VIN
LP8556
MCU
VBOOST
SW
1.1 ”9OUT / VIN ”15
L1 D1
VDD
CIN COUT
LED1
LED2
LED3
LED4
LED5
LED6
GNDs
PWM
SDA
SCL
ISET
FSET
VLDO
CVLDO
RFSET
RISET
2.7V - 20V 7V ± 43V
EN / VDDIO
EN / VDDIO 1.62V ± 3.6V
VOUT
Optional
Product
Folder
Order
Now
Technical
Documents
Tools &
Software
Support &
Community
Reference
Design
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.
LP8556
SNVS871L JULY 2012REVISED MAY 2019
LP8556 High-Efficiency LED Backlight Driver For Tablets
1
1 Features
1 High-efficiency DC/DC boost converter with
integrated 0.19-power MOSFET and three
switching frequency options: 312 kHz, 625 kHz,
and 1250 kHz
2.7-V to 36-V Boost switch input voltage range
supports multi-cell Li-Ion batteries
(2.7-V to 20-V VDD input range)
7-V to 43-V Boost switch output voltage range
supports as few as 3 WLEDs in series per
channel and as many as 12
Configurable channel count (1 to 6)
Up to 50 mA per channel
PWM and / or I2C brightness control
Phase-shift PWM mode reduces audible noise
Adaptive dimming for higher LED drive optical
efficiency
Programmable edge-rate control and spread
spectrum scheme minimize switching noise and
improve EMI performance
LED fault (short and open) detection, UVLO, TSD,
OCP, and OVP (up to 6 threshold options)
Available in tiny 20-pin, 0.4-mm pitch DSBGA
package and 24-pin, 0.5-mm pitch WQFN
package
2 Applications
LED backlights for tablet LCDs
space
Simplified Schematic
3 Description
The LP8556 device is a white-LED driver featuring an
asynchronous boost converter and six high precision
current sinks that can be controlled by a PWM signal
or an I2C master.
The boost converter uses adaptive output voltage
control for setting the optimal LED driver voltages as
low as 7 V and as high as 43 V. This feature
minimizes the power consumption by adjusting the
output voltage to the lowest sufficient level under all
conditions. The converter can operate at three
switching frequencies: 312 kHz, 625 kHz, and
1250 kHz, which can be set with an external resistor
or pre-configured via EPROM. Programmable slew
rate control and spread spectrum scheme minimize
switching noise and improve EMI performance.
LED current sinks can be set with the PWM dimming
resolution of up to 15 bits. Proprietary adaptive
dimming mode allows higher system power saving. In
addition, phase shifted LED PWM dimming allows
reduced audible noise and smaller boost output
capacitors.
The LP8556 device has a full set of fault-protection
features that ensure robust operation of the device
and external components. The set consists of input
undervoltage lockout (UVLO), thermal shutdown
(TSD), overcurrent protection (OCP), up to 6 levels of
overvoltage protection (OVP), LED open and short
detection.
The LP8556 device operates over the ambient
temperature range of –30°C to +85°C. It is available
in space-saving 20-pin DSBGA and 24-pad WQFN
packages.
Device Information(1)
PART NUMBER PACKAGE BODY SIZE
LP8556 DSBGA (20) 2.401 mm × 1.74 mm (MAX)
WQFN (24) 4.00 mm × 4.00 mm (NOM)
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
2
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Table of Contents
1 Features.................................................................. 1
2 Applications ........................................................... 1
3 Description............................................................. 1
4 Revision History..................................................... 2
5 Device Options....................................................... 3
6 Pin Configuration and Functions......................... 4
7 Specifications......................................................... 6
7.1 Absolute Maximum Ratings ...................................... 6
7.2 ESD Ratings.............................................................. 6
7.3 Recommended Operating Conditions....................... 6
7.4 Thermal Information.................................................. 7
7.5 Electrical Characteristics........................................... 7
7.6 Electrical Characteristics Boost Converter .......... 8
7.7 Electrical Characteristics LED Driver................... 9
7.8 Electrical Characteristics PWM Interface............. 9
7.9 Electrical Characteristics Logic Interface .......... 10
7.10 I2C Serial Bus Timing Parameters (SDA, SCL).... 10
7.11 Typical Characteristics.......................................... 11
8 Detailed Description............................................ 12
8.1 Overview................................................................. 12
8.2 Functional Block Diagram....................................... 12
8.3 Feature Description................................................. 13
8.4 Device Functional Modes........................................ 28
8.5 Programming........................................................... 28
8.6 Register Maps......................................................... 32
9 Application and Implementation ........................ 45
9.1 Application Information............................................ 45
9.2 Typical Application ................................................. 47
10 Power Supply Recommendations ..................... 51
