19-3358; Rev 1; 8/05
KIT
ATION
EVALU
LE
B
A
IL
A
AV
High-Efficiency, 32V Step-Up Converters
with TA Derating Option for 2 to 8 White LEDs
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 overdriving the white LEDs during high ambient temperatures, 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 spacesaving, 8-pin 3mm x 3mm TDFN package.
Applications
Cell Phones and Smart Phones
Features
♦ Up to 8 LEDs at 25mA
♦ Temperature Derating Function to Allow Fewer
LEDs for Same Light (MAX8596Z)
♦ 86% Efficiency (PLEDs / PIN)
♦ 1.7% Current-Regulation Accuracy
♦ Output Overvoltage Protection
♦ Flexible Dimming Control
Analog
Direct-PWM Internal Filter
♦ 1MHz PWM Switching Frequency
♦ 0.1µF Output Capacitor
♦ 12mVP-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
Ordering Information
PDAs, Palmtops, and Wireless Handhelds
e-Books and Subnotebooks
PART
White LED Display Backlighting
TEMP RANGE PIN-PACKAGE
PKG
CODE
MAX8595ZETA-T -40°C to +85°C 8 TDFN 3mm x 3mm T833-1
MAX8595ZETA+T -40°C to +85°C 8 TDFN 3mm x 3mm T833-1
MAX8596ZETA-T -40°C to +85°C 8 TDFN 3mm x 3mm T833-1
MAX8596ZETA+T -40°C to +85°C 8 TDFN 3mm x 3mm T833-1
+Denotes lead-free package.
Dual Mode is a trademark of Maxim Integrated Products, Inc.
Pin Configuration
Typical Operating Circuit
IN
GND
COMP
8
7
6
5
LX
MAX8595Z
MAX8596Z
OUT
COMP
GND
CS
2 TO 9 LEDs
1
2
3
4
CS
200Hz TO 200kHz
CTRL
0.1µF
IN
MAX8595Z
CTRL MAX8596Z PGND
OUT
ANALOG OR
PWM DIMMING
PGND
2.2µF
TOP VIEW
LX
OUTPUT
UP TO 34V
INPUT
2.6V TO 5.5V
TDFN
3mm x 3mm x 0.8mm
A "+" SIGN WILL REPLACE THE FIRST PIN INDICATOR ON LEAD-FREE PACKAGES.
________________________________________________________________ Maxim Integrated Products
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.
1
MAX8595Z/MAX8596Z
General Description
MAX8595Z/MAX8596Z
High-Efficiency, 32V Step-Up Converters
with TA Derating Option for 2 to 8 White LEDs
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 (VIN + 2V)
COMP, CS to GND ......................................-0.3V to (VIN + 0.3V)
ILX ...................................................................................1.0ARMS
Continuous Power Dissipation (TA = +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
(VIN = 3.0V, L = 22µH, CIN = 2.2µF, COUT = 0.1µF, CCOMP = 0.1µF, RSENSE = 13Ω, VCTRL = 1.5V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
CONDITIONS
Supply Voltage
UVLO Threshold
MIN
VIN rising or falling
2.10
UVLO Hysteresis
Quiescent Current
CTRL = GND,
VOUT = VIN
OVLO Threshold
UNITS
5.5
V
2.55
V
VOUT rising
mV
0.5
0.7
TA = +25°C
0.3
2
TA = +85°C
1
32
OVLO Hysteresis
34
36
2
VOUT = 32V, VCTRL > 0.24V
Output Voltage Range
2.38
MAX
30
No switching
Shutdown Supply Current
OUT Input Bias Current
TYP
2.6
OUT = IN, CTRL = GND
9
mA
µA
V
V
20
35
TA = +25°C
0.01
1
µA
TA = +85°C
0.1
32
V
VIN VD
(Note 2)
ERROR AMPLIFIER
CTRL to CS Regulation
CS Input Bias Current
VCTRL = 1.50V,
VIN = 2.6V to 5.5V
VCS = VCTRL / 5
TA = +25°C
0.295
0.300
0.305
TA = 0°C to +85°C
0.292
0.300
0.308
TA = -40°C to +85°C
0.290
0.300
0.310
TA = +25°C
0.01
1
TA = +85°C
0.03
MAX8595Z, VCTRL = 3.0V
CS Maximum Brightness Clamp
Voltage
CTRL Voltage for CS Maximum
Brightness Clamp
CS Derating Function Start
Temperature
2
MAX8596Z,
VCTRL = 3.0V
TA = -40°C to +25°C
310
330
347
330
345
360
