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MAX629
28V, Low-Power, High-Voltage,
Boost or Inverting DC-DC Converter
General Description
Features
The MAX629 low-power DC-DC converter features an
internal N-channel MOSFET switch and programmable
current limiting. It is designed to supply positive or negative bias voltages up to ±28V from input voltages in the
0.8V to VOUT range and can be configured for boost,
flyback, and SEPIC topologies.
●● Internal, 500mA, 28V N-Channel Switch
(No External FET Required)
●● Generates Positive or Negative Output Voltages
●● 80μA Supply Current
●● 1μA Max Shutdown Current
The MAX629’s current-limited pulse-frequency-modulation (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.
●● Up to 300kHz Switching Frequency
The MAX629’s combination of low supply current, logiccontrolled shutdown, small package, and tiny external
components makes it an extremely compact and efficient
high-voltage biasing solution that’s ideal for battery-powered applications. The MAX629 is available in an 8-pin
SO package.
Ordering Information
Applications
●● Adjustable Current Limit Allows Use of Small,
Inexpensive Inductors
●● 8-Pin SO Package
PART
TEMP. RANGE
PIN-PACKAGE
MAX629C/D
0°C to +70°C
Dice*
MAX629ESA
-40°C to +85°C
8 SO
*Dice are tested at TA = +25°C, DC parameters only.
Note: To order tape-and-reel shipping, add “-T” to the end of
the part number.
●● Positive or Negative LCD Bias Generators
●● High-Efficiency DC-DC Boost Converters
●● Varactor Tuning Diode Bias
Pin Configuration appears at end of data sheet.
●● Palmtop Computers
●● 2-Cell and 3-Cell Battery-Powered Applications
Typical Operating Circuit
VIN
+2.7V
TO +5.5V
VIN
+2.7V
TO +5.5V
SHDN
VCC
LX
VOUT
28V
SHDN
VCC
LX
ISET
ISET
FB
POL
POL
MAX629
MAX629
GND
GND
POSITIVE OUTPUT VOLTAGE
NEGATIVE OUTPUT VOLTAGE
REF
19-1219; Rev 2; 8/20
FB
REF
-VOUT
-28V
MAX629
28V, Low-Power, High-Voltage,
Boost or Inverting DC-DC Converter
Absolute Maximum Ratings
Supply Voltage (VCC to GND)..................................-0.3V to +6V
SHDN to 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
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.
Package Information
Package Code
S8-4
Outline Number
21-0041
Land Pattern Number
90-0096
Thermal Resistance, Single-Layer Board:
Junction to Ambient θJA (C/W)
132°
Junction to Case θJC (C/W)
38°
Electrical Characteristics
(VCC = +5V, CREF = 0.1μF, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note1)
PARAMETER
VCC Input Voltage (Note 2)
VCC Supply Current
VCC Shutdown Current
VCC Undervoltage Lockout
Input Supply Voltage (Note 2)
SHDN, POL, ISET Logic
Levels
Positive Output Voltage
Negative Output Voltage
LX Switch-Current Limit
