Datasheet

ADP1610
Rev. A | Page 13 of 20
The regulator loop gain is calculated using the following
equation:
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. The
following are recommended Schottky diode manufacturers:
OUT
CSCOMPMEA
OUT
IN
OUT
FB
VL
ZGZG
V
V
V
V
A ×××××=
(14)
where:
A
VL
is the loop gain.
V
FB
is the feedback regulation voltage, 1.230 V.
V
OUT
is the regulated output voltage.
V
IN
is the input voltage.
G
MEA
is the error amplifier transconductance gain.
Z
COMP
is the impedance of the series RC network from COMP
to GND.
G
CS
is the current sense transconductance gain (the inductor
current divided by the voltage at COMP), which is internally
set by the ADP1610.
Z
OUT
is the impedance of the load and output capacitor.
• ON Semiconductor
• Diodes, Inc.
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 calculated by the following equations:
OUT
MAXIN
OUT
MIN
V
VV
D
−
−
=
(12)
To determine the crossover frequency, it is important to note
that at that frequency the compensation impedance (Z
COMP
) is
dominated by the resistor, and the output impedance (Z
OUT
) is
dominated by the impedance of the output capacitor. Therefore,
when solving for the crossover frequency, the equation (by
definition of the crossover frequency) is simplified to
where V
IN-MAX
is the maximum input voltage.
LOOP COMPENSATION
1
2
1
=
××π
×××××=
OUT
C
CSCOMPMEA
OUT
IN
OUT
FB
VL
Cf
GRG
V
V
V
V
A (15)
The ADP1610 uses external components to compensate the
regulator loop, allowing optimization of the loop dynamics
for a given application.
where:
f
C
is the crossover frequency.
R
COMP
is the compensation resistor.
The step-up converter produces an undesirable right-half plane
zero in the regulation feedback loop. This requires compensating
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:
R
COMP
is calculated using the following equation:
L
R
V
V
RHPF
LOAD
OUT
IN
Z
×π
×
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=
2
)(
2
(13)
GCSGVV
VVCf
R
MEA
INFB
OUTOUTOUT
C
COMP
×××
××××π
=
2
(16)
V
FB
= 1.23, G
MEA
= 100 S, and G
CS
= 2 S is calculated using the
following equation:
where:
F
Z
(RHP) is the right-half plane zero.
R
LOAD
is the equivalent load resistance or the output voltage
divided by the load current.
IN
OUTOUTOUT
C
COMP
V
VVCf
R
×××××
=
4
1055.2
(17)
When the compensation resistor is known, the zero formed
by the compensation capacitor and resistor is to be set to one-
fourth of the crossover frequency using the following equation:
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.
COMPC
COMP
Rf
C
××π
=
2
(18)
where C
COMP
is the compensation capacitor.