19-3485; Rev 2; 7/06
IT
TION K
VALUA
E
BLE
AVAILA
High-Efficiency, 36V Step-Up Converters
with T
A
Derating Option for 2 to 9 White LEDs
General Description
Features
♦
Up to Nine LEDs at 25mA
♦
Temperature Derating Function to Allow Fewer
LEDs for Same Light (MAX8596X)
♦
86% Efficiency (P
LEDs
/ P
IN
)
♦
1.7% Current-Regulation Accuracy
♦
Output Overvoltage Protection
♦
Flexible Dimming Control
Analog
Direct-PWM Internal Filter
♦
1MHz PWM Switching Frequency
♦
0.1µF Output Capacitor
♦
12mV
P-P
Low Input Ripple
♦
Soft-Start Eliminates Inrush Current
♦
2.6V to 6V Input Range
♦
0.3µA Shutdown Current
♦
Pin Compatible with the MAX1561 and MAX1599
♦
TDFN 3mm x 3mm x 0.8mm Package with
Exposed Paddle
MAX8595X/MAX8596X
The MAX8595X/MAX8596X drive up to nine white LEDs
with constant current and high efficiency to provide
LCD backlighting in cell phones, PDAs, and other
handheld devices. The series connection allows the
LED currents to be identical for uniform brightness and
minimizes the number of traces to the LEDs. The
MAX8595X regulates constant LED current over the
entire temperature range. The MAX8596X features an
ambient-temperature derating function to avoid over-
driving the white LEDs during high ambient tempera-
tures, enabling higher drive current below +42°C.
A single Dual Mode™ input provides a simple means of
brightness adjustment and on/off control. Fast 1MHz
current-mode PWM operation allows for small input and
output capacitors and a small inductor while minimizing
ripple on the input supply/battery. Soft-start eliminates
inrush current during startup.
The MAX8595X/MAX8596X are available in a space-
saving, 8-pin, 3mm x 3mm TDFN package.
Applications
Cell Phones and Smart Phones
PDAs, Palmtops, and Wireless Handhelds
e-Books and Subnotebooks
White LED Display Backlighting
Ordering Information
PART
MAX8595XETA-T
MAX8595XETA+T
MAX8596XETA-T
MAX8596XETA+T
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-
PACKAGE
8 TDFN-EP*
8 TDFN-EP*
8 TDFN-EP*
8 TDFN-EP*
PKG
CODE
T833-1
T833-1
T833-1
T833-1
+Denotes
lead-free package.
Dual Mode is a trademark of Maxim Integrated Products, Inc.
*EP
= Exposed paddle.
T = Tape and reel.
Typical Operating Circuit
PGND
LX
INPUT
2.6V TO 6V
2.2µF
IN
ANALOG OR
PWM DIMMING
LX
OUT
OUTPUT
UP TO 38V
Pin Configuration
GND
COMP
TOP VIEW
8
7
6
5
MAX8595X
MAX8596X
0.1µF
1
OUT
2
IN
3
CTRL
4
CS
MAX8595X
CTRL
MAX8596X
PGND
COMP
GND
CS
200Hz TO 200kHz
2 TO 9 LEDs
TDFN
3mm x 3mm x 0.8mm
A "+" SIGN WILL REPLACE THE FIRST
PIN INDICATOR ON LEAD-FREE PACKAGES.
________________________________________________________________
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.
