MAX629 [MAXIM]
28V, Low-Power, High-Voltage, Boost or Inverting DC-DC Converter; 28V ，低功耗，高电压，升压或反相DC -DC转换器
| 型号： | MAX629 |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | 28V, Low-Power, High-Voltage, Boost or Inverting DC-DC Converter |
| 文件： | 总12页 (文件大小：137K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-1219; Rev 1; 6/97
2 8 V, Lo w -P o w e r, Hig h -Vo lt a g e ,
Bo o s t o r In ve rt in g DC-DC Co n ve rt e r
MAX629
_______________Ge n e ra l De s c rip t io n
____________________________Fe a t u re s
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 neg-
ative bias voltages up to ±28V from input voltages in
♦ Internal, 500mA, 28V N-Channel Switch
(No External FET Required)
♦ Generates Positive or Negative Output Voltages
♦ 80µA Supply Current
the 0.8V to V
range, and can be configured for
OUT
boost, flyback, and SEPIC topologies.
♦ 1µA Max Shutdown Current
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.
♦ Up to 300kHz Switching Frequency
♦ Adjustable Current Limit Allows Use of Small,
Inexpensive Inductors
♦ 8-Pin SO Package
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.
______________Ord e rin g In fo rm a t io n
PART
TEMP. RANGE
0°C to +70°C
PIN-PACKAGE
Dice*
MAX629C/D
MAX629ESA
-40°C to +85°C
8 SO
________________________Ap p lic a t io n s
Positive or Negative LCD Bias Generators
High-Efficiency DC-DC Boost Converters
Varactor Tuning Diode Bias
*Dice are tested at T = +25°C, DC parameters only.
A
Note: To order tape-and-reel shipping, add “-T” to the end of
the part number.
Palmtop Computers
Pin Configuration appears at end of data sheet.
2-Cell and 3-Cell Battery-Powered Applications
___________________________________________________Typ ic a l Op e ra t in g Circ u it
V
IN
V
IN
+2.7V
+2.7V
TO +5.5V
TO +5.5V
V
28V
OUT
V
CC
V
CC
SHDN
SHDN
ISET
LX
LX
FB
-V
OUT
-28V
ISET
POL
POL
FB
MAX629
GND
MAX629
GND
REF
REF
POSITIVE OUTPUT VOLTAGE
NEGATIVE OUTPUT VOLTAGE
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
2 8 V, Lo w -P o w e r, Hig h -Vo lt a g e ,
Bo o s t o r In ve rt in g DC-DC Co n ve rt e r
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (V to GND) ..................................-0.3V to +6V
SHDN to GND...........................................................-0.3V to +6V
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
CC
ISET, REF, FB, POL to GND .......................-0.3V to (V + 0.3V)
CC
LX to GND ..............................................................-0.3V to +30V
Continuous Power Dissipation (T = +70°C)
A
SO (derate 5.88mW/°C above +70°C)..........................471mW
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.