11 Layout................................................................... 51
11.1 Layout Guidelines ................................................. 51
11.2 Layout Examples................................................... 52
12 Device and Documentation Support................. 54
12.1 Receiving Notification of Documentation Updates 54
12.2 Community Resources.......................................... 54
12.3 Trademarks........................................................... 54
12.4 Electrostatic Discharge Caution............................ 54
12.5 Glossary................................................................ 54
13 Mechanical, Packaging, and Orderable
Information........................................................... 54
4 Revision History
Changes from Revision K (March 2019) to Revision L Page
Deleted 03H register from Table 9....................................................................................................................................... 32
Deleted 8.6.1.4 Identification section from the Register Bit Explanations............................................................................ 33
Changes from Revision J (January 2018) to Revision K Page
Added separate ESD Rating for the WQFN package - changed from "±2000" to "±1000".................................................... 6
Changes from Revision I (March 2016) to Revision J Page
Added content in VBOOST_RANGE description of CFG9E................................................................................................ 38
Changes from Revision H (December 2014) to Revision I Page
Changed "25 mA" to "23 mA" - E00, E08 and E09 SQ rows, E09, E11 TME rows............................................................... 3
Changed Handing Ratings table to ESD Ratings .................................................................................................................. 6
Added updated Thermal Information ..................................................................................................................................... 7
Changed "8" to "10" in PWMres row...................................................................................................................................... 9
Changed subtracted 1 from bit value of all Table 4 PWM [Hz] (Resolution)" entries ......................................................... 20
Changed subtracted 1 from bit value of all Table 5 PWM [Hz] (Resolution)" entries except 2402 .................................... 21
Changed subtracted 1 from bit value of all Table 11 PWM [Hz] (Resolution)" entries ....................................................... 45
Changed "via EPROM" in Table 13 title to "With an External Resistor" ............................................................................. 46
Changed subtracted 1 from bit values of all Table 13 PWM [Hz] (Resolution)" entries except 2402 ................................. 46
3
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Changes from Revision G (November 2013) to Revision H Page
Added Pin Configuration and Functions section, Handling Ratings table, Feature Description section, Device
Functional Modes,Application and Implementation section, Power Supply Recommendations section, Layout
section, Device and Documentation Support section, and Mechanical, Packaging, and Orderable Information
section ................................................................................................................................................................................... 1
Changes from Revision E (August 2013) to Revision G Page
Changed Description of "1=" for OCP row in Fault table, STATUS Register Section.......................................................... 34
Changed A7h values for E02, E03, E04, E06, E07, E09, E11 DSGBA EPROM Bit Explanations tables........................... 36
Deleted E00, E01, E08, E10, E12, E13 columns and A8H row from 3 EPROM Bit Explanations table.............................. 36
Changed values for E00, E08, E09 WQFN EPROM Settings table..................................................................................... 37
(1) For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI
website at www.ti.com.
5 Device Options
ORDERABLE DEVICE(1) PACKAGE
TYPE DEVICE OPTION LED
CHANNEL
COUNT
MAXIMUM LED
CURRENT
BOOST OUTPUT
VOLTAGE
RANGE
LP8556SQ-E00/NOPB
LP8556SQE-E00/NOPB
LP8556SQX-E00/NOPB
WQFN “PWM Only” Recommended for
systems without an I2C master.
5
23 mA 16 V to 34.5 V
LP8556SQ-E08/NOPB
LP8556SQE-E08/NOPB
LP8556SQX-E08/NOPB 4
LP8556SQ-E09/NOPB
LP8556SQE-E09/NOPB
LP8556SQX-E09/NOPB 6
LP8556TME-E02/NOPB
LP8556TMX-E02/NOPB
DSBGA
“PWM and I2C” - Recommended for
systems with an I2C master. 6 25 mA 16 V to 30 V
LP8556TME-E03/NOPB
LP8556TMX-E03/NOPB “PWM Only” Recommended for
systems without an I2C master.
5 20 mA 16 V to 34.5 V
LP8556TME-E04/NOPB
LP8556TMX-E04/NOPB 6 20 mA 16 V to 25 V
LP8556TME-E05/NOPB
LP8556TMX-E05/NOPB “Non-programmed” This option is
for evaluation purposes only.
Can be
programmed
to any
available. 25 mA Can be
programmed to
any available.
LP8556TME-E06/NOPB
LP8556TMX-E06/NOPB “PWM Only” Recommended for
systems without an I2C master.
