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PDF TK65424 Data sheet ( Hoja de datos )
| Número de pieza | TK65424 | |
| Descripción | STEP-DOWN CONVERTER WITH BATTERY MONITOR | |
| Fabricantes | TOKO | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de TK65424 (archivo pdf) en la parte inferior de esta página. Total 28 Páginas | ||
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ADVANCED INFORMATION
TK654xx
ADVANCED
INFORMATION
STEP-DOWN CONVERTER WITH BATTERY MONITOR
FEATURES
s Minimum External Component Count (1 coil, 1 cap)
s Miniature 6 Pin SOT23L-6 Surface Mount Package
s Up To 95% Efficient
s Extremely Low Operating Current (24 µA)
s Low Quiescent Current (18 µA)
s Low Ripple
s Fast Transient Response
s Linear Dropout Characteristics
s Short Circuit Protection
s Regulates Down to 1.8 V
s Synchronous Rectification
s Internal Battery Monitor
DESCRIPTION
The TK654xx low power step-down converter is designed
for portable battery systems, capable of operating from a
single Li-ion battery cell or multiple alkaline or rechargeable
(NiCd or NiMH) battery cells (up to 6 V). The TK654xx
provides the power switch, synchronous rectifier, and the
control circuit for a buck step-down converter. Only two
external components are required to complete the step-
down conversion.
APPLICATIONS
s Battery Powered Systems
s Cellular Telephones
s Pagers
s Personal Communications Equipment
s Radio Controlled Systems
s Toys
Driving the SB pin low will disable the TK654xx and drop
the quiescent current on the input supply to approximately
18 µA.
Pulse Current Amplitude control is used to regulate the
voltage at the VOUT pin of the IC. When the output voltage
of the TK654xx drops below the regulation threshold, a
current pulse is transferred from the input supply to the
output. The TK654xx utilizes a proprietary control scheme,
where the average amplitude of the current pulse is varied
depending upon the current loads. The proprietary
architecture allows fast transient response and minimal
ripple while maintaining ease-of-use and low component
count.
The TK654xx is available in a miniature 6-pin SOT23L-6
surface mount package.
TK654xxM
The TK654xx provides laser-trimmed output voltages
ranging from 1.8 V to 3.3 V. The low resistance MOSFET
switch and synchronous rectifier allow average currents
up to 200 mA, while maintaining peak efficiencies up to
95%. A low-battery threshold and turn-off threshold can
be individually programmed by the user, utilizing a single
resistor divider connected to the Low Battery Input (LBI)
pin. When the resistively-divided supply voltage on the
LBI pin drops below approximately 1.22 V, the Low Battery
Output (LBO) pin will become asserted. The dual-function
LBI pin can alternatively be used as a Standby (SB) pin.
ORDERING INFORMATION
TK654xxM
Voltage Code
Tape/Reel Code
VOLTAGE CODE
18 = 1.8 V 27 = 2.7 V
21 = 2.1 V 30 = 3.0 V
24 = 2.4 V 33 = 3.3 V
25 = 2.5 V
TAPE/REEL CODE
TL: Tape Left
LBO
VOUT
SW
BLOCK DIAGRAM
VIN
VOUT
LBI/SB
REF
CONTROL
CIRCUIT
OFF LBO
BATTERY
MONITOR
LBI/SB
GND
VIN
SW
GND
LBO
September 1999 TOKO, Inc.
Page 1
1 page  
ADVANCED INFORMATION
TK654xx
26
25.5
25
24.5
24
23.5
23
22.5
22
2
200
150
TYPICAL PERFORMANCE CHARACTERISTICS
USING TEST CIRCUIT (CONT.)
TK65418
CONVERTER QUIESCENT
CURRENT vs.
INPUT SUPPLY VOLTAGE
No Load
26
25.5
TK65433
CONVERTER QUIESCENT
CURRENT vs.
INPUT SUPPLY VOLTAGE
No Load
25
24.5
24
23.5
23
345
VIN (V)
TK65418
CONVERTER QUIESCENT
CURRENT vs.
