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MAX685EEE+ |MAX685EEEMAXN/a2950avaiDual-Output (Positive and Negative), DC-DC Converter for CCD and LCD
MAX685EEE+TMAXIMN/a2500avaiDual-Output (Positive and Negative), DC-DC Converter for CCD and LCD
MAX685EEE-T |MAX685EEETMAXIMN/a596avaiDual-Output (Positive and Negative), DC-DC Converter for CCD and LCD


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MAX685EEE+-MAX685EEE+T-MAX685EEE-T
Dual-Output (Positive and Negative), DC-DC Converter for CCD and LCD
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.
Applications

CamcordersLCDs
Digital CamerasCCD Imaging Devices
Notebooks
Features
Dual Output Using a Single InductorLow-Noise Output, 30mVp-p RippleOutput Voltages up to 24V and down to -9V
(up to 45V and down to -16V with added
components)
Internal Switches in a Small 24-Pin 4mm x 4mm
Thin QFN Package
220kHz/400kHz Fixed-Frequency PWM OperationFrequency Can Be Synchronized to External
Clock
Power-OK IndicatorSelectable Power-On Sequencing0.1µA Logic-Controlled Shutdown
MAX685
Dual-Output (Positive and Negative),
DC-DC Converter for CCD and LCD

MAX685
VDD
OFF
INPUT
2.7V TO 5.5V
LXN
FBP
LXP
FBN
REFGND
NEGATIVE
OUTPUT
DOWN TO -9V,
10mA
POSITIVE
OUTPUT
UP TO 24V,
10mA
SHDN
SYNC
SEQ
POK
POS
NEG
OPTIONAL
POWER-OK
INDICATOR2322212019891112
MAX685
24-TQFN (4mm x 4mm)

TOP VIEW
N.C.
POK
SEQ
SHDN
I.C.LXPLXPLXNLXNI.C.
N.C.
PGND
PGND
PGND
FBP
REF
FBN
GNDN.C.N.C.
SYNCypical Operating Circuit
19-1353; Rev 1; 6/03
PART

MAX685EEE-40°C to +85°C
TEMP RANGEPIN-PACKAGE

16 QSOP
EVALUATION KIT MANUAL
FOLLOWS DATA SHEET
Pin Configuration
Ordering Information

MAX685ETG-40°C to +85°C24 TQFN
MAX685
Dual-Output (Positive and Negative),
DC-DC Converter for CCD and LCD
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS

(VDD= VP = 5V, 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.
VDD, VP to GND........................................................-0.3V to +6V
PGND to GND.......................................................-0.3V to +0.3V
VDDto VP...............................................................-0.3V to +0.3V
LXN, POK to GND..................................................-0.3V to +30V
LXP to VDD..............................................................-15V to +0.3V
REF, SEQ, SHDNto GND...........................-0.3V to (VDD+ 0.3V)
FBP, FBN, SYNC to GND.........................................-0.3V to +6V
Continuous Power Dissipation (TA= +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
2.7V < VDD< 5.5V
2.7V < VDD< 5.5V
VDD= 5.5V (Note 1)
No load
VDD= VP
No load
C3 = C4 = 10µF, ILOAD= 5mA
IOUT= 0 to 10mA, C1 = 10µF
VDD= rising
VDD= 4.5V to 5.5V
VFBP= 1.35V, VFBN= -0.1V
VDD= 4.5V, VOUT+≥14.25V, VOUT-≤-7.125V,
Figure 3= +25°C
VDD= 4.5V
SYNC = SEQ = SHDN= GND
SYNC = VDD
CONDITIONS
0.11Input Bias Current0.7 x VDDLogic-High Input0.3 x VDDLogic-Low Input±0.01±0.1FBP, FBN Input Leakage Current-161036FBN Threshold Voltage1.211.241.27FBP Threshold Voltage50UVLO Hysteresis2.352.52.65UVLO Threshold0.110Shutdown Supply Current-9-1.27Negative Output Voltage RangeVP242.75.5Input Voltage Range
Positive Output Voltage Range
mVp-p30Output Voltage Ripple
%/mA0.13Load Regulation
%/V0.2Line Regulation300500Idle Quiescent Current10Output Current440LX Current Limit0.62LXP, LXN On-Resistance0.8Quiescent Current
UNITSMINTYPMAXPARAMETER

