Electronic Components Datasheet Search |
|
TK65020 Datasheet(PDF) 9 Page - TOKO, Inc |
|
TK65020 Datasheet(HTML) 9 Page - TOKO, Inc |
9 / 14 page ADVANCED INFORMATION January 1999 TOKO, Inc. Page 9 TK65020 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 TK65020 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 TK65020 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 TK65020 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 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. |
Similar Part No. - TK65020 |
|
Similar Description - TK65020 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |