Datasheet

MAX15035
15A Step-Down Regulator with Internal Switches
18 ______________________________________________________________________________________
Output Voltages Greater than 2V
Although REFIN is limited to a 0 to 2V range, the out-
put-voltage range is unlimited since the MAX15035 uti-
lizes a high-impedance feedback input (FB). By adding
a resistive voltage-divider from the output to FB to ana-
log ground (Figure 6), the MAX15035 supports output
voltages above 2V. However, the controller also uses
FB to determine the on-time, so the voltage-divider
influences the actual switching frequency, as detailed
in the On-Time One-Shot section.
Internal Integration
An integrator amplifier forces the DC average of the FB
voltage to equal the target voltage. This internal amplifi-
er integrates the feedback voltage and provides a fine
adjustment to the regulation voltage (Figure 2), allowing
accurate DC output-voltage regulation regardless of the
compensated feedback ripple voltage and internal
slope-compensation variation. The integrator amplifier
has the ability to shift the output voltage by ±55mV (typ).
The MAX15035 disables the integrator by connecting the
amplifier inputs together at the beginning of all downward
REFIN transitions done in pulse-skipping mode. The inte-
grator remains disabled until 20μs after the transition is
completed (the internal target settles) and the output is in
regulation (edge detected on the error comparator).
Power-Good Outputs (PGOOD)
and Fault Protection
PGOOD is the open-drain output that continuously
monitors the output voltage for undervoltage and over-
voltage conditions. PGOOD is actively held low in shut-
down (EN = GND), and during soft-start and
soft-shutdown. Approximately 200μs (typ) after the soft-
start terminates, PGOOD becomes high impedance as
long as the feedback voltage is above the UVP thresh-
old (REFIN - 200mV) and below the OVP threshold
(REFIN + 300mV). PGOOD goes low if the feedback
voltage drops 200mV below the target voltage (REFIN)
or rises 300mV above the target voltage (REFIN), or the
SMPS controller is shut down. For a logic-level PGOOD
C1
1μF
EN
OFFON
V
DD
V
CC
C2
1μF
PGOOD
R10
100kΩ
REFIN
IN
LX
C
BST
0.1μF
L1
C
OUT
TON
GND/OPEN/REF/V
DD
BST
PGND
FB
REF
ILIM
REF
R
TON
332kΩ
R5
49.4kΩ
R4
49.9kΩ
AGND
AGND
PWR
PWR
PWR
AGND
AGND
PWR
2
34
36
4
37
29
18–26, EP3
30
5, 16, EP2
6–15
AGND
3, 28, EP1
38
SKIP
35
32
33
OUTPUT
3.3V
INPUT
7V TO 24V
5V BIAS
SUPPLY
MAX15035
C
IN
PWR
R7
20kΩ
R6
13.0kΩ
AGND
C3
1000pF
5V
BIAS
7V TO 15V
INPUT
OPTIONAL
5.6V
1kΩ
Figure 6. High Output-Voltage Application Using a Feedback Divider
SEE TABLE 1 FOR COMPONENT SELECTION.