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PDF TD6811B Data sheet ( Hoja de datos )
| Número de pieza | TD6811B | |
| Descripción | 1.5MHz 1.2A Synchronous Step-Down Regulator Dropout | |
| Fabricantes | Techcode | |
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T echcode®
DATASHEET
1.5MHz 1.2A Synchronous Step-Down Regulator Dropout TD6811B
General Description
Features
The TD6811B is a high efficiency monolithic
synchronous buck regulator using a constant frequency,
current mode architecture. The device is available in an
adjustable version and fixed output voltages of 1.5V and
1.8V. Supply current during operation is only 20mA and
drops to ≤1mA in shutdown. The 2.5V to 5.5V input
voltage range makes the TD6811B ideally suited for
single Li-Ion battery-powered applications. 100% duty
cycle provides low dropout operation, extending battery
life in portable systems.Automatic Burst Mode operation
increases efficiency at light loads, further extending
battery life.
Switching frequency is internally set at 1.5MHz, allowing
the use of small surface mount inductors and capacitors.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode. Low
output voltages are easily supported with the 0.6V
feedback reference voltage. The TD6811B is available in
TSOT23-5 package.
z High Efficiency: Up to 96%
z High Efficiency at light
loads(Vin=5V,Vout=3.3V,Ilod=3mA η>82%)
z Very Low Quiescent Current: Only 20uA During
Operation
z 1.2A Output Current
z 2.5V to 5.5V Input Voltage Range
z 1.5MHz Constant Frequency Operation
z No Schottky Diode Required
z Low Dropout Operation: 100% Duty Cycle
z 0.6V Reference Allows Low Output Voltages
z Shutdown Mode Draws ≤1uA Supply Current
z Current Mode Operation for Excellent Line and Load
Transient Response
z Overtemperature Protected
z TSOT23-5 Package is Available
Applications
z Cellular Telephones
z Personal Information Appliances
z Wireless and DSL Modems
z Digital Still Cameras
z MP3 Players
z Portable Instruments
Package Types
TSOT23‐5
Figure 1. Package Types of TD6811B
December, 20, 2009 Techcode Semiconductor Limited www.techcodesemi.com
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T echcode®
DATASHEET
1.5MHz 1.2A Synchronous Step-Down Regulator Dropout TD6811B
Electrical Characteristics(Cont.)
Unless otherwise specified, VIN= 3.6V TA=25 ºC.
Symbol
IPK
VLOADREG
Parameter
Peak Inductor Current
Output Voltage Load
Regulation
Conditions
VIN = 3V, VFB = 0.5V or
VOUT = 90%, Duty Cycle <
35%
Min.
1.55
VIN Input Voltage Range
2.5
IS
fOSC
RPFET
RNFET
ILSW
VRUN
Input DC Bias Current
Active Mode
Sleep Mode
VFB = 0.5V or VOUT =
90%, ILOAD = 0A
VFB = 0.62V or VOUT =
103%, ILOAD = 0A
Shutdown
VRUN = 0V, VIN = 4.2V
Oscillator Frequency
VFB = 0.6V or VOUT =
100%
1.2
VFB = 0V or VOUT = 0V
RDS(ON) of P-Channel
FET
RDS(ON) of N-Channel
FET
SW Leakage
ISW = 100mA
ISW = -100mA
VRUN = 0V, VSW = 0V or
5V, VIN = 5V
RUN Threshold
0.3
IRUN
RUN Leakage Current
Typ.
1.6
Max.
1.7
Unit
A
0.5 %
5.5 V
300 400
20 35
0.1 1
1.5 1.8
400
0.30 0.40
0.30 0.40
0.01 1
1
0.01
1.5
1
uA
uA
uA
MHz
KHz
Ω
Ω
uA
V
uA
December, 20, 2009 Techcode Semiconductor Limited www.techcodesemi.com
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T echcode®
1.5MHz 1.2A Synchronous Step-Down Regulator Dropout
Function Description(Cont.)
DATASHEET
TD6811B
Low Supply Operation
The TD6811B will operate with input supply voltages as
low as 2.5V, but the maximum allowable output current is
reduced at this low voltage. Figure 2 shows the reduction
in the maximum output current as a function of input
voltage for various output voltages.
Slope Compensation and Inductor Peak
Current
Slope compensation provides stability in constant
frequency architectures by preventing subharmonic
oscillations at high duty cycles. It is accomplished
internally by adding a compensating ramp to the inductor
current signal at duty cycles in excess of 40%. Normally,
this results in a reduction of maximum inductor peak
current for duty cycles >40%. However, the TD6811B
uses a patent-pending scheme that counteracts this
compensating ramp, which allows the maximum inductor
peak current to remain unaffected throughout all duty
cycles.
The basic TD6811B application circuit is shown in Figure
3. External component selection is driven by the load
requirement and begins with the selection of L followed
by CIN and COUT.
Inductor Selection
For most applications, the value of the inductor will fall in
the range of 1mH to 4.7mH. Its value is chosen based on
the desired ripple current. Large value inductors lower
ripple current and small value inductors result in higher
ripple currents. Higher VIN or VOUT also increases the
ripple current as shown in equation 1. A reasonable
starting point for setting ripple current is DIL = 480mA
(40% of 1200mA).
The DC current rating of the inductor should be at least
equal to the maximum load current plus half the ripple
current to prevent core saturation. Thus, a 1320mA rated
inductor should be enough for most applications
(1200mA + 120mA). For better efficiency, choose a low
DC-resistance
inductor.
The inductor value also has an effect on Burst Mode
operation. The transition to low current operation begins
when the inductor current peaks fall to approximately
200mA. Lower inductor values (higher DIL) will cause
this to occur at lower load currents, which can cause a
dip in efficiency in the upper range of low current
operation. In Burst Mode operation, lower inductance
values will cause the burst frequency to increase.
Maximum Output Current vs Input Voltag
December, 20, 2009 Techcode Semiconductor Limited www.techcodesemi.com
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| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet TD6811B.PDF ] | |
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