Rainbow Electronics MAX8848Z User Manual

19-5233; Rev 0; 4/10

EVALUATION KIT

AVAILABLE

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.

The MAX8848Y/MAX8848Z are available in 16-pin,
3mm x 3mm thin QFN packages.

Applications

White LED Backlighting

Cellular Phones

PDAs, Digital Cameras, and Camcorders

Ordering Information

PART DIMMING PIN-PACKAGE

MAX8848YETE+T

MAX8848ZETE+T PWM 16 Thin QFN-EP* AHP

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.

Serial pulse/

PWM

16 Thin QFN-EP* AHQ

TOP

MARK

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

INPUT

2.7V TO 5.5V

1µF

LED ENABLE

AND

DIMMING

CONTROL

0.22µF

1µF

C1P C1N C2P C2N

IN

GND

MAX8848Y

ENA

(ENB)

<CPWM>

MAX8848Z

1µF

NEG

LED1

LED2

LED3

LED4

LED5

LED6

LED7

1µF

EP

D1

D2

D3

D4

D5

D6

D7

MAX8848Y/MAX8848Z

NOTE: ( ) FOR MAX8848Y, < > FOR MAX8848Z

_______________________________________________________________ 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 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

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

(VIN = 3.6V, V

MAX8848Y/MAX8848Z

PARAMETER CONDITIONS MIN TYP MAX UNITS

IN Operating Voltage 2.7 5.5 V

Undervoltage Lockout (UVLO)
Threshold

Undervoltage Lockout
Hysteresis

IN Shutdown Supply Current VEN_ = 0V, all outputs off

IN Operating Supply Current

Thermal Shutdown Threshold +160
Thermal Shutdown Hysteresis 20

PWM DIMMING CONTROL (MAX8848Z)

PWM Low-Level Input 0.4 V
PWM High-Level Input 1.4 V

EN_ PWM Input Signal
Frequency Range

PWM Dimming Filter Corner
Frequency

Current Dimming Range Duty cycle = 0 to 100% 0 24 mA
PWM Dimming Resolution
SERIAL-PULSE LOGIC (MAX8848Y)
EN_ Logic Input High Voltage 1.4 V
EN_ Logic Input Low Voltage 0.4 V

EN_ Logic-Input Current VIL = 0V or VIH = 5.5V

= 0V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2)

GND

VIN rising 2.35 2.45 2.55 V

Charge pump inactive, 2 LEDs enabled at 0.1mA setting 120 150

Charge pump active, 1MHz switching, all LEDs enabled
at 0.1mA setting

C

= 0.22FF

CPWM

C

= 0.22FF

CPWM

1% P duty cycle P 100%

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

100 mV

TA = +25NC
TA = +85NC

TA = +25NC
TA = +85NC

0.2 200 kHz

-1 0.01 +1

0.4 2.5

0.4

1.6 mA

2 Hz

0.24 mA/%

0.1

FA

FA

NC
NC

FA

2 ______________________________________________________________________________________

High-Performance Negative Charge Pump

for 7 White LEDs in 3mm x 3mm Thin QFN

ELECTRICAL CHARACTERISTICS (continued)

(VIN = 3.6V, V

PARAMETER CONDITIONS MIN TYP MAX UNITS

EN_ Low Shutdown Delay
t

SHDN

EN_ t

LO

EN_ t

HI

Initial EN_ t

CHARGE PUMP

Switching Frequency 1 MHz
Soft-Start Time 0.5 ms
Output Regulation Voltage VIN - V

Open-Loop NEG Output
Resistance

NEG Shutdown Discharge
Resistance

LED1–LED7 CURRENT REGULATOR

Current Setting Range Serial-pulse interface or PWM 0.1 24.0 mA

LED_ Current Accuracy

Derating Function Start
Temperature

Derating Function Slope From derating function start temperature -2.5

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

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

V

LED_

= 0V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2)

GND

5 8 ms

See Figure 2 1 500
See Figure 2 1

INIT

= 0.5V.

See Figure 2, first EN_ high pulse 120

NEG

(V

- 0.5 x VIN)/I

NEG

VEN_ = 0V, all outputs off 10

V

= 0.5V for charge

LED_

pump inactive,
V

= -0.9V,

LED_

V

= -1.4V

NEG_

Charge pump inactive,
24mA setting

Charge pump active,
24mA setting

V

falling 135 150 165 mV

LED_

NEG

24mA setting, TA = +25NC

24mA setting, TA = -40NC
to derating function start
temperature (Note 3)

1.6mA setting, TA = +25NC Q5

TA = +25NC
TA = +85NC
TA = +25NC
TA = +85NC

TA = +25NC
TA = +85NC

4.3 5 V

-2

-5 +5

Fs
Fs
Fs

2 4

kI

Q1

+60

85 125

95
110
124

100 mV

0.01 5

0.1

+2

NC

%/NC

mV

FA

I

%

MAX8848Y/MAX8848Z

_______________________________________________________________________________________ 3

High-Performance Negative Charge Pump
for 7 White LEDs in 3mm x 3mm Thin QFN

Typical Operating Characteristics

(VIN = 3.6V, V

= VIN, circuit of Figure 1, TA = +25°C, unless otherwise noted.)

