ADP1864AUJZ Analog Devices Inc, ADP1864AUJZ Datasheet - Page 10

• Manufacturer Part Number: ADP1864AUJZ
• Description: CONTROLLER, CURRENT MODE, TSOT-6
• Manufacturer: Analog Devices Inc

Specifications of ADP1864AUJZ

• Primary Input Voltage: 14V
• No. Of Outputs: 1
• Output Voltage: 14V
• Output Current: 5A
• Voltage Regulator Case Style: TSOT
• No. Of Pins: 6
• Operating Temperature Range: -40°C To +125°C
• Svhc: No SVHC
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ADP1864
APPLICATION INFORMATION
DUTY CYCLE
To determine the worst-case inductor ripple current, output
voltage ripple, and slope compensation factor, determine the
system maximum and minimum duty cycle. The duty cycle is
calculated by the equation
where V
A typical Schottky diode has a forward voltage drop of 0.5 V.
RIPPLE CURRENT
Choose the peak-to-peak inductor ripple current between 20%
and 40% of the maximum load current at the system’s highest
input voltage. A good starting point for a design is to pick the
peak-to-peak ripple current at 30% of the load current.
SENSE RESISTOR
Choose the sense resistor value to provide the desired current
limit. The internal current comparator measures the peak
current (sum of load current and positive inductor ripple
current) and compares it against the current limit threshold.
The current sense resistor value is calculated by the equation
where PCSV is the peak current sense voltage, typically 0.125 V.
To ensure the design provides the required output load current
over all system conditions, consider the variation in PCSV over
temperature (see the Specifications section) as well as increases
in ripple current due to inductor tolerance.
If the system is being operated with >40% duty cycle, incor-
porate the slope compensation factor into the calculation.
where SF is the slope factor correction ratio, taken from
Figure 14, at the system maximum duty cycle (minimum
input voltage).
ΔI
Duty
R
R
SENSE
SENSE
(PEAK)
D
is the diode forward drop.
Cycle
(
(
MIN
MIN
= 0.3 × I
)
)
=
=
(
DC
I
I
LOAD
LOAD
LOAD(MAX)
)
=
SF
(
(
MAX
MAX
V
V
OUT
PCSV
×
IN
)
)
PCSV
+
+
+
+
V
Δ
Δ
V
D
I
I
D
(
(
PEAK
PEAK
2
2
)
)
Rev. A | Page 10 of 16
INDUCTOR VALUE
The inductor value choice is important because it dictates the
inductor ripple and, therefore, the voltage ripple at the output.
When operating the part at greater than 40% duty cycle, keep
the inductor value low enough for the slope compensation to
remain effective.
The inductor ripple current is inversely related to the inductor
value.
where f is the oscillator frequency.
Smaller inductor values are usually less expensive, but increase
the ripple current and the output voltage ripple. Too large an
inductor value results in added expense and can impede effective
load transient responses at >40% duty cycle because it reduces
the effect of slope compensation.
Start with the highest input voltage, and assuming the ripple
current is 30% of the maximum load current,
From this starting point, modify the inductance to obtain the
right balance of size, cost, and output voltage ripple, while
maintaining the inductor ripple current between 20% and 40%
of the maximum load current.
Δ
L
1.05
0.95
0.85
0.75
0.65
0.55
0.45
0.35
I
=
(
PEAK
0
0
3 .
)
×
(
V
=
0.1
I
Figure 14. Slope Factor (SF) vs. Duty Cycle
IN
LOAD
(
V
−
IN
0.2
L
V
(
MAX
−
OUT
×
V
0.3
f
OUT
)
)
×
)
f
0.4
×
DUTY CYCLE
×
⎛
⎜
⎜
⎝
⎛
⎜
⎜
⎝
V
V
V
0.5
OUT
V
OUT
IN
IN
+
+
+
0.6
+
V
V
V
V
D
D
D
D
0.7
⎞
⎟
⎟
⎠
⎞
⎟
⎟
⎠
0.8
0.9
1
.0