LX On-Resistance
LX Leakage Current
Maximum LX On-Time
Minimum LX Off-Time
FB Set Point
CONDITIONS
VFB = 1.3V
SHDN = GND
100mV hysteresis
Voltage applied to L1 (VIN)
VIH
VIL
Circuit of Figure 2
Circuit of Figure 3
ISET = VCC
ISET = GND
VCC = 5V
VCC = 3.3V
VLX = 28V, TA = +85°C
MIN
2.7
80
0.04
2.3
0.8
-|VIN|
0.39
0.20
POL = GND
POL = VCC
POL = GND, VFB < 1V
POL = VCC, VFB > 0.25V
POL = GND (positive TA = 0°C to +85°C
output)
TA = -40°C to +85°C
POL = VCC (negative TA = 0°C to +85°C
output)
TA = -40°C to +85°C
6.5
0.7
2.0
3.0
3.0
1.225
1.218
-15
-25
TA = 0°C to +85°C
TA = -40°C to +85°C
1.225
1.218
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VCC = 2.7V to 5.5V,
no load on REF
2.5
MAX
5.5
120
1
2.65
|VOUT|
2.4
FB Input Bias Current
REF Output Voltage
TYP
0.45
0.25
0.6
0.7
0.05
8.5
1.0
3.2
4.5
4.5
1.250
0
5
1.250
0.4
28
-28
0.51
0.33
1.2
1.4
2.5
10.0
1.3
3.8
6.0
6.0
1.275
1.282
15
25
50
1.275
1.282
UNITS
V
µA
µA
V
V
V
V
V
A
Ω
µA
µs
µs
V
mV
nA
V
Maxim Integrated │ 2
MAX629
28V, 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.) (Note1)
TYP
MAX
UNITS
REF Load Regulation
PARAMETER
IREF = 0µA to 100µA, CREF = 0.47µF (Note 3)
CONDITIONS
MIN
10
25
mV
Line Regulation
Circuit of Figure 2, VOUT = 24V, VCC = 3V to
5.5V, ILOAD = 5mA
0.2
%/V
Load Regulation
Circuit of Figure 2, VOUT = 24V, VCC = 5V, ILOAD
= 0mA to 5mA
0.15
%
Thermal Shutdown Threshold
Die temperature
150
°C
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.
Typical Operating Characteristics
(SHDN = VCC , CREF = 0.1μF, TA = +25°C, unless otherwise noted.)
85
C
80
D
75
E, F
70
60
100
10
1
MAX629-03
D
50
0
4
8
12
16
20
100
95
70
A: VIN = 12V, ISET = VCC
B: VIN = 12V, ISET = GND
C: VIN = 5V, ISET = VCC or GND
D: VIN = 3V, ISET = VCC or GND
1
10
LOAD CURRENT (mA)
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100
EFFICIENCY (%)
D
B
C
A
85
80
A
B, C
D
75
70
65
A = VIN = 5V, ISET = VCC
B = VIN = 5V, ISET = GND
C = VIN = 3V, ISET = VCC
D = VIN = 3V, ISET = GND
60
55
50
0.1
1
10
LOAD CURRENT (mA)
100
90
MAX629-06
MAXIMUM LOAD CURRENT vs. INPUT VOLTAGE
(VOUT = -18V, -12V)
75
0.1
100
EFFICIENCY vs. LOAD CURRENT
(VOUT = -12V)
80
55
C
B
EFFICIENCY vs. LOAD CURRENT
(VOUT = -18V)
90
60
150
A
INPUT VOLTAGE (V)
85
65
200
0
100
10
250
LOAD CURRENT (mA)
90
EFFICIENCY (%)
0.1
A: VOUT = 12V,
ISET = VCC
B: VOUT = 12V,
ISET = GND
C: VOUT =24V,
ISET = VCC
D: VOUT = 24V,
ISET = GND
LOAD CURRENT (mA)
95
50
VOUT = 12V,
ISET = VCC or GND
A: VIN = 9V
B: VIN = 5V
C: VIN = 3V
65
MAX629-04
100
1
75
MAXIMUM LOAD CURRENT (mA)
0.1
C
80
MAX629-05
60
B
85
70
D: VIN = 5V, ISET = GND
E: VIN = 3V, ISET = VCC
F: VIN = 3V, ISET = GND
65
A
90
A
B
EFFICIENCY (%)
EFFICIENCY (%)
90
95
MAXIMUM LOAD CURRENT vs.
