19-0790; Rev 1; 9/07
KIT
ATION
EVALU
E
L
B
AVAILA
Ultra-Efficient Charge Pumps for
Six White/RGB LEDs in 3mm x 3mm Thin QFN
The MAX8647/MAX8648 drive up to six white LEDs or
two sets of RGB LEDs with regulated constant current
for display backlight and fun light applications. By utilizing an inverting charge pump and extremely lowdropout adaptive current regulators, these ICs achieve
very high efficiency over the full 1-cell Li+ battery voltage range and even with large LED forward voltage
mismatch. The 1MHz fixed-frequency switching allows
for tiny external components. The regulation scheme is
optimized to ensure low EMI and low input ripple. The
MAX8647/MAX8648 include thermal shutdown, openand short-circuit protection.
The MAX8647 features an I 2C serial port, while the
MAX8648 features a three-wire serial-pulse logic interface. Both devices support independent on/off and
dimming for main and subbacklights. The dimming
ranges are pseudo-logarithmic from 24mA to 0.1mA
and off in 32 steps. Both devices include a temperature
derating function to safely allow bright 24mA full-scale
output current setting while automatically reducing current to protect LEDs at high ambient temperatures
above +60°C.
The MAX8647/MAX8648 are available in a 16-pin, 3mm
x 3mm thin QFN package (0.8mm max height).
Applications
White LED Backlighting, Single or Dual Display
Features
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
Six Adaptive Current Regulators
Independent Voltage Supply for Each LED
Individual LED Brightness Control (MAX8647)
24mA to 0.1mA Dimming Range
I2C Interface (MAX8647)
Serial-Pulse Dimming Logic (MAX8648)
±2% Accuracy, ±0.4% Matching (typ)
Low 70µA Quiescent Current
Low 1µA Shutdown Current
Inrush Current Limit
TA Derating Function Protects LEDs
16-Pin, 3mm x 3mm Thin QFN Package
Ordering Information
TOP
MARK
PKG
CODE
MAX8647ETE+ I2C interface 16 Thin QFN-EP*
AFD
T1633-5
Serial-pulse
16 Thin QFN-EP*
logic
AFE
T1633-5
PART
MAX8648ETE+
DIMMING
PIN
PACKAGE
Note: All devices are specified over the -40°C to +85°C extended
temperature range.
+Denotes a lead-free package.
*EP = Exposed paddle.
Wide-Gamut RGB LED Display Backlighting
Typical Operating Circuit
Camera Flash or RGB Indicators
Cellular Phones and Smartphones
1μF
PDAs, Digital Cameras, and Camcorders
LED3
LED4
LED5
TOP VIEW
LED2
Pin Configuration
12
11
10
9
C1P
INPUT
2.7V TO 5.5V
1μF
C1N
C2P
C2N
IN
EP
1μF
GND
LED1 13
8
LED6
SDA (ENC) 14
7
NEG
6
C1N
5
C2N
MAX8647ETE
MAX8648ETE
SCL (ENB) 15
1
2
3
4
GND
C1P
C2P
+
IN
VDD (ENA) 16
THIN QFN
WHITE
OR RGB LED
MAX8648
LED1
LED2
SERIALPULSE
INTERFACE
1μF
NEG
ENA
LED3
ENB
LED4
ENC
LED5
LED6
D1
D2
D3
D4
D5
D6
( ) DESIGNATE PINS ON THE MAX8648
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim's website at www.maxim-ic.com.
1
MAX8647/MAX8648
General Description
MAX8647/MAX8648
Ultra-Efficient Charge Pumps for
Six White/RGB LEDs in 3mm x 3mm Thin QFN
ABSOLUTE MAXIMUM RATINGS
VDD, IN, SCL, SDA, ENA, ENB, ENC to GND........-0.3V to +6.0V
VDD, IN, SCL, SDA, ENA, ENB, ENC to NEG ........-0.3V to +6.0V
NEG to GND .............................................................-6V to +0.3V
C2N to GND .............................................................-6V to +0.3V
C1P, C2P to GND .......................................-0.3V to (VIN + 0.3V)
C2P to C1N ..................................................-0.3V to (VIN + 0.3V)
LED_, C1N, C2N to NEG .............................-0.3V to (VIN + 0.3V)
Continuous Power Dissipation (TA = +70°C)
16-Pin Thin QFN 3mm x 3mm (derate 20.8mW/°C
above +70°C).............................................................1667mW
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
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 in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VVDD = VIN = 3.6V, VGND = 0V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
IN Operating Voltage
2.7
5.5
V
VDD Operating Voltage
1.7
5.5
V
2.55
V