5 25 mA 16 V to 39 V
LP8556TME-E07/NOPB
LP8556TMX-E07/NOPB 4 20 mA 12.88 V to 30 V
LP8556TME-E09/NOPB
LP8556TMX-E09/NOPB 6 23 mA 16 V to 34.5 V
LP8556TME-E11/NOPB
LP8556TMX-E11/NOPB “PWM and I2C” - Recommended for
systems with an I2C master. 3 23 mA 7 V to 21 V
724
823
922
1021
1120
1219
131415161718
654321
PIN 1 ID
EN / VDDIO
NC
PWM
GND
GND
LED1
SCL
SDA
GND_SW
GND_SW
SW
SW
LED2
LED3
GND
LED4
LED5
LED6
GND
ISET
VDD
FSET
VBOOST
VLDO
PIN 1 ID
7 24
8 23
9 22
10 21
11 20
12 19
13 14 15 16 17 18
6 5 4 3 2 1
EN/VDDIO
NC
PWM
GND
GND
LED1
LED2
LED3
GND
LED4
LED5
LED6
GND
ISET
VDD
FSET
VBOOST
VLDO
SW
SW
GND_SW
GND_SW
SDA
SCL
4
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6 Pin Configuration and Functions
YFQ Package
20-Pin DSBGA
Top View
RTW Package
24-Pin WQFN
Top View
YFQ Package
20-Pin DSBGA
Bottom View
RTW Package
24-Pin WQFN
Bottom View
5
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(1) A: Analog Pin, G: Ground Pin, P: Power Pin, I: Digital Input Pin, I/O: Digital Input/Output Pin
Pin Functions
PIN TYPE(1) DESCRIPTION
DSBGA WQFN NAME
A1, B1 1, 2 SW A A connection to the drain terminal of the integrated power MOSFET.
A2, B2 3, 4 GND_SW G A connection to the source terminal of the integrated power MOSFET.
A3 5 SDA I/O I2C data input/output pin
A4 6 SCL I I2C clock input pin
B3 9 PWM I PWM dimming input. Supply a 75-Hz to 25-kHz PWM signal to control
dimming. This pin must be connected to GND if unused.
B4 7 EN / VDDIO P Dual-purpose pin serving both as a chip enable and as a power supply
reference for PWM, SDA, and SCL inputs. Drive this pin with a logic
gate capable of sourcing a minimum of 1 mA.
C1 22 VDD P Device power supply pin. Provide 2.7-V to 20-V supply to this pin. This
pin is an input of the internal LDO regulator. The output of the internal
LDO is what powers the device.
C2 20 VBOOST A Boost converter output pin. The internal feedback (FB) and overvoltage
protection (OVP) circuitry monitors the voltage on this pin. Connect the
converter output capacitor bank close to this pin.
C3 21 FSET A
A connection for setting the boost frequency and PWM output dimming
frequency by using an external resistor. Connect a resistor, RFSET,
between this pin and the ground reference (see Table 5). This pin may
be left floating if PWM_FSET_EN = 0 AND BOOST_FSET_EN = 0
(see Table 10).
C4 14 LED3 A LED driver - current sink terminal. If unused, it may be left floating.
D1 19 VLDO P Internal LDO output pin. Connect a capacitor, CVLDO, between this pin
and the ground reference.
D2 23 ISET A A connection for the LED current set resistor. Connect a resistor,
RISET, between this pin and the ground reference. This pin may be left
floating if ISET_EN = 0 (see Table 10).
D3 10, 11, 15, 24,
DAP GND I Ground pin.
D4 13 LED2 A LED driver - current sink pin. If unused, it may be left floating.
E1 18 LED6 A LED driver - current sink pin. If unused, it may be left floating.
E2 17 LED5 A LED driver - current sink pin. If unused, it may be left floating.
E3 16 LED4 A LED driver - current sink pin. If unused, it may be left floating.
E4 12 LED1 A LED driver - current sink pin. If unused, it may be left floating.
8 NC No Connect pin.
6
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(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, and functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating
Conditions is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability, see the
Electrical Characteristics tables.
(2) If Military/Aerospace specified devices are required, contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
(3) In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may
have to be de-rated. 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).
7 Specifications
7.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)(1)(2)
MIN MAX UNIT
VDD –0.3 24
V
Voltage on Logic Pins (SCL, SDA, PWM) –0.3 6
Voltage on Analog Pins (VLDO, EN / VDDIO) –0.3 6
Voltage on Analog Pins (FSET, ISET) –0.3 VLDO + 0.3
V (LED1...LED6, SW, VBOOST) 0.3 50
Junction Temperature (TJ-MAX)(3) 125 °C
Maximum Lead Temperature (Soldering) 260 °C
Storage temperature, Tstg –65 150 °C
(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
(2) JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
7.2 ESD Ratings VALUE UNIT
V(ESD) Electrostatic
discharge
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001, DSBGA Package(1) ±2000 VHuman-body model (HBM), per ANSI/ESDA/JEDEC JS-001, WQFN Package(1) ±1000
Charged-device model (CDM), per JEDEC specification JESD22-C101(2) ±500
(1) All voltages are with respect to the potential at the GND pins.
7.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)(1)
MIN MAX UNIT
VDD 2.7 20 V
EN / VDDIO 1.62 3.6 V
V (LED1...LED6, SW, VBOOST) 0 48 V
Junction temperature, TJ–30 125 °C
Ambient temperature, TA–30 85 °C
7
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(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report (SPRA953).
