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LP8551
SNVS673E – APRIL 2010 – REVISED SEPTEMBER 2014
LP8551 High-Efficiency LED Backlight Driver for Notebooks
1 Features
3 Description
•
The LP8551 is a white LED driver with integrated
boost converter. It has four adjustable current sinks
which can be controlled by PWM input or with I2Ccompatible serial interface.
High-Voltage DC/DC Boost Converter with
Integrated FET; Four Switching Frequency
Options: 156/312/625/1250 kHz
2.7-V to 22-V Input Voltage Range to Support 1x
to 5x Cell Li-Ion Batteries
50-mA High-Precision LED Current Sinks
Adaptive LED Current Sink Headroom Control for
Maximum System Efficiency
Programmable PWM Resolution 8 to 13 Bits
I2C and PWM Input Duty Cycle Brightness Control
PWM Output Frequency and LED Current Set
Through Resistors
4 LED Outputs with LED Fault (short/open)
Detection
Low Input Voltage, Overtemperature, Overcurrent
Detection, and Shutdown
Minimum Number of External Components
1
•
•
•
•
•
•
•
•
•
2 Applications
•
•
Notebook and Tablet LCD Display LED Backlight
LED Lighting
The boost converter has adaptive output voltage
control based on the LED driver voltages. This
feature minimizes the power consumption by
adjusting the voltage to lowest sufficient level in all
conditions.
LED outputs have 8-bit current resolution and up to
13-bit PWM resolution to achieve smooth and precise
brightness control. Proprietary Phase Shift PWM
control is used for LED outputs to reduce peak
current from the boost converter, thus making the
boost capacitors smaller. The Phase Shifting scheme
also eliminates audible noise.
Internal EEPROM is used for storing the configuration
data. This makes it possible to have minimum
external component count and make the solution very
small.
The LP8551 has safety features which make it
possible to detect LED outputs with open or short
fault. As well, low input voltage and boost overcurrent
conditions are monitored, and chip is turned off in
case of these events. Thermal de-rating function
prevents overheating of the device by reducing
backlight brightness when set temperature has been
reached.
Device Information(1)
PART NUMBER
LP8551
PACKAGE
DSBGA (25)
BODY SIZE (MAX)
2.49 mm x 2.49 mm
(1) For all available packages, see the orderable addendum at
the end of the datasheet.
Simplified Schematic
VBATT
L1
5.5 V ± 22 V
CVLDO
D1
CIN 15 éH
5V
LED Drive Efficiency
10 V ± 40 V
210 mA ± 400 mA
39 pF
10 éF
COUT
4.7 éF
1 éF
VDDIO reference voltage
RISET
VDDIO
VLDO
SW
VIN
FB
ISET
RFSET
OUT1
FSET
SCLK
SDA
LP8551
PWM
EN
Can be left floating
if not used
OUT2
OUT3
MCU
OUT4
FAULT
GNDs
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.
LP8551
SNVS673E – APRIL 2010 – REVISED SEPTEMBER 2014
www.ti.com
Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Device Default Values ...........................................
Pin Configuration and Functions .........................
Specifications.........................................................
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
7.9
7.10
7.11
7.12
1
1
1
2
3
4
5
Absolute Maximum Ratings ...................................... 5
Handling Ratings ...................................................... 5
Recommended Operating Conditions....................... 5
Thermal Information .................................................. 6
Electrical Characteristics........................................... 6
Boost Converter Electrical Characteristics ............... 6
LED Driver Electrical Characteristics ........................ 7
PWM Interface Characteristics ................................. 7
Undervoltage Protection............................................ 8
Logic Interface Characteristics................................ 8
I2C Serial Bus Timing Parameters (SDA, SCLK).... 9
Typical Characteristics .......................................... 10
8
Detailed Description ............................................ 11
8.1
8.2
8.3
8.4
8.5
8.6
9
Overview .................................................................
Functional Block Diagram .......................................
Feature Description.................................................
Device Functional Modes........................................
Programming ..........................................................
Register Map...........................................................
11
11
12
20
21
25
Application and Implementation ........................ 34
9.1 Application Information............................................ 34
9.2 Typical Applications ............................................... 34
10 Power Supply Recommendations ..................... 37
11 Layout................................................................... 38
11.1 Layout Guidelines ................................................. 38
11.2 Layout Example .................................................... 40
12 Device and Documentation Support ................. 41
12.1 Trademarks ........................................................... 41
12.2 Electrostatic Discharge Caution ............................ 41
12.3 Glossary ................................................................ 41
13 Mechanical, Packaging, and Orderable
Information ........................................................... 41
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision D (January 2014) to Revision E
•
Page
Changed formatting to match new TI datasheet guidelines; added Device Information and Handling Ratings tables,
Layout, and Device and Documentation Support sections; reformatted Functional Description to Detailed
Description and Applications to Applications and Implementation sections, added note to beginning of Apps &
Implementations section; moved some waveforms to new Applications Plots subsection. .................................................. 1
Changes from Revision C (April 2013) to Revision D
Page
•
Added EEPROM note........................................................................................................................................................... 24
•
Added EEPROM note........................................................................................................................................................... 28
2
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SNVS673E – APRIL 2010 – REVISED SEPTEMBER 2014
5 Device Default Values
Table 1. Default EEPROM Memory Values
ADDRESS
DEFAULT VALUES LP8551
A0H
0111 1111
A1H
1011 0101
A2H
1010 1110
A3H
0111 1011
A4H
0010 0000
A5H
0000 1001
A6H
0000 0000
A7H
0000 0101
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SNVS673E – APRIL 2010 – REVISED SEPTEMBER 2014
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6 Pin Configuration and Functions
25
DSBGA
Top View
25
DSBGA
Bottom View
1
2
3
4
5
5
A
GND
SW
GND
SW
EN
PWM
FB
FB
B
SW
SW
ISET
FSET
GND_S
C
VIN
NC
FAULT
VDDIO
D
VLDO
GND
SCLK
E
NC
NC
OUT4
4
3
2
1
PWM
EN
GND
SW
GND
SW
A
GND_S
FSET
ISET
SW
SW
B
OUT3
OUT3
VDDIO
FAULT
NC
VIN
C
SDA
OUT2
OUT2
SDA
SCLK
GND
VLDO
D
GND_L
OUT1
OUT1
GND_L
OUT4
NC
NC
E
Pin Functions
PIN
DESCRIPTION
NAME
A1
GND_SW
G
Boost switch ground
A2
GND_SW
G
Boost switch ground
(1)
4
TYPE (1)
NUMBER
A3
EN
I
Enable input pin
A4
PWM
A
PWM dimming input. This pin must be connected to GND if not used.
A5
FB
A
Boost feedback input
B1
SW
A
Boost switch
B2
SW
A
Boost switch
B3
ISET
A
Set resistor for LED current. This pin can be left floating if not used.
B4
FSET
A
PWM frequency set resistor. This pin can be left floating if not used.
B5
GND_S
G
Signal ground
C1
VIN
P
Input power supply up to 22 V. If 2.7 V ≤ VBATT < 5.5 V (Figure 25) then an external 5-V rail
must be used for VLDO and VIN.
Not connected
C2
NC
-
C3
FAULT
OD
C4
VDDIO
P
Digital IO reference voltage (1.65 V to 5 V) for I2C interface. If brightness is controlled with
PWM input pin then this pin can be connected to GND.
C5
OUT3
A
Current sink output
D1
VLDO
P
LDO output voltage. External 5-V rail can be connected to this pin in low voltage application.
D2
GND
G
Ground
D3
SCLK
I
Serial clock. This pin must be connected to GND if not used.
D4
SDA
I/O
Serial data. This pin must be connected to GND if not used.
D5
OUT2
A
Current sink output
E1
NC
-
Not connected
E2
NC
-
Not connected
E3
OUT4
A
Current sink output
E4
GND_L
G
LED ground
E5
OUT1
A
Current sink output
Fault indication output. If not used, can be left floating.
A: Analog Pin, G: Ground Pin, P: Power Pin, I: Input Pin, I/O: Input/Output Pin, O: Output Pin, OD: Open Drain Pin
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7 Specifications
7.1 Absolute Maximum Ratings
Over operating free-air temperature range (unless otherwise noted)
(1)
MIN
MAX
VIN
–0.3
24
VLDO
–0.3
6
Voltage on logic pins (PWM, EN, SCLK, SDA)
–0.3
6
Voltage on logic pin (FAULT)
–0.3
to VDDIO + 0.3
Voltage on analog pins (VDDIO, ISET, FSET)
–0.3
6
V (OUT1...OUT4, SW, FB)
–0.3
44
Continuous power dissipation (2)
UNIT
V
Internally limited
Junction temperature (TJ-MAX)
125
°C
Maximum lead temperature (soldering) (3)
(1)
(2)
(3)
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 150°C (typ.) and
disengages at TJ = 130°C (typ.).
For detailed soldering specifications and information, please refer to TI's AN-1112 (SNVA009): DSBGA Wafer Level Chip Scale
Package.
7.2 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)
–2000
2000
Charged device model (CDM), per JEDEC specification
JESD22-C101, all pins (2)
–1000
1000
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.