Undervoltage-Lockout (UVLO)
Threshold
VIN rising
2.35
Undervoltage-Lockout Hysteresis
IN Shutdown Supply Current
(All Outputs Off)
VDD Shutdown Supply Current
IN Operating Supply Current
VDD Operating Supply Current
2.45
100
VSCL = VSDA = VDD (MAX8647),
VEN_ = 0V (MAX8648)
TA = +25°C
0.4
TA = +85°C
0.4
TA = +25°C
0.1
TA = +85°C
0.1
Charge pump inactive, two LEDs enabled at 0.1mA
setting
70
Charge pump active, 1MHz switching, all LEDs
enabled at 0.1mA setting
1.6
Charge pump inactive, two LEDs enabled at 0.1mA
setting, TA = +25°C
0.1
Charge pump active, 1MHz switching, all LEDs
enabled at 0.1mA setting, TA = +85°C
0.1
mV
2.5
1.0
100
µA
µA
µA
mA
1.0
µA
Thermal-Shutdown Threshold
+160
°C
Thermal-Shutdown Hysteresis
20
°C
I2C INTERFACE (MAX8647)
Logic-Input High Voltage (SDA, SCL)
VDD = 1.7V to 5.5V, hysteresis = 0.2 x VDD (typ)
Logic-Input Low Voltage (SDA, SCL)
VDD = 1.7V to 5.5V, hysteresis = 0.2 x VDD (typ)
Filtered Pulse Width (tSP)
VIN = 2.7V to 5.5V, VDD = 1.7V to 5.5V (Note 2)
Logic-Input Current (SDA, SCL)
2
VIL = 0V or VIH = 5.5V
TA = +25°C
TA = +85°C
0.7 x
VDD
-1
V
0.01
0.1
_______________________________________________________________________________________
0.3 x
VDD
V
50
ns
+1
µA
Ultra-Efficient Charge Pumps for
Six White/RGB LEDs in 3mm x 3mm Thin QFN
(VVDD = VIN = 3.6V, VGND = 0V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
SDA Output Low Voltage
CONDITIONS
MIN
ISDA = 3mA, for acknowledge (Note 2)
TYP
MAX
0.03
0.40
V
400
kHz
I2C Clock Frequency
UNITS
Bus Free Time Between START and
STOP (tBUF)
(Note 2)
1.3
Hold Time Repeated START Condition
(tHD_STA)
(Note 2)
0.6
0.1
µs
SCL Low Period (tLOW)
(Note 2)
1.3
0.2
µs
SCL High Period (tHIGH)
(Note 2)
0.6
0.2
µs
Setup Time Repeated START
Condition (tSU_STA)
(Note 2)
0.6
0.1
µs
SDA Hold Time (tHD_DAT)
(Note 2)
0
-0.01
µs
SDA Setup Time (tSU_DAT)
(Note 2)
100
50
ns
Setup Time for STOP Condition
(tSU_STO)
(Note 2)
0.6
0.1
µs
µs
SERIAL-PULSE LOGIC (EN_) (MAX8648)
Logic-Input High Voltage
VIN = 2.7V to 5.5V
Logic-Input Low Voltage
VIN = 2.7V to 5.5V
1.4
Logic-Input Current
VIL = 0V or VIH = 5.5V
EN Low Shutdown Delay tSHDN
See Figure 3 and the Shutdown Mode section; EN_
needs to be longer than 4ms to ensure LED is
powered off
V
0.4
TA = +25°C
-1
TA = +85°C
tLO (Figure 3)
0.01
4
Initial tHI (Figure 3)
First EN_ high pulse
µA
ms
1
tHI (Figure 3)
+1
0.1
V
500
µs
1
µs
120
µs
CHARGE PUMP
Switching Frequency
Soft-Start Time
4.3
1
MHz
0.5
ms
5.0
V
Charge-Pump Regulation Voltage
(VIN - VNEG)
Open-Loop NEG Output Resistance
(VNEG - 0.5 x VIN) / INEG
2.5
NEG Discharge Resistance in
Shutdown or When the Charge Pump
is Inactive
All LEDs off, EN_ = GND
10
5
Ω
kΩ
LED1–LED6 CURRENT REGULATOR
Current Setting Range
Current Accuracy
Through an I2C or serial-pulse interface
VLED_ = 0.5V for
charge-pump inactive,
VLED_ = -0.9V,
VNEG_ = -1.4V
0.1
24mA setting, TA = +25°C
-2
24mA setting, TA = -40°C
to derating function start
temperature (Note 2)
-5
1.6mA setting, TA = +25°C
-15
24.0
±1
+5
±5
mA
+2
%
+15
_______________________________________________________________________________________
3
MAX8647/MAX8648
ELECTRICAL CHARACTERISTICS (continued)
ELECTRICAL CHARACTERISTICS (continued)
(VVDD = VIN = 3.6V, VGND = 0V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
CONDITIONS
MIN
TYP
Derating-Function Start Temperature
Derating-Function Slope
From derating-function start temperature
LED_ RDSON
-2.5
%/°C
Utilizing the charge pump
4
LED_ Current Regulator Switchover
Threshold (Inactive to Active)
VLED_ falling
Ω
Not utilizing the charge pump
60
120
Utilizing the charge pump
90
200
150
175
125
LED_ Current Regulator Switchover
Hysteresis
UNITS
°C
3
24mA setting
(Note 3)
MAX
+60
Not utilizing the charge pump
LED_ Dropout
mV
mV
100
LED_ Leakage in Shutdown
All LEDs off
TA = +25°C
0.01
TA = +85°C
0.1
mV
5
µA
Note 1: Limits are 100% production tested at TA = +25°C. Specifications over the operating temperature range are guaranteed by design.
