RT8204BGQW Richtek USA Inc, RT8204BGQW Datasheet - Page 15

• Manufacturer Part Number: RT8204BGQW
• Description: IC SYNC BUCK W/LDO CTRLR 16WQFN
• Manufacturer: Richtek USA Inc

Specifications of RT8204BGQW

• Topology: Step-Down (Buck) Synchronous (1), Linear (LDO) (1)
• Function: Any Function
• Number Of Outputs: 2
• Voltage/current - Output 1: Controller
• Voltage/current - Output 2: Controller
• W/led Driver: No
• W/supervisor: No
• W/sequencer: No
• Voltage - Supply: 4.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-WFQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

where V
Note that in order for the device to regulate in a controlled
manner, the ripple content at the feedback pin, V
be approximately 15mV at minimum V
no smaller than 10mV. If V
than 15mV, the above component values should be
revisited in order to improve this. Quite often a small
capacitor, C1, is required in parallel with the top feedback
resistor, R1, in order to ensure that V
The value of C1 can be calculated as follows, where R2 is
the bottom feedback resistor.
Firstly calculating the value of Z1 required :
Secondly calculating the value of C1 required to achieve
this :
Finally using the equation as follows to verify the value of
V
where V
minimum V
f
V
V
DS8204B-03 March 2011
C1 =
V
Z1 =
V
sw_VBAT(MIN)
BAT
FB
FB_VBAT(MIN)
FB_VBAT(MIN)
OUT
× ⎢
:
.
⎡
⎢
⎢
⎢
⎢
⎣
0.015
R2+
2
= V
R2
× ×
FB
ripple_VBAT(MIN)
UGATE
PHASE
π
Figure 5. Setting The Output Voltage
FB
BOOT
VOUT
is 0.75V.
R1
GND
BAT
1
is the switching frequency in minimum V
(
×
FB
is the ripple voltage into FB pin in minimum
Z1 R1
f
×
SW_VBAT(MIN)
1
(
+ × ×
;
V
⎡
⎢
⎣
= V
1
2
−
ripple_VBAT(MIN)
+ ⎜
ripple_VBAT(MIN)
1
π
⎛
⎝
R2
R1
)
V
IN
R2
f
SW_VBAT(MIN)
is the output ripple voltage in
⎞
⎟
⎠
⎤
⎥
⎦
1
ripple
F
at minimum V
−
R1
R2
0.015
FB
BAT
×
C1
C1
is large enough.
)
Z1
, and worst case
⎤
⎥
⎥
⎥
⎥
⎥
⎦
V
Ω
OUT
V
BAT
C2
FB
, should
is less
BAT
;
For application that output voltage is higher than 3.3V,
user can also use a voltage divider to keep VOUT pin
voltage within 0.75V to 2.8V as shown in Figure 6. For
this case, T
Where R
output signal of resistor divider. Since the switching
frequency is
For a given switching frequency, we can obtain the R
as below
Output Inductor Selection
The switching frequency (on-time) and operating point (%
ripple or L
If R
If R
F =
If R
If R
L =
S
R
R
TON
TON
TON
TON
Figure 6. Output Voltage Setting for V
TON
TON
T
ON
L
V
IR
IN
UGATE
PHASE
V
≥
≥
< 2M
< 2M
BOOT
VOUT
=
=
TON
×
OUT
×
GND
×
IR
VIN
(V
2M
I
2M
FB
ON
T
V
V
) determine the inductor value as follows :
LOAD(MAX)
ON
OUT
OUT
IN
is T
Ω
Ω
can be determined as below :
Ω
Ω
V
V
- V
then T
then
IN
IN
then T
then
ON
R
−
−
OUT
TON
0.5
0.4
set resistor and the V
Application
)
ON
×
×
ON
V
V
V
IN
OUT_FB
OUT_FB
= 3.85p
V
V
= 3.55p
OUT
OUT
V
OUT_FB
×
×
×
×
RT8204B
R
F
F
R3
R
R4
S
S
TON
TON
×
×
www.richtek.com
V
3.85p
3.55p
1
1
V
OUT
IN
R1
R2
×
IN
OUT_FB
×
V
−
V
−
> 3.3V
OUT_FB
V
0.5
OUT
0.4
OUT_FB
C2
is the
TON
15