ADP2109 Analog Devices, ADP2109 Datasheet - Page 13

• Manufacturer Part Number: ADP2109
• Description: Compact 600 mA, 3 MHz, Step-Down Converter with Output Discharge
• Manufacturer: Analog Devices

The peak-to-peak output voltage ripple for a chosen output
capacitor and inductor values is calculated using the following
equation:
Capacitors with lower equivalent series resistance (ESR) are
preferred to guarantee low output voltage ripple, as shown in the
following equation:
The effective capacitance needed for stability, which includes
temperature and dc bias effects, is 7 μF.
Table 7. Suggested 10 μF Capacitors
Vendor
Murata
Taiyo Yuden
TDK
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:
To minimize supply noise, place the input capacitor as close as
possible to the VIN pin of the ADP2109 IC. As with the output
capacitor, a low ESR capacitor is recommended.
The list of recommended capacitors is shown in Table 8.
Table 8. Suggested 4.7 μF Capacitors
Vendor
Murata
Taiyo Yuden
TDK
THERMAL CONSIDERATIONS
Because of the high efficiency of the ADP2109, only a small
amount of power is dissipated inside the ADP2109 package,
which reduces thermal constraints.
V
ESR
I
CIN
RIPPLE
COUT
≥
I
=
LOAD
≤
X5R
X5R
X5R
(
Type
X5R
Type
X5R
X5R
2
V
π
I
(
MAX
RIPPLE
RIPPLE
×
f
)
SW
Model
GRM188R60J106
JMK107BJ106
C1608JB0J106K
Model
GRM188R60J475ME19
JMK107BJ475
C1608X5R0J475
V
)
V
×
OUT
IN
2
×
(
V
L
V
IN
×
IN
C
−
V
OUT
OUT
=
)
Case
Size
0603
0603
0603
8
×
f
I
SW
Case
Size
0603
0603
0603
RIPPLE
×
C
Voltage
Rating (V)
6.3
6.3
6.3
OUT
Voltage
Rating
(V)
6.3
6.3
6.3
Rev. A | Page 13 of 16
However, in applications with maximum loads at high ambient
temperature, low supply voltage, and high duty cycle, the heat
dissipated in the package is great enough that it may cause the
junction temperature of the die to exceed the maximum junction
temperature of 125°C. If the junction temperature exceeds
150°C, the converter goes into thermal shutdown. It recovers
when the junction temperature falls below 130°C.
The junction temperature of the die is the sum of the ambient
temperature of the environment and the temperature rise of the
package due to power dissipation, as shown in the following
equation:
where:
T
T
T
dissipation to it.
The rise in temperature of the package is directly proportional
to the power dissipation in the package. The proportionality
constant for this relationship is the thermal resistance from the
junction of the die to the ambient temperature, as shown in the
following equation:
where:
T
θ
ambient temperature of the package.
PD is the power dissipation in the package.
PCB LAYOUT GUIDELINES
Poor layout can affect ADP2109 performance causing
electromagnetic interference (EMI) and electromagnetic
compatibility (EMC) problems, ground bounce, and voltage
losses. Poor layout can also affect regulation and stability.
A good layout is implemented using the following rules:
•
•
•
•
JA
J
A
R
R
is the junction temperature.
is the rise in temperature of the package due to power
is the rise of temperature of the package.
is the ambient temperature.
is the thermal resistance from the junction of the die to the
T
T
Place the inductor, input capacitor, and output capacitor
close to the IC using short tracks. These components carry
high switching frequencies and the large tracks act like
antennas.
Route the output voltage path away from the inductor and
SW node to minimize noise and magnetic interference.
Maximize the size of ground metal on the component side
to help with thermal dissipation.
Use a ground plane with several vias connecting to the
component side ground to further reduce noise interfe-
rence on sensitive circuit nodes.
J
R
= T
= θ
A
JA
+ T
× PD
R
ADP2109