High-Efficiency, 36V Step-Up Converters
with T
A
Derating Option for 2 to 9 White LEDs
MAX8595X/MAX8596X
ABSOLUTE MAXIMUM RATINGS
IN to GND .................................................................-0.3V to +7V
PGND to GND .......................................................-0.3V to +0.3V
LX, OUT to GND .....................................................-0.3V to +40V
CTRL to GND...................-0.3V to the lower of +6V or (V
IN
+ 2V)
COMP ..........................................................-0.3V to (V
IN
+ 0.3V)
I
LX
...................................................................................1.0A
RMS
I
CS
........................................................25mA (V
CS
< V
IN
+ 1.2V)
CS to GND ...................................................-0.3V to (V
IN
+ 1.2V)
Continuous Power Dissipation (T
A
= +70°C)
8-Pin TDFN 3mm x 3mm
(derate 24.4mW/°C above +70°C) ............................ 1950mW
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
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
= 3.0V, L = 22µH, C
IN
= 2.2µF, C
OUT
= 0.1µF, C
COMP
= 0.1µF, R
SENSE
= 13Ω, V
CTRL
= 1.5V, T
A
= -40°C to +85°C, unless other-
wise noted. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
Supply Voltage
UVLO Threshold
UVLO Hysteresis
Quiescent Current
Shutdown Supply Current
OVLO Threshold
OVLO Hysteresis
V
OUT
= 32V, V
CTRL
> 0.24V
OUT Input Bias Current
OUT = IN, CTRL = GND
(Note 2)
T
A
= +25°C
T
A
= +85°C
V
IN
-
V
D
T
A
= +25°C
T
A
= 0°C to +85°C
T
A
= -40°C to +85°C
T
A
= +25°C
T
A
= +85°C
310
T
A
= -40°C to +25°C
T
A
= +42°C
T
A
= +85°C
330
0.295
0.292
0.290
0.300
0.300
0.300
0.01
0.03
330
345
343
106.5
1.65
1.72
+42
V
°C
347
360
mV
9
No switching
CTRL = GND,
V
OUT
= V
IN
V
OUT
rising
T
A
= +25°C
T
A
= +85°C
36
V
IN
rising or falling
CONDITIONS
MIN
2.6
2.10
2.38
30
0.5
0.3
1
38
2
20
0.01
0.1
36
V
35
1
µA
40
0.7
2
TYP
MAX
6.0
2.55
UNITS
V
V
mV
mA
µA
V
V
Output Voltage Range
ERROR AMPLIFIER
0.305
0.308
0.310
1
µA
V
CTRL to CS Regulation
V
CTRL
= 1.50V,
V
IN
= 2.6V to 5.5V
V
CS
= V
CTRL
/ 5
MAX8595X, V
CTRL
= 3.0V
CS Input Bias Current
CS Maximum Brightness Clamp
Voltage
MAX8596X,
V
CTRL
= 3.0V
MAX8595Z
MAX8596Z
MAX8596Z, V
CTRL
= 3.0V
CTRL Voltage for CS Maximum
Brightness Clamp
CS Derating Function Start
Temperature
2
_______________________________________________________________________________________
High-Efficiency, 36V Step-Up Converters
with T
A
Derating Option for 2 to 9 White LEDs
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 3.0V, L = 22µH, C
IN
= 2.2µF, C
OUT
= 0.1µF, C
COMP
= 0.1µF, R
SENSE
= 13Ω, V
CTRL
= 1.5V, T
A
= -40°C to +85°C, unless other-
wise noted. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
CS Derating Function Slope
CTRL Input Resistance
CTRL Dual-Mode Threshold
CTRL Dual-Mode Hysteresis
CTRL Shutdown Enable Delay
CS to COMP Transconductance
COMP Input Resistance to
Ground
OSCILLATOR
Operating Frequency
Minimum Duty Cycle
Maximum Duty Cycle
n-CHANNEL SWITCH
LX On-Resistance
LX Leakage Current
LX Current Limit
I
LX
= 190mA
V
LX
= 36V, CTRL = GND
Duty cycle = 90%
T
A
= +25°C
T
A
= +85°C
500
0.8
0.01
1
700
900
1.35
5
Ω
µA
mA
PWM mode
Pulse skipping
CTRL = IN, CS = GND
94
0.75
1.0
12
0
95
1.25
MHz
%
%
(Note 3)
V
COMP
= 1.5V
In shutdown, UVLO or OVLO
6.0
32
V
CTRL
< 1.5V
CONDITIONS
MAX8596X, V
CTRL
= 3.0V, T
A
= +42°C to +85°C
250
100
MIN
TYP
-5.5
500
170
5
8.2
50
20
10.5
82
780
240
MAX
UNITS
mV/°C
kΩ
mV
mV
ms
µS
kΩ
MAX8595X/MAX8596X
Note 1:
Parameters are 100% production tested at T
A
= +25°C. Limits over the operating temperature range are regulated by
design and characterization.
Note 2:
V
D
is the forward-voltage drop of the Schottky diode in Figure 1.
Note 3:
Time from CTRL going below the Dual-Mode threshold to IC shutdown.
_______________________________________________________________________________________
3
High-Efficiency, 36V Step-Up Converters
with T
A
Derating Option for 2 to 9 White LEDs
MAX8595X/MAX8596X
Typical Operating Characteristics
(Circuit of Figure 1, V
IN
= 3.6V, I
LED
= 25mA, L = 22µH, C
IN
= 2.2µF, C
OUT
= 0.1µF, C
COMP
= 0.1µF, R
SENSE
= 13Ω, 4 LEDs, T
A
= +25°C,
unless otherwise noted.)
