AAT1415-Q8-T AAT [Advanced Analog Technology, Inc.], AAT1415-Q8-T Datasheet - Page 27

• Manufacturer Part Number: AAT1415-Q8-T
• Description: FIVE-CHANNEL DC-DC CONVERTER WITH A 2.5V LDO
• Manufacturer: AAT [Advanced Analog Technology, Inc.]

Schottky Diode Selection
Choose a Schottky diode who’s maximum reverse
voltage rating is greater than the value in Table 4, and
who’s current rating is greater than the peak inductor
current.
Current, L: Inductance,
Current Unit: Ampere
Topology
V : Input Voltage,
Inverting
IN
Boost
Buck
Table 3. Inductor Peak Current
Mode
CCM
DCM
CCM
DCM
CCM
DCM
V
OUT
f
SW
(
D=
I
I
: Output Voltage,
D =
D =
∆ I =
(1 D)
O
O
∆ I =
2
2 (V
2 V
I
L
−
: Switch Frequency, Peak
O
+
+
L
V
1
⋅
⋅
⋅
V
(
V
OUT
L f
∆
∆
−
V
2
IN
2
OUT
I
I
Advanced Analog Technology, Inc.
OUT
⋅
IN
V
L
L
V
OUT
+
V
V
Peak Current
SW
OUT
V
OUT
L
OUT
,
, (
OUT
L f
∆
−
IN
)
2
⋅
I
f
⋅
V
+ V
L
f
f
SW
∆
⋅
SW
−
SW
I
OUT
SW
⋅ ⋅ −
I
O
,
L
D (1 D)
⋅ −
V
IN
(1 D)
⋅
IN
=
–
⋅
L
⋅
L
) V
)
V
f
)
V
⋅
SW
IN
I : Output
⋅
IN
O
–
Advanced Analog Technology, Inc . –
I
OUT
O
,
⋅
台 灣 類 比 科 技 股 份 有 限 公 司
⋅
D
L
,
,
⋅
I
O
Page 27 of 32
Version 3.00
External MOSFET Selection
The boost controller and Inverting controller drive
external logic-level MOSFETs. MOSFETs’ maximum
drain-to-source voltage (
greater than the value in Table 4. Their on-resistance
(
transfer capacitance (
Input Capacitor
The input current to converters are discontinuous, and
therefore input capacitors are required to supply the AC
current to converters while maintaining the DC input
voltage. A low ESR capacitor is required to keep the
noise at the IC to a minimum. Ceramic capacitors are
preferred,
capacitors may also suffice. For insuring stable
operation a bypass ceramic 0.1µF capacitor should be
placed as close to the IC VDD pin as possible.
Output Capacitor
The output capacitor is required to maintain the DC
output voltage. Low ESR capacitors are preferred to
keep the output voltage ripple low. The characteristics
of the output capacitor also affect the stability of the
regulation control system. Ceramic, tantalum, or low
ESR electrolytic capacitors are recommended. In the
case of ceramic capacitors, the impedance at the
switching frequency is dominated by the capacitance,
and so the output voltage ripple is mostly independent
of the ESR. The output voltage ripple is estimated to
be:
V
Table 4. Diode and MOS Minimum Voltage Rating
R
RIPPLE
DS(ON)
Topology
Inverting
Boost
Buck
≈
–
), total gate charge (
2
but
π
×
f
SW
∆
tantalum
I
L
AAT1415/AAT1415A
×
C
C
OUT
RSS
Minimum Voltage Rating
V
) are the lower the better.
DS(MAX)
or
V + V
low-ESR
IN
V
Q
V
OUT
) rating must be
G
IN
OUT
) and reverse
electrolytic
May 2008