19-1327; Rev 1; 2/98
KIT
ATION
EVALU
BLE
AVAILA
DAC-Controlled Boost/Inverter
LCD Bias Supply with Internal Switch
General Description
____________________________Features
o
Internal 500mA, 28V N-Channel Switch
(no external FET required)
o
Adjustable Output Voltage to +27.5V or -27.5V
o
6-Bit DAC-Controlled Output Voltage
o
Up to 90% Efficiency
o
Small 16-Pin QSOP Package
(Same size as 8-pin SO)
o
Power-OK Indicator
o
65µA Quiescent Current
o
1.5µA Shutdown Current
o
Up to 300kHz Switching Frequency
MAX686
The MAX686 DAC-controlled boost/inverter IC converts
a positive input voltage to a positive or negative LCD
bias voltage up to +27.5V or -27.5V. The device features
an internal N-channel MOSFET switch, programmable
current limiting, and an internal 6-bit digital-to-
analog converter (DAC) for digital adjustment of the
output voltage. It comes in a small 16-pin QSOP pack-
age (same size as an 8-pin SO).
The MAX686 uses a current-limited, pulse-frequency-
modulation (PFM) control scheme to provide high effi-
ciency over a wide range of load conditions. Its high
switching frequency (up to 300kHz) allows the use of
small external components.
An
LCDON
output allows the LCD bias voltage to be
automatically disabled when the display logic voltage is
removed, protecting the display. The MAX686 has a
+2.7V to +5.5V input voltage range for the IC, and a
+0.8V to +27.5V input voltage range for the inductor.
Typical quiescent supply current is 65µA. Shutdown
current is 1.5µA.
The MAX686 offers high-level integration to save space,
reduce power consumption, and increase battery life,
making it an excellent choice for battery-powered
portable equipment. The MAX629 is similar to the
MAX686, except that it does not contain a built-in DAC.
Both devices have evaluation kits to facilitate designs.
Ordering Information
PART
MAX686C/D
MAX686EEE
TEMP. RANGE
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
Dice*
16 QSOP
*Dice
are specified at T
A
= +25°C, DC parameters only.
Functional Diagram appears at end of data sheet.
Applications
Positive or Negative LCD Bias
Personal Digital Assistants
Notebook Computers
Portable Data-Collection Terminals
Palmtop Computers
Varactor Tuning Diode Bias
V
IN
= 0.8V TO 27.5V
Typical Operating Circuit
22µH
MBR0530L
V
OUT
V
CC
= 2.7V TO 5.5V
0.1µF
R2
V
CC
V
DD
LX
DACOUT
LCDON
R3
Pin Configuration
TOP VIEW
PGND 1
UP 2
DN 3
POL 4
V
DD
5
ISET 6
SHDN 7
DACOUT 8
16 LX
15 N.C.
14 LCDON
FB
UP
DAC CONTROL
DN
ON/OFF
SHDN
POL
GND
POK
REF
ISET
PGND
0.1µF
MAX686
R1
MAX686
13 GND
12 V
CC
11 POK
10 FB
9
REF
QSOP
________________________________________________________________
Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 408-737-7600 ext. 3468.
