19-3097; Rev 2; 8/05
KIT
ATION
EVALU
BLE
AVAILA
White LED 1x/1.5x Charge Pump
for Main and Sub-Displays
General Description
Features
♦
Powers Main and Sub-Display LEDs
♦
85% Average Efficiency (P
LED
/ P
BATT
) Over Li+
Battery Discharge
♦
2% LED Current Matching
♦
Up to 30mA/LED Drive Capability
♦
Adaptive 1x/1.5x Mode Switchover
♦
Low Input Ripple and EMI
♦
Individual 5% to 100% Dimming Through
Single-Wire Serial Pulse Interface
♦
Low 0.1µA Shutdown Current
♦
2.7V to 5.5V Supply Voltage Range
♦
Soft-Start Limits Inrush Current
♦
Output-Overvoltage Protection
♦
Thermal-Shutdown Protection
♦
16-Pin Thin QFN 4mm x 4mm Package
MAX1575
The MAX1575 charge pump drives up to four white
LEDs in the main display and up to two white LEDs in
the sub-display with regulated constant current for uni-
form intensity. By utilizing adaptive 1x/1.5x charge-
pump modes and very-low-dropout current regulators,
it achieves high efficiency over the full 1-cell lithium-
battery input voltage range. A 1MHz fixed-frequency
switching allows for tiny external components, and the
regulation scheme is optimized to ensure low EMI and
low input ripple.
The MAX1575 uses an external resistor to set the full-
scale 100% LED current. Two enable inputs, ENM and
ENS, are used for simple on/off controls for the main and
sub-displays, respectively. By repeatedly pulsing either
enable input, the LEDs can be dimmed in multiple steps
down to 5%. Once the desired brightness is set, the
MAX1575 maintains that brightness setting as long as
the enable input is kept high. If an enable input is kept
low for more than 2ms, the LED current for the respec-
tive display is set to zero. If both enable inputs are kept
low for more than 2ms, the MAX1575 enters shutdown.
The MAX1575 is available in a 16-pin 4mm x 4mm thin
QFN package (0.8mm max height).
Ordering Information
PART
MAX1575ETE
MAX1575ETE+
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
16 Thin QFN 4mm x 4mm
16 Thin QFN 4mm x 4mm
Applications
Cell Phones with Main and Sub-Displays
PDAs/Smart Phones with Up to Six White LEDs
+
Denotes lead-free package.
Typical Operating Circuit
1μF
Pin Configuration
C1P
C1N
OUT
1μF
LED1
LED2
LED3
GND
TOP VIEW
2.7V TO 5.5V
1μF
IN
12
C1N 13
IN 14
C2N 15
C1P 16
+
1
C2P
11
10
9
8
7
LED4
LED5
LED6
ENM
MAX1575
GND
LED1
ENABLE MAIN
ON/OFF
AND DIMMING
ENABLE SUB
ON/OFF
AND DIMMING
LED2
ENM
LED3
ENS
SET
LED6
R
SET
C2P
C2N
LED4
LED5
SUB
MAIN
MAX1575
6
5
2
OUT
3
SET
4
ENS
THIN QFN
4mm x 4mm
1μF
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
White LED 1x/1.5x Charge Pump
for Main and Sub-Displays
MAX1575
ABSOLUTE MAXIMUM RATINGS
IN, OUT, ENM, ENS to GND..................................-0.3V to +6.0V
SET, LED_, C1N, C2N to GND.....................-0.3V to (V
IN
+ 0.3V)
C1P, C2P to GND.............................................................-0.3V to
the greater of (V
OUT
+ 1V) or (V
IN
+ 1V)
OUT Short Circuit to GND ..........................................Continuous
