APW7134 データシートの表示（PDF） - Kingbright
部品番号
コンポーネント説明
メーカー
APW7134 Datasheet PDF : 16 Pages
| |||
APW7134
Application Description (Cont.)
Output Capacitor Selection
Output Voltage Setting
Evaluate the ∆VOUT1 by the ideal of energy equalization.
According to the definition of Q,
Q
=
1
2
1
2
∆IL
⋅
1
2
TS
=
COUT
⋅ ∆VOUT1
(6)
where T is the inverse of switching frequency and the
S
∆IL
is
the
inductor
current
ripple.
Move
the
C
OUT
to
the
left side to estimate the value of ∆VOUT1 as equation (7).
∆VOUT 1
=
∆IL ⋅ TS
8 ⋅ COUT
(7)
As mentioned above, one part of output voltage ripple
is the product of the inductor current ripple and ESR
of output capacitor. The equation (8) explains the out-
put voltage ripple estimation.
∆VOUT
=
∆IL
⋅ ESL +
TS
8 ⋅ COUT
(8)
APW7134 has the adjustable version for output volt
age setting by the users. A suggestion of maximum
value
of
R
2
is
200KΩ
to
keep
the
minimum
current
that provides enough noise rejection ability through
the resistor divider. The output voltage programmed
by the equation:
VOUT
=
0.6
⋅
1 +
R1
R2
(11)
VOUT
APW7134
R1
FB
R2
Thermal Considerations
Layout Considerations
APW7134 is a high efficiency switching converter, it
means less power loss transferred into heat. Due to
the on resistance difference between internal power
PMOSFET and NMOSFET, the power dissipation in
the high converting ratio is greater than low converting
ratio. The worst case is in the dropout operation, the
mainly conduction loss dissipate on the internal power
PMOSFET. The power dissipation nearly defined as:
( ) [ ( )] PD = IOUT 2 RDS_ONP ⋅D +RDS_ONN ⋅ 1−D
(9)
The high current paths (GND1/GND2, IN1/IN2 and
SW1/SW2) should be placed very close to the device
with short, direct and wide traces. Input capacitors
should be placed as close as possible to the respec-
tive IN and GND pins. The external feedback resistors
shall be placed next to the FB pins. Keep the switch-
ing nodes SW1/SW2 short and away from the feed-
back network.
APW7134 has internal over temperature protection.
W hen the junction temperature reaches 150
centigrade, APW7134 will turn off both internal power
PMOSFET and NMOSFET. The estimation of the junc-
tion temperature, T , defined as:
J
TJ = PD ⋅ θ JA
(10)
where the θJA is the thermal resistance of the package
utilized by APW7134.
Copyright © ANPEC Electronics Corp.
12
Rev. A.1 - Aug., 2006
www.anpec.com.tw
Share Link: 