|
|
PDF RT8208B Data sheet ( Hoja de datos )
| Número de pieza | RT8208B | |
| Descripción | Programmable Output Voltage Single Synchronous Buck Controller | |
| Fabricantes | Richtek | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de RT8208B (archivo pdf) en la parte inferior de esta página. Total 18 Páginas | ||
|
No Preview Available !
RT8208A/B
Programmable Output V oltage Single Synchronous
Buck Controller
General D escription
The RT8208A/B is a con stant-on-time PWM controller
which provide s f our re sistor programmable DC output
voltages by controlling the G0 and G1 digital input. The
output voltage is programmable from 0.75V to 3.3V. The
RT8208A/B offers the lowest total solution cost in systems
where need output voltage slewing. The RT8208A/B
provides an automatic masking power good output during
output voltage transition.
The constant-on-time PWM control scheme handles wide
input/output ratios with ease and provides 100ns “instant-
on” respon se to loa d tra nsient while maintaining a
relatively constant frequency. It provides the high efficiency,
excellent tra nsient respon se, a nd DC output a ccuracy
needed for stepping down high voltage batteries to
generate low voltage CPU core, graphics, I/O and chipset
RAM supplies in notebook computers.
The RT8208A/B achieves high efficiency at a reduced cost
by eliminating the current sense resistor in traditional
current mode PWMs. Efficiency is further enha nced by
its ability to drive very large synchronous rectifier
MOSFETs. The buck conversion allows this device to
directly step down from high voltage batteries for the highest
possible efficiency. Additional features include soft-start,
under voltage prote ction, programmable over current
protection and non-overlapping gate drive.The RT8208A/
B is available in a WQFN-16L 3x3 package.
Pin Configuration s
(TOP VIEW)
16 15 14 13
VO UT
VD D
FB
PGOOD
1
2
3
4
GND
17
12 UGAT E
11 PHASE
10 CS
9 VDDP
5 678
WQFN-16L 3x3
Features
z Ultra-High Efficiency
z Resistor Programmable Output Voltage from 0.75V
to 3.3V with Integrated Transition Support
z Quick Load Step Response within 100ns
z 1% VFB Accuracy over Line and Load
z 4.5V to 26V Battery Input Range
z Resistor Programmable Frequency
z Integrated Bootstrap Switch
z Resistor Programmable Positive Current Limit by
Low Side RDS(ON) Sense (Lossless Limit)
z Negative Current Limiter
z Voltage Transient Overshoot Eliminator*
z Over Voltage Protection
z Under Voltage Protection
z 4 Steps Current Limit During Soft-Start
z Power Good Indicator
z RoHS Compliant and Halogen Free
* Paten Pending
Application s
z Notebook Computers
z System Power Supplies
z I/O Supplies
z Programmable-Output Power Supplies
Ordering Information
RT8208
Package Type
QW : WQFN-16L 3x3 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Z : ECO (Ecological Element with
Halogen Free and Pb free)
Note :
Turn-on D0/D1 MOSFET
A : G0/G1 High
B : G0/G1 Low
Richtek products are :
` RoHS compli ant and compatible with the current require-
ments of IPC/JEDEC J-ST D-020.
` Suitable for use in SnPb or Pb-free soldering processes.
