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ADP5052ACPZ-R7 Datasheet(HTML) 25 Page - Analog Devices

Part No. ADP5052ACPZ-R7
Description  5-Channel Integrated Power Solution with Quad Buck Regulators and 200 mA LDO Regulator
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Maker  AD [Analog Devices]
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ADP5052ACPZ-R7 Datasheet(HTML) 25 Page - Analog Devices

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Data Sheet
ADP5052
Rev. 0 | Page 25 of 40
The output voltage ripple is determined by the ESR of the output
capacitor and its capacitance value. Use the following equations
to select a capacitor that can meet the output ripple requirements:
RIPPLE
OUT
SW
L
RIPPLE
OUT
V
f
I
C
_
_
8
×
×
=
L
RIPPLE
OUT
ESR
I
V
R
=
_
where:
ΔIL is the inductor ripple current.
fSW is the switching frequency.
ΔVOUT_RIPPLE is the allowable output voltage ripple.
RESR is the equivalent series resistance of the output capacitor.
Select the largest output capacitance given by COUT_UV, COUT_OV,
and COUT_RIPPLE to meet both load transient and output ripple
requirements.
The voltage rating of the selected output capacitor must be
greater than the output voltage. The minimum rms current
rating of the output capacitor is determined by the following
equation:
12
_
L
rms
C
I
I
OUT
=
INPUT CAPACITOR SELECTION
The input decoupling capacitor attenuates high frequency noise
on the input and acts as an energy reservoir. Use a ceramic capac-
itor and place it close to the PVINx pin. The loop composed of
the input capacitor, the high-side NFET, and the low-side NFET
must be kept as small as possible. The voltage rating of the input
capacitor must be greater than the maximum input voltage. Make
sure that the rms current rating of the input capacitor is larger
than the following equation:
(
)
D
D
I
I
OUT
rms
CIN
×
×
=
1
_
where D is the duty cycle (D = VOUT/VIN).
LOW-SIDE POWER DEVICE SELECTION
Channel 1 and Channel 2 include integrated low-side MOSFET
drivers, which can drive low-side N-channel MOSFETs (NFETs).
The selection of the low-side N-channel MOSFET affects the
performance of the buck regulator.
The selected MOSFET must meet the following requirements:
Drain-to-source voltage (VDS) must be higher than 1.2 × VIN.
Drain current (ID) must be greater than 1.2 × ILIMIT_MAX, where
ILIMIT_MAX is the selected maximum current-limit threshold.
The selected MOSFET can be fully turned on at VGS = 4.5 V.
Total gate charge (Qg at VGS = 4.5 V) must be less than 20 nC.
Lower Qg characteristics provide higher efficiency.
When the high-side MOSFET is turned off, the low-side MOSFET
supplies the inductor current. For low duty cycle applications, the
low-side MOSFET supplies the current for most of the period.
To achieve higher efficiency, it is important to select a MOSFET
with low on resistance. The power conduction loss for the low-
side MOSFET can be calculated using the following equation:
PFET_LOW = IOUT2 × RDSON × (1 − D)
where:
RDSON is the on resistance of the low-side MOSFET.
D is the duty cycle (D = VOUT/VIN).
Table 11 lists recommended dual MOSFETs for various current-
limit settings. Ensure that the MOSFET can handle thermal
dissipation due to power loss.
Table 11. Recommended Dual MOSFETs
Vendor
Part No.
VDS (V)
ID (A)
RDSON
(mΩ)
Qg
(nC)
Size
(mm)
IR
IRFHM8363
30
10
20.4
6.7
3 × 3
IRLHS6276
20
3.4
45
3.1
2 × 2
Fairchild
FDMA1024
20
5.0
54
5.2
2 × 2
FDMB3900
25
7.0
33
11
3 × 2
FDMB3800
30
4.8
51
4
3 × 2
FDC6401
20
3.0
70
3.3
3 × 3
Vishay
Si7228DN
30
23
25
4.1
3 × 3
Si7232DN
20
25
16.4
12
3 × 3
Si7904BDN
20
6
30
9
3 × 3
Si5906DU
30
6
40
8
3 × 2
Si5908DC
20
5.9
40
5
3 × 2
SiA906EDJ
20
4.5
46
3.5
2 × 2
AOS
AON7804
30
22
26
7.5
3 × 3
AON7826
20
22
26
6
3 × 3
AO6800
30
3.4
70
4.7
3 × 3
AON2800
20
4.5
47
4.1
2 × 2
PROGRAMMING THE UVLO INPUT
The precision enable input can be used to program the UVLO
threshold of the input voltage, as shown in Figure 38. To limit
the degradation of the input voltage accuracy due to the internal
1 MΩ pull-down resistor tolerance, ensure that the bottom resistor
in the divider is not too large—a value of less than 50 kΩ is
recommended.
The precision turn-on threshold is 0.8 V. The resistive voltage
divider for the programmable VIN start-up voltage is calculated
as follows:
VIN_STARTUP = (0.8 nA + (0.8 V/RBOT_EN)) × (RTOP_EN + RBOT_EN)
where:
RTOP_EN is the resistor from VIN to EN.
RBOT_EN is the resistor from EN to ground.


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