MAX629ESA+ ,28V, Low-Power, High-Voltage, Boost or Inverting DC-DC ConverterApplications*Dice are tested at T = +25°C, DC parameters only.APositive or Negative LCD Bias Genera ..
MAX629ESA+ ,28V, Low-Power, High-Voltage, Boost or Inverting DC-DC Converterfeatures an♦ Internal, 500mA, 28V N-Channel Switch internal N-channel MOSFET switch and programmabl ..
MAX629ESA+T ,28V, Low-Power, High-Voltage, Boost or Inverting DC-DC ConverterApplications___________Typical Operating CircuitV VIN IN+2.7V +2.7VTO +5.5V TO +5.5VV OUTV VCC CC28 ..
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MAX629ESA+-MAX629ESA+T-MAX629ESA-T
28V, Low-Power, High-Voltage, Boost or Inverting DC-DC Converter
_______________General DescriptionThe MAX629 low-power DC-DC converter features an
internal N-channel MOSFET switch and programmable
current limiting. It is designed to supply positive or neg-
ative bias voltages up to ±28V from input voltages in
the 0.8V to VOUTrange, and can be configured for
boost, flyback, and SEPIC topologies.
The MAX629’s current-limited pulse-frequency-modula-
tion (PFM) control scheme provides high efficiency over
a wide range of load conditions. An internal, 0.5A N-
channel MOSFET switch reduces the total part count,
and a high switching frequency (up to 300kHz) allows
for tiny surface-mount magnetics.
The MAX629’s combination of low supply current, logic-
controlled shutdown, small package, and tiny external
components makes it an extremely compact and effi-
cient high-voltage biasing solution that’s ideal for bat-
tery-powered applications. The MAX629 is available in
an 8-pin SO package.
________________________ApplicationsPositive or Negative LCD Bias Generators
High-Efficiency DC-DC Boost Converters
Varactor Tuning Diode Bias
Palmtop Computers
2-Cell and 3-Cell Battery-Powered Applications
____________________________FeaturesInternal, 500mA, 28V N-Channel Switch
(No External FET Required)Generates Positive or Negative Output Voltages80μA Supply Current1μA Max Shutdown CurrentUp to 300kHz Switching FrequencyAdjustable Current Limit Allows Use of Small,
Inexpensive Inductors8-Pin SO Package8V, Low-Power, High-Voltage,
Boost or Inverting DC-DC ConverterMAX629
SHDN
VIN
+2.7V
TO +5.5V
VCC
GND
ISET
POL
REF
POSITIVE OUTPUT VOLTAGEMAX629
SHDN-VOUT
-28V
VOUT
28V
VIN
+2.7V
TO +5.5V
VCC
GND
REF
POL
NEGATIVE OUTPUT VOLTAGEISET
___________________________________________________Typical Operating Circuit19-1219; Rev 1; 6/97
PARTTEMP. RANGEPIN-PACKAGE
______________Ordering Information
Note:To order tape-and-reel shipping, add “-T” to the end of
the part number.
*Dice are tested at TA= +25°C, DC parameters only.
Pin Configuration appears at end of data sheet.MAX629C/D0°C to +70°CDice*
MAX629ESA-40°C to +85°C8 SO
EVALUATION KIT MANUALAVAILABLE
8V, Low-Power, High-Voltage,Boost or Inverting DC-DC Converter
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VCC= +5V, CREF= 0.1μF, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note1)
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.
