LM27965
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SNVS380B – MAY 2006 – REVISED FEBRUARY 2013
LM27965 Dual Display White LED Driver with I2C Compatible Brightness Control
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FEATURES
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DESCRIPTION
91% Peak LED Drive Efficiency
No Inductor Required
0.3% Current Matching
Drives LEDs with up to 30mA per LED
180mA of total drive current
I2C Compatible Brightness Control Interface
Adaptive 1× - 3/2× Charge Pump
Resistor-Programmable Current Settings
External Chip RESET Pin
Extended Li-Ion Input: 2.7V to 5.5V
Small low profile industry standard leadless
package, WQFN 24 : (4mm x 4mm x 0.8mm)
25mm2 total solution size
Two I2C Compatible Chip Address Options:
0x36 for LM27965SQ and 0x38 for
LM27965SQ-M
The LM27965 is a highly integrated charge-pumpbased dual-display LED driver. The device can drive
up to 9 LEDs in parallel with a total output current of
180mA. Regulated internal current sinks deliver
excellent current and brightness matching in all LEDs.
The LED driver current sinks are split into three
independently controlled groups. The primary group
can beconfigurabled with 4 or 5 LEDs, for
backlighting a larger main display and the second
group can be configured with 2 or 3 LEDs, for
backlighing a smaller secondary display. An
additional, independently controlled led driver is
provided for driving an indicator or general purpose
LED. The LM27965 has an I2C compatible interface
that allows the user to independently control the
brightness on each bank of LEDs.
The device provides excellent efficiency without the
use of an inductor by operating the charge pump in a
gain of 3/2, or in Pass-Mode. The proper gain for
maintaining current regulation is chosen based on
LED forward voltage, so that efficiency is maximized
over the input voltage range.
APPLICATIONS
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Mobile Phone Display Lighting
PDA Backlighting
General LED Lighting
The LM27965 is available in a small 24-pin WQFN-24
package.
TYPICAL APPLICATION CIRCUIT
MAIN DISPLAY
VIN
+
CIN
-
VIN
1 PF
D1A
D2A
D3A
D4A
SUB DISPLAY
D5A
D1B D2B
INDICATOR
LED
D1C
D3B
POUT
COUT
C1
1 PF
1 PF
LM27965
C2
1 PF
GND
SCL
2
I C
Compatible
Interface
ISET
RSET
SDIO
VIO
RESET
Capacitors: TDK C1608X5R1A105k ,
or equivalent
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2006–2013, Texas Instruments Incorporated
LM27965
SNVS380B – MAY 2006 – REVISED FEBRUARY 2013
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CONNECTION DIAGRAM
24 Pin WQFN Package
See Package Number RTW0024A
6
5
4
3
2
1
1
2
3
4
5
6
7
24
24
7
8
23
23
8
9
22
22
10
21
21
10
11
20
20
11
19
19
9
DAP
DAP
12
13
14
15
16
17
18
12
18
17
Top View
16
15
14
13
Bottom View
Pin Functions
Pin Descriptions
Pin Name
Pin No.
Pin Descriptions
VIN
24
Input voltage. Input range: 2.7V to 5.5V.
POUT
23
Charge Pump Output Voltage
C1, C2
19, 22 (C1)
20, 21 (C2)
Flying Capacitor Connections
D5A, D4A, D3A, D2A,
D1A
12, 13, 14, 15, 16
LED Drivers - GroupA
D1B, D2B, D3B
4, 5, 6
LED Drivers - GroupB
D1C
3
LED Driver - Indicator LED
ISET
17
Placing a resistor (RSET) between this pin and GND sets the full-scale LED current for DxA ,
DxB, and D1C LEDs.
