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PDF TD6811 Data sheet ( Hoja de datos )
| Número de pieza | TD6811 | |
| 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
TD6811
General Description
Features
The TD6811 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 TD6811 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 TD6811 is available in
TSOT23-5 package.
z High Efficiency: Up to 96%
z High Efficiency at light loads
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
TSOT235
Figure 1. Package Types of TD6811
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1 page  
T echcode®
DATASHEET
1.5MHz 1.2A Synchronous Step-Down Regulator Dropout
TD6811
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
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5 Page 
T echcode®
1.5MHz 1.2A Synchronous Step-Down Regulator Dropout
Function Description(Cont.)
DATASHEET
TD6811
Low Supply Operation
The TD6811 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 TD6811 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 TD6811 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
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| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet TD6811.PDF ] | |
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