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PDF MAX629 Data sheet ( Hoja de datos )
| Número de pieza | MAX629 | |
| Descripción | 28V / Low-Power / High-Voltage / Boost or Inverting DC-DC Converter | |
| Fabricantes | Maxim Integrated | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de MAX629 (archivo pdf) en la parte inferior de esta página. Total 12 Páginas | ||
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19-1219; Rev 1; 6/97
EVALUAATVIOANILKAIBTLMEANUAL
28V, Low-Power, High-Voltage,
Boost or Inverting DC-DC Converter
_______________General Description
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
the 0.8V to VOUT range, 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.
________________________Applications
Positive 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
____________________________Features
o Internal, 500mA, 28V N-Channel Switch
(No External FET Required)
o Generates Positive or Negative Output Voltages
o 80µA Supply Current
o 1µA Max Shutdown Current
o Up to 300kHz Switching Frequency
o Adjustable Current Limit Allows Use of Small,
Inexpensive Inductors
o 8-Pin SO Package
______________Ordering Information
PART
MAX629C/D
MAX629ESA
TEMP. RANGE
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
Dice*
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.
Pin Configuration appears at end of data sheet.
___________________________________________________Typical Operating Circuit
VIN
+2.7V
TO +5.5V
VCC
SHDN
LX
ISET
POL FB
MAX629
REF
GND
VIN
+2.7V
TO +5.5V
VOUT
28V
VCC
SHDN
ISET
POL
LX
MAX629 FB
REF
GND
-VOUT
-28V
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
1 page  
28V, Low-Power, High-Voltage,
Boost or Inverting DC-DC Converter
______________________________________________________________Pin Description
PIN NAME
FUNCTION
1
SHDN
Active-Low Shutdown Input. A logic low puts the MAX629 in shutdown mode and reduces supply current to
1µA.
2
POL
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.
3
REF
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.
4
FB
Feedback Input for setting output voltage. Connect to an external voltage divider. See Setting the Output
Voltage.
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 Internal N-Channel DMOS Switch Drain
8 VCC Power-Supply Input
_______________Detailed Description
The MAX629 low-power, boost DC-DC converter pro-
vides 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 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 Scheme
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-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 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 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
_______________________________________________________________________________________ 5
5 Page 
28V, Low-Power, High-Voltage,
Boost or Inverting DC-DC Converter
________________________________________________________Package Information
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet MAX629.PDF ] | |
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