EN_

EFFICIENCY vs. SUPPLY VOLTAGE

EFFICIENCY vs. Li+ BATTERY VOLTAGE

(7 MATCHED LEDs)

100

20.8mA/LED

90

(%)

BATT

/P

80

LED

70

EFFICIENCY P

60

50

2.7 4.2

MAX8848Y/MAX8848Z

EFFICIENCY vs. Li+ BATTERY VOLTAGE

16.0mA/LED

6.4mA/LED

1.6mA/LED
VIN FALLING

3.93.63.33.0

SUPPLY VOLTAGE (V)

MAX8848Y toc01

100

90

(%)

BATT

/P

80

LED

70

EFFICIENCY P

60

50

4.2 3.0
Li+ BATTERY VOLTAGE (V, TIME WEIGHTED)

SUPPLY CURRENT vs. SUPPLY VOLTAGE

(7 MISMATCHED LEDs)

100

20.8mA/LED

90

(%)

BATT

/P

80

LED

70

EFFICIENCY P

60

50

4.2 3.0

6.4mA/LED

1.6mA/LED

Li+ BATTERY VOLTAGE (V, TIME WEIGHTED)

16mA/LED

3.43.53.63.73.83.9

250

200

MAX8848Y toc04

150

100

SUPPLY CURRENT (mA)

50

0

2.7 4.2

(7 MATCHED LEDs)

20.8mA/LED

6.4mA/LED

1.6mA/LED

(7 MATCHED LEDs)

SUPPLY VOLTAGE (V)

16mA/LED

16.0mA/LED

1.6mA/LED

VIN FALLING

20.8mA/LED

6.4mA/LED

3.93.63.33.0

EFFICIENCY vs. SUPPLY VOLTAGE

(7 MISMATCHED LEDs)

100

VIN FALLING

90

MAX8848Y toc02

(%)

BATT

/P

80

LED

70

EFFICIENCY P

60

50

3.43.53.63.73.83.9

2.7 4.2

1.6mA/LED

SUPPLY VOLTAGE (V)

20.8mA/LED

MAX8848Y toc03

16.0mA/LED

6.4mA/LED

3.93.63.33.0

SUPPLY CURRENT vs. Li+ BATTERY

VOLTAGE (7 MATCHED LEDs)

250

200

MAX8848Y toc05

150

100

SUPPLY CURRENT (mA)

50

0

20.8mA/LED

16.0mA/LED

6.4mA/LED

1.6mA/LED

4.2 3.0
Li+ BATTERY VOLTAGE (V, TIME WEIGHTED)

MAX8848Y toc06

3.43.53.63.73.83.9

SUPPLY CURRENT vs. SUPPLY VOLTAGE

(7 MISMATCHED LEDs)

250

200

150

100

SUPPLY CURRENT (mA)

50

0

2.7 4.2
SUPPLY VOLTAGE (V)

20.8mA/LED

16.0mA/LED

6.4mA/LED

1.6mA/LED

VIN FALLING

MAX8848Y toc07

SUPPLY CURRENT (mA)

3.93.63.33.0

INPUT CURRENT vs. Li+ BATTERY

VOLTAGE (7 MISMATCHED LEDs)

250

200

150

100

50

0

4.2 3.0
Li+ BATTERY VOLTAGE (V, TIME WEIGHTED)

20.8mA/LED

16.0mA/LED

6.4mA/LED

1.6mA/LED

INPUT VOLTAGE RIPPLE (PEAK-TO-PEAK)

vs. INPUT VOLTAGE

40

MAX8848Y toc08

3.43.53.63.73.83.9

20.8mA/LED

30

16.0mA/LED

20

6.4mA/LED

10

INPUT VOLTAGE RIPPLE (mV)

1.6mA/LED

0

2.7 4.2

LEDS HAVE MISMATCHED V

INPUT VOLTAGE (V)

4 ______________________________________________________________________________________

MAX8848Y

VIN FALLING

3.93.63.33.0

F

MAX8848Y toc09

High-Performance Negative Charge Pump

for 7 White LEDs in 3mm x 3mm Thin QFN

Typical Operating Characteristics (continued)

(VIN = 3.6V, V

= VIN, circuit of Figure 1, TA = +25°C, unless otherwise noted.)

EN_

LED CURRENT MATCHING

vs. SUPPLY VOLTAGE

17.0
MAX8848Y

16.8
16mA/LED, VIN FALLING

16.6

16.4

16.2

16.0

15.8

LED CURRENT (mA)

15.6

15.4

15.2

15.0

2.7 5.5
SUPPLY VOLTAGE (V)

MAX8848Y toc10

5.14.73.9 4.33.53.1

LED CURRENT vs. TEMPERATURE

30

24mA/LED

25

20

15

LED CURRENT (mA)

10

5

0

-40 85
TEMPERATURE (°C)

MAX8848Y toc11

603510-15

MAX8848Y/MAX8848Z

V

ENA/ENB

1x MODE OPERATING WAVEFORM

= 4V)

(V

IN

V

IN

I

IN

I

ILED1

ALL LEDS ON
24mA/LED

1µs/div

STARTUP AND SHUTDOWN RESPONSE

(MAX8848Y)

V

IN

I

N

I

ILED1

ENA = ENB
24mA/LED

2ms/div

MAX8848Y toc12

MAX8848Y toc14

100mV/div
AC-COUPLED

100mA/div

0A

20mA/div
0A

2V/div

200mV/div
AC-COUPLED

200mA/div
0A

20mA/div
0A

1.5x MODE OPERATING WAVEFORM
= 3V)

(V

I

ILED1

V

I

IN

IN

IN

ALL LEDS ON
24mA/LED

1µs/div

MAX8848Y toc13

100mV/div
AC-COUPLED

100mA/div

0A

20mA/div
0A

SINGLE-WIRE SERIAL-PULSE DIMMING

RESPONSE (MAX8848Y)

= V

V

ENA

ENB

1x MODE

TOTAL

I

I

LED1

LED

ALL LEDS OPERATING

10ms/div

MAX8848Y toc15

5V/div
0V

50mA/div

0A

20mA/div
0A

_______________________________________________________________________________________ 5