RT8203GA Richtek USA Inc, RT8203GA Datasheet - Page 20

• Manufacturer Part Number: RT8203GA
• Description: IC CTRLR SMPS STPDN DUAL 28SSOP
• Manufacturer: Richtek USA Inc

Specifications of RT8203GA

• Output Isolation: Isolated
• Frequency Range: Adjustable, Selectable
• Voltage - Input: 7 V ~ 24 V
• Voltage - Output: Selectable
• Power (watts): 1.05W
• Operating Temperature: -10°C ~ 85°C
• Package / Case: 28-SSOP (0.150", 3.90mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

RT8203
Power-Up Sequencing and On/Off Controls (ONx)
ON3 and ON5 control SMPS power-up sequencing. When
RT8203 applies in the single channel mode, ON3 or ON5
enables the respective outputs when ONx voltage rising
above 2.4V, and disables the respective outputs when ONx
voltage falling below 1.3V.
Connecting one of ONx to VCC and the other one
connecting to V
after the former one regulates.
If both of ONx forced connecting to V
always wait the other one regulating and no one will
regulate.
Output Voltage Setting (FBx)
Connect FBx directly to GND to enable the fixed, preset
SMPS output voltages (3.3V and 5V). Connect a resistor
voltage-divider at FBx between VOUTx and GND to adjust
the respective output voltage between 2V and 5.5V
(Figure 6). Choose R2 to be approximately 10kΩ, and solve
for R1 using the equation :
where V
LDO5 connects to VOUT5 through an internal switch only
when VOUT5 above the LDO5 automatic switch threshold
(4.65V). LDO3 connects to VOUT3 through an internal
switch only when VOUT3 is above the
switch threshold (2.93V). This is the most effective way
when the fixed output voltages are used. Once LDOx is
supplied from VOUTx, the internal linear regulator turns
off. This reduces internal power dissipation and improves
efficiency when LDOx is powered with a high input voltage.
www.richtek.com
20
V
OUTx
Figure 6. Setting VOUTx with a Resistor-Divider
= V
FBx
FBx
is 2.0V (typ.).
UGATEx
PHASEx
BOOTx
VOUTx
REF
×
GND
FBx
⎡
⎢
⎣
1
can force the latter one output starts
+ ⎜
⎛
⎝
R2
R1
⎞
⎟
⎠
⎤
⎥
⎦
V
IN
R1
R2
REF
LDO3 automatic
V
OUTx
, both outputs
Output Inductor Selection
The switching frequency (on-time) and operating point (%
ripple or LIR) determine the inductor value as follows :
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
I
This inductor ripple current also impacts transient-response
performance, especially at low VIN -VOUTx differences.
Low inductor values allow the inductor current to slew faster,
replenishing charge removed from the output filter
capacitors by a sudden load step. The peak amplitude of
the output transient (V
transient. The (V
maximum duty factor, which can be calculated from the
on-time and minimum off-time :
Where the minimum off-time (T
and K is from Table 1.
Output Capacitor Selection
The output filter capacitor must have low enough ESR to
meet output ripple and load transient requirements, yet
have high enough ESR to satisfy stability requirements.
Moreover, the capacitance value must be high enough to
absorb the inductor energy going from a full-load to no-
load condition without tripping the OVP circuit.
For CPU core voltage converters and other applications
where the output is subject to violent load transients, the
output capacitor's size depends on how much ESR is
needed to prevent the output from dipping too low under a
load transient. Ignoring the sag due to finite capacitance :
L =
ESR
V
PEAK
PEAK
SAG
T
= I
) :
ON
L
≤
=
IR
LOAD(MAX
×
2 C
I
×
LOAD(MAX)
(V
×
I
LOAD(MAX)
V
IN
P-P
OUT
( I
- V
Δ
)
+ [(L
LOAD
SAG
OUT
×
V
) also features a function of the
OUTx
IR
SAG
)
)
2
/ 2) x I
) is also a function of the output
× ×
L (K
⎡
⎢
⎣
K
⎛
⎜
⎝
LOAD(MAX)
OFF (MIN)
V
IN
DS8203-04 March 2011
V
OUTx
V
- V
V
IN
IN
OUTx
) = 400ns (typical)
]
+T
OFF(MIN)
⎞
⎟
⎠
−
T
OFF(MIN)
)
⎤
⎥
⎦