MAX629
ELECTRICAL CHARACTERISTICS
(V = +5V, C
CC
= 0.1µF, T = -40°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.) (Note1)
REF
A
A
PARAMETER
Input Voltage (Note 2)
Supply Current
CONDITIONS
MIN
TYP
MAX
5.5
UNITS
V
V
2.7
CC
V
CC
V
= 1.3V
80
0.04
2.5
120
1
µA
µA
V
FB
V
CC
Shutdown Current
Undervoltage Lockout
SHDN = GND
V
CC
100mV hysteresis
2.3
0.8
2.4
2.65
V
OUT
Input Supply Voltage (Note 2)
Voltage applied to L1 (V
)
V
IN
V
IH
V
SHDN, POL, ISET Logic Levels
V
IL
0.4
28
Positive Output Voltage
Negative Output Voltage
Circuit of Figure 2
Circuit of Figure 3
V
V
- V
-28
0.51
0.33
1.2
IN
ISET = V
0.39
0.45
0.25
0.6
CC
LX Switch-Current Limit
LX On-Resistance
A
ISET = GND
0.20
V
CC
= 5V
Ω
V
CC
= 3.3V
0.7
1.4
LX Leakage Current
Maximum LX On-Time
V
= 28V, T = +85°C
A
0.05
8.5
2.5
µA
µs
LX
6.5
0.7
10.0
1.3
POL = GND
POL = V
1.0
2.0
3.2
3.8
CC
Minimum LX Off-Time
FB Set Point
µs
V
POL = GND, V < 1V
3.0
4.5
6.0
FB
POL = V
V
> 0.25V
3.0
4.5
6.0
CC, FB
T
= 0°C to +85°C
= -40°C to +85°C
= 0°C to +85°C
= -40°C to +85°C
1.225
1.218
-15
1.250
1.275
1.282
15
A
POL = GND
(positive output)
T
A
T
A
0
POL = V
(negative output)
CC
mV
nA
V
T
A
-25
25
FB Input Bias Current
REF Output Voltage
5
50
T
A
= 0°C to +85°C
1.225
1.218
1.250
1.275
1.282
V
= 2.7V to 5.5V,
CC
no load on REF
T
A
= -40°C to +85°C
2
_______________________________________________________________________________________
2 8 V, Lo w -P o w e r, Hig h -Vo lt a g e ,
Bo o s t o r In ve rt in g DC-DC Co n ve rt e r
MAX629
ELECTRICAL CHARACTERISTICS (continued)
(V = +5V, C
CC
= 0.1µF, T = -40°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.) (Note 1)
REF
A
A
PARAMETER
CONDITIONS
= 0µA to 100µA, C = 0.47µF (Note 3)
MIN
TYP
MAX
UNITS
REF Load Regulation
I
10
25
mV
REF
REF
Circuit of Figure 2, V
= 24V, V = 3V to 5.5V,
CC
OUT
Line Regulation
Load Regulation
0.2
%/V
I
= 5mA
LOAD
Circuit of Figure 2, V
= 24V, V = 5V,
CC
OUT
0.15
150
%
I
= 0mA to 5mA
LOAD
Thermal Shutdown Threshold
Die temperature
°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.
__________________________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s
(SHDN = V , C
= 0.1µF, T = +25°C, unless otherwise noted.)
A
CC
REF
EFFICIENCY vs. LOAD CURRENT
EFFICIENCY vs. LOAD CURRENT
MAXIMUM LOAD CURRENT vs.
INPUT VOLTAGE (V = +24V, +12V)
OUT
(V = +24V)
OUT
(V = +12V)
OUT
100
95
90
85
80
75
70
65
60
100
95
90
85
80
75
70
65
60
300
250
200
A: V = 12V,
OUT
V
= 24V
IN
OUT
A
ISET = V
CC
A: V = 12V, ISET = V
B: V = 12V, ISET = GND
C: V = 5V, ISET = V
CC
B: V = 12V,
OUT
ISET = GND
A
B
IN
A
B
IN
CC
C: V =24V,
OUT
ISET = V
CC
C
D: V = 24V,
OUT
C
C
D
150
100
50
D
ISET = GND
B
E, F
V
OUT
= 12V,
ISET = V or GND
A: V = 9V
IN
CC
D: V = 5V, ISET = GND
IN
E: V = 3V, ISET = V
B: V = 5V
IN
CC
IN
F: V = 3V, ISET = GND
IN
C: V = 3V
IN
0
0.1
1
10
100
0.1
1
10
100
0
4
8
12
16
20
LOAD CURRENT (mA)
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
MAXIMUM LOAD CURRENT vs. INPUT VOLTAGE
EFFICIENCY vs. LOAD CURRENT
(V = -18V)
EFFICIENCY vs. LOAD CURRENT
(V = -18V, -12V)
OUT
(V = -12V)
OUT
OUT
90
80
70
60
100
95
90
85
80
75
70
65
60
55
50
100
95
90
85
80
75
70
65
60
55
50
A
B
A: V = -12V, ISET = V
A
B
C
D
50
40
30
20
10
0
OUT
CC
A
B, C
D
B: V = -18V, ISET = V
OUT
CC
C: V = -12V, ISET = GND
OUT
D: V = -18V, ISET = GND
OUT
C
A: V = 12V, ISET = V
IN
CC
A = V = 5V, ISET = V
IN CC
B: V = 12V, ISET = GND
IN
B = V = 5V, ISET = GND
IN
D
C: V = 5V, ISET = V or GND
IN
CC
C = V = 3V, ISET = V
IN CC
D: V = 3V, ISET = V or GND
IN
CC
D = V = 3V, ISET = GND
IN
0
4
8
12
16
20
0.1
1
10
100
0.1
1
10
100
INPUT VOLTAGE (V)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
_______________________________________________________________________________________
3
2 8 V, Lo w -P o w e r, Hig h -Vo lt a g e ,
Bo o s t o r In ve rt in g DC-DC Co n ve rt e r
____________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s (c o n t in u e d )
(SHDN = V , C
= 0.1µF, T = +25°C, unless otherwise noted.)
