General Description
The MAX1606 is a step-up DC-DC converter that con-
tains a 0.5A internal power switch and a 0.5A output
isolation switch in an 8-pin µMAX package. The IC
operates from a 2.4V to 5.5V supply voltage but can
boost battery voltages as low as 0.8V up to 28V.
The MAX1606 uses a unique control scheme that pro-
vides high efficiency over a wide range of load condi-
tions. An internal 0.5A MOSFET reduces external
component count, and a high switching frequency (up
to 500kHz) allows for tiny surface-mount components.
The current limit can be set to 500mA, 250mA, or
125mA, allowing the user to reduce the output ripple
and component size in low-current applications.
Additional features include a low quiescent supply cur-
rent and a true shutdown mode that saves power by
disconnecting the output from the input. The MAX1606
is ideal for small LCD panels with low current require-
ments but can also be used in other applications. A
MAX1606 evaluation kit is available to help speed up
design time.
________________________Applications
LCD Bias Generators
Cellular or Cordless Phones
Palmtop Computers
Personal Digital Assistants (PDAs)
Organizers
Handy Terminals
Features
♦Adjustable Output Voltage up to 28V
♦20mA at 20V from a Single Li+ Battery
♦True Shutdown (Output Disconnected from Input)
♦Output Short-Circuit Protection
♦88% Efficiency
♦Up to 500kHz Switching Frequency
♦Selectable Inductor Current Limit
(125mA, 250mA, or 500mA)
♦0.1µA Shutdown Current
♦8-Pin µMAX Package
MAX1606
28V Internal Switch LCD Bias Supply
with True Shutdown
________________________________________________________________ Maxim Integrated Products 1
1
2
3
4
8
7
6
5
SW
SHDN
LIM
LXGND
VCC
FB
BATT
MAX1606
µMAX
TOP VIEW
Pin Configuration
VIN = 0.8V TO 5.5V
VCC = 2.4V TO 5.5V
VOUT = VIN TO 28V
ON
OFF SHDN
VCC
LIM
SW
BATT
GND
LX
FB
MAX1606
Typical Operating Circuit
19-1744; Rev 1; 1/04
For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
Ordering Information
PART TEMP RANGE PIN-PACKAGE
MAX1606EUA
-40°C to +85°C8 µMAX
MAX1606
28V Internal Switch LCD Bias Supply
with True Shutdown
2_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC = 3.3V, VCC = BATT = SHDN, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°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.
VCC, FB, BATT, SW to GND .....................................-0.3V to +6V
BATT to SW ..............................................................-0.3V to +6V
SHDN, LIM to GND.....................................-0.3V to (VCC + 0.3V)
LX to GND ..............................................................-0.3V to +30V
Current into LX or BATT..............................................600mARMS
Current out of SW .......................................................600mARMS
Output Short-Circuit Duration ........................................Indefinite
Continuous Power Dissipation (TA= +70°C)