7.3 Recommended Operating Conditions (1) (2)
Over operating free-air temperature range (unless otherwise noted)
MIN
Input voltage (VIN) (Figure 22)
Input voltage (VIN + VLDO)(Figure 25)
NOM
MAX
5.5
22
4.5
5.5
1.65
5
0
40
Junction temperature (TJ)
–30
125
Ambient temperature (TA) (3)
–30
85
VDDIO
V(OUT1 to OUT4, SW, FB)
(1)
(2)
(3)
UNIT
V
°C
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
All voltages are with respect to the potential at the GND pins.
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).
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7.4 Thermal Information
DSBGA (YZR)
THERMAL METRIC (1)
RθJA
(1)
(2)
Junction-to-ambient thermal resistance
UNIT
25 PINS
(2)
40 to 73
°C/W
For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
Junction-to-ambient thermal resistance is highly application and board-layout dependent. In applications where high maximum power
dissipation exists, special care must be paid to thermal dissipation issues in board design.
7.5 Electrical Characteristics (1) (2)
Limits are for TA = 25°C and VIN = 12 V, VDDIO = 2.8 V, CVLDO = 1 μF, L1 = 15 μH, CIN = 10 μF, COUT = 10 μF, unless
otherwise specified. RISET = 16 kΩ (3)
SYMBOL
PARAMETER
Standby supply current
Normal mode supply current
fOSC
Internal oscillator frequency
accuracy
VLDO
Internal LDO voltage
ILDO
Internal LDO external loading
(3)
(4)
MIN
TYP
Internal LDO disabled
EN=L and PWM=L
MAX
1
LDO enabled, boost enabled, no current
going through LED outputs
5-MHz PLL Clock
IIN
(1)
(2)
TEST CONDITIONS
(4)
UNIT
μA
3
10-MHz PLL Clock
3.7
20-MHz PLL Clock
4.7
40-MHz PLL Clock
6.7
–4%
–7% (4)
mA
4%
7% (4)
4.5 (4)
5
5.5 (4)
5
V
mA
All voltages are with respect to the potential at the GND pins.
Minimum (Min) and Maximum (Max) limits are specified by design, test, or statistical analysis. Typical numbers are not specified, but do
represent the most likely norm.
Low-ESR surface-mount ceramic capacitors (MLCCs) used in setting electrical characteristics.
Limits apply over the full operating ambient temperature range (–30°C ≤ TA ≤ 85°C).
7.6 Boost Converter Electrical Characteristics
Limits are for TA = 25°C and VIN = 12 V, VDDIO = 2.8 V, CVLDO = 1 μF, L1 = 15 μH, CIN = 10 μF, COUT = 10 μF, unless
otherwise specified. RISET = 16 kΩ (1)
SYMBOL
PARAMETER
RDSON
Switch ON resistance
VMAX
Boost maximum output voltage
TEST CONDITIONS
MIN
TYP
MAX
UNIT
ISW = 0.5 A
0.12
Ω
40
V
9 V ≤ VBATT, VOUT = 35 V
450
6 V ≤ VBATT, VOUT = 35 V
300
3 V ≤ VBATT, VOUT = 25 V
180
ILOAD
Maximum continuous load
current
VOUT/VIN
Conversion ratio
fSW = 1.25 MHz
fSW
Switching frequency
BOOST_FREQ
BOOST_FREQ
BOOST_FREQ
BOOST_FREQ
VOV
Overvoltage protection voltage
tPULSE
Switch pulse minimum width
no load
50
ns
tSTARTUP
Start-up time
See
(2)
6
ms
IMAX
SW pin current limit
IMAX_SEL = 0
IMAX_SEL = 1
(1)
(2)
6
mA
10
= 00
= 01
= 10
= 11
156
312
625
1250
VBOOST + 1.6V
1.4
2.5
kHz
V
A
Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics.
Start-up time is measured from the moment boost is activated until the VOUT crosses 90% of its target value.
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7.7 LED Driver Electrical Characteristics
Limits are for TA = 25°C and VIN = 12 V, VDDIO = 2.8 V, CVLDO = 1 μF, L1 = 15 μH, CIN = 10 μF, COUT = 10 μF, unless
otherwise specified. RISET = 16 kΩ (1)
TYP
MAX
ILEAKAGE
SYMBOL
Leakage current
Outputs OUT1...OUT4, VOUT = 40 V
0.1
1
IMAX
Maximum source current
OUT1...OUT4
EN_I_RES = 0, CURRENT[7:0] = FFh
30
EN_I_RES = 1, CURRENT[7:0] = FFh
50
IOUT
Output current accuracy (2)
Output current set to 23 mA, EN_I_RES = 1
IMATCH
Matching (2)
Output current set to 23 mA, EN_I_RES = 1
PWMRES
VSAT
(3)
(4)
(5)
PWM output resolution (4)
LED switching frequency (4)
fLED
(1)
(2)
PARAMETER
Saturation voltage (5)
TEST CONDITIONS
MIN
–3%
–4% (3)
UNIT
μA
mA
3%
4% (3)
0.5%
fLED = 5 kHz, fPLL = 5 MHz
10
fLED = 10 kHz, fPLL = 5 MHz
9
fLED = 20 kHz, fPLL = 5 MHz
8
fLED = 5 kHz, fPLL = 40 MHz
13
fLED = 10 kHz, fPLL = 40 MHz
12
fLED = 20 kHz, fPLL = 40 MHz
11
bits
PWM_FREQ[4:0] = 00000b
PLL clock 5 MHz
600
PWM_FREQ[4:0] = 11111b
PLL clock 5 MHz
19.2k
Output current set to 20 mA
105
220 (3)
Output current set to 30 mA
160
290 (3)
Hz
mV
Low-ESR surface-mount ceramic capacitors (MLCCs) used in setting electrical characteristics.
Output Current Accuracy is the difference between the actual value of the output current and programmed value of this current.
Matching is the maximum difference from the average. For the constant current sinks on the part (OUT1 to OUT4), the following are
determined: the maximum output current (MAX), the minimum output current (MIN), and the average output current of all outputs (AVG).
Two matching numbers are calculated: (MAX-AVG)/AVG and (AVG-MIN/AVG). The largest number of the two (worst case) is
considered the matching figure. The typical specification provided is the most likely norm of the matching figure for all parts. Note that
some manufacturers have different definitions in use.
Limits apply over the full operating ambient temperature range (–30°C ≤ TA ≤ 85°C).
PWM output resolution and frequency depend on the PLL settings. Please see section PWM Frequency Setting for full description.
Saturation voltage is defined as the voltage when the LED current has dropped 10% from the value measured at 1 V.
7.8 PWM Interface Characteristics
Limits are for TA = 25°C and VIN = 12 V, VDDIO = 2.8 V, CVLDO = 1 μF, L1 = 15 μH, CIN = 10 μF, COUT = 10 μF, unless
otherwise specified. RISET = 16 kΩ (1)
SYMBOL
PARAMETER
TEST CONDITIONS
MIN
TYP
ƒPWM
PWM frequency range
tMIN_ON
Minimum pulse ON time
1
tMIN_OFF
Minimum pulse OFF time
1
tSTARTUP
Turnon delay from standby to
backlight on
PWM input active, EN pin rise from low to
high
TSTBY
Turnoff Delay
PWM Input Resolution
PWMRES
(1)
0.1
MAX
25
UNIT
kHz
μs
6
ms
PWM input low time for turn off, slope
disabled
50
ms
ƒIN
ƒIN
ƒIN
ƒIN
10
11
12
13
bits
<
<
<
<
9 kHz
4.5 kHz
2.2 kHz
1.1 kHz
Low-ESR surface-mount ceramic capacitors (MLCCs) used in setting electrical characteristics.
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7.9 Undervoltage Protection
Limits are for TA = 25°C and VIN = 12 V, VDDIO = 2.8 V, CVLDO = 1 μF, L1 = 15 μH, CIN = 10 μF, COUT = 10 μF, unless
otherwise specified. RISET = 16 kΩ (1)
SYMBOL
PARAMETER
TEST CONDITIONS
MIN
UVLO[1:0] = 00
VUVLO
(1)
VIN UVLO Threshold Voltage
TYP
MAX
UNIT
Disabled
UVLO[1:0] = 01, falling
2.55
2.70
2.94
UVLO[1:0] = 01, rising
2.62
2.76
3.00
UVLO[1:0] = 10, falling
5.11
5.40
5.68
UVLO[1:0] = 10, rising
5.38
5.70
5.98
UVLO[1:0] = 11, falling
7.75
8.10
8.45
UVLO[1:0] = 11, rising
8.36
8.73
9.20
V
Low-ESR surface-mount ceramic capacitors (MLCCs) used in setting electrical characteristics.