Full-Scale LED Current = 200 × (1.25V ÷ RSET)
SCL
1
Serial Clock Pin
SDIO
2
Serial Data Input/Output Pin
VIO
7
Serial Bus Voltage Level Pin
RESET
10
Harware Reset Pin. High = Normal Operation, Low = RESET
GND
9, 18, DAP
NC
8, 11
Ground
No Connect
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
2
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(1) (2) (3)
Absolute Maximum Ratings
VIN pin voltage
-0.3V to 6.0V
SCL, SDIO, VIO,
RESET pin voltages
-0.3V to (VIN+0.3V)
w/ 6.0V max
IDxx Pin Voltages
-0.3V to (VPOUT+0.3V)
w/ 6.0V max
Continuous Power Dissipation
Internally Limited
(4)
Junction Temperature (TJ-MAX)
150ºC
Storage Temperature Range
-65ºC to +150º C
(5)
Maximum Lead Temperature (Soldering)
ESD Rating (6)
Human Body Model
(1)
(2)
(3)
(4)
(5)
(6)
2.0kV
Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under
which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed
performance limits and associated test conditions, see the Electrical Characteristics tables.
All voltages are with respect to the potential at the GND pins.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office / Distributors for
availability and specifications.
Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 170°C (typ.) and
disengages at TJ = 165°C (typ.).
For detailed soldering specifications and information, please refer to National Semiconductor Application Note 1187: Leadless
Leadframe Package (AN-1187).
The human body model is a 100pF capacitor discharged through 1.5kΩ resistor into each pin. (MIL-STD-883 3015.7)
Operating Rating
(1) (2)
Input Voltage Range
2.7V to 5.5V
LED Voltage Range
2.0V to 4.0V
Junction Temperature (TJ) Range
-30°C to +100°C
Ambient Temperature (TA) Range (3)
(1)
(2)
(3)
-30°C to +85°C
Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under
which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed
performance limits and associated test conditions, see the Electrical Characteristics tables.
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 =
100°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 (θJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (θJA × PD-MAX).
Thermal Properties
Junction-to-Ambient Thermal
Resistance (θJA), RTW0024A Package
(1)
41.3°C/W
(1)
Junction-to-ambient thermal resistance is highly dependent on application and board layout. In applications where high maximum power
dissipation exists, special care must be paid to thermal dissipation issues in board design. For more information, please refer to National
Semiconductor Application Note 1187: Leadless Leadframe Package (AN-1187).
Electrical Characteristics (1)
(2)
Limits in standard typeface are for TJ = 25°C, and limits in boldface type apply over the full operating temperature range.
Unless otherwise specified: VIN = 3.6V; VRESET = VIN; VIO = 1.8V VDxA = VDxB = VDxC = 0.4V; RSET = 12.7kΩ; BankA = BankB =
BankC = Fullscale Current; ENA, ENB, ENC, EN5A, EN3B Bits = “1”; C1 = C2 = CIN= COUT= 1.0µF; Specifications related to
output current(s) and current setting pins (IDxx and ISET) apply to BankA and BankB. (3)
(1)
(2)
(3)
All voltages are with respect to the potential at the GND pins.
Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the
most likely norm.
CIN, CPOUT, C1, and C2 : Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics
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Electrical Characteristics(1) (2) (continued)
Limits in standard typeface are for TJ = 25°C, and limits in boldface type apply over the full operating temperature range.
Unless otherwise specified: VIN = 3.6V; VRESET = VIN; VIO = 1.8V VDxA = VDxB = VDxC = 0.4V; RSET = 12.7kΩ; BankA = BankB =
BankC = Fullscale Current; ENA, ENB, ENC, EN5A, EN3B Bits = “1”; C1 = C2 = CIN= COUT= 1.0µF; Specifications related to
output current(s) and current setting pins (IDxx and ISET) apply to BankA and BankB. (3)
Symbol
IDxx
Parameter
Condition
Min
Typ
Max
Units
Output Current Regulation
BankA or BankB Enabled
3.0V ≤ VIN ≤ 5.5V
ENA = '1' or ENB = '1' and ENC= '0'
18.2
(-9.5%)
20.1
22.0
(+9.5%)
mA
(%)
Output Current Regulation
BankC Enabled
3.0V ≤ VIN ≤ 5.5V
ENC = '1' and ENA = ENB= '0'
19.2
(-7.7%)
20.8
22.4
(+7.7%)
mA
(%)
Maximum Diode Current per Dxx
Output (4)
RSET = 8.33kΩ
30
mA
20
DxA
Output Current Regulation
BankA, BankB, and BankC Enabled
(4)
3.2V ≤ VIN ≤ 5.5V
VLED = 3.6V
20
DxB
mA
20
DxC
BankA
0.3
1.7
BankB
0.3
1.4
IDxx-MATCH
LED Current Matching (5)
3.0V ≤ VIN ≤ 5.5V
ROUT
Open-Loop Charge Pump Output
Resistance
Gain = 3/2
VDxTH
VDxx 1x to 3/2x Gain Transition
Threshold
VDxA and/or VDxB Falling
RSET = 16.9kΩ
175
mV
VHR
Current sink Headroom Voltage
Requirement
IDxx = 95% ×IDxx (nom.)