Note 2: Guaranteed by design.
Note 3: LED dropout voltage is defined as the LED_ to GND voltage at which current into LED_ drops 10% from the value at VLED_ = 0.5V.
Typical Operating Characteristics
(VIN = 3.6V, VEN_ = VIN, circuit of Figure 1, TA = +25°C, unless otherwise noted.)
EFFICIENCY vs. SUPPLY VOLTAGE
(DRIVING SIX MATCHED LEDs)
20.8mA/LED
60
50
16mA/LED
1.6mA/LED
40
6.4mA/LED
30
20
80
20.8mA/LED
70
1.6mA/LED
16mA/LED
60
6.4mA/LED
50
90
80
70
60
16mA/LED
50
1.6mA/LED
40
30
20
10
10
0
3.0
3.3
3.6
INPUT VOLTAGE (V)
3.9
4.2
LEDs HAVE MISMATCHED VF
0
40
2.7
4
MAX8647/48 toc03
90
EFFICIENCY (%)
70
100
MAX8647/48 toc02
80
100
EFFICIENCY PLED/PBATT (%)
90
EFFICIENCY vs. SUPPLY VOLTAGE
(DRIVING SIX LEDs)
EFFICIENCY vs. Li+ BATTERY VOLTAGE
(DRIVING SIX MATCHED LEDs)
MAX8647/48 toc01
100
EFFICIENCY (%)
MAX8647/MAX8648
Ultra-Efficient Charge Pumps for
Six White/RGB LEDs in 3mm x 3mm Thin QFN
4.2 3.9
3.8
3.7
3.6
3.5 3.4 3.0
Li+ BATTERY VOLTAGE (V, TIME-WEIGHTED)
2.7
3.0
3.3
3.6
INPUT VOLTAGE (V)
_______________________________________________________________________________________
3.9
4.2
Ultra-Efficient Charge Pumps for
Six White/RGB LEDs in 3mm x 3mm Thin QFN
20.8mA/LED
50
6.4mA/LED
40
30
20
60
3.0
3.3
3.6
4.2
3.9
80
6.4mA/LED
70
20.8mA/LED
60
50
LEDs HAVE MISMATCHED VF
40
2.7
4.2 3.9
3.8
3.7
LEDs HAVE MISMATCHED VF
40
3.6
4.2 3.9
3.5 3.4 3.0
3.8
3.7
3.6
3.5 3.4 3.0
INPUT VOLTAGE (V)
Li+ BATTERY VOLTAGE (V, TIME-WEIGHTED)
Li+ BATTERY VOLTAGE (V, TIME-WEIGHTED)
INPUT CURRENT vs. INPUT VOLTAGE
(DRIVING SIX LEDs)
INPUT CURRENT vs. Li+ BATTERY
VOLTAGE (DRIVING SIX LEDs)
INPUT CURRENT
vs. INPUT VOLTAGE (RGB MODULE)
120
ILED = 16mA
LEDs HAVE MISMATCHED VF
60
ILED = 6.4mA
40
20.8mA/LED
120
16mA/LED
100
80
60
6.4mA/LED
40
20
0
3.2
4.2
3.7
ILED = 16mA
60
50
40
ILED = 4.8mA
30
ILED = 1.6mA
10
0
0
2.7
70
20
1.6mA/LED
20
ILED = 1.6mA
ILED = 20.8mA
80
4.2 3.9
3.8
3.7
3.6
2.7
3.5 3.4 3.0
3.2
4.2
3.7
Li+ BATTERY VOLTAGE (V, TIME-WEIGHTED)
INPUT VOLTAGE (V)
INPUT CURRENT vs. Li+ BATTERY
VOLTAGE (RGB MODULE)
INPUT RIPPLE VOLTAGE vs. SUPPLY
VOLTAGE (DRIVING SIX WHITE LEDs)
LED CURRENT MATCHING
vs. INPUT VOLTAGE (16mA/LED)
70
16mA/LED
60
50
40
30
6.4mA/LED
20
14
12
16mA/LED
10
8
6.4mA/LED
LEDs HAVE
MISMATCHED VF
6
4
0
3.8
3.7
3.6
3.5 3.4 3.0
Li+ BATTERY VOLTAGE (V, TIME-WEIGHTED)
16.8
16.6
16.4
16.2
16.0
15.8
15.6
15.2
1.6mA/LED
0
4.2 3.9
17.0
15.4
2
1.6mA/LED
10
20.8mA/LED
LED CURRENT (mA)
20.8mA/LED
80
16
INPUT RIPPLE VOLTAGE (mVRMS)
RGB MODULE: LUMEX SML-LX3632SISUGSBC
90
MAX8647/48 toc10
INPUT VOLTAGE (V)
MAX8647/48 toc12
80
140
RGB MODULE: LUMEX SML-LX3632SISUGSBC
90
INPUT CURRENT (mA)
140
100
160
INPUT CURRENT (mA)
160
LEDs HAVE MISMATCHED VF
180
100
MAX8647/48 toc08
ILED = 20.8mA
180
200
MAX8647/48 toc07
200
INPUT CURRENT (mA)
1.6mA/LED
LEDs HAVE MISMATCHED VF
0
INPUT CURRENT (mA)
70
90
50
10
100
