19-3329; Rev 3; 3/10
KIT
ATION
EVALU
E
L
B
AVAILA
High-Efficiency LCD Boost
with True Shutdown
Features
♦ 15V or Adjustable Output Voltage Up to 28V
♦ Safety Features Protect Against Output Faults
♦ 20mA at 20V from a Single Li+ Battery
♦
♦
♦
♦
True Shutdown
87% Efficiency
Up to 800kHz Switching Frequency
Small, 6-Pin SOT23 and µDFN (MAX8570 Only)
Packages
Ordering Information
PART
TEMP RANGE
PINPACKAGE
MAX8570ELT+T
-40°C to +85°C
6L μDFN
MAX8570EUT+T
-40°C to +85°C
6 SOT23
ABTJ
MAX8571EUT+T
-40°C to +85°C
6 SOT23
ABTK
MAX8572EUT+T
-40°C to +85°C
6 SOT23
ABTL
MAX8573EUT+T
-40°C to +85°C
6 SOT23
ABTM
MAX8574EUT+T
-40°C to +85°C
6 SOT23
ABTN
ACW
MAX8575EUT+T
-40°C to +85°C
6 SOT23
+Denotes a lead(Pb)-free RoHS-compliant package.
T = Tape and reel.
ABTO
Selector Guide
Applications
LCD Bias Generators
TOP
MARK
CURRENT LIMIT
OUTPUT VOLTAGE
MAX8570
110mA
Adjustable
MAX8571
250mA
Adjustable
Palmtop Computers
MAX8572
110mA
15V
Personal Digital Assistants (PDAs)
MAX8573
250mA
15V
MAX8574
500mA
Adjustable
MAX8575
500mA
15V
Polymer LEDs (OLED)
Cellular or Cordless Phones
PART
Organizers
Handy Terminals
Pin Configurations
Typical Operating Circuit
TOP VIEW
VOUT = VCC TO 28V
+
FB 1
GND 2
MAX8570
MAX8571
MAX8574
SHDN 3
6
VCC
5
SW
4
LX
VCC = 2.7V TO 5.5V
SW
LX
VCC
MAX8572
MAX8573
MAX8575 OUT
SOT23
Pin Configurations continued at end of data sheet.
ON
SHDN
GND
OFF
True Shutdown is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________ Maxim Integrated Products
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
1
MAX8570–MAX8575
General Description
The MAX8570 family of LCD step-up converters uses
an internal n-channel switch and an internal p-channel
output isolation switch. These converters operate from
a 2.7V to 5.5V supply voltage and deliver up to 28V at
the output.
A unique control scheme provides the highest efficiency over a wide range of load conditions. The internal
MOSFET switch reduces external component count and
a high switching frequency (up to 800kHz) allows for
tiny surface-mount components. Three current-limit
options are available. The MAX8570 and MAX8572 use
a 110mA current limit to reduce ripple and component
size in low-current applications. For high-power requirements, the MAX8574 and MAX8575 use a 500mA current limit and supply up to 20mA at 20V. The MAX8571
and MAX8573 use a 250mA current limit for a compromise between ripple and power. Built-in safety features
protect the internal switch and down-stream components from fault conditions.
Additional features include a low quiescent current and
a True Shutdown™ mode to save power. The MAX8570/
MAX8571/MAX8574 allow the user to set the output
voltage between 3V and 28V, and the MAX8572/
MAX8573/MAX8575 have a preset 15V output. These
step-up converters are ideal for small LCD panels with
low current requirements, but can also be used in other
applications. The MAX8571 evaluation kit is available to
help reduce design time.
