Download MAX8848Y/MAX8848Z High-Performance Negative Charge Pump EVALUATION KIT AVAILABLE

EVALUATION KIT AVAILABLE
MAX8848Y/MAX8848Z
High-Performance Negative Charge Pump
for 7 White LEDs in 3mm x 3mm Thin QFN
General Description
The MAX8848Y/MAX8848Z negative charge pumps
drive up to 7 white LEDs with regulated constant current
for display backlight applications. By utilizing an inverting 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 fixedfrequency switching allows for tiny external components.
The regulation scheme is optimized to ensure low EMI
and low input ripple. The MAX8848Y/MAX8848Z include
thermal shutdown, open- and short-circuit protection.
The MAX8848Y/MAX8848Z support independent LED
on/off and dimming control. The MAX8848Y dimming
ranges are pseudo-logarithmic from 24mA to 0.1mA and
off in 32 steps. All devices include a temperature derating function to safely allow bright 24mA full-scale output
current while automatically reducing current gradually
to protect LEDs at high ambient temperatures above
+60NC.
Features
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 (MAX8848Y)
S 24mA to 0mA PWM Dimming (MAX8848Z)
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
Typical Operating Circuit
1µF
The MAX8848Y/MAX8848Z are available in 16-pin,
3mm x 3mm thin QFN packages.
Applications
White LED Backlighting
INPUT
2.7V TO 5.5V
C1P
MAX8848ZETE+T
NEG
PIN-PACKAGE
Serial pulse/
PWM
16 Thin QFN-EP*
PWM
16 Thin QFN-EP*
EP
MAX8848Y
MAX8848Z
TOP
MARK
LED ENABLE
AND
DIMMING
CONTROL
ENA
(ENB)
D1
LED1
D2
LED2
D3
LED3
AHQ
AHP
C2N
1µF
GND
Ordering Information
MAX8848YETE+T
C2P
IN
PDAs, Digital Cameras, and Camcorders
DIMMING
C1N
1µF
Cellular Phones
PART
1µF
<CPWM>
D4
LED4
0.22µF
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.
D5
LED5
D6
LED6
D7
LED7
NOTE: ( ) FOR MAX8848Y, < > FOR MAX8848Z
For pricing, delivery, and ordering information, please contact Maxim Direct
at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.
19-5233; Rev 0; 4/10
MAX8848Y/MAX8848Z
High-Performance Negative Charge Pump
for 7 White LEDs in 3mm x 3mm Thin QFN
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 (VIN + 0.3V)
C2P to C1N.................................................-0.3V to (VIN + 0.3V)
LED_, C1N, C2N, ENA, ENB to NEG..........-0.3V to (VIN + 0.3V)
Continuous Power Dissipation (TA = +70°C)
16-Pin Thin QFN Multilayer PCB
(derate 20.8mW/°C above +70°C)..........................1666.7mW
Junction-to-Case Thermal Resistance (θJC) (Note 1)......10°C/W
Junction-to-Ambient Thermal Resistance (θJA) (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.maximintegrated.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
(VIN = 3.6V, VGND = 0V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2)
PARAMETER
CONDITIONS
IN Operating Voltage
