General Description
The MAX1606 is a step-up DC-DC converter that contains 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 provides high efficiency over a wide range of load conditions. 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 current 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 requirements 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
Pin Configuration
V
IN
= 0.8V TO 5.5V
V
CC
= 2.4V TO 5.5V
V
OUT
= V
IN
TO 28V
ON
OFF
SHDN
V
CC
LIM
SW
BATT
GND
LX
FB
MAX1606
Typical Operating Circuit
19-1744; Rev 0; 7/00
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
TOP VIEW
BATT
1
FB
2
3
V
CC
4
8
SW
7
MAX1606
µMAX
SHDN
6
LIM
5
LXGND
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 (V
CC
+ 0.3V)
LX to GND ..............................................................-0.3V to +30V
Current into LX or BATT..............................................600mA
RMS
Current out of SW .......................................................600mA
RMS
Output Short-Circuit Duration ........................................Indefinite
Continuous Power Dissipation (T
A
= +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
)
µ
VCC Supply Voltage V
BATT Input Voltage Range V
VCC Undervoltage Lockout V
VCC Quiescent Supply Current I
VCC Shutdown Supply Current SHDN = GND 0.1 1 µA
BATT Input Supply Current I
BATT Shutdown Supply Current SHDN = GND 0.1 1 µA
VCC Line Regulation ∆V
BATT Line Regulation ∆V
Load Regulation ∆V
Efficiency L1 = 100µH, V
Feedback Set Point V
Feedback Input Bias Current I
INDUCTOR CONNECTIONS (LX, SW)
LX Voltage Range V
LX On-Resistance R
LX Leakage Current VLX = 28V 2 µA
Maximum LX On-Time t
Minimum LX Off-Time t
SW Leakage Current SW = GND, V
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
CC
BATT
UVLO
CC
BATT
LNR
LNR
LDR
FB
FB
LX(MAX
(Note 1) 2.4 5.5 V
(Note 1) 0.8 5.5 V
VCC falling, 30mV typical hysteresis 2.0 2.2 2.37 V
VFB = 1.3V 160 320 µA
VFB = 1.3V 20 40 µA
V
= 18V, I
OUT
= V
V
CC
LIM
V
= 18V, I
OUT
= V
V
CC
LIM
V
= 18V, VCC = V
OUT
I
= 0mA to 20mA
LOAD
= 1mA, V
LOAD
= 2.4V to 5.5V
= 1mA,
LOAD
= 3.3V, V
BATT
BATT
BATT
= 3.6V, I
= 3.6V,
BATT
= 0.8V to 5.5V
= V
= 3.3V,
LIM
= 10mA 88 %
LOAD
0.1 %/V
0.05 %/V
0.05 %/mA
1.225 1.25 1.275 V
VFB = 1.3V 5 100 nA
LX
LIM = V
CC
0.40 0.50 0.56
LIM = floating 0.20 0.25 0.285LX Switch Current Limit I
28 V
LIM = GND 0.10 0.125 0.15
LX
ON
OFF
VCC = 5V, I
VCC = 3.3V, ILX = 100mA 1 2
VFB > 1.1V 0.8 1.0 1.2
VFB < 0.8V (soft-start) 3.9 5.0 6.0
= 100mA 0.8
LX
10 13 16 µs
= 5.5V 1
BATT
A
Ω
µs
A
)
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.)
)
CONTROL INPUTS (SHDN, LIM)
SHDN Input Threshold
SHDN Input Bias Current I
LIM Input Low Level 2.4V ≤ VCC ≤ 5.5V 0.4 V
LIM Input Float Level
LIM Input High Level 2.4V ≤ VCC ≤ 5.5V
LIM Input Bias Current I
PMOS ISOLATION SWITCH (BATT to SW)
PMOS Current Limit V
PMOS On-Resistance R
Soft-Start Time t
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
V
IH
V
IL
SHDN
LIM
DS(ON
SS
2.4V ≤ VCC ≤ 5.5V
