19-5196; Rev 0; 4/10
TION KIT
EVALUA BLE
AVAILA
High-Performance Negative Charge Pump
for 6 White LEDs in 3mm x 3mm Thin QFN
General Description
The MAX8847Y/MAX8847Z negative charge pumps
drive up to 6 white LEDs with regulated constant current
for display backlight applications. By utilizing an invert-
ing charge pump and extremely low-dropout adaptive
current regulators, these ICs achieve very high efficiency
over the full 1-cell Li+ battery voltage range 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 MAX8847Y/MAX8847Z include
thermal shutdown, open- and short-circuit protection.
The MAX8847Y/MAX8847Z support independent LED
on/off and dimming control. The MAX8847Z has PWM
dimming control for LED1–LED6. The MAX8847Y has
PWM dimming control for LED1–LED4 and serial-pulse
dimming control for LED5 and LED6. The serial-pulse
dimming ranges are pseudo-logarithmic from 24mA to
0.1mA and off in 32 steps. All devices include a tempera-
ture derating function to safely allow bright 24mA full-
scale output current while automatically reducing current
gradually to protect LEDs at high ambient temperatures
above +60°C.
The MAX8847Y/MAX8847Z are available in 16-pin,
3mm x 3mm thin QFN packages.
S
Negative 1x/1.5x Charge Pump
S
Adaptive Current Regulators
S
Independent Voltage Supply for Each LED
S
24mA to 0.1mA Serial-Pulse Dimming (MAX8847Y)
S
24mA to 0mA PWM Dimming (MAX8847Z)
S
2% (max) LED Current Accuracy, 1% (typ) Matching
S
Low 120µA Quiescent Current
S
Low 0.4µA Shutdown Current
S
Inrush Current Limit
S
Temperature Derating Function
S
16-Pin, 3mm x 3mm Thin QFN Packages
Features
MAX8847Y/MAX8847Z
Typical Operating Circuit
1µF
1µF
INPUT
2.7V TO 5.5V
1µF
C1P
IN
GND
C1N
C2P
C2N
1µF
NEG
EP
LED1
D1
Applications
White LED Backlighting
Cellular Phones
PDAs, Digital Cameras, and Camcorders
LED ENABLE
AND
DIMMING
CONTROL
ENA
ENB
MAX8847Y
MAX8847Z
LED2
D2
Ordering Information
PART
MAX8847YETE+T
MAX8847ZETE+T
DIMMING
Serial pulse/
PWM
PWM
PIN-PACKAGE
16 Thin QFN-EP*
16 Thin QFN-EP*
TOP
MARK
AHQ
AHP
CPWM
0.22µF
LED3
D3
LED4
D4
LED5
D5
Note:
All devices are specified over the -40°C to +85°C
extended temperature range.
+Denotes
a lead(Pb)-free/RoHS-compliant package.
*EP
= Exposed pad.
LED6
D6
_______________________________________________________________
Maxim Integrated Products
1
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.
High-Performance Negative Charge Pump
for 6 White LEDs in 3mm x 3mm Thin QFN
MAX8847Y/MAX8847Z
ABSOLUTE MAXIMUM RATINGS
IN to GND .............................................................-0.3V to +6.0V
IN to NEG .............................................................-0.3V to +6.0V
NEG, C2N to GND ..................................................-6V to +0.3V
C1P, C2P, CPWM, ENA, ENB to GND .......-0.3V to (V
IN
+ 0.3V)
C2P to C1N ................................................-0.3V to (V
IN
+ 0.3V)
LED_, C1N, C2N, ENA, ENB to NEG .........-0.3V to (V
IN
+ 0.3V)
Continuous Power Dissipation (T
A
= +70°C)
16-Pin Thin QFN Multilayer PCB
(derate 20.8mW/°C above +70°C)..........................1666.7mW
Junction-to-Case Thermal Resistance (θ
JC
) (Note 1) .....10°C/W
Junction-to-Ambient Thermal Resistance (θ
JA
) (Note 1)
Multilayer PCB..............................................................48°C/W
Operating Temperature Range .......................... -40°C to +85°C
Junction Temperature .....................................................+150°C
Storage Temperature Range............................ -65°C to +150°C
Lead Temperature (soldering, 10s) ................................+300°C
Soldering Temperature (reflow) ......................................+260°C
Note 1:
Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-
layer board. For detailed information on package thermal considerations, refer to
www.maxim-ic.com/thermal-tutorial.
