ADP1871ACPZ-1.0-R7 Analog Devices Inc, ADP1871ACPZ-1.0-R7 Datasheet - Page 25

• Manufacturer Part Number: ADP1871ACPZ-1.0-R7
• Description: 1.0MHz, Light Load Eff Enabled
• Manufacturer: Analog Devices Inc

Specifications of ADP1871ACPZ-1.0-R7

• Frequency - Max: 1MHz
• Pwm Type: Current Mode
• Number Of Outputs: 1
• Duty Cycle: 45%
• Voltage - Supply: 2.95 V ~ 20 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 10-WFDFN, CSP Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: ADP1871ACPZ-1.0-R7; ADP1871ACPZ-1.0-R7TR

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 might 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 their current-mode architecture, the ADP1870/ADP1871
require Type II compensation. To determine the component
values needed for compensation (resistance and capacitance
values), it is necessary to examine the converter’s overall loop
gain (H) at the unity gain frequency (f
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 filter’s transfer function at high frequencies
simplifies to
at the crossover frequency (s = 2πf
Figure 80. Capacitance vs. DC Voltage Characteristics for Ceramic Capacitors
–100
H
Z
–10
–20
–30
–40
–50
–60
–70
–80
–90
20
10
FILTER
0
= V/V
COMP
0
1
10µF TDK 25V, X7R, 1210 C3225X7R1E106M
22µF MURATA 25V, X7R, 1210 GRM32ER71E226KE15L
47µF MURATA 16V, X5R, 1210 GRM32ER61C476KE15L
=
and C
sC
=
5
1
G
OUT
COMP
M
X5R (16V)
×
G
component values.
10
CS
DC VOLTAGE (V
×
X7R (50V)
V
X5R (25V)
V
FILT
OUT
REF
15
)
CROSS
×
Z
SW
DC
).
COMP
)
20
/10) when H = 1 V/V:
×
Z
FILT
25
30
Rev. A | Page 25 of 44
Error Amplifier Output Impedance (Z
Assuming that C
be omitted from the output impedance equation of the error
amplifier. The transfer function simplifies to
and
where f
frequency for the ADP1870.
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 ADP1870, it is recommended that the
user set the crossover frequency between 1/10
switching frequency.
The relationship between C
follows:
The zero frequency is set to 1/4
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
=
=
=
=
A
=
=
12
12
2
CS
1
1
R
π
2
f
COMP
CROSS
×
×
×
×
f
1
C2
SW
R
π
f
R
SW
f
is significantly smaller than C
COMP
×
ON
CROSS
(
R
+
f
1
f
CROSS
COMP
CROSS
f
(A/V)
×
1
ZERO
C
M
COMP
+
)
COMP
×
f
×
f
ZERO
ZERO
th
CS
2
and f
)
π
)
of the crossover frequency.
f
ADP1870/ADP1871
)
G
CROSS
M
ZERO
G
C
CS
OUT
COMP
(zero frequency) is as
×
)
th
th
V
of the crossover
and 1/15
V
COMP
OUT
REF
, C
C2
th
can
of the