80
MAX8647/48 toc06
90
100
EFFICIENCY PLED/PBATT (%)
70
16mA/LED
MAX8647/48 toc11
EFFICIENCY (%)
80
100
MAX8647/48 toc05
90
EFFICIENCY PLED/PBATT (%)
MAX8647/48 toc04
100
60
EFFICIENCY vs. Li+ BATTERY VOLTAGE
(DRIVING SIX LEDs)
EFFICIENCY vs. Li+ BATTERY VOLTAGE
(DRIVING SIX LEDs)
MAX8647/48 toc09
EFFICIENCY vs. SUPPLY VOLTAGE
(DRIVING SIX LEDs)
2.7
15.0
3.2
3.7
SUPPLY VOLTAGE (V)
4.2
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
INPUT VOLTAGE (V)
_______________________________________________________________________________________
5
MAX8647/MAX8648
Typical Operating Characteristics (continued)
(VIN = 3.6V, VEN_ = VIN, circuit of Figure 1, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
(VIN = 3.6V, VEN_ = VIN, circuit of Figure 1, TA = +25°C, unless otherwise noted.)
1x MODE OPERATING WAVEFORMS
(VIN = 4V)
LED CURRENT vs. TEMPERATURE
1.5x MODE OPERATING WAVEFORMS
(VIN = 3V)
MAX8647/48 toc15
MAX8647/48 toc14
MAX8647/48 toc13
30
25
LED CURRENT (mA)
MAX8647/MAX8648
Ultra-Efficient Charge Pumps for
Six White/RGB LEDs in 3mm x 3mm Thin QFN
AC-COUPLED
100mV/div
AC-COUPLED
VIN
100mV/div
VIN
20
100mA/div
IIN
15
100mA/div
IIN
0A
0A
10
20mA/div
20mA/div
5
ILED
ALL LEDs ON
ILED = 24mA
0A
ILED
ALL LEDs ON
ILED = 24mA
0
-40
-15
10
35
60
85
400ns/div
400ns/div
TEMPERATURE (°C)
STARTUP AND SHUTDOWN
(MAX8648)
SINGLE-WIRE PULSE DIMMING
(MAX8648)
MAX8647/48 toc16
ENA = ENB = ENC
MAX8647/48 toc17
2V/div
VEN_
AC-COUPLED
20mV/div
VIN
IIN
200mA/div
5V/div
OPERATING IN 1x
MODE, ALL 6 LEDs
OPERATING
VEN_
TOTAL ILED5
0A
20mA/div
ILED5
2V/div
0A
0A
1ms/div
10ms/div
LINE-TRANSIENT RESPONSE
(VIN = 4.3V TO 3.8V TO 4.3V)
LINE-TRANSIENT RESPONSE WITH MODE
CHANGE (VIN = 3.8V TO 3.4V TO 3.8V)
MAX8647/48 toc18
MAX8647/48 toc19
4.3V
VIN
3.8V
VIN
IIN
200mA/div
IIN
3.8V
3.4V
200mA/div
0A
24mA
20mA/div
ILED6
1ms/div
6
0mA
ILED6
24mA
20mA/div
1ms/div
_______________________________________________________________________________________
0A
Ultra-Efficient Charge Pumps for
Six White/RGB LEDs in 3mm x 3mm Thin QFN
PIN
NAME
FUNCTION
1
IN
Supply Voltage Input. The input voltage range is 2.7V to 5.5V. Bypass IN to GND with a
1µF ceramic capacitor as close as possible to the IC. IN is high impedance during
shutdown. Connect IN to the anodes of all the LEDs.
2
2
GND
Ground. Connect GND to system ground and the input bypass capacitor as close as
possible to the IC.
3
3
C1P
Transfer Capacitor 1 Positive Connection. Connect a 1µF ceramic capacitor from C1P
to C1N.
4
4
C2P
Transfer Capacitor 2 Positive Connection. Connect a 1µF ceramic capacitor from C2P
to C2N.
5
5
C2N
Transfer Capacitor 2 Negative Connection. Connect a 1µF ceramic capacitor from C2P
to C2N. An internal 10kΩ resistor pulls C2N to GND during shutdown.
6
6
C1N
Transfer Capacitor 1 Negative Connection. Connect a 1µF ceramic capacitor from C1P
to C1N.
