 Microchip Technology Inc. DS20006081A-page 25
MIC2874
APPENDIX A: REVISION HISTORY
Revision A (October 2018)
• Converted Micrel document MIC2874 to
Microchip data sheet DS20006081A.
• Minor text changes throughout document.
MIC2874
DS20006081A-page 28 2018 Microchip Technology Inc.
NOTES:
DS20006081A-page 30 2018 Microchip Technology Inc.
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08/15/18

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Model: MIC2874

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