8-Pin µMAX (derate 4.1mW/°C above +70°C).............330mW
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
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
VCC Supply Voltage VCC (Note 1) 2.4 5.5 V
BATT Input Voltage Range
VBATT
(Note 1) 0.8 5.5 V
VCC Undervoltage Lockout
VUVLO
VCC falling, 30mV typical hysteresis 2.0 2.2
2.37
V
VCC Quiescent Supply Current ICC VFB = 1.3V
160
320 µA
VCC Shutdown Supply Current SHDN = GND 0.1 1 µA
BATT Input Supply Current IBATT VFB = 1.3V 20 40 µA
BATT Shutdown Supply Current SHDN = GND 0.1 1 µA
VCC Line Regulation
∆VLNR
VOUT = 18V, ILOAD = 1mA, VBATT = 3.6V,
VCC = VLIM = 2.4V to 5.5V 0.1 %/V
BATT Line Regulation
∆VLNR
VOUT = 18V, ILOAD = 1mA,
VCC = VLIM = 3.3V, VBATT = 0.8V to 5.5V
0.05
%/V
Load Regulation
∆VLDR
VOUT = 18V, VCC = VBATT = VLIM = 3.3V,
ILOAD = 0mA to 20mA
0.05
Efficiency L1 = 100µH, VBATT = 3.6V, ILOAD = 10mA 88 %
Feedback Set Point VFB
1.225 1.25 1.275
V
Feedback Input Bias Current IFB VFB = 1.3V 5 100 nA
INDUCTOR CONNECTIONS (LX, SW)
LX Voltage Range VLX 28 V
LIM = VCC
0.40 0.50 0.56
LIM = floating
0.20 0.25 0.285
LX Switch Current Limit
ILX
(
MAX
)
LIM = GND
0.10 0.125 0.15
A
VCC = 5V, ILX = 100mA 0.8
LX On-Resistance RLX VCC = 3.3V, ILX = 100mA 1 2 Ω
LX Leakage Current VLX = 28V 2 µA
Maximum LX On-Time tON 10 13 16 µs
VFB > 1.1V 0.8 1.0 1.2
Minimum LX Off-Time tOFF VFB < 0.8V (soft-start) 3.9 5.0 6.0 µs
SW Leakage Current SW = GND, VBATT = 5.5V
1
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
CONTROL INPUTS (SHDN, LIM)
VIH 2.4V ≤ VCC ≤ 5.5V 0.8 ×
VCC
SHDN Input Threshold
VIL 2.4V ≤ VCC ≤ 5.5V 0.2 ×
VCC
V
SHDN Input Bias Current ISHDN VCC = 5.5V, V
SHDN = 0 to 5.5V -1 +1 µA
LIM Input Low Level 2.4V ≤ VCC ≤ 5.5V 0.4 V
LIM Input Float Level 2.4V ≤ VCC ≤ 5.5V,
ILIM = ±0.5µA
( V
C C
/ 2)
- 0.25V
( V
C C
/ 2)
+ 0.25V
V
LIM Input High Level 2.4V ≤ VCC ≤ 5.5V
VCC
- 0.4V
V
SHDN = VCC, LIM = GND or VCC -2 +2
LIM Input Bias Current ILIM SHDN = GND 0.1 1 µA
PMOS ISOLATION SWITCH (BATT to SW)
PMOS Current Limit V
C C
= 2.5V, V
BATT = 1.5V 0.6
0.75
1.5 A
PMOS On-Resistance
RDS
(
ON
)
VCC = 2.5V, VBATT = 1.5V, ISW = 100mA
0.25
0.4 Ω
Soft-Start Time tSS VCC = 2.5V, VBATT = 1.5V,
RSW = 50Ω to GND 0.3 ms
MAX1606
28V Internal Switch LCD Bias Supply
with True Shutdown
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS
(VCC = 3.3V, VCC = BATT = SHDN, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 3.3V, VCC = BATT = SHDN, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
VCC Supply Voltage VCC (Note 1) 2.4 5.5 V
BATT Input Voltage Range
VBATT
(Note 1) 0.8
VOUT
V
VCC Undervoltage Lockout
VUVLO
VCC falling, 30mV typical hysteresis
2.00 2.37
V
VCC Quiescent Supply Current ICC VFB = 1.3V 360 µA
VCC Shutdown Supply Current SHDN = GND 1 µA
BATT Input Supply Current IBATT VFB = 1.3V 40 µA
BATT Shutdown Supply Current SHDN = GND 1 µA
Feedback Set Point VFB
