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参数资料
| 型号： | TK65130MTL |
| 厂商： | ASAHI KASEI POWER DEVICES CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING REGULATOR, 102 kHz SWITCHING FREQ-MAX, PDSO6 |
| 封装： | SOT-23L, SMT-6 |
| 文件页数： | 6/20页 |
| 文件大小： | 158K |
| 代理商： | TK65130MTL |
Page 14
January 2001 TOKO, Inc.
TK651xxM
SINGLE-CELL APPLICATION (CONT.)
Compared to the simple boost circuit, this Filtered Test
Circuit adds the following circuitry: the RC filter into the V
IN
pin, the RC snubber, the RC filter at the converter output,
and the pull-up resistor to the LOI pin.
The RC filter at the V
IN pin is used only to prevent the ripple
voltage at the battery terminals from prematurely causing
undervoltage lockout of the IC. This is only needed when
the inductor value is relatively small and the battery
resistance is relatively high and the V
IN range must extend
as low as possible.
The snubber (optional) is composed of a series RC network
from the switch pin to ground (or to the output or input if
preferred). Its function is to dampen the resonant LC circuit
which rings during the inductor current deadtime. When the
current flowing in the inductor through the output diode
decays to zero, the parasitic capacitance at the switch pin
from the switch, the diode, and the inductor winding has
energy which rings back into the inductor, flowing back into
the battery. If there is no snubbing, it is feasible that the
switch pin voltage could ring below ground. Although the IC
is well protected against latch-up, this ringing may be
undesirable due to radiated noise. To be effective, the
snubber capacitor should be large (e.g., 5 ~ 20 times) in
comparison to the parasitic capacitance. If it is unnecessarily
large, it dissipates extra energy every time the converter
switches. The resistor of the snubber should be chosen
such that it drops a substantial voltage as the ringing
parasitic capacitance attempts to pull the snubber capacitor
along for the ride. If the resistor is too small (e.g., zero), the
snubber capacitance just adds to the ringing energy. If the
resistor is too large (e.g., infinite), it effectively disengages
the snubber capacitor from fighting the ringing.
The RC filter at the converter output attenuates the
conducted noise; the converter may not require this.
Finally, the pull-up resistors at the LOI pin are needed only
if this output signal is used. Most of this circuitry which
appears in the test circuit has been added to minimize
ripple and noise effects. But when this is not critical, the
circuit can be minimized.
When any DC-DC converter is used to convert power in RF
circuits (e.g., pagers) the spectral noise generated by the
converter, whether conducted or radiated, is of concern.
The oscillator of the TK651xx has been trimmed and
stabilized to 83 +/- 4 kHz with the intention of greatly
minimizing interference at the common IF frequency of 455
kHz.
In comparison with conventional IC solutions, where the
oscillator frequency is not controlled tightly, the TK651xx
can achieve as much as 20-30 dB improvements in RF
interference reduction by means of its accurately controlled
oscillator frequency. This IF frequency is halfway between
the fifth and sixth harmonics of the oscillator. The fifth
harmonic of the maximum oscillator frequency and the
sixth harmonic of the minimum oscillator frequency still
leave a 39 kHz band centered around 455 kHz within which
a fundamental harmonic of the oscillator will not fall. Since
the TK651xx operates by Pulse Burst Modulation (PBM),
the switching pattern can be a subharmonic of the oscillator
frequency. The simplest example, and the one
to be
avoided the most, is that of the converter causing every
other oscillator pulse to be skipped. This means that the
switching pattern would have a fundamental frequency of
one-half the oscillator frequency, or 41.5 kHz. This is the
eleventh harmonic, which lands at 456.5 kHz, right in the IF
band. Fortunately, the energy is rather weak at the eleventh
harmonic. Even more fortunate is the ease with which that
regulation mode is avoided.
The internal regulator comparator has a finite hysteresis.
When an additional output filter is used (e.g., the RC filter
of the test circuit, or an LC filter), the ripple at the regulation
node is minimized. This limits the rate at which the oscillator
can be gated. In practice, this means that rather than
exhibiting a switching pattern of skipping every other
oscillator pulse, it would be more likely to exhibit a switching
pattern of three or four pulses followed by the same number
of pulses skipped. Although this also tends to increase the
output ripple, it is low frequency and has low magnitude
(e.g., 10 kHz and 10 mV) which tends to be of little
consequence.
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