TA = +42°C
343
TA = +85°C
106.5
MAX8595Z
1.65
MAX8596Z
1.72
MAX8596Z, VCTRL = 3.0V
+42
_______________________________________________________________________________________
V
µA
mV
V
°C
High-Efficiency, 32V Step-Up Converters
with TA Derating Option for 2 to 8 White LEDs
(VIN = 3.0V, L = 22µH, CIN = 2.2µF, COUT = 0.1µF, CCOMP = 0.1µF, RSENSE = 13Ω, VCTRL = 1.5V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
CONDITIONS
CS Derating Function Slope
MAX8596Z, VCTRL = 3.0V, TA = +42°C to +85°C
CTRL Input Resistance
VCTRL < 1.5V
CTRL Dual-Mode Threshold
MIN
TYP
MAX
-5.5
mV/°C
250
500
780
100
170
240
CTRL Dual-Mode Hysteresis
UNITS
5
kΩ
mV
mV
CTRL Shutdown Enable Delay
(Note 3)
6.0
8.2
10.5
ms
CS to COMP Transconductance
VCOMP = 1.5V
32
50
82
µS
COMP Input Resistance to
Ground
In shutdown, UVLO or OVLO
20
kΩ
OSCILLATOR
Operating Frequency
Minimum Duty Cycle
Maximum Duty Cycle
0.75
1.0
PWM mode
12
Pulse skipping
0
CTRL = IN, CS = GND
94
1.25
MHz
%
95
%
N-CHANNEL SWITCH
LX On-Resistance
ILX = 190mA
LX Leakage Current
VLX = 36V, CTRL = GND
LX Current Limit
Duty cycle = 90%
0.8
1.35
TA = +25°C
0.01
5
TA = +85°C
1
500
700
900
Ω
µA
mA
Note 1: Parameters are 100% production tested at TA = +25°C. Limits over the operating temperature range are regulated by
design and characterization.
Note 2: VD 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
MAX8595Z/MAX8596Z
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(Circuit of Figure 1, VIN = 3.6V, ILED = 25mA, L = 22µH, CIN = 2.2µF, COUT = 0.1µF, CCOMP = 0.1µF, RSENSE = 13Ω, 4 LEDs,
TA = +25°C, unless otherwise noted.)
EFFICIENCY
vs. LED CURRENT
EFFICIENCY
vs. INPUT VOLTAGE
3 LEDs
80
75
4 LEDs
70
6 LEDs
85
EFFICIENCY (%)
EFFICIENCY (%)
85
6 LEDs
65
8 LEDs
60
MAX8595Z toc02
95
90
90
MAX8595Z toc01
100
80
8 LEDs
3 LEDs
75
70
65
55
50
60
3
2
4
5
6
5
0
10
15
20
25
INPUT VOLTAGE (V)
LED CURRENT (mA)
LED CURRENT
vs. DIRECT-PWM DIMMING
LED CURRENT
vs. AMBIENT TEMPERATURE
20
15
10
MAX8595Z toc04
24
MAX8596,
ILED = 25mA AT TA = +25°C
22
LED CURRENT (mA)
25
30
26
MAX8595Z toc03
30
LED CURRENT (mA)
MAX8595Z/MAX8596Z
High-Efficiency, 32V Step-Up Converters
with TA Derating Option for 2 to 8 White LEDs
20
18
MAX8595,
ILED = 15mA
16
14
12
5
10
0
8
0
20
40
60
80
100
-40
DUTY CYCLE (%)
-20
0
20
40
SWITCHING WAVEFORMS
VCTRL
2V/div
0
10V/div
IIN
100mA/div
0
200mV/div
AC-COUPLED
VOUT
ILED
40mA/div
0
100mA/div
IL
100
MAX8595Z toc06
20mV/div
AC-COUPLED
VLX
80
SOFT-START AND SHUTDOWN RESPONSE
MAX8595Z toc05
VIN
60
TEMPERATURE (°C)
VOUT
10V/div
0
500ns/div
4
20ms/div
_______________________________________________________________________________________
High-Efficiency, 32V Step-Up Converters
with TA Derating Option for 2 to 8 White LEDs
DIRECT-PWM DIMMING RESPONSE
CTRL STEP RESPONSE
MAX8595Z toc08
MAX8595Z toc07
VCTRL
1V/div
2V/div
32kHz 50%
DUTY CYCLE
0
VCTRL
0
IIN
100mA/div
20mV/div
AC-COUPLED
VIN
0
0
ILED
40mA/div
0
VOUT
10V/div
500mV/div
AC-COUPLED
VOUT
0
ILED
10mA/div
0
0
10µs/div
20ms/div
Pin Description
PIN
NAME
1
OUT
2
IN
FUNCTION
Overvoltage Sense. When VOUT is greater than 34V (typ), the internal n-channel MOSFET turns off
until VOUT drops below 32V (typ), then the IC re-enters soft-start. Connect a 0.1µF ceramic capacitor
from OUT to ground. In shutdown, VOUT is one diode drop below VIN.