7.10 Logic Interface Characteristics
Limits apply over the full operating ambient temperature range (–30°C ≤ TA ≤ 85°C), and VIN = 12 V, VDDIO = 2.8 V, CVLDO = 1
μF, L1 = 15 μH, CIN = 10 μF, COUT = 10 μF, unless otherwise specified. RISET = 16 kΩ (1)
SYMBOL
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
LOGIC INPUT EN
VIL
Input low level
VIH
Input high level
1.2
II
Input current
–1
0.4
V
1
μA
0.4
V
1
μA
0.2xVDDIO
V
V
LOGIC INPUT PWM
VIL
Input low level
VIH
Input high level
2.2
II
Input current
–1
V
LOGIC INPUTS SCL, SDA
VIL
Input low level
VIH
Input high level
II
Input current
0.8xVDDIO
V
μA
LOGIC OUTPUTS SDA, FAULT
VOL
Output low level
IOUT = 3 mA (pullup current)
IL
Output leakage current
VOUT = 2.8 V
(1)
(2)
8
0.3 (2)
–1
0.5
V
1
μA
Low-ESR surface-mount ceramic capacitors (MLCCs) used in setting electrical characteristics.
Limits are TA = 25 °C.
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7.11 I2C Serial Bus Timing Parameters (SDA, SCLK) (1)
SYMBOL
PARAMETER
MIN
MAX
UNIT
400
kHz
ƒSCLK
Clock frequency
1
Hold time (repeated) START condition
0.6
μs
2
Clock low time
1.3
μs
3
Clock high time
600
ns
4
Setup time for a repeated START condition
600
ns
5
Data hold time
50
ns
6
Data setup time
7
Rise time of SDA and SCL
20+0.1Cb
300
ns
8
Fall time of SDA and SCL
15+0.1Cb
300
ns
9
Setup time for STOP condition
600
ns
10
Bus free time between a STOP and a START condition
1.3
μs
Cb
Capacitive load parameter for each bus line
Load of 1 pF corresponds to 1 ns.
10
(1)
100
ns
200
ns
Specified by design. VDDIO = 1.65 V to 5.5 V.
Figure 1. I2C Timing Parameters
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7.12 Typical Characteristics
Unless otherwise specified: VBATT= 12 V, CVLDO= 1 μF, L1 = 33 μH, CIN= 10 μF, COUT= 10 μF.
ƒLED= 9.6 kHz
L1 = 15 μH
ƒLED= 9.6 kHz
Figure 2. LED Drive Efficiency
Figure 3. LED Drive Efficiency
1,200
INPUT CURRENT (mA)
1,000
800
VBOOST = 40V
VBOOST = 35V
600
400
200
VBOOST = 30V
LOAD = 150 mA
0
6
8
10
12
14
16
18
20
VBATT (V)
Figure 4. Boost Converter Efficiency
Figure 5. Battery Current
50
ILED (mA)
40
CURRENT[7:0] = FFh
30
20
10
0
CURRENT[7:0] = 7Fh
0 10 20 30 40 50 60 70 80 90 100
RISET (k
)
Figure 6. ILED vs. RISET
10
Figure 7. Boost Line Transient Response
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8 Detailed Description
8.1 Overview
The LP8551 is a high-voltage LED driver for medium sized LCD backlight applications. It includes high-voltage
boost converter. Boost voltage automatically sets to the correct level needed to drive the LED strings. This is
done by monitoring LED output voltage drop in real time.
Four constant current sinks with PWM control are used for driving LEDs. Constant current value is set with
EEPROM bits and with RISET resistor. Brightness (PWM) is controlled either with I2C register or with PWM input.
PWM frequencies are set with EEPROM bits and with RFSET resistor. Special Phase-Shift PWM mode can be
used to reduce boost output current peak, thus reducing output ripple, capacitor size, and audible noise.
Safety features include LED fault detection with open and short detection. LED fault detection prevents system
overheating in case of open in some of the LED strings. Chip internal temperature is constantly monitored and,
based on this, the LP8551 can reduce the brightness of the backlight to reduce thermal loading once certain trip
point is reached. Threshold is programmable in EEPROM. If chip internal temperature reaches too high, the
boost converter and LED outputs are completely turned off until the internal temperature has reached acceptable
level. Boost converter is protected against too high load current and over-voltage. The LP8551 notifies the
system about the fault through I2C register and with FAULT pin.
EEPROM programmable functions include:
• PWM frequencies
• Phase shift PWM mode
• LED constant current
• Boost output frequency
• Temperature thresholds
• Slope for brightness changes
• PWM output resolution
• Boost control bits
External components RISET and RFSET can also be used for selecting the output current and PWM frequencies.
8.2 Functional Block Diagram
VBATT
VLDO
VIN
SW
LDO
OSC
TSD
TEMP
SENSOR
FB
BOOST
GND_SW
OUT1
PLL
OUT2
OUT3
VDDIO
PWM
PWM
DETECTOR
OUT4
LED
DRIVERS
ISET
MCU
SCLK
SDA
RISET
LOGIC
2
I C/
INTERFACE
FSET
RFSET
GND_LED
FAULT
EN
EEPROM
GNDs
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8.3 Feature Description
8.3.1 Clock Generation
The LP8551 has internal 5-MHz oscillator which is used for clocking the boost converter, state machine, PWM
outputs, PWM input duty cycle measurement, internal timings such as slope time for output brightness changes.
For PWM output generation the 5-MHz clock can be multiplied with the internal PLL to achieve higher resolution.
The higher the clock frequency for PWM generation block, the higher the resolution but the tradeoff is higher IQ
of the part. Clock multiplication is set with EEPROM Bits.
PWM_FREQ[4:0]
or External
VBOOST
set resistor RFSET PSPWM 0/1
PLL
5 MHz...40 MHz
Phase
Detector
5 MHz internal
oscillator
Filter
VCO
PWM generation
LED Drivers 1-4
BOOST_FREQ
N = 4, 8, 16, 32
Divider
1/N
Counter
1/N
State machine,
PWM input, internal
timings, Slope etc.
Boost
PWM_RESOLUTION[1:0]
Figure 8. Principle of the Clock Generation
8.3.2 Brightness Control Methods
The LP8551 controls the brightness of the backlight with PWM. PWM control is received either from PWM input
pin or from I2C register bits. The PWM source selection is done with bits as follows:
BRT_MODE[1]
BRT_MODE[0]
PWM SOURCE
0
0
PWM input pin duty cycle control. Default.
0
1
PWM input pin duty cycle control.
1
0
Brightness register
1
1
PWM direct control (PWM in = PWM out)
8.3.2.1 PWM Input Duty Cycle
With PWM input pin duty cycle control the output PWM is controlled by PWM input duty cycle. PWM detector
block measures the duty cycle in the PWM pin and uses this 13-bit value to generate the output PWM. Output
PWM can have different frequency than input in this mode and also phase shift PWM mode can be used. Slope
is effective in this mode. PWM input resolution is defined by the input PWM clock frequency.
8.3.2.2 Brightness Register Control
With brightness register control the output PWM is controlled with 8-bit resolution register bits. Phase
shift scheme can be used with this, and the output PWM frequency can be freely selected. Slope is effective in
this mode.
8.3.2.3 PWM Direct Control
With PWM direct control the output PWM directly follows the input PWM. Due to the internal logic structure the
input is anyway clocked with the 5 MHz clock or the PLL clock. PSPWM mode is not possible in this mode. Slope
is not effective in this mode.
12
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8.3.2.4 PWM Calculation Data Flow
Figure 9 shows the PWM calculation data flow. In PWM direct control mode most of the blocks are bypassed,
and this flow chart does not apply.
HYSTERESIS 5 MHz
clock
[1:0]
PWM input
signal
PWM
detector
BRT_MODE
[1:0]
13-bit
Temperature
sensor
Brightness
register
Brightness
control
PWM_FREQ[4:0]
13-bit
Resolution
selector
SLOPE[3:0]
8...13-bit
16-bit
Sloper
PWM
comparator
13-bit
12-bit
PLL clock 5...40 MHz
PWM_RESOLUTION
[1:0]
PWM
Counter
0/1
...
LED Drivers
1-4
8-bit
Figure 9. PWM Calculation Data Flow
8.3.2.5 PWM Detector
The PWM detector block measures the duty cycle of the input PWM signal. Resolution depends on the input
signal frequency. Hysteresis selection sets the minimum allowable change to the input. If smaller change is
detected, it is ignored. With hysteresis the constant changing between two brightness values is avoided if there is
small jitter in the input signal.
8.3.2.6 Brightness Control
Brightness control block gets 13-bit value from the PWM detector, 12-bit value from the temperature sensor, and
also 8-bit value from the brightness register. selects whether to use PWM input duty cycle
value or the brightness register value as described earlier. Based on the temperature sensor value the duty cycle
is reduced if the temperature has reached the temperature limit set to the EEPROM bits.
8.3.2.7 Resolution Selector
Resolution selector takes the necessary MSB bits from the input data to match the output resolution. For
example if 11-bit resolution is used for output, then 11 MSB bits are selected from the input.
8.3.2.8 Sloper
Sloper makes the smooth transition from one brightness value to another. Slope time can be adjusted from 0 to
500 ms with EEPROM bits. The sloper output is 16-bit value.
8.3.2.9 PWM Comparator
The PWM counter clocks the PWM comparator based on the duty cycle value. Output of the PWM comparator
controls directly the LED drivers. If PSPWM mode is used, then the signal to each LED output is delayed certain
amount.