Undervoltage Lockout (UVLO)
Threshold
MIN
TYP
2.7
VIN rising
2.35
Undervoltage Lockout
Hysteresis
2.45
MAX
UNITS
5.5
V
2.55
V
100
TA = +25NC
0.4
TA = +85NC
0.4
mV
2.5
IN Shutdown Supply Current
VEN_ = 0V, all outputs off
Charge pump inactive, 2 LEDs enabled at 0.1mA setting
120
IN Operating Supply Current
Charge pump active, 1MHz switching, all LEDs enabled
at 0.1mA setting
1.6
mA
Thermal Shutdown Threshold
+160
NC
Thermal Shutdown Hysteresis
20
NC
150
FA
FA
PWM DIMMING CONTROL (MAX8848Z)
PWM Low-Level Input
0.4
PWM High-Level Input
1.4
EN_ PWM Input Signal
Frequency Range
CCPWM = 0.22FF
PWM Dimming Filter Corner
Frequency
CCPWM = 0.22FF
Current Dimming Range
Duty cycle = 0 to 100%
PWM Dimming Resolution
1% P duty cycle P 100%
V
V
0.2
200
2
0
kHz
Hz
24
0.24
mA
mA/%
SERIAL-PULSE LOGIC (MAX8848Y)
EN_ Logic Input High Voltage
1.4
V
EN_ Logic Input Low Voltage
EN_ Logic-Input Current
2 0.4
VIL = 0V or VIH = 5.5V
TA = +25NC
TA = +85NC
-1
0.01
0.1
+1
V
FA
Maxim Integrated
MAX8848Y/MAX8848Z
High-Performance Negative Charge Pump
for 7 White LEDs in 3mm x 3mm Thin QFN
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 3.6V, VGND = 0V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2)
PARAMETER
CONDITIONS
EN_ Low Shutdown Delay
tSHDN
EN_ tLO
EN_ tHI
See Figure 2
Initial EN_ tINIT
See Figure 2, first EN_ high pulse
MIN
TYP
5
8
1
See Figure 2
MAX
UNITS
ms
500
Fs
1
Fs
120
Fs
CHARGE PUMP
Switching Frequency
Soft-Start Time
4.3
1
MHz
0.5
ms
5
V
Output Regulation Voltage
VIN - VNEG
Open-Loop NEG Output
Resistance
(VNEG - 0.5 x VIN)/INEG
2
NEG Shutdown Discharge
Resistance
VEN_ = 0V, all outputs off
10
4
I
kI
LED1–LED7 CURRENT REGULATOR
Current Setting Range
LED_ Current Accuracy
Serial-pulse interface or PWM
VLED_= 0.5V for charge
pump inactive,
VLED_ = -0.9V,
VNEG_= -1.4V
0.1
24mA setting, TA = +25NC
-2
24mA setting, TA = -40NC
to derating function start
temperature (Note 3)
-5
1.6mA setting, TA = +25NC
LED_ Dropout Voltage
(Note 4)
LED_ Current Regulator
Switchover Threshold
(Inactive to Active)
From derating function start temperature
Charge pump inactive,
24mA setting
85
95
Charge pump active,
24mA setting
TA = +25NC
110
TA = +85NC
124
135
150
%/NC
125
mV
165
100
All LEDs off
%
NC
-2.5
TA = +25NC
TA = +85NC
LED_ Current Regulator
Switchover Hysteresis
LED_ Leakage in Shutdown
+5
+60
VLED_ falling
mA
+2
Q5
Derating Function Start
Temperature
Derating Function Slope
24.0
Q1
TA = +25NC
0.01
TA = +85NC
0.1
mV
mV
5
FA
Note 2: Limits are 100% production tested at TA = +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
VLED_ = 0.5V.
Maxim Integrated
3
MAX8848Y/MAX8848Z
High-Performance Negative Charge Pump
for 7 White LEDs in 3mm x 3mm Thin QFN
Typical Operating Characteristics
(VIN = 3.6V, VEN_ = VIN, circuit of Figure 1, TA = +25°C, unless otherwise noted.)