2.4V ≤ VCC ≤ 5.5V
VCC = 5.5V, V
2.4V ≤ V
I
LIM
SHDN = VCC, LIM = GND or V
SHDN = GND 0.1 1
C C
VCC = 2.5V, V
VCC = 2.5V, V
R
SW
≤ 5.5V,
CC
= ±0.5µA
= 2.5V, V
= 50Ω to GND
= 0 to 5.5V -1 1 µA
SHDN
CC
= 1.5V 0.65 0.85 1.5 A
BATT
= 1.5V, ISW = 100mA 0.25 0.4 Ω
BATT
= 1.5V,
BATT
0.8 ×
V
CC
( V
/ 2)
C C
- 0.25V
V
CC
- 0.4V
-2 2
0.3 ms
0.2 ×
V
CC
( V
/ 2)
C C
+ 0.25V
V
V
V
µA
VCC Supply Voltage V
BATT Input Voltage Range V
VCC Undervoltage Lockout V
VCC Quiescent Supply Current I
VCC Shutdown Supply Current SHDN = GND 1 µA
BATT Input Supply Current I
BATT Shutdown Supply Current SHDN = GND 1 µA
Feedback Set Point V
Feedback Input Bias Current I
INDUCTOR CONNECTIONS (LX, SW)
LX Voltage Range V
LX Switch Current Limit I
LX On-Resistance R
LX Leakage Current VLX = 28V 2 µA
Maximum LX On-Time t
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
CC
BATT
UVLO
CC
BATT
FB
FB
LX
LX(MAX
ON
(Note 1) 2.4 5.5 V
(Note 1) 0.8 5.5 V
VCC falling, 30mV typical hysteresis 2.0 2.37 V
VFB = 1.3V 360 µA
VFB = 1.3V 40 µA
1.215 1.285 V
VFB = 1.3V 100 nA
LIM = V
CC
LIM = floating 0.18 0.30
LIM = GND 0.08 0.17
VCC = 3.3V, ILX = 100mA 2 Ω
LX
0.35 0.58
917µs
28 V
A
)
Typical Operating Characteristics
(VCC= 3.3V, V
BATT
= 3.6V, L1 = 10µH, SHDN = LIM = VCC, V
OUT(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 (V
BATT
) 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)
Minimum LX Off-Time t
SW Leakage Current SW = GND, V
CONTROL INPUTS (SHDN, LIM)
SHDN Input Threshold
SHDN Input Bias Current I
LIM Input Low Level 2.4V ≤ VCC ≤ 5.5V 0.4 V
LIM Input Float Level
LIM Input High Level 2.4V ≤ VCC ≤ 5.5V
LIM Input Bias Current I
PMOS ISOLATION SWITCH (BATT to SW)
PMOS Current Limit VCC = 2.5V, V
PMOS On-Resistance R
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
OFF
V
V
SHDN
VFB > 1.1V 0.75 1.25
VFB < 0.8V (soft-start) 3.8 6.0
= 5.5V
BATT
IH
IL
2.4V ≤ VCC ≤ 5.5V
2.4V ≤ VCC ≤ 5.5V
VCC = 5.5V, V
2.4V ≤ V
I
= ±0.5µA
LIM
CC
SHDN
≤ 5.5V,
= 0 to 5.5V -1 1 µA
0.8 ×
V
CC
( V
C C
- 0.25V
V
CC
/ 2)
0.2 ×
( V
+ 0.25V
- 0.4V
LIM
DS(ON
SHDN = VCC, LIM = GND or V
CC
SHDN = GND 1
= 1.5V 0.65 1.5 A
BATT
VCC = 2.5V, V
= 1.5V, ISW = 100mA 0.4 Ω
BATT
-2 2
V
C C
1
CC
/ 2)
µs
µA
V
V
V
µA
OUTPUT VOLTAGE vs. SUPPLY VOLTAGE
18.2
18.1
18.0
17.9
17.8
OUTPUT VOLTAGE (V)
17.7
17.6
2.0 3.5 4.02.5 3.0 4.5 5.0 5.5
18.2
MAX1606 toc01
I
OUT
I
OUT
VCC (V)
= 5mA
= 1mA
18.1
18.0
17.9
17.8
OUTPUT VOLTAGE (V)
17.7
17.6
OUTPUT VOLTAGE vs. BATTERY VOLTAGE
I
= 5mA
OUT
I
= 1mA
OUT
0231 456
V
(V)
BATT
18.2
18.1
MAX1606 toc02
18.0
17.9
17.8
OUTPUT VOLTAGE (V)
17.7
17.6
OUTPUT VOLTAGE vs. LOAD CURRENT
LIM = GND
LIM = OPEN
0105 152025
LOAD CURRENT (mA)
LIM = V
CC
MAX1606 toc03
MAX1606
28V Internal Switch LCD Bias Supply
with True Shutdown
_______________________________________________________________________________________ 5
Typical Operating Characteristics (continued)
(VCC= 3.3V, V
BATT
= 3.6V, L1 = 10µH, SHDN = LIM = VCC, V
OUT(NOM)
= 18V (Figure 3), TA= +25°C, unless otherwise noted.)
