ADP1882-1.0-EVALZ Analog Devices Inc, ADP1882-1.0-EVALZ Datasheet - Page 25

• Manufacturer Part Number: ADP1882-1.0-EVALZ
• Description: 1 MHz Synchronous Current-Mode Buck Controller Eval. Board
• Manufacturer: Analog Devices Inc

Specifications of ADP1882-1.0-EVALZ

• Silicon Manufacturer: Analog Devices
• Application Sub Type: PWM Buck Controller
• Kit Application Type: Power Management - Voltage Regulator
• Silicon Core Number: ADP1882
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Ceramic capacitors are known to have low ESR. However, the
trade-off of using X5R technology is that up to 80% of its capaci-
tance may be lost due to derating as the voltage applied across
the capacitor is increased (see Figure 80). Although X7R series
capacitors can also be used, the available selection is limited to
only up to 22 μF.
Electrolytic capacitors satisfy the bulk capacitance requirements
for most high current applications. Because the ESR of electrolytic
capacitors is much higher than that of ceramic capacitors, when
using electrolytic capacitors, several MLCCs should be mounted
in parallel to reduce the overall series resistance.
COMPENSATION NETWORK
Due to its current-mode architecture, the ADP1882/ADP1883
require Type II compensation. To determine the component values
needed for compensation (resistance and capacitance values),
it is necessary to examine the overall loop gain (H) of the con-
verter at the unity gain frequency (f
as follows:
Examining each variable at high frequency enables the unity-
gain transfer function to be simplified to provide expressions
for the R
Output Filter Impedance (Z
Examining the transfer function of the filter at high frequencies
simplifies to
at the crossover frequency (s = 2πf
Figure 80. Capacitance vs. DC Voltage Characteristics for Ceramic Capacitors
H = 1 V/V = G
Z
–100
–10
–20
–30
–40
–50
–60
–70
–80
–90
FILT
20
10
0
COMP
0
=
sC
10µF TDK 25V, X7R, 1210 C3225X7R1E106M
22µF MURATA 25V, X7R, 1210 GRM32ER71E226KE15L
47µF MURATA 16V, X5R, 1210 GRM32ER61C476KE15L
and C
1
OUT
5
COMP
M
X5R (16V)
× A
component values.
10
CS
DC VOLTAGE (V
×
X7R (50V)
V
X5R (25V)
V
FILT
OUT
REF
15
)
CROSS
SW
× Z
/10) when H = 1 V/V,
DC
).
COMP
)
20
× Z
FILT
25
30
Rev. 0 | Page 25 of 40
Error Amplifier Output Impedance (Z
Assuming C
omitted from the output impedance equation of the error
amplifier. The transfer function simplifies to
and
where f
frequency for the ADP1882.
Error Amplifier Gain (G
The error amplifier gain (transconductance) is
Current-Sense Loop Gain (G
The current-sense loop gain is
where:
A
(see the Programming Resistor (RES) Detect Circuit and Valley
Current-Limit Setting sections).
R
Crossover Frequency
The crossover frequency is the frequency at which the overall
loop (system) gain is 0 dB (H = 1 V/V). For current-mode
converters such as the ADP1882, it is recommended that the
user set the crossover frequency between 1/10 and 1/15 of the
switching frequency.
The relationship between C
follows:
The zero frequency is set to 1/4 of the crossover frequency.
Combining all of the above parameters results in
ON
CS
(V/V) is programmable for 3 V/V, 6 V/V, 12 V/V, and 24 V/V
is the channel impedance of the lower-side MOSFET.
G
G
C
Z
R
f
f
f
CROSS
CROSS
M
ZERO
COMP
COMP
COMP
CS
ZERO
= 500 μA/V
=
, the zero frequency, is set to be 1/4 of the crossover
=
=
=
=
A
C2
=
=
2
12
12
CS
1
1
R
π
2
is significantly smaller than C
f
COMP
×
×
CROSS
×
×
f
1
SW
R
π
f
R
SW
f
COMP
×
ON
CROSS
(
R
+
f
1
f
CROSS
COMP
CROSS
f
(A/V)
×
1
ZERO
C
M
COMP
+
)
COMP
×
×
f
f
ZERO
ZERO
2
CS
)
π
and f
)
f
ADP1882/ADP1883
G
)
CROSS
M
ZERO
A
C
CS
OUT
COMP
(zero frequency) is as
COMP
×
)
V
V
, C
OUT
REF
C2
can be