EFFICIENCY vs. Li+ BATTERY VOLTAGE
(7 MATCHED LEDs)
70
16.0mA/LED
6.4mA/LED
60
1.6mA/LED
3.0
2.7
3.3
3.6
3.9
80
6.4mA/LED
70
16mA/LED
1.6mA/LED
60
VIN FALLING
20.8mA/LED
90
80
70
16.0mA/LED
60
6.4mA/LED
50
50
4.2
4.2 3.9
3.8
3.7
3.6
3.0
2.7
3.5 3.4 3.0
3.3
SUPPLY VOLTAGE (V)
EFFICIENCY vs. Li+ BATTERY VOLTAGE
(7 MISMATCHED LEDs)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(7 MATCHED LEDs)
SUPPLY CURRENT vs. Li+ BATTERY
VOLTAGE (7 MATCHED LEDs)
6.4mA/LED
16mA/LED
1.6mA/LED
20.8mA/LED
150
16.0mA/LED
100
60
50
50
0
6.4mA/LED
4.2 3.9
3.8
3.7
3.6
250
200
20.8mA/LED
150
16.0mA/LED
100
6.4mA/LED
50
1.6mA/LED
0
3.0
2.7
3.5 3.4 3.0
4.2
MAX8848Y toc06
200
SUPPLY CURRENT (mA)
80
VIN FALLING
SUPPLY CURRENT (mA)
MAX8848Y toc04
90
70
250
1.6mA/LED
3.3
3.6
3.9
4.2
4.2 3.9
3.8
3.7
3.6
3.5 3.4 3.0
SUPPLY VOLTAGE (V)
Li+ BATTERY VOLTAGE (V, TIME WEIGHTED)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(7 MISMATCHED LEDs)
INPUT CURRENT vs. Li+ BATTERY
VOLTAGE (7 MISMATCHED LEDs)
INPUT VOLTAGE RIPPLE (PEAK-TO-PEAK)
vs. INPUT VOLTAGE
16.0mA/LED
100
6.4mA/LED
50
MAX8848Y toc08
20.8mA/LED
150
16.0mA/LED
100
6.4mA/LED
50
1.6mA/LED
3.3
3.6
SUPPLY VOLTAGE (V)
3.9
20.8mA/LED
30
MAX8848Y
4.2
VIN FALLING
16.0mA/LED
20
6.4mA/LED
10
1.6mA/LED
0
0
3.0
LEDS HAVE MISMATCHED VF
1.6mA/LED
0
2.7
40
INPUT VOLTAGE RIPPLE (mV)
20.8mA/LED
150
200
SUPPLY CURRENT (mA)
200
250
MAX8848Y toc07
VIN FALLING
MAX8848Y toc09
Li+ BATTERY VOLTAGE (V, TIME WEIGHTED)
250
SUPPLY CURRENT (mA)
3.9
Li+ BATTERY VOLTAGE (V, TIME WEIGHTED)
20.8mA/LED
4 3.6
SUPPLY VOLTAGE (V)
100
MAX8848Y toc03
90
100
1.6mA/LED
VIN FALLING
50
EFFICIENCY PLED/PBATT (%)
20.8mA/LED
EFFICIENCY PLED/PBATT (%)
80
MAX8848Y toc02
90
100
EFFICIENCY vs. SUPPLY VOLTAGE
(7 MISMATCHED LEDs)
MAX8848Y toc05
EFFICIENCY PLED/PBATT (%)
20.8mA/LED
EFFICIENCY PLED/PBATT (%)
100
MAX8848Y toc01
EFFICIENCY vs. SUPPLY VOLTAGE
(7 MATCHED LEDs)
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
3.9
4.2
INPUT VOLTAGE (V)
Maxim Integrated
MAX8848Y/MAX8848Z
High-Performance Negative Charge Pump
for 7 White LEDs in 3mm x 3mm Thin QFN
Typical Operating Characteristics (continued)
(VIN = 3.6V, VEN_ = VIN, circuit of Figure 1, TA = +25°C, unless otherwise noted.)