7.4 Thermal Information
THERMAL METRIC(1) LP8556
UNITYFQ (DSBGA) RTW (WQFN)
20 PINS 24 PINS
RθJA Junction-to-ambient thermal resistance 66.2 35.0 °C/W
RθJC(top) Junction-to-case (top) thermal resistance 0.5 32.2 °C/W
RθJB Junction-to-board thermal resistance 15.1 13.7 °C/W
ψJT Junction-to-top characterization parameter 1.9 0.3 °C/W
ψJB Junction-to-board characterization parameter 15.0 13.8 °C/W
RθJC(bot) Junction-to-case (bottom) thermal resistance n/a 3.3 °C/W
(1) All voltages are with respect to the potential at the GND pins.
(2) Minimum (MIN) and Maximum (MAX) limits are verified by design, test, or statistical analysis. Typical numbers are for information only.
(3) Verified by design and not tested in production.
7.5 Electrical Characteristics
Unless otherwise specified: VDD = 12 V, EN / VDDIO = 1.8 V, TA= 25°C(1)(2)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
VDDIO Supply voltage for digital I/Os 1.62 3.6 V
VDD Input voltage for the internal LDO 2.7 20 V
IDD
Standby supply current EN / VDDIO = 0 V, LDO disabled,
–30°C TA85°C 1.6 μA
Normal mode supply current LDO enabled, boost disabled 0.9 1.5 mA
LDO enabled, boost enabled, no load 2.2 3.65
fOSC Internal oscillator frequency
accuracy –4% 4%
–30°C TA85°C –7% 7%
VLDO LDO output voltage VDD 3.1 V 2.95 3.05 3.15 V
2.7 V VDD < 3.1 V VDD 0.05
TTSD Thermal shutdown threshold See(3) 150 °C
TTSD_hyst Thermal shutdown hysteresis 20 °C
8
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(1) Minimum (MIN) and Maximum (MAX) limits are verified by design, test, or statistical analysis. Typical numbers are for information only.
(2) Verified by design and not tested in production.
(3) Start-up time is measured from the moment boost is activated until the VBOOST crosses 90% of its target value.
(4) 1.8 A is the maximum ISW_LIM supported with the DSBGA package. For applications requiring the ISW_LIM to be greater than 1.8 A and
up to 2.6 A, WQFN package should be considered.
7.6 Electrical Characteristics Boost Converter
over operating free-air temperature range (unless otherwise noted)(1)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
RDS_ON Switch ON resistance ISW = 0.5A 0.19
VBOOST_MIN Boost minimum output
voltage VBOOST_RANGE = 0
VBOOST_RANGE = 1 7
16 V
VBOOST_MAX Boost maximum output
voltage
VBOOST_MAX = 100, VBOOST_RANGE = 0
VBOOST_MAX = 101, VBOOST_RANGE = 0
VBOOST_MAX = 110, VBOOST_RANGE = 0
VBOOST_MAX = 111, VBOOST_RANGE = 0
19
24.0
28.0
32
21
25
30
34
22
27
32
37 V
VBOOST_MAX = 010, VBOOST_RANGE = 1
VBOOST_MAX = 011, VBOOST_RANGE = 1
VBOOST_MAX = 100, VBOOST_RANGE = 1
VBOOST_MAX = 101, VBOOST_RANGE = 1
VBOOST_MAX = 110, VBOOST_RANGE = 1
VBOOST_MAX = 111, VBOOST_RANGE = 1
17.9
22.8
27.8
32.7
37.2
41.8
21
25
30
34.5
39
43
23.1
27.2
31.5
36.6
40.8
44.2
V
ILOAD_MAX Maximum continuous output
load current
VIN = 3 V, VOUT = 18 V 220 mAVIN = 3 V, VOUT = 24 V 160
VIN = 3 V, VOUT = 30 V 120
VOUT/VIN Conversion ratio(2) fSW = 625 kHz 15
fSW = 1250 kHz 12
fSW Switching frequency BOOST_FREQ = 00
BOOST_FREQ = 01
BOOST_FREQ = 10
312
625
1250 kHz
VOVP Overvoltage protection
voltage VBOOST_RANGE = 1 VBOOST + 1.6 V
VUVLO VIN undervoltage lockout
threshold
UVLO_EN = 1 V
UVLO_TH = 0, falling
UVLO_TH = 1, falling 2.5
5.2
VUVLO_hyst VUVLO hysteresis VUVLO[rising]
VUVLO[falling] UVLO_TH = 0 50 mV
UVLO_TH = 1 100
tPULSE Switch minimum pulse width No load 50 ns
tSTARTUP Start-up time See(3) 8 ms
ISW_LIM SW pin current limit(4)
IBOOST_LIM_2X = 0 IBOOST_LIM = 00
IBOOST_LIM = 01
IBOOST_LIM = 10
IBOOST_LIM = 11
0.66
0.88
1.12
1.35
0.9
1.2
1.5
1.8
1.16
1.40
1.73
2.07 A
IBOOST_LIM_2X = 1 IBOOST_LIM = 00
IBOOST_LIM = 01
IBOOST_LIM = 10
1.6
2.1
2.6 A
ΔVSW /
toff_on SW pin slew rate during OFF
to ON transition EN_DRV3 = 0 AND EN_DRV2 = 0
EN_DRV3 = 0 AND EN_DRV2 = 1
EN_DRV3 = 1 AND EN_DRV2 = 1
3.7
5.3
7.5 V/ns
ΔVSW /
ton_off SW pin slew rate during ON
to OFF transition EN_DRV3 = 0 AND EN_DRV2 = 0
EN_DRV3 = 0 AND EN_DRV2 = 1
EN_DRV3 = 1 AND EN_DRV2 = 1
1.9
4.4
4.8 V/ns
ΔtON / tSW
Peak-to-peak switch ON
time deviation to SW period
ratio (spread spectrum
feature) SSCLK_EN = 1 1%
9
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(1) Minimum (MIN) and Maximum (MAX) limits are specified by design, test, or statistical analysis. Typical numbers are not verified, but do
represent the most likely norm.