Input Voltage Supply. The input voltage range is 2.6V to 5.5V. Connect a 2.2µF ceramic capacitor
from IN to GND.
3
CTRL
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.
4
CS
Current-Sense Feedback Input. Connect a resistor from CS to GND to set the LED bias current. The
voltage at CS regulates to VCTRL / 5 or 0.330V (0.343V for the MAX8596Z), whichever is lower.
5
COMP
Compensation Input. Connect a 0.1µF ceramic capacitor (CCOMP) from COMP to GND. CCOMP
stabilizes the converter, controls soft-start, and lowpass filters direct PWM dimming at CTRL. CCOMP
discharges to 0V through an internal 20kΩ resistor in shutdown.
6
GND
7
PGND
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.
8
LX
Inductor Connection. Connect LX to the node between the inductor and the Schottky diode. LX is
high impedance in shutdown.
—
EP
Exposed Pad. Connect to a large ground plane for maximum package heat dissipation. Connect
directly to GND and PGND under the IC.
_______________________________________________________________________________________
5
MAX8595Z/MAX8596Z
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = 3.6V, ILED = 25mA, L = 22µH, CIN = 2.2µF, COUT = 0.1µF, CCOMP = 0.1µF, RSENSE = 13Ω, 4 LEDs,
TA = +25°C, unless otherwise noted.)
MAX8595Z/MAX8596Z
High-Efficiency, 32V Step-Up Converters
with TA Derating Option for 2 to 8 White LEDs
Detailed Description
The high efficiency and small size of the MAX8595Z/
MAX8596Z make them ideally suited to drive up to 9
series-connected LEDs. These devices operate as a
boost DC-DC converter that regulates output current
rather than voltage. The MAX8595Z/MAX8596Z provide
even illumination by sourcing the same output current
through each LED, eliminating the need for expensive
factory calibration. The fast 1MHz internal oscillator
allows for a small inductor and small input and output
capacitors while minimizing input and output ripple.
The single analog control input (CTRL) allows easy
adjustment of LED brightness and on/off control. This
allows simple logic-level on/off control, analog voltage
control, or PWM duty-cycle control of both brightness
and shutdown. In shutdown, supply current is reduced
to a low 0.3µA (typ). A soft-start gradually illuminates
the LEDs, eliminating the inrush current during startup.
The MAX8596Z has the additional feature of derating
LED current as ambient temperature rises. Above
+42°C, the CS regulation voltage is reduced at a rate of
5.5mV/°C, thus reducing the LED current.
2.6V TO 5.5V
2.2µF
22µH
IN
LX
PWM
CONTROL
PGND
fOSC
1MHz
OUT
OVERVOLTAGE
PROTECT
0.1µF
0.1µF
COMP
1.25V CLAMP OR
TEMP DERATE CLAMP
gm
CTRL
ANALOG
OR DIRECT
PWM
DIMMING
121kΩ
279kΩ
100kΩ
CS
RSENSE
13Ω
Soft-Start
The MAX8595Z/MAX8596Z attain soft-start by charging
CCOMP gradually with a current source. When VCOMP
rises above 1.25V, the internal MOSFET begins switching at a reduced duty cycle. When VCOMP rises above
2.25V, the duty cycle is at its maximum. See the
Typical Operating Characteristics for an example of
soft-start operation.
