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 efficien-
cy 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 require-
ments, the MAX8574 and MAX8575 use a 500mA cur-
rent limit and supply up to 20mA at 20V. The MAX8571
and MAX8573 use a 250mA current limit for a compro-
mise between ripple and power. Built-in safety features
protect the internal switch and down-stream compo-
nents 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.
Applications
LCD Bias Generators
Polymer LEDs (OLED)
Cellular or Cordless Phones
Palmtop Computers
Personal Digital Assistants (PDAs)
Organizers
Handy Terminals
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
MAX8570–MAX8575
High-Efficiency LCD Boost
with True Shutdown
________________________________________________________________
Maxim Integrated Products
1
Ordering Information
19-3329; Rev 3; 3/10
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
EVALUATION KIT
AVAILABLE
PART TEMP RANGE PIN-
PACKAGE
TOP
MARK
MAX8570ELT+T -40°C to +85°C 6L μDFN ACW
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
MAX8575EUT+T -40°C to +85°C 6 SOT23 ABTO
GND
LX
1
+
6V
CC
5SW
FB
MAX8570
MAX8571
MAX8574
SOT23
TOP VIEW
2
34SHDN
Pin Configurations
PART
CURRENT LIMIT
OUTPUT VOLTAGE
MAX8570 110mA Adjustable
MAX8571 250mA Adjustable
MAX8572 110mA 15V
MAX8573 250mA 15V
MAX8574 500mA Adjustable
MAX8575 500mA 15V
Selector Guide
True Shutdown is a trademark of Maxim Integrated Products, Inc.
MAX8572
MAX8573
MAX8575
SW
VCC
LX
OUT
GND
ON
OFF
VCC = 2.7V TO 5.5V
VOUT = VCC TO 28V
SHDN
Typical Operating Circuit
+
Denotes a lead(Pb)-free RoHS-compliant package.
T = Tape and reel.
Pin Configurations continued at end of data sheet.
MAX8570–MAX8575
High-Efficiency LCD Boost
with True Shutdown
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC = VSHDN = 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)
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.
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
PARAMETER CONDITIONS MIN TYP MAX UNITS
VCC Input Voltage Range 2.70 5.50 V
VCC Undervoltage Lockout VCC rising, 50mV typical hysteresis 2.33 2.5 2.65 V
VCC Supply Current 25 35 μA
TA = +25°C 0.05 1
VCC Shutdown Current SHDN = GND, VCC = 5.5V TA = -40°C to +85°C 0.05 μA
Line Regulation Circuit of Figure 3, VOUT = 15V, ILOAD = 5mA,
VCC = 2.7V to 5.5V 0.1 %/V
Load Regulation Circuit of Figure 3, VOUT = 15V, ILOAD = 0 to 5mA 0.1 %/mA
TA = 0°C to +85°C 1.216 1.226 1.236
FB Regulation Voltage TA = -40°C to +85°C 1.2137 1.2383 V
FB Input Bias Current -50 -4 +50 nA
TA = 0°C to +85°C 14.85 15 15.15
OUT Regulation Voltage TA = -40°C to +85°C 14.813 15.187 V
OUT Input Bias Current VOUT = 15V 2.4 4.4 μA
LX Voltage Range 28 V
MAX8571/MAX8573 0.217 0.241 0.267
MAX8570/MAX8572 0.088 0.101 0.108LX Switch Current Limit (Note 2)
MAX8574/MAX8575 0.425 0.484 0.540
A
MAX8571/MAX8573/MAX8574/MAX8575, ILX = 100mA 0.9 1.5
LX On-Resistance MAX8570/MAX8572, ILX = 50mA 1.5 2.4
Ω
TA = +25°C 0.01 2
LX Leakage Current VLX = 28V TA = -40°C to +85°C 0.05 μA
Maximum LX On-Time 81114μs
VFB > 1V or VOUT > 12.2V 0.8 1 1.2
Minimum LX Off-Time VFB = 0.25V or VOUT = 3.4V 4.0 5 6.0 μs
Current-Limit Propagation Delay 55 ns
SHDN Low Level (VIL) 2.7V ≤ VCC ≤ 5.5V 0.7 V
4.2V ≤ VCC ≤ 5.5V 1.5
SHDN High Level (VIH)2.7V ≤ VCC < 4.2V 1.4 V
SHDN Leakage Current -1 +1 μA
MAX8570–MAX8575
High-Efficiency LCD Boost
with True Shutdown
_______________________________________________________________________________________
3
EFFICIENCY vs. SUPPLY VOLTAGE
MAX8570/71/73/74/75 toc06
SUPPLY VOLTAGE (V)
EFFICIENCY (%)
5.14.74.33.93.53.1
75
80
85
90
95
100
70
2.7 5.5
L1 = TOKO A914BYW-470M
47μH, 1mA LOAD
47μH, 5mA LOAD
L1 = MURATA LQH32CN220K23
22μH, 5mA LOAD 22μH, 1mA LOAD
Typical Operating Characteristics
(MAX8571, VCC = 3.6V, VOUT = 18V, Circuit of Figure 2, TA= +25°C, unless otherwise noted.)
OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE (MAX8571)
MAX8570/71/73/74/75 toc01
SUPPLY VOLTAGE (V)
OUTPUT VOLTAGE (V)
5.14.73.9 4.33.53.1
17.6
17.7
17.8
17.9
18.0
18.1
18.2
18.3
18.4
18.5
17.5
2.7 5.5
L1 = MURATA LQH32CN220K23
R1 = 3.9MΩ, R2 = 287kΩ
5mA LOAD
1mA LOAD
OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE (FIGURE 3, MAX8573)
MAX8570/71/73/74/75 toc02
SUPPLY VOLTAGE (V)
OUTPUT VOLTAGE (V)
5.14.73.9 4.33.53.1
14.6
14.7
14.8
14.9
15.0
15.1
15.2
15.3
15.4
15.5
14.5
2.7 5.5
L1 = MURATA LQH32CN220K23
5mA LOAD
1mA LOAD
OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE (MAX8574)
MAX8570/71/73/74/75 toc03
SUPPLY VOLTAGE (V)
OUTPUT VOLTAGE (V)
4.64.34.03.73.4
17.2
18.2
18.0
17.8
17.6
17.4
18.4
18.6
18.8
19.0
17.0
3.1 4.9
L1 = TOKO S1024-100M
R1 = 1.1MΩ, R2 = 75kΩ, C4 = 4.7pF
5mA LOAD
20mA LOAD
OUTPUT VOLTAGE
vs. LOAD CURRENT
MAX8570/71/73/74/75 toc04
LOAD CURRENT (mA)
OUTPUT VOLTAGE (V)
20155 10
17.6
17.8
18.0
18.2
18.4
18.6
18.8
19.0
17.4
025
L1 = MURATA LQH32CN220K23
R1 = 3.9MΩ, R2 = 287kΩ, C4 = 10pF
MAX8570 MAX8571
MAX8574, R1 = 1.1MΩ, R2 = 75kΩ, C4 = 4.7pF
OUTPUT VOLTAGE vs. TEMPERATURE
MAX8570/71/73/74/75 toc05
TEMPERATURE (°C)
OUTPUT VOLTAGE (V)
603510-15
17.7
17.8
17.9
18.0
18.1
18.2
18.3
18.4
17.6
-40 85
1mA LOAD
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).