DS8208A/B-04 May 2011
www.richtek.com
1
http://www.Datasheet4U.com
1 page  
RT8208A/B
Parameter S
D0 Pull-Down Resistance
D1 Pull-Down Resistance
On-Time
Minimum Off-Time
VOUT Shutdown Discharge
Resistance
Current Sensing
ymbol
Test Conditions
D0 to GND, G0 = 5V
D1 to GND, G1 = 5V
VPHASE = 12V, VOUT = 2.5V,
RTON = 250kΩ
EN/DEM = GND
Current Limiter Source Current
Current Comparator Offset
Zero Crossing Threshold
CS to GND
PHASE to GND, EN/DEM = 5V
Fault Protection
Current Limit (Threshold)
Current Limit Setting Range
Output UV Threshold
OVP Threshold
OV Fault Delay
VDD Under Voltage Lockout
Threshold
Current Limit Step Duration at
Soft-Start
UVP Blanking Time
VFB_OVP
GND to PHASE, VCS = 50mV
GND to PHASE, VCS = 200mV
CS to GND
UVP Detection
OVP Detection
FB forced above OV threshold
Rising edge, PWM disabled below
this level
Hysteresis
Each step
From EN signal going high
Thermal Shutdown
Thermal Shutdown Hysteresis
TSH DN
Driver On-Resistance
UGATE Drive Source
RUGATEsr BOOT to PH ASE = 5V
UGATE Drive Sink
RUGATEsk BOOT to PH ASE = 5V
LGATE Drive Source
RLGATEsr LGATE, High State
LGATE Drive Sink
UGATE Gate Driver Source/Sink
Current
LGATE Gate Driver Source
Current
LGATE Gate Driver Sink Current
RLGATEsk LG ATE, Low State
UGATE to PHASE = 2.5V,
BOOT to PHASE = 5V
LGATE forced to 2.5V
LGATE forced to 2.5V
Dead Time
LGATE Rising (Phase = 1.5V)
UGATE Rising
Internal Boost Charging Switch
On-Resistance
VDDP to BOOT, 10mA
DS8208A/B-04 May 2011
Min Typ
-- 10
-- 10
336 420 504
Max
--
--
Unit
Ω
Ω
ns
250 400 550
ns
-- 2 0 - -
Ω
9
−10
−10 -
10
--
-
11
10
5m
μA
mV
V
40 50 60
190 200 210
mV
50 -- 200 mV
60 70 80
%
120 125 130 %
-- 20 -- μs
4.1 4.3 4.5 V
-- 80 -
- mV
-- 128 -
- clks
-- 512 -- clks
-- 155 -- °C
-- 10 -- °C
-- 2
-- 1
-- 1
-- 0.5
-- 1 -
-- 1 -
-- 3
-- 30
-- 3 0 -
-- --
5
5
5
2.5
-
-
--
--
-
80
Ω
Ω
Ω
Ω
A
A
A
ns
Ω
To be continued
www.richtek.com
5
5 Page 
RT8208A/B
IL
Slope = (VIN -VOUT) / L
iL, peak
iLoad = iL, peak / 2
0 tON
t
Figure 1. Boundary Condition of CCM/DEM
UGATE
PHASE
LGATE
VOUT
GND
FB
G0
G1
VIN
VOUT
R1
R2
The switching wavef orms may a ppear noisy a nd
asynchronous when light loading causes diode-emulation
operation, but this is a normal operating condition that
results in high light-load efficiency. Trade-offs inDEM noise
vs. light-load efficiency is 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 ef ficiency (assuming that the coil resista nce
remains f ixed) a nd less output voltage ri pple. The
disadvantages for using higher inductor values include
larger physical size and degraded load-transient response
(especially at low input voltage levels).
Forced-CCM Mode (EN = floating)
The low noise, forced-CCM mode (EN=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 loa ds 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 come s at a cost: The no-loa d battery
current can be up to 10mA to 40mA, depending on the
external MOSFETs.
Output Voltage Setting (FB)
The output voltage can be adjusted from 0.75V to 3.3V by
setting the feedback resistor R1 and R2, see Figure 2.
With G0 and G1 in low state, the output voltage is at the
lowest value. Choose R2 to be approximately 20kΩ, and
solve for R1 using the equation :
VO=UT
REFV×
⎛⎜⎝1+
R1
R2
⎞
⎟⎠
where VREF is 0.75V in typical.
DS8208A/B-04 May 2011
Figure 2. Setting VOUT with a ResistorDivider
Output Voltage Transition Control
The RT8208A/B provides two digital control inputG0 and
G1 to allow sele ction among four output voltage s. The
output voltage is regulated by comparing the FB pin
(connected to VOUT via an external resistor divider) to
the internal 0.75V reference. The G0 and G1 digital input
control the gate of internal respective MOSFET whose
drain is connected to D0 and D1 respectively. Using Gx,
the user controls whetherDx is grounded or open, which
then controls the resistor divider ratio f or VOUT. A logic
high signal on Gx will connect Dx to ground.
When the Gx input changes state, this cha nge quickly
causes three actions:
1. D0 changes state.
2. The power good PGOOD output is temporarily latched
into its present state. This prevents chattering or false
tripping while VOUT moves to the new level.
3. When the Gx changes state whether DEM is set or
not, then enter the PWM mode a nd counts 32 clock
cycles. For the duration of 32 clock cycles, the OVP
and UVP function is masked. This behavior allows the
output to slew down to the new level without tripping
the OVP or UVP function when theGx change causes
rapid change ofDx, which in turns cause a rapid change
at FB.
Output voltage is regulated through the FB pin via resistors
R1 through R4 as shown in Figure 3.
www.richtek.com
11
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet RT8208B.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| RT8208A | Programmable Output Voltage Single Synchronous Buck Controller | Richtek |
| RT8208B | Programmable Output Voltage Single Synchronous Buck Controller | Richtek |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |