ADP1883 Analog Devices, ADP1883 Datasheet - Page 24

• Manufacturer Part Number: ADP1883
• Description: Synchronous Current-Mode Buck Controller with Constant On-time, 0.8 V Reference Voltage, and Power Saving Mode
• Manufacturer: Analog Devices

ADP1882/ADP1883
APPLICATIONS INFORMATION
FEEDBACK RESISTOR DIVIDER
The required resistor divider network can be determined for
a given V
is fixed at 0.8 V. Selecting values for R
minimum output load current of the converter. Therefore, for
a given value of R
following expression:
INDUCTOR SELECTION
The inductor value is inversely proportional to the inductor
ripple current. The peak-to-peak ripple current is given by
where K
The equation for the inductor value is given by
where:
V
V
f
1.0 MHz).
When selecting the inductor, choose an inductor saturation
rating that is above the peak current level, and then calculate
the inductor current ripple (see the Valley Current-Limit
Setting section and Figure 79).
SW
Figure 79. Peak Current vs. Valley Current Threshold for 33%, 40%, and 50%
IN
OUT
is the controller switching frequency (300 kHz, 600 kHz, and
is the high voltage input.
R
is the desired output voltage.
Δ
L
T
I
52
50
48
46
44
42
40
38
36
34
32
30
28
26
24
22
20
18
16
14
12
10
=
= R
8
L
I
6
OUT
is typically 0.33.
(
=
V
Δ
B
K
IN
I
value because the internal band gap reference (V
×
8
L
I
−
×
×
(
V
V
10
I
f
OUT
B
LOAD
OUT
SW
, the R
0
12
8 .
of Inductor Ripple Current
−
)
VALLEY CURRENT LIMIT (A)
×
≈
0
V
8 .
14
T
V
I
V
value can be determined using the
LOAD
OUT
V)
IN
3
16
18
20
T
and R
ΔI = 40%
22
ΔI = 50%
24
B
determines the
ΔI = 33%
26
28
30
REF
Rev. 0 | Page 24 of 40
)
Table 7. Recommended Inductors
L
(μH)
0.12
0.22
0.47
0.72
0.9
1.2
1.0
1.4
2.0
0.8
OUTPUT RIPPLE VOLTAGE (ΔV
The output ripple voltage is the ac component of the dc output
voltage during steady state. For a ripple error of 1.0%, the output
capacitor value needed to achieve this tolerance can be deter-
mined using the following equation. Note that an accuracy of
1.0% is possible only during steady state conditions, not during
load transients.
OUTPUT CAPACITOR SELECTION
The primary objective of the output capacitor is to facilitate the
reduction of the output voltage ripple; however, the output
capacitor also assists in the output voltage recovery during load
transient events. For a given load current step, the output
voltage ripple generated during this step event is inversely
proportional to the value chosen for the output capacitor. The
speed at which the output voltage settles during this recovery
period depends on where the crossover frequency (loop
bandwidth) is set. This crossover frequency is determined by
the output capacitor, the equivalent series resistance (ESR) of
the capacitor, and the compensation network.
To calculate the small-signal voltage ripple (output ripple
voltage) at the steady state operating point, use the following
equation:
where ESR is the equivalent series resistance of the output
capacitors.
To calculate the output load step, use the following equation:
where Δ V
a given positive load current step (ΔI
ΔV
C
C
OUT
OUT
DCR
(mΩ)
0.33
0.33
0.8
1.65
1.6
1.8
3.3
3.2
2.6
RR
DROOP
= (0.01) × V
=
=
Δ
2
I
×
I
(A)
55
30
50
35
28
25
20
24
22
27.5
SAT
L
is the amount that V
×
f
SW
⎛
⎜
⎜
⎝
8
×
Dimensions
(mm)
10.2 × 7
10.2 × 7
14.2 × 12.8
10.5 × 10.2
13 × 12.8
10.5 × 10.2
10.5 × 10.2
14 × 12.8
13.2 × 12.8
×
(
OUT
Δ
F
SW
V
DROOP
×
[
Δ
Δ
I
V
LOAD
−
RIPPLE
(
Manufacturer
Wurth Electronics
Wurth Electronics
Wurth Electronics
Wurth Electronics
Wurth Electronics
Wurth Electronics
Wurth Electronics
Wurth Electronics
Wurth Electronics
Sumida
Δ
1
OUT
I
LOAD
LOAD
RR
−
is allowed to deviate for
)
(
).
Δ
×
I
L
ESR
×
ESR
))
)
]
Model
Number
744303012
744303022
744355147
744325072
744355090
744325120
7443552100
744318180
7443551200
CEP125U-0R8
⎞
⎟
⎟
⎠