EFFICIENCY vs. SUPPLY VOLTAGE
100
I
= 5mA
90
80
70
EFFICIENCY (%)
60
50
40
2.0 3.5 4.02.5 3.0 4.5 5.0 5.5
OUT
I
= 1mA
OUT
L1 = 10µH, LIM = V
L1 = 100µH, LIM = OPEN
VCC (V)
EFFICIENCY vs. LOAD CURRENT
(L1 = 47µH)
100
90
80
70
EFFICIENCY (%)
60
50
LIM = OPEN
LIM = GND
CC
LIM = V
EFFICIENCY vs. BATTERY VOLTAGE
100
90
MAX1606 toc04
80
70
60
50
EFFICIENCY (%)
40
30
20
021 3456
EFFICIENCY vs. LOAD CURRENT
(L1 = 100µH)
100
90
MAX1607 toc07
CC
80
70
EFFICIENCY (%)
60
50
LIM = OPEN
LIM = GND
EFFICIENCY vs. LOAD CURRENT
(L1 = 10µH)
MAX1606 toc05
100
90
80
70
EFFICIENCY (%)
60
50
40
0105 152025
LIM = OPEN
LIM = GND
LOAD CURRENT (mA)
I
= 5mA
OUT
I
= 1mA
OUT
L1 = 10µH, LIM = V
L1 = 100µH, LIM = OPEN
V
(V)
BATT
CC
PEAK INDUCTOR CURRENT LIMIT
vs. SUPPLY VOLTAGE
600
V
= 3.6V
BATT
500
MAX1607 toc08
400
LIM = V
CC
300
200
CURRENT LIMIT (mA)
100
LIM = V
LIM = V
CC
LIM = OPEN
LIM = GND
MAX1606 toc06
CC
MAX1606 toc09
40
010155202530
LOAD CURRENT (mA)
PEAK INDUCTOR CURRENT LIMIT
vs. BATTERY VOLTAGE
600
VCC = 3.3V
500
400
300
200
CURRENT LIMIT (mA)
100
0
0.5 2.51.5 3.5 4.5 5.5
V
BATT
(V)
LIM = V
LIM = OPEN
LIM = GND
CC
MAX1606 toc10
40
010155202530
LOAD CURRENT (mA)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
180
160
140
120
100
(mA)
CC
I
80
60
40
20
0
021345
VCC (V)
MAX1606 toc11
0
2.0 3.5 4.02.5 3.0 4.5 5.0 5.5
VCC (V)
SUPPLY CURRENT
vs. LOAD CURRENT
4.0
3.5
3.0
2.5
(mA)
2.0
CC
I
1.5
1.0
0.5
0
0 5 10 15 20 25
LIM = GND
(125mA)
LIM = OPEN
(250mA)
LOAD CURRENT (mA)
LIM = V
(500mA)
MAX1606 toc12
CC
MAX1606
28V Internal Switch LCD Bias Supply
with True Shutdown
6 _______________________________________________________________________________________
Pin Description
Typical Operating Characteristics (continued)
(VCC= 3.3V, V
BATT
= 3.6V, L1 = 10µH, SHDN = LIM = VCC, V
OUT(NOM)
= 18V (Figure 3), TA= +25°C, unless otherwise noted.)
0
17.9V
500mA
18.1V
18V
0
10mA
40µs/div
LOAD TRANSIENT
MAX1606 toc14
A: I
OUT
= 1mA TO 10mA, 10mA/div
B: V
OUT
= 18V, 100mV/div
C: I
L1
, 500mA/div
A
B
C
6V
4V
2V
18.1V
18V
17.9V
LINE TRANSIENT
MAX1606 toc13
A
B
500mA
20V
10V
SHUTDOWN WAVEFORM
4V
2V
0
0
0
MAX1606 toc15
A
B
C
400µs/div
= 1.8kΩ
OUT
A: V
= VCC = 2.4V TO 5.5V, 2V/div
BATT
= 18V, R
B: V
OUT
OUT
100µs/div
= 3.6kΩ, 100mV/div
A: V
B: V
C: I
L1
, 2V/div
SHDN
, 10V/div, R
OUT
, 500mA/div
PIN NAME FUNCTION
Inductor Supply Voltage, 0.8V to 5.5V. Internally connected to the source of a P-channel
1 BATT
2FB
3VCCIC Supply Voltage, 2.4V to 5.5V. Bypass VCC to GND with a 1µF or greater capacitor.
4 GND Ground
5LX
6 LIM
7 SHDN
8SW
MOSFET used to isolate the output from the input during shutdown. Bypass with a 10µF or
greater capacitor.
Feedback Input. Connect to a resistive divider network between the output and GND to set the
output voltage between V
and 28V. The feedback threshold is 1.25V.
BATT
Inductor Switching Connection. Internally connected to the drain of a 28V N-channel MOSFET.
LX is high impedance in shutdown.
Inductor Current-Limit Selection. Connect LIM to V
for 500mA, leave LIM floating for 250mA,
CC
or connect LIM to GND for 125mA.
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 Pchannel MOSFET between BATT and SW. Connect SHDN to V
for normal operation.
CC
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.