REF A
CC
SUPPLY CURRENT
vs. INPUT VOLTAGE
REFERENCE VOLTAGE
vs. REFERENCE LOAD CURRENT
700
1.255
1.250
1.245
1.240
1.235
1.230
V
= V
V
= V = 5V
IN CC
IN CC
C4 = 0.47µF
600
500
400
300
200
100
0
MAX629
I
IN
I
IN
I
CC
0
1
2
3
4
5
0
20 40 60 80 100 120 140 160
INPUT VOLTAGE (V)
REFERENCE LOAD CURRENT (µA)
LOAD-TRANSIENT RESPONSE
(I = V , I = 500mA)
LOAD-TRANSIENT RESPONSE
(I = GND, I = 250mA)
OUTPUT VOLTAGE RIPPLE
SET
CC LIM
SET
LIM
0mA
0mA
A
A
A
B
5mA
5mA
B
B
200µs/div
100µs/div
10µs/div
V
= +24V, ISET = V
V
= +24V, ISET = GND
V
= +24V, I
= 5mA
OUT
OUT
CC
OUT
LOAD
A: LOAD CURRENT, 0mA TO 5mA, 2.5mA/div
B: V , AC-COUPLED, 10mV/div
A: LOAD CURRENT, 0mA TO 5mA, 2.5mA/div
B: V AC-COUPLED, 10mV/div
A: ISET = V , 20mV/div
B: ISET = GND, 20mV/div
CC
OUT
OUT,
SHUTDOWN TRANSIENT
SHUTDOWN TRANSIENT
(POSITIVE CONFIGURATION)
(NEGATIVE CONFIGURATION)
5V
SHDN
0V
5V
SHDN
0V
24V
0V
V
OUT
V
OUT
0V
-20V
50ms/div
250ms/div
V
CC
= V = 5V, R = 4kΩ
SVTAR=T-VUP=D5EVL,ARY, =V 4kΩ= V = 5V, I
= 5mA
IN
L
CC
IN
L
CC
IN
LOAD
4
_______________________________________________________________________________________
2 8 V, Lo w -P o w e r, Hig h -Vo lt a g e ,
Bo o s t o r In ve rt in g DC-DC Co n ve rt e r
MAX629
______________________________________________________________P in De s c rip t io n
PIN
NAME
FUNCTION
Active-Low Shutdown Input. A logic low puts the MAX629 in shutdown mode and reduces supply current to
1µA.
1
SHDN
Polarity Input. Changes polarity and threshold of FB to allow regulation of either positive or negative output
2
3
4
5
POL
REF
FB
voltages. Set POL = GND for positive output voltage, or set POL = V for negative output voltage.
CC
1.25V Reference Output. Bypass to GND with a 0.1µF capacitor for I
≤ 10µA. REF can source 100µA to
REF
drive external loads. For 10µA ≤ I
≤ 100µA, bypass REF with a 0.47µF capacitor.
REF
Feedback Input for setting output voltage. Connect to an external voltage divider. See Setting the Output
Voltage.