INPUT VOLTAGE (VOUT = +24V, +12V)
300
MAXIMUM LOAD CURRENT (mA)
VOUT = 24V
A: VIN = 12V, ISET = VCC
B: VIN = 12V, ISET = GND
C: VIN = 5V, ISET = VCC
95
100
MAX629-01
100
EFFICIENCY vs. LOAD CURRENT
(VOUT = +12V)
MAX629-02
EFFICIENCY vs. LOAD CURRENT
(VOUT = +24V)
A
80
70
B
60
50
40
30
C
20
A: VOUT = -12V, ISET = VCC
B: VOUT = -18V, ISET = VCC
C: VOUT = -12V, ISET = GND
D: VOUT = -18V, ISET = GND
D
10
0
0
4
8
12
16
20
INPUT VOLTAGE (V)
Maxim Integrated │ 3
MAX629
28V, Low-Power, High-Voltage,
Boost or Inverting DC-DC Converter
Typical Operating Characteristics (continued)
(SHDN = VCC , CREF = 0.1μF, TA = +25°C, unless otherwise noted.)
VIN = VCC
1.250
500
IIN
1.245
400
IIN
300
1.240
200
ICC
0
1
2
3
1.235
4
1.230
5
INPUT VOLTAGE (V)
0
20
40
MAX629-09
80
100 120 140 160
LOAD-TRANSIENT RESPONSE
(ISET = GND, ILIM = 250mA)
MAX629-10
LOAD-TRANSIENT RESPONSE
(ISET = VCC, ILIM = 500mA)
OUTPUT VOLTAGE RIPPLE
A
60
REFERENCE LOAD CURRENT (µA)
0mA
MAX629-11
100
0
VIN = VCC = 5V
C4 = 0.47µF
REFERENCE VOLTAGE (V)
SUPPLY CURRENT (µA)
600
1.255
MAX629-07
700
REFERENCE VOLTAGE
vs. REFERENCE LOAD CURRENT
MAX629-08
SUPPLY CURRENT
vs. INPUT VOLTAGE
0mA
A
A
5mA
5mA
B
B
B
200µs/div
10µs/div
100µs/div
VOUT = +24V, ISET = VCC
A: LOAD CURRENT, 0mA TO 5mA, 2.5mA/div
B: VOUT, AC-COUPLED, 10mV/div
VOUT = +24V, ILOAD = 5mA
A: ISET = VCC, 20mV/div
B: ISET = GND, 20mV/div
VOUT = +24V, ISET = GND
A: LOAD CURRENT, 0mA TO 5mA, 2.5mA/div
B: VOUT, AC-COUPLED, 10mV/div
MAX629-12
5V
5V
SHDN
SHDN
0V
0V
24V
MAX629-13
SHUTDOWN TRANSIENT
(NEGATIVE CONFIGURATION)
SHUTDOWN TRANSIENT
(POSITIVE CONFIGURATION)
0V
VOUT
VOUT
0V
-20V
50ms/div
VCC = VIN = 5V, RL = 4kΩ
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20ms/div
50ms/div
VCC = VIN =DELAY,
5V, RL =VCC
4kΩ== 5
START-UP
Maxim Integrated │ 4
MAX629
28V, Low-Power, High-Voltage,
Boost or Inverting DC-DC Converter
Pin Description
PIN
NAME
FUNCTION
1
SHDN
2
POL
3
REF
4
FB
5
ISET
Current-Limit Set Input. Connect to VCC for a 500mA LX current limit or connect to GND for a 250mA
LX current limit. See Setting the Current Limit.
6
GND
Ground
7
LX
8
VCC
Active-Low Shutdown Input. A logic low puts the MAX629 in shutdown mode and reduces supply
current to 1µA.
Polarity 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 = VCC for negative output
voltage.
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.
Feedback Input for setting output voltage. Connect to an external voltage divider. See Setting the
Output Voltage.
Internal N-Channel DMOS Switch Drain
Power-Supply Input
Detailed Description
The MAX629 low-power, boost DC-DC converter provides either positive or negative output voltages up to
±28V 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 varactor tuning. The
MAX629’s unique control scheme provides high efficiency
and a wide range of output voltages with only 80μA quiescent supply current, making it ideal for battery-powered
applications. The internal 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 Scheme
A combination of peak-current limiting and a pair of oneshots controls the MAX629 switching, determining the
maximum on-time and constant off-time. During the oncycle, 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 negative output voltages. When the output
is well below regulation, however, the off-time is increased
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to 5μs to provide soft-start during start-up. The switching
frequency, which depends upon the load, can be as high
as 300kHz.