EFFICIENCY
vs. INPUT VOLTAGE
MAX8595X toc01
EFFICIENCY
vs. LED CURRENT
6 LEDs
85
EFFICIENCY (%)
80
75
70
65
60
3 LEDs
MAX8595X toc02
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
2
3
4
INPUT VOLTAGE (V)
5
6
8 LEDs
4 LEDs
6 LEDs
3 LEDs
90
8 LEDs
0
5
10
15
20
25
30
LED CURRENT (mA)
LED CURRENT
vs. DIRECT-PWM DIMMING
MAX8595X toc03
LED CURRENT
vs. AMBIENT TEMPERATURE
24
22
LED CURRENT (mA)
20
18
16
14
12
MAX8595,
I
LED
= 15mA
MAX8596,
I
LED
= 25mA AT T
A
= +25°C
MAX8595X toc04
30
25
LED CURRENT (mA)
20
15
10
5
26
10
0
0
20
40
60
80
100
DUTY CYCLE (%)
8
-40
-20
0
20
40
60
80
100
TEMPERATURE (°C)
SWITCHING WAVEFORMS
MAX8595X toc05
SOFT-START AND SHUTDOWN RESPONSE
MAX8595X toc06
V
IN
20mV/div
AC-COUPLED
10V/div
V
CTRL
2V/div
0
V
LX
I
IN
V
OUT
200mV/div
AC-COUPLED
I
LED
I
L
100mA/div
V
OUT
100mA/div
0
40mA/div
0
10V/div
0
500ns/div
20ms/div
4
_______________________________________________________________________________________
High-Efficiency, 36V Step-Up Converters
with T
A
Derating Option for 2 to 9 White LEDs
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V
IN
= 3.6V, I
LED
= 25mA, L = 22µH, C
IN
= 2.2µF, C
OUT
= 0.1µF, C
COMP
= 0.1µF, R
SENSE
= 13Ω, 4 LEDs, T
A
= +25°C,
unless otherwise noted.)
MAX8595X/MAX8596X
CTRL STEP RESPONSE
MAX8595X toc07
DIRECT-PWM DIMMING RESPONSE
MAX8595X toc08
V
CTRL
1V/div
0
V
CTRL
2V/div
32kHz 50%
DUTY CYCLE
0
20mV/div
AC-COUPLED
0
500mV/div
AC-COUPLED
0
I
IN
100mA/div
0
V
IN
I
LED
40mA/div
0
10V/div
0
20ms/div
V
OUT
V
OUT
I
LED
0
10µs/div
10mA/div
Pin Description
PIN
1
NAME
OUT
FUNCTION
Overvoltage Sense. When V
OUT
is greater than 38V (typ), the internal n-channel MOSFET turns off
until V
OUT
drops below 36V (typ), then the IC reenters soft-start. Connect a 0.1µF ceramic capacitor
from OUT to ground. In shutdown, V
OUT
is one diode drop below V
IN
.
Input Voltage Supply. The input voltage range is 2.6V to 6.0V. Connect a 2.2µF ceramic capacitor
from IN to GND.
Brightness Control Input. The voltage applied to CTRL controls LED brightness. Varying the voltage
from 0.24V to 1.65V (1.72V for the MAX8596X) adjusts the brightness from dim to 100% brightness,
respectively. Any voltage above 1.65V (1.72V) does not increase brightness. Hold CTRL below
100mV to shut down the IC after an 8.2ms delay.
Current-Sense Feedback Input. Connect a resistor from CS to GND to set the LED bias current. The
voltage at CS regulates to V
CTRL
/ 5 or 0.330V (0.343V for the MAX8596X), whichever is lower.
Compensation Input. Connect a 0.1µF ceramic capacitor (C
COMP
) from COMP to GND. C
COMP
stabilizes the converter, controls soft-start, and lowpass filters direct PWM dimming at CTRL. C
COMP
discharges to 0V through an internal 20kΩ resistor in shutdown.
Ground. Connect to PGND and the exposed pad directly under the IC.
Power Ground. Connect to GND and the exposed pad directly under the IC.
Inductor Connection. Connect LX to the node between the inductor and the Schottky diode. LX is
high impedance in shutdown.
Exposed Pad. Connect to a large ground plane for maximum package heat dissipation. Connect
directly to GND and PGND under the IC.
2
IN
3
CTRL
4
CS
5
6
7
8
—
COMP
GND
PGND
LX
EP
_______________________________________________________________________________________
5