Continuous Power Dissipation (T
A
= +70°C)
16-Pin Thin QFN 4mm x 4mm
(derate 16.9 mW/°C above +70°C) ............................1349mW
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
(V
IN
= 3.6V, V
GND
= 0V, ENM = ENS = IN, R
SET
= 6.81kΩ, C
IN
= C1 = C2 = C
OUT
= 1µF, T
A
= -40°C to +85°C, unless otherwise
noted. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
IN Operating Voltage
Undervoltage-Lockout Threshold
Undervoltage-Lockout Hysteresis
OUT Overvoltage-Protection Threshold
No-Load Supply Current
Shutdown Supply Current
Soft-Start Time
SET Bias Voltage
SET Leakage in Shutdown
SET Current Range
SET-to-LED_ Current Ratio (I
LED_
/ I
SET
)
LED Current Accuracy
LED-to-LED Current Matching (Note 2)
Maximum LED_ Sink Current
LED_ Dropout Voltage
LED_ 1x-to-1.5x Transition Threshold
LED Leakage in Shutdown
Maximum OUT Current
Open-Loop OUT Resistance
Switching Frequency
OUT Pulldown Resistance
ENM, ENS High Voltage
ENM, ENS Low Voltage
ENM, ENS Input Current
Shutdown Delay
ENM = ENS = GND
V
IN
= 2.7V to 5.5V
V
IN
= 2.7V to 5.5V
V
EN_
= 0V or 5.5V
From falling edge of ENM and ENS
1.0
0.01
2
1.6
0.4
1
3.3
ENM = ENS = GND
T
A
= 0°C to +85°C
T
A
= -40°C to +85°C
100% setting
T
A
= +25°C to +85°C
T
A
= -40°C to +85°C
T
A
= +25°C to +85°C
T
A
= -40°C to +85°C
R
SET
= 4.53kΩ
(Note 3)
V
LED
falling
ENM = ENS = GND, V
LED_
= 5.5V
V
IN
≥
3.4V, V
OUT
= 3.9V, 100% setting
1x mode (V
IN
- V
OUT
) / I
OUT
1.5x mode (1.5 x V
IN
- V
OUT
) / I
OUT
120
1
4.2
1
5
2.5
10
90
-8
-9.5
-5
-6.5
27.4
30.0
60
100
0.01
100
110
1
±1.5
10
30
234
±2
+8
+9.5
+5
+6.5
V
OUT
rising
1MHz switching in 1.5x mode
No switching in 1x mode,10% setting
ENM = ENS = OUT = GND
V
IN
falling
CONDITIONS
MIN
2.7
2.25
2.45
35
5
2
0.5
0.1
2
0.6
0.01
1
130
130
2
TYP
MAX
5.5
2.60
UNITS
V
V
mV
V
mA
µA
ms
V
µA
µA
A/A
%
%
mA
mV
mV
µA
mA
Ω
MHz
kΩ
V
V
µA
ms
2
_______________________________________________________________________________________
White LED 1x/1.5x Charge Pump
for Main and Sub-Displays
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 3.6V, V
GND
= 0V, ENM = ENS = IN, R
SET
= 6.81kΩ, C
IN
= C1 = C2 = C
OUT
= 1µF, T
A
= -40°C to +85°C, unless otherwise
noted. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
t
LO
(ENM, ENS) (Figure 1)
t
HI
(ENM, ENS) (Figure 1)
Initial t
HI
(ENM, ENS) (Figure 1)
Thermal-Shutdown Threshold
Thermal-Shutdown Hysteresis
Only required for first EN_ pulse
CONDITIONS
MIN
0.5
0.5
50
+160
20
TYP
MAX
500
UNITS
µs
µs
µs
°C
°C
MAX1575
Note 1:
Specifications to -40°C are guaranteed by design and not production tested.
Note 2:
LED current matching is defined as: (I
LED
- I
AVG
) / I
AVG
Note 3:
Dropout voltage is defined as the LED_-to-GND voltage at which current into the LED drops 10% from the LED current at
V
LED_
= 0.2V.
Typical Operating Characteristics
(V
IN
= 3.6V, ENM = ENS = IN, circuit of Figure 2, T
A
= +25°C, unless otherwise noted.)