0 < IREF< 50µA
No load-2VREFLoad Regulation1.231.2501.27VREFOutput Voltage
SHUTDOWN (SHDN)
UNDERVOLTAGE LOCKOUT
REFERENCE VOLTAGE
FB INPUTS
LOGIC INPUTS (SEQ, SHDN, SYNC)
MAX685
Dual-Output (Positive and Negative),
DC-DC Converter for CCD and LCD
ELECTRICAL CHARACTERISTICS (continued)

(VDD= VP = 5V, TA= 0°C to +85°C unless otherwise noted. Typical values are at TA= +25°C.)
ELECTRICAL CHARACTERISTICS

(VDD, VP = 5V, TA= -40°C to +85°C unless otherwise noted.) (Note 2)
Note 1:
Negative output voltage can be larger magnitude for lower values of VDD. The voltage between VDDand VOUT-must not
exceed 14.5V.
Note 2:
Specifications to -40°C are guaranteed by design, not production tested.
VDD= 5.5V (Note 1)
VDD= VP
No load
VDD= rising
VIN= 4.5V, VOUT+≥14.25V, VOUT-≤-7.125V,
Figure 3
SYNC = GND
SYNC = SEQ = SHDN= GND
CONDITIONS
-9-1.27Negative Output Voltage RangeVP242.75.5Input Voltage Range
Positive Output Voltage Range1.2051.275FBP Threshold Voltage2.352.65UVLO Threshold10Maximum Output Current500Idle Quiescent Current10Shutdown Supply Current
UNITSMINMAXPARAMETER
CONDITIONS

SYNC = VDD
SYNC = GNDkHz320400480Oscillator Frequency (internal)175220265
kHz200480Sync Frequency Range (external)
IPOK = 2mA
FBN falling
FBP rising0.4POK Output Low Voltage
UNITSMINTYPMAX
79108
PARAMETER

FBN POK Threshold1.0901.1221.150FBP POK Threshold
VPOK = 10VµA1POK Output Off Current
2.7V < VDD≤5.5V
No load0.3 x VDDLogic-Low Input-2040FBN Threshold Voltage
2.7V < VDD≤5.5VV0.7 x VDDLogic-High Input
FBP risingV1.0901.150FBP POK Threshold
FBN fallingmV54108FBN POK Threshold
SYNC INPUT
POK COMPARATORS

No loadV1.2251.275VREF Output Voltage
SHUTDOWN
UNDERVOLTAGE LOCKOUT
FB INPUTS AND REFERENCE VOLTAGE
LOGIC INPUTS (SEQ, SHDN, SYNC)
POK COMPARATORS
REFERENCE VOLTAGE
vs. TEMPERATURE
MAX685-13
TEMPERATURE (°C)
REFERENCE VOLTAGE (V)
VIN = 5.0V
VIN = 3.3V
MAX685
Dual-Output (Positive and Negative),
DC-DC Converter for CCD and LCD
26810
EFFICIENCY vs. LOAD CURRENT
(POSITIVE OUTPUT LOADED)

MAX685-01
LOAD CURRENT (mA)
EFFICIENCY (%)
VIN = 5.0V
VIN = 3.3V2351679810
EFFICIENCY vs. LOAD CURRENT
(NEGATIVE OUTPUT LOADED)

MAX685-02
LOAD CURRENT (mA)
EFFICIENCY (%)
VIN = 5.0V
VIN = 3.3V26810
EFFICIENCY vs. LOAD CURRENT
(BOTH OUTPUTS LOADED)

MAX685-03
LOAD CURRENT (mA)
EFFICIENCY (%)
VIN = 5.0V
VIN = 3.3V
NO-LOAD CURRENT vs.
INPUT VOLTAGE
MAX685-04
INPUT VOLTAGE (V)
NO-LOAD CURRENT (mA)
LX SWITCHING FREQUENCY
vs. INPUT VOLTAGE
MAX865-07
INPUT VOLTAGE (V)
OSCILLATOR FREQUENCY (kHz)
SYNC = VDD
REFERENCE LOAD REGULATION
MAX685-06
LOAD CURRENT (µA)
REFERENCE VOLTAGE (V)
Typical Operating Characteristics

(Circuit of Figure 3, VOUT+= 15V, VOUT- = -7.5V, TA= +25°C, unless otherwise noted.)
MAX685
Dual-Output (Positive and Negative),
DC-DC Converter for CCD and LCD

11mA
5mA/div
100mV/div
1mA
IOUT+
VOUT+
2ms/div
VOUT+ LOAD-TRANSIENT RESPONSE

MAX685-08-1mA
5mA/div
100mV/div
-11mA
IOUT-
VOUT-
2ms/div
VOUT- LOAD-TRANSIENT RESPONSE