LED CURRENT MATCHING
vs. SUPPLY VOLTAGE
LED CURRENT vs. TEMPERATURE
24mA/LED
25
16.4
LED CURRENT (mA)
LED CURRENT (mA)
16.6
MAX8848Y toc11
MAX8848Y
16mA/LED, VIN FALLING
16.8
30
MAX8848Y toc10
17.0
16.2
16.0
15.8
15.6
15.4
20
15
10
5
15.2
15.0
2.7
3.1
3.5
3.9
4.3
4.7
5.1
0
5.5
-40
-15
10
35
60
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
1x MODE OPERATING WAVEFORM
(VIN = 4V)
1.5x MODE OPERATING WAVEFORM
(VIN = 3V)
MAX8848Y toc12
85
MAX8848Y toc13
VIN
100mV/div
AC-COUPLED
IIN
100mA/div
VIN
100mV/div
AC-COUPLED
IIN
100mA/div
0A
0A
IILED1
20mA/div
0A
ALL LEDS ON
24mA/LED
IILED1
20mA/div
0A
ALL LEDS ON
24mA/LED
1µs/div
1µs/div
STARTUP AND SHUTDOWN RESPONSE
(MAX8848Y)
SINGLE-WIRE SERIAL-PULSE DIMMING
RESPONSE (MAX8848Y)
MAX8848Y toc14
VENA/ENB
MAX8848Y toc15
2V/div
200mV/div
AC-COUPLED
VIN
IN
5V/div
VENA = VENB
0V
1x MODE
ALL LEDS OPERATING
TOTAL
ILED
50mA/div
200mA/div
0A
0A
20mA/div
0A
ILED1
IILED1
ENA = ENB
24mA/LED
2ms/div
Maxim Integrated
20mA/div
0A
10ms/div
5
MAX8848Y/MAX8848Z
High-Performance Negative Charge Pump
for 7 White LEDs in 3mm x 3mm Thin QFN
Typical Operating Characteristics (continued)
(VIN = 3.6V, VEN_ = VIN, circuit of Figure 1, TA = +25°C, unless otherwise noted.)
LINE TRANSIENT RESPONSE
(VIN = 3.8V TO 3.4V TO 3.8V)
LINE TRANSIENT RESPONSE
(VIN = 4.3V TO 3.8V TO 4.3V)
MAX8848Y toc17
MAX8848Y toc16
4.3V
VIN
3.8V
4.3V
3.8V
1V/div
3.8V
3.4V
VIN
1V/div
200mA/div
IIN
0A
200mA/div
IIN
0A
ILED1
ILED1
20mA/div
0A
ALL LEDS ON
24mA/LED
20mA/div
0A
ALL LEDS ON
24mA/LED
1ms/div
1ms/div
LINE TRANSIENT RESPONSE
(VIN = 3.5V TO 3.0V TO 3.5V)
PWM DIMMING RESPONSE
MAX8848Y toc19
MAX8848Y toc18
3.5V
VIN
3.0V
3.5V
1V/div
100mA/div
0A
IIN
5V/div
VENA
100mA/div
IIN
0A
12mA
16mA
ILED1
ALL LEDS ON
16mA/LED
20mA/div
ILED1
20mA/div
0A
MAX8848Z
40µs/div
1ms/div
PWM DIMMING LINEARITY
MAX8848Y toc20
25
LED CURRENT (mA)
20
15
10
5
MAX8848Z
0
0
20
40
60
80
100
PWM DUTY CYCLE (%)
6 Maxim Integrated
MAX8848Y/MAX8848Z
High-Performance Negative Charge Pump
for 7 White LEDs in 3mm x 3mm Thin QFN
LED4
LED3
LED2
TOP VIEW
LED5
Pin Configuration
12
11
10
9
LED6 13
LED7 14
MAX8848Y
MAX8848Z
CPWM (ENB) 15
EP
2
3
4
C2P
IN
1
C1P
+
GND
ENA 16
8
LED1
7
NEG
6
C1N
5
C2N
THIN QFN
( ) FOR MAX8848Y ONLY
Pin Description
PIN
NAME
FUNCTION
1
IN
Supply Voltage Input. The input voltage range is 2.7V to 5.5V. Bypass IN to GND
with a 1FF 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 1FF ceramic capacitor from
C1P to C1N.
4
4
C2P
Transfer Capacitor 2 Positive Connection. Connect a 1FF ceramic capacitor from
C2P to C2N.
5
5
C2N
Transfer Capacitor 2 Negative Connection. Connect a 1FF ceramic capacitor
from C2P to C2N. An internal 10kI resistor pulls C2N to GND during shutdown.
6
6
C1N
Transfer Capacitor 1 Negative Connection. Connect a 1FF ceramic capacitor
from C1P to C1N.
7
7
NEG
Charge-Pump Negative Output. Connect a 1FF ceramic capacitor from NEG to
GND. In shutdown, an internal 10kI resistor pulls NEG to GND. Connect the
exposed pad to NEG directly under the IC.
