ADP1610ARMZ-R7(Rev0) View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
ADP1610ARMZ-R7 Datasheet PDF : 16 Pages
| |||
ADP1610
DIODE SELECTION
The output rectifier conducts the inductor current to the output
capacitor and load while the switch is off. For high efficiency,
minimize the forward voltage drop of the diode. For this reason,
Schottky rectifiers are recommended. However, for high voltage,
high temperature applications, where the Schottky rectifier
reverse leakage current becomes significant and can degrade
efficiency, use an ultrafast 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 output diode is rated to handle the average output load
current with the minimum duty cycle. The minimum duty cycle
of the ADP1610 is
D MIN
=
VOUT − VIN −MAX
VOUT
(12)
where VIN-MAX is the maximum input voltage.
Table 6. Schottky Diode Manufacturers
Vendor
Phone No.
Motorola
602-244-3576
Diodes, Inc.
805-446-4800
Sanyo
310-322-3331
Web Address
www.mot.com
www.diodes.com
www.irf.com
LOOP COMPENSATION
The ADP1610 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
zero in the regulation feedback loop. This requires compensat-
ing the regulator such that the crossover frequency occurs well
below the frequency of the right-half plane zero. The right-half
plane zero is determined by the following equation:
FZ
(RHP)
=
⎜⎜⎝⎛
VIN
VOUT
⎟⎟⎠⎞ 2
×
RLOAD
2π× L
(13)
where:
FZ(RHP) is the right-half plane zero.
RLOAD is the equivalent load resistance or the output voltage
divided by the load current.
To stabilize the regulator, make sure that the regulator crossover
frequency is less than or equal to one-fifth of the right-half
plane zero and less than or equal to one-fifteenth of the
switching frequency.
The regulator loop gain is
AVL
= VFB
VOUT
× VIN
VOUT
× G MEA ×
Z COMP
× GCS ×
Z OUT
(14)
where:
AVL is the loop gain.
VFB is the feedback regulation voltage, 1.230 V.
VOUT is the regulated output voltage.
VIN is the input voltage.
GMEA is the error amplifier transconductance gain.
ZCOMP is the impedance of the series RC network from COMP to
GND.
GCS is the current sense transconductance gain (the inductor
current divided by the voltage at COMP), which is internally set
by the ADP1610.
ZOUT is the impedance of the load and output capacitor.
To determine the crossover frequency, it is important to note
that, at that frequency, the compensation impedance (ZCOMP) is
dominated by the resistor, and the output impedance (ZOUT) is
dominated by the impedance of the output capacitor. So, when
solving for the crossover frequency, the equation (by definition
of the crossover frequency) is simplified to
|
AVL
|
=
VFB
VOUT
× VIN
VOUT
×
GMEA×
RCOMP×
GCS
×
2π
×
1
fC ×COUT
=1
(15)
where:
fC is the crossover frequency.
RCOMP is the compensation resistor.
Solving for RCOMP,
R
= COMP
2π × f C ×COUT × VOUT × VOUT
VFB × VIN × GMEA × GCS
(16)
For VFB = 1.23, GMEA = 100 µS, and GCS = 2 S,
RCOMP
=
2.55 ×104
×
fC
× COUT
VIN
× VOUT
× VOUT
(17)
Once the compensation resistor is known, set the zero formed
by the compensation capacitor and resistor to one-fourth of the
crossover frequency, or
CCOMP
=
π×
fC
2
× RCOMP
(18)
where CCOMP is the compensation capacitor.
Rev. 0 | Page 12 of 16
Share Link: 