Current-Limit Set Input. Connect to V for a 500mA LX current limit, or connect to GND for a 250mA LX
CC
current limit. See Setting the Current Limit.
ISET
6
7
8
GND
LX
Ground
Internal N-Channel DMOS Switch Drain
Power-Supply Input
V
CC
ulation, however, the off-time is increased to 5µs to pro-
_______________De t a ile d De s c rip t io n
vide soft-start during start-up. The switching frequency,
whic h d e p e nd s up on the loa d , c a n b e a s hig h a s
300kHz.
The MAX629 low-power, boost DC-DC converter pro-
vides either positive or negative output voltages up to
± 28V from a wid e ra ng e of inp ut volta g e s . 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.
S h u t d o w n Mo d e
Whe n SHDN is low, the MAX629 e nte rs s hutd own
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 V for normal operation.
CC
The outp ut volta g e b e ha vior in s hutd own mod e
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.
Co n t ro l S c h e m e
A 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-c yc le , the inte rna l s witc h c los e s , a nd c urre nt
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
__________________De s ig n P ro c e d u re
= V ) or 250mA (ISET = GND) (s e e Se tting the
CC
S e t t in g t h e Ou t p u t Vo lt a g e
For 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
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-
_______________________________________________________________________________________
5
2 8 V, Lo w -P o w e r, Hig h -Vo lt a g e ,
Bo o s t o r In ve rt in g DC-DC Co n ve rt e r
POL
MIN OFF-TIME
1.25V
GENERATOR
REF
REF
TRIG
POLARITY
MAX629
START-UP
Q
MAX629
ERROR
AMP
LX
F/F
R
S
Q
FB
START-UP
COMPARATOR
ISET
TRIG
Q
MAX ON-TIME
GENERATOR
(10µs)
1V
SHDN
CONTROL
V
CC
GND
Figure 1. Functional Diagram
without a significant loss of accuracy. Begin by select-
ing R2 to be in the 10kΩ to 200kΩ range, and calculate
R1 using the applicable equation from the following
subsections.
the FB threshold voltage to GND so that negative volt-
ages can be regulated. Choose R2 and calculate R1 as
follows:
| V
|
OUT
R1 = R2 x
Positive Output Voltages
For positive output voltages, use the typical boost con-
figuration shown in Figure 2, connecting POL to GND.
V
REF
where V
= 1.25V.
REF
This sets the threshold voltage at FB to equal V
.
REF
Figure 3 demonstrates generation of a negative output
volta g e b y following the MAX629 with a n inve rting
Choose the value of R2 and calculate R1 as follows:
V
charge pump. This configuration limits
V
OUT
to values
OUT
R1 = R2 x
− 1
between - V and -28V. If smaller negative output volt-
IN
V
REF
ages are required, D2’s cathode can be connected to
V . This alternative configuration permits output volt-
IN
where V
= 1.25V.
REF
ages smaller than - V , but cannot be used for output
IN
voltages more negative than - 28V - V . It produces
roughly one-half the output current as the standard con-
figuration and is typically 5% less efficient.
Negative Output Voltages
For negative output voltages, configure R1 and R2 as
shown in Figure 3, connecting POL to V . This sets
IN
CC
6
_______________________________________________________________________________________
2 8 V, Lo w -P o w e r, Hig h -Vo lt a g e ,
Bo o s t o r In ve rt in g DC-DC Co n ve rt e r
MAX629
Typical Operating Circuit is recommended for most
a p p lic a tions . La rg e r ind uc ta nc e s re d uc e the p e a k
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 com-
parator propagation delay. If input voltages below 2V
will b e c ommon, re d uc ing the ind uc ta nc e 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.
S e t t in g t h e Cu rre n t Lim it
External current-limit selection provides added control
over the MAX629’s output performance. A higher cur-
rent 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 V . When lower output current is
CC
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 cheap-
er, higher-ESR capacitors. Connect ISET to GND to
select the 250mA current-limit option.
Inductors with a ferrite core or equivalent are recom-
mended; 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.