8.3.2.10 Current Setting
Maximum current of the LED outputs is controlled with CURRENT[7:0] EEPROM register bits linearly from 0 to
30 mA. If = 1 the maximum LED output current can be scaled also with external resistor, RISET.
RISET controls the LED current as follows:
(1)
Default value for CURRENT[7:0] = 7Fh (127d). Therefore, the output current can be calculated as follows:
(2)
For example, if a 16-kΩ RISET resistor is used, then the LED maximum current is 23 mA.
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NOTE
Formula is only approximation for the actual current.
8.3.2.11 PWM Frequency Setting
PWM frequency is selected with PWM_FREQ[4:0] EEPROM register. If PLL clock frequency multiplication is
used, it affects the output PWM frequency as well. EEPROM bits select the PLL
output frequency and hence the PWM frequency and resolution. PWM resolution setting affects the PLL clock
frequency (5 MHz to 40 MHz). Highlighted frequencies with boldface can be selected also with external resistor
RFSET. To activate RFSET frequency selection the EEPROM bit must be 1.
14
PWM_RES[1:0]
00
01
10
11
PWM_FREQ[4:0]
5 MHz
10 MHz
20 MHz
40 MHz
11111
19232
-
-
-
8
11110
16828
-
-
-
8
11101
14424
-
-
-
8
11100
12020
-
-
-
8
11011
9616
19232
-
-
9
11010
7963
15927
-
-
9
11001
6386
12771
-
-
9
11000
4808
9616
19232
-
10
10111
4658
9316
18631
-
10
10110
4508
9015
18030
-
10
10101
4357
8715
17429
-
10
10100
4207
8414
16828
-
10
10011
4057
8114
16227
-
10
10010
3907
7813
15626
-
10
10001
3756
7513
15025
-
10
10000
3606
7212
14424
-
10
01111
3456
6912
13823
-
10
01110
3306
6611
13222
-
10
01101
3155
6311
12621
-
10
01100
3005
6010
12020
-
10
01011
2855
5710
11419
-
10
01010
2705
5409
10818
-
10
01001
2554
5109
10217
-
10
01000
2404
4808
9616
19232
11
00111
2179
4357
8715
17429
11
00110
1953
3907
7813
15626
11
00101
1728
3456
6912
13823
11
00100
1503
3005
6010
12020
11
00011
1202
2404
4808
9616
12
00010
1052
2104
4207
8414
12
00001
826
1653
3306
6611
12
00000
601
1202
2404
4808
13
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RESOLUTION (BITS)
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RFSET resistance values with corresponding PWM frequencies:
PWM_RES[1:0]
00
01
10
11
RFSET (kΩ)
5 MHz
CLOCK
RESOLUTION
10 MHz
CLOCK
RESOLUTION
20 MHz
CLOCK
RESOLUTION
40 MHz
CLOCK
RESOLUTION
10...15
19232
8
19232
9
19232
10
19232
11
26...29
16828
8
15927
9
16227
10
17429
11
36...41
14424
8
12771
9
14424
10
15626
11
50...60
12020
8
9616
10
12020
10
12020
11
85...100
9616
9
8715
10
9616
11
9616
12
135...150
7963
9
7813
10
7813
11
8414
12
200...300
6386
9
6311
10
6010
11
6811
12
450...
4808
10
4808
11
4808
12
4808
13
8.3.2.12 Phase Shift PWM (PSPWM) Scheme
The PSPWM scheme allows delaying the time when each LED output is active. When the LED output are not
activated simultaneously, the peak load current from the boost output is greatly decreased. This reduces the
ripple seen on the boost output and allows smaller output capacitors. Reduced ripple also reduces the output
ceramic capacitor audible ringing. PSPWM scheme also increases the load frequency seen on boost output by
x4 and therefore transfers the possible audible noise to so high frequency that human ear cannot hear it.
Description of the PSPWM mode is seen on the following diagram. PSPWM mode is enabled by setting
EEPROM bit to 1. Shift time is the delay between outputs and it is defined as 1 / (fPWM x 4). If the
bit is 0, then the delay is 0 and all outputs are active simultaneously.
Shift time
tSHIFT = 1/(FPWM x 4)
Cycle time
1/(FPWM)
OUT1
OUT2
OUT3
OUT4
Figure 10. PSPWM Mode
8.3.2.13 Slope
Slope time can be programmed with EEPROM bits from 0 to 500 ms. The same slope time is
used for sloping up and down. Advanced slope makes brightness changes smooth for eye.
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Brightness (PWM)
Sloper Input
Brightness (PWM)
PWM Output
Time
Normal slope
Advanced slope
Time
Slope Time
Figure 11. Sloper Operation
8.3.2.14 Driver Headroom Control
Driver headroom can be controlled with EEPROM bits. Driver headroom control sets the
minimum threshold for the voltage over the LED output which has the smallest driver headroom and controls the
boost output voltage accordingly. Boost output voltage step size is 125 mV. The LED output which has the
smallest forward voltage is the one which has highest VF across the LEDs. The strings with highest forward
voltage is detected automatically. To achieve best possible efficiency smallest possible headroom voltage should
be selected. If there is high variation between LED strings, the headroom can be raised slightly to prevent any
visual artifacts.
8.3.3 Boost Converter
8.3.3.1 Operation
The LP8551 boost DC/DC converter generates a 10-V to 40-V supply voltage for the LEDs from 2.7-V to 22-V
input voltage. The output voltage can be controlled either with EEPROM register bits or
automatic adaptive voltage control can be used. The converter is a magnetic switching PWM mode DC/DC
converter with a current limit. The topology of the magnetic boost converter is called CPM (current programmed
mode) control, where the inductor current is measured and controlled with the feedback. Switching frequency is
selectable between 156 kHz and 1.25 MHz with EEPROM bit . When
EEPROM register bit is set to 1, then boost activates automatically when backlight is enabled.
In adaptive mode the boost output voltage is adjusted automatically based on LED driver headroom voltage.
Boost output voltage control step size is, in this case, 125 mV, to ensure as small as possible driver headroom
and high efficiency. Enabling the adaptive mode is done with EEPROM bit. If boost is started with
adaptive mode enabled, then the initial boost output voltage value is defined with the EEPROM
register bits in order to eliminate long output voltage iteration time when boost is started for the first time.
Figure 12 shows the boost topology with the protection circuitry:
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FB
SW
Startup
VREF
Light
Load
OVP
R
R
+
gm
-
+
R
S
Boost output
voltage
adjustment
Osc/
ramp
R
Switch
Driver
OCP
6
Active Load
+
-
Figure 12. Boost Topology with Protection Circuitry
8.3.3.2 Protection
Three different protection schemes are implemented:
1. Overvoltage protection, limits the maximum output voltage.
– Overvoltage protection limit changes dynamically based on output voltage setting.
– Keeps the output below breakdown voltage.
– Prevents boost operation if battery voltage is much higher than desired output.
2. Overcurrent protection, limits the maximum inductor current.
3. Duty cycle limiting.
8.3.3.3 Manual Output Voltage Control
User can control the boost output voltage with EEPROM register bits when adaptive mode is
disabled.
VBOOST[4:0]
VOLTAGE (TYPICAL)
BIN
DEC
VOLTS
00000
0
10
00001
1
11
00010
2
12
00011
3
13
00100
4
14
...
...
...
11101
29
39
11110
30
40
11111
31
40
8.3.3.4 Adaptive Boost Control
Adaptive boost control function adjusts the boost output voltage to the minimum sufficient voltage for proper LED
driver operation. The output with highest VF LED string is detected and boost output voltage adjusted
accordingly. Driver headroom can be adjusted with EEPROM bits from approximately
300 mV to 1200 mV. Boost adaptive control voltage step size is 125 mV. Boost adaptive control operates
similarly with and without PSPWM.
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VBOOST
Driver
headroom
OUT1 string VF
OUT4 string VF
OUT3 string VF
OUT2 string VF
OUT1 string VF
VBOOST
Time
Figure 13. Boost Adaptive Control Principle with PSPWM
8.3.4 Fault Detection
The LP8551 has fault detection for LED fault, low-battery voltage, overcurrent, and thermal shutdown. The open
drain output pin (FAULT) can be used to indicate occurred fault. The cause for the fault can be read from status
register. Reading the fault register also resets the fault. Setting the EN pin low also resets the faults, even if an
external 5-V line is used to power VLDO pin.
8.3.4.1 LED Fault Detection
With LED fault detection, the voltages across the LED drivers are constantly monitored. LED fault detection is
enabled with EEPROM bit. Shorted or open LED string is detected.
If LED fault is detected:
• The corresponding LED string is taken out of boost adaptive control loop;
• Fault bits are set in the fault register to identify whether the fault has been open/short and how many strings
are faulty; and
• Fault open-drain pin is pulled down.
LED fault sensitivity can be adjusted with EEPROM bit which sets the allowable variation
between LED output voltage to 3.3 V or 5.3 V. Depending on application and how much variation there can be in
normal operation between LED string forward voltages this setting can be adjusted.
Fault is cleared by setting EN pin low or by reading the fault register.
