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19-1353; Rev 1; 6/03
ANUAL
N KIT M EET
ATIO
SH
EVALU
S DATA
OLLOW
F
Dual-Output (Positive and Negative),
DC-DC Converter for CCD and LCD
Features
o
Dual Output Using a Single Inductor
o
Low-Noise Output, 30mVp-p Ripple
o
Output Voltages up to 24V and down to -9V
(up to 45V and down to -16V with added
components)
o
Internal Switches in a Small 24-Pin 4mm x 4mm
Thin QFN Package
o
220kHz/400kHz Fixed-Frequency PWM Operation
o
Frequency Can Be Synchronized to External
Clock
o
Power-OK Indicator
o
Selectable Power-On Sequencing
o
0.1µA Logic-Controlled Shutdown
General Description
The MAX685 DC-DC converter provides low-noise dual
outputs for powering CCD imaging devices and LCDs.
This device uses a single inductor to provide indepen-
dently regulated positive and negative outputs.
Integrated power switches are included in a small 24-
Pin 4mm x 4mm Thin QFN package to save space and
reduce cost. A 16-pin QSOP package is also available.
Each output delivers up to 10mA from a +2.7V to +5.5V
input voltage range. Output voltages are set indepen-
dently up to 24V and down to -9V. With a few additional
low-cost components, the output voltages can be set at
up to 45V and down to -16V. Output ripple magnitude is
30mVp-p. The MAX685 uses a fixed-frequency, pulse-
width-modulated (PWM) control scheme at 220kHz or
400kHz to permit output noise filtering and to reduce
the size of external components. The frequency can
also be synchronized to an external clock signal
between 200kHz and 480kHz.
The MAX685 has a power-OK indicator output (POK)
that signals when both outputs are within regulation. A
logic-controlled shutdown completely turns off both out-
puts and reduces supply current to 0.1µA. The user
can also set which output turns on first.
The preassembled MAX685 evaluation kit is available to
reduce design time.
MAX685
Ordering Information
PART
MAX685EEE
MAX685ETG
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
16 QSOP
24 TQFN
Applications
Camcorders
Digital Cameras
Notebooks
LCDs
CCD Imaging Devices
INPUT
2.7V TO 5.5V
Typical Operating Circuit
Pin Configuration
LXN
LXN
LXP
LXP
VP
V
DD
LXN
POSITIVE
OUTPUT
UP TO 24V,
10mA
TOP VIEW
I.C.
I.C.
FBP
ON
OFF
18
17
16
N.C.
PGND
PGND
PGND
FBP
REF
SHDN
MAX685
24
23
22
21
20
N.C.
VP
VP
POK
SEQ
SHDN
1
2
3
4
5
6
10
11
12
7
8
9
19
OPTIONAL
POS
NEG
SYNC
LXP
NEGATIVE
OUTPUT
DOWN TO -9V,
10mA
MAX685
15
14
13
SEQ
FBN
POWER-OK
INDICATOR
POK
GND
REF
V
DD
N.C.
________________________________________________________________
Maxim Integrated Products
SYNC
24-TQFN (4mm x 4mm)
GND
N.C.
FBN
1
For pricing delivery, and ordering information please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Dual-Output (Positive and Negative),
DC-DC Converter for CCD and LCD
MAX685
ABSOLUTE MAXIMUM RATINGS
V
DD
, VP to GND........................................................-0.3V to +6V
PGND to GND .......................................................-0.3V to +0.3V
V
DD
to VP...............................................................-0.3V to +0.3V
LXN, POK to GND ..................................................-0.3V to +30V
LXP to V
DD
..............................................................-15V to +0.3V
REF, SEQ,
SHDN
to GND...........................-0.3V to (V
DD
+ 0.3V)
FBP, FBN, SYNC to GND .........................................-0.3V to +6V
Continuous Power Dissipation (T
A
= +70°C)
16-Pin QSOP (derate 8.3mW/°C above +70°C)............667mW
24-Pin TQFN (derate 20.8mW/°C above +70°C) ........1667mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +165°C
Lead Temperature (soldering, 10s) .................................+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
DD
= VP = 5V,
T
A
= 0°C to +85°C
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Input Voltage Range
Positive Output Voltage Range
Negative Output Voltage Range
Output Current
LX Current Limit
LXP, LXN On-Resistance
Quiescent Current
Idle Quiescent Current
Line Regulation
Load Regulation
Output Voltage Ripple
SHUTDOWN (SHDN)
Shutdown Supply Current
UNDERVOLTAGE LOCKOUT
UVLO Threshold
UVLO Hysteresis