DAC-Controlled Boost/Inverter
LCD Bias Supply with Internal Switch
MAX686
ABSOLUTE MAXIMUM RATINGS
Voltage
V
CC
, ISET, POK, POL,
SHDN,
UP, DN, V
DD
to GND ...........................................-0.3V to +6V
FB, REF, DACOUT to GND.......................-0.3V to (V
CC
+ 0.3V)
PGND to GND .....................................................-0.3V to +0.3V
LX,
LCDON
to GND..............................................-0.3V to +30V
Current
LX (sinking) .....................................................................600mA
LCDON
(sinking)...............................................................10mA
Continuous Power Dissipation (T
A
= +70°C)
QSOP (derate 8.30mW/°C above +70°C) ......................667mW
Operating Temperature Ranges
MAX686C/D ..........................................................0°C to +70°C
MAX686EEE.......................................................-40°C to +85°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10sec) .............................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
CC
= V
DD
= V
IN
= +5V, C
REF
= 0.1µF,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Supply Voltage (Note 1)
Input Voltage
Supply Current
Shutdown Current
V
CC
Undervoltage Lockout
V
CC
Undervoltage Lockout
Hysteresis
V
CC
DAC Reset Threshold
Line Regulation
Load Regulation
LX
LX Voltage Range
LX Switch Current Limit
LX On-Resistance
LX Leakage Current
Maximum LX On-Time
V
RESET
Boost configuration, V
OUT
= 27.5V,
I
LOAD
= 5mA, V
CC
= V
DD
= 2.7V to 5.5V
Boost configuration, V
OUT
= 27.5V,
I
LOAD
= 0mA to 5mA
V
LX
I
LX
R
LX
I
LXLEAK
t
ON
POL = GND, V
FB
> 1.2V
Minimum LX Off-Time
t
OFF
POL = V
CC
, V
FB
< 0.15V
POL = GND, V
FB
< 0.8V
POL = V
CC
, V
FB
> 0.4V
ISET = V
CC
ISET = GND
V
CC
= V
DD
= 5V, I
LX
= 100mA
V
CC
= V
DD
= 3.3V, I
LX
= 100mA
V
LX
= 28V
8
0.8
2.8
4
4
10
1
3.5
5
5
0.42
0.21
0.50
0.25
0.6
0.8
0.5
SYMBOL
V
CC
, V
DD
V
IN
I
CC
+ I
DD
I
SHDN
V
LOCK
Voltage applied to L1
POL = GND, V
FB
= 1.3V, I
DACOUT
= 0mA
SHDN
= GND
Rising or falling
2.10
CONDITIONS
MIN
2.7
0.8
65
1.3
2.5
100
1.5
0.1
0.01
2.1
TYP
MAX
5.5
V
OUT
125
4
2.65
UNITS
V
V
µA
µA
V
mV
V
%/V
%/mA
28
0.58
0.29
1.2
1.6
1.5
12
1.2
4.2
6
6
V
A
Ω
µA
µs
µs
2
_______________________________________________________________________________________
DAC-Controlled Boost/Inverter
LCD Bias Supply with Internal Switch
MAX686
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= V
DD
= V
IN
= +5V, C
REF
= 0.1µF,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
REFERENCE AND FB INPUT
REF Output Voltage
REF Load Regulation
FB Set Point
FB Input Bias Current
V
FB
I
FB
1.100
1.125
12
I
LCDON
V
LCDON
= 0.4V, V
POK
= 1.25V
V
LCDON
= 28V, V
POK
= GND
V
REF
-
0.015
0
6
MSA
DNL
R
DACOUT
2.7V < V
CC
= V
DD
< 5.5V
2.7V < V
CC
= V
DD
< 5.5V
UP, DN, T
A
= +25°C
UP, DN, T
A
= +25°C
UP, DN, T
A
= +25°C
2.4
±1
1
1
1
Mid-scale = V
REF
x 32/63
Guaranteed monotonic
-2
-1
1.5
0.7
2
1
2
6
0.02
1
V
REF
+
0.015
15
V
REF
V
CC
= V
DD
= 2.7V to 5.5V, no load
I
REF
= 0µA to 25µA, C
REF
= 0.1µF
I
REF
= 0µA to 50µA, C
REF
= 0.47µF
POL = GND
POL = V
CC
1.225