7
7
NEG
Charge-Pump Negative Output. Connect a 1µF ceramic capacitor from NEG to GND. In
shutdown, an internal 10kΩ resistor pulls NEG to GND. Connect the exposed paddle to
NEG directly under the IC.
LED Current Regulators. Current flowing into LED_ is based on the internal registers.
Connect LED_ to the cathodes of the external LEDs. LED_ is high impedance during
shutdown. For the MAX8647, program any unused LED_ to off and LED_ can be
shorted to ground or left unconnected. For the MAX8648, short any unused LED_ to IN
prior to power-up to disable the corresponding current regulator.
MAX8647
MAX8648
1
8–13
8–13
LED6–LED1
14
—
SDA
I2C Data Input. Data is read on the rising edge of SCL.
15
—
SCL
I2C Clock Input. Data is read on the rising edge of SCL.
16
—
VDD
Logic-Input Supply Voltage. Connect to the supply voltage driving SDA and SCL.
Bypass VDD to GND with a 0.1µF ceramic capacitor.
—
14, 15, 16
ENC, ENB, ENA
—
—
EP
Enable and Serial-Pulse Dimming Control. ENA controls LED1, LED2, and LED3. ENB
controls LED4 and LED5. ENC controls LED6. Drive EN_ logic-high to turn on the IC
and enable the corresponding LED_ at 24mA each. Drive an individual EN_ logic-low
for greater than 4ms to turn off the corresponding-current regulators or drive all three
EN_ low to place the IC in shutdown. See the Serial-Pulse Dimming Control (MAX8648)
section.
Exposed Paddle. Connect to NEG.
_______________________________________________________________________________________
7
MAX8647/MAX8648
Pin Description
MAX8647/MAX8648
Ultra-Efficient Charge Pumps for
Six White/RGB LEDs in 3mm x 3mm Thin QFN
Detailed Description
The MAX8647/MAX8648 have an inverting charge
pump and six current regulators capable of 24mA each
to drive six white LEDs or two sets of RGB LEDs. The
current regulators are matched to within ±0.4% (typ)
providing uniform white LED brightness for LCD backlight applications. To maximize efficiency, the current
regulators operate with as little as 0.15V voltage drop.
Individual white LED current regulators conduct current
to GND or NEG to extend usable battery life. In the
case of mismatched forward voltage of white LEDs,
only the white LEDs requiring higher voltage are
switched to pull current to NEG instead of GND, further
raising efficiency and reducing battery current drain.
used. Figure 2 shows a timing diagram for the I2C protocol. The MAX8647 is a slave-only device, relying
upon a master to generate a clock signal. The master
(typically a microprocessor) initiates data transfer on
the bus and generates SCL to permit data transfer. A
master device communicates with the MAX8647 by
transmitting the proper 8-bit address (0x9A) followed
by the 8-bit control byte. Each 8-bit control byte consists of a 3-bit command code and 5 bits of data (Table
1). Each transmit sequence is framed by a START (A)
condition and a STOP (L) condition (Figure 2). Each
word transmitted over the bus is 8 bits long and is
always followed by an ACKNOWLEDGE CLOCK
PULSE (K). The power-on default settings for D4 to D0
are all 0, which indicates that all LED_ are off.
Current-Regulator Switchover
Serial-Pulse Dimming Control (MAX8648)
When V IN is higher than the forward voltage of the
white LED plus the 0.15V headroom of the current regulator, the LED current returns through GND. If this condition is satisfied for all six white LEDs, the charge
pump remains inactive. When the input voltage drops
so that the current-regulator headroom cannot be maintained for any of the individual white LEDs, the inverting
charge pump activates and generates a voltage on the
NEG pin that is no greater than 5V below VIN. Each current regulator contains circuitry that detects when it is
in dropout and switches that current-regulator return
path from GND to NEG. Since this is done on an LEDby-LED basis, the LED current is switched for only the
individual LED requiring higher voltage, thus minimizing
power consumption.
When the LEDs are enabled by driving EN_ high, the
MAX8648 ramps LED current to 24mA. Dim the LEDs
by pulsing EN_ low (1µs to 500µs pulse width). Each
pulse reduces the LED current based on the LED dimming table, Table 3. After the current reaches 0.1mA,
the next pulse restores the current to 24mA. Figure 3
shows a timing diagram for EN_. ENA controls LED1,
LED2, and LED3. ENB controls LED4 and LED5. ENC
controls LED6.
Low LED Current Levels
The MAX8647/MAX8648 internally generate a PWM signal to obtain higher resolution at lower currents. See
Single-Wire Pulse Dimming in the Typical Operating
Characteristics section. As the ILED setting is below
6.4mA, the IC adjusts not only ILED DC current, but the
duty cycle is controlled by the PWM signal. The frequency of the PWM dimming signal is set at 1kHz with
a minimum duty cycle of 1/16 to avoid the LED flicking
effect to human eyes. Table 1 shows the current level
and the corresponding duty cycle.