(IDxx (nom) ≈ 15mA)
RSET = 16.9kΩ
110
mV
IQ
Quiescent Supply Current
Gain = 1.5x, No Load
2.90
3.32
mA
ISD
Shutdown Supply Current
All ENx bits = "0"
3.4
5.4
µA
VSET
ISET Pin Voltage
2.7V ≤ VIN ≤ 5.5V
1.25
IDxA-B-C /
ISET
Output Current to Current Set Ratio
BankA, BankB, BankC
fSW
Switching Frequency
tSTART
Start-up Time
fPWM
Internal Diode Current PWM
Frequency
VRESET
Reset Voltage Thresholds
(6)
2.75
Gain = 1
%
Ω
1
V
200
0.89
POUT = 90% steady state
Reset
2.7V ≤ VIN ≤ 5.5V
Normal
Operation
1.27
1.57
MHz
250
µs
20
kHz
0
0.45
1.2
VIN
1.4
VIN
V
V
I2C Compatible Interface Voltage Specifications (SCL, SDIO, VIO)
(7)
VIO
Serial Bus Voltage Level
2.7V ≤ VIN ≤ 5.5V
VIL
Input Logic Low "0"
2.7V ≤ VIN ≤ 5.5V, VIO= 3.0V
0
0.3 ×
VIO
V
VIH
Input Logic High "1"
2.7V ≤ VIN ≤ 5.5V, VIO= 3.0V
0.7 ×
VIO
VIO
V
VOL
Output Logic Low "0"
ILOAD = 3mA
400
mV
(4)
(5)
(6)
(7)
4
The maximum total output current for the LM27965 should be limited to 180mA. The total output current can be split among any of the
three banks (IDxA = IDxB = IDxC = 30mA Max.). Under maximum output current conditions, special attention must be given to input voltage
and LED forward voltage to ensure proper current regulation. See the Maximum Output Current section of the datasheet for more
information.
For the two groups of current sinks on a part (BankA and BankB), the following are determined: the maximum sink current in the group
(MAX), the minimum sink current in the group (MIN), and the average sink current of the group (AVG). For each group, 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 for the bank. The matching figure for a given part is considered to be the highest matching figure of the two banks. The typical
specification provided is the most likely norm of the matching figure for all parts.
For each Dxxpin, headroom voltage is the voltage across the internal current sink connected to that pin. For Group A, B, and C current
sinks, VHRx = VOUT -VLED. If headroom voltage requirement is not met, LED current regulation will be compromised.
SCL and SDIO signals are referenced to VIO and GND for minimum VIO voltage testing.
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Electrical Characteristics(1) (2) (continued)
Limits in standard typeface are for TJ = 25°C, and limits in boldface type apply over the full operating temperature range.
Unless otherwise specified: VIN = 3.6V; VRESET = VIN; VIO = 1.8V VDxA = VDxB = VDxC = 0.4V; RSET = 12.7kΩ; BankA = BankB =
BankC = Fullscale Current; ENA, ENB, ENC, EN5A, EN3B Bits = “1”; C1 = C2 = CIN= COUT= 1.0µF; Specifications related to
output current(s) and current setting pins (IDxx and ISET) apply to BankA and BankB. (3)
Symbol
Parameter
2
Condition
I C Compatible Interface Timing Specifications (SCL, SDIO, VIO)
Min
Typ
Max
Units
(8)
t1
SCL (Clock Period)
2.5
µs
t2
Data In Setup Time to SCL High
100
ns
t3
Data Out stable After SCL Low
0
ns
t4
SDIO Low Setup Time to SCL Low
(Start)
100
ns
t5
SDIO High Hold Time After SCL High
(Stop)
100
ns
(8)
SCL and SDIO should be glitch-free in order for proper brightness control to be realized.