MAX8848Y
MAX8848Z
1
Maxim Integrated
7
MAX8848Y/MAX8848Z
High-Performance Negative Charge Pump
for 7 White LEDs in 3mm x 3mm Thin QFN
Pin Description (continued)
PIN
MAX8848Y
8–14
8 MAX8848Z
8–14
NAME
FUNCTION
LED1–LED7
LED Current Regulators. Current flowing into LED_ is based on the ENA/ENB
input. Connect LED_ to the cathodes of the external LEDs. LED_ is high impedance during shutdown. Short any unused LED_ to IN prior to power-up to disable
the corresponding current regulator.
15
—
ENB
Enable and Serial-Pulse Dimming Control Input B for the MAX8848Y. ENB controls LED6 and LED7. Drive ENB high to turn on the LED6 and LED7 current
regulators at 24mA. Drive ENB low for greater than 8ms to turn off the current
regulators or drive both ENA and ENB low to place the IC in shutdown. In addition to the enable function, ENB can also be used to control the LED6 and LED7
serial-pulse dimming.
—
15
CPWM
Filter Capacitor Connection for PWM Dimming for the MAX8848Z. Connect a
capacitor from CPWM to GND to form a filter with the internal 360kI resistor. The
recommended capacitor for a 2Hz corner frequency is 0.22FF.
Enable and PWM/Serial-Pulse Dimming Control Input A. ENA controls LED1–
LED5 for the MAX8848Y, and LED1–LED7 for MAX8848Z. Drive ENA high to turn
on all the controlled LED current regulators at 24mA. Drive ENA low for greater
than 8ms to turn off the current regulators or drive both ENA and ENB low to
place the IC in shutdown. Drive ENA with a PWM signal from 200Hz to 200kHz to
dim LED1–LED7 for the MAX8848Z. See the PWM Dimming Control (MAX8848Z)
section. For the MAX8848Y, ENA controls the LED1–LED5 serial-pulse dimming.
16
16
ENA
—
—
EP
Exposed Paddle. Connect EP to NEG directly under the IC.
Maxim Integrated
MAX8848Y/MAX8848Z
High-Performance Negative Charge Pump
for 7 White LEDs in 3mm x 3mm Thin QFN
C2
1µ F
C1P
VIN
2.7V TO 5.5V
C3
1µ F
C1N
IN
C2P
C2N
NEG
INVERTING CHARGE PUMP
C1
1 µF
FB
GND
1MHz
OSCILLATOR
C4
1µF
EP
SEL
MIN
VIN
CURRENT
REGULATOR
ENABLE
AND
DIMMING
CONTROL
INPUTS
ENA
LED
ENABLE
LED1
(ENB)
CURRENT
REGULATOR
PWM
DIMMING
LED2
<CPWM>
C25
0.22µF
360kI
CURRENT
REGULATOR
LED3
CURRENT
SOURCE
CONTROL
CURRENT
REGULATOR
LED4
THERMAL
DERATING
AND
PROTECTION
CURRENT
REGULATOR
LED5
CURRENT
REGULATOR
LED6
MAX8848Y
MAX8848Z
CURRENT
REGULATOR
LED7
NOTE: () FOR MAX8848Y ONLY, < > FOR MAX8848Z ONLY
Figure 1. Functional Diagram and Application Circuit
Maxim Integrated
9
MAX8848Y/MAX8848Z
High-Performance Negative Charge Pump
for 7 White LEDs in 3mm x 3mm Thin QFN
Detailed Description
The MAX8848Y/MAX8848Z have an inverting charge
pump and seven current regulators capable of 24mA
each to drive up to 7 white LEDs. The current regulators
are matched to within 1% (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.
Current Regulator Switchover
When VIN is higher than the LED forward voltage plus the
150mV dropout voltage of the current regulator, the LED
current returns through GND. If this condition is satisfied for all active white LEDs, the charge pump remains
inactive. When the input voltage drops so that the current regulator voltage (VLED_) cannot be maintained for
any of the individual white LEDs, the inverting charge
pump activates and generates a voltage on NEG that is
no greater than 5V below VIN. For any current regulator
that is detected at the switchover threshold voltage of
150mV (typ, VIN falling), internal circuitry switches that
current regulator’s return path from GND to NEG to provide enough voltage across that regulator to overcome
dropout. When VLED_ rises to 250mV (typ), the return
of that current regulator is switched back from NEG to
GND. Each current regulator is independently monitored
to detect when switchover is required. Since the LED
current is switched for only the individual LED current
regulators requiring higher voltage, power consumption
is minimized.
Enable and Dimming Control Input
(ENA, ENB)
ENA and ENB inputs have dual functions: LED on/off
control and PWM or serial-pulse dimming control. See
Table 1 for details. For the MAX8848Y, ENA functions as
on/off control and serial-pulse dimming control for LED1–
LED5. ENB functions as on/off control and serial-pulse
dimming control for LED6 and LED7. For the MAX8848Z,
only ENA functions as on/off control as well as PWM dimming control for LED1–LED7.
PWM Dimming Control (MAX8848Z)
When VIN is above its undervoltage lockout threshold,
UVLO, apply a PWM signal to ENA to set the corresponding WLED current (see Table 1) that is proportional
to the signal duty cycle (0% duty cycle corresponds to
zero LED current and 100% duty cycle corresponds to
full LED current). The allowed PWM frequency range is
from 200Hz to 200kHz. If PWM dimming control is not
required, ENA works as a simple on/off control.
Serial-Pulse Dimming Control (MAX8848Y)
The MAX8848Y uses ENA/ENB as a serial-pulse control
interface to program the intensity of LED1–LED7. When
the LEDs are enabled by driving ENA/ENB high, the
MAX8848Y ramps LED current to 24mA. Subsequent
pulses on ENA/ENB reduce the LED current from 24mA
to 0.1mA in 31 steps. After the current reaches 0.1mA,
the next pulse restores the current to 24mA. See Table 2
Table 1. ENA and ENB Enable and Dimming Control
PART
ENA
MAX8848Y
LED1–LED5 enable and serial-pulse dimming control
MAX8848Z
LED1–LED7 enable and PWM dimming control
10 ENB
LED6 and LED7 enable and serial-pulse
dimming control
—
Maxim Integrated
MAX8848Y/MAX8848Z
High-Performance Negative Charge Pump
for 7 White LEDs in 3mm x 3mm Thin QFN
for the LED current values and the corresponding ENA/
ENB pulse count. Figure 2 shows a timing diagram for
ENA/ENB.
If dimming control is not required, ENA/ENB works as
a simple on/off logic control. Drive ENA/ENB high for
0
1
2
3
4
at least 120Fs to enable the LED current regulators, or
drive ENA/ENB low for greater than 8ms (typ) to place
the LED current regulators in shutdown. The LED current
regulators operate at 100% brightness and off under
these conditions.
5
26
27
28
29
30
31
INITIAL tHI
tINIT > 120µs
EN_
24mA
ILED_
tLO
1µs TO 500µs
22.4mA 20.8mA
19.2mA 17.6mA
tSHDN
tHI
> 1µs
24mA
22.4mA
8ms (TYP)
16.0mA
0.6mA 0.5mA
0.4mA 0.3mA
0.2mA 0.1mA
SHDN
SHDN
Figure 2. Timing Charateristics for LED Serial-Pulse Dimming Control
Table 2. ENA/ENB Serial-Pulse Dimming Count and Programmed LED_ Currents
EN_ PULSE
COUNT
PROGRAMMED LED_ CURRENT
(mA)
EN_ PULSE
COUNT
PROGRAMMED LED_ CURRENT
(mA)
Startup or EN_high
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
24.0
22.4
20.8
19.2
17.6
16.0
14.4
12.8
11.2
9.6
8.0
6.4
5.6
4.8
4.0
3.2
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
2.8
2.4
2.0
1.6
1.4
1.2
1.0
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
24.0
Maxim Integrated
11
MAX8848Y/MAX8848Z
High-Performance Negative Charge Pump
for 7 White LEDs in 3mm x 3mm Thin QFN
Low LED Current Levels
The MAX8848Y internally generates a PWM signal to
obtain higher resolution at lower currents. See the SingleWire Serial-Pulse Dimming Response (MAX8848Y) graph
in the Typical Operating Characteristics section. When
the LED current is set below 6.4mA, the IC adjusts not
only LED DC current, but the duty cycle that is controlled
by the PWM signal. The frequency of the PWM dimming
signal is set at 16kHz with a minimum duty cycle of 1/8 to
avoid the LED flickering effect to human eyes and also to
avoid interference in the audio frequency range. Table 3
shows the current level and the corresponding duty cycle.
