Datasheet

MAX618
28V, PWM, Step-Up DC-DC Converter
8 _______________________________________________________________________________________
GND
LX
C
OUT
L
PGND
R2
R1
C
P
VL
COMP
C
COMP
IN
SHDN
UP TO 28V
V
IND
UP TO 28V
C
IND
IN
OUT
MAX618
2.7V TO 5.5V
4.7μF
1μF
FB
LX
C
IND
C
OUT
L
PGND
GND
R1
VL
COMP
C
COMP
IN
SHDN
UP TO 28V
V
IND
UP TO 28V
OUT
MAX618
IN
3V TO 28V
4.7μF
1μF
R2
C
P
FB
Figure 3. Dual-Supply Operation (V
IN
= 2.7V to 5.5V)
Figure 4. Dual-Supply Operation (V
IN
= 3V to 28V)
Table 2. Input Configurations
VL can be overdriven by an external supply between
2.7V and 5.5V. In systems with +3.3V or +5V logic
power supplies available, improve efficiency by power-
ing VL and V
IN
directly from the logic supply as shown
in Figure 3.
Operating Configurations
The MAX618 can be connected in one of three configura-
tions described in Table 2 and shown in Figures 1, 3, and
4. The VL linear regulator allows operation from a single
supply between +3V and +28V as shown in Figure 1.
The circuit in Figure 3 allows a logic supply to power
the MAX618 while using a separate source for DC-DC
conversion power (inductor voltage). The logic supply
(between 2.7V and 5.5V) connects to VL and IN. VL =
IN; voltages of 3.3V or more improve efficiency by pro-
viding greater gate drive for the internal MOSFET.
The circuit in Figure 4 allows separate supplies to
power IN and the inductor voltage. It differs from the
connection in Figure 3 in that the MAX618 chip supply
is not limited to 5.5V.
CIRCUIT
Figure 1
Input voltage connects
to IN and inductor.
CONNECTION
V
IN
RANGE
3V to V
OUT
(up to 28V)
V
IN
INDUCTOR
VOLTAGE
BENEFITS/COMMENTS
• Single-supply operation.
• SHDN must be connected to or pulled up to VL. On/off
control requires an open-drain or open-collector connection
to SHDN.
Figure 3
Figure 4
0 to V
OUT
(up to 28V)
0 to V
OUT
(up to 28V)
• Increased efficiency.
• SHDN can be driven by logic powered from the supply con-
nected to IN and VL, or can be connected to or pulled up to
VL.
• Input power source (inductor voltage) is separate from the
MAX618’s bias (V
IN
= VL) and can be less than or greater
than V
IN
.
• Input power source (inductor voltage) is separate from the
MAX618’s bias (V
IN
) and can be less than or greater than
V
IN
.
• SHDN must be connected to or pulled up to VL. On/off
control requires an open-drain or open-collector connection
to SHDN.
IN and inductor volt-
age supplied by sepa-
rate sources.
IN and VL connect
together. Inductor volt-
age supplied by a
separate source.
2.7V to 5.5V
3V to 28V