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BLOCK DIAGRAM
1 PF
C1+
VIN
2.7V to 5.5V
COUT
1 PF
1 PF
C1-
C2+
C2-
POUT
D1A D2A D3A D4A D5A
D1B D2B D3B
BankA Current Sinks
BankB
Current Sinks
3/2X and 1X
Regulated Charge Pump
1 PF
GAIN
CONTROL
VLED
SENSE
SoftStart
1.27 MHz.
Switch
Frequency
RESET
1.25V
Ref.
D1C Current
Sink
VLED
SENSE
Brightness
Control
Brightness
Control
Brightness
Control
20kHz PWM
Current Clock
General Purpose Register
SCL
2
SDIO
D1C
I C Interface
Block
Brightness Control Registers
Bank A and Bank B
Brightness Control Register
D1C
VIO
LM27965
ISET
GND
RSET
6
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Typical Performance Characteristics
Unless otherwise specified: TA = 25°C; VIN = 3.6V; VRESET = VIN; VLEDxA = VLEDxB = VLED1C = 3.6V; RSET = 16.9kΩ; C1=C2= CIN
= CPOUT = 1µF; ENA = ENB = ENC =EN5A = EN3B = '1'.
LED Drive Efficiency
vs
Input Voltage
Input Current
vs
Input Voltage
Figure 1.
Figure 2.
BankA Current Regulation
vs
Input Voltage
BankB Current Regulation
vs
Input Voltage
Figure 3.
Figure 4.
BankC Current Regulation
vs
Input Voltage
BankA Current Matching
vs
Input Voltage
Figure 5.
Figure 6.
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Typical Performance Characteristics (continued)
Unless otherwise specified: TA = 25°C; VIN = 3.6V; VRESET = VIN; VLEDxA = VLEDxB = VLED1C = 3.6V; RSET = 16.9kΩ; C1=C2= CIN
= CPOUT = 1µF; ENA = ENB = ENC =EN5A = EN3B = '1'.
BankB Current Matching
vs
Input Voltage
BankA Diode Current
vs
Brightness Register Code
Figure 7.
Figure 8.
BankB Diode Current
vs
Brightness Register Code
Figure 9.
8
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CIRCUIT DESCRIPTION
OVERVIEW
The LM27965 is a white LED driver system based upon an adaptive 3/2× - 1× CMOS charge pump capable of
supplying up to 180mA of total output current. With three separately controlled banks of constant current sinks,
the LM27965 is an ideal solution for platforms requiring a single white LED driver for main display, sub display,
and indicator lighting. The tightly matched current sinks ensure uniform brightness from the LEDs across the
entire small-format display.
Each LED is configured in a common anode configuration, with the peak drive current being programmed
through the use of an external RSET resistor. An I2C compatible interface is used to enable the device and vary
the brightness within the individual current sink banks. For BankA and BankB, 32 levels of brightness control are
available. The brightness control is achieved through a mix of analog and pulse width modulated (PWM)
methods. BankC has 4 analog brightness levels available.
CIRCUIT COMPONENTS
Charge Pump
The input to the 3/2× - 1x charge pump is connected to the VIN pin, and the regulated output of the charge pump
is connected to the VOUT pin. The recommended input voltage range of the LM27965 is 3.0V to 5.5V. The
device’s regulated charge pump has both open loop and closed loop modes of operation. When the device is in
open loop, the voltage at VOUT is equal to the gain times the voltage at the input. When the device is in closed
loop, the voltage at VOUT is regulated to 4.6V (typ.). The charge pump gain transitions are actively selected to
maintain regulation based on LED forward voltage and load requirements.
LED Forward Voltage Monitoring
The LM27965 has the ability to switch converter gains (1x or 3/2x) based on the forward voltage of the LED load.
This ability to switch gains maximizes efficiency for a given load. Forward voltage monitoring occurs on all diode
pins within BankA and BankB. At higher input voltages, the LM27965 will operate in pass mode, allowing the
POUT voltage to track the input voltage. As the input voltage drops, the voltage on the DXX pins will also drop
(VDXX = VPOUT – VLEDx). Once any of the active Dxx pins reaches a voltage approximately equal to 175mV, the
charge pump will switch to the gain of 3/2. This switch-over ensures that the current through the LEDs never
becomes pinched off due to a lack of headroom across the current sinks.