-15
1.225
1.250
1
1.5
1.250
0
1.275
15
±50
1.150
±50
1.275
10
V
mV
V
mV
nA
V
nA
mV
mA
µA
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
POWER OK COMPARATOR,
LCDON
OUTPUT
POK Threshold
V
POK
V
POK
rising
POK Input Current
POK Hysteresis
LCDON
Sink Current
LCDON
Leakage Current
DAC OUTPUT
(Notes 2, 3)
Full-Scale Output Voltage
Zero-Scale Output Voltage
Resolution
Mid-Scale Accuracy
Differential Nonlinearity
Output Resistance in Shutdown
V
FS
V
ZS
-50µA < I
DACOUT
< 0µA
0µA < I
DACOUT
< 20µA
I
POK
V
REF
V
mV
bits
%
LSB
kΩ
V
V
µA
µs
µs
µs
LOGIC INPUTS: POL, ISET, UP, DN,
SHDN
Input Low Level
V
IL
Input High Level
Input Bias Current
Pulse Width High
Pulse Width Low
Pulse Separation
V
IH
I
BIAS
t
PWH
t
PWL
t
PWS
_______________________________________________________________________________________
3
DAC-Controlled Boost/Inverter
LCD Bias Supply with Internal Switch
MAX686
ELECTRICAL CHARACTERISTICS
(V
CC
= V
DD
= V
IN
= +5V, C
REF
= 0.1µF,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 4)
PARAMETER
Supply Voltage (Note 1)
Input Voltage
Supply Current
Shutdown Current
V
CC
Undervoltage Lockout
LX
LX Voltage Range
LX Switch Current Limit
LX On-Resistance
LX Leakage Current
Maximum LX On-Time
SYMBOL
V
CC
, V
DD
V
IN
I
CC
+ I
DD
I
SHDN
V
LOCK
V
LX
I
LX
R
LX
I
LXLEAK
t
ON
POL = GND, V
FB
> 1.2V
Minimum LX Off-Time
t
OFF
POL = V
CC
, V
FB
< 0.15V
POL = GND, V
FB
< 0.8V
POL = V
CC
, V
FB
> 0.4V
REFERENCE AND FB INPUT
REF Output Voltage
REF Load Regulation
FB Set Point
FB Input Bias Current
V
FB
I
FB
1.05
2
V
REF
-
0.02
0
6
MSA
Mid-scale = V
REF
x 32/63
2.7V < V
CC
= V
DD
< 5.5V
2.7V < V
CC
= V
DD
< 5.5V
2.4
±1
-3
3
0.7
V
REF
+
0.02
15
V
REF
V
CC
= V
DD
= 2.7V to 5.5V, no load
I
REF
= 0µA to 25µA, C
REF
= 0.1µF
POL = GND
POL = V
CC
1.22
-15
ISET = V
CC
ISET = GND
V
CC
= V
DD
= 5V, I
LX
= 100mA
V
CC
= V
DD
= 3.3V, I
LX
= 100mA
V
LX
= 28V
7.5
0.7
2.8
3.8
3.8
1.22
0.4
0.2
Voltage applied to L1
POL = GND, VFB = 1.3V, I
DACOUT
= 0mA
SHDN
= GND
Rising or falling
2.10
CONDITIONS
MIN
2.7
0.8
TYP
MAX
5.5
V
OUT
125
4
2.65
28
0.6
0.3
1.2
1.6
1.5
12.5
1.3
4.2
6.2
6.2
1.28
10
1.28
15
±50
1.20
±50
V
LCDON
= 0.4V, V
POK
= 1.25V
V
mV
V
mV
nA
V
nA
mA
µs
UNITS
V
V
µA
µA
V
V
A
Ω
µA
µs
POWER OK COMPARATOR,
LCDON
OUTPUT
POK Threshold
V
POK
V
POK
rising
POK Input Current
LCDON
Sink Current
DAC OUTPUT
(Notes 2, 3)
Full-Scale Output Voltage
Zero-Scale Output Voltage
Resolution
Mid-Scale Accuracy
LOGIC INPUTS: POL, ISET, UP, DN,
SHDN
Input Low Level
V
IL
Input High Level
Input Bias Current
V
IH
I
BIAS
V
FS
V
ZS
-50µA < I
DACOUT
< 0µA
0µA < I
DACOUT
< 20µA
I
POK
I
LCDON
V
mV
Bits
%
V
V
µA
Note 1:
The MAX686 requires a supply voltage at V
CC
= V
DD
between +2.7V and +5.5V; however, the voltage that supplies the
inductor can vary from +0.8V to +27.5V, depending on circuit operating conditions.
Note 2:
The DAC output is set to its midpoint value at power-on.
Note 3:
The DAC setting is guaranteed to remain valid as long as V
CC
is greater than the V
CC
DAC Reset Threshold.
Note 4:
Specifications to -40°C are guaranteed by design, not production tested.