EFFICIENCY vs. SUPPLY VOLTAGE
DRIVING SIX WHITE LEDs
MAX1575 toc01
INPUT CURRENT vs. SUPPLY VOLTAGE
DRIVING SIX WHITE LEDs
180
160
INPUT CURRENT (mA)
140
120
100
80
60
40
2mA/LED
SUPPLY VOLTAGE FALLING
8mA/LED
MAX1575 toc02
INPUT CURRENT vs. SUPPLY VOLTAGE
DRIVING FOUR WHITE LEDs
180
160
INPUT CURRENT (mA)
140
120
100
80
60
40
20
0
2mA/LED
2.7
3.0
3.3
3.6
3.9
4.2
8mA/LED
20mA/LED
SUPPLY VOLTAGE FALLING
MAX1575 toc03
100
90
80
EFFICIENCY (%)
70
60
50
40
30
SUPPLY VOLTAGE FALLING
20
2.7
3.0
3.3
3.6
3.9
2mA/LED
8mA/LED
20mA/LED
200
20mA/LED
200
20
0
4.2
2.7
3.0
3.3
3.6
3.9
4.2
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
INPUT CURRENT vs. SUPPLY VOLTAGE
DRIVING TWO WHITE LEDs
MAX1575 toc04
INPUT RIPPLE vs. SUPPLY VOLTAGE
DRIVING SIX WHITE LEDs
MAX1575 toc05
LED CURRENT MATCHING
vs. SUPPLY VOLTAGE
MAX1575 toc06
200
180
160
INPUT CURRENT (mA)
140
120
100
80
60
40
20
0
2.7
3.0
3.3
3.6
3.9
8mA/LED
2mA/LED
20mA/LED
SUPPLY VOLTAGE FALLING
70
60
INPUT RIPPLE (mV
P-P
)
50
40
30
20
10
0
8mA/LED
2mA/LED
20mA/LED
22
21
LED CURRENT (mA)
20
19
18
17
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
4.2
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
3
White LED 1x/1.5x Charge Pump
for Main and Sub-Displays
MAX1575
Typical Operating Characteristics (continued)
(V
IN
= 3.6V, ENM = ENS = IN, circuit of Figure 2, T
A
= +25°C, unless otherwise noted.)
OUTPUT CURRENT vs. SUPPLY VOLTAGE
DRIVING SIX LEDs AT 20mA EACH
MAX1575 toc07
LED CURRENT vs. R
SET
MAX1575 toc08
OPERATING WAVEFORMS (1x)
MAX1575 toc09
123
122
OUTPUT CURRENT (mA)
121
120
119
118
100
V
OUT
200mV/div
AC-COUPLED
50mV/div
AC-COUPLED
LED CURRENT (mA)
V
IN
10
I
IN
50mA/div
100% BRIGHTNESS SETTING
117
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
SUPPLY VOLTAGE (V)
1
1
10
R
SET
(kΩ)
100
400ns/div
0mA
OPERATING WAVEFORMS (1.5x)
MAX1575 toc10
STARTUP WAVEFORMS
MAX1575 toc11
MAIN STARTUP WITH SUB-DISPLAY ON
MAX1575 toc12
V
OUT
V
ENM
200mV/div
AND V
ENS
AC-COUPLED
50mV/div
AC-COUPLED
I
IN
50mA/div
5V/div
V
ENM
5V/div
V
IN
100mA/div
0
I
IN
100mA/div
0
I
IN
V
OUT
2V/div
0
0
400ns/div
1ms/div
1ms/div
V
OUT
500mV/div
DIMMING RESPONSE
MAX1575 toc13
LINE TRANSIENT 3.8V TO 3.3V TO 3.8V
MAX1575 toc14
V
ENM
AND V
ENS
2V/div
V
IN
1V/div
50mA/div
I
OUT
0
V
OUT
1V/div
AC-COUPLED
50mA/div
I
OUT
V
OUT
10ms/div
2V/div
0mA
40μs/div
4
_______________________________________________________________________________________
White LED 1x/1.5x Charge Pump
for Main and Sub-Displays
MAX1575
Pin Description
PIN
1
2
3
NAME
C2P
OUT
SET
FUNCTION
Transfer-Capacitor 2 Positive Connection. Connect a 1µF ceramic capacitor from C2P to C2N.
Output. Connect a 1µF ceramic capacitor from OUT to GND. Connect OUT to the anodes of all the LEDs.
OUT is internally pulled down with 5kΩ during shutdown.