MAX8570–MAX8575
High-Efficiency LCD Boost
with True Shutdown
ABSOLUTE MAXIMUM RATINGS
VCC, SHDN to GND ..................................................-0.3V to +6V
SW to GND .................................................-0.3V to (VCC + 0.3V)
FB to GND (MAX8570/MAX8571/
MAX8574)...............................................-0.3V to (VCC + 0.3V)
OUT to GND (MAX8572/MAX8573/MAX8575) .......-0.3V to +30V
LX to GND ..............................................................-0.3V to +30V
ILX, ICC ..............................................................................600mA
Continuous Power Dissipation (TA = +70°C)
μDFN (derate 4.5mW/°C above +70°C)....................357.8mW
SOT23-6 (derate 8.7mW/°C above +70°C)...............695.7mW
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
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
(VCC = V SHDN = 3.6V, SW open, VFB = 1.3V (MAX8570/MAX8571/MAX8574) or VOUT = 16V (MAX8572/MAX8573/MAX8575), TA =
-40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
CONDITIONS
MIN
VCC Input Voltage Range
VCC Undervoltage Lockout
VCC rising, 50mV typical hysteresis
2.33
V
35
μA
TA = +25°C
0.05
1
TA = -40°C to +85°C
0.05
Line Regulation
Circuit of Figure 3, VOUT = 15V, ILOAD = 5mA,
VCC = 2.7V to 5.5V
0.1
Circuit of Figure 3, VOUT = 15V, ILOAD = 0 to 5mA
0.1
TA = -40°C to +85°C
1.2137
LX On-Resistance
LX Leakage Current
-50
-4
+50
TA = 0°C to +85°C
14.85
15
15.15
TA = -40°C to +85°C
14.813
15.187
2.4
SHDN Low Level (VIL)
SHDN High Level (VIH)
SHDN Leakage Current
2
V
0.241
0.267
0.088
0.101
0.108
MAX8574/MAX8575
0.425
0.484
0.540
MAX8571/MAX8573/MAX8574/MAX8575, ILX = 100mA
0.9
1.5
MAX8570/MAX8572, ILX = 50mA
1.5
2.4
TA = +25°C
0.01
2
TA = -40°C to +85°C
0.05
8
11
14
VFB > 1V or VOUT > 12.2V
0.8
1
1.2
VFB = 0.25V or VOUT = 3.4V
4.0
5
6.0
55
2.7V ≤ VCC ≤ 5.5V
4.2V ≤ VCC ≤ 5.5V
1.5
1.4
-1
_______________________________________________________________________________________
A
Ω
μA
μs
μs
ns
0.7
2.7V ≤ VCC < 4.2V
V
μA
0.217
Current-Limit Propagation Delay
nA
28
MAX8570/MAX8572
VLX = 28V
V
4.4
MAX8571/MAX8573
Maximum LX On-Time
Minimum LX Off-Time
1.236
1.2383
LX Voltage Range
LX Switch Current Limit (Note 2)
%/mA
1.216
VOUT = 15V
1.226
μA
%/V
TA = 0°C to +85°C
FB Input Bias Current
OUT Input Bias Current
V
2.65
SHDN = GND, VCC = 5.5V
OUT Regulation Voltage
UNITS
5.50
25
VCC Shutdown Current
FB Regulation Voltage
MAX
2.5
VCC Supply Current
Load Regulation
TYP
2.70
V
V
+1
μA
High-Efficiency LCD Boost
with True Shutdown
(VCC = V SHDN = 3.6V, SW open, VFB = 1.3V (MAX8570/MAX8571/MAX8574) or VOUT = 16V (MAX8572/MAX8573/MAX8575), TA =
-40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
CONDITIONS
SW PMOS Current Limit
SW PMOS On-Resistance
MIN
TYP
MAX
VCC = 3.6V, VSW = 0V, VFB = 0V, ICC (peak)
0.45
0.75
1.10
VCC = 3.6V, VSW = 0V, VFB = 0V, ICC (average)
0.15
0.30
0.60
VCC = 2.7V, VFB = 0V, ISW = 100mA
SW PMOS Leakage Current
SW = GND, VCC = 5.5V, VFB = 0V
SW Soft-Start Time
VCC = 2.7V, CSW = 4.7μF
1.5
2.5
TA = +25°C
0.01
1
TA = -40°C to +85°C
0.02
0.2
UNITS
A
Ω
μA
1
ms
Note 1: Parameters are production tested at TA = +25°C. Limits over temperature are guaranteed by design.
