Datasheet

ADP5037 Data Sheet
Rev. D | Page 20 of 28
The peak-to-peak output voltage ripple for the selected output
capacitor and inductor values is calculated using the following
equation:
OUTSW
IN
OUTSW
RIPPLE
RIPPLE
CLf
V
Cf
I
V
×××
≈
××
=
2
)2(
8
π
Capacitors with lower effective series resistance (ESR) are
preferred to guarantee low output voltage ripple, as shown in
the following equation:
RIPPLE
RIPPLE
COUT
I
V
ESR
≤
The effective capacitance needed for stability, which includes
temperature and dc bias effects, is a minimum of 7 µF and a
maximum of 40 µF.
The buck regulators require 10 µF output capacitors to guarantee
stability and response to rapid load variations and to transition into
and out of the PWM/PSM modes. A list of suggested capacitors is
shown in Table 10. In certain applications where one or both buck
regulator powers a processor, the operating state is known
because it is controlled by software. In this condition, the
processor can drive the MODE pin according to the operating
state; consequently, it is possible to reduce the output capacitor
from 10 µF to 4.7 µF because the regulator does not expect a
large load variation when working in PSM mode (see Figure 50).
Input Capacitor
Higher value input capacitors help to reduce the input voltage
ripple and improve transient response. Maximum input
capacitor current is calculated using the following equation:
IN
OUT
IN
OUT
MAXLOAD
CIN
V
VVV
II
)(
)(
−
≥
To minimize supply noise, place the input capacitor as close as
possible to the VINx pin of the buck. As with the output capacitor,
a low ESR capacitor is recommended.
The effective capacitance needed for stability, which includes
temperature and dc bias effects, is a minimum of 3 µF and a
maximum of 10 µF. A list of suggested capacitors is shown in
Table 10 and Table 11.
Table 10. Suggested 10 μF Capacitors
Vendor Type Model
Case
Size
Voltage
Rating
(V)
Murata X5R GRM188R60J106 0603 6.3
TDK X5R C1608JB0J106K 0603 6.3
Panasonic X5R ECJ1VB0J106M 0603 6.3
Table 11. Suggested 4.7 μF Capacitors
Vendor Type Model
Case
Size
Voltage
Rating
(V)
Murata X5R GRM188R60J475ME19D 0402 6.3
Taiyo Yuden X5R JMK107BJ475 0402 6.3
Panasonic X5R ECJ-0EB0J475M 0402 6.3
Table 12. Suggested 1.0 μF Capacitors
Vendor Type Model
Case
Size
Voltage
Rating (V)
Murata X5R GRM155B30J105K 0402 6.3
TDK X5R C1005JB0J105KT 0402 6.3
Panasonic X5R ECJ0EB0J105K 0402 6.3
Taiyo
Yuden
X5R LMK105BJ105MV-F 0402 10.0
VIN1
VIN3
EN1
PWM
PSM/PWM
2.3V TO
5.5V
SW1
FB1
R2
R1
VOUT1
PGND1
MODE
C5
10µF
V
OUT1
@
800mA
L1 1µH
EN1
BUCK1
MODE
C3
1µF
C2
4.7µF
C1
4.7µF
AVIN
C
AVIN
0.1µF
C4
1µF
VIN2
EN2
AGND
EN2
BUCK2
MODE
EN3
1.7V TO
5.5V
EN4
VIN4
ON
OFF
ON
OFF
ON
OFF
EN3
LDO1
(ANALOG)
ADP5037
HOUSEKEEPING
SW2
FB2
R4
R3
VOUT2
PGND2
C6
10µF
V
OUT2
@
800mA
L2 1µH
FB3
R6
R5
VOUT3
C7
1µF
V
OUT3
@
300mA
FB4
R8
R7
VOUT4
C8
1µF
V
OUT4
@
300mA
EN4
LDO2
(DIGITAL)
09887-021
Figure 50. Processor System Power Management with PSM/PWM Control