In d u c t o r S e le c t io n
The MAX629’s high switching frequency allows for the
use of a small inductor. The 47µH inductor shown in the
V
+0.8V
TO +15V
IN
V
IN
+0.8V
TO +24V
V
C1
10µF
35V
CC
C1
10µF
35V
V
*
+2.7V
TO +5.5V
CC
+2.7V
TO +5.5V
*
L1
47µH
L1
47µH
C3
0.1µF
C3
0.1µF
C5
2.2µF
R3
2Ω
D1
MBR0540L
V
+24V
OUT
V
CC
V
CC
D1 = D2 = MBR0540L
D2
D1
SHDN
LX
SHDN
LX
FB
V
C2
10µF
35V
OUT
R1
576k
1%
C
F
150pF
ISET
POL
-20V
MAX629
GND
ISET
POL
C2
10µF
35V
CF
150pF
R1
576k
1%
R2
31.6k
1%
MAX629
FB
R2
35.7k
1%
REF
C4
REF
0.1µF
GND
C4
0.1µF
* FOR SINGLE-SUPPLY OPERATION
* FOR SINGLE-SUPPLY OPERATION
*FOR SINGLE-SUPPLY OPERATION
*FOR SINGLE-SUPPLY OPERATION
Figure 2. +24V for a Positive LCD Bias
Figure 3. -20V for a Negative LCD Bias
_______________________________________________________________________________________
7
2 8 V, Lo w -P o w e r, Hig h -Vo lt a g e ,
Bo o s t o r In ve rt in g DC-DC Co n ve rt e r
source, and reduces noise caused by the MAX629’s
switching action. The input source impedance deter-
mines the size of the capacitor required at the input
Dio d e S e le c t io n
The MAX629’s high switching frequency demands a
hig h-s p e e d re c tifie r. Sc hottky d iod e s , s uc h a s 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 pre-
ferred due to their low forward voltage. However, ultra-
high-speed silicon rectifiers are also acceptable. Table
1 lists Schottky diode suppliers.
(V ). As with the output filter capacitor, a low-ESR
IN
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
MAX629
close as possible to the V and GND pins.
CC
Reference Capacitor
Bypass REF to GND with a 0.1µF ceramic capacitor for
REF currents up to 10µA. REF can source up to 100µA
Ca p a c it o r S e le c t io n
Output Filter Capacitor
The p rima ry c rite rion for s e le c ting the outp ut filte r
capacitor is low effective series resistance (ESR). The
product of the peak inductor current and the output fil-
ter capacitor’s ESR determines the amplitude of the
hig h-fre q ue nc y rip p le s e e n on the outp ut volta g e .
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.
of current for external loads. For 10µA ≤ I
≤ 100µA,
REF
bypass REF with a 0.47µF capacitor.
Feed-Forward Capacitor
Parallel a capacitor (C ) across R1 to compensate the
F
feedback loop and ensure stability (Figures 2 and 3).
Values up to 270pF are recommended for most appli-
c a tions . Choos e the lowe s t c a p a c itor va lue tha t
e ns ure s s ta b ility; hig h c a p a c ita nc e va lue s ma y
degrade line regulation.
__________Ap p lic a t io n s In fo rm a t io n
Input Bypass Capacitor
Although the output current of many MAX629 applica-
tions ma y b e re la tive ly s ma ll, the inp ut mus t b e
designed to withstand current transients equal to the
ind uc tor c urre nt limit. The inp ut b yp a s s c a p a c itor
re d uc e s the p e a k c urre nts d ra wn from the volta g e
Ad ju s t in g t h e Ou t p u t Vo lt a g e
Many biasing applications require an adjustable output
voltage, which is easily obtained using the configura-
tion 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
Table 1. Component Suppliers
R . The output voltage of this circuit is given by:
B
R1
SUPPLIER
CAPACITORS
PHONE
FAX
V
= V
+
(V − V
)
OUT
INIT
FB
BIAS
RB
AVX: TPS series
(803) 946-0690 (803) 626-3123
(714) 969-2491 (714) 960-6492
(603) 224-1961 (603) 224-1430
where V
is the fixed output voltage as calculated in
INIT
Matsuo: 267 series
Sprague: 595D series
DIODES
the section Setting the Output Voltage, and V is equal
to either V
0V for the negative configuration. Proper choice of R
FB
(1.25V) for the positive configuration or
REF
B
provides a wide range of available output voltages
using simple external components to generate V
Motorola: MBR0530L
Nihon: EC11 FS1 series
INDUCTORS
(602) 303-5454 (602) 994-6430
(805) 867-2555 (805) 867-2698
.