Note 2: Specified currents are measured at DC. Actual LX current limits are slightly higher in circuit due to current-limit comparator
delay. Actual currents (with 2μH) are 110mA (MAX8570/MAX8572), 250mA (MAX8571/MAX8573), and 500mA
(MAX8574/MAX8575).
Typical Operating Characteristics
(MAX8571, VCC = 3.6V, VOUT = 18V, Circuit of Figure 2, TA = +25°C, unless otherwise noted.)
18.0
1mA LOAD
17.9
17.8
17.7
1mA LOAD
15.2
15.1
15.0
14.9
5mA LOAD
14.8
17.5
2.7
3.1
3.5
3.9
4.3
14.6
14.5
4.7
5.1
5.5
3.1
3.5
3.9
4.3
18.2
18.0
17.8
5.1
10
15
LOAD CURRENT (mA)
3.4
25
4.0
4.3
18.2
18.1
18.0
17.9
100
L1 = TOKO A914BYW-470M
95
47μH, 5mA LOAD
47μH, 1mA LOAD
90
80
22μH, 1mA LOAD
22μH, 5mA LOAD
75
1mA LOAD
-15
4.9
85
17.8
-40
4.6
EFFICIENCY vs. SUPPLY VOLTAGE
MAX8570/71/73/74/75 toc05
18.3
17.6
20
3.7
SUPPLY VOLTAGE (V)
17.7
5
L1 = TOKO S1024-100M
R1 = 1.1MΩ, R2 = 75kΩ, C4 = 4.7pF
3.1
5.5
MAX8571
R1 = 3.9MΩ, R2 = 287kΩ, C4 = 10pF
0
17.6
17.0
4.7
18.4
OUTPUT VOLTAGE (V)
18.4
MAX8570/71/73/74/75 toc04
MAX8574, R1 = 1.1MΩ, R2 = 75kΩ, C4 = 4.7pF
17.4
20mA LOAD
17.8
OUTPUT VOLTAGE vs. TEMPERATURE
L1 = MURATA LQH32CN220K23
MAX8570
18.0
SUPPLY VOLTAGE (V)
18.8
17.6
18.2
17.2
L1 = MURATA LQH32CN220K23
2.7
OUTPUT VOLTAGE
vs. LOAD CURRENT
18.6
18.4
17.4
SUPPLY VOLTAGE (V)
19.0
5mA LOAD
18.6
14.7
L1 = MURATA LQH32CN220K23
R1 = 3.9MΩ, R2 = 287kΩ
17.6
OUTPUT VOLTAGE (V)
18.8
MAX8570/71/73/74/75 toc03
15.3
19.0
MAX8570/71/73/74/75 toc06
18.1
15.4
EFFICIENCY (%)
OUTPUT VOLTAGE (V)
18.2
MAX8570/71/73/74/75 toc02
5mA LOAD
18.3
15.5
OUTPUT VOLTAGE (V)
MAX8570/71/73/74/75 toc01
18.5
18.4
OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE (MAX8574)
OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE (FIGURE 3, MAX8573)
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE (MAX8571)
L1 = MURATA LQH32CN220K23
70
10
35
TEMPERATURE (°C)
60
85
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
3
MAX8570–MAX8575
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics (continued)
(MAX8571, VCC = 3.6V, VOUT = 18V, Circuit of Figure 2, TA = +25°C, unless otherwise noted.)