Shutdown Mode
When SHDN is 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. SHDN is a logic-level input;
connect it to VCC for 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 Voltage
For either positive or negative output voltage applications, set the MAX629’s output voltage using two external
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 without
Maxim Integrated │ 5
MAX629
28V, Low-Power, High-Voltage,
Boost or Inverting DC-DC Converter
POL
REF
MIN OFF-TIME
GENERATOR
POLARITY TRIG
1.25V
REF
MAX629
START-UP Q
ERROR
AMP
LX
F/F
S
FB
Q
R
START-UP
COMPARATOR
ISET
TRIG
1V
SHDN
VCC
MAX ON-TIME
GENERATOR
(10µs)
Q
CONTROL
GND
Figure 1. Functional Diagram
a significant loss of accuracy. Begin by selecting R2 to be
in the 10kΩ to 200kΩ range, and calculate R1 using the
applicable equation from the following subsections.
Positive Output Voltages
For positive output voltages, use the typical boost configuration 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:
V
R1 =
R2 × OUT − 1
VREF
where VREF = 1.25V.
Negative Output Voltages
For negative output voltages, configure R1 and R2 as
shown in Figure 3, connecting POL to VCC. This sets the
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FB threshold voltage to GND so that negative voltages
can be regulated. Choose R2 and calculate R1 as follows:
R1
= R2 ×
| VOUT |
VREF
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 voltages are
required, D2’s cathode can be connected to VIN. This
alternative configuration permits output voltages 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 configuration and is typically 5% less efficient.
Maxim Integrated │ 6
MAX629
28V, Low-Power, High-Voltage,
Boost or Inverting DC-DC Converter
Setting the Current Limit
External current-limit selection provides added control
over the MAX629’s output performance. A higher current
limit increases the amount of energy stored in the inductor
during each cycle, which provides a higher output current
capability. For higher output current applications, choose
the 500mA current-limit option by connecting ISET to
VCC. When lower output current is required, the 250mA
current limit can provide several advantages. First, a
smaller inductor can be used, which saves board area
and cost. Second, the smaller energy transfer per cycle
reduces output ripple for a given capacitor, providing
design flexibility between board area, cost, and output ripple by allowing cheaper, higher-ESR capacitors. Connect
ISET to GND to select the 250mA current-limit option.
Inductor Selection
The MAX629’s high switching frequency allows for the
use of a small inductor. The 47μH inductor shown in
the Typical Operating Circuit is recommended for most
VIN
+0.8V
TO +24V
VCC
+2.7V
TO +5.5V
Inductors with a ferrite core or equivalent are recommended; powder iron cores are not recommended for
use with high switching frequencies. The inductor’s incremental saturation rating must exceed the selected current
limit. For highest efficiency, use an inductor with a low DC
resistance (under 100mΩ). See Table 1 for a list of inductor suppliers.
VIN
+0.8V
TO +15V
VCC
+2.7V
TO +5.5V
C1
10µF
35V
*
L1
47µH
C3
0.1µF
SHDN
VCC
ISET
FB
R2
31.6k
1%
POL
REF
GND
Figure 2. +24V for a Positive LCD Bias
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VOUT
+24V
LX
R1
576k
1%
C1
10µF
35V
*
L1
47µH
C3
0.1µF
D1
MBR0540L
MAX629
C4
0.1µF
applications. Larger inductances reduce the peak inductor current, but may limit output current capability at low
input voltages and provide slower start-up times. Smaller
inductances require less board space, but may cause
greater peak current due to current-sense comparator
propagation delay. If input voltages below 2V will be common, reducing the inductance to 22μH might improve performance; however, maximum load current and efficiency
may decline. It is important to thoroughly test operation
under all input and output conditions to ensure proper
component selection.
