RT8202AGQW Richtek USA Inc, RT8202AGQW Datasheet - Page 11
RT8202AGQW
Manufacturer Part Number
RT8202AGQW
Description
IC PWM CTRLR SYNC BUCK 16WQFN
Manufacturer
Richtek USA Inc
Datasheet
1.RT8202AGQW.pdf
(18 pages)
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
-
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Company:
Part Number:
RT8202AGQW
Manufacturer:
RCT
Quantity:
100
Part Number:
RT8202AGQW
Manufacturer:
RICHTEK/立锜
Quantity:
20 000
The switching waveforms may appear noisy and
asynchronous when light loading causes diode-emulation
operation, but this is a normal operating condition that
results in high light-load efficiency. Trade-offs in DEM noise
vs. light-load efficiency are made by varying the inductor
value. Generally, low inductor values produce a broader
efficiency vs. load curve, while higher values result in higher
full-load efficiency (assuming that the coil resistance
remains fixed) and less output voltage ripple. The
disadvantages for using higher inductor values include
larger physical size and degrades load-transient response
(especially at low input voltage levels).
Forced-CCM Mode (EN/DEM = floating)
The low noise, forced-CCM mode (EN/DEM = floating)
disables the zero-crossing comparator, which controls the
low-side switch on-time. This causes the low side gate-
drive waveform to become the complement of the high
side gate-drive waveform. This in turn causes the inductor
current to reverse at light loads as the PWM loop to
maintain a duty ratio V
mode is to keep the switching frequency fairly constant,
but it comes at a cost : The no-load battery current can
be up to 10mA to 40mA, depending on the external
MOSFETs.
Current Limit Setting (OCP)
RT8202/A/B has cycle-by-cycle current limiting control.
The current limit circuit employs a unique “valley” current
sensing algorithm. If the magnitude of the current-sense
signal at OC is above the current limit threshold, the PWM
is not allowed to initiate a new cycle (Figure 2).
DS8202/A/B-04 March 2011
Figure 1. Boundary condition of CCM/DEM
I
0
L
Slope = (V
t
ON
IN
OUT
-V
OUT
/V
) / L
IN
. The benefit of forced-CCM
i
i
L, peak
Load
t
= i
L, peak
/ 2
Current sensing of the RT8202/A/B can be accomplished
in two ways. Users can either use a current sense resistor
or the on-state of the low side MOSFET (R
resistor sensing, a sense resistor is placed between the
source of low-side MOSFET and PGND (Figure 3(a)).
R
3(b)). There is a compromise between current-limit
accuracy and sense resistor power dissipation.
In both cases, the R
PHASE pin sets the over current threshold. This resistor
R
RT8202/A/B which is turned on when the low side
MOSFET turns on. When the voltage drop across the
sense resistor or low side MOSFET equals the voltage
across the R
The high side MOSFET will not be turned on until the
voltage drop across the sense element (resistor or
MOSFET) falls below the voltage across the R
Choose a current limit resistor by following Equation :
R
Carefully observe the PC board layout guidelines to ensure
that noise and DC errors do not corrupt the current-sense
signal seen by OC and PGND. Mount the IC close to the
low-side MOSFET and sense resistor with short, direct
DS(ON)
ILIM
ILIM
PHASE
LGATE
= I
OC
is connected to a 20μA current source within the
sensing is more efficient and less expensive (Figure
LIMIT
(a)
Figure 3. Current-Sense Methods
I
0
ILIM
x R
L
R
Figure 2. Valley Current-Limit
ILIM
SENSE
resistor, positive current limit will activate.
ILIM
/ 20μA
resistor between the OC pin and
RT8202/A/B
PHASE
LGATE
OC
I
I
I
L, peak
Load
LIM
R
www.richtek.com
(b)
ILIM
t
DS(ON)
ILIM
resistor.
). For
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