Datasheet

_______________ Detailed Description
The MAX618 pulse-width modulation (PWM) DC-DC
converter with an internal 28V switch operates in a wide
range of DC-DC conversion applications including
boost, SEPIC, and flyback configurations. The MAX618
uses fixed-frequency PWM operation and Maxim’s pro-
prietary Idle Mode control to optimize efficiency over a
wide range of loads. It also features a shutdown mode
to minimize quiescent current when not in operation.
PWM Control Scheme and
Idle Mode Operation
The MAX618 combines continuous-conduction PWM
operation at medium to high loads and Idle Mode oper-
ation at light loads to provide high efficiency over a
wide range of load conditions. The MAX618 control
scheme actively monitors the output current and auto-
matically switches between PWM and Idle Mode to
optimize efficiency and load regulation. Figure 2 shows
a functional diagram of the MAX618’s control scheme.
The MAX618 normally operates in low-noise, continu-
ous-conduction PWM mode, switching at 250kHz. In
PWM mode, the internal MOSFET switch turns on with
each clock pulse. It remains on until either the error
comparator trips or the inductor current reaches the 2A
switch-current limit. The error comparator compares the
feedback-error signal, current-sense signal, and slope-
compensation signal in one circuit block. When the
switch turns off, energy transfers from the inductor to
MAX618
28V, PWM, Step-Up DC-DC Converter
_______________________________________________________________________________________________________ 5
Pin Description
PGND
ECB1Q503L
LX
FB
1μF
4.7μF
V
L
C
OUT
C
P
R1
R2
C
IND
V
OUT
IN
L
SHDN
GND
COMP
UP TO 28V
3V TO 28V
V
IN
C
COMP
MAX618
V
OUT
R1 R2 C
IND
LC
OUT
C
P
C
COMP
8V 402kΩ 93.1kΩ 150μF12μH 150μF 220pF 0.082μF
12V 715kΩ 100kΩ 100μF15μH 100μH 56pF 0.1μF
28V 574kΩ 32.4kΩ 86μF39μH33μF 47pF 0.47μF
Figure 1. Single-Supply Operation
Feedback Input. Connect a resistor-divider network to set V
OUT
. FB threshold is 1.5V.FB7
LDO Regulator Supply Input. IN accepts inputs up to +28V. Bypass to GND with a 1μF ceramic capacitor
as close to pins 10 and 12 as possible.
IN10
Internal 3.1V LDO Regulator Output. Bypass to GND with a 4.7μF capacitor.VL11
Power Ground, source of internal N-channel switchPGND13, 14, 15
Compensation Input. Bypass to GND with the capacitance value shown in Table 2.COMP6
Shutdown Input. A logic low puts the MAX618 in shutdown mode and reduces supply current to 3μA.
SHDN must not exceed VL. In shutdown, the output falls to V
IN
less one diode drop.
SHDN
5
PIN
Drain of internal N-channel switch. Connect the inductor between IN and LX.LX2, 3, 4
GroundGND
1, 8, 9,
12, 16
FUNCTIONNAME