Supply Voltage (VCCto GND)..................................-0.3V to +6V
SHDNto GND...........................................................-0.3V to +6V
ISET, REF, FB, POL to GND.......................-0.3V to (VCC+ 0.3V)
LX to GND..............................................................-0.3V to +30V
Continuous Power Dissipation (TA= +70°C)
SO (derate 5.88mW/°C above +70°C)..........................471mW
Operating Temperature Range...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +165°C
Lead Temperature (soldering, 10sec).............................+300°C
CONDITIONS2.75.5VCCInput Voltage (Note 2)
UNITSMINTYPMAXPARAMETERVFB= 1.3VμA80120VCCSupply Current
100mV hysteresisV2.32.52.65VCCUndervoltage Lockout
SHDN= GNDμA0.041VCCShutdown Current0.390.450.51
Circuit of Figure 2
VLX= 28V, TA= +85°CμA0.052.5LX Leakage Current
POL = GND
Minimum LX Off-Time6.58.510.0Maximum LX On-Time
0.200.250.33LX Switch-Current Limit28Positive Output Voltage
POL = GND, VFB< 1V3.04.56.0
POL = VCC2.03.23.8
POL = GND
(positive output)V1.2181.282
1.2251.2501.275550FB Input Bias Current
VCC= 5VW0.61.2
VCC= 3.3V0.71.4LX On-Resistance= 0°C to +85°C= -40°C to +85°C= 0°C to +85°C= -40°C to +85°C
POL = VCC
(negative output)mV-2525
FB Set Point-15015
VCC= 2.7V to 5.5V,
no load on REFV1.2181.282REF Output VoltageTA= 0°C to +85°C= -40°C to +85°C
VIHV2.4SHDN, POL, ISET Logic LevelsVIL0.4
Voltage applied to L1 (VIN)V0.8‰VOUT‰Input Supply Voltage (Note 2)
Circuit of Figure 3V-‰VIN‰-28Negative Output Voltage
ISET = VCC
ISET = GND
POL = VCC, VFB> 0.25V3.04.56.0
8V, Low-Power, High-Voltage,Boost or Inverting DC-DC Converter
ELECTRICAL CHARACTERISTICS (continued)(VCC= +5V, CREF= 0.1μF, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)
Note 1:Specifications to -40°C are guaranteed by design and not production tested.
Note 2:The IC itself requires a supply voltage between +2.7V and +5.5V; however, the voltage that supplies power to the inductor
can vary from 0.8V to 28V, depending on circuit operating conditions.
Note 3:For reference currents less than 10μA, a 0.1μF reference-bypass capacitor is adequate.
Circuit of Figure 2, VOUT= 24V, VCC= 3V to 5.5V,
ILOAD= 5mA%/V0.2Line Regulation
Die temperature°C150
IREF= 0μA to 100μA, CREF= 0.47μF (Note 3)
Thermal Shutdown Threshold
Circuit of Figure 2, VOUT= 24V, VCC= 5V,
ILOAD= 0mA to 5mA%0.15Load Regulation
CONDITIONS1025REF Load Regulation
UNITSMINTYPMAXPARAMETER
__________________________________________Typical Operating Characteristics(SHDN= VCC, CREF= 0.1μF, TA= +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
(VOUT = +24V)
AX629-01
LOAD CURRENT (mA)
(%10
D: VIN = 5V, ISET = GND
E: VIN = 3V, ISET = VCC
F: VIN = 3V, ISET = GND
VOUT = 24V
A: VIN = 12V, ISET = VCC
B: VIN = 12V, ISET = GND
C: VIN = 5V, ISET = VCC
E, F
EFFICIENCY vs. LOAD CURRENT
(VOUT = +12V)
AX629-02
LOAD CURRENT (mA)
(%10
VOUT = 12V,
ISET = VCC or GND
A: VIN = 9V
B: VIN = 5V
C: VIN = 3V
MAXIMUM LOAD CURRENT vs.