MAX685-09
100mV/div
VOUT+
VOUT-
VDD, VP2V/div
100mV/div
1ms/div
INPUT 4V TO 5V, +15V AT 10mA, -7.5V AT 10mA
LINE-TRANSIENT RESPONSE

MAX685-10
5V/div
VOUT+
VOUT-
5V/div
2ms/div
START-UP, SEQ = LOW, VDD = VP = 5.0V,
+15V AT 10mA, -7.5V AT 10mA
START-UP (SEQ = LOW)

MAX685-11
5V/div
VOUT+
VOUT-5V/div
2ms/div
START-UP, SEQ = HIGH, VDD = VP = 5.0V,
+15V AT 10mA, -7.5V AT 10mA
START-UP (SEQ = HIGH)

MAX685-12
Typical Operating Characteristics (continued)

(Circuit of Figure 3, VOUT+= 15V, VOUT- = -7.5V, TA= +25°C, unless otherwise noted.)
_______________Detailed Description
The MAX685 DC-DC converter accepts an input voltage
between +2.7V and +5.5V and generates both a positive
and negative voltage, using a single inductor (Figure 1).
It alternates between acting as a step-up converter and
as an inverting converter on a cycle-by-cycle basis. Both
output voltages are independently regulated.
Each output is separately controlled by a pulse-width-
modulated (PWM) current mode regulator. This allows
the part to operate at a fixed frequency for use in noise-
sensitive applications. An internal oscillator runs at
220kHz or 400kHz, or can be synchronized to an exter-
nal signal. Since switching alternates between the two
regulators, each operates at half the oscillator frequency
(110kHz, 200kHz, or half the sync frequency). The oscil-
lator can be synchronized to a 200kHz to 480kHz clock.
On the first cycle of operation, the part operates as a
step-up converter. LXP connects to VDD, LXN pulls to
ground, and the inductor current rises. Once the induc-
tor current rises to a level set by the positive-side error
amplifier, LXN releases and the inductor current flows
through D2 to the positive output. When the inductor
current drops to zero (which happens each cycle under
normal, discontinuous operation), LXN returns to the
input voltage.
On the second cycle, LXN is held at ground. LXP is
pulled up to the input voltage until the current reaches
the limit set by the negative error amplifier. Then LXP is
released and the inductor current flows through D1 to
the negative output. Once the inductor current reaches
zero, the voltage at LXP returns to ground. The wave-
forms at LXN and LXP are shown in Figure 2 for a typi-
cal pair of cycles.
MAX685
Dual-Output (Positive and Negative),
DC-DC Converter for CCD and LCD
Pin Description
PIN
16-QSOP

P-Channel Switching Inductor Node. LXP turns off when the part enters shutdown.LXP1
FUNCTIONNAME

Internally Connected. Do not externally connect.I.C.2, 15
Open-Drain Power-OK Output. POK is high when both outputs are in regulation. Connect POK
to VDDwith a 100kΩpull-up resistor to VDD.POK4
Power Input. Connect to VDD.VP3
Shutdown Input. Both outputs go to 0V in shutdown. Connect to VDDfor automatic startup.SHDN6
Supply Input. Bypass VDDwith a 1.0µF or greater ceramic capacitor to GND.VDD8
Sync Input. This pin synchronizes the oscillator to an external clock frequency between 200kHz
and 480kHz. Connect SYNC to GND (220kHz) or VDD(400kHz) for internal oscillator frequency.SYNC7
Power-Up Sequence Select Input. Connect SEQ to GND to power the negative output voltage
first. Connect SEQ to VDDto power the positive output first.SEQ5
GroundGND9
1.25V Reference Voltage Output. Bypass with 0.22µF to GND.REF11
Power Ground. Connect PGND to GND.PGND13, 14
Feedback for the Positive Output Voltage. Connect a resistor-divider between the positive out-
put and GND with the center to FBP to set the positive output voltage.FBP12
Feedback Input for the Negative Output Voltage. Connect a resistor-divider between the nega-
tive output and REF with the center to FBN to set the negative output voltage.FBN10
N-Channel Switching Inductor Node. LXN pulls to GND through the internal transistor when the
part is shut down.LXN16
This pin in not internally connected.N.C.—
19, 24
2, 3
15, 16, 17
PIN
24-TQFN

22, 23
20, 21
1, 9, 10,
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