(2) 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 OUT6), 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.
(3) Verified by design and not tested in production.
(4) Saturation voltage is defined as the voltage when the LED current has dropped 10% from the value measured at 1 V.
7.7 Electrical Characteristics LED Driver
over operating free-air temperature range (unless otherwise noted)(1)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
ILED_LEAKAGE Leakage current Outputs LED1...LED6, VOUT = 48 V 0.1 1 µA
ILED_MAX Maximum sink current
LED1...LED6 50 mA
ILED LED current accuracy(2) Output current set to 23 mA –3% 1% 3%
Output current set to 23 mA,
–30°C TA85°C –4% 1% 4%
IMATCH Matching Output current set to 23 mA 0.5%
PWMDUTY LED PWM output pulse duty
cycle(3)
100 Hz < fPWM 200 Hz 0.02% 100%
200 Hz < fPWM 500 Hz 0.02% 100%
500 Hz < fPWM 1 kHz 0.02% 100%
1 kHz < fPWM 2 kHz 0.04% 100%
2 kHz < fPWM 5 kHz 0.1% 100%
5 kHz < fPWM 10 kHz 0.2% 100%
10 kHz < fPWM 20 kHz 0.4% 100%
20 kHz < fPWM 30 kHz 0.6% 100%
30 kHz < fPWM 39 kHz 0.8% 100%
fLED PWM output frequency PWM_FREQ = 1111 38.5 kHz
VSAT Saturation voltage(4) Output current set to 23 mA 200 mV
(1) Minimum (MIN) and Maximum (MAX) limits are specified by design, test, or statistical analysis. Typical numbers are for information only.
(2) Verified by design and not tested in production.
7.8 Electrical Characteristics PWM Interface(1)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
fPWM PWM frequency range(2) 75 25 000 Hz
tMIN_ON Minimum pulse ON time 1 μs
tMIN_OFF Minimum pulse OFF time 1
tSTARTUP Turnon delay from standby to
backlight on PWM input active, VDDIO pin transitions
from 0 V to 1.8 V 10 ms
tSTBY Turnoff delay PWM input low time for turnoff 50 ms
PWMRES PWM input resolution ƒIN < 9 kHz 10 bits
10
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(1) Minimum (MIN) and Maximum (MAX) limits are specified by design, test, or statistical analysis. Typical numbers are for information only.
7.9 Electrical Characteristics Logic Interface (1)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
LOGIC INPUTS (PWM, SDA, SCL)
VIL Input low level –30°C TA85°C 0.3 ×
VDDIO V
VIH Input high level –30°C TA85°C 0.7 ×
VDDIO V
IIInput current (VDDIO = 0 V or 3.6 V), (VI= 0 V or 3.6 V),
–30°C TA85°C –1 1 µA
LOGIC OUTPUTS (SDA)
VOL Output low level IOUT = 3 mA (pull-up current) 0.3 V
IOUT = 3 mA (pull-up current),
–30°C TA85°C 0.3 0.4
ILOutput leakage current VOUT = 5 V, –30°C TA85°C –1 1 µA
(1) Verified by design and not tested in production.
7.10 I2C Serial Bus Timing Parameters (SDA, SCL)(1)
MIN MAX UNIT
ƒSCL Clock frequency 400 kHz
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 set-up time 100 ns
7 Rise time of SDA and SCL 20 + 0.1Cb300 ns
8 Fall time of SDA and SCL 15 + 0.1Cb300 ns
9 Setup time for STOP condition 600 ns
10 Bus-free time between a STOP and a START condition 1.3 µs
CbCapacitive load parameter for each bus line load of 1 pF corresponds to 1 ns. 10 200 ns
Figure 1. I2C-Compatible Timing
VSW
20V/DIV
IL
500 mA/DIV
IOUT
100 mA/DIV
VBOOSTac
200 mV/DIV
1 Ps/DIV
EN/VDDIO
2V/DIV
VSW
20V/DIV
VBOOST
20V/DIV
4 ms/DIV
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7.11 Typical Characteristics
Unless otherwise specified: VIN = 3.8 V, CVLDO = 10 μF, L1 = 4.7 μH, CIN = 2.2 μF, COUT = 4.7 μF, ƒSW = 1.25 MHz.