Shutdown
The MAX8595Z/MAX8596Z enter shutdown when VCTRL
is less than 100mV for more than 8.2ms. In shutdown,
supply current is reduced to 0.3µA (typ) by powering
down the entire IC except for the CTRL voltage-detection circuitry. CCOMP is discharged during shutdown,
allowing the device to re-initiate soft-start when it is
enabled. Although the internal n-channel MOSFET does
not switch in shutdown, there is still a DC current path
between the input and the LEDs through the inductor
and Schottky diode. The minimum forward voltage of the
LED array must exceed the maximum input voltage to
ensure that the LEDs remain off in shutdown. However,
with 2 or more LEDs, the forward voltage is large
enough to keep leakage current low, less than 1µA
(typ). Typical shutdown timing characteristics are shown
in the Typical Operating Characteristics.
Overvoltage Protection
Overvoltage lockout (OVLO) occurs when V OUT is
above 34V (typ). The protection circuitry stops the inter6
8.2ms
170mV
SHUTDOWN
GND
Figure 1. Functional Diagram and Typical Application Circuit
nal MOSFET from switching and causes V COMP to
decay towards 0V. The device comes out of OVLO and
into soft-start when VOUT falls below 32V (typ).
Ambient Temperature Derating Function
(MAX8596Z)
The MAX8596Z limits the maximum LED current
depending on the die temperature. VCS is limited to
343mV up to +42°C. Once the temperature reaches
+42°C, the maximum VCS declines by 5.5mV/°C until
the minimum 106.5mV threshold is reached at +85°C.
Due to the package’s exposed paddle, the die temperature is always very close to the PC board temperature.
The temperature derating function allows the LED current to be safely set higher at normal operating temperatures, thereby allowing either a brighter display or
fewer LEDs to be used for normal display brightness.
See the Typical Operating Characteristics for LED
Current vs. Ambient Temperature.
_______________________________________________________________________________________
High-Efficiency, 32V Step-Up Converters
with TA Derating Option for 2 to 8 White LEDs
Adjusting LED Current
Adjusting the output current of the MAX8595Z/
MAX8596Z changes the brightness of the LEDs. An
analog input (CTRL) and the sense-resistor value set
the output current. Output current is given by:
ILED = VCTRL / (5 x RSENSE)
The VCTRL voltage range for adjusting output current is
0.24V to 1.65V (or 1.72V for the MAX8596Z). To set the
maximum current, calculate RSENSE when VCTRL is at
its maximum as follows:
For the MAX8595Z, RSENSE = 1.65 / (5 x ILED(MAX))
For the MAX8596Z, RSENSE = 1.72 / (5 x ILED(MAX))
Power dissipation in RSENSE is typically less than 10mW,
allowing the use of a small surface-mount resistor.
PWM Dimming Control
CTRL is also used as a digital input allowing LED
brightness control with a logic-level PWM signal
applied directly to CTRL. The frequency range is from
200Hz to 200kHz, while 0% duty cycle corresponds to
zero current and 100% duty cycle corresponds to full
current. The error amplifier and compensation capacitor form a lowpass filter so PWM dimming results in DC
current to the LEDs without the need for any additional
RC filters; see the Typical Operating Characteristics.
Capacitor Selection
Ceramic capacitors with X5R, X7R, or better dielectric
are recommended for stable operation over the entire
operating temperature range. The exact values of input
and output capacitors are not critical. The typical value
for the input capacitor is 2.2µF, and the typical value for
the output capacitor is 0.1µF. Higher-value capacitors
can be used to reduce input and output ripple, but at
the expense of size and higher cost. CCOMP stabilizes
the converter and controls soft-start. Connect a 0.1µF
capacitor from COMP to GND. For stable operation,
COUT must not exceed 10 times CCOMP.
