Datasheet

cycles (hiccup timeout delay) before attempting a new
soft-start sequence. The hiccup-mode protection remains
active during the soft-start time.
Undervoltage Lockout
The MAX15046 provides an internal undervoltage lockout
(UVLO) circuit to monitor the voltage on V
CC
. The UVLO
circuit prevents the MAX15046 from operating when V
CC
is lower than V
UVLO
. The UVLO threshold is 4V, with
400mV hysteresis to prevent chattering on the rising/
falling edge of the supply voltage. DL and DH stay low
to inhibit switching when the device is in undervoltage
lockout.
Thermal-Overload Protection
Thermal-overload protection limits total power dissipation
in the MAX15046. When the junction temperature of the
device exceeds +150°C, an on-chip thermal sensor shuts
down the device, forcing DL and DH low, which allows
the device to cool. The thermal sensor turns the device
on again after the junction temperature cools by 20°C.
The regulator shuts down and soft-start resets during
thermal shutdown. Power dissipation in the LDO regulator
and excessive driving losses at DH/DL trigger thermal-
overload protection. Carefully evaluate the total power
dissipation (see the Power Dissipation section) to avoid
unwanted triggering of the thermal-overload protection in
normal operation.
Applications Information
Effective Input-Voltage Range
The MAX15046 operates from 4.5V to 40V input supplies
and regulates output down to 0.6V. The minimum voltage
conversion ratio (V
OUT
/V
IN
) is limited by the minimum
controllable on-time. For proper fixed-frequency PWM
operation, the voltage conversion ratio must obey the fol-
lowing condition:
OUT
ON(MIN) SW
IN
V
tf
V
>×
where t
ON(MIN)
is 125ns and f
SW
is the switching fre-
quency in Hertz. Pulse skipping occurs to decrease the
effective duty cycle when the desired voltage conversion
does not meet the above condition. Decrease the switch-
ing frequency or lower the input voltage V
IN
to avoid pulse
skipping.
The maximum voltage conversion ratio is limited by the
maximum duty cycle (D
max
):
OUT max DROP2 max DROP1
max
IN IN
V D V (1-D ) V
D-
VV
×+ ×
<
where V
DROP1
is the sum of the parasitic voltage drops in
the inductor discharge path, including synchronous recti-
fier, inductor, and PCB resistance. V
DROP2
is the sum of
the voltage drops by the resistance in the charging path,
including high-side switch, inductor, and PCB resistance.
In practice, provide adequate margin to the above condi-
tions for good load-transient response.
Setting the Output Voltage
Set the MAX15046 output voltage by connecting a resis-
tive divider from the output to FB to GND (Figure 2). When
using Type II compensation, select R
2
from between 4kΩ
and 16kΩ. Calculate R
1
with the following equation:
OUT
12
FB
V
R R -1
V


=





where V
FB
= 0.59V (see the Electrical Characteristics
table) and V
OUT
can range from 0.6V to (0.85 x V
IN
).
When using Type III compensation, calculate the values
of R1 and R2 as shown in the Type III Compensation
Network (Figure 4) section.
Figure 2. Adjustable Output Voltage
FB
R
1
OUT
R
2
MAX15046
MAX15046 40V, High-Performance, Synchronous
Buck Controller
www.maximintegrated.com
Maxim Integrated │ 13