Current-Set Input. Connect a resistor (R
SET
) from SET to GND to set the maximum LED current. I
LED(MAX)
=
234
×
0.6V / R
SET
. SET is internally biased to 0.6V. SET is high impedance during shutdown.
Enable and Dimming Control for LED5 and LED6 (Sub-Display). The first time ENS goes high (50µs min),
LED5 and LED6 turn on at 100% brightness. Pulsing ENS low dims the LEDs in multiple steps. If ENS is held
low for more than 2ms (typ), LED5 and LED6 turn off. When ENM and ENS are both held low for more than
2ms (typ), the IC goes into shutdown mode. See Figure 1.
Enable and Dimming Control for LED1–LED4 (Main Display). The first time ENM goes high (50µs min),
LED1–LED4 turn on at 100% brightness. Pulsing ENM low dims the LEDs in multiple steps. If ENM is held low for
more than 2ms (typ), LED1–LED4 turn off. When ENM and ENS are both held low for more than 2ms (typ), the IC
goes into shutdown mode. See Figure 1.
Sub-Display LEDs Cathode Connection. Current flowing into LED_ is described in the ENS and SET
descriptions above. The charge pump regulates the lowest-enabled LED_ voltage to 180mV. Connect LED_
to IN if the LED is not populated. LED_ is high impedance during shutdown.
Main-Display LEDs Cathode Connection. Current flowing into LED_ is described in the ENM and SET
descriptions above. The charge pump regulates the lowest-enabled LED_ voltage to 180mV. Connect LED_
to IN if the LED is not populated. LED_ is high impedance during shutdown.
Ground. Connect GND as close as possible to system ground and to the ground of the input bypass
capacitor.
Transfer-Capacitor 1 Negative Connection. Connect a 1µF ceramic capacitor from C1P to C1N.
Supply Voltage Input. Connect a 1µF ceramic capacitor from IN to GND. The input voltage range is 2.7V to
5.5V. IN is high impedance during shutdown.
Transfer-Capacitor 2 Negative Connection. Connect a 1µF ceramic capacitor from C2P to C2N.
Transfer-Capacitor 1 Positive Connection. Connect a 1µF ceramic capacitor from C1P to C1N.
Exposed Paddle. Connect the exposed paddle to GND.
4
ENS
5
ENM
6
7
8
9
10
11
12
13
14
15
16
—
LED6
LED5
LED4
LED3
LED2
LED1
GND
C1N
IN
C2N
C1P
EP
Detailed Description
The MAX1575 charge pump drives up to four white
LEDs in the main display and up to two white LEDs in
the sub-display with regulated constant current for
uniform intensity. By utilizing adaptive 1x/1.5x charge-
pump modes and very-low-dropout current regulators, it
achieves high efficiency over the 1-cell lithium-battery
input voltage range. 1MHz fixed-frequency switching
allows for tiny external components and low input ripple.
When the input voltage rises above V
OUT
by about 50mV,
the MAX1575 switches back to 1x mode.
Soft-Start
The MAX1575 includes soft-start circuitry to limit inrush
current at turn-on. When starting up, the output capacitor
is charged directly from the input with a ramped current
source (with no charge-pump action) until the output volt-
age approaches the input voltage. Once this occurs, the
charge pump determines if 1x or 1.5x mode is required.
In the case of 1x mode, the soft-start is terminated and
normal operation begins. During the soft-start time, the
output current is set to 5% of the maximum set by R
SET
.
In the case of 1.5x mode, soft-start operates until the low-
est of LED1–LED6 reaches regulation. If an overload con-
dition occurs, soft-start repeats every 2ms. If the output is
shorted to ground (or <1.25V), the part reverts to soft-
start and the ramped current source.
5
1x to 1.5x Switchover
When V
IN
is higher than V
OUT
, the MAX1575 operates in
1x mode and V
OUT
is pulled up to V
IN
. The internal cur-
rent regulators regulate the LED current. As V
IN
drops,
V
LED_
eventually falls below the switchover threshold of
100mV and the MAX1575 starts switching in 1.5x mode.
_______________________________________________________________________________________
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