RT8205L RICHTEK [Richtek Technology Corporation], RT8205L Datasheet - Page 23

• Manufacturer Part Number: RT8205L
• Description: High Efficiency, Main Power Supply Controller for Notebook Computer
• Manufacturer: RICHTEK [Richtek Technology Corporation]

Output Voltage Setting (FBx)
Connect a resistor voltage divider at the
VOUTx and GND to adjust the respective output voltage
between 2V and 5.5V (Figure 6). Refering to Figure 5 as
an example, choose R2 to be approximately 10kΩ, and
solve for R1 using the equation :
where V
DS8205L/M-05 June 2011
V
OUTx
=> High
=> High
=> High
=> High
=> High
=> High
=> High
“>1V”
“>1V”
“>1V”
“>1V”
“>1V”
“>1V”
“>1V”
Low
EN
(V)
Figure 6. Setting V
=
FBX
UGATEx
PHASEx
LGATEx
V
VOUTx
FBX
is 2V.
FBx
×
ENTRIP2 is
On without
⎛
⎜
⎝
ENTRIP1
1
60μs)
+
(after
Off
Off
On
On
On
On
⎛
⎜
⎝
X
X
R2
R1
⎞
⎟
⎠
OUTx
⎞
⎟
⎠
V
IN
with resistor divider
(after ENTRIP1
is On without
ENTRIP2
60μs)
Off
On
On
Off
On
On
X
X
FBx
R1
R2
Table 3. Power Up Sequencing
pin between
V
OUTx
REF
Off
On
On
On
On
On
On
On
Output Inductor Selection
The switching frequency (on-time) and operating point (%
ripple or LIR) determine the inductor value as shown in
the following equation :
where LIR is the ratio of the peak to peak ripple current to
the average inductor current.
Find a low loss inductor having the lowest possible DC
resistance that fits in the allotted dimensions. Ferrite cores
are often the best choice, although powdered iron is
inexpensive and can work well at 200kHz. The core must
be large enough not to saturate at the peak inductor current
(I
The calculation above shall serve as a general reference.
To further improve the transient response, the output
inductance can be reduced even further. This needs to be
considered along with the selection of the output capacitor.
VREG5
L
I
PEAK
PEAK
=
Off
On
On
On
On
On
On
On
t
ON
LIR I
) :
=
×
I
LOAD(MAX)
×
(V
LOAD(MAX)
IN
−
VREG3
V
Off
On
On
On
On
On
On
On
OUTx
+
⎡
⎣
(LIR 2 I
)
(after SMPS2
/ )
SMPS1
is on)
×
On
Off
Off
Off
Off
On
On
On
RT8205L/M
LOAD(MAX)
www.richtek.com
(after SMPS1
⎤
⎦
SMPS2
is on)
Off
Off
Off
On
On
Off
On
On
23