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RT8223P Datasheet(PDF) 21 Page - Richtek Technology Corporation

Part # RT8223P
Description  High Efficiency, Main Power Supply Controller for Notebook Computer
PDF  23 Pages
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Manufacturer  RICHTEK [Richtek Technology Corporation]
Direct Link  http://www.richtek.com
Logo RICHTEK - Richtek Technology Corporation

RT8223P Datasheet(HTML) 21 Page - Richtek Technology Corporation

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RT8223P
21
DS8223P-01
June 2011
www.richtek.com
Table 3. Power Up Sequencing
EN
(V)
ENC
(V)
ENTRIP1
ENTRIP2
REF
VREG5
VREG3
SMPS1
SMPS2
Low
Low
X
X
Off
Off
Off
Off
Off
“>2.4V”
=> High
Low
X
X
On
On
On
Off
Off
“>2.4V”
=> High
“>2V”
=> High
Off
Off
On
On
On
Off
Off
“>2.4V”
=> High
“>2V”
=> High
Off
On
On
On
On
Off
On
“>2.4V”
=> High
“>2V”
=> High
On
Off
On
On
On
On
Off
“>2.4V”
=> High
“>2V”
=> High
On
On
On
On
On
On
On
Output Voltage Setting (FBx)
Connect a resistor voltage-divider at the FBx pin between
VOUTx and GND to adjust the respective output voltage
between 2V and 5.5V (Figure 4). Referring to Figure 4 as
an example, choose R2 to be approximately 10k
Ω, and
solve for R1 using the equation :
OUTX
FBX
R1
VV
1
R2
⎛⎞
⎛⎞
=× +
⎜⎟
⎜⎟
⎝⎠
⎝⎠
where VFBX is 2V.
Figure 4. Setting VOUTX with a Resistor Voltage Divider
Output Inductor Selection
The switching frequency (on-time) and operating point (%
ripple or LIR) determine the inductor value as shown in
the following equation :
()
ON
IN
OUTx
LOAD(MAX)
tV
V
L
LIR I
×−
=
×
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
(IPEAK) :
PEAK
LOAD(MAX)
LOAD(MAX)
II
(LIR/2) 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.
Output Capacitor Selection
The capacitor value and ESR determine the amount of
output voltage ripple and load transient response. Thus,
the capacitor value must be greater than the largest value
calculated from below equations :
()
2
OUTx
LOAD
OFF(MIN)
IN
SAG
IN
OUTx
OUT
OUTx
OFF(MIN)
IN
V
(I
)
L
K
t
V
V
VV
2C
V
K
t
V
Δ× ×
×
+
=
⎡⎤
⎛⎞
−
××
×
×
−
⎢⎥
⎜⎟
⎝⎠
⎣⎦
2
2
LOAD
SOAR
OUT
OUTx
(I
)
L
V
CV
Δ×
=
××
PHASEx
LGATEx
R1
R2
VOUTx
VIN
UGATEx
VOUTx
FBx



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