MAX17512ATP+ Maxim Integrated, MAX17512ATP+ Datasheet - Page 12

• Manufacturer Part Number: MAX17512ATP+
• Description: Current & Power Monitors & Regulators High Speed Valley Current Regulator
• Manufacturer: Maxim Integrated

Specifications of MAX17512ATP+

• Product: Current Regulators
• Supply Voltage - Max: 18 V
• Supply Voltage - Min: 6.5 V
• Input Voltage Range: 6.5 V to 18 V

Figure 5. Programming the High-Side Switch On-Time
The device employs a modified constant on-time valley
current-control scheme (see the
to generate the programmed inductor current and induc-
tor ripple current. The heart of this control scheme is the
one-shot that sets the high-side switch on-time. This fast,
low-jitter, adjustable one-shot includes circuitry that var-
ies the on-time in response to the resistance value con-
nected between the RTON pin and SGND terminals. The
resistor (R
as follows:
where t
For example, a 36kI resistor should be connected
between the RTON pin and SGND to program 100ns
high-side MOSFET on-time (see
Ensure that the junction temperature of the device
does not exceed
conditions specified for the design. The internal linear
regulator power dissipation, which occurs when the
device uses its internal linear regulator to power the
control and driver circuitry, can be calculated using the
following equation:
where V
I
supply current can be calculated as follows:
Programming the Constant On-Time (RTON)
AVIN
is the operating supply current. The I
ON
AVIN
RTON
is in ns.
High-Speed, Constant On-Time, Valley Current
I
AVIN
=
is the voltage applied at the AVIN pin and
R
RTON
) can be calculated for a given on-time
R
=
=
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RTON
I
P
VINQ
IN
+125NC under
RTON
V
+
t
Thermal Considerations
AVIN
I
ON
PVCCSW
2520
MAX17512
−
×
30
Control Scheme
I
Figure
AVIN
in k
Regulator for Tracking Applications
+
I
Ω
AVCCQ
5).
the operating
AVIN
operating
section)
where I
the switching current drawn from PVCC for a given fre-
quency of operation, and I
from AVCC.
The power required for the device to operate for the
design, in which the external V
power the control and driver circuitry, can be calculated
using the following equation:
where V
pins, V
input supply current, I
drawn from PVCC for a given frequency of operation, and
I
The internal high-side and low-side nMOSFETs experience
conduction loss and transition loss when switching between
on and off states. The conduction and switching transition
losses for a MOSFET can be calculated as follows:
where I
ance, and t
internal MOSFET.
Additional loss occurs in the system in every switching
cycle due to energy stored in the drain-source capaci-
tance of the internal MOSFET being lost when the MOSFET
turns on, and discharges the drain-source capacitance
voltage to zero. This loss is estimated as follows:
where C
MOSFET, V
and f
The total power loss in the device can be calculated from
the following equation:
where P
side and low-side MOSFETs, P
transition loss in both the high-side and low-side switches,
and P
AVCCQ
P
LOSS
P
IN
P
TRANSITION
SW
TCAP
=
REG
RMS
=
VINQ
TCONDUCTION
(
IN
is the current drawn from AVCC.
is the frequency of operation.
V
DS
P
IN
IN
P
is the voltage applied at the PVIN and AVIN
DSMAX
is the total drain-source capacitance loss.
is the external regulator voltage, I
P
R
CAP
is the RMS current, R
×
+
CONDUCTION
is the drain-source capacitance of the
is the input supply current, I
I
and t
P
VINQ
TCONDUCTION
=
=
0.5 C
is the maximum drain-source voltage,
0.5 V
F
)
+
=
×
are the rise and fall times of the
×
PVCCSW
is the conduction loss in the high-


V
INMAX
DS
REG
AVCCQ
×
I
RMS
V
×
+
DSMAX
REG
MAX17512
(
TTRANSITION
×
is the switching current
I
P
PVCCSW
I
2
PK
TTRANSITION
DSON
is the current drawn
×
regulator is used to
R
×
2
DSON
(
t
×
R
is the on-resist-
f
+
SW
+
t
I
F
AVCCQ
PVCCSW
VINQ
is the total
)
×
+
f
P
SW
TCAP
is the
)


is