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PDF RT8202B Data sheet ( Hoja de datos )
| Número de pieza | RT8202B | |
| Descripción | Single Synchronous Buck Controller | |
| Fabricantes | Richtek | |
| Logotipo |  |
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RT8202/A/B
Single Synchronous Buck Controller
General Description
The RT8202/A/B PWM controller provides high efficiency,
excellent transient response, and high DC output accuracy
needed for stepping down high voltage batteries to
generate low voltage CPU core, I/O, and chipset RAM
supplies in notebook computers.
The constant on-time PWM control scheme handles wide
input/output voltage ratios with ease and provides 100ns
“instant-on” response to load transients while maintaining
a relatively constant switching frequency.
The RT8202/A/B achieves high efficiency at a reduced
cost by eliminating the current sense resistor found in
traditional current mode PWMs. Efficiency is further
enhanced by its ability to drive very large synchronous
rectifier MOSFETs. The buck conversion allows this device
to directly step down high voltage batteries for the highest
possible efficiency. The RT8202/A/B is intended for CPU
core, chipset, DRAM, or other low voltage supplies as
low as 0.75V. RT8202 is available in WQFN-16L 4x4,
RT8202A is available in WQFN-16L 3x3 and RT8202B is
available in WQFN-14L 3.5x3.5 packages.
Ordering Information
RT8202/A/B
Features
z Ultra-High Efficiency
z Resistor Programmable Current Limit by Low Side
RDS(ON) Sense (Lossless Limit) or Sense Resistor
(High Accuracy)
z Quick Load Step Response within 100ns
z 1% VOUT Accuracy over Line and Load
z Adjustable 0.75V to 3.3V Output Range
z 4.5V to 26V Battery Input Range
z Resistor Programmable Frequency
z Over/Under Voltage Protection
z 2 Steps Current Limit During Soft-Start
z Drives Large Synchronous-Rectifier FETs
z Power Good Indicator
z RoHS Compliant and 100% Lead (Pb)-Free
Applications
z Notebook Computers
z CPU Core Supply
z Chipset/RAM Supply as Low as 0.75V
Pin Configurations
(TOP VIEW)
Package Type
QW : WQFN-16L 4x4 (W-Type) (RT8202)
QW : WQFN-16L 3x3 (W-Type) (RT8202A)
QW : WQFN-14L 3.5x3.5 (W-Type) (RT8202B)
Lead Plating System
P : Pb Free
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
` RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
` Suitable for use in SnPb or Pb-free soldering processes.
Marking Information
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area.
DS8202/A/B-05 April 2011
16 15 14 13
VOUT
VDD
FB
PGOOD
1
2
3
4
GND
17
12 UGATE
11 PHASE
10 OC
9 VDDP
5678
WQFN-16L 4x4/WQFN-16L 3x3
TON
VOUT
VDD
FB
PGOOD
2
3
4
5
6
1 14
GND
15
78
13 UGATE
12 PHASE
11 OC
10 VDDP
9 LGATE
WQFN-14L 3.5x3.5
www.richtek.com
1
Free Datasheet http://www.Datasheet4U.com
1 page  
RT8202/A/B
Parameter
FB Reference Voltage
FB Input Bias Current
Symbol
VFB
Test Conditions
VDD = 4.5 to 5.5V
FB = 0.75V
Min
0.742
−1
Output Voltage Range
VOUT
On-Time
Minimum Off-Time
VOUT Shutdown Discharge
Resistance
Current Sensing
ILIM Source Current
Current Comparator Offset
VIN = 15V, VOUT = 1.25V, RTON = 1M
0.75
267
250
EN/DEM = GND
--
LGATE = High
GND − OC
18
−10
Current Limit Setting Range RILIM
Zero Crossing Threshold
Fault Protection
GND − PHASE, EN/DEM = 5V
2.5
−10
Current Limit Sense
Voltage
Output UV Threshold
OVP Threshold
OV Fault Delay
VDD UVLO Threshold
Soft-Start Ramp Time
UV Blank Time
Thermal Shutdown
Thermal Shutdown
Hysteresis
Driver On-Resistance
VRILIM
GND − PHASE, RILIM = 2.5k
GND − PHASE, RILIM = 10k
With respect to error comparator
threshold
FB forced above OV threshold
Rising edge, Hysteresis = 20mV,
PWM disabled below this level
From EN high to internal VREF reach
0.71V (0Æ95%)
From EN signal going high
35
170
60
10
--
4.1
--
--
--
--
UGATE Driver Pull Up
BOOT − PHASE = 5V
UGATE Driver Sink
RUGATEsk BOOT − PHASE = 5V
LGATE Driver Pull Up
LGATE, High State (Source)
LGATE Driver Pull Down
UGATE Driver Source/Sink
Current
LGATE Driver Source
Current
LGATE Driver Sink Current
LGATE, Low State (Sink)
UGATE − PHASE = 2.5V,
BOOT − PHASE = 5V
LGATE forced to 2.5V
LGATE forced to 2.5V
--
--
--
--
--
--
--
Dead Time
LGATE Rising (PHASE = 1.5V)
UGATE Rising
--
--
DS8202/A/B-05 April 2011
Typ Max Unit
0.75 0.758 V
0.1 1 μA
-- 3.3 V
334 401 ns
400 550 ns
20 -- Ω
20 22 μA
-- 10 mV
-- 10 kΩ
-- 5 mV
50 65 mV
200 230 mV
70 80 %
15 20 %
20 -- μs
4.3 4.5 V
1.35 -- ms
3.1 -- ms
155 -- °C
10 -- °C
1.5 5
Ω
1.5 5
Ω
1.5 5
Ω
0.6 2.5 Ω
1 -- A
1 -- A
3 -- A
30 --
ns
30 --
To be continued
www.richtek.com
5
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5 Page 
RT8202/A/B
IL
Slope = (VIN -VOUT) / L
iL, peak
iLoad = iL, peak / 2
IL
IL, peak
ILoad
ILIM
0 tON
t
Figure 1. Boundary condition of CCM/DEM
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 VOUT/VIN. The benefit of forced-CCM
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).
0t
Figure 2. Valley Current-Limit
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 (RDS(ON)). For
resistor sensing, a sense resistor is placed between the
source of low-side MOSFET and PGND (Figure 3(a)).
RDS(ON) sensing is more efficient and less expensive (Figure
3(b)). There is a compromise between current-limit
accuracy and sense resistor power dissipation.
PHASE
LGATE
OC
RILIM
PHASE
LGATE
OC
RILIM
(a) (b)
Figure 3. Current-Sense Methods
In both cases, the RILIM resistor between the OC pin and
PHASE pin sets the over current threshold. This resistor
RILIM is connected to a 20μA current source within the
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 RILIM resistor, positive current limit will activate.
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 RILIM resistor.
Choose a current limit resistor by following Equation :
RILIM = ILIMIT x RSENSE / 20μA
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
DS8202/A/B-05 April 2011
www.richtek.com
11
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| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet RT8202B.PDF ] | |
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