MAX629ESA Maxim Integrated Products, MAX629ESA Datasheet - Page 7

• Manufacturer Part Number: MAX629ESA
• Description: IC CONV 28V BOOST/INVERT 8-SOIC
• Manufacturer: Maxim Integrated Products
• Type: Step-Up (Boost), Inverting, Flyback, Sepicr

Specifications of MAX629ESA

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: ±28V
• Current - Output: 500mA
• Frequency - Switching: 300kHz
• Voltage - Input: 2.7 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Power - Output: 471mW
• Output Voltage: 28 V
• Input Voltage: 2.7 V to 5.5 V
• Supply Current: 80 uA
• Switching Frequency: 300 KHz
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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
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.
The MAX629’s high switching frequency allows for the
use of a small inductor. The 47µH inductor shown in the
Figure 2. +24V for a Positive LCD Bias
*FOR SINGLE-SUPPLY OPERATION
V
+2.7V
TO +5.5V
V
+0.8V
TO +24V
IN
CC
* FOR SINGLE-SUPPLY OPERATION
0.1 F
C4
*
0.1 F
C3
SHDN
ISET
POL
REF
_______________________________________________________________________________________
MAX629
V
GND
10 F
CC
CC
35V
C1
Setting the Current Limit
. When lower output current is
LX
FB
Boost or Inverting DC-DC Converter
MBR0540L
Inductor Selection
L1
47 H
31.6k
576k
D1
1%
1%
R1
R2
28V, Low-Power, High-Voltage,
C
150pF
F
V
+24V
OUT
C2
10 F
35V
Typical Operating Circuit is recommended for most
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 com-
parator 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.
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.
Figure 3. -20V for a Negative LCD Bias
V
+0.8V
V
+2.7V
TO +5.5V
*FOR SINGLE-SUPPLY OPERATION
TO +15V
IN
CC
* FOR SINGLE-SUPPLY OPERATION
*
0.1 F
C3
SHDN
ISET
POL
MAX629
GND
10 F
V
35V
CC
C1
REF
LX
FB
2.2 F
C5
L1
47 H
R3
2
C4
0.1 F
D2
D1 = D2 = MBR0540L
35.7k
576k
1%
1%
R1
R2
D1
CF
150pF
V
-20V
OUT
C2
10 F
35V
7