4
_______________________________________________________________________________________
DAC-Controlled Boost/Inverter
LCD Bias Supply with Internal Switch
__________________________________________Typical Operating Characteristics
(Circuits of Figures 1 and 2, V
CC
= V
DD
= V
IN
= +5V, L1 = 22µH,
SHDN
= V
CC
, C
REF
= 0.1µF, TA = +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
(V
OUT
= +24V)
MAX686 TOC01
MAX686
EFFICIENCY vs. LOAD CURRENT
(V
OUT
= +12V)
MAX686 TOC02
EFFICIENCY vs. LOAD CURRENT
(V
OUT
= -12V)
A: V
IN
= 9V, ISET = GND
B: V
IN
= 9V, ISET = V
CC
80
A
EFFICIENCY (%)
75
E
70
F
C: V
IN
= 5V, ISET = GND
D: V
IN =
5V, ISET = V
CC
E: V
IN =
3V, ISET = GND
F: V
IN
= 3V, ISET = V
CC
0.1
1
10
100
B
C
D
MAX686 TOC03
95
90
85
EFFICIENCY (%)
80
75
70
65
60
0.1
1
10
D
E F
A
B
C
95
90
85
EFFICIENCY (%)
80
75
70
65
60
A
C
E
85
B
D
F
A: V
IN
= 12V, ISET = V
CC
B: V
IN
= 12V, ISET = GND
C: V
IN
= 5V, ISET = V
CC
D: V
IN
= 5V, ISET = GND
E: V
IN
= 3V, ISET = GND
F: V
IN
= 3V, ISET = V
CC
100
A: V
IN
= 9V, ISET = V
CC
B: V
IN
= 9V, ISET = GND
C: V
IN
= 5V, ISET = V
CC
D: V
IN
= 5V, ISET = GND
E: V
IN
= 3V, ISET = GND
F: V
IN
= 3V, ISET = V
CC
0.1
1
10
100
1000
65
60
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
EFFICIENCY vs. LOAD CURRENT
(V
OUT
= -18V)
B
80
75
EFFICIENCY (%)
70
F
65
60
55
50
0.1
1
A: V
IN
= 9V, ISET = GND
B: V
IN
= 9V, ISET = V
CC
C: V
IN
= 5V, ISET = GND
D: V
IN
= 5V, ISET = V
CC
E: V
IN
= 3V, ISET = GND
F: V
IN
= 3V, ISET = V
CC
10
100
LOAD CURRENT (mA)
A
C
E
D
MAX686 TOC04
MAXIMUM OUTPUT CURRENT vs.
INPUT VOLTAGE (V
OUT
= +12V, +24V)
MAX686 TOC05
MAXIMUM OUTPUT CURRENT vs.
INPUT VOLTAGE (V
OUT
= -12V, -18V)
A&C
B&D
B
C
10
D
MAX686 TOC06
85
1000
100
A
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
A
100
B
C
D
10
A: V
OUT
= 12V, ISET = V
CC
B: V
OUT
= 12V, ISET = GND
C: V
OUT
= 24V, ISET = V
CC
D: V
OUT
= 24V, ISET = GND
1
0
2
4
6
8
10
12
14
INPUT VOLTAGE (V)
1
0
2
4
6
A: V
OUT
= -12V, ISET = V
CC
B: V
OUT
= -18V, ISET = V
CC
C: V
OUT
= -12V, ISET = GND
D: V
OUT
= -18V, ISET = GND
8
10
12
14
16
18
INPUT VOLTAGE (V)
INPUT CURRENT
vs. INPUT VOLTAGE
MAX686 TOC07
REFERENCE VOLTAGE
vs. LOAD CURRENT
1.251
REFERENCE VOLTAGE (V)
1.250
1.249
1.248
1.247
1.246
1.245
1.244
6
0
20
40
60
80
100
120
140
LOAD CURRENT (µA)
V
OUT
50mV/div
AC-COUPLED
V
IN
= V
CC
= 5V
C
REF
= 0.1µF
MAX686 TOC08
OUTPUT VOLTAGE RIPPLE
MAX686 TOC09
1000
1.252
INPUT CURRENT (µA)
100
V
OUT
50mV/div
AC-COUPLED
ISET = GND
10
V
CC
= V
IN
= V
DD
INPUT CURRENT = I
CC
+ I
DD
V
OUT
= 18V, NO LOAD
0
1
2
3
4
5
ISET = V
CC
V
OUT
= 24V
I
LOAD
= 5mA
20µs/div
1
INPUT VOLTAGE (V)
_______________________________________________________________________________________
5
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