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 switching MOSFET with a 0.8Ω on-resistance and selectable
current limit (Figure 1) and consumes 160µA of supply
current. During startup, the MAX1606 extends the minimum off-time, limiting initial battery surge current. The
MAX1606 uses a P-channel MOSFET to isolate the output from the input during true shutdown mode. This isolation switch also includes short-circuit current limiting,
which protects the inductor and diode during a short-circuit fault.
Control Scheme
The MAX1606 features a minimum off-time, current-limited 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).
Figure 1. Functional Diagram
Figure 2. Setting the Peak Inductor Current Limit
VIN = 0.8V TO 5.5V BATT
SW
C2
= 2.4V TO 5.5V
V
CC
C1
ON
OFF
V
CC
(2.4V TO 5.5V)
V
CC
V
CC
LIM
SHDN
SHUTDOWN
LOGIC
V
CC
(2.4V TO 5.5V)
LOGIC
CONTROL
ERROR
AMPLIFIER
V
CC
MAX1606
CURRENT
LIMIT
1.25V
L1
10µH
LX
N
I
LIM
FB
V
CC
(2.4V TO 5.5V)
D1
C
FF
V
CC
V
= V
TO 28V
OUT
IN
C
OUT
R1
R2
MAX1606 MAX1606 MAX1606
LIM
GND
I
= 500mA I
PEAK
NO CONNECTION
LIM
GND
= 250mA I
PEAK
LIM
GND
PEAK
= 125mA
MAX1606
28V Internal Switch LCD Bias Supply
with True Shutdown
8 _______________________________________________________________________________________
Setting the Output Voltage (FB)
Adjust the output voltage by connecting a voltagedivider from the output (V
OUT
) to FB (Figure 3). Select
R2 between 10kΩ and 200kΩ. Calculate R1 with the following equation:
R1 = R2 [(V
OUT
/ VFB) – 1]
where VFB= 1.25V and V
OUT
may range from V
BATT
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 current (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 spacesensitive, low-power applications. Connect LIM to V
CC
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 disconnected from the input, and LX enters a high-impedance
state. The capacitance and load at the output determine the rate at which V
OUT
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 V
IN
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 V
BATT
and V
CC
Separate voltage sources can supply the inductor
(V
BATT
) and the IC (VCC). Since the chip bias is provided by a logic supply (2.4V to 5.5V), this allows the output power to be sourced directly from low-voltage
batteries (0.8V to 5.5V). Conversely, V
BATT
and V
CC
can also be supplied from one supply if it remains within VCC’s operating limits (2.4V to 5.5V).
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 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 maximum current limit from being reached before the maximum on-time expires. The inductor’s saturation current
rating should be greater than the peak switching current. 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 (I
LX(MAX)
) required for the
application may be calculated from the following equation:
where t
OFF(MIN)
= 0.8µs, and V
BATT(MIN)
is the minimum voltage used to supply the inductor. The set current 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 highspeed 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
Figure 3. Typical Application Circuit
L1
10µH
V
= 0.8V TO 5.5V
BATT
C2
10µF
= 2.4V TO 5.5V
V
CC
C1
1µF
ON
OFF
SW
BATT
V
CC
LIM
SHDN
MAX1606
GND
D1
LX
C
FF
10pF
FB
1MΩ
75k
V
OUT
R1
R2
= 18V
C
OUT
1µF
I
LX MAX
()
VI
×
OUT OUT MAX
≥
V
BATT MIN
()
()
VV t
OUT BATT MIN OFF MIN
()
+
−
×
() ()
L
×2
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 surface-mount output capacitor. For small ceramic capacitors, 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, VCCand V
BATT
, require bypass capacitors.
Bypass VCCwith a 1µF ceramic capacitor as close to
the IC as possible. The BATT input supplies high currents 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 voltages. A 10pF capacitor is sufficient for most applications. 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 layouts. Note that increasing CFFmay 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 output 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 ripple, 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 somewhat looser than with the standard positive output circuit, 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 typical values used for a positive-output design. When
loaded, the negative output voltage will be slightly
lower (closer to ground by approximately a diode forward voltage) than the inverse of the voltage on C4.
Figure 4. Negative Voltage for LCD Bias
Chip Information
TRANSISTOR COUNT: 3883
= 0.8V TO 5.5V
V
IN
C5
10µF
V
= 2.4V TO 5.5V
CC
C6
1µF
ON
OFF
SW
BATT
V
CC
LIM
SHDN
L1
10µH
MAX1606
D1, D2 = CENTRAL SEMICONDUCTOR
CMPD7000 (DUAL)
D3 = CENTRAL SEMICONDUCTOR
CMSD4448 (1N4148)
1Ω
D1
R3
D3
C1
0.1µF
LX
FB
GND
C4
0.01µF
C2
1µF
R1
240k
V
NEG
R2
16.5k
= -19V
C1
1nF
D2
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
© 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
Package Information
Loading...