REFERENCE VOLTAGE
V
REF
Output Voltage
V
REF
Load Regulation
FB INPUTS
FBP Threshold Voltage
FBN Threshold Voltage
FBP, FBN Input Leakage Current
LOGIC INPUTS
(SEQ,
SHDN,
SYNC)
Logic-Low Input
Logic-High Input
Input Bias Current
2.7V < V
DD
< 5.5V
2.7V < V
DD
< 5.5V
0.7 x V
DD
0.1
1
0.3 x V
DD
V
V
µA
No load
No load
1.21
-16
1.24
10
±0.01
1.27
36
±0.1
V
mV
µA
No load
0 < I
REF
< 50µA
1.23
1.250
-2
1.27
V
mV
V
DD
= rising
2.35
2.5
50
2.65
V
mV
SYNC = SEQ =
SHDN
= GND
0.1
10
µA
V
DD
= 5.5V (Note 1)
V
DD
= 4.5V, V
OUT+
≥
14.25V, V
OUT-
≤
-7.125V,
Figure 3
T
A
= +25°C
V
DD
= 4.5V
SYNC = V
DD
V
FBP
= 1.35V, V
FBN
= -0.1V
V
DD
= 4.5V to 5.5V
I
OUT
= 0 to 10mA, C1 = 10µF
C3 = C4 = 10µF, I
LOAD
= 5mA
V
DD
= VP
CONDITIONS
MIN
2.7
VP
-9
10
440
0.6
0.8
300
0.2
0.13
30
500
2
TYP
MAX
5.5
24
-1.27
UNITS
V
V
V
mA
mA
Ω
mA
µA
%/V
%/mA
mVp-p
2
_______________________________________________________________________________________
Dual-Output (Positive and Negative),
DC-DC Converter for CCD and LCD
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= VP = 5V,
T
A
= 0°C to +85°C
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
SYNC INPUT
Sync Frequency Range (external)
Oscillator Frequency (internal)
POK COMPARATORS
FBP POK Threshold
FBN POK Threshold
POK Output Low Voltage
POK Output Off Current
FBP rising
FBN falling
I
POK
= 2mA
V
POK
= 10V
1.090
54
1.122
79
1.150
108
0.4
1
V
mV
V
µA
SYNC = GND
SYNC = V
DD
200
175
320
220
400
480
265
480
kHz
kHz
CONDITIONS
MIN
TYP
MAX
UNITS
MAX685
ELECTRICAL CHARACTERISTICS
(V
DD
, VP = 5V,
T
A
= -40°C to +85°C
unless otherwise noted.) (Note 2)
PARAMETER
Input Voltage Range
Positive Output Voltage Range
Negative Output Voltage Range
Maximum Output Current
Idle Quiescent Current
SHUTDOWN
Shutdown Supply Current
UNDERVOLTAGE LOCKOUT
UVLO Threshold
FBP Threshold Voltage
FBN Threshold Voltage
VREF Output Voltage
LOGIC INPUTS
(SEQ,
SHDN,
SYNC)
Logic-Low Input
Logic-High Input
POK COMPARATORS
FBP POK Threshold
FBN POK Threshold
FBP rising
FBN falling
1.090
54
1.150
108
V
mV
2.7V < V
DD
≤
5.5V
2.7V < V
DD
≤
5.5V
0.7 x V
DD
0.3 x V
DD
V
V
V
DD
= rising
No load
No load
No load
2.35
1.205
-20
1.225
2.65
1.275
40
1.275
V
V
mV
V
FB INPUTS AND REFERENCE VOLTAGE
SYNC = SEQ =
SHDN
= GND
10
µA
V
DD
= 5.5V (Note 1)
V
IN
= 4.5V, V
OUT+
≥
14.25V, V
OUT-
≤
-7.125V,
Figure 3
SYNC = GND
V
DD
= VP
CONDITIONS
MIN
2.7
VP
-9
10
500
MAX
5.5
24
-1.27
UNITS
V
V
V
mA
µA
Note 1:
Negative output voltage can be larger magnitude for lower values of V
DD
. The voltage between V
DD
and V
OUT-
must not
exceed 14.5V.
Note 2:
Specifications to -40°C are guaranteed by design, not production tested.
_______________________________________________________________________________________
3
Dual-Output (Positive and Negative),
DC-DC Converter for CCD and LCD
MAX685
Typical Operating Characteristics
(Circuit of Figure 3, V
OUT+
= 15V, V
OUT-
= -7.5V, T
A
= +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
(POSITIVE OUTPUT LOADED)
MAX685-01
EFFICIENCY vs. LOAD CURRENT
(NEGATIVE OUTPUT LOADED)
MAX685-02
EFFICIENCY vs. LOAD CURRENT
(BOTH OUTPUTS LOADED)
85
80
EFFICIENCY (%)
75
70
65
60
55
50
V
IN
= 5.0V
V
IN
= 3.3V
MAX685-03
90
V
IN
= 5.0V
EFFICIENCY (%)
80
V
IN
= 3.3V
85
V
IN
= 5.0V
80
75
EFFICIENCY (%)
70
65
60
55
V
IN
= 3.3V
90
70
60
0
2
4
6
8
10
LOAD CURRENT (mA)
50
0
1
2
3
4
5
6
7
8
9
10
LOAD CURRENT (mA)
0
2
4
6
8
10
LOAD CURRENT (mA)
NO-LOAD CURRENT vs.
INPUT VOLTAGE
MAX685-04
REFERENCE LOAD REGULATION
MAX685-06
2.0
1.250
NO-LOAD CURRENT (mA)
1.5
REFERENCE VOLTAGE (V)
1.0
1.249
0.5
0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
1.248
0
5
10 15 20 25 30 35 40 45 50
LOAD CURRENT (µA)
LX SWITCHING FREQUENCY
vs. INPUT VOLTAGE
MAX865-07
REFERENCE VOLTAGE
vs. TEMPERATURE
MAX685-13
250
240
OSCILLATOR FREQUENCY (kHz)
230
1.254
1.252
REFERENCE VOLTAGE (V)
1.250
1.248
1.246
1.244
1.242
1.240
V
IN
= 3.3V
V
IN
= 5.0V
220
210
200
190
180
170
160
150
2.7
3.2
3.7
4.2
4.7
5.2
5.7
INPUT VOLTAGE (V)
SYNC = V
DD
-40
-20
0
20
40
60
80
100
TEMPERATURE (°C)
4
_______________________________________________________________________________________
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