8.3.4.2 Undervoltage Detection
The LP8551 has detection for too-low VIN voltage. Threshold level for the voltage is set with EEPROM register
bits as seen in Table 2:
Table 2.
UVLO[1:0]
THRESHOLD (V)
00
OFF
01
2.7V
10
5.4V
11
8.1V
When undervoltage is detected, the LED outputs and boost shut down, the FAULT pin is pulled down, and
corresponding fault bit is set in fault register. LEDs and boost starts again when the voltage has increased above
the threshold level. Hysteresis is implemented to threshold level to avoid continuous triggering of fault when
threshold is reached.
Fault is cleared by setting EN pin low or by reading the fault register.
8.3.4.3 Overcurrent Protection
The LP8551 has detection for too-high loading on the boost converter. When overcurrent fault is detected, the
LP8551 shuts down.
Fault is cleared by setting EN pin low or by reading the fault register.
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8.3.4.4 Device Thermal Regulation
The LP8551 has an internal temperature sensor which can be used to measure the junction temperature of the
device and protect the device from overheating. During thermal regulation, LED PWM is reduced by 2% of full
scale per °C whenever the temperature threshold is reached. Temperature regulation is enabled automatically
when chip is enabled. 11-bit temperature value can be read from Temp MSB and Temp LSB registers, MSB
should be read first. Temperature limit can be programmed in EEPROM as shown in the following table.
Thermal regulation function does not generate fault signal.
TEMP_LIM[1:0]
OVER-TEMP LIMIT (°C)
00
OFF
01
110
10
120
11
130
8.3.4.5 Thermal Shutdown
If the LP8551 reaches thermal shutdown temperature (150°C), the LED outputs and boost shut down to protect it
from damage. Also the FAULT pin is pulled down to indicate the fault state. The device activates again when
temperature drops below 130°C degrees.
Fault is cleared by setting EN pin low or by reading the fault register.
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8.4 Device Functional Modes
RESET
EN = H (pin)
VLDO ok
EN = L (VLDO low)
or POR = H
STANDBY
EN = H (pin) and BL_CTL = 1
or PWM = H (pin)
BL_CTL = 0 and
PWM = L
INTERNAL
STARTUP
SEQUENCE
VREF = 95% OK*
TSD = H
~2 ms Delay
EN_BOOST = 1*
EN_BOOST = 0*
BOOST STARTUP
EN_BOOST
rising edge*
~4 ms Delay
NORMAL MODE
*) TSD = L
Figure 14. Modes of Operation
8.4.1 Modes of Operation
RESET:
In the RESET mode all the internal registers are reset to the default values. Reset is entered
always when VLDO voltage is low. EN pin is enable for the internal LDO. Power On Reset (POR)
activates during the chip startup or when the supply voltage VLDO fall below POR level. Once VLDO
rises above POR level, POR inactivates, and the chip continues to the STANDBY mode.
STANDBY: The STANDBY mode is entered if the register bit BL_CTL is LOW and external PWM input is not
active and POR is not active. This is the low power consumption mode, when only internal 5-V LDO
is enabled. Registers can be written in this mode and the control bits are effective immediately after
start up.
START-UP: When BL_CTL bit is written high or PWM signal is high, the INTERNAL START-UP SEQUENCE
powers up all the needed internal blocks (VREF, Bias, Oscillator etc.). Internal EPROM and
EEPROM are read in this mode. To ensure the correct oscillator initialization etc., a 2-ms delay is
generated by the internal state-machine. If the chip temperature rises too high, the Thermal
Shutdown (TSD) disables the chip operation and STARTUP mode is entered until no thermal
shutdown event is present.
BOOST START-UP: Soft start for boost output is generated in the BOOST START-UP mode. The boost output
is raised in low current PWM mode during the 4-ms delay generated by the state-machine. All LED
outputs are off during the 4-ms delay to ensure smooth startup. The Boost start-up is entered from
Internal Start-up Sequence if EN_BOOST is HIGH.
NORMAL:
20
During NORMAL mode the user controls the chip using the external PWM input or with Control
Registers through I2C. The registers can be written in any sequence and any number of bits can be
altered in a register in one write.
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8.5 Programming
8.5.1 I2C-Compatible Serial Bus Interface
8.5.1.1 Interface Bus Overview
The I2C-compatible synchronous serial interface provides access to the programmable functions and registers on
the device. This protocol uses a two-wire interface for bidirectional communications between the IC's connected
to the bus. The two interface lines are the Serial Data Line (SDA) and the Serial Clock Line (SCLK). These lines
should be connected to a positive supply, via a pull-up resistor and remain HIGH even when the bus is idle.
Every device on the bus is assigned a unique address and acts as either a Master or a Slave depending on
whether it generates or receives the SCLK. The LP8551 is always a slave device.
8.5.1.2 Data Transactions
One data bit is transferred during each clock pulse. Data is sampled during the high state of the serial clock
SCLK. Consequently, throughout the clock’s high period, the data should remain stable. Any changes on the
SDA line during the high state of the SCLK and in the middle of a transaction, aborts the current transaction.
New data should be sent during the low SCLK state. This protocol permits a single data line to transfer both
command/control information and data using the synchronous serial clock.
SDA
SCL
Data Line
Stable:
Data Valid
Change
of Data
Allowed
Figure 15. Bit Transfer
Each data transaction is composed of a Start Condition, a number of byte transfers (set by the software) and a
Stop Condition to terminate the transaction. Every byte written to the SDA bus must be 8 bits long and is
transferred with the most significant bit first. After each byte, an Acknowledge signal must follow. The following
sections provide further details of this process.
Data Output
by
Transmitter
Transmitter Stays Off the
Bus During the
Acknowledgment Clock
Data Output
by
Receiver
Acknowledgment
Signal From Receiver
SCL
1
2
3-6
7
8
9
S
Start
Condition
Figure 16. Start and Stop
The Master device on the bus always generates the Start and Stop Conditions (control codes). After a Start
Condition is generated, the bus is considered busy and it retains this status until a certain time after a Stop
Condition is generated. A high-to-low transition of the data line (SDA) while the clock (SCLK) is high indicates a
Start Condition. A low-to-high transition of the SDA line while the SCLK is high indicates a Stop Condition.
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Programming (continued)
SDA
SCL
S
P
Start
Condition
Stop
Condition
Figure 17. Start and Stop Conditions
In addition to the first Start Condition, a repeated Start Condition can be generated in the middle of a transaction.
This allows another device to be accessed, or a register read cycle.
8.5.1.3 Acknowledge Cycle
The Acknowledge Cycle consists of two signals: the acknowledge clock pulse the master sends with each byte
transferred, and the acknowledge signal sent by the receiving device.
The master generates the acknowledge clock pulse on the ninth clock pulse of the byte transfer. The transmitter
releases the SDA line (permits it to go high) to allow the receiver to send the acknowledge signal. The receiver
must pull down the SDA line during the acknowledge clock pulse and ensure that SDA remains low during the
high period of the clock pulse, thus signaling the correct reception of the last data byte and its readiness to
receive the next byte.
8.5.1.4 “Acknowledge After Every Byte” Rule
The master generates an acknowledge clock pulse after each byte transfer. The receiver sends an acknowledge
signal after every byte received.
There is one exception to the “acknowledge after every byte” rule. When the master is the receiver, it must
indicate to the transmitter an end of data by not-acknowledging (“negative acknowledge”) the last byte clocked
out of the slave. This “negative acknowledge” still includes the acknowledge clock pulse (generated by the
master), but the SDA line is not pulled down.
8.5.1.5 Addressing Transfer Formats
Each device on the bus has a unique slave address. The LP8551 operates as a slave device with 7-bit address
combined with data direction bit. Slave address is 2Ch as 7-bit or 58h for write and 59h for read in 8-bit format.
Before any data is transmitted, the master transmits the address of the slave being addressed. The slave device
should send an acknowledge signal on the SDA line, once it recognizes its address.
The slave address is the first seven bits after a Start Condition. The direction of the data transfer (R/W) depends
on the bit sent after the slave address — the eighth bit.
When the slave address is sent, each device in the system compares this slave address with its own. If there is a
match, the device considers itself addressed and sends an acknowledge signal. Depending upon the state of the
R/W bit (1:read, 0:write), the device acts as a transmitter or a receiver.
MSB
LSB
ADR6
Bit7
ADR5
bit6
ADR4
bit5
ADR3
bit4
ADR2
bit3
ADR1
bit2
ADR0
bit1
x
x
x
x
x
x
x
R/W
bit0
2
I C SLAVE address (chip address)
Figure 18. I2C Chip Address
8.5.1.6 Control Register Write Cycle
• Master device generates start condition.
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Programming (continued)
•
•
•
•
•
•
•
•
Master device sends slave address (7 bits) and the data direction bit (r/w = 0).
Slave device sends acknowledge signal if the slave address is correct.
Master sends control register address (8 bits).
Slave sends acknowledge signal.
Master sends data byte to be written to the addressed register.
Slave sends acknowledge signal.
If master sends further data bytes the control register address is incremented by one after acknowledge
signal.
Write cycle ends when the master creates stop condition.
8.5.1.7 Control Register Read Cycle
• Master device generates a start condition.