1mA LOAD
70
60
50
MAX8570, MURATA LQH32CN220K23
90
80
MAX8571, MURATA LQH32CN220K23
70
MAX8574, TOKO A914BYW-220M
60
100
MAX8570, L1 = MURATA LQH32CN470K23
90
EFFICIENCY (%)
80
100
50
VCC = 3.6V
80
MAX8571, L1 = TOKO A914BYW-470M
70
60
50
L1 = MURATA LQH32CN220K23
40
0
2
4
6
8
10
12
40
0.1
1
BATTERY VOLTAGE (V)
MAX8571
300
MAX8570
100
80
60
40
0
3.5
3.9
4.3
4.7
5.1
5.5
80
L1 = MURATA LQH32CN220K23
0
5
SUPPLY VOLTAGE (V)
60
50
40
MAX8573,
FIGURE 3
30
L1 = MURATA
LQH32CN220K23
0
1
2
3
4
LINE TRANSIENT 3V TO 5.5V
(FIGURE 3, MAX8573)
MAX8570/71/73/74/75 toc14
MAX8570/71/73/74/75 toc13
200mV/div
(AC-COUPLED)
200mV/div
(AC-COUPLED)
VOUT
VCC
VCC
2V/div
2V/div
0
0
100μs/div
100μs/div
3.6kΩ LOAD, R1 = 3.9MΩ, R2 = 287kΩ
5
SUPPLY VOLTAGE (V)
LINE TRANSIENT 3V TO 5.5V (MAX8571)
4
NO SWITCHING
0
15
10
LOAD CURRENT (mA)
VOUT
R1 = 3.9MΩ
R2 = 287kΩ
R1 = 7.87MΩ
R2 = 576kΩ
70
10
0
3.1
100
20
20
100
10
NO-LOAD CURRENT vs. SUPPLY VOLTAGE
MAX8570/71/73/74/75 toc11
500
2.7
1
LOAD CURRENT (mA)
120
SUPPLY CURRENT (mA)
MAX8574
200
0.1
SUPPLY CURRENT vs. LOAD CURRENT
MAX8570/71/73/74/75 toc10
700
400
100
LOAD CURRENT (mA)
PEAK INDUCTOR CURRENT LIMIT
vs. SUPPLY VOLTAGE
600
10
MAX8570/71/73/74/75 toc12
40
SUPPLY CURRENT (μA)
EFFICIENCY (%)
90
EFFICIENCY vs. LOAD CURRENT
WITH 47μH INDUCTOR
MAX8570/71/73/74/75 toc08
5mA LOAD
EFFICIENCY (%)
MAX8570/71/73/74/75 toc07
100
EFFICIENCY vs. LOAD CURRENT
WITH 22μH INDUCTOR
MAX8570/71/73/74/75 toc09
EFFICIENCY vs. BATTERY VOLTAGE
(FIGURE 4)
CURRENT LIMIT (mA)
MAX8570–MAX8575
High-Efficiency LCD Boost
with True Shutdown
3kΩ LOAD
_______________________________________________________________________________________
6
High-Efficiency LCD Boost
with True Shutdown
LOAD TRANSIENT
STARTUP AND SHUTDOWN WAVEFORMS
MAX8570/71/73/74/75 toc15
MAX8570/71/73/74/75 toc16
5V/div
VSHDN
VOUT
100mV/div
(AC-COUPLED)
BOOST SOFT-START
SW TURN-ON
10V/div
VOUT
0
5mA/div
IOUT
0
ILX
200mA/div
0
100µs/div
400µs/div
1.8Ω LOAD
Pin Description
PIN
MAX8570
(µDFN)
MAX8570/ MAX8572/
MAX8571/ MAX8573/
MAX8574 MAX8575
(SOT23)
(SOT23)
NAME
FUNCTION
3
1
—
FB
Feedback for Setting the Output Voltage. Connect FB to the center of a resistor
voltage-divider from the output to GND to set positive output voltages.
—
—
1
OUT
Output. The output voltage is preset to 15V. Connect a 1µF ceramic capacitor
from OUT to GND. In shutdown, OUT is pulled to GND by an internal 7.5MΩ
resistor.
2
2
2
GND
Ground
Shutdown Input. A logic-low at SHDN places the part in low-power shutdown
mode. Pull SHDN high or connect to VCC for normal operation.
1
3
3
SHDN
6
4
4
LX
Inductor Switching Connection
5
5
5
SW
Isolation Switch Output. Internally connected to the drain of a p-channel
MOSFET used to isolate the output from the input during shutdown. Connect a
4.7µF ceramic capacitor from SW to GND. If True Shutdown is not required, SW
can be left open with the input supply connected directly to the inductor.
4
6
6
VCC
Input Voltage Supply. Connect a 2.7V to 5.5V input supply to VCC. Connect a
1µF ceramic capacitor from VCC to GND.