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
(V
IN
= 3.6V, V
GND
= 0V, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 2)
PARAMETER
IN Operating Voltage
Undervoltage Lockout (UVLO)
Threshold
Undervoltage Lockout
Hysteresis
IN Shutdown Supply Current
V
EN
_ = 0V, all outputs off
T
A
= +25NC
T
A
= +85NC
V
IN
rising
CONDITIONS
MIN
2.7
2.35
2.45
100
0.4
0.4
120
1.6
+160
20
0.4
1.4
C
CPWM
= 0.22FF
C
CPWM
= 0.22FF
Duty cycle = 0 to 100%
1%
P
duty cycle
P
100%
1.4
0.4
V
IL
= 0V or V
IH
= 5.5V
T
A
= +25NC
T
A
= +85NC
-1
0.01
0.1
+1
0
0.24
0.2
2
24
200
150
2.5
TYP
MAX
5.5
2.55
UNITS
V
V
mV
FA
FA
mA
NC
NC
V
V
kHz
Hz
mA
mA/%
V
V
FA
Charge pump inactive, 2 LEDs enabled at 0.1mA setting
IN Operating Supply Current
Thermal Shutdown Threshold
Thermal Shutdown Hysteresis
PWM DIMMING CONTROL
PWM Low-Level Input
PWM High-Level Input
EN_ PWM Input Signal
Frequency Range
PWM Dimming Filter Corner
Frequency
Current Dimming Range
PWM Dimming Resolution
EN_ Logic Input High Voltage
EN_ Logic Input Low Voltage
EN_ Logic-Input Current
Charge pump active, 1MHz switching, all LEDs enabled
at 0.1mA setting
SERIAL-PULSE LOGIC (MAX8847Y LED5 and LED6 only)
2
______________________________________________________________________________________
High-Performance Negative Charge Pump
for 6 White LEDs in 3mm x 3mm Thin QFN
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 3.6V, V
GND
= 0V, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 2)
PARAMETER
EN_ Low Shutdown Delay
t
SHDN
EN_ t
LO
EN_ t
HI
Initial EN_ t
INIT
CHARGE PUMP
Switching Frequency
Soft-Start Time
Output Regulation Voltage
Open-Loop NEG Output
Resistance
NEG Shutdown Discharge
Resistance
Current Setting Range
V
IN
- V
NEG
(V
NEG
- 0.5 x V
IN
)/I
NEG
V
EN
_ = 0V, all outputs off
4.3
1
0.5
5
2
10
4
MHz
ms
V
I
kI
See Figure 2
See Figure 2
See Figure 2, first EN_ high pulse
CONDITIONS
MIN
5
1
1
120
TYP
8
500
MAX
UNITS
ms
Fs
Fs
Fs
MAX8847Y/MAX8847Z
LED1–LED6 CURRENT REGULATOR
Serial-pulse interface or PWM
V
LED_
= 0.5V for charge
pump inactive,
V
LED_
= -0.9V,
V
NEG_
= -1.4V
24mA setting, T
A
= +25NC
24mA setting, T
A
= -40NC
to derating function start
temperature (Note 3)
1.6mA setting, T
A
= +25NC
0.1
-2
-5
Q5
+60
From derating function start temperature
Charge pump inactive,
24mA setting
Charge pump active,
24mA setting
V
LED_
falling
T
A
= +25NC
T
A
= +85NC
T
A
= +25NC
T
A
= +85NC
135
-2.5
85
95
110
124
150
165
mV
125
mV
NC
%/NC
Q1
24.0
+2
+5
%
mA
LED_ Current Accuracy
Derating Function Start
Temperature
Derating Function Slope
LED_ Dropout Voltage
(Note 4)
LED_ Current Regulator
Switchover Threshold
(Inactive to Active)
LED_ Current Regulator
Switchover Hysteresis
LED_ Leakage in Shutdown
All LEDs off
T
A
= +25NC
T
A
= +85NC
100
0.01
0.1
5
mV
FA
Note 2:
Limits are 100% production tested at T
A
= +25°C. Limits over the operating temperature range are guaranteed by design.
Note 3:
Guaranteed by design. Not production tested.
Note 4:
LED dropout voltage is defined as the LED_ to GND voltage at which current into LED_ drops 10% from the value at
V
LED_
= 0.5V.
_______________________________________________________________________________________
3
High-Performance Negative Charge Pump
for 6 White LEDs in 3mm x 3mm Thin QFN
MAX8847Y/MAX8847Z
Typical Operating Characteristics
(V
IN
= 3.6V, V
EN_
= V
IN
, circuit of Figure 1, T
A
= +25°C, unless otherwise noted.)
