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參數(shù)資料
| 型號： | TK65221 |
| 廠商： | TOKO Inc. |
| 英文描述： | STEP-UP VOLTAGE CONVERTER WITH VOLTAGE MONITOR |
| 中文描述： | 升壓電壓電壓監(jiān)控轉(zhuǎn)爐 |
| 文件頁數(shù)： | 13/20頁 |
| 文件大小： | 141K |
| 代理商： | TK65221 |
ADVANCED INFORMATION
January 1999 TOKO, Inc.
Page 13
TK652xx
SINGLE-CELL APPLICATION (CONT.)
same battery is powering the TK652xx at the V
IN
pin (i.e.,
the normal case), then the IC may become inoperable due
to insufficient V
IN
. This is why the application test circuit
features an RC filter into the V
IN
pin. The current draw is
very small, so the voltage drop across this filter resistor is
negligible. The filter serves to average out the input ripple
caused by the battery resistance. Note that this filter is
optional, and the net effect of its use is the extension of
battery life by allowing the battery to be discharged more
deeply.
A more power-efficient method comes at the price of a
large capacitor. This can be placed in parallel with the
battery to help channel the converter current pulses away
from the battery. The capacitor must have low ESR
compared to the battery resistance in order to accomplish
this effectively.
Still another solution is to filter the DC input with an LC
filter. However, it is more likely that the filter will be either
too large or too lossy. It is of questionable benefit to smooth
the input if the DC loss through the filter is large.
Assuming that input ripple voltage at the battery terminal
and converter input is large, and that we filter the V
IN
pin of
the IC as in the test circuit, then the parameter “V
IN
” in the
previous equations is not usable, and we will need to use
parameters to represent both the source voltage andthe
source resistance.
SWITCH ON-RESISTANCE, INDUCTOR WINDING
RESISTANCE, AND CAPACITANCE ESR
The on-resistance of the TK652xx’s internal switch is
about 1 Ohm maximum. Using the previously stated
example of 100 mA peak current, the voltage drop across
the switch would reach 100 mV during the on-time. This
subtracts from the voltage which is impressed across the
inductor to store energy during the on-time. As a result,
less energy is delivered to the output during the off-time.
If the winding resistance of the inductor increases to 1 Ohm
or greater, the voltage drop across the winding resistance
also subtracts from the voltage used to store energy in the
core. Thus, efficiency degradation occurs.
As the inductor delivers energy into the output capacitor
during the off-time, its current decays at a rate proportional
to the voltage drop across it. The idealized equations
assume that the voltage at the switching node is clamped
at a diode drop above the output voltage. However, the
ESR of the output capacitor can increase the voltage drop
across the inductor by the additional voltage dropped
across the ESR when the peak current flows in it. For
example, the voltage across a capacitor with an ESR of 2
Ohms (not unusual at cold temperature) would jump by
200 mV when 100 mA peak current began to flow in it. This
extra voltage drop would cause the inductor current to
ramp down more quickly, thus, depleting the available
output current. Possible choices for low ESR capacitors
are: Panasonic TE series (surface mount); AVX TPS
series (surface mount); Matsuo 267 series (surface mount);
Sanyo OS-CON series.
LBI AND LOI FEATURES
In a properly designed system that has its maximum load
current under the limit of the maximum output current of the
converter, the Low Battery Indicator (LBI) signal is the first
indicator that the battery is getting low.
The latched Low
Output indicator (LOI) signal is the second and final
indicator that the battery should be replaced.
The LBI output provides a warning signal to a system
controller that the battery is near the end of its life and will
need replacing soon. The LBI threshold voltage is between
1.05 and 1.15 V. There is no hysteresis in its on-off trigger
levels.
The LOI output can provide a reset signal to a micropro-
cessor or other external system controller. When the
output voltage falls below the LOI threshold (during start-
up of the converter or under a current overload fault
condition), the LOI signal is asserted low, indicating that
the system controller )e.g., microprocessor) should be in a
reset mode. This method of reset control can be used to
prevent improper system operation which might occur at
low supply voltage levels. The LOI threshold voltage is
between 87% and 93% of the regulated output voltage
value. The LOI threshold also has about 40 mV hysteresis
between its on-off trigger levels.
When the output voltage dips below the LOI threshold
and
the LBI signal is asserted low,
the LOI signal will be
latched low by the LBI signal.
That is,
the LOI signal will
remain asserted low until the LBI signal goes high
,
even if the output voltage regains its regulated value.
Although the converter can start-up and work with the
battery voltage even as low as 0.9 V,
the battery should
be replaced when the LOI is latched low.
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| TK65221M | 制造商:TOKO 制造商全稱:TOKO, Inc 功能描述:STEP-UP VOLTAGE CONVERTER WITH VOLTAGE MONITOR |
| TK65221MTL | 制造商:TOKO 制造商全稱:TOKO, Inc 功能描述:STEP-UP VOLTAGE CONVERTER WITH VOLTAGE MONITOR |
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| TK65224 | 制造商:TOKO 制造商全稱:TOKO, Inc 功能描述:STEP-UP VOLTAGE CONVERTER WITH VOLTAGE MONITOR |
| TK65224M | 制造商:TOKO 制造商全稱:TOKO, Inc 功能描述:STEP-UP VOLTAGE CONVERTER WITH VOLTAGE MONITOR |
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