ADP1621ARMZ-R7 Analog Devices Inc, ADP1621ARMZ-R7 Datasheet - Page 16

• Manufacturer Part Number: ADP1621ARMZ-R7
• Description: IC CTRLR DC/DC PWM STEPUP 10MSOP
• Manufacturer: Analog Devices Inc
• Type: Step-Up (Boost)r

Specifications of ADP1621ARMZ-R7

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Current - Output: 1A
• Frequency - Switching: 100kHz ~ 1.5MHz
• Voltage - Input: 2.9 ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Primary Input Voltage: 5.5V
• No. Of Outputs: 1
• Output Current: 1A
• No. Of Pins: 10
• Operating Temperature Range: -40°C To +125°C
• Msl: MSL 1 - Unlimited
• Frequency Max: 1.5MHz
• Termination Type: SMD
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: ADP1621-EVALZ - BOARD EVALUATION FOR ADP1621
• Voltage - Output: -
• Power - Output: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant
• Other names: ADP1621ARMZ-R7; ADP1621ARMZ-R7TR

ADP1621
The total power dissipation determines the diode junction
temperature, which is given by
where T
perature, and θ
of the diode package. The diode junction temperature must not
exceed its maximum rating at the given power dissipation level.
For high efficiency, Schottky diodes are recommended. The low
forward-voltage drop of a Schottky diode reduces the power losses
during the MOSFET off time, and the fast switching speed reduces
the switching losses during the MOSFET transitions. However,
for high voltage, high temperature applications where the reverse
leakage current of the Schottky diode can become significant
and degrade efficiency, use an ultrafast-recovery junction diode.
Make sure that the diode is rated to handle the average output
load current. Many diode manufacturers derate the current
capability of the diode as a function of the duty cycle. Verify
that the diode is rated to handle the average output load current
with the minimum duty cycle. Also, ensure that the peak inductor
current is less than the maximum rated current of the diode.
MOSFET SELECTION
When turned on, the external n-channel MOSFET allows
energy to be stored in the magnetic field of the inductor. When
the MOSFET is turned off, this energy is delivered to the load to
boost the output voltage.
The choice of the external power MOSFET directly affects the
boost converter performance. Choose the MOSFET based on
the following: threshold voltage (V
maximum voltage and current ratings, and gate charge.
The minimum operating voltage of the ADP1621 is 2.9 V.
Choose a MOSFET with a V
minimum input supply voltage at PIN used in the application.
Ensure that the maximum V
a few volts greater than the maximum voltage that is applied to
PIN. Ensure that the maximum V
exceeds the maximum V
on parasitics, the MOSFET may be exposed to voltage spikes that
exceed the sum of V
Estimate the rms current in the MOSFET under continuous
conduction mode by
where D is the duty cycle. Derate the MOSFET current at least
20% to account for inductor ripple and changes in the forward-
voltage drop of the diode.
T
I
MOSFET
J
,
DIODE
J,DIODE
,
RMS
is the junction temperature, T
=
JA
T
A
is the junction-to-ambient thermal resistance
=
+
OUT
I
1
P
LOAD
−
DIODE
and the forward-voltage drop of the diode.
D
OUT
×
×
by at least 5 V to 10 V. Depending
T
GS
θ
D
that is at least 0.3 V less than the
JA
rating of the MOSFET is at least
DS
T
), on resistance (R
rating of the MOSFET
A
is the ambient tem-
DSON
),
(17)
(18)
Rev. A | Page 16 of 32
The MOSFET power dissipation due to conduction is thus
where P
on resistance. The variable K is a factor that models the increase
of R
where T
multiple n-channel MOSFETs can be placed in parallel to reduce
the effective R
The power dissipation due to switching transition loss is
approximated by
where P
time, and t
times are functions of both the gate drive circuitry and the
MOSFET used in the application.
The total power dissipation of the MOSFET is the sum of the
conduction and transition losses:
where P
that the maximum power dissipation is significantly less than
the maximum power rating of the MOSFET.
The total power dissipation also determines the MOSFET
junction temperature, which is given by
where T
temperature, and θ
resistance of the MOSFET package. The MOSFET junction
temperature must not exceed its maximum rating at the given
power dissipation level.
If lossless current sensing is not used, there will also be power
dissipation in the external current-sense resistor, R
dissipation, P
is given by
LOOP COMPENSATION
The ADP1621 uses external components to compensate the
regulator loop, allowing optimization of the loop dynamics for
a given application.
The step-up converter produces an undesirable right-half plane
(RHP) zero in the regulation feedback loop. This RHP zero
requires compensating the regulator such that the crossover
DSON
T
K
P
P
P
P
C
SW
CS
MOSFET
J
=
,
C
MOSFET
SW
MOSFET
J,MOSFET
J,MOSFET
=
with temperature:
=
is the conduction power loss, and R
. 0
=
⎛
⎜
⎝
is the switching power loss, t
F
⎛
⎜
⎝
005
I
1
(
is the MOSFET fall time. The MOSFET rise and fall
V
I
1
LOAD
−
=
CS
LOAD
is the total MOSFET power dissipation. Ensure
OUT
−
DSON
/
is the MOSFET junction temperature. Note that
=
is the junction temperature, T
D
, in the external resistor due to conduction losses
o
P
D
C
C
T
⎞
⎟
⎠
×
.
+
A
+
⎞
⎟
⎠
2
JA
(
2
V
×
T
+
P
is the junction-to-ambient thermal
×
J,MOSFET
D
SW
D
P
D
)
MOSFET
×
×
×
R
I
1
R
LOAD
DSON
−
CS
2
−
D
×
25
×
θ
×
JA
(
o
(
1
C
t
R
+
)
+
K
t
)
R
F
is the MOSFET rise
)
×
DSON
f
A
SW
is the ambient
is the MOSFET
CS
. The power
(19)
(20)
(21)
(22)
(23)
(24)