_______________________________________________________________________________________
5
MAX8570–MAX8575
Typical Operating Characteristics (continued)
(MAX8571, VCC = 3.6V, VOUT = 18V, Circuit of Figure 2, TA = +25°C, unless otherwise noted.)
MAX8570–MAX8575
High-Efficiency LCD Boost
with True Shutdown
VCC
SW
LX
SHDN
THERMAL
SHUTDOWN
OUT
(MAX8572/MAX8573/
MAX8575 ONLY)
ILIM
MAX8570–
MAX8575
CONTROL
LOGIC
FB
(MAX8570/MAX8571/
MAX8574 ONLY)
EA
1.226V
GND
Figure 1. Functional Diagram
L1
22μH
L1
22μH
D1
C3
4.7μF
VCC = 2.7V TO 5.5V
C1
1μF
ON
VCC
VOUT = VCC TO 28V
LX
SW
MAX8570
MAX8571
MAX8574
C4
10pF
R1
D1
C2
1μF
C3
4.7μF
VCC = 2.7V TO 5.5V
FB
C1
1μF
R2
ON
GND
SHDN
D1
VCC
VOUT = VBATT TO 28V
MAX8570
MAX8571
MAX8574
C4
10pF
R1
D1
C2
1μF
C3
4.7μF
VCC = 2.7V TO 5.5V
FB
C1
1μF
R2
MAX8570
MAX8571
MAX8574
C4
10pF
C2
1μF
R1
R2
FB
C6
0.1μF D3
-VOUT
SHDN
GND
Figure 4. Using a Separate Input Supply for the Inductor
VCC
+VOUT
LX
SW
D2
ON
SHDN
OFF
6
GND
L1
22μH
LX
SW
ON
C2
1μF
Figure 3. Typical Application Circuit with 15V Preset Output
Voltage
L1
22μH
VBATT = 0.8V TO 28V
C1
1μF
VCC
MAX8572
MAX8573
MAX8575 OUT
VOUT = 15V
OFF
Figure 2. Typical Application Circuit with Adjustable Output
Voltage
VCC = 2.7V TO 5.5V
LX
SHDN
OFF
C3
4.7μF
SW
GND
OFF
Figure 5. Negative Output Voltage for LCD Bias
_______________________________________________________________________________________
C5
1μF
High-Efficiency LCD Boost
with True Shutdown
The MAX8570 family of compact, step-up DC-DC converters operates from a 2.7V to 5.5V supply. Consuming
only 25µA of supply current, these ICs include an internal MOSFET switch with a low on-resistance. A trueshutdown feature disconnects the battery from the load
and reduces the supply current to 0.05µA (typ). These
DC-DC converters are available with either a fixed 15V
output or are adjustable up to 28V. Three current-limit
options are available: 110mA, 250mA, and 500mA. See
the Selector Guide on page 1.
Control Scheme
The MAX8570 family features a minimum off-time current-limited control scheme operating in discontinuous
mode. An internal p-channel MOSFET switch connects
VCC to SW to provide power to the inductor when the
converter is operating. When the converter is shut
down, this switch disconnects the input supply from the
inductor (see Figure 1).
To boost the output voltage, an n-channel MOSFET
switch turns on and allows current to ramp up in the
inductor. Once this current reaches the current limit,
the switch turns off and the inductor current flows
through D1 to supply the output. The switching frequency varies depending on the load and input voltage
and can be up to 800kHz.
Setting the Output Voltage
The output voltage of the MAX8570, MAX8571, and
MAX8574 is adjustable from VCC to 28V by using a
resistor voltage-divider (see Figure 2). Select R2 from
10kΩ to 600kΩ and calculate R1 with the following
equation:
⎛V
⎞
R1 = R2 ⎜ OUT − 1⎟
⎝ VFB
⎠
where VFB = 1.226V and VOUT can range from VCC to
28V. For best accuracy, ensure that the bias current
through the feedback resistors is at least 2µA.
The MAX8572, MAX8573, and MAX8575 have a fixed
15V output. When using these parts, connect OUT
directly to the output (see Figure 3).