• Master device sends slave address (7 bits) and the data direction bit (r/w = 0).
• Slave device sends acknowledge signal if the slave address is correct.
• Master sends control register address (8 bits).
• Slave sends acknowledge signal.
• Master device generates repeated start condition.
• Master sends the slave address (7 bits) and the data direction bit (r/w = 1).
• Slave sends acknowledge signal if the slave address is correct.
• Slave sends data byte from addressed register.
• If the master device sends acknowledge signal, the control register address is incremented by one. Slave
device sends data byte from addressed register.
• Read cycle ends when the master does not generate acknowledge signal after data byte and generates stop
condition.
Table 3. Data Read and Write Cycles
ADDRESS MODE
Data Read
[Ack]
[Ack]
[Ack]
[Register Data]
… additional reads from subsequent register address possible
Data Write
[Ack]
[Ack]
[Ack]
… additional writes to subsequent register address possible
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8.5.1.8 Register Read and Write Detail
Slave Address
(7 bits)
S
'0' A
Control Register Add.
A
(8 bits)
Register Data
(8 bits)
A P
Data transfered,
byte + Ack
R/W
From Slave to Master
A - ACKNOWLEDGE (SDA Low)
S - START CONDITION
From Master to Slave
P - STOP CONDITION
Register Write Format
Figure 19. LP8551 Register Write Format
S
Slave Address
(7 bits)
'0' A
Control Register Add.
A Sr
(8 bits)
Slave Address
(7 bits)
R/W
Data- Data
(8 bits)
'1' A
A/
P
NA
Data transfered, byte +
Ack/NAck
R/W
Direction of the transfer
will change at this point
From Slave to Master
From Master to Slave
A - ACKNOWLEDGE (SDA Low)
NA - ACKNOWLEDGE (SDA High)
S - START CONDITION
Sr - REPEATED START CONDITION
P - STOP CONDITION
Register Read Format
Figure 20. LP8551 Register Read Format
8.5.2 EEPROM
EEPROM memory stores various parameters for chip control. The 64-bit EEPROM memory is organized as 8 x 8
bits. The EEPROM structure consists of a register front-end and the non-volatile memory (NVM). Register data
can be read and written through the serial interface, and data is effective immediately. To read and program
NVM, separate commands need to be sent. Erase and program voltages are generated on-chip charge pump, no
other voltages than normal input voltage are required. A complete EEPROM memory map is shown in the Device
Default Values section.
NOTE
EEPROM NVM can be programmed or read by customer for bench validation.
Programming for production devices should be done in TI production test, where
appropriate checks are performed to confirm EEPROM validity. Writing to EEPROM
Control register of production devices is not recommended. If special EEPROM
configuration is required, please contact the TI Sales Office for availability.
EE_PROG = 1
EEPROM
NVM
EEPROM
REGISTERS
Address A0h...A7h
2
I C
8 x 8 bits
Startup or
EE_READ=1
User
Device Control
REGISTERS
ADDRESS 00h...72h
Device Control
Figure 21. EEPROM Control Structure
24
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8.6 Register Map
ADDR
REGISTER
00H
Brightness Control
D7
01H
Device Control
02H
Fault
OPEN
03H
ID
PANEL
04H
Direct Control
05H
Temp MSB
06H
Temp LSB
72H
EEPROM_control
D6
D5
D4
D3
D2
D1
D0
BRT[7:0]
BRT_MODE[1:0]
SHORT
2_CHANNELS
1_CHANNEL
BL_FAULT
DEFAULT
0000 0000
OCP
TSD
MFG[3:0]
BL_CTL
0000 0000
UVLO
0000 0000
REV[2:0]
1111 1100
OUT[4:1]
0000 0000
TEMP[10:3]
0000 0000
TEMP[2:0]
0000 0000
EE_READY
EE_INIT
EE_PROG
EE_READ
0000 0000
8.6.1 Register Bit Explanations
8.6.1.1 Brightness Control
Address 00h
Reset value 0000 0000b
BRIGHTNESS CONTROL REGISTER
7
6
5
4
3
2
1
0
2
1
0
BRT[7:0]
Name
Bit
Access
BRT
7:0
R/W
Description
Backlight PWM 8-bit linear control.
8.6.1.2 Device Control
Address 01h
Reset value 0000 0000b
DEVICE CONTROL REGISTER
7
6
5
4
3
BRT_MODE[1:0]
Name
Bit
Access
BRT_MODE
2:1
R/W
BL_CTL
Description
PWM source mode
00b = PWM input pin duty cycle control (default)
01b = PWM input pin duty cycle control
10b = Brightness register
11b = Direct PWM control from PWM input pin
BL_CTL
0
R/W
Enable backlight
0 = Backlight disabled and chip turned off if BRT_MODE[1:0] = 10. In external PWM
pin control the state of the chip is defined with the PWM pin, and this bit has no
effect.
1 = Backlight enabled and chip turned on if BRT_MODE[1:0] = 10. In external PWM
pin control the state of the chip is defined with the PWM pin, and this bit has no
effect.
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8.6.1.3 Fault
Address 02h
Reset value 0000 0000b
FAULT REGISTER
7
6
5
4
3
2
1
0
OPEN
SHORT
2_CHANNELS
1_CHANNEL
BL_FAULT
OCP
TSD
UVLO
Name
Bit
Access
OPEN
7
R
Description
LED open fault detection
0 = No fault
1 = LED open fault detected. Fault pin is pulled to GND. Fault is cleared by reading
the register 02h or setting EN pin low.
SHORT
6
R
LED short fault detection
0 = No fault
1 = LED short fault detected. Fault pin is pulled to GND. Fault is cleared by reading
the register 02h or setting EN pin low.
2_CHANNELS
5
R
LED fault detection
0 = No fault
1 = 2 or more channels have generated either short or open fault. Fault pin is pulled to
GND. Fault is cleared by reading the register 02h or setting EN pin low.
1_CHANNEL
4
R
LED fault detection
0 = No fault
1 = 1 channel has generated either short or open fault. Fault pin is pulled to GND.
Fault is cleared by reading the register 02h or setting EN pin low.
BL_FAULT
3
R
LED fault detection
0 = No fault
1 = LED fault detected. Generated with OR function of all LED faults. Fault pin is
pulled to GND. Fault is cleared by reading the register 02h or setting EN pin low.
OCP
2
R
Overcurrent protection
0 = No fault
1 = Overcurrent detected in boost output. OCP detection block monitors the boost
output and if the boost output has been too low for more than 50 ms it generates an
OCP fault and disables the boost. Fault pin is pulled to GND. Fault is cleared by
reading the register 02h or setting EN pin low. After clearing the fault boost starts up
again.
TSD
1
R
Thermal shutdown
0 = No fault
1 = Thermal fault generated, 150°C reached. Boost is converted, and LED outputs are
disabled until the temperature has dropped down to 130°C. Fault pin is pulled to GND.
Fault is cleared by reading the register 02h or setting EN pin low.
UVLO
0
R
Undervoltage detection
0 = No fault
1 = Undervoltage detected in VIN pin. Boost is converted, and LED outputs are
disabled until VIN voltage is above the threshold voltage. Threshold voltage is set with
EEPROM bits from 3V...9V. Fault pin is pulled to GND. Fault is cleared by reading the
register 02h or setting EN pin low.
26
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8.6.1.4 Identification
Address 03h
Reset value 1111 1100b
IDENTIFICATION REGISTER
7
6
5
PANEL
4
3
2
1
MFG[3:0]
0
REV[2:0]
Name
Bit
Access
PANEL
7
R
Description
Panel ID code
MFG
6:3
R
Manufacturer ID code
REV
2:0
R
Revision ID code
5
4
8.6.1.5 Direct Control
Address 04h
Reset value 0000 0000b
DIRECT CONTROL REGISTER
7
6
3
2
1
0
OUT[4:1]
Name
Bit
Access
OUT
3:0
R/W
Description
Direct control of the LED outputs
0 = Normal operation. LED output are controlled with PWM.
1 = LED output is forced to 100% PWM.
8.6.1.6 Temp MSB
Address 05h
Reset value 0000 0000b
Temp MSB register
7
6
5
4
3
2
1
0
TEMP[10:3]
Name
Bit
Access
TEMP
7:0
R
Description
Device internal temperature sensor reading first 8 MSB. MSB must be read before LSB,
because reading of MSB register latches the data.
8.6.1.7 Temp LSB
Address 06h
Reset value 0000 0000b
TEMP LSB REGISTER
7
6
5
4
3
2
1
0
TEMP[2:0]
Name
Bit
Access
TEMP
7:5
R
Description
Device internal temperature sensor reading last 3 LSB. MSB must be read before LSB,
because reading of MSB register latches the data.
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8.6.1.8 EEPROM Control
Address 72h
Reset value 0000 0000b
EEPROM CONTROL REGISTER
7
6
5
4
3
EE_READY
Name
Bit
Access
EE_READY
7
R
2
1
0
EE_INIT
EE_PROG
EE_READ
Description
EEPROM ready
0 = EEPROM programming or read in progress
1 = EEPROM ready, not busy
EE_INIT
2
R/W
EEPROM initialization bit. This bit must be written 1 before EEPROM read or
programming.
