RT8202AGQW Richtek USA Inc, RT8202AGQW Datasheet - Page 13

• Manufacturer Part Number: RT8202AGQW
• Description: IC PWM CTRLR SYNC BUCK 16WQFN
• Manufacturer: Richtek USA Inc

Specifications of RT8202AGQW

• Pwm Type: Current Mode
• Number Of Outputs: 1
• Voltage - Supply: 4.5 V ~ 5.5 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 16-WFQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Duty Cycle: -

Output Voltage Setting (FB)
The output voltage can be adjusted from 0.75V to 3.3V by
setting the feedback resistor R1 and R2 (Figure 5). Choose
R2 to be approximately 10kΩ, and solve for R1 using the
equation:
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
DS8202/A/B-04 March 2011
Z1 =
C1 =
V
V
sw_VBAT(MIN)
BAT
FB
FB_VBAT(MIN)
FB_VBAT(MIN)
OUT
× ⎢
:
.
⎡
⎢
⎢
⎢
⎢
⎣
0.015
R2+
2
= V
R2
× ×
FB
ripple_VBAT(MIN)
π
FB
is 0.75V.
R1
BAT
1
(
is the switching frequency in minimum V
×
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
)
R2
f
SW_VBAT(MIN)
is the output ripple voltage in
⎞
⎟
⎠
⎤
⎥
⎦
1
ripple
F
at minimum V
−
0.015
FB
BAT
×
C1
is large enough.
)
, and worst case
⎤
⎥
⎥
⎥
⎥
⎥
⎦
Ω
V
BAT
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
If R
If R
F =
If R
If R
S
R
R
TON
TON
TON
TON
Figure 6. Output Voltage Setting for V
TON
TON
V
IN
UGATE
PHASE
V
≥
≥
< 2M
< 2M
BOOT
VOUT
=
=
UGATE
PHASE
TON
OUT
Figure 5. Setting The Output Voltage
GND
×
BOOT
VOUT
VIN
GND
2M
2M
FB
ON
T
V
V
ON
FB
OUT
OUT
is T
Ω
Ω
can be determined as below :
Ω
Ω
V
V
then T
then
IN
IN
then T
then
ON
R
−
−
TON
0.5
0.4
set resistor and the V
V
IN
Application
ON
×
×
ON
V
V
V
IN
OUT_FB
OUT_FB
= 3.85p
V
V
= 3.55p
OUT
OUT
V
RT8202/A/B
OUT_FB
R1
R2
×
×
×
×
R
F
F
R3
R4
R
S
S
TON
TON
C1
×
×
Z1
www.richtek.com
V
3.85p
3.55p
1
1
V
OUT
IN
V
R1
R2
×
IN
OUT_FB
OUT
×
V
−
V
−
> 3.3V
OUT_FB
V
0.5
C2
OUT
0.4
OUT_FB
C2
is the
TON
13