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PDF TD8577 Data sheet ( Hoja de datos )

Número de pieza TD8577
Descripción 5V 2.1A 1.2MHz Synchronous Boost Converter
Fabricantes Techcode 
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Techcode®
5V 2.1A 1.2MHz Synchronous Boost Converter
DATASHEET
TD8577
General Description
Features
The TD8577 devices provide a power supply solution for
products powered by either a one-cell Li-Ion or Li-polymer, or
a two to three-cell alkaline, NiCd or NiMH battery. The
converter generates a stable output voltage that is adjusted
by an external resistor divider or fixed internally on the chip.
It provides high efficient power conversion and is capable of
delivering output currents up to 1 A at 5 V at a supply voltage
down to 1.8 V. The implemented boost converter is based on
a fixed frequency, pulse-width- modulation (PWM) controller
using a synchronous rectifier to obtain maximum efficiency.
At low load currents the converter enters Power Save mode
to maintain a high efficiency over a wide load current range.
The Power Save mode can be disabled, forcing the converter
to operate at a fixed switching frequency. It can also operate
synchronized to an external clock signal that is applied to the
SYNC pin. the maximum peak current in the boost switch is
limited to a value of 5000 mA.
The converter can be disabled to minimize battery drain.
During shutdown, the load is completely disconnected from
the battery. A low-EMI mode is implemented to reduce
ringing and, in effect, lower
radiated electromagnetic energy when the converter enters
the discontinuous conduction mode. The device is packaged
in a 16-pin QFN package measuring 4 mm x 4 mm (RSA) or in
a 16-pin TSSOP16.or in a DFN3x3-12 packages
92% Efficient Synchronous Boost Converter With
1000-mA Output Current From 1.8-V Input
Device Quiescent Current: 20-μA (Typ)
Input Voltage Range: 1.8-V to 5.5-V
Adjustable Output Voltage Options Up to 5.5-V
Power Save Mode for Improved Efficiency at Low Output
Power
Low Battery Comparator
Low EMI-Converter (Integrated Antiringing Switch)
Load Disconnect During Shutdown
Over-Temperature Protection
Available in a Small 4 mm x 4 mm QFN-16 or in a
TSSOP-16 or in a DFN3*3-12 package
Applications
Power Bank
Tablet
Portable Equiment
October, 20, 2011.
Techcode Semiconductor Limited
1
www.techcodesemi.com

1 page




TD8577 pdf
Techcode®
5V 2.1A 1.2MHz Synchronous Boost Converter
DATASHEET
TD8577
Electrical Characteristics
PARAMETER
TEST CONDITIONS
VI Input voltage range
VO TD8577 output voltage range
VFB TD8577 feedback voltage
f Oscillator frequency
Frequency range for synchronization
Switch current limit
VOUT= 5 V
Start-up current limit
SWN switch on resistance
VOUT= 5 V
SWP switch on resistance
VOUT= 5 V
Total accuracy
Line regulation
Load regulation
Quiescent current
IO = 0 mA, VEN = VBAT = 1.8 V,
VBAT
VOUT =5 V
IO = 0 mA, VEN = VBAT = 1.8 V,
VOUT
VOUT = 5 V
Shutdown current
VEN= 0 V, VBAT = 2.4 V
CONTROL STAGE
PARAMETER
TEST CONDITIONS
VUVLO Under voltage lockout threshold
VLBI voltage decreasing
VIL LBI voltage threshold
VLBI voltage decreasing
LBI input hysteresis
LBI input current
EN = VBAT or GND
LBO output low voltage
VO = 3.3 V, IOI = 100 µA
LBO output low current
LBO output leakage current
VLBO= 7 V
MIN
1.8
1.8
490
900
900
4500
-3%
TYP
500
1200
5000
0.4 x ISW
55
55
10
10
0.1
MIN TYP
1.5
490 500
10
0.01
0.04
100
0.01
EN, SYNC input low voltage
VIL
VIH EN, SYNC input high voltage
EN, SYNC input current
Overtemperature protection
Overtemperature hysteresis
Clamped on GND or VBAT
0.8 × VBAT
0.01
140
20
MAX
5.5
5.5
510
1500
1500
5500
3%
0.6%
0.6%
25
20
1
MAX
510
0.1
0.4
0.1
0.2 ×
VBAT
0.1
UNIT
V
V
mV
kHz
kHz
mA
mA
mΩ
mΩ
µA
µA
µA
UNIT
V
mV
mV
µA
V
µA
µA
V
V
µA
°C
°C
October, 20, 2011.
Techcode Semiconductor Limited
5
www.techcodesemi.com