Shutdown Mode
The MAX8848Y/MAX8848Z are in shutdown mode when
both ENA and ENB are held low for 8ms or longer. In
shutdown, NEG is pulled to GND with a 10kΩ internal
resistor.
Temperature Derating Function
The MAX8848Y/MAX8848Z contain a derating function that automatically limits the LED current at high
temperatures in accordance with the recommended
derating curve of popular white LEDs. 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 die temperature is above +60°C. The typical derating
function characteristic is shown in the Typical Operating
Characteristics.
Table 3. Internal PWM Duty Cycle vs. LED
Set Current
ILED
(mA)
DUTY
MAXIMUM
CYCLE
ILED (mA)*
(n/8)
ILED
(mA)
MAXIMUM
ILED (mA)*
DUTY
CYCLE
(n/8)
6.4
6.4
8
1.2
1.6
6
5.6
6.4
7
1.0
1.6
5
4.8
6.4
6
0.8
0.8
8
4.0
6.4
5
0.7
0.8
7
3.2
3.2
8
0.6
0.8
6
2.8
3.2
7
0.5
0.8
5
2.4
3.2
6
0.4
0.8
4
2.0
3.2
5
0.3
0.8
3
1.6
1.6
8
0.2
0.8
2
1.6
7
0.1
0.8
1
1.4
*Maximum ILED is the full reference current when the internal
PWM signal has 100% duty cycle at the lower level currents.
12 Power-Up LED Short Detection and
Open-Fault Protection
The MAX8848Y/MAX8848Z contain special circuitry to
detect short-circuit 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 detection after startup, the current regulator
continues the current regulated operation until IC power
is cycled and the short circuit is detected during the
subsequent startup.
An open-circuit LED failure drives the voltage on the corresponding LED current regulator output below the switchover threshold, enabling the negative charge pump.
Thermal Shutdown
The MAX8848Y/MAX8848Z include a thermal-limit circuit
that shuts down the IC above approximately +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. Add a lowpass
filter to the input of the MAX8848Y/MAX8848Z to further
reduce input ripple. Alternatively, increasing CIN from
1.0µF to 2.2µF (or 4.7µF) cuts input ripple in half (or in
fourth) with only a small increase in footprint.
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).
PCB Layout and Routing
The MAX8848Y/MAX8848Z are high-frequency switchedcapacitor voltage inverters. For best circuit performance,
use a solid ground plane and place all capacitors as
close as possible to the IC. Use large traces for the
power-supply inputs to minimize losses due to parasitic
trace resistance and to route heat away from the device.
Refer to the MAX8848Z evaluation kit data sheet for an
example PCB layout.
Maxim Integrated
MAX8848Y/MAX8848Z
High-Performance Negative Charge Pump
for 7 White LEDs in 3mm x 3mm Thin QFN
Chip Information
PROCESS: BiCMOS
Maxim Integrated
Package Information
For the latest package outline information and land patterns, go
to www.maximintegrated.com/packages. Note that a “+”, “#”,
or “-” in the package code indicates RoHS status only. Package
drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
PACKAGE TYPE
PACKAGE CODE
DOCUMENT NO.
16 Thin QFN-EP
T1633+5
21-0136
13
MAX8848Y/MAX8848Z
High-Performance Negative Charge Pump
for 7 White LEDs in 3mm x 3mm Thin QFN
Revision History
REVISION
NUMBER
REVISION
DATE
0
4/10
DESCRIPTION
Initial release
PAGES
CHANGED
—
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent
licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and
max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
14
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Maxim Integrated
Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.