Only active Dxx pins will be monitored. For example, if only BankA is enabled, the LEDs in BankB will not affect
the gain transition point. If both banks are enabled, all diodes will be monitored, and the gain transition will be
based upon the diode with the highest forward voltage. Diode pins D5A and D3B can have the diode sensing
circuity disabled through the general purpose register if those drivers are not going to be used.
BankC (D1C) is not a monitored LED current sink.
RESETPin
The LM27965 has a hardware reset pin (RESET) that allows the device to be disabled by an external controller
without requiring an I2C write command. Under normal operation, the RESET pin should be held high (logic '1') to
prevent an unwanted reset. When the RESET is driven low (logic '0'), all internal control registers reset to the
default states and the part becomes disabled. Please see the Electrical Characteristics section of the datasheet
for required voltage thresholds.
I2C Compatible Interface
DATA VALIDITY
The data on SDIO line must be stable during the HIGH period of the clock signal (SCL). In other words, state of
the data line can only be changed when CLK is LOW.
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SCL
SDIO
data
change
allowed
data
valid
data
change
allowed
data
valid
data
change
allowed
Figure 10. Data Validity Diagram
A pull-up resistor between VIO and SDIO must be greater than [(VIO-VOL) / 3mA] to meet the VOL requirement
on SDIO. Using a larger pull-up resistor results in lower switching current with slower edges, while using a
smaller pull-up results in higher switching currents with faster edges.
START AND STOP CONDITIONS
START and STOP conditions classify the beginning and the end of the I2C session. A START condition is
defined as SDIO signal transitioning from HIGH to LOW while SCL line is HIGH. A STOP condition is defined as
the SDIO transitioning from LOW to HIGH while SCL is HIGH. The I2C master always generates START and
STOP conditions. The I2C bus is considered to be busy after a START condition and free after a STOP condition.
During data transmission, the I2C master can generate repeated START conditions. First START and repeated
START conditions are equivalent, function-wise.
SDIO
SCL
S
P
START condition
STOP condition
Figure 11. Start and Stop Conditions
TRANSFERING DATA
Every byte put on the SDIO line must be eight bits long, with the most significant bit (MSB) transferred first. Each
byte of data has to be followed by an acknowledge bit. The acknowledge related clock pulse is generated by the
master. The master releases the SDIO line (HIGH) during the acknowledge clock pulse. The LM27965 pulls
down the SDIO line during the 9th clock pulse, signifying an acknowledge. The LM27965 generates an
acknowledge after each byte is received.
After the START condition, the I2C master sends a chip address. This address is seven bits long followed by an
eighth bit which is a data direction bit (R/W). The LM27965 address is 36h (38h for -M version). For the eighth
bit, a “0” indicates a WRITE and a “1” indicates a READ. The second byte selects the register to which the data
will be written. The third byte contains data to write to the selected register.
10
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ack from slave
ack from slave
ack from slave
start
msb Chip Address lsb
w
ack
msb Register Add lsb
ack
msb DATA lsb
ack
stop
start
Id = 36h
w
ack
addr = 10h
ack
DGGUHVV K¶06 data
ack
stop
SCL
SDIO
Figure 12. Write Cycle
w = write (SDIO = "0")
r = read (SDIO = "1")
ack = acknowledge (SDIO pulled down by either master or slave)
id = chip address, 36h for LM27965 or 38h for LM27965-M
I2C COMPATIBLE CHIP ADDRESS
The chip address for LM27965 is 0110110, or 36h. The chip address for LM27965-M is 0111000, or 38h.