EE_PROG
1
R/W
EEPROM programming.
0 = Normal operation
1 = Start the EEPROM programming sequence. EE_INIT must be written 1 before
EEPROM programming can be started. Programs data currently in the EEPROM
registers to non volatile memory (NVM). Programming sequence takes about 200
ms. Programming voltage is generated inside the chip.
EE_READ
0
R/W
EEPROM read
0 = Normal operation
1 = Reads the data from NVM to the EEPROM registers. Can be used to restore
default values if EEPROM registers are changed during testing.
Programming sequence (program data permanently from registers to NVM):
1. Turn on the chip by writing BL_CTL bit to 1 and BRT_MODE[1:0] to 10b (05h to address 01h)
2. Write data to EEPROM registers (address A0h…A7h)
3. Write EE_INIT to 1 in address 72h. (04h to address 72h)
4. Write EE_PROG to 1 and EE_INIT to 0 in address 72h. (02h to address 72h)
5. Wait 200 ms.
6. Write EE_PROG to 0 in address 72h. (00h to address 72h)
Read sequence (load data from NVM to registers):
1. Turn on the chip by writing BL_CTL bit to 1 and BRT_MODE[1:0] to 10b (05h to address 01h).
2. Write EE_INIT to 1 in address 72h. (04h to address 72h)
3. Write EE_READ to 1 and EE_INIT to 0 in address 72h. (01h to address 72h)
4. Wait 200 ms.
5. Write EE_READ to 0 in address 72h. (00h to address 72h)
NOTE
Data written to EEPROM registers is effective immediately even if the EEPROM
programming sequence has not been done. When power is turned off, the device,
however, loses the data if it is not programmed to the NVM. During start-up the device
automatically loads the data from NVM to registers.
NOTE
EEPROM NVM can be programmed or read by customer for bench validation.
Programming for production devices should be done in TI production test, where
appropriate checks are performed to confirm EEPROM validity. Writing to EEPROM
Control register of production devices is not recommended. If special EEPROM
configuration is required, please contact the TI Sales Office for availability.
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8.6.2 EEPROM Bit Explanations
8.6.2.1 EEPROM Register Map
ADD
R
REGIST
ER
D7
D6
D5
D4
A0H
eeprom
addr 0
A1H
eeprom
addr 1
BOOST_FREQ[1:0]
EN_LED_FAULT
A2H
eeprom
addr 2
ADAPTIVE_SPEED[1:0]
ADV_SLOPE
A3H
eeprom
addr 3
UVLO[1:0]
A4H
eeprom
addr 4
PWM_RESOLUTION[1:0]
A5H
eeprom
addr 5
A6H
eeprom
addr 6
A7H
eeprom
addr 7
D3
D2
D1
D0
CURRENT[7:0]
TEMP_LIM[1:0]
SLOPE[2:0]
EN_ADAPT
EN_BOOST
EN_PSPWM
EN_I_RES
BOOST_IMAX
PWM_FREQ[4:0]
LED_FAULT_THR
DRV_HEADR[2:0]
VBOOST[4:0]
EN_F_RES
HYSTERESIS[1:0]
8.6.2.2 EEPROM Address 0
Address A0h
EEPROM ADDRESS 0 REGISTER
7
6
5
4
3
2
1
0
CURRENT[7:0]
Name
Bit
Access
CURRENT
7:0
R/W
Description
Backlight current adjustment. If EN_I_RES = 0 the maximum backlight current is
defined only with these bits as described below. If EN_I_RES = 1, then the external
resistor connected to ISET pin also scales the LED current. With 16 kΩ resistor and
CURRENT set to 7Fh the output current is then 23 mA.
EN_I_RES = 0
EN_I_RES = 1
0000 0000
0 mA
0 mA
0000 0001
0.12 mA
(1/255) x 600 x 1.23V/RISET
0000 0010
0.24 mA
(2/255) x 600 x 1.23V/RISET
...
...
...
0111 1111
15.00 mA
(127/255) x 600 x 1.23V/RISET
...
...
...
1111 1101
29.76 mA
(253/255) x 600 x 1.23V/RISET
1111 1110
29.88 mA
(254/255) x 600 x 1.23V/RISET
1111 1111
30.00 mA
(255/255) x 600 x 1.23V/RISET
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8.6.2.3 EEPROM Address 1
Address A1h
EEPROM ADDRESS 1 U
7
6
BOOST_FREQ[1:0]
5
EN_LED_FAULT
Name
Bit
Access
BOOST_FREQ
7:6
R/W
4
3
2
TEMP_LIM[1:0]
1
0
SLOPE[2:0]
Description
Boost Converter Switch Frequency
00 = 156 kHz
01 = 312 kHz
10 = 625 kHz
11 = 1250 kHz
EN_LED_FAULT
5
R/W
Enable LED fault detection
0 = LED fault detection disabled
1 = LED fault detection enabled
TEMP_LIM
4:3
R/W
Thermal deration function temperature threshold
00 = thermal deration function disabled
01 = 110°C
10 = 120°C
11 = 130°C
SLOPE
2:0
R/W
Slope time for brightness change
000 = Slope function disabled, immediate brightness change
001 = 50 ms
010 = 75 ms
011 = 100 ms
100 = 150 ms
101 = 200 ms
110 = 300 ms
111 = 500 ms
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8.6.2.4 EEPROM Address 2
Address A2h
EEPROM ADDRESS 2 REGISTER
7
6
ADAPTIVE_SPEED[1:0]
5
4
ADV_SLOPE
Name
Bit
Access
ADAPTIVE
SPEED[1]
7
R/W
3
2
1
EN_ADAPT
EN_BOOST
BOOST_IMAX
0
Description
Boost converter adaptive control speed adjustment
0 = Normal mode
1 = Adaptive mode optimized for light loads. Activating this helps the voltage droop with
light loads during boost / backlight start-up.
ADAPTIVE
SPEED[0]
6
ADV_SLOPE
5
R/W
Boost converter adaptive control speed adjustment
0 = Adjust boost once for each phase shift cycle or normal PWM cycle
1 = Adjust boost every 16th phase shift cycle or normal PWM cycle
R/W
Advanced slope
0 = Advanced slope is disabled
1 = Use advanced slope for brightness change to make brightness changes smooth for
eye
EN_ADAPT
3
R/W
Enable boost converter adaptive mode
0 = adaptive mode disabled, boost converter output voltage is set with VBOOST
EEPROM register bits
1 = adaptive mode enabled. Boost converter startup voltage is set with VBOOST
EEPROM register bits, and after startup voltage is reached the boost converter adapts
to the highest LED string VF. LED driver output headroom is set with DRV_HEADR
EEPROM control bits.
EN_BOOST
2
R/W
Enable boost converter
0 = boost is disabled
1 = boost is enabled and turns on automatically when backlight is enabled
BOOST_IMAX
1
R/W
Boost converter inductor maximum current
0 = 1.4 A
1 = 2.5 A (recommended)
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8.6.2.5 EEPROM Address 3
Address A3h
EEPROM ADDRESS 3 REGISTER
7
6
5
UVLO[1:0]
4
3
EN_PSPWM
Name
Bit
Access
UVLO
7:6
R/W
2
1
0
PWM_FREQ[4:0]
Description
00 = Disabled
01 = 2.7 V
10 = 5.4 V
11 = 8.1 V
EN_PSPWM
5
R/W
Enable phase shift PWM scheme
0 = phase shift PWM disabled, normal PWM mode used
1 = phase shift PWM enabled
PWM_FREQ
4:0
R/W
PWM output frequency setting. See PWM Frequency Setting for full
description of selectable PWM frequencies.
8.6.2.6 EEPROM Address 4
Address A4h
EEPROM ADDRESS 4 REGISTER
7
6
PWM_RESOLUTION[1:0]
5
4
EN_I_RES
LED_FAULT_THR
Name
Bit
Access
PWM RESOLUTION
7:6
R/W
3
2
1
0
DRV_HEADR[2:0]
Description
PWM output resolution selection. Actual resolution depends also on the output
frequency. See PWM Frequency Setting for full description.
00 = 8...10 bits (19.2 kHz...4.8 kHz)
01 = 9...11 bits (19.2 kHz... 4.8 kHz)
10 = 10...12 bits (19.2 kHz...4.8 kHz)
11 = 11...13 bits (19.2 kHz...4.8 kHz)
EN_I_RES
5
R/W
Enable LED current set resistor
0 = Resistor is disabled and current is set only with CURRENT EEPROM register bits
1 = Enable LED current set resistor. LED current is defined by the RISET resistor and the
CURRENT EEPROM register bits.
LED_FAULT_THR
4
R/W
LED fault detector thresholds. VSAT is the saturation voltage of the driver, typically 200
mV.
0 = 3.3V
1 = 5.3V
DRV_HEADR
2:0
R/W
LED output driver headroom control. VSAT is the saturation voltage of the driver, typically
200 mV.