1.215 1.285
V
Feedback Input Bias Current IFB VFB = 1.3V 100 nA
INDUCTOR CONNECTIONS (LX, SW)
LX Voltage Range VLX 28 V
LIM = VCC
0.35 0.58
LIM = floating
0.18 0.30
LX Switch Current Limit
ILX
(
MAX
)
LIM = GND
0.08 0.17
A
LX On-Resistance RLX VCC = 3.3V, ILX = 100mA 2 Ω
LX Leakage Current VLX = 28V 2 µA
Maximum LX On-Time tON 917µs
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
VFB > 1.1V
0.75 1.25
Minimum LX Off-Time tOFF VFB < 0.8V (soft-start) 3.8 6.0 µs
SW Leakage Current SW = GND, VBATT = 5.5V
1
µA
CONTROL INPUTS (SHDN, LIM)
VIH 2.4V ≤ VCC ≤ 5.5V 0.8 ×
VCC
SHDN Input Threshold
VIL 2.4V ≤ VCC ≤ 5.5V 0.2 ×
VCC
V
SHDN Input Bias Current
I
SHDN
VCC = 5.5V, V
SHDN = 0 to 5.5V -1 +1 µA
LIM Input Low Level 2.4V ≤ VCC ≤ 5.5V 0.4 V
LIM Input Float Level 2.4V ≤ VCC ≤ 5.5V,
ILIM = ±0.5µA
( V
C C
/ 2)
- 0.25V
( V
C C
/ 2)
+ 0.25V
V
LIM Input High Level 2.4V ≤ VCC ≤ 5.5V
VCC
- 0.4V
V
SHDN = VCC, LIM = GND or VCC -2 +2
LIM Input Bias Current ILIM SHDN = GND 1 µA
PMOS ISOLATION SWITCH (BATT to SW)
PMOS Current Limit VCC = 2.5V, VBATT = 1.5V
0.60
1.5 A
PMOS On-Resistance
RDS
(
ON
)
VCC = 2.5V, VBATT = 1.5V, ISW = 100mA 0.4 Ω
17.6
17.8
17.7
18.0
17.9
18.1
18.2
2.0 3.5 4.02.5 3.0 4.5 5.0 5.5
OUTPUT VOLTAGE vs. SUPPLY VOLTAGE
MAX1606 toc01
VCC (V)
OUTPUT VOLTAGE (V)
IOUT = 5mA
IOUT = 1mA
17.6
17.8
17.7
18.0
17.9
18.1
18.2
0231456
OUTPUT VOLTAGE vs. BATTERY VOLTAGE
MAX1606 toc02
VBATT (V)
OUTPUT VOLTAGE (V)
IOUT = 5mA
IOUT = 1mA
17.6
17.8
17.7
18.0
17.9
18.1
18.2
0105152025
OUTPUT VOLTAGE vs. LOAD CURRENT
MAX1606 toc03
LOAD CURRENT (mA)
OUTPUT VOLTAGE (V)
LIM = VCC
LIM = GND
LIM = OPEN
Typical Operating Characteristics
(VCC = 3.3V, VBATT = 3.6V, L1 = 10µH, SHDN = LIM = VCC, VOUT(NOM) = 18V (Figure 3), TA= +25°C, unless otherwise noted.)
Note 1: The MAX1606 requires a supply voltage between +2.4V and +5.5V; however, the input voltage (VBATT) used to power the
inductor can vary from +0.8V to 5.5V.
Note 2: Specifications to -40°C are guaranteed by design and not production tested.
MAX1606
28V Internal Switch LCD Bias Supply
with True Shutdown
4_______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 3.3V, VCC = BATT = SHDN, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)
MAX1606
28V Internal Switch LCD Bias Supply
with True Shutdown
_______________________________________________________________________________________ 5
40
60
50
80
70
90
100
2.0 3.5 4.02.5 3.0 4.5 5.0 5.5
EFFICIENCY vs. SUPPLY VOLTAGE
MAX1606 toc04
VCC (V)
EFFICIENCY (%)
IOUT = 5mA
IOUT = 1mA
L1 = 10µH, LIM = VCC
L1 = 100µH, LIM = OPEN
40
60
50
80
70
90
100
0105152025
EFFICIENCY vs. LOAD CURRENT
(L1 = 10µH)
MAX1606 toc06
LOAD CURRENT (mA)
EFFICIENCY (%)
LIM = GND
LIM = OPEN
LIM = VCC
Typical Operating Characteristics (continued)
(VCC = 3.3V, VBATT = 3.6V, L1 = 10µH, SHDN = LIM = VCC, VOUT(NOM) = 18V (Figure 3), TA= +25°C, unless otherwise noted.)