CF
150pF
C2
10µF
35V
SHDN
C5
2.2µF
VCC
LX
R3
2Ω
D1 = D2 = MBR0540L
POL
MAX629
FB
GND
REF
VOUT
-20V
D1
D2
ISET
R1
576k
1%
CF
150pF
C2
10µF
35V
R2
35.7k
1%
C4
0.1µF
Figure 3. -20V for a Negative LCD Bias
Maxim Integrated │ 7
MAX629
28V, Low-Power, High-Voltage,
Boost or Inverting DC-DC Converter
Diode Selection
The MAX629’s high switching frequency demands a
high-speed rectifier. Schottky diodes, such as the 1N5819
or MBR0530L, are recommended. Make sure that the
diode’s peak current rating exceeds the peak current
set by ISET, and that its breakdown voltage exceeds the
output voltage. Schottky diodes are preferred due to their
low forward voltage. However, ultrahigh-speed silicon
rectifiers are also acceptable. Table 1 lists Schottky diode
suppliers.
Capacitor Selection
Output Filter Capacitor
The primary criterion for selecting the output filter capacitor is low effective series resistance (ESR). The product
of the peak inductor current and the output filter capacitor’s ESR determines the amplitude of the high-frequency
ripple seen on the output voltage. These requirements
can be balanced by appropriate selection of the current
limit, as discussed in the Setting the Current Limit section. Table 1 lists some low-ESR capacitor suppliers. See
the Output Voltage Ripple graph in the Typical Operating
Characteristics section.
Input Bypass Capacitor
Although the output current of many MAX629 applications
may be relatively small, the input must be designed to
withstand current transients equal to the inductor current
limit. The input bypass capacitor reduces the peak currents drawn from the voltage source and reduces noise
Table 1. Component Suppliers
SUPPLIER
PHONE
FAX
CAPACITORS
AVX: TPS series
(803) 946-0690 (803) 626-3123
Matsuo: 267 series
(714) 969-2491 (714) 960-6492
Sprague: 595D series
(603) 224-1961 (603) 224-1430
DIODES
Motorola: MBR0530L
(602) 303-5454 (602) 994-6430
Nihon: EC11 FS1 series
(805) 867-2555 (805) 867-2698
INDUCTORS
Coilcraft: DO1608 and
DT1608 series
(847) 639-6400 (847) 639-1469
Murata-Erie: LQH4
series
(814) 237-1431 (814) 238-0490
Sumida: CD43, CD54,
and CDRH62B series
(847) 956-0666 (847) 956-0702
TDK: NLC565050 series (847) 390-4373 (847) 390-4428
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caused by the MAX629’s switching action. The input
source impedance determines the size of the capacitor required at the input (VIN). As with the output filter
capacitor, a low-ESR capacitor is recommended. A 10μF,
low-ESR capacitor is adequate for most applications,
although smaller bypass capacitors may also be acceptable. Bypass the IC separately with a 0.1μF ceramic
capacitor placed as close as possible to the VCC and
GND pins.
Reference Capacitor
Bypass REF to GND with a 0.1μF ceramic capacitor for
REF currents up to 10μA. REF can source up to 100μA
of current for external loads. For 10μA ≤ IREF ≤ 100μA,
bypass REF with a 0.47μF capacitor.
Feed-Forward Capacitor
Parallel a capacitor (CF) across R1 to compensate the
feedback loop and ensure stability (Figure 2 and Figure 3).
Values up to 270pF are recommended for most applications. Choose the lowest capacitor value that ensures
stability; high capacitance values may degrade line regulation.