EFFICIENCY vs. SUPPLY VOLTAGE
(6 MATCHED LEDs)
MAX8847Y toc01
EFFICIENCY vs. Li+ BATTERY VOLTAGE
(6 MATCHED LEDs)
MAX8847Y toc02
EFFICIENCY vs. SUPPLY VOLTAGE
(6 MISMATCHED LEDs)
MAX8847Y toc03
100
20.8mA/LED
EFFICIENCY P
LED
/P
BATT
(%)
90
80
70
6.4mA/LED
60
1.6mA/LED
50
2.7
3.0
3.3
3.6
3.9
V
IN
FALLING
16.0mA/LED
100
20.8mA/LED
EFFICIENCY P
LED
/P
BATT
(%)
100
90
80
70
16.0mA/LED
60
50
1.6mA/LED
2.7
3.0
6.4mA/LED
3.3
3.6
V
IN
FALLING
3.9
20.8mA /LED
80
16mA/LED
70
1.6mA/LED
6.4mA/LED
60
50
4.2
4.2 3.9
3.8
3.7
3.6
3.5 3.4 3.0
EFFICIENCY P
LED
/P
BATT
(%)
90
4.2
SUPPLY VOLTAGE (V)
Li+ BATTERY VOLTAGE (V, TIME WEIGHTED)
SUPPLY VOLTAGE (V)
EFFICIENCY vs. Li+ BATTERY VOLTAGE
(6 MISMATCHED LEDs)
MAX8847Y toc04
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(6 MATCHED LEDs)
V
IN
FALLING
SUPPLY CURRENT (mA)
150
20.8mA/LED
100
16.0mA/LED
MAX8847Y toc05
SUPPLY CURRENT vs. Li+ BATTERY
VOLTAGE (6 MATCHED LEDs)
MAX8847Y toc06
100
20.8mA/LED
EFFICIENCY P
LED
/P
BATT
(%)
90
80
70
1.6mA/LED
60
50
4.2 3.9
3.8
3.7
3.6
6.4mA/LED
16mA/LED
200
200
SUPPLY CURRENT (mA)
150
20.8mA/LED
100
16mA/LED
50
6.4mA /LED
1.6mA /LED
50
6.4mA/LED
1.6mA/LED
0
0
2.7
3.0
3.3
3.6
3.9
4.2
3.5 3.4 3.0
4.2 3.9
3.8
3.7
3.6
3.5 3.4 3.0
Li+ BATTERY VOLTAGE (V, TIME WEIGHTED)
SUPPLY VOLTAGE (V)
Li+ BATTERY VOLTAGE (V, TIME WEIGHTED)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(6 MISMATCHED LEDs)
V
IN
FALLING
SUPPLY CURRENT (mA)
150
20.8mA/LED
100
16.0mA/LED
MAX8847Y toc07
SUPPLY CURRENT vs. Li+ BATTERY
VOLTAGE (6 MISMATCHED LEDs)
MAX8847Y toc08
200
200
SUPPLY CURRENT (mA)
150
20.8mA/LED
100
16mA/LED
50
6.4mA/LED
1.6mA/LED
50
6.4mA/LED
1.6mA/LED
0
2.7
3.0
3.3
3.6
3.9
4.2
SUPPLY VOLTAGE (V)
0
4.2 3.9
3.8
3.7
3.6
3.5 3.4 3.0
Li+ BATTERY VOLTAGE (V, TIME WEIGHTED)
4
______________________________________________________________________________________
High-Performance Negative Charge Pump
for 6 White LEDs in 3mm x 3mm Thin QFN
Typical Operating Characteristics (continued)
(V
IN
= 3.6V, V
EN_
= V
IN
, circuit of Figure 1, T
A
= +25°C, unless otherwise noted.)
MAX8847Y/MAX8847Z
INPUT VOLTAGE RIPPLE (PEAK TO PEAK)
vs. INPUT VOLTAGE
MAX8847Y toc09
LED CURRENT MATCHING
vs. SUPPLY VOLTAGE
17.6
17.2
LED CURRENT (mA)
16.8
16.4
16.0
15.6
15.2
14.8
14.4
14.0
MAX8847Z
16mA/LED, V
IN
FALLING
MAX8847Y toc10
30
25
20.8mA/LED
18.0
INPUT VOLTAGE RIPPLE (mV)
MAX8847Z
V
IN
FALLING
16.0mA/LED
20
15
10
5
0
2.7
3.0
3.3
3.6
3.9
4.2
INPUT VOLTAGE (V)
1.6mA/LED
LEDS HAVE
MISMATCHED V
F
6.4mA/LED
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
SUPPLY VOLTAGE (V)
LED CURRENT vs. TEMPERATURE
MAX8847Y toc11
30
25
LED CURRENT (mA)
20
15
10
5
24mA/LED
0
-40
-15
10
35
60
1x MODE OPERATING WAVEFORM
(V
IN
= 4V)
MAX8847Y toc12
V
IN
50mV/div
AC-COUPLED
100mA /div
I
IN
0A
I
LED1
85
ALL LEDS ON
24mA/LED
1µs/div
20mA /div
0A
TEMPERATURE (°C)
1.5x MODE OPERATING WAVEFORM
(V
IN
= 3V)
V
IN
STARTUP AND SHUTDOWN RESPONSE
(MAX8847Y)
MAX8847Y toc14
MAX8847Y toc13
100mV/div
AC-COUPLED
V
ENA/ENB
ENA = ENB
24mA /LED
2V/div
100mA/div
I
IN
0A
20mA /div
I
LED1
1µs/div
ALL LEDS ON
24mA/LED
0A
V
IN
200mV/div
AC-COUPLED
I
IN
100mA /div
0A
20mA /div
0A
20ms/div
I
LED1
_______________________________________________________________________________________
5
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