40
60
50
80
70
90
100
010155202530
EFFICIENCY vs. LOAD CURRENT
(L1 = 47µH)
MAX1607 toc07
LOAD CURRENT (mA)
EFFICIENCY (%)
LIM = GND
LIM = VCC
LIM = OPEN
40
60
50
80
70
90
100
010155202530
EFFICIENCY vs. LOAD CURRENT
(L1 = 100µH)
MAX1607 toc08
LOAD CURRENT (mA)
EFFICIENCY (%)
LIM = GND LIM = VCC
LIM = OPEN
0
200
100
400
300
500
600
2.0 3.5 4.02.5 3.0 4.5 5.0 5.5
PEAK INDUCTOR CURRENT LIMIT
vs. SUPPLY VOLTAGE
MAX1606 toc09
VCC (V)
CURRENT LIMIT (mA)
LIM = OPEN
LIM = GND
LIM = VCC
VBATT = 3.6V
0
200
100
400
300
500
600
0.5 2.51.5 3.5 4.5 5.5
PEAK INDUCTOR CURRENT LIMIT
vs. BATTERY VOLTAGE
MAX1606 toc10
VBATT (V)
CURRENT LIMIT (mA)
LIM = OPEN
LIM = GND
LIM = VCC
VCC = 3.3V
0
40
20
100
80
60
160
140
120
180
021345
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX1606 toc11
VCC (V)
ICC (mA)
20
30
40
50
60
70
80
90
100
0213456
EFFICIENCY vs. BATTERY VOLTAGE
MAX1606 toc05
VBATT (V)
EFFICIENCY (%)
L1 = 10µH, LIM = VCC
L1 = 100µH, LIM = OPEN
IOUT = 5mA
IOUT = 1mA
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
051015 20 25
SUPPLY CURRENT
vs. LOAD CURRENT
MAX1606 toc12
LOAD CURRENT (mA)
ICC (mA)
LIM = OPEN
(250mA)
LIM = VCC
(500mA)
LIM = GND
(125mA)
MAX1606
28V Internal Switch LCD Bias Supply
with True Shutdown
6_______________________________________________________________________________________
Pin Description
PIN NAME FUNCTION
1BATT
Inductor Supply Voltage, 0.8V to 5.5V. Internally connected to the source of a P-channel
MOSFET used to isolate the output from the input during shutdown. Bypass with a 10µF or
greater capacitor.
2FB
Feedback Input. Connect to a resistive divider network between the output and GND to set the
output voltage between VBATT and 28V. The feedback threshold is 1.25V.
3V
CC IC Supply Voltage, 2.4V to 5.5V. Bypass VCC to GND with a 1µF or greater capacitor.
4GND Ground
5LX
Inductor Switching Connection. Internally connected to the drain of a 28V N-channel MOSFET.
LX is high impedance in shutdown.
6LIM Inductor Current-Limit Selection. Connect LIM to VCC for 500mA, leave LIM floating for 250mA,
or connect LIM to GND for 125mA.
7SHDN
Active-Low Shutdown Input. A logic low shuts down the device and reduces the supply current
to 0.1µA. When shutdown, the MAX1606 isolates the output from the input by turning off the P-
channel MOSFET between BATT and SW. Connect SHDN to VCC for normal operation.
8SW
Isolation Switch Output, Inductor Connection. Internally connected to the drain of a P-channel
MOSFET used to isolate the output from the input during shutdown.