Applications Information
Adjusting the Output Voltage
Many biasing applications require an adjustable output
voltage, which is easily obtained using the configuration
in Figure 4. In this circuit, an external bias voltage (which
may be generated by a potentiometer, a DAC, or other
means) is coupled to FB through the resistor RB. The
output voltage of this circuit is given by:
VOUT =
VINIT +
R1
(VFB − VBIAS )
RB
where VINIT is the fixed output voltage as calculated in
the section Setting the Output Voltage, and VFB is equal
to either VREF (1.25V) for the positive configuration or
0V for the negative configuration. Proper choice of RB
provides a wide range of available output voltages using
simple external components to generate VBIAS.
Input Voltage Range
Although, in many cases, the MAX629 and the inductor
are powered from the same source, it is often advantageous in battery-powered applications to power the
device from an available regulated supply and to power
the inductor directly from a battery. The MAX629 requires
a +2.7V to +5.5V supply at VCC, but the inductor can be
powered from as low as +0.8V, significantly increasing
Maxim Integrated │ 8
MAX629
28V, Low-Power, High-Voltage,
Boost or Inverting DC-DC Converter
VOUT
R1
RB
FB
MAX629
VBIAS
R2
GND
(REF)
( ) ARE FOR NEGATIVE OUTPUT VOLTAGE CONFIGURATIONS.
Figure 4. Adjustable Output Voltage
usable battery life. Using separate supplies for VCC and
VIN also reduces noise injection onto VCC by isolating it
from the switching transients, allowing a smaller, lessexpensive input filter capacitor to be used in many applications. If input voltages below 2V will be common, reducing the inductor to 22μH may improve performance in this
voltage range, at the potential cost of some decrease in
maximum load current and efficiency.
In the negative configuration shown in Figure 3, the inverting charge pump injects current into LX with each cycle.
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The amount of charge injected increases at higher VIN,
and may prematurely trip the internal currentlimit threshold. Resistor R3 increases the usable input voltage range
by limiting the peak injected current. The 2Ω resistor
shown provides a usable input voltage range beyond VIN
= 15V. In applications with a different input voltage range,
R3 can be increased or decreased as necessary, with a
resulting efficiency change of roughly 0.5%/Ω.
Layout Considerations
Proper PC board layout is essential due to high current
levels and fast switching waveforms that radiate noise.
It is recommended that initial prototyping be performed
using the MAX629 evaluation kit or equivalent PC boardbased design. Breadboards or proto-boards should never
be used when prototyping switching regulators. It is important to connect the GND pin, the input bypass-capacitor
ground lead, and the output filter capacitor ground lead
to a single point (star ground configuration) to minimize
ground noise and improve regulation. Also, minimize lead
lengths to reduce stray capacitance, trace resistance, and
radiated noise, with preference given to the feedback circuit, the ground circuit, and LX. Place R1 and R2 as close
to the feedback pin as possible. Place the input bypass
capacitor as close as possible to VCC and GND.
Refer to the MAX629 evaluation kit data sheet for an
example of proper board layout.
Maxim Integrated │ 9
MAX629
28V, Low-Power, High-Voltage,
Boost or Inverting DC-DC Converter
Pin Configuration
Chip Information
PTRANSISTOR COUNT: 653
SUBSTRATE CONNECTED TO GNDS
TOP VIEW
SHDN 1
POL 2
REF 3
MAX629
FB 4
8
VCC
7
LX
6
GND
5
ISET
SO
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Maxim Integrated │ 10
MAX629
28V, Low-Power, High-Voltage,
Boost or Inverting DC-DC Converter
SOICN.EPS
Package Information
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Maxim Integrated │ 11
MAX629
28V, Low-Power, High-Voltage,
Boost or Inverting DC-DC Converter
Revision History
REVISION
NUMBER
REVISION
DATE
DESCRIPTION
PAGES
CHANGED
0
—
Initial release
—
1
1/99
Updated Electrical Characteristics table
2
2
8/20
Added Package Information with Thermal Resistance Values
2
For pricing, delivery, and ordering information, please visit Maxim Integrated’s online storefront at https://www.maximintegrated.com/en/storefront/storefront.html.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
© 2020 Maxim Integrated Products, Inc. │ 12