ELECTRICAL CHARACTERISTICS (continued)
(VCC = VSHDN = 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 TYP MAX UNITS
VCC = 3.6V, VSW = 0V, VFB = 0V, ICC (peak) 0.45 0.75 1.10
SW PMOS Current Limit VCC = 3.6V, VSW = 0V, VFB = 0V, ICC (average) 0.15 0.30 0.60 A
SW PMOS On-Resistance VCC = 2.7V, VFB = 0V, ISW = 100mA 1.5 2.5 Ω
TA = +25°C 0.01 1
SW PMOS Leakage Current SW = GND, VCC = 5.5V, VFB = 0V TA = -40°C to +85°C 0.02 μA
SW Soft-Start Time VCC = 2.7V, CSW = 4.7μF 0.2 1 ms
MAX8570–MAX8575
High-Efficiency LCD Boost
with True Shutdown
4 _______________________________________________________________________________________
EFFICIENCY vs. BATTERY VOLTAGE
(FIGURE 4)
MAX8570/71/73/74/75 toc07
BATTERY VOLTAGE (V)
EFFICIENCY (%)
108642
50
60
70
80
90
100
40
012
L1 = MURATA LQH32CN220K23
5mA LOAD
1mA LOAD
VCC = 3.6V
EFFICIENCY vs. LOAD CURRENT
WITH 22μH INDUCTOR
MAX8570/71/73/74/75 toc08
LOAD CURRENT (mA)
EFFICIENCY (%)
101
50
60
70
80
90
100
40
0.1 100
MAX8574, TOKO A914BYW-220M
MAX8571, MURATA LQH32CN220K23
MAX8570, MURATA LQH32CN220K23
EFFICIENCY vs. LOAD CURRENT
WITH 47μH INDUCTOR
MAX8570/71/73/74/75 toc09
LOAD CURRENT (mA)
EFFICIENCY (%)
101
50
60
70
80
90
100
40
0.1 100
MAX8570, L1 = MURATA LQH32CN470K23
MAX8571, L1 = TOKO A914BYW-470M
PEAK INDUCTOR CURRENT LIMIT
vs. SUPPLY VOLTAGE
MAX8570/71/73/74/75 toc10
SUPPLY VOLTAGE (V)
CURRENT LIMIT (mA)
5.14.74.33.93.53.1
100
200
300
400
500
600
700
0
2.7 5.5
MAX8574
MAX8571
MAX8570
SUPPLY CURRENT vs. LOAD CURRENT
MAX8570/71/73/74/75 toc11
LOAD CURRENT (mA)
SUPPLY CURRENT (mA)
105
20
40
60
80
100
120
0
015
L1 = MURATA LQH32CN220K23
NO-LOAD CURRENT vs. SUPPLY VOLTAGE
MAX8570/71/73/74/75 toc12
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (μA)
541 2 3
10
20
30
40
50
60
70
80
0
06
R1 = 3.9MΩ
R2 = 287kΩ
R1 = 7.87MΩ
R2 = 576kΩ
MAX8573,
FIGURE 3
L1 = MURATA
LQH32CN220K23 NO SWITCHING
LINE TRANSIENT 3V TO 5.5V (MAX8571)
MAX8570/71/73/74/75 toc13
100μs/div
VCC
VOUT
200mV/div
(AC-COUPLED)
2V/div
0
3.6kΩ LOAD, R1 = 3.9MΩ, R2 = 287kΩ
LINE TRANSIENT 3V TO 5.5V
(FIGURE 3, MAX8573)
MAX8570/71/73/74/75 toc14
100μs/div
VCC
VOUT 200mV/div
(AC-COUPLED)
2V/div
0
3kΩ LOAD
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
_______________________________________________________________________________________ 5
PIN
MAX8570
(µDFN)
MAX8570/
MAX8571/
MAX8574
(SOT23)
MAX8572/
MAX8573/
MAX8575
(SOT23)
NAME FUNCTION
31—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
133SHDN 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.
6 4 4 LX Inductor Switching Connection
555SW
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.
466V
CC Input Voltage Supply. Connect a 2.7V to 5.5V input supply to VCC. Connect a
1µF ceramic capacitor from VCC to GND.
Pin Description
LOAD TRANSIENT
MAX8570/71/73/74/75 toc15
100µs/div
VOUT
IOUT
100mV/div
(AC-COUPLED)
5mA/div
0
STARTUP AND SHUTDOWN WAVEFORMS
MAX8570/71/73/74/75 toc16
400µs/div
VOUT
ILX
5V/div
10V/div
200mA/div
1.8Ω LOAD
0
0
VSHDN
BOOST SOFT-START
SW TURN-ON
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
6 _______________________________________________________________________________________
MAX8570–
MAX8575
EA
ILIM
THERMAL
SHUTDOWN OUT
FB
(MAX8570/MAX8571/
MAX8574 ONLY)
GND
(MAX8572/MAX8573/
MAX8575 ONLY)
LX
SW
VCC
1.226V
CONTROL
LOGIC
SHDN
Figure 1. Functional Diagram
MAX8570
MAX8571
MAX8574
SW
VCC
LX
FB
GND
ON
OFF
VCC = 2.7V TO 5.5V
VOUT = VBATT TO 28V
R1
R2
C3
4.7μF
L1
22μH
C1
1μF
SHDN
C2
1μF
C4
10pF
VBATT = 0.8V TO 28V
D1
Figure 4. Using a Separate Input Supply for the Inductor
MAX8570
MAX8571
MAX8574
SW
VCC
LX
FB
GND
ON
OFF
VCC = 2.7V TO 5.5V
+VOUT
-VOUT
R1
C3
4.7μF
L1
22μH
C1
1μF
SHDN
C2
1μF
C5
1μF
C4
10pF
C6
0.1μF
D1
D3
D2
R2
Figure 5. Negative Output Voltage for LCD Bias
MAX8570
MAX8571
MAX8574
SW
VCC
LX
FB
GND
ON
OFF
VCC = 2.7V TO 5.5V
VOUT = VCC TO 28V
R1
R2
C3
4.7μF
L1
22μH
C1
1μF
SHDN
C2
1μF
C4
10pF
D1
Figure 2. Typical Application Circuit with Adjustable Output
Voltage
MAX8572
MAX8573
MAX8575
SW
VCC
LX
OUT
GND
ON
OFF
VCC = 2.7V TO 5.5V
VOUT = 15V
C3
4.7μF
L1
22μH
C1
1μF
SHDN
C2
1μF
D1
Figure 3. Typical Application Circuit with 15V Preset Output