I2C Interface (MAX8647)
An I 2 C 2-wire serial interface is provided on the
MAX8647 to control the LEDs. The serial interface
consists of a serial-data line (SDA) and a serial-clock
line (SCL). Standard I 2 C write-byte commands are
8
If dimming control is not required, EN_ work as simple
100% brightness or off controls. Drive EN_ high to enable
the LEDs, or drive EN_ low to disable. The IC is shutdown when all three EN_ are low for 4ms or longer.
Table 1. Internal PWM Duty Cycle vs. LED
Set Current
ILED
(mA)
DUTY CYCLE
(n/16)
ILED
(mA)
DUTY CYCLE
(n/16)
6.4
16
1.2
12
5.6
14
1.0
10
4.8
12
0.8
8
4.0
10
0.7
7
3.2
16
0.6
6
2.8
14
0.5
5
2.4
12
0.4
4
2.0
10
0.3
3
1.6
16
0.2
2
1.4
14
0.1
1
_______________________________________________________________________________________
Ultra-Efficient Charge Pumps for
Six White/RGB LEDs in 3mm x 3mm Thin QFN
VIN
2.7V TO 5.5V
C2
1μF
C1N C2P
C1P
IN
C2N
TP7
NEG
INVERTING
CHARGE PUMP
C1
1μF
MAX8647/MAX8648
C3
1μF
EP
GND
C4
1μF
SEL
MIN
1MHz
OSCILATOR
CURRENT
REGULATOR
VIN
LED1
VDD (ENA)
SCL (ENB)
SDA (ENC)
I2C OR
SERIAL PULSE
INTERFACE
AND CONTROL
CURRENT
SOURCE
CONTROL
BIAS
CURRENT
REGULATOR
LED2
CURRENT
REGULATOR
LED3
CURRENT
REGULATOR
LED4
CURRENT
REGULATOR
LED5
CURRENT
REGULATOR
LED6
THERMAL
SHUTDOWN
MAX8647
MAX8648
( ) ARE FOR THE MAX8648
Figure 1. Block Diagram and Application Circuit
Shutdown Mode
The MAX8647 is shutdown when all LEDs are turned off
through the I2C port. In shutdown, the I2C port is still
active and ready to receive a command.
The MAX8648 is shutdown when all three EN_ are held
low for 4ms or longer. In shutdown, NEG is pulled to
GND with a 10kΩ internal resistor.
_______________________________________________________________________________________
9
MAX8647/MAX8648
Ultra-Efficient Charge Pumps for
Six White/RGB LEDs in 3mm x 3mm Thin QFN
Table 2. I2C Control Data Byte—Device Address 0x9A
SDA CONTROL BYTE
COMMAND
FUNCTION
DATA
C2
C1
C0
D4
D3
D2
D1
D0
Not used
0
0
0
—
—
—
—
—
LED1 current
0
0
1
24.0mA to 0.1mA and off in 32 steps
LED2 current
0
1
0
24.0mA to 0.1mA and off in 32 steps
LED3 current
0
1
1
24.0mA to 0.1mA and off in 32 steps
LED4 current
1
0
0
24.0mA to 0.1mA and off in 32 steps
LED5 current
1
0
1
24.0mA to 0.1mA and off in 32 steps
LED6 current
1
1
0
24.0mA to 0.1mA and off in 32 steps
Not used
1
1
1
—
—
—
—
—
Note: C2 is MSB and D0 is LSB. The power-on default settings for D4 to D0 are all 0, which indicates that all LED_ are off.
Table 3. MAX8647 I2C Data vs. LED Currents
mA
D4
D3
D2
D1
D0
mA
1
24
0
1
1
1
1
2.8
0
22.4
0
1
1
1
0
2.4
0
1
20.8
0
1
1
0
1
2
1
0
0
19.2
0
1
1
0
0
1.6
0
1
1
17.6
0
1
0
1
1
1.4
1
0
1
0
16
0
1
0
1
0
1.2
1
1
0
0
1
14.4
0
1
0
0
1
1
1
1
0
0
0
12.8
0
1
0
0
0
0.8
1
0
1
1
1
11.2
0
0
1
1
1
0.7
1
0
1
1
0
9.6
0
0
1
1
0
0.6
1
0
1
0
1
8
0
0
1
0
1
0.5
1
0
1
0
0
6.4
0
0
1
0
0
0.4
1
0
0
1
1
5.6
0
0
0
1
1
0.3
1
0
0
1
0
4.8
0
0
0
1
0
0.2
0
0
0
1
0.1
0
0
0
0
OFF
D4
D3
D2
D1
D0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
1
4
0
1
0
0
0
0
3.2
0
Temperature Derating Function
The MAX8647/MAX8648 contain a derating function that
automatically limits the LED current at high temperatures
to help protect the LEDs from damage. The derating
function enables the safe usage of higher LED current at
room temperature, thus reducing the number of LEDs
required to backlight the display. The derating circuit
lowers the LED current at approximately 2.5%/°C once
the IC is above +60°C. The typical derating function
characteristic is shown in the Typical Operating
Characteristics.