17.9V
18.1V
18V
2V
4V A
B
6V
100µs/div
LINE TRANSIENT
MAX1606 toc13
A: VBATT = VCC = 2.4V TO 5.5V, 2V/div
B: VOUT = 18V, ROUT = 3.6kΩ, 100mV/div
0
0
500mA
20V
10V
0
2V
4V
400µs/div
SHUTDOWN WAVEFORM
MAX1606 toc15
A
B
C
A: VSHDN, 2V/div
B: VOUT, 10V/div, ROUT = 1.8kΩ
C: IL1, 500mA/div
Typical Operating Characteristics (continued)
(VCC = 3.3V, VBATT = 3.6V, L1 = 10µH, SHDN = LIM = VCC, VOUT(NOM) = 18V (Figure 3), TA= +25°C, unless otherwise noted.)
0
7.9V
0mA
8.1V
18V
0
0mA
IOUT
10mA/div
40µs/div
MAX1606 toc14
VOUT = 18V, IOUT = 1mA TO 10mA
VCC = 3.3V, VIN,VBATT = 3.6V
VOUT
100mV/div
IL1
500mA/div
MAX1606
28V Internal Switch LCD Bias Supply
with True Shutdown
_______________________________________________________________________________________ 7
Detailed Description
The MAX1606 step-up DC-DC converter operates from a
2.4V to 5.5V supply and converts voltages as low as
0.8V up to 28V. The device includes an internal switch-
ing MOSFET with a 0.8Ωon-resistance and selectable
current limit (Figure 1) and consumes 160µA of supply
current. During startup, the MAX1606 extends the mini-
mum off-time, limiting initial battery surge current. The
MAX1606 uses a P-channel MOSFET to isolate the out-
put from the input during true shutdown mode. This isola-
tion switch also includes short-circuit current limiting,
which protects the inductor and diode during a short-cir-
cuit fault.
Control Scheme
The MAX1606 features a minimum off-time, current-limit-
ed control scheme. The duty cycle is governed by a pair
of one-shots that set a minimum off-time and a maximum
on-time. The switching frequency can be up to 500kHz
and depends upon the load and input voltage. The peak
current limit of the internal N-channel MOSFET is pin
selectable and may be set at 125mA, 250mA, or 500mA
(Figure 2).
N
ON
OFF
SHDN
VIN = 0.8V TO 5.5V BATT
VCC
LIM
SHUTDOWN
LOGIC
1.25V
FB
LX D1
R1
R2
SW
L1
10µH
LOGIC
CONTROL
VCC = 2.4V TO 5.5V
C1
C2
VOUT = VIN TO 28V
COUT
CFF
MAX1606
CURRENT
LIMIT
ERROR
AMPLIFIER
ILIM
Figure 1. Functional Diagram
Figure 2. Setting the Peak Inductor Current Limit
GND
LIM
GND
VCC VCC
LIM
GND
VCC
LIM NO CONNECTION
VCC
(2.4V TO 5.5V)
VCC
(2.4V TO 5.5V)
VCC
(2.4V TO 5.5V)
IPEAK = 500mA IPEAK = 250mA IPEAK = 125mA
MAX1606 MAX1606 MAX1606
MAX1606
28V Internal Switch LCD Bias Supply
with True Shutdown
8_______________________________________________________________________________________
Setting the Output Voltage (FB)
Adjust the output voltage by connecting a voltage-
divider from the output (VOUT) to FB (Figure 3). Select
R2 between 10kΩand 200kΩ. Calculate R1 with the fol-
lowing equation:
R1 = R2 [(VOUT / VFB) – 1]
where VFB = 1.25V and VOUT may range from VBATT to
28V. The input bias current of FB has a maximum value
of 100nA, which allows large-value resistors to be used.
For less than 1% error, the current through R2 should
be greater than 100 times the feedback input bias cur-
rent (IFB).
