MAX15023 Maxim Integrated Products, MAX15023 Datasheet - Page 16

• Manufacturer Part Number: MAX15023
• Description: Dual-Output Synchronous Buck Controller
• Manufacturer: Maxim Integrated Products

www.datasheet4u.com
Wide 4.5V to 28V Input, Dual-Output
Synchronous Buck Controller
In case of a nonideal short circuit applied at the output,
the output voltage equals the output impedance times the
limited inductor current during this phase. After reaching
the maximum allowable limit of the soft-start duration
(twice the normal soft-start time), the controller remains off
for 7936 clock cycles before trying to soft-start again.
The MAX15023 has an internal undervoltage lockout
(UVLO) circuit to monitor the voltage on V
UVLO circuit prevents the MAX15023 from operating if
the voltages for the MOSFET drivers or for the internal
control functions are too low. The V
is 3.8V (typ), with 430mV hysteresis to prevent chatter-
ing on the rising/falling edge of the supply voltage.
Before V
DL_ and DH_ stay low to inhibit switching.
Thermal-overload protection limits total power dissipation
in the MAX15023. When the device’s die-junction tem-
perature exceeds T
sor shuts down the device, forcing DL_ and DH_ low,
allowing the IC to cool. The thermal sensor turns the
device on again after the junction temperature cools by
20°C. During thermal shutdown, the regulators shut
down, and soft-start is reset. Thermal-overload protection
can be triggered by power dissipation in the LDO regula-
tor, by excessive driving losses, or by both. Therefore,
carefully evaluate the total power dissipation (see the
Power Dissipation section) to avoid unwanted triggering
of the thermal-overload protection in normal operation.
Although the MAX15023 controllers can operate from
input supplies up to 28V and regulate down to 0.6V, the
minimum voltage conversion ratio (V
limited by the minimum controllable on-time. For proper
fixed-frequency PWM operation, the voltage conversion
ratio should obey the following condition:
where t
frequency in Hertz. If the desired voltage conversion
does not meet the above condition, then pulse skipping
occurs to decrease the effective duty cycle. To avoid
this, decrease the switching frequency or lower the
input voltage V
16
______________________________________________________________________________________
ON(MIN)
CC
reaches UVLO rising threshold voltage,
IN
is 100ns (max) and f
.
Effective Input Voltage Range
V
Thermal-Overload Protection
OUT
V
J
I
N
= +150°C, an on-chip thermal sen-
>
t
ON(MIN)
Undervoltage Lockout
Design Procedure
×
f
CC
SW
SW
OUT
falling threshold
is the switching
/V
IN
) might be
CC
. The
The maximum voltage conversion ratio is limited by the
maximum duty cycle (D
where V
in the inductor discharge path, including synchronous
rectifier, inductor, and PCB resistances. V
sum of the resistances in the charging path, including
high-side switch, inductor, and PCB resistances. In
practice, the above condition should be met with ade-
quate margin for good load-transient response.
Each controller has an enable input referenced to an
analog voltage (1.2V). When the voltage exceeds 1.2V,
the regulator is enabled. To set a specific turn-on
threshold that can act as a secondary UVLO, a resistive
divider circuit can be used (see Figure 2)
Select R
200kΩ. Calculate R
lowing equation:
where V
EN_ off-time duration must be longer than 4096/f
ensure proper soft-start operation, where f
Figure 2. Adjustable Enable Voltage
V
OUT
V
IN
DROP1
EN_H_
<
2
D
(EN_ to SGND resistor) to a value lower than
max
= 1.2V (typical).
is the sum of the parasitic voltage drops
MA15023
−
R
Setting the Enable Input (EN_)
D
1
max
1
=
(V
R
2
MON
×
max
EN_
⎡
⎢
⎢
⎣
⎛
⎜
⎝
V
DROP2
V
):
V
EN H
to EN_ resistor) with the fol-
MON
_ _
+
V
⎞
⎟
⎠
(1 D
IN
−
−
1
⎤
⎥
⎥
⎦
V
MON
R
R
max
1
2
SW
DROP2
) V
×
is in hertz.
DROP1
SW
is the
to