10
Power-Up LED Detection and
Fault Protection
The MAX8648 contains special circuitry to detect shortcircuit conditions at power-up and disable the corresponding current regulator to avoid wasting battery
current. Connect any unused LED_ to IN to disable the
corresponding current regulator. If an LED fails short
circuit, the current regulator continues the current regulated operation until power to the IC is cycled and the
short circuit is detected. An open-circuit LED failure drives the voltage on the corresponding LED_ output
______________________________________________________________________________________
Ultra-Efficient Charge Pumps for
Six White/RGB LEDs in 3mm x 3mm Thin QFN
tLOW
B
C
tHIGH
D
E
F
G
H
I
J
K
L
MAX8647/MAX8648
A
M
SCL
SDA
tSU_STA
tHD_STA
tSU_DAT
tHD_DAT
tSU_STO
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO SLAVE (OP/SUS BIT)
H = LSB OF DATA CLOCKED INTO SLAVE
I = SLAVE PULLS SMBDATA LINE LOW
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
E = SLAVE PULLS SMBDATA LINE LOW
tBUF
J = ACKNOWLEDGE CLOCKED INTO MASTER
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION, DATA EXECUTED BY SLAVE
M = NEW START CONDITION
Figure 2. Definition of Timing for I2C Bus
Table 4. MAX8648 Pulse Dimming Step vs. LED Currents
mA
MAX8648 DIMMING STEPS
mA
MAX8648 DIMMING STEPS
24.0
Startup or EN_ high
2.8
16
22.4
1
2.4
17
20.8
2
2.0
18
19.2
3
1.6
19
17.6
4
1.4
20
16.0
5
1.2
21
14.4
6
1.0
22
12.8
7
0.8
23
11.2
8
0.7
24
9.6
9
0.6
25
8.0
10
0.5
26
6.4
11
0.4
27
5.6
12
0.3
28
4.8
13
0.2
29
4.0
14
0.1
30
3.2
15
24.0
31
below the switch over threshold enabling the inverting
charge pump.
For the MAX8647, program any unused LED_ to off
using the I2C interface. Unused LED_ can be connected to IN or left unconnected.
Thermal Shutdown
The MAX8647/MAX8648 includes a thermal-limit circuit
that shuts down the IC above about +160°C. The IC
turns on after it cools by approximately 20°C.
Applications Information
Input Ripple
For LED drivers, input ripple is more important than output ripple. The amount of input ripple depends on the
source supply’s output impedance. Adding a lowpass
filter to the input of the MAX8647/MAX8648 further
reduces input ripple. Alternatively, increasing CIN to
2.2µF (or 4.7µF) cuts input ripple in half (or in fourth)
with only a small increase in footprint.
______________________________________________________________________________________
11
MAX8647/MAX8648
Ultra-Efficient Charge Pumps for
Six White/RGB LEDs in 3mm x 3mm Thin QFN
0
1
2
3
4
5
26
27
28
29
30
31
INITIAL tHI
> 120μs
EN_
24mA
22.4
20.8
19.2
tHI
> 1μs
tLO
1μs TO 500μs
17.6
24mA 22.4
tSHDN
4ms
16.0
ILED_
0.6
0mA
0.5
0.4
0.3
0.2
0.1mA
0mA
Figure 3. EN_ Timing Diagram
Capacitor Selection
Ceramic capacitors are recommended due to their small
size, low cost, and low ESR. Select ceramic capacitors
that maintain their capacitance over temperature and
DC bias. Capacitors with X5R or X7R temperature characteristics generally perform well. Recommended values are shown in the Typical Operating Circuit. Using a
larger value input capacitor helps to reduce input ripple
(see the Input Ripple section).
Driving LEDs with Multiple Supplies
It is not necessary for the LED anodes to connect to IN.
Figure 7 shows an example using separate supplies to
power the LED_ groups of the MAX8648. In this example, the voltage source (V1) provides power for RGB
LEDs (LED1, LED2, and LED3). V2 provides power for
backlight LEDs (LED4 and LED5), and V3 provides
power for a red charge indicator (LED6).
PCB Layout and Routing
The MAX8647/MAX8648 have a high-frequency,
switched-capacitor voltage inverter. For best circuit performance, use a solid copper plane and place C1–C4 as
close as possible to the MAX8647/MAX8648. Figure 4
shows the MAX8648 evaluation kit example layout.