Current-Limit Select Pin (LIM)
The MAX1606 allows a selectable inductor current limit
of 125mA, 250mA, or 500mA (Figure 2). This allows
flexibility in designing for higher current applications or
for smaller, compact designs. The lower current limit
allows the use of a physically smaller inductor in space-
sensitive, low-power applications. Connect LIM to VCC
for 500mA, leave floating for 250mA, or connect to
GND for 125mA.
Shutdown (
SHDN
)
Pull SHDN low to enter shutdown. During shutdown the
supply current drops to 0.1µA, the output is discon-
nected from the input, and LX enters a high-impedance
state. The capacitance and load at the output deter-
mine the rate at which VOUT decays. SHDN can be
pulled as high as 6V, regardless of the input and output
voltages.
With the 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 VIN when the converter is shutdown and
allowing the output to draw power from the input. The
MAX1606 features true shutdown, which uses an internal
P-channel MOSFET to disconnect the output from the
input when the MAX1606 is shutdown. This eliminates
power drawn from the input during shutdown.
Separate/Same Power for VBATT and VCC
Separate voltage sources can supply the inductor
(VBATT) and the IC (VCC). Since the chip bias is provid-
ed by a logic supply (2.4V to 5.5V), this allows the out-
put power to be sourced directly from low-voltage
batteries (0.8V to 5.5V). Conversely, VBATT and VCC
can also be supplied from one supply if it remains with-
in VCC’s operating limits (2.4V to 5.5V).
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 start
up at lower input voltages and exhibit less ripple, but
also provide reduced output power. This occurs when
the inductance is sufficiently large to prevent the maxi-
mum current limit from being reached before the maxi-
mum on-time expires. The inductor’s saturation current
rating should be greater than the peak switching cur-
rent. However, it is generally acceptable to bias the
inductor into saturation by as much as 20%, although
this will slightly reduce efficiency.
Picking the Current Limit
The peak LX current limit (ILX(MAX)) required for the
application may be calculated from the following equa-
tion:
where tOFF(MIN) = 0.8µs, and VBATT(MIN) is the mini-
mum voltage used to supply the inductor. The set cur-
rent limit must be greater than this calculated value.
Select the appropriate current limit by connecting LIM
to VCC, GND, or leaving it unconnected (see Current-
Limit Select Pin and Figure 2).
Diode Selection
The high switching frequency of 500kHz requires a high-
speed rectifier. Schottky diodes, such as the Motorola
MBRS0530 or the Nihon EP05Q03L, are recommended.
To maintain high efficiency, the average current rating of
the Schottky diode should be greater than the peak
IVI
V
VV t
L
LX MAX OUT OUT MAX
BATT MIN
OUT BATT MIN OFF MIN
() ()
()
() ()
≥×+
−
()
×
×2
VBATT = 0.8V TO 5.5V
VCC = 2.4V TO 5.5V
VOUT = 18V
ON
OFF SHDN
VCC
LIM
SW
BATT
GND
LX
FB
MAX1606
COUT
1µF
C2
10µF
C1
1µF
CFF
10pF
D1
R1
1MΩ
R2
75k
L1
10µH
Figure 3. Typical Application Circuit
MAX1606
28V Internal Switch LCD Bias Supply
with True Shutdown
_______________________________________________________________________________________ 9
switching current. Choose a reverse breakdown voltage
greater than the output voltage.
Capacitors
For most applications, use a small 1µF ceramic sur-
face-mount output capacitor. For small ceramic capaci-
tors, the output ripple voltage is dominated by the
capacitance value. If tantalum or electrolytic capacitors
are used, the higher ESR increases the output ripple
voltage. Decreasing the ESR reduces the output ripple
voltage and the peak-to-peak transient voltage.
Surface-mount capacitors are generally preferred
because they lack the inductance and resistance of
their through-hole equivalents.
Two inputs, VCC and VBATT, require bypass capacitors.
Bypass VCC with a 1µF ceramic capacitor as close to
the IC as possible. The BATT input supplies high cur-
rents to the inductor and requires local bulk bypassing
close to the inductor. A 10µF low-ESR surface-mount
capacitor is sufficient for most applications.