TEMPERATURE
6
22.5
22
3.5
200
4 4.5 5 5.5
VIN (V)
TK65433
CONVERTER QUIESCENT
CURRENT vs.
TEMPERATURE
No Load
No Load
150
6
100 100
50 50
0
-50 -25 0 25 50 75 100 125
TEMPERATURE (°C)
TK65418
STANDBY CURRENT vs.
INPUT SUPPLY VOLTAGE
25
0
-50 -25 0 25 50 75 100 125
TEMPERATURE (°C)
TK65433
STANDBY CURRENT vs.
INPUT SUPPLY VOLTAGE
25
20 20
15 15
10 10
5
2 2.5 3 3.5 4 4.5 5 5.5 6
VIN (V)
September 1999 TOKO, Inc.
5
2 2.5 3 3.5 4 4.5 5 5.5 6
VIN (V)
Page 5
5 Page 
ADVANCED INFORMATION
TK654xx
THEORY OF OPERATION (CONT.)
cycle will be dependent upon the duration of the preceding
"on" cycle and the sensed input and the output voltages.
The approximate duration of the "off" cycle can be predicted
as follows:
TOFF = TON X (VIN - VOUT) / VOUT
During the majority of the "off" cycle, a power switch is
turned on. The turn-on point of the switch is synchronized
with the initiation of the "off" cycle. The turn-off point is near
the end of the "off" cycle. The addition of this switch
reduces the voltage drop across the external rectifying
device and provides significant improvements in converter
efficiency.
BATTERY MONITOR SECTION
In a typical voltage monitor, which uses an external resistive
divider for setting the voltage monitor threshold, the input
bias current to the monitor pin is essentially zero. In this
type of scenario, the voltage on the monitor input would be
a resistively divided version of the battery voltage. The
Battery Monitor of the TK654xx introduces a small feedback
current (-ILBI) which introduces a “plateau” into the transfer
characteristics between the battery voltage and the voltage
monitoring pin. The width of this plateau is dependent
upon the current range of the feedback current (-ILBI) and
the values of the external resistor network. Figure 2
illustrates the typical relationship between the battery
voltage (VIN), the feedback current (-ILBI) and the voltage
on the monitoring pin (VLBI).
In selecting a resistor divider network, there are typically
two degrees of freedom when selecting values. The first
criteria in selecting the divider is the ratio of the two
resistors. Selecting the ratio defines the upper threshold of
the voltage monitor. The second degree of freedom when
selecting the resistor divider is the absolute resistance
values. This second degree of freedom can be utilized to
set a secondary monitoring threshold (VOFF) lesser than
the first.
Typically, when the battery voltage is relatively high, the
voltage on the LBI input pin will be a resistively divided
version of the battery voltage.
As the battery voltage drops, the voltage on the VLBI pin will
drop proportionately. When the voltage on the LBI input pin
passes through approximately 1.22 V, the output of the
first comparator (LBO) will transition from a high to a low
state and the synchronous rectifier N-channel MOSFET
will stop being switched. There is about 50 mV of hysteresis
between the LBO trip point and its reset point. Shortly after
the LBO output has been asserted, as the input voltage
continues to drop, the magnitude of the current out of the
VLBI pin will begin to flow and proportionately increase as
the input voltage decreases. An op-amp feedback loop
internal to the Battery Monitor of the TK654xx will attempt
to maintain the voltage on the VLBI pin at a constant value
of approximately 1.22 V (thus, the plateau). As the battery
voltage continues to drop, there comes a point where the
feedback current stops increasing at about 720 nA. At this
point, the voltage on the LBI pin will resume a proportional
drop with the input voltage and the TK654xx converter will
turn off.
For details on how to properly select the resistor divider,
refer to the “Design Considerations” section.
VLBO
VIN VOFF
VLBI
-ILBI
0 nA
1.22 V
720 nA
LBO
OFF
FIGURE 2: BATTERY MONITOR OPERATION
GRAPHS
September 1999 TOKO, Inc.
Page 11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet TK65424.PDF ] | |
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