000 = VSAT + 125 mV
001 = VSAT + 250 mV
010 = VSAT + 375 mV
011 = VSAT + 500 mV
100 = VSAT + 625 mV
101 = VSAT + 750 mV
110 = VSAT + 875 mV
111 = VSAT + 1000 mV
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8.6.2.7 EEPROM Address 5
Address A5h
EEPROM ADDRESS 5 REGISTER
7
6
5
4
3
2
1
0
VBOOST[4:0]
Name
Bit
Access
VBOOST
4:0
R/W
Description
Boost voltage control from 10V to 40V with 1V step. If adaptive boost control is
enabled, this sets the initial start voltage for the boost converter. If adaptive mode
is disabled, this directly sets the output voltage of the boost converter.
0 0000 = 10V
0 0001 = 11V
0 0010 = 12V
...
1 1101 = 39V
1 1110 = 40V
1 1111 = 40V
8.6.2.8 EEPROM Address 7
Address A7h
EEPROM ADDRESS 7 REGISTER
7
6
5
4
3
2
EN_F_RES
Name
Bit
Access
EN_F_RES
2
R/W
1
0
HYSTERESIS[1:0]
Description
Enable PWM output frequency set resistor
0 = Resistor is disabled and PWM output frequency is set with PWM_FREQ EEPROM
register bits
1 = PWM frequency set resistor is enabled. RFSET defines the output PWM frequency. See
PWM Frequency Setting for full description of the PWM frequencies.
HYSTERESIS
1:0
R/W
PWM input hysteresis function. Defines how small changes in the PWM input are ignored to
remove constant switching between two values.
00 = OFF
01 = 1-bit hysteresis with 11-bit resolution
10 = 1-bit hysteresis with 10-bit resolution
11 = 1-bit hysteresis with 8-bit resolution
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9 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.
9.1 Application Information
The LP8551 is designed for LCD backlighting for portable devices, such as laptops and tablets. 4 LED current
sinks allow driving up to 40 LEDs with high efficiency. Boost converter optimizes the system efficiency by
adjusting the LED current driver headroom to optimal level in each case. Due to a flexible input voltage
configuration, the LP8551 can be used also in various applications since the input voltage supports 1x to 5x
series Li-Ion cells. Main limiting factor for output power is inductor current limit, which is calculated in the Detailed
Design Procedure. The following design procedure can be used to select component values for the LP8551.
9.2 Typical Applications
9.2.1 Application Using Internal LDO
VBATT
L1
5.5 V ± 22 V
CVLDO
10 V ± 40 V
210 mA ± 400 mA
D1
CIN 15 éH
5V
39 pF
10 éF
COUT
4.7 éF
1 éF
VDDIO reference voltage
RISET
VDDIO
VLDO
SW
VIN
FB
ISET
RFSET
OUT1
FSET
SCLK
SDA
LP8551
PWM
EN
Can be left floating
if not used
OUT2
OUT3
MCU
OUT4
FAULT
GNDs
Figure 22. LP8551 with Internal LDO
9.2.1.1 Design Requirements
34
DESIGN PARAMETER
EXAMPLE VALUE
Input voltage range
5.5 V to 22 V
Brightness Control
PWM input duty cycle (default), I2C can be used as well
PWM output frequency
With RFSET resistor 85 kΩ to 100 kΩ; 9.8 kHz with PSPWM enabled
LED Current
With RISET resistor 15 kΩ; 25 mA / channel
Brightness slopes
200-ms linear slope + advanced slope
External set resistors
Enabled
Inductor
10 µH to 33 µH, with 2.5-A saturation current
Boost SW frequency
625 kHz
SW current limit
2.5 A
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9.2.1.2 Detailed Design Procedure
9.2.1.2.1 Recommended External Components
9.2.1.2.1.1 Inductor Selection
There are two main considerations when choosing an inductor: the inductor should not saturate, and the inductor
current ripple should be small enough to achieve the desired output voltage ripple. Different saturation current
rating specifications are followed by different manufacturers so attention must be given to details. Saturation
current ratings are typically specified at 25°C. However, ratings at the maximum ambient temperature of
application should be requested from the manufacturer. Shielded inductors radiate less noise and should be
preferred.
The saturation current should be greater than the sum of the maximum load current and the worst case average
to peak inductor current.
Equation 3 below shows the worst case conditions.
IOUTMAX
ISAT >
+ IRIPPLE
'¶
VIN
(VOUT ± VIN)
x
Where IRIPPLE =
VOUT
(2 x L x f)
Where D =
•
•
•
•
•
•
•
(VOUT ± VIN)
(VOUT)
DQG'¶= (1 - D)
IRIPPLE: Average to peak inductor current
IOUTMAX: Maximum load current
VIN: Maximum input voltage in application
L: Min inductor value including worst case tolerances
f: Minimum switching frequency
D: Duty cycle for CCM Operation
VOUT: Output voltage
(3)
Example using above equations:
• VIN = 12 V
• VOUT = 38 V
• IOUT = 400 mA
• L = 15 μH − 20% = 12 μH
• f = 1.25 MHz
• ISAT = 1.6 A
As a result the inductor should be selected according to the ISAT. A more conservative and recommended
approach is to choose an inductor that has a saturation current rating greater than the maximum current limit of
2.5 A. A 15-μH inductor with a saturation current rating of 2.5 A is recommended for most applications. The
inductor’s resistance should be less than 300 mΩ for good efficiency. For high efficiency choose an inductor with
high frequency core material such as ferrite to reduce core losses. To minimize radiated noise, use shielded core
inductor. Inductor should be placed as close to the SW pin and the IC as possible. Special care should be used
when designing the PCB layout to minimize radiated noise and to get good performance from the boost
converter. For more information on the PCB layout recommendations, please see Layout Guidelines.
9.2.1.2.1.2 Output Capacitor
A ceramic capacitor with 50-V voltage rating or higher is recommended for the output capacitor. The DC-bias
effect can reduce the effective capacitance by up to 80%, which needs to be considered in capacitance value
selection. For light loads a 4.7-μF capacitor is sufficient. Effectively the capacitance should be 4 μF for < 150-mA
loads. For maximum output voltage/current 10-μF capacitor (or two 4.7-μF capacitors) is recommended to
minimize the output ripple.
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LP8551
SNVS673E – APRIL 2010 – REVISED SEPTEMBER 2014
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9.2.1.2.1.3 LDO Capacitor
A 1-μF ceramic capacitor with 10-V voltage rating is recommended for the LDO capacitor.
9.2.1.2.1.4 Output Diode
A Schottky diode should be used for the output diode. Peak repetitive current should be greater than inductor
peak current (2.5 A) to ensure reliable operation. Average current rating should be greater than the maximum
output current. Schottky diodes with a low forward drop and fast switching speeds are ideal for increasing
efficiency in portable applications. Choose a reverse breakdown voltage of the Schottky diode significantly larger
(approximately 60 V) than the output voltage. Do not use ordinary rectifier diodes, since slow switching speeds
and long recovery times cause the efficiency and the load regulation to suffer.
9.2.1.3 Application Curves
Typical Boost and LED Current waveforms with ƒLED= 9.6 kHz.
Figure 23. 10% LED PWM Duty Cycle
Figure 24. 60% LED PWM Duty Cycle
9.2.2 Application with Low-Input Voltage
In Single Li-Ion cell powered application the internal circuitry of LP8551 can be powered from external 5-V rail.
Boost is powered directly from Li-Ion battery and VLDO and VIN pins are connected to external 5-V rail. Current
draw from the 5-V rail is maximum 10 mA. A separate 5-V rail to VIN/VLDO can be used also in higher input
voltage application to improve efficiency or add increase input voltage range above 22 V in some cases. There
are no power sequencing requirement for VIN/VLDO and VBATT other than VBATT must be available when enabling
backlight to prevent a false overcurrent fault.
L1
VBATT 2.7 V...
D1
CIN 15 éH
10 éF
+5V input rail
1 éF
VDDIO reference voltage
RISET
10 V ± 40 V *
39 pF
VDDIO
VLDO
SW
VIN
COUT
4.7 éF
CVLDO
FB
ISET
RFSET
OUT1
FSET
SCLK
SDA
LP8551
PWM
EN
Can be left floating
if not used
FAULT
OUT2
OUT3
MCU
OUT4
GNDs
*) Conversion ratio of 10
should not be exceeded
Figure 25. LP8551 with Low-Input Voltage
36
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LP8551
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9.2.2.1 Design Requirements
DESIGN PARAMETER
EXAMPLE VALUE
Input voltage range, VBATT
2.7 V to VOUT
5-V input rail, VLDO/VIN
4.5 V to 5.5 V, 10 mA
Brightness Control
PWM input duty cycle (default), I2C can be used as well
PWM output frequency
With RFSET resistor 85 kΩ to100 kΩ; 9.8 kHz with PSPWM enabled
LED Current
With RISET resistor 15 kΩ; 25 mA / channel
Brightness slopes
200-ms linear slope + advanced slope
External set resistors
Enabled
Inductor
10 µH to 33 µH, with 2.5-A saturation current
Boost SW frequency
625 kHz
SW current limit
2.5 A
9.2.2.2 Detailed Design Procedure
Component selection follows Detailed Design Procedure section above. VLDO capacitor voltage rating can be set
based on the 5-V rail voltage specification, which must be
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