MSB
LSB
ADR6
bit7
ADR5
bit6
ADR4
bit5
ADR3
bit4
ADR2
bit3
ADR1
bit2
ADR0
bit1
LM27965
0
1
1
0
1
1
0
LM27965-M
0
1
1
1
0
0
0
R/W
bit0
2
I C Slave Address (chip address)
Figure 13. Chip Address
INTERNAL REGISTERS OF LM27965
Register
Internal Hex Address
Power On Value
General Purpose Register
10h
0010 0000
Bank A Brightness Control Register
A0h
1110 0000
Bank B Brightness Control Register
B0h
1110 0000
Bank C Brightness Control Register
C0h
1111 1100
MSB
0
bit7
LSB
0
bit6
1
bit5
EN3B
bit4
EN5A
bit3
ENC
bit2
ENB
bit1
ENA
bit0
Figure 14. General Purpose Register Description
Internal Hex Address: 10h
NOTE
ENA: Enables DxA LED drivers (Main Display)
ENB: Enables DxB LED drivers (Aux Lighting)
ENC: Enables D1C LED driver (Indicator Lighting)
EN5A: Enables D5A LED voltage sense
EN3B: Enables D3B LED driver and voltage sense
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DxA Brightness Control
Register Address: 0xA0
MSB
1
bit7
1
bit6
1
bit5
1
bit6
1
bit5
DxA2
bit2
DxA1
bit1
DxB4
bit4
DxB3
bit3
1
bit6
1
bit5
1
bit4
1
bit3
DxA0
bit0
LSB
DxB2
bit2
DxB1
bit1
DxC Brightness Control
Register Address: 0xC0
MSB
1
bit7
DxA3
bit3
DxB Brightness Control
Register Address: 0xB0
MSB
1
bit7
DxA4
bit4
LSB
DxB0
bit0
LSB
1
bit2
D1C1
bit1
D1C0
bit0
Figure 15. Brightness Control Register Description
Internal Hex Address: 0xA0 (BankA), 0xB0 (BankB), 0xC0 (BankC)
NOTE
DxA4-DxA0: Sets Brightness for DxA pins (BankA). 11111=Fullscale
DxB4-DxB0: Sets Brightness for DxB pins (BankB). 11111=Fullscale
Bit7 to Bit 5: Not Used
DxC1-DxC0: Sets Brightness for DxC pin. 11 = Fullscale
Bit7 to Bit2:Not Used
Full-Scale Current set externally by the following equation:
IDxx = 200 × 1.25V / RSET
Table 1. Brightness Level Control Table (BankA and BankB)
12
Brightness Code (hex)
Analog Current (% of FullScale)
Duty Cycle (%)
Perceived Brightness Level (%)
00
20
1/16
1.25
01
20
2/16
2.5
02
20
3/16
3.75
03
20
4/16
5
04
20
5/16
6.25
05
20
6/16
7.5
06
20
7/16
8.75
07
20
8/16
10
08
20
9/16
11.25
09
20
10/16
12.5
0A
20
11/16
13.75
0B
20
12/16
15
0C
20
13/16
16.25
0D
20
14/16
17.5
0E
20
15/16
18.75
0F
20
16/16
20
10
40
10/16
25
11
40
11/16
27.5
12
40
12/16
30
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Table 1. Brightness Level Control Table (BankA and BankB) (continued)
Brightness Code (hex)
Analog Current (% of FullScale)
Duty Cycle (%)
Perceived Brightness Level (%)
13
40
13/16
32.5
14
40
14/16
35
15
40
15/16
37.5
16
40
16/16
40
17
70
11/16
48.125
18
70
12/16
52.5
56.875
19
70
13/16
1A
70
14/16
61.25
1B
70
15/16
65.625
1C
70
16/16
70
1D
100
13/16
81.25
1E
100
15/16
93.75
1F
100
16/16
100
BankC Brightness Levels (%of Full-Scale) = 20%, 40%, 70%, 100%
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APPLICATION INFORMATION
SETTING LED CURRENT
The current through the LEDs connected to DxA and DxB can be set to a desired level simply by connecting an
appropriately sized resistor (RSET) between the ISET pin of the LM27965 and GND. The DxA and DxB LED
currents are proportional to the current that flows out of the ISET pin and are a factor of 200 times greater than the
ISET current. The feedback loops of the internal amplifiers set the voltage of the ISET pin to 1.25V (typ.). The
statements above are simplified in the equations below:
IDxA/B/C (A)= 200 × (VISET / RSET)
RSET (Ω)= 200 × (1.25V / IDxA/B/C)
(1)
(2)
Once the desired RSET value has been chosen, the LM27965 has the ability to internally dim the LEDs using a
mix of Pulse Width Modulation (PWM) and analog current scaling. The PWM duty cycle is set through the I2C
compatible interface. LEDs connected to BankA and BankB current sinks (DxA and DxB) can be dimmed to 32
different levels/duty-cycles. The internal PWM frequency for BankA and BankB is fixed at 20kHz. BankC(D1C)
has 4 analog current levels.