INPUT VOLTAGE (VOUT = +24V, +12V)
AX629-03
INPUT VOLTAGE (V)
(m12416
A: VOUT = 12V,
ISET = VCC
B: VOUT = 12V,
ISET = GND
C: VOUT =24V,
ISET = VCC
D: VOUT = 24V,
ISET = GND
EFFICIENCY vs. LOAD CURRENT
(VOUT = -18V)
X629-04
LOAD CURRENT (mA)
(%10
A: VIN = 12V, ISET = VCC
B: VIN = 12V, ISET = GND
C: VIN = 5V, ISET = VCC or GND
D: VIN = 3V, ISET = VCC or GND
EFFICIENCY vs. LOAD CURRENT
(VOUT = -12V)
X629-05
LOAD CURRENT (mA)
(%10
A = VIN = 5V, ISET = VCC
B = VIN = 5V, ISET = GND
C = VIN = 3V, ISET = VCC
D = VIN = 3V, ISET = GND
B, C20
MAXIMUM LOAD CURRENT vs. INPUT VOLTAGE
(VOUT = -18V, -12V)AX629-06
INPUT VOLTAGE (V)
(m81216
A: VOUT = -12V, ISET = VCC
B: VOUT = -18V, ISET = VCC
C: VOUT = -12V, ISET = GND
D: VOUT = -18V, ISET = GND
8V, Low-Power, High-Voltage,Boost or Inverting DC-DC ConverterSUPPLY CURRENT
vs. INPUT VOLTAGE
INPUT VOLTAGE (V)
(m345
VIN = VCC
ICC
IIN
IIN
REFERENCE VOLTAGE
vs. REFERENCE LOAD CURRENT
AX629-08
REFERENCE LOAD CURRENT (mA)
(V80100120140160
VIN = VCC = 5V
C4 = 0.47mF
OUTPUT VOLTAGE RIPPLEAX629-09
VOUT = +24V, ILOAD = 5mA
A: ISET = VCC, 20mV/div
B: ISET = GND, 20mV/div
10ms/div
SHUTDOWN TRANSIENT
(POSITIVE CONFIGURATION)AX629-12
VCC = VIN = 5V, RL = 4kW
50ms/div
SHDN
24V
VOUT
LOAD-TRANSIENT RESPONSE
(ISET = VCC, ILIM = 500mA)AX629-10
VOUT = +24V, ISET = VCC
A: LOAD CURRENT, 0mA TO 5mA, 2.5mA/div
B: VOUT, AC-COUPLED, 10mV/div
5mA
0mA
200ms/div
LOAD-TRANSIENT RESPONSE
(ISET = GND, ILIM = 250mA)AX629-11
VOUT = +24V, ISET = GND
A: LOAD CURRENT, 0mA TO 5mA, 2.5mA/div
B: VOUT, AC-COUPLED, 10mV/div
0mA
5mA
100ms/div
SHUTDOWN TRANSIENT
(NEGATIVE CONFIGURATION)AX629-13
START-UP DELAY, VCC = VIN = 5V, ILOAD = 5mA
20ms/div
VCC = VIN = 5V, RL = 4kW
50ms/div
VOUT
-20V
SHDN
____________________________Typical Operating Characteristics (continued)(SHDN= VCC, CREF= 0.1μF, TA= +25°C, unless otherwise noted.)
8V, Low-Power, High-Voltage,Boost or Inverting DC-DC Converter
______________________________________________________________Pin DescriptionCurrent-Limit Set Input. Connect to VCCfor a 500mA LX current limit, or connect to GND for a 250mA LX
current limit. See Setting the Current Limit.ISET5
GroundGND6
Feedback Input for setting output voltage. Connect to an external voltage divider. See Setting the Output
Voltage.FB4
1.25V Reference Output. Bypass to GND with a 0.1μF capacitor for IREF≤10μA. REF can source 100μA to
drive external loads. For 10μA ≤IREF≤100μA, bypass REF with a 0.47μF capacitor.REF3
PINPolarity Input. Changes polarity and threshold of FB to allow regulation of either positive or negative output
voltages. Set POL = GND for positive output voltage, or set POL = VCCfor negative output voltage.POL2
Active-Low Shutdown Input. A logic low puts the MAX629 in shutdown mode and reduces supply current to
1μA.SHDN1
FUNCTIONNAMEInternal N-Channel DMOS Switch DrainLX7
Power-Supply InputVCC8
_______________Detailed DescriptionThe MAX629 low-power, boost DC-DC converter pro-
vides either positive or negative output voltages up to28V from a wide range of input voltages. It is
designed primarily for use in low-power, high-voltage
applications such as LCD biasing and set-top box var-
actor tuning. The MAX629’s unique control scheme
provides high efficiency and a wide range of output
voltages with only 80μA quiescent supply current, mak-
ing it ideal for battery-powered applications. The inter-
nal N-channel DMOS switch has a pin-programmable
current limit (250mA and 500mA), allowing optimization
of output current and component size. Figure 1 shows
the MAX629 functional diagram.