Shutdown (SHDN)
Drive SHDN low to enter shutdown. During shutdown
the supply current drops to 0.05µA (typ), the output is
disconnected from the input, and LX enters a highimpedance state. The capacitance and load at the output determine the rate at which VOUT decays. SHDN
can be pulled as high as 6V regardless of the input and
output voltages.
With a typical step-up converter circuit, the output
remains connected to the input through the inductor and
output rectifier, holding the output voltage to one diode
drop below VCC when the converter is shut down and
allowing the output to draw power from the input. The
MAX8570 family features True-Shutdown mode, disconnecting the output from the input with an internal pchannel MOSFET switch when shut down. This
eliminates power draw from the input during shutdown.
Soft-Start
The MAX8570 family uses two soft-start mechanisms.
When the true-shutdown feature is used (SW is connected as in Figure 2 and Figure 3), the gate of the
internal high-side p-channel switch turns on slowly to
prevent inrush current. This takes approximately 200µs.
When SW is fully turned on, the internal n-channel
switch begins boosting the input to set the output voltage. When VFB is less than 0.5V (with or without the use
of True Shutdown), the minimum off-time of the internal
n-channel switch increases from 1µs to 5µs to control
inrush current.
Separate Power for Inductor
Separate power supplies can be used for the IC and
the inductor. This allows power to be used from a battery or supply with a voltage as low as 0.8V, or higher
than the VCC operating range of the converter. When
using a separate inductor supply, SW is left unconnected and the supply is connected directly to the inductor
(see Figure 4). Note that in this configuration the output
is no longer disconnected from the input during shutdown. In shutdown the output voltage goes to a diode
drop below the inductor supply voltage.
Protection Features
The MAX8570 family has protection features designed
to make it extremely robust to application errors (see
Table 1). If the output capacitor in the application is
missing, the MAX8570 family protects the internal
switch from being damaged. If the top feedback resistor or the external diode is disconnected, the converter
stops switching and the output is resistively loaded to
ground. Similarly, if the external diode polarity is
reversed, the converter discontinues switching. If the
bottom feedback resistor is missing, the output stays at
a diode drop less than the inductor supply voltage or
1.226V (whichever is greater). In fact, in response to
most fault conditions, the MAX8570 family protects not
only itself, but also the downstream circuitry.
_______________________________________________________________________________________
7
MAX8570–MAX8575
Detailed Description
MAX8570–MAX8575
High-Efficiency LCD Boost
with True Shutdown
Table 1. Protection Features
RESULT WITH COMPETING
STEP-UP CONVERTERS
COMMON APPLICATION FAULTS
RESULT WITH MAX8570 FAMILY
OUT voltage rises until the output
capacitor is destroyed and/or
downstream components are damaged.
Converter stops switching.
Output cap missing and FB open.
OUT voltage rises until the output
capacitor is destroyed and/or
downstream components are damaged.
LX may boost one or two times before the FB
voltage exceeds the trip point. In the rare case
where the capacitive loading and external
loading on OUT is small enough that the energy
in one cycle can slew it more than 50V, the
internal MOSFET will clamp between 35V and
70V (nondestructively).
FB shorted to GND.
OUT voltage rises until the output
capacitor is destroyed and/or
downstream components are damaged.
Converter stops switching and OUT is resistively
loaded to GND.
Diode missing or disconnected.
Diode reverse polarity.
Inductor energy forces LX node high,
possibly damaging the internal switch.
OUT is resistively loaded to GND and the
converter stops switching.
FB node open.
Unpredictable, possibly boosting output
voltage beyond acceptable design
range.
FB node driven above its regulation point, the
converter stops switching, and OUT is resistively
loaded to GND.
OUT shorted to ground.
Current ramps up through inductor and
diode, generally destroying one of the
devices.
True off-switch detects short, opens when
current reaches pMOS current limit, and restarts
soft-start. This protects the inductor and diode.
OUT to FB resistor missing or
disconnected.
Design Procedure
Inductor Selection
Smaller inductance values typically offer smaller physical size for a given series resistance or saturation current. Circuits using larger inductance values may
provide more output power. The inductor’s saturation
current rating should be greater than the peak switching current. Recommended inductor values range from
10μH to 100μH.
value. See the Selector Guide on page 1 for selecting
the IC with the correct current limit.