5 Page





TD8577 arduino
Techcode®
5V 2.1A 1.2MHz Synchronous Boost Converter
DATASHEET
TD8577
Function Description
Controller Circuit
The controller circuit of the device is based on a fixed frequency
multiple feedforward controller topology. Input voltage, output
voltage, and voltage drop on the NMOS switch are monitored
and forwarded to the regulator. So changes in the operating
conditions of the converter directly affect the duty cycle and
must not take the indirect and slow way through the control
loop and the error amplifier. The control loop, determined by
the error amplifier,only has to handle small signal errors. The
input for it is the feedback voltage on the FB pin or, at fixed
output voltage versions, the voltage on the internal resistor
divider. It is compared with the internal reference voltage to
generate an accurate and stable output voltage.
The peak current of the NMOS switch is also sensed to limit the
maximum current flowing through the switch and the inductor.
The typical peak current limit is set to 5000 mA. An internal
temperature sensor prevents the device from getting
overheated in case of excessive power dissipation.
Synchronous Rectifier
The device integrates an N-channel and a P-channel MOSFET
transistor to realize a synchronous rectifier. Because the
commonly used discrete Schottky rectifier is replaced with a low
RDS(ON) PMOS switch, the power conversion efficiency reaches
96%. To avoid ground shift due to the high currents in the NMOS
switch, two separate ground pins are used. The reference for all
control functions is the GND pin. The source of the NMOS switch
is connected to PGND. Both grounds must be connected on the
PCB at only one point close to the GND pin. A special circuit is
applied to disconnect the load from the input during shutdown
of the converter. In conventional synchronous rectifier circuits,
the backgate diode of the high-side PMOS is forward biased in
shutdown and allows current flowing from the battery to the
output. This device however uses a special circuit which takes
the cathode of the backgate diode of the high-side PMOS and
disconnects it from the source when the regulator is not enabled
(EN = low).
Synchronous Rectifier(Cont.)
The benefit of this feature for the system design engineer is
that the battery is not depleted during shutdown of the
converter. No additional components have to be added to
the design to make sure that the battery is disconnected
from the output of the converter.
Device Enable
The device is put into operation when EN is set high. It is put into
a shutdown mode when EN is set to GND. In shutdown mode,
the regulator stops switching, all internal control circuitry
including the low-battery comparator is switched off, and the
load is isolated from the input (as described in the Synchronous
Rectifier Section). This also means that the output voltage can
drop below the input voltage during shutdown. During start-up
of the converter, the duty cycle and the peak current are limited
in order to avoid high peak currents drawn from the battery.
Undervoltage Lockout
An undervoltage lockout function prevents device start-up if
the supply voltage on VBAT is lower than approximately 1.6
V. When in operation and the battery is being discharged, the
device automatically enters the shutdown mode if the
voltage on VBAT drops below approximately 1.6 V. This
undervoltage lockout function is implemented in order to
prevent the malfunctioning of the converter.
Softstart
When the device enables the internal start-up cycle starts with
the first step, the precharge phase. During precharge, the
rectifying switch is turned on until the output capacitor is
charged to a value close to the input voltage. The rectifying
switch current is limited in that phase. This also limits the output
current under short-circuit conditions at the output. After
charging the output capacitor to the input voltage the device
starts switching. Until the output voltage is reached, the boost
switch current limit is set to 40% of its nominal value to avoid
high peak currents at the battery during startup. When the
output voltage is reached, the regulator takes control and the
switch current limit is set back to 100%.
October, 20, 2011.
Techcode Semiconductor Limited
11
www.techcodesemi.com

11 Page







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