A feed-forward capacitor connected from the output to
FB improves stability over a wide range of battery volt-
ages. A 10pF capacitor is sufficient for most applica-
tions. Larger values (up to 47pF) may be needed with
lower current-limit settings (LIM = GND or open) and
low input voltages, or with nonoptimum PC board lay-
outs. Note that increasing CFF may slightly affect load
regulation.
PC Board Layout and Grounding
Careful printed circuit layout is important for minimizing
ground bounce and noise. Keep the MAX1606’s
ground pin and the ground leads of the input and out-
put capacitors less than 0.2in (5mm) apart. In addition,
keep all connections to FB and LX as short as possible.
In particular, external feedback resistors should be as
close to FB as possible. To minimize output voltage rip-
ple, and to maximize output power and efficiency, use a
ground plane and solder GND directly to the ground
plane. Refer to the MAX1606EVKIT evaluation kit for a
layout example.
Applications Information
Negative Voltage for LCD Bias
The MAX1606 can also generate a negative output by
adding a diode-capacitor charge-pump circuit (D1, D2,
and C3) to the LX pin as shown in Figure 4. Feedback
is still connected to the positive output, which is not
loaded, allowing a very small capacitor value at C4. For
best stability and lowest ripple, the time constant of the
R1-R2 series combination and C4 should be near or
less than that of C2 and the effective load resistance.
Output load regulation of the negative output is some-
what looser than with the standard positive output cir-
cuit, and may rise at very light loads due to coupling
through the capacitance of D2. If this is objectionable,
reduce the resistance of R1 and R2, while maintaining
their ratio, to effectively preload the output with a few
hundred microamps. This is why the R1-R2 values
shown in Figure 4 are about four-times lower than typi-
cal values used for a positive-output design. When
loaded, the negative output voltage will be slightly
lower (closer to ground by approximately a diode for-
ward voltage) than the inverse of the voltage on C4.
VCC = 2.4V TO 5.5V
D3
R2
16.5k
R1
240k
ON
L1
10µH
C6
1µF
C5
10µFC4
0.01µF
C1
1nF
C1
0.1µF
R3
1Ω
VIN = 0.8V TO 5.5V
D1, D2 = CENTRAL SEMICONDUCTOR
CMPD7000 (DUAL)
D3 = CENTRAL SEMICONDUCTOR
CMSD4448 (1N4148)
VNEG = -19V
D2
D1 C2
1µF
SHDN
VCC
LIM
SW
BATT
GND
LX
FB
MAX1606
OFF
Figure 4. Negative Voltage for LCD Bias
Chip Information
TRANSISTOR COUNT: 3883
MAX1606
28V Internal Switch LCD Bias Supply
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.
10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
©2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
8LUMAXD.EPS
PACKAGE OUTLINE, 8L uMAX/uSOP
1
1
21-0036 J
REV.DOCUMENT CONTROL NO.APPROVAL
PROPRIETARY INFORMATION
TITLE:
MAX
0.043
0.006
0.014
0.120
0.120
0.198
0.026
0.007
0.037
0.0207 BSC
0.0256 BSC
A2 A1
c
eb
A
L
FRONT VIEW SIDE VIEW
E H
0.6±0.1
0.6±0.1
ÿ0.50±0.1
1
TOP VIEW
D
8
A2 0.030
BOTTOM VIEW
16∞
S
b
L
H
E
D
e
c
0∞
0.010
0.116
0.116
0.188
0.016
0.005
8
4X S
INCHES
-
A1
A
MIN
0.002
0.950.75
0.5250 BSC
0.25 0.36
2.95 3.05
2.95 3.05
4.78
0.41
0.65 BSC
5.03
0.66
6∞0∞
0.13 0.18
MAX
MIN
MILLIMETERS
-1.10
0.05 0.15
α
α
DIM
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.)