Inductor Selection
Inductor values range from 10µH to 47µH. A 22µH
inductor optimizes the efficiency for most applications
while maintaining low 12mVP-P input ripple. With input
voltages near 5V, a larger value of inductance can be
more efficient. To prevent core saturation, ensure that
the inductor-saturation current rating exceeds the peak
inductor current for the application. Calculate the peak
inductor current with the following formula:
IPEAK =
VOUT(MAX) × ILED(MAX)
0.9 × VIN(MIN)
+
VIN(MIN) × 0.9µs
2 ×L
Schottky Diode Selection
The high switching frequency of the MAX8595Z/
MAX8596Z demands a high-speed rectification diode
(D1) for optimum efficiency. A Schottky diode is recommended due to its fast recovery time and low forwardvoltage drop. Ensure that the diode’s average and
peak current rating exceed the average output current
and peak inductor current. In addition, the diode’s
reverse breakdown voltage must exceed VOUT. The
RMS diode current can be approximated from:
IDIODE(RMS) = IOUT × IPEAK
Applications Information
PC Board Layout
Due to fast switching waveforms and high-current
paths, careful PC board layout is required. An evaluation kit (MAX8596ZEVKIT) is available to speed design.
When laying out a board, minimize trace lengths
between the IC and RSENSE, the inductor, the diode,
the input capacitor, and the output capacitor. Keep
traces short, direct, and wide. Keep noisy traces, such
as the LX node trace, away from CS. The IN bypass
capacitor (CIN) should be placed as close to the IC as
possible. PGND and GND should be connected directly to the exposed paddle underneath the IC. The
ground connections of C IN and COUT should be as
close together as possible. The traces from IN to the
inductor and from the Schottky diode to the LEDs can
be longer.
Chip Information
TRANSISTOR COUNT: 2143
PROCESS: BiCMOS
_______________________________________________________________________________________
7
MAX8595Z/MAX8596Z
Design Procedure
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
6, 8, &10L, DFN THIN.EPS
MAX8595Z/MAX8596Z
High-Efficiency, 32V Step-Up Converters
with TA Derating Option for 2 to 8 White LEDs
D2
D
A2
PIN 1 ID
N
0.35x0.35
b
PIN 1
INDEX
AREA
E
[(N/2)-1] x e
REF.
E2
DETAIL A
e
k
A1
CL
CL
A
L
L
e
e
PACKAGE OUTLINE, 6,8,10 & 14L,
TDFN, EXPOSED PAD, 3x3x0.80 mm
-DRAWING NOT TO SCALE-
21-0137
G
1
2
COMMON DIMENSIONS
MIN.
MAX.
D
0.70
2.90
0.80
3.10
E
A1
2.90
0.00
3.10
0.05
L
k
0.20
0.40
0.25 MIN.
A2
0.20 REF.
SYMBOL
A
PACKAGE VARIATIONS
PKG. CODE
N
D2
E2
e
JEDEC SPEC
b
[(N/2)-1] x e
DOWNBONDS
ALLOWED
T633-1
6
1.50±0.10
2.30±0.10
0.95 BSC
MO229 / WEEA
0.40±0.05
1.90 REF
NO
T633-2
6
1.50±0.10
2.30±0.10
0.95 BSC
MO229 / WEEA
0.40±0.05
1.90 REF
NO
T833-1
8
1.50±0.10
2.30±0.10
0.65 BSC
MO229 / WEEC
0.30±0.05
1.95 REF
T833-2
8
1.50±0.10
2.30±0.10
0.65 BSC
MO229 / WEEC
0.30±0.05
1.95 REF
NO
T833-3
8
1.50±0.10
2.30±0.10
0.65 BSC
MO229 / WEEC
0.30±0.05
1.95 REF
YES
NO
T1033-1
10
1.50±0.10
2.30±0.10
0.50 BSC
MO229 / WEED-3
0.25±0.05
2.00 REF
NO
T1433-1
14
1.70±0.10
2.30±0.10
0.40 BSC
----
0.20±0.05
2.40 REF
YES
T1433-2
14
1.70±0.10
2.30±0.10
0.40 BSC
----
0.20±0.05
2.40 REF
NO
PACKAGE OUTLINE, 6,8,10 & 14L,
TDFN, EXPOSED PAD, 3x3x0.80 mm
-DRAWING NOT TO SCALE-
21-0137
G
2
2
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2005 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products, Inc.
工商网监
湘ICP备2023018690号