Control SchemeA combination of peak-current limiting and a pair of
one-shots controls the MAX629 switching, determining
the maximum on-time and constant off-time. During the
on-cycle, the internal switch closes, and current
through the inductor ramps up until either the fixed
10μs maximum on-time expires (at low input voltages)
or the switch’s peak current limit is reached. The peak
switch current limit is selectable to either 500mA (ISET VCC) or 250mA (ISET = GND) (see Setting the
Current Limit). After the on-cycle terminates, the switch
turns off, charging the output capacitor through the
diode. In normal operation, the minimum off-time is set
to 1μs for positive output voltages and 3.5μs for nega-
tive output voltages. When the output is well below reg-
ulation, however, the off-time is increased to 5μs to pro-
vide soft-start during start-up. The switching frequency,
which depends upon the load, can be as high as
300kHz.
Shutdown ModeWhen SHDNis low, the MAX629 enters shutdown
mode. In this mode, the feedback and control circuit,
reference, and internal biasing circuitry turn off. The
shutdown current drops to less than 1μA. SHDNis a
logic-level input; connect it to VCCfor normal operation.
The output voltage behavior in shutdown mode
depends on the output voltage polarity. In the positive
output voltage configuration (Figure 2), the output is
directly connected to the input through the diode (D1)
and the inductor (L1). When the device is in shutdown
mode, the output voltage falls to one diode drop below
the input voltage, and any load connected to the output
may still conduct current. In the negative output voltage
configuration (Figure 3), there is no DC connection
between the input and the output, and in shutdown
mode the output is pulled to GND.
__________________Design Procedure
Setting the Output VoltageFor either positive or negative output voltage applica-
tions, set the MAX629’s output voltage using two exter-
nal resistors, R1 and R2, as shown in Figures 2 and 3.
Since the input bias current at FB has a 50nA maximum
value, large resistors can be used in the feedback loop
8V, Low-Power, High-Voltage,Boost or Inverting DC-DC Converterwithout a significant loss of accuracy. Begin by select-
ing R2 to be in the 10kΩto 200kΩrange, and calculate
R1 using the applicable equation from the following
subsections.
Positive Output VoltagesFor positive output voltages, use the typical boost con-
figuration shown in Figure 2, connecting POL to GND.
This sets the threshold voltage at FB to equal VREF.
Choose the value of R2 and calculate R1 as follows:
where VREF= 1.25V.
Negative Output VoltagesFor negative output voltages, configure R1 and R2 as
shown in Figure 3, connecting POL to VCC. This sets
the FB threshold voltage to GND so that negative volt-
ages can be regulated. Choose R2 and calculate R1 as
follows:
where VREF= 1.25V.
Figure 3 demonstrates generation of a negative output
voltage by following the MAX629 with an inverting
charge pump. This configuration limits ‰VOUT‰to values
between -‰VIN‰and -28V. If smaller negative output volt-
ages are required, D2’s cathode can be connected to
VIN. This alternative configuration permits output volt-
ages smaller than -‰VIN‰,but cannot be used for output
voltages more negative than -‰28V - VIN‰.It produces
roughly one-half the output current as the standard con-
figuration and is typically 5% less efficient.
R1 = R2 x V|OUT
REF
R1 = R2 x V
OUT
REF -1
MAX629
MIN OFF-TIME
GENERATOR
TRIG
ISET
F/F
GND
START-UP
MAX ON-TIME
GENERATOR
(10ms)
CONTROL
REF
VCC
START-UP
COMPARATOR
ERROR
AMP
1.25V
REF
POL
TRIG
SHDN
POLARITY
Figure 1. Functional Diagram