Figure 2. Steady-State Operation Waveforms Figure 3. Start-Up Waveforms
LED Current Sinks
VBOOST
PWM Control
Headroom
Control
LED1
LED2
LED3
LED4
LED5
LED6
Boost Converter
SW
Switching
Frequency
312, 625, 1250
kHz
Oscillator
Thermal
shutdown
Reference
Voltage
LDO
VLDO
VDD
PWM
POR
PWM Detector
Fault Detection
(Open LED,
OCP, OVP)
VIN
SDA
SCL I2C Slave
BRIGHTNESS
CONTROL
EPROM
BOOST_FREQ
BOOST_FREQ
PWM_FREQ
FSET ISET
VOUT
EN/VDDIO
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8 Detailed Description
8.1 Overview
LP8556 is a white LED driver featuring an asynchronous boost converter and six high-precision current sinks that
can be controlled by a PWM signal or an I2C master.
The boost converter uses adaptive output voltage control for setting the optimal LED driver voltages as high as
43 V. This feature minimizes the power consumption by adjusting the voltage to the lowest sufficient level under
all conditions. The converter can operate at three switching frequencies: 312, 625, and 1250 kHz pre-configured
via EPROM or can be set through an external resistor. Programmable slew rate control and spread spectrum
scheme minimize switching noise and improve EMI performance.
LED current sinks can be set with the PWM dimming resolution of up to 15 bits. Proprietary adaptive dimming
mode allows higher system power saving. In addition, phase shifted LED PWM dimming allows reduced audible
noise and smaller boost output capacitors.
The LP8556 device has a full set of safety features that ensure robust operation of the device and external
components. The set consists of input undervoltage lockout, thermal shutdown, overcurrent protection, up to six
levels of overvoltage protection, LED open, and short detection.
8.2 Functional Block Diagram
Light
Load
SW
R R
OCP
R
SR
6+
-
+
-
Osc/
ramp
gm
-
+
VREF
VBOOST
VFB
Active Load
Startup OVP Edge Rate
Control
Spread
Spectrum
R
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(1) See Table 5.
8.3 Feature Description
8.3.1 Boost Converter
8.3.1.1 Boost Converter Operation
The LP8556 boost DC-DC converter generates a 7-V to approximately 43-V of boost output voltage from a 2.7-V
to 36-V boost input voltage. The boost output voltage minimum, maximum value and range can be set digitally by
pre-configuring EPROM memory (VBOOST_RANGE, VBOOST, and VBOOST_MAX fields).
The converter is a magnetic switching PWM mode DC-DC boost converter with a current limit. It uses CPM
(current programmed mode) control, where the inductor current is measured and controlled with the feedback.
During start-up, the soft-start function reduces the peak inductor current. The LP8556 has an internal 20-MHz
oscillator which is used for clocking the boost. Figure 4 shows the boost block diagram.
Figure 4. LP8556 Boost Converter Block Diagram
8.3.1.2 Setting Boost Switching Frequency
The LP8556 boost converter switching frequency can be set either by an external resistor (BOOST_FSET_EN =
1 selection), RFSET, or by pre-configuring EPROM memory with the choice of boost frequency (BOOST_FREQ
field). Table 1 summarizes setting of the switching frequency. Note that the RFSET is shared for setting the PWM
dimming frequency in addition to setting the boost switching frequency. Setting the boost switching frequency
and PWM dimming frequency using an external resistor is separately shown in Table 5.
Table 1. Configuring Boost Switching Frequency via EPROM
RFSET [] BOOST_FSET_EN BOOST_FREQ[1:0] ƒSW [kHz]
don't care 0 00 312
don't care 0 01 625
don't care 0 10 1250
don't care 0 11 undefined
See (1) 1 don't care See(1)
OUT1 string VF
OUT2 string VF
OUT3 string VF
OUT4 string VF
OUT5 string VF
OUT6 string VF
OUT1 string VF
Time
VBOOST Driver
headroom
VBOOST
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8.3.1.3 Output Voltage Control
The LP8556 device supports two modes of controlling the boost output voltage: Adaptive Boost Voltage Control
(see Adaptive Control) and Manual Boost Output Control (see Manual Control).
8.3.1.3.1 Adaptive Control
LP8556 supports a mode of output voltage control called Adaptive Boost Control mode. In this mode, the voltage
at the LED pins is periodically monitored by the control loop and adaptively adjusted to the optimum value based
on the comparator thresholds set using LED DRIVER_HEADROOM, LED_COMP_HYST, BOOST_STEP_UP,
BOOST_STEP_DOWN fields in the EPROM. Settings under LED DRIVER_HEADROOM along with
LED_COMP_HYST fields determine optimum boost voltage for a given condition. Boost voltage is raised if the
voltage measured at any of the LED strings falls below the threshold setting determined with LED
DRIVER_HEADROOM field. Likewise, boost voltage is lowered if the voltage measured at any of the LED strings
is above the combined setting determined under LED DRIVER_HEADROOM and LED_COMP_HYST fields.
LED_COMP_HYST field serves to fine tune the headroom voltage for a given peak LED current. The boost
voltage up/down step size can be controlled with the BOOST_STEP_UP and BOOST_STEP_DN fields.
The initial boost voltage is configured with the VBOOST field. This field also sets the minimum boost voltage.
The VBOOST_MAX field sets the maximum boost voltage. When an LED pin is open, the monitored voltage
never has enough headroom, and the adaptive mode control loop keeps raising the boost voltage. The
VBOOST_MAX field allows the boost voltage to be limited to stay under the voltage rating of the external
components.
NOTE
Only LED strings that are enabled are monitored and PS_MODE field determines which
LED strings are enabled.
The adaptive mode is selected using ADAPTIVE bit set to 1 (CFGA EPROM Register) and is the recommended
mode of boost control.
Figure 5. Boost Adaptive Control Principle
8.3.1.3.2 Manual Control
User can control the boost output voltage with the VBOOST EPROM field when adaptive mode is not used.
Equation 1 shows the relationship between the boost output voltage and the VBOOST field.
VBOOST = VBOOST_MIN + 0.42 × VBOOST[dec] (1)
The expression is only valid when the calculated values are between the minimum boost output voltage and the
maximum boost output voltage. The minimum boost output voltage is set with the VBOOST_RANGE field. The
maximum boost output voltage is set with the VBOOST_MAX EPROM field.
Duty cycle D = 1 - VIN / VOUT
tSW = 1/fSW
Slew rate control,
programmable
Spread spectrum scheme,
programmable pseudo
random duty cycle changes
minimize EMI
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8.3.1.4 EMI Reduction
The LP8556 device features two EMI reduction schemes.
The first scheme, Programmable Slew Rate Control, uses a combination of three drivers for boost switch.
Enabling all three drivers allows boost switch on/off transition times to be the shortest. On the other hand,
enabling just one driver allows boost switch on/off transition times to be the longest. The longer the transition
times, the lower the switching noise on the SW pin. Note that the shortest transition times bring the best
efficiency as the switching losses are the lowest.
EN_DRV2 and EN_DRV3 bits in the EPROM determine the boost switch driver configuration. Refer to the SW
pin slew rate parameter listed under Electrical Characteristics Boost Converter for the slew rate options.
The second EMI reduction scheme is the spread spectrum. This scheme deliberately spreads the frequency
content of the boost switching waveform, which inherently has a narrow bandwidth, makes the bandwidth of the
switching waveform wider, and ultimately reduces its EMI spectral density.
Figure 6. Principles of EMI Reduction Scheme
8.3.2 Brightness Control
LP8556 enables various methods of brightness control. The brightness can be controlled using an external PWM
signal or the Brightness register accessible by users via an I2C interface or both. How these two input sources
are selected and combined is set by the BRT_MODE EPROM bits and described in BRT_MODE = 00 through
BRT_MODE = 11,Figure 7, and Table 2. The LP8556 can also be preconfigured via EPROM memory to allow
direct and unaltered brightness control by an external PWM signal. This mode of operation is obtained by setting
PWM_DIRECT EPROM bit to 1 (CFG5[7] = 1).
8.3.2.1 BRT_MODE = 00
With BRT_MODE = 00, the LED output is controlled by the PWM input duty cycle. The PWM detector block
measures the duty cycle at the PWM pin and uses this 16-bit value to generate an internal to the device PWM
data. Before the output is generated, the PWM data goes through the PWM curve-shaper block. Then, the data
goes into the adaptive dimming function which determines the range of the PWM and Current control as
described in Output Dimming Schemes. The outcome of the adaptive dimming function is 12-bit current and/or
up to 6 PWM output signals. The current is then passed through the non-linear compensation block while the
output PWM signals are channeled through the dither block.
8.3.2.2 BRT_MODE = 01
With BRT_MODE = 01, the PWM output is controlled by the PWM input duty cycle and the Brightness register.
The PWM detector block measures the duty cycle at the PWM pin and uses this 16-bit value to generate the
PWM data. Before the output is generated, the PWM data is first multiplied with BRT[7:0] register, then it goes
through the PWM Curve Shaper block. Then, the data goes into the Adaptive Dimming function which
determines the range of the PWM and Current control as described in Output Dimming Schemes. The outcome
of the Adaptive Dimming function is 12-bit current and/or up to 6 PWM output signals. The current is then passed
through the non-linear compensation block while the output PWM signals are channeled through the Dither
block.
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8.3.2.3 BRT_MODE = 10
With BRT_MODE = 10, the PWM output is controlled only by the Brightness register. From BRT[7:0] register, the
data goes through the PWM Curve Shaper block. Then, the data goes into the Adaptive Dimming function which
determines the range of the PWM and Current control as described in Output Dimming Schemes. The outcome
of the Adaptive Dimming function is 12-bit Current and / or up to 6 PWM output signals. The current is then
passed through the non-linear compensation block while the output PWM signals are channeled through the
Dither block.
8.3.2.4 BRT_MODE = 11
With BRT_MODE = 11, the PWM control signal path is similar to the path when BRT_MODE = 01 except that the
PWM input signal is multiplied with BRT[7:0] data after the Curve-Shaper block.
Table 2. Brightness Control Methods Truth Table
PWM_DIRECT BRT_MODE [1:0] BRIGHTNESS CONTROL SOURCE OUTPUT ILED FORM
0 00 External PWM signal
Adaptive. See Output
Dimming Schemes
0 01 External PWM signal and Brightness Register
(multiplied before Curve Shaper)
0 10 Brightness Register
0 11 External PWM signal and Brightness Register
(multiplied after Curve Shaper)
1 don't care External PWM signal Same as the external
PWM input
PWM
Detector Temp
Limiter Curve
Shaper Adaptive
Dimming
Non-linear
Compensation
Dither PWM
Gen
Brightness
PWM
Input
CURRENT
PWM
BRT_MODE = 01
PWM
Detector Temp
Limiter Curve
Shaper Adaptive
Dimming
Non-linear
Compensation
Dither PWM
Gen
PWM
Input
CURRENT
PWM
BRT_MODE = 00
Temp
Limiter Curve
Shaper Adaptive
Dimming
Non-linear
Compensation
Dither PWM
Gen
Brightness
CURRENT
PWM
BRT_MODE = 10
PWM
Detector
Adaptive
Dimming
Non-linear
Compensation
Dither PWM
Gen
PWM
Input
CURRENT
PWM
BRT_MODE = 11
Temp
Limiter Curve
Shaper
Brightness
Current [11:0]
Current_Max [2:0]
Current [11:0]
Current_Max [2:0]
Current [11:0]
Current_Max [2:0]
Current [11:0]
Current_Max [2:0]
PWM_TO_I_THRESHOLD [3:0]
PWM_TO_I_THRESHOLD [3:0]
PWM_TO_I_THRESHOLD [3:0]
PWM_TO_I_THRESHOLD [3:0]
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Figure 7. Brightness Control Signal Path Block Diagrams
LED CURRENT
25% 100%
Max current is set with CURRENT and CURRENT_MAX EPROM bits
or CURRENT and CURRENT_MAX EPROM bits and RISET resistor
25%
50%
100%
PURE CURRENT CONTROL
(PWM_TO_I_THRESHOLD = 0000b)
BRIGHTNESS
50%
LED CURRENT
25% 50% 100%
PWM CONTROL
(PWM_TO_I_THRESHOLD = 1111b)
BRIGHTNESS
Max current is set with CURRENT and CURRENT_MAX EPROM bits
or CURRENT and CURRENT_MAX EPROM bits and RISET resistor
100%
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8.3.2.5 Output Dimming Schemes
The LP8556 device supports three types of output dimming control methods: PWM Control, Pure Current Control
and Adaptive Dimming (Hybrid PWM and Current) Control.
8.3.2.5.1 PWM Control
PWM control is the traditional way of controlling the brightness using PWM of the outputs with the same LED
current across the entire brightness range. Brightness control is achieved by varying the duty cycle proportional
to the input PWM. PWM frequency is set either using an external set fesistor (RFSET) or using the PWM_FREQ
EPROM field. The maximum LED current is set by using an external set Resistor (RISET), CURRENT, and
CURRENT_MAX EPROM bits. PWM frequency can also be set by simply using the CURRENT and
CURRENT_MAX EPROM bits.
NOTE
The output PWM signal is de-coupled and generated independent of the input PWM signal
eliminating display flicker issues and allowing better noise immunity.
Figure 8. PWM Only Output Dimming Scheme
8.3.2.5.2 Pure Current Control
In Pure Current Control mode, brightness control is achieved by changing the LED current proportionately from
maximum value to a minimum value across the entire brightness range. Like in PWM Control mode, the
maximum LED current is set by using an external set Resistor (RISET), CURRENT, and CURRENT_MAX EPROM
bits. The maximum LED current can also be set by just using the CURRENT and CURRENT_MAX EPROM bits.
Current resolution in this mode is 12 bits.
Figure 9. Pure Current or Analog Output Dimming Scheme