19-3558; Rev 0; 8/04
KIT
ATION
EVALU
BLE
AVAILA
High-Efficiency, 32V Step-Up Converters
with T
A
Derating Option for 2 to 8 White LEDs
General Description
Features
♦
Up to 8 LEDs at 25mA
♦
Temperature Derating Function to Allow Fewer
LEDs for Same Light (MAX8596Z)
♦
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 5.5V Input Range
♦
0.3µA Shutdown Current
♦
Pin Compatible with the MAX1561 and MAX1599
♦
TDFN 3mm x 3mm x 0.8mm Package with
Exposed Paddle
MAX8595Z/MAX8596Z
The MAX8595Z/MAX8596Z drive up to 8 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
MAX8595Z regulates constant LED current over the
entire temperature range. The MAX8596Z 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 MAX8595Z/MAX8596Z 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
TEMP
RANGE
PIN-PACKAGE
PKG
CODE
MAX8595ZETA
-40°C to +85°C 8 TDFN 3mm x 3mm T833-1
MAX8596ZETA
-40°C to +85°C 8 TDFN 3mm x 3mm T833-1
Dual Mode is a trademark of Maxim Integrated Products, Inc.
Typical Operating Circuit
INPUT
2.6V TO 5.5V
2.2µF
IN
ANALOG OR
PWM DIMMING
LX
OUT
OUTPUT
UP TO 34V
Pin Configuration
PGND
LX
GND
COMP
TOP VIEW
8
7
6
5
MAX8595Z
CTRL
MAX8596Z
PGND
COMP
GND
CS
0.1µF
MAX8595Z
MAX8596Z
1
OUT
2
IN
3
CTRL
4
CS
200Hz TO 200kHz
2 TO 8 LEDs
TDFN
3mm x 3mm x 0.8mm
________________________________________________________________
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, 32V Step-Up Converters
with T
A
Derating Option for 2 to 8 White LEDs
MAX8595Z/MAX8596Z
ABSOLUTE MAXIMUM RATINGS
IN to GND .................................................................-0.3V to +6V
PGND to GND .......................................................-0.3V to +0.3V
LX, OUT to GND .....................................................-0.3V to +37V
CTRL to GND...................-0.3V to the lower of +6V or (V
IN
+ 2V)
COMP, CS to GND ......................................-0.3V to (V
IN
+ 0.3V)
I
LX
...................................................................................1.0A
RMS
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
32
V
IN
rising or falling
CONDITIONS
MIN
2.6
2.10
2.38
30
0.5
0.3
1
34
2
20
0.01
0.1
32
V
35
1
µA
36
0.7
2
TYP
MAX
5.5
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
MAX8595Z, V
CTRL
= 3.0V
CS Input Bias Current
CS Maximum Brightness Clamp
Voltage
MAX8596Z,
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, 32V Step-Up Converters
with T
A
Derating Option for 2 to 8 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
MAX8596Z, 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
MAX8595Z/MAX8596Z
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, 32V Step-Up Converters
with T
A
Derating Option for 2 to 8 White LEDs
MAX8595Z/MAX8596Z
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
MAX8595Z toc01
EFFICIENCY
vs. LED CURRENT
6 LEDs
85
EFFICIENCY (%)
80
75
70
65
60
3 LEDs
MAX8595Z 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
MAX8595Z 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
MAX8595Z 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
MAX8595Z toc05
SOFT-START AND SHUTDOWN RESPONSE
MAX8595Z 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, 32V Step-Up Converters
with T
A
Derating Option for 2 to 8 White LEDs
MAX8595Z/MAX8596Z
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.)
CTRL STEP RESPONSE
MAX8595Z toc07
DIRECT-PWM DIMMING RESPONSE
MAX8595Z 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 34V (typ), the internal n-channel MOSFET turns off
until V
OUT
drops below 32V (typ), then the IC re-enters 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 5.5V. 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 MAX8596Z) 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 MAX8596Z), 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
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