Please refer to the I2C Compatible Interface section of this datasheet for detailed instructions on how to adjust
the brightness control registers.
MAXIMUM OUTPUT CURRENT, MAXIMUM LED VOLTAGE, MINIMUM INPUT VOLTAGE
The LM27965 can drive 8 LEDs at 22.5mA each (BankA and BankB) from an input voltage as low as 3.2V, so
long as the LEDs have a forward voltage of 3.6V or less (room temperature).
The statement above is a simple example of the LED drive capabilities of the LM27965. The statement contains
the key application parameters that are required to validate an LED-drive design using the LM27965: LED
current (ILEDx), number of active LEDs (Nx), LED forward voltage (VLED), and minimum input voltage (VIN-MIN).
The equation below can be used to estimate the maximum output current capability of the LM27965:
ILED_MAX = [(1.5 x VIN) - VLED - (IADDITIONAL × ROUT)] / [(Nx x ROUT) + kHRx]
ILED_MAX = [(1.5 x VIN ) - VLED - (IADDITIONAL × 2.75Ω)] / [(Nx x 2.75Ω) + kHRx]
(3)
(4)
IADDITIONAL is the additional current that could be delivered to the other LED banks.
ROUT – Output resistance. This parameter models the internal losses of the charge pump that result in voltage
droop at the pump output POUT. Since the magnitude of the voltage droop is proportional to the total output
current of the charge pump, the loss parameter is modeled as a resistance. The output resistance of the
LM27965 is typically 2.75Ω (VIN = 3.6V, TA = 25°C). In equation form:
VPOUT = (1.5 × VIN) – [(NA× ILEDA + NB × ILEDB ) × ROUT]
(5)
kHR – Headroom constant. This parameter models the minimum voltage required to be present across the current
sinks for them to regulate properly. This minimum voltage is proportional to the programmed LED current, so the
constant has units of mV/mA. The typical kHR of the LM27965 is 8mV/mA. In equation form:
(VPOUT – VLEDx) > kHRx × ILEDx
(6)
Typical Headroom Constant Values
kHRA = 8mV/mA
kHRB = 8mV/mA
(7)
(8)
Equation 3 is obtained from combining the ROUT Equation 5 with the kHRx Equation 6 and solving for ILEDx.
Maximum LED current is highly dependent on minimum input voltage and LED forward voltage. Output current
capability can be increased by raising the minimum input voltage of the application, or by selecting an LED with a
lower forward voltage. Excessive power dissipation may also limit output current capability of an application.
14
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Total Output Current Capability
The maximum output current that can be drawn from the LM27965 is 180mA. Each driver bank has a maximum
allotted current per Dxx sink that must not be exceeded.
DRIVER TYPE
MAXIMUM Dxx CURRENT
DxA
30mA per DxA Pin
DxB
30mA per DxB Pin
DxC
30mA per DxB Pin
The 180mA load can be distributed in many different configurations. Special care must be taken when running
the LM27965 at the maximum output current to ensure proper functionality.
PARALLEL CONNECTED AND UNUSED OUTPUTS
Outputs D1A-5A or D1B-D3B may be connected together to drive one or two LEDs at higher currents. In such a
configuration, all five parallel current sinks (BankA) of equal value can drive a single LED. The LED current
programmed for BankA should be chosen so that the current through each of the outputs is programmed to 20%
of the total desired LED current. For example, if 60mA is the desired drive current for a single LED, RSET should
be selected such that the current through each of the current sink inputs is 12mA.
Connecting the outputs in parallel does not affect internal operation of the LM27965 and has no impact on the
Electrical Characteristics and limits previously presented. The available diode output current, maximum diode
voltage, and all other specifications provided in the Electrical Characteristics table apply to this parallel output
configuration, just as they do to the standard 5-LED application circuit.
