ST2S08B STMicroelectronics, ST2S08B Datasheet - Page 12

• Manufacturer Part Number: ST2S08B
• Description: Dual synchronous rectification, 1.5 A, 1.5 MHz adjustable step-down switching regulator
• Manufacturer: STMicroelectronics

Specifications of ST2S08B

• Typical Efficiency: > 80 % at VOUT= 1.2 V
• Non-switching Quiescent Current: max 1 mA over temperature range

Application information
8.4
8.5
12/18
Equation 4
In addition to the inductance value, in order to avoid saturation, the maximum saturation
current of the inductor must be higher than that of the I
Input and output capacitor selection
It is recommended to use ceramic capacitors with X5R or X7R dielectric and low ESR as
input and output capacitors, in order to filter any disturbance present in the input line and to
obtain stable operation. The output capacitor is very important for satisfying the output
voltage ripple requirements.
The output voltage ripple (V
be calculated as:
Equation 5
where Δ I
The use of ceramic capacitors with voltage ratings in the range higher than 1.5 times the
maximum input or output voltage is recommended.
Layout considerations
Due to the high switching frequency and peak current, the layout is an important design step
for all switching power supplies. Important parameters (efficiency, output voltage ripple,
switching noise immunity, etc.) can be affected if the PCB layout is not designed paying
close attention to the following DC-DC general layout rules:
●
●
●
●
Moreover, the exposed pad ground connection must be properly designed in order to
facilitate heat dissipation from the exposed pad to the ground layer using PCB vias.
I
PEAK
V
O
_
RIPPLE
Short, wide traces must be implemented for mains current and for power ground paths.
The input capacitor must be placed as close as possible to the IC pins as well as the
inductor and output capacitor.
The FB pin connection to the external resistor divider is a high impedance node, so
interference can be minimized by placing the routing of the feedback node as far as
possible from the high current paths. To reduce pick-up noise, the resistor divider must
be placed very close to the device.
A common ground node minimizes ground noise.
The exposed pad of the package must be connected to the common ground node.
=
I (
O
L
/
=
is the ripple current and F
. 0
Δ
) 8
I
L
+
×
2
⎡
⎢
⎣
V
ESR
×
O
V
×
IN
V (
+
_
IN
8
MAX
×
_
C
MAX
OUT
O_RIPPLE
×
F
1
SW
Doc ID 18290 Rev 1
−
×
V
F
O
×
SW
L
)
), in continuous mode, for the step-down channel, can
⎤
⎥
⎦
SW
is the switching frequency.
PEAK
.
ST2S08B