Voltage
MAX8570–MAX8575
High-Efficiency LCD Boost
with True Shutdown
_______________________________________________________________________________________ 7
Detailed Description
The MAX8570 family of compact, step-up DC-DC con-
verters operates from a 2.7V to 5.5V supply. Consuming
only 25µA of supply current, these ICs include an inter-
nal MOSFET switch with a low on-resistance. A true-
shutdown 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 cur-
rent-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 fre-
quency 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
10kΩto 600kΩand calculate R1 with the following
equation:
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 high-
impedance state. The capacitance and load at the out-
put 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, discon-
necting the output from the input with an internal p-
channel 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 con-
nected 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 volt-
age. 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 bat-
tery 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 unconnect-
ed 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 shut-
down. 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 resis-
tor 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.
RRV
V
OUT
FB
12 1=−
⎛
⎝
⎜⎞
⎠
⎟
MAX8570–MAX8575
High-Efficiency LCD Boost
with True Shutdown
8 _______________________________________________________________________________________
Design Procedure
Inductor Selection
Smaller inductance values typically offer smaller physi-
cal size for a given series resistance or saturation cur-
rent. Circuits using larger inductance values may
provide more output power. The inductor’s saturation
current rating should be greater than the peak switch-
ing current. Recommended inductor values range from
10μH to 100μH.
Selecting the Current Limit
The peak LX current limit (ILX(MAX)) required for the
application is calculated from the following equation:
where POUT(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
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 recom-
mended 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.
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 volt-
age 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.
IP
V
P
LX MAX OUT MAX
BATT MIN
OUT
() ()
()
..≥× + ×125 125 (()
()
()MAX
BATT MIN
OUT MAX
VsP
L
⎛
⎝
⎜⎞
⎠
⎟+μ×
2
3
COMMON APPLICATION FAULTS RESULT WITH COMPETING
STEP-UP CONVERTERS RESULT WITH MAX8570 FAMILY
OUT to FB resistor missing or
disconnected.
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.
Table 1. Protection Features
MAX8570–MAX8575
High-Efficiency LCD Boost
with True Shutdown
_______________________________________________________________________________________ 9
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.
Applications Information
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 magni-
tude than the positive output by a forward diode drop. If
there is little or no load on the positive output, the nega-
tive 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.
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.
MAX8570–MAX8575
High-Efficiency LCD Boost
with True Shutdown
10 ______________________________________________________________________________________
Chip Information
PROCESS: BiCMOS
Package Information
For the latest package outline information and land patterns, go
to www.maxim-ic.com/packages.
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
6L μDFN L622+1 21-0164
6 SOT23 U6SN+1 21-0058
GND
LX
16V
CC
5SW
OUT
MAX8572
MAX8573
MAX8575
SOT23
2
34SHDN
+
GND
VCC
1
+
6LX
5SW
SHDN
MAX8570
μDFN
TOP VIEW
2
34FB
Pin Configurations (continued)
MAX8570–MAX8575
High-Efficiency LCD Boost
with True Shutdown
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.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
2 8/09 Added μDFN package 1, 2, 5, 9, 10
3 3/10 Added soldering temperature, corrected unit of measurement error, and
updated figure reference 2, 5, 9
