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PDF TD6821 Data sheet ( Hoja de datos )
| Número de pieza | TD6821 | |
| Descripción | 1.5MHz Dual 1.5A Synchronous Step Down Regulator | |
| Fabricantes | Techcode | |
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T echcode®
1.5MHz Dual 1.5A Synchronous Step Down Regulator
DATASHEET
TD6821
General Description
Features
The TD6821 are high-efficiency 1.5MHz synchronous
step-down DC-DC regulator ICs capable of delivering
up to 1.5A output currents, respectively. The
TD6821 operates over a wide input voltage range
from 3V to 5.5V and integrate main switch and
synchronous switch with very low RDS(ON) to minimize
the conduction loss.
z low Rds(on) for internal switches (top/bottom):
z 3-5.5V input voltage range
z 1.5MHz switching frequency minimizes
the external components
z Internal softstart limits the inrush current
z 100% dropout operation
z Compact and thermally enhanced package:
SOP8-PP
Low output voltage ripple and small external inductor
and capacitor sizes are achieved with
1.5MHz switching frequency.
Applications
z LCD TV WiFi
Card GPS
z Access Point Router
z Set Top Box
Package Types
Figure 1. Package Types of TD6821
December, 20, 2005. Techcode Semiconductor Limited www.techcodesemi.com
1
1 page  
T echcode®
1.5MHz Dual 1.5A Synchronous Step Down Regulator
Electrical Characteristics
DATASHEET
TD6821
VCC = 5V Vout=2.5V,L=2.2uH,Cout=10uF,Imax=1A, Ta = 25℃ unless otherwise specified.
Parameters
Symbol
Test Condition
Input voltage
VIN
Shutdown Supply Current
ISTBY
VEN=0V
Feedback Voltage
VFB
Feedback Bias Current
IFB VFB=Vin
Oscillator Frequency
FOSC
NFET RON
RDS(ON)N
PFET RON
RDS(ON)N
PFET Current Limit
ILIM
EN rising threshold
VENH
EN falling threshold
VENL
Input UVLO threshold
VUVLO
UVLO hyesteresis
VHYS
Min ON Time
Max Duty Cyele
Thermal Shutdown Temperature
TSD
Min.
3
0.588
-50
Typ.
0.6
1.5
Max.
5.5
10
0.612
200
150
1.8
1.5
0.4
2.4
0.1
50
100
160
Unit
V
uA
V
nA
MHz
mΩ
mΩ
A
V
V
V
V
ns
%
ºC
December, 20, 2005. Techcode Semiconductor Limited www.techcodesemi.com
5
5 Page 
T echcode®
1.5MHz Dual 1.5A Synchronous Step Down Regulator
Function Description
DATASHEET
TD6821
Main Control Loop
The TD6821 uses a constant frequency, current mode
step-down architecture. Both the main (P-channel
MOSFET) and synchronous (N-channel MOSFET)
switches are internal. During normal operation, the
internal top power MOSFET is turned on each cycle
when the oscillator sets the RS latch, and turned off
when the current comparator, ICOMP, resets the RS
latch. The peak inductor current at which ICOMP resets
the RS latch, is controlled by
the output of error amplifier EA. When the load current
increases, it causes a slight decrease in the feedback
voltage, FB, relative to the 0.6V reference, which in turn,
causes the EA amplifier’s output voltage to increase until
the average inductor current matches the new load
current. While the top MOSFET is off, the bottom
MOSFET is turned on until either the inductor current
starts to reverse, as indicated by the current reversal
comparator IRCMP, or the beginning of the next clock
cycle.
Burst Mode Operation
The TD6821 is capable of Burst Mode operation in
which the internal power MOSFETs operate
intermittently based on load demand.
In Burst Mode operation, the peak current of the inductor
is set to approximately 200mA regardless of the output
load. Each burst event can last from a few cycles at light
loads to almost continuously cycling with short sleep
intervals at moderate loads. In between these burst
events, the power MOSFETs and any unneeded
circuitry are turned off, reducing the quiescent current to
20mA. In this sleep state, the load current is being
supplied solely from the output capacitor. As the output
voltage droops,
the EA amplifier’s output rises above the sleep threshold
signaling the BURST comparator to trip and turn the top
MOSFET on. This process repeats at a rate that is
dependent on the load demand.
ShortCircuit Protection
When the output is shorted to ground, the frequency of
the oscillator is reduced to about 400kHz, 1/4 the
nominal frequency. This frequency foldback ensures that
the inductor current has more time to decay, thereby
preventing runaway. The oscillator’s frequency will
progressively increase to 1.5MHz when VFB or VOUT
rises above 0V.
Dropout Operation
As the input supply voltage decreases to a value
approaching the output voltage, the duty cycle increases
toward the maximum on-time. Further reduction of the
supply voltage forces the main switch to remain on for
more than one cycle until it reaches 100% duty cycle.
The output voltage will then be determined by the input
voltage minus the voltage drop across the P-channel
MOSFET and the inductor.
An important detail to remember is that at low input
supply voltages, the RDS(ON) of the P-channel switch
increases (see Typical Performance Characteristics).
Therefore, the user should calculate the power
dissipation when the TD6821 is used at 100% duty cycle
with low input voltage (See Thermal Considerations in
the Applications Information
section).
December, 20, 2005. Techcode Semiconductor Limited www.techcodesemi.com
11
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet TD6821.PDF ] | |
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