Both BankA and BankB utilize LED forward voltage sensing circuitry on each Dxx pin to optimize the chargepump gain for maximum efficiency. Due to the nature of the sensing circuitry, it is not recommended to leave any
of the DxA (D1A-D4A) or DxB (D1B-D2B) pins open if either diode bank is going to be used during normal
operation. Leaving DxA and/or DxB pins unconnected will force the charge-pump into 3/2× mode over the entire
VIN range negating any efficiency gain that could have been achieved by switching to 1× mode at higher input
voltages.
If D5A is not used, it is recommended that the driver pin be grounded and the general purpose register bit EN5A
be set to 0 to ensure proper gain transitions.
The D3B driver can be completely turned on or off on the fly using the general purpose register. The diode
monitoring circuity is enabled and disabled with the driver. If D3B is not used, it is recommended that the driver
pin be grounded and the general purpose register bit EN3B be set to 0 to ensure proper gain transitions.
Care must be taken when selecting the proper RSET value. The current on any Dxx pin must not exceed the
maximum current rating for any given current sink pin.
POWER EFFICIENCY
Efficiency of LED drivers is commonly taken to be the ratio of power consumed by the LEDs (PLED) to the power
drawn at the input of the part (PIN). With a 3/2× - 1× charge pump, the input current is equal to the charge pump
gain times the output current (total LED current). The efficiency of the LM27965 can be predicted as follows:
PLEDTOTAL = (VLEDA × NA × ILEDA) + (VLEDB × NB × ILEDB) + (VLEDC × ILEDC)
PIN = VIN × IIN
PIN = VIN × (GAIN × ILEDTOTAL + IQ)
E = (PLEDTOTAL ÷ PIN)
(9)
(10)
(11)
(12)
The LED voltage is the main contributor to the charge-pump gain selection process. Use of low forward-voltage
LEDs (3.0V- to 3.5V) will allow the LM27965 to stay in the gain of 1× for a higher percentage of the lithium-ion
battery voltage range when compared to the use of higher forward voltage LEDs (3.5V to 4.0V). See the LED
Forward Voltage Monitoring section of this datasheet for a more detailed description of the gain selection and
transition process.
For an advanced analysis, it is recommended that power consumed by the circuit (VIN x IIN) for a given load be
evaluated rather than power efficiency.
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POWER DISSIPATION
The power dissipation (PDISS) and junction temperature (TJ) can be approximated with the equations below. PIN is
the power generated by the 3/2× - 1× charge pump, PLED is the power consumed by the LEDs, TA is the ambient
temperature, and θJA is the junction-to-ambient thermal resistance for the WQFN-24 package. VIN is the input
voltage to the LM27965, VLED is the nominal LED forward voltage, N is the number of LEDs and ILED is the
programmed LED current.
PDISS = PIN - PLEDA - PLEDB - PLEDC
PDISS= (GAIN × VIN × IBANKA + BANKB + BANKC ) - (VLEDA × NA × ILEDA) - (VLEDB × NB × ILEDB) - (VLEDC × ILEDC)
TJ = TA + (PDISS x θJA)
(13)
(14)
(15)
The junction temperature rating takes precedence over the ambient temperature rating. The LM27965 may be
operated outside the ambient temperature rating, so long as the junction temperature of the device does not
exceed the maximum operating rating of 100°C. The maximum ambient temperature rating must be derated in
applications where high power dissipation and/or poor thermal resistance causes the junction temperature to
exceed 100°C.
THERMAL PROTECTION
Internal thermal protection circuitry disables the LM27965 when the junction temperature exceeds 170°C (typ.).
This feature protects the device from being damaged by high die temperatures that might otherwise result from
excessive power dissipation. The device will recover and operate normally when the junction temperature falls
below 165°C (typ.). It is important that the board layout provide good thermal conduction to keep the junction
temperature within the specified operating ratings.
CAPACITOR SELECTION
The LM27965 requires 4 external capacitors for proper operation (C1 = C2 = CIN = COUT = 1µF). Surface-mount
multi-layer ceramic capacitors are recommended. These capacitors are small, inexpensive and have very low
equivalent series resistance (ESR
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