BIAS
In p u t Vo lt a g e Ra n g e
Although, in many cases, the MAX629 and the inductor
are powered from the same source, it is often advanta-
geous in battery-powered applications to power the
d e vic e from a n a va ila b le re g ula te d s up p ly a nd to
power the inductor directly from a battery. The MAX629
Coilcraft: DO1608 and
DT1608 series
(847) 639-6400 (847) 639-1469
(814) 237-1431 (814) 238-0490
(847) 956-0666 (847) 956-0702
(847) 390-4373 (847) 390-4428
Murata-Erie: LQH4 series
Sumida: CD43, CD54,
and CDRH62B series
requires a +2.7V to +5.5V supply at V , but the induc-
CC
TDK: NLC565050 series
tor can be powered from as low as +0.8V, significantly
8
_______________________________________________________________________________________
2 8 V, Lo w -P o w e r, Hig h -Vo lt a g e ,
Bo o s t o r In ve rt in g DC-DC Co n ve rt e r
MAX629
limit threshold. Resistor R3 increases the usable input
voltage range by limiting the peak injected current. The
V
OUT
2Ω re sistor shown provide s a usa b le input volta ge
R1
range beyond V = 15V. In applications with a different
IN
R
B
inp ut volta g e ra ng e , R3 ma y b e inc re a s e d or
decreased as necessary, with a resulting efficiency
change of roughly 0.5%/Ω.
FB
V
BIAS
MAX629
R2
La yo u t Co n s id e ra t io n s
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
us ing the MAX629 e va lua tion kit or e q uiva le nt PC
board-based design. Breadboards or proto-boards
should never be used when prototyping switching reg-
ulators.
GND
(REF)
( ) ARE FOR NEGATIVE OUTPUT VOLTAGE CONFIGURATIONS.
Figure 4. Adjustable Output Voltage
increasing usable battery life. Using separate supplies
for V and V also reduces noise injection onto V
CC
It is imp orta nt to c onne c t the GND p in, the inp ut
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 feed-
back pin as possible. Place the input bypass capacitor
CC
IN
by isolating it from the switching transients, allowing a
smaller, less-expensive 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 effi-
ciency.
as close as possible to V and GND.
In the negative configuration shown in Figure 3, the
inverting charge pump injects current into LX with each
c yc le . The a mount of c ha rg e inje c te d inc re a s e s a t
CC
Refer to the MAX629 evaluation kit data sheet for an
example of proper board layout.
higher V , and may prematurely trip the internal current-
IN
_______________________________________________________________________________________
9
2 8 V, Lo w -P o w e r, Hig h -Vo lt a g e ,
Bo o s t o r In ve rt in g DC-DC Co n ve rt e r
__________________P in Co n fig u ra t io n
___________________Ch ip In fo rm a t io n
TRANSISTOR COUNT: 653
SUBSTRATE CONNECTED TO GND
TOP VIEW
MAX629
SHDN
POL
REF
1
2
3
4
8
7
6
5
V
CC
LX
MAX629
GND
ISET
FB
SO
10 ______________________________________________________________________________________
2 8 V, Lo w -P o w e r, Hig h -Vo lt a g e ,
Bo o s t o r In ve rt in g DC-DC Co n ve rt e r
MAX629
________________________________________________________P a c k a g e In fo rm a t io n
______________________________________________________________________________________ 11
2 8 V, Lo w -P o w e r, Hig h -Vo lt a g e ,
Bo o s t o r In ve rt in g DC-DC Co n ve rt e r
NOTES
MAX629
12 ______________________________________________________________________________________
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