ADP1870ACPZ-0.3-R7 Analog Devices Inc, ADP1870ACPZ-0.3-R7 Datasheet - Page 29

• Manufacturer Part Number: ADP1870ACPZ-0.3-R7
• Description: 300kHz, Light Load Eff Enabled
• Manufacturer: Analog Devices Inc

Specifications of ADP1870ACPZ-0.3-R7

• Frequency - Max: 300kHz
• Pwm Type: Current Mode
• Number Of Outputs: 1
• Duty Cycle: 84%
• 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: ADP1870ACPZ-0.3-R7; ADP1870ACPZ-0.3-R7TR

where:
P
LDO block across VIN and VREG.
C
V
V
I
P
For example, if the external MOSFET characteristics are θ
(10-lead MSOP) = 171.2°C/W, f
C
then the power loss is
The rise in package temperature (for 10-lead MSOP) is
Assuming a maximum ambient temperature environment of 85°C,
which is below the maximum junction temperature of 125°C.
DESIGN EXAMPLE
The ADP1870/ADP1871 are easy to use, requiring only a few
design criteria. For example, the example outlined in this section
uses only four design criteria: V
V
Input Capacitor
The maximum input voltage ripple is usually 1% of the
minimum input voltage (11.8 V × 0.01 = 120 mV).
P
BIAS
DISS(LDO)
DR(LOSS)
DISS
total
REG
IN
upperFET
IN
is the high voltage input.
= 12 V (typical), and f
is the dc input bias current.
(
is the C
= 57.12 mW
= 55.6 mW
= 132.73 mW
= 22.7°C
V
V
= 120 mV − (15 A × 0.001) = 45 mV
= 120 μF
is the LDO output voltage and bias voltage.
T
T
C
LDO
P
+
=
+
P
=
P
=
=
DR
DISS
RIPP
MAX,RIPPLE
DISS
R
J
[
(
5 (
IN,min
171
V
(
77
= 3.3 nF, C
. 4
13
)
is the MOSFET driver loss.
(
=
0 .
=
is the power dissipated through the pass device in the
REG
LOSS
=
62
(
.
(
T
= 120 mV
TOTAL
13
×
LDO
θ
2 .
V
P
R
×
(
)
×
JA
=
GD
DR
300
°C
−
(
mW
×
=
(
)
300
4
×
(
f
5
T
LOSS
+ C
[
=
)
= V
SW
V
×
f
×
P
A
V
SW
=
(
DR
132
I
DR
×
10
C
V
lowerFET
)
+
=
LOAD
)
P
10
GS
V
RIPP
lowerFET
×
×
IN
(
+
3
DISS
55
LOSS
22
MAX
(
.
(
3
×
of the external MOSFET.
05
(
300
f
V
−
,
×
3
6 .
− (I
7 .
MAX
SW
(
IN
3 .
LDO
)
3
V
= 3.3 nF, V
,
mW
°C
RIPPLE
mW
V
3 .
C
×
REG
×
−
SW
LOAD,MAX
REG
upperFET
×
10
)
10
V
+
10
+
REG
)
= 300 kHz.
−
85
3
+
9
×
P
=
−
OUT
×
9
×
DR
(
I
°C
)
SW
4
V
×
BIAS
5
f
3
×
(
0 .
SW
= 1.8 V, I
×
3 .
DR
. 4
LOSS
DR
× ESR)
(
= 300 kHz, I
=
300
62
+
f
)
×
]
107
SW
= 4.62 V, and V
+
×
. 0
10
)
+
I
C
002
×
×
BIAS
. 0
total
−
.
15
10
72
C
9
002
))
×
LOAD
total
)
3
A
]
°C
×
5
×
))
V
105
+
×
= 15 A (pulsing),
REG
BIAS
V
. 0
REG
002
mV
= 2 mA,
+
REG
+
I
)
BIAS
I
= 5.0 V,
BIAS
)
JA
)
Rev. A | Page 29 of 44
(4)
Choose five 22 μF ceramic capacitors. The overall ESR of five
22 μF ceramic capacitors is less than 1 mΩ.
Inductor
Determine inductor ripple current amplitude as follows:
so calculating for the inductor value
The inductor peak current is approximately
Therefore, an appropriate inductor selection is 1.0 μH with
DCR = 3.3 mΩ (Würth Elektronik 7443552100) from Table 8
with peak current handling of 20 A.
Current Limit Programming
The valley current is approximately
Assuming a lower-side MOSFET R
the valley current limit from Table 7 and Figure 71 indicates, a
programming resistor (RES) of 100 kΩ corresponds to an A
of 24 V/V.
Choose a programmable resistor of R
sense gain of 24 V/V.
Output Capacitor
Assume that a load step of 15 A occurs at the output and no more
than 5% is allowed for the output to deviate from the steady state
operating point. In this case, the ADP1870’s advantage is that
because the frequency is pseudo-fixed, the converter is able to
respond quickly because of the immediate, though temporary,
increase in switching frequency.
Assuming that the overall ESR of the output capacitor ranges
from 5 mΩ to 10 mΩ,
I
P
= 1.03 μH
15 A + (5 A × 0.5) = 17.5 A
= 0.003 × (15 A)
15 A − (5 A × 0.5) = 12.5 A
ΔV
= 1.11 mF
C
Δ
L
=
P
=
RMS
CIN
DCR
I ≈
OUT
=
2
(
L
5
13
DROOP
×
= I
= (I
(
(
V
LOSS
V
2 .
300
=
×
LOAD
I
IN,MAX
Δ
V
RMS
LOAD
2
)
300
= 0.05 × 1.8 V = 90 mV
3
I
=
×
×
−
L
/2 = 7.5 A
)
10
DCR
2
1
f
×
×
SW
15
× ESR = (7.5 A)
8 .
−
= 5 A
3
10
f
V
×
SW
V
A
×
×
3
Δ
2
(
OUT
)
90
(
I
= 675 mW
I
×
Δ
2
L
LOAD
V
13
mV
)
1
×
DROOP
8 .
2 .
V
)
V
V
V
IN,MAX
OUT
)
2
ADP1870/ADP1871
× 1 mΩ = 56.25 mW
ON
RES
of 4.5 mΩ and 13 A as
= 100 kΩ for a current-
CS