Diode Selection
The high switching frequency of up to 800kHz requires
a high-speed rectifier. Schottky diodes are recommended due to their low forward-voltage drop. To
maintain high efficiency, the average current rating of
the diode should be greater than the peak switching
current. Choose a reverse breakdown voltage greater
than the output voltage.
Selecting the Current Limit
The peak LX current limit (ILX(MAX)) required for the
application is calculated from the following equation:
ILX(MAX) ≥ 1. 25 ×
2
⎛
POUT(MAX) ⎞
POUT(MAX)
+ ⎜ 1 . 25 ×
⎟ + 3μ s ×
VBATT(MIN)
V
L
BATT(MIN) ⎠
⎝
POUT(MAX)
where P OUT(MAX) is the maximum output power
required by the load and VBATT(MIN) is the minimum
supply voltage used to supply the inductor (this is VCC
unless a separate supply is used for the inductor). The
IC current limit must be greater than this calculated
8
Capacitors
Small ceramic surface-mount capacitors with X7R or
X5R temperature characteristics are recommended
due to their small size, low cost, low equivalent series
resistance (ESR), and low equivalent series inductance
(ESL). If nonceramic capacitors are used, it is important
that they have low ESR to reduce the output ripple voltage and peak-peak load-transient voltage.
For most applications, use a 1μF ceramic capacitor for
the output and VCC bypass capacitors. For SW or the
inductor supply, a 4.7μF or greater ceramic capacitor
is recommended.
_______________________________________________________________________________________
High-Efficiency LCD Boost
with True Shutdown
Applications Information
PC Board Layout
Careful printed circuit layout is important for minimizing
ground bounce and noise. Keep the GND pin and
ground pads for the input and output capacitors as
close together as possible. Keep the connection to LX
as short as possible. Locate the feedback resistors as
close as possible to the FB pin and keep the feedback
traces routed away from noisy areas such as LX. Refer
to the MAX8571EVKIT for a layout example.
Negative Output Voltage for LCD Bias
A negative output voltage can be generated by adding
a diode/capacitor charge pump as shown in Figure 5. In
this configuration, the negative output is lower in magnitude than the positive output by a forward diode drop. If
there is little or no load on the positive output, the negative output drifts from its nominal voltage. To prevent
this, it may be necessary to preload the positive output
with a few hundred microamps, which can be done by
selecting lower than normal values of R1 and R2.
_______________________________________________________________________________________
9
MAX8570–MAX8575
For the MAX8570/MAX8571/MAX8574 a feed-forward
capacitor (C4 in Figures 2 and 4) connected from the
output to FB improves stability over a wide range of
battery voltages. A 10pF capacitor is recommended for
the MAX8571 and MAX8574. A 10pF to 47pF capacitor
is recommended for the MAX8570. Note that increasing
C4 degrades line and load regulation.
High-Efficiency LCD Boost
with True Shutdown
MAX8570–MAX8575
Pin Configurations (continued)
TOP VIEW
+
+
SHDN 1
GND 2
MAX8570
FB 3
6
LX
OUT 1
5
SW
GND 2
4
VCC
SHDN 3
μDFN
5
SW
4
LX
Package Information
For the latest package outline information and land patterns, go
to www.maxim-ic.com/packages.
PACKAGE TYPE
10
VCC
SOT23
Chip Information
PROCESS: BiCMOS
MAX8572
MAX8573
MAX8575
6
PACKAGE CODE
DOCUMENT NO.
6L μDFN
L622+1
21-0164
6 SOT23
U6SN+1
21-0058
______________________________________________________________________________________
High-Efficiency LCD Boost
with True Shutdown
REVISION
NUMBER
REVISION
DATE
2
8/09
Added μDFN package
3/10
Added soldering temperature, corrected unit of measurement error, and
updated figure reference
3
DESCRIPTION
PAGES
CHANGED
1, 2, 5, 9, 10
2, 5, 9
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 11
© 2010 Maxim Integrated Products
Maxim is a registered trademark of Maxim Integrated Products, Inc.
MAX8570–MAX8575
Revision History
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