12
Figure 4. MAX8648 Evaluation Kit Layout for C1–C4
Chip Information
PROCESS: BiCMOS
______________________________________________________________________________________
Ultra-Efficient Charge Pumps for
Six White/RGB LEDs in 3mm x 3mm Thin QFN
C2P
C2N
C1P
1μF
INPUT
2.7V TO 5.5V
NEG
GND
I2C PORT
ON/OFF AND
BRIGHTNESS
VLOGIC
1.7V TO 5.5V
EP
GND
WHITE OR
RGB LED
MAX8647
SDA
LED2
SCL
LED3
SERIALPULSE
INTERFACE
D4
D5
ENB
LED4
ENC
LED5
D1
D2
D3
D4
D5
D6
Figure 6. MAX8648 Typical Application Circuit
1μF
C1P
1μF
C1N
C2P
C2N
1μF
NEG
IN
EP
1μF
GND
WHITE OR
RGB LED
MAX8648
LED1
LED2
SERIALPULSE
INTERFACE
LED3
LED6
Figure 5. MAX8647 Typical Application Circuit
INPUT
2.7V TO 5.5V
ENA
D6
LED6
LED1
LED2
D3
LED5
0.1μF
MAX8648
D2
LED4
VDD
WHITE OR
RGB LED
D1
LED1
1μF
IN
1μF
EP
C2N
NEG
IN
1μF
C2P
C1N
ENA
LED3
ENB
LED4
ENC
LED5
LED6
V1
V2
V3
D1
D2
D3
D4
D5
BACKLIGHT
INPUT
2.7V TO 5.5V
C1N
1μF
RGB
C1P
1μF
1μF
MAX8647/MAX8648
1μF
D6
RED CHARGE
INDICATOR
Figure 7. Driving LEDs with Multiple Supplies
______________________________________________________________________________________
13
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
(NE - 1) X e
E
MARKING
12x16L QFN THIN.EPS
MAX8647/MAX8648
Ultra-Efficient Charge Pumps for
Six White/RGB LEDs in 3mm x 3mm Thin QFN
E/2
D2/2
(ND - 1) X e
D/2
AAAA
e
CL
D
D2
k
CL
b
0.10 M C A B
E2/2
L
E2
0.10 C
C
L
0.08 C
C
L
A
A2
A1
L
L
e
e
PACKAGE OUTLINE
8, 12, 16L THIN QFN, 3x3x0.8mm
21-0136
14
______________________________________________________________________________________
I
1
2
Ultra-Efficient Charge Pumps for
Six White/RGB LEDs in 3mm x 3mm Thin QFN
PKG
8L 3x3
12L 3x3
REF.
MIN. NOM. MAX.
MIN. NOM. MAX.
MIN. NOM. MAX.
A
0.70
0.75
0.80
0.70
0.75
0.80
0.70
0.75
0.80
b
0.25
0.30
0.35
0.20
0.25
0.30
0.20
0.25
0.30
D
2.90
3.00
3.10
2.90
3.00
3.10
2.90
3.00
3.10
E
2.90
3.00
3.10
2.90
3.00
3.10
2.90
3.00
3.10
e
L
N
0.55
0.75
0.45
0.55
ND
2
3
NE
2
3
0
A1
A2
k
0.02
0.05
0
0.20 REF
0.25
-
0.65
0.30
12
8
0.02
0.25
-
0.40
0.50
16
4
4
0.05
0
0.20 REF
-
EXPOSED PAD VARIATIONS
0.50 BSC.
0.50 BSC.
0.65 BSC.
0.35
16L 3x3
0.02
0.05
0.20 REF
-
0.25
-
PKG.
CODES
E2
D2
MIN.
NOM.
MAX.
MIN.
NOM.
MAX.
PIN ID
JEDEC
TQ833-1
0.25
0.70
1.25
0.25
0.70
1.25
0.35 x 45°
T1233-1
0.95
1.10
1.25
0.95
1.10
1.25
0.35 x 45°
WEEC
WEED-1
T1233-3
0.95
1.10
1.25
0.95
1.10
1.25
0.35 x 45°
WEED-1
WEED-1
T1233-4
0.95
1.10
1.25
0.95
1.10
1.25
0.35 x 45°
T1633-2
0.95
1.10
1.25
0.95
1.10
1.25
0.35 x 45°
WEED-2
T1633F-3
0.65
0.80
0.95
0.65
0.80
0.95
0.225 x 45°
WEED-2
T1633FH-3
0.65
0.80
0.95
0.65
0.80
0.95
0.225 x 45°
WEED-2
T1633-4
0.95
1.10
1.25
0.95
1.10
1.25
0.35 x 45°
WEED-2
T1633-5
0.95
1.10
1.25
0.95
1.10
1.25
0.35 x 45°
WEED-2
-
NOTES:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994.
ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES.
N IS THE TOTAL NUMBER OF TERMINALS.
THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO
JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED
WITHIN THE ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR
MARKED FEATURE.
DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.20 mm AND 0.25 mm
FROM TERMINAL TIP.
ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY.
DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION.
COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS.
DRAWING CONFORMS TO JEDEC MO220 REVISION C.
MARKING IS FOR PACKAGE ORIENTATION REFERENCE ONLY.
NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY.
WARPAGE NOT TO EXCEED 0.10mm.
PACKAGE OUTLINE
8, 12, 16L THIN QFN, 3x3x0.8mm
21-0136
I
2
2
Revision History
Pages changed at Rev 1: 3, 15
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 15
© 2007 Maxim Integrated Products
SPRINGER
is a registered trademark of Maxim Integrated Products, Inc.
MAX8647/MAX8648
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
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