Datasheet

At high input-to-output differential, and high switching
frequency, the on-time drops to the order of 100ns.
Even though the MAX15036/MAX15037 can control the
on-time as low as 100ns, the internal current-limit circuit
may not detect the overcurrent within this time. In that
case, the output current during the fault may exceed the
current limit specified in the Electrical Characteristics
table. The MAX15036/MAX15037 may still be protected
against the output short-circuit fault through the
overtemperature shutdown. However, the output switch
current may be as high as 5.6A. If the minimum on-time
for a given frequency and duty cycle is less than
200ns, choose the inductor with a saturation current of
greater than 5.6A.
Power-On Reset ( RESET )
(MAX15036 Only)
RESET is an active-low open-drain output that goes low
when V
OUT
falls below 92.5% of its nominal set point.
RESET goes high impedance when V
OUT
rises above
92.5% of its nominal set point, the soft-start period is
complete, and the 200ms (typ) timeout period has
elapsed. Connect a pullup resistor from RESET to a
logic voltage or to V
L
. The internal open-drain MOSFET
at RESET can sink 3mA while providing a TTL-compati-
ble logic-low signal. Connect RESET to SGND or leave
unconnected when not used.
Power-Good (PGOOD)
(MAX15037 Only)
PGOOD is an open-drain, active-high output that goes
low when V
OUT
is below 92.5% of its nominal set point
and goes high impedance when V
OUT
goes above
92.5% its nominal set point. Connect a pullup resistor
from PGOOD to a logic voltage or to V
L
. PGOOD can sink
up to 3mA while still providing a TTL-compatible logic-low
output. Pulling EN low forces PGOOD low. Connect
PGOOD to SGND or leave unconnected when not used.
Thermal-Overload Protection
During a continuous output short-circuit or overload
condition, the die junction temperature in the
MAX15036/MAX15037 can exceed its limit. The
MAX15036/MAX15037 provide an internal thermal shut-
down to turn off the device when the die temperature
reaches +170°C. A thermal sensor monitors the die
temperature and turns the device on again when the
temperature reduces by +25°C. During thermal shut-
down, the internal power MOSFET shuts off, DL pulls to
SGND, V
L
shuts down, RESET (MAX15036)/PGOOD
(MAX15037) goes low, and soft-start resets.
Applications Information
Setting the Switching Frequency
The controller generates the switching frequency (f
SW
)
through the internal oscillator or the signal at SYNC
(f
SYNC
), when driven by an external oscillator. The
switching frequency is equal to f
SW
or f
SYNC
.
A resistor, R
OSC
, from OSC to SGND sets the internal
oscillator. The relationship between f
SW
and R
OSC
is:
where f
SW
is in Hertz, and R
OSC
is in ohms. For exam-
ple, a 1.25MHz switching frequency is set with R
OSC
=
10kΩ. Higher frequencies allow designs with lower
inductor values and less output capacitance.
Consequently, peak currents and I
2
R losses are lower
at higher switching frequencies, but core losses, gate-
charge currents, and switching losses increase.
Rising clock edges on SYNC are interpreted as a syn-
chronization input. If the SYNC signal is lost, the internal
oscillator takes control of the switching rate, returning
the switching frequency to that set by R
OSC
. This main-
tains output regulation even with intermittent SYNC sig-
nals. When using an external synchronization signal, set
R
OSC
so that (0.8 x f
SYNC
) ≤ f
SW
≤ (1.2 x f
SYNC
).
Buck Converter
Use the internal n-channel power MOSFET as a high-
side switch to configure the MAX15036/MAX15037 as a
buck converter. In this configuration, SOURCE is con-
nected to the inductor, DRAIN is connected to the
input, and BST/VDD connects to the cathode of the
bootstrap diode and capacitor. Figures 5 and 6 show
the typical application circuits for MAX15036/
MAX15037, respectively, in a buck configuration.
R
125 10
f
OSC
8
SW
=
×
MAX15036/MAX15037
2.2MHz, 3A Buck or Boost Converters
with an Integrated High-Side Switch
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