Electronic Components Datasheet Search |
|
TK65423M Datasheet(PDF) 10 Page - TOKO, Inc |
|
TK65423M Datasheet(HTML) 10 Page - TOKO, Inc |
10 / 28 page Page 10 TK654xx September 1999 TOKO, Inc. ADVANCED INFORMATION THEORY OF OPERATION Figure 1 illustrates a circuit diagram for a simple buck (step-down) converter. Typically, the input voltage (V IN) is greater than the output voltage (V OUT). By modulating the switching action of switch SW1, the output voltage (V OUT) can be regulated to a constant voltage that is relatively independent of variations in the input supply (V IN) or the current load on the V OUT node. The TK654xx contains all the control circuitry, logic, and power switch (SW1) for implementing a simple step-down or "buck" converter, as shown in Figure 1. In general, a switching converter utilizing the TK654xx controller will be operating in one of three states: 1. "ON" STATE: During this state of operation SW1 will be turned on. Current through the inductive element (L) will be increasing at a rate proportional to the voltage difference between V IN and VOUT. In this state, there is a direct current path from the input supply to the output load through the inductor L. 2. "OFF" STATE: During this state of operation SW1 will be turned off. Current through the inductive element will be greater than zero and flowing either through the external schottky rectifier (D) or the synchronous rectifier internal to the TK654xx. During the "off" state, current through the inductive element (L) will be decreasing at a rate approximately proportional to V OUT. In this state, the current drawn from the input supply is essentially zero. Current to the load is provided by stored energy in the inductive element. 3. "NULL" STATE: During this state of operation SW1 will be turned off. Current through the inductive element will be approximately zero. The internal synchronous rectifier will be turned off. All current demands of the load will be provided by the output filter capacitor (C). In this state, the current drawn from the input supply is essentially zero. Since the inductive current is zero, no additional energy is available from the inductor. If the current demands of the load are very light, the current will be provided by the stored charge in the output filter capacitor. If the voltage of the filter capacitor drops below the regulation threshold, an "on" state will be initiated and additional energy will be transferred from the input supply to the output. The control scheme for the TK654xx forces the converter to step through the "on," "off," and "null" states in sequence. Assume that the controller is initially in the "null" state and V OUT is greater than the regulation threshold. As soon as the output voltage drops below this threshold, the controller will switch from "null" state to the "on" state. During the "on" state, current through inductor (L) will be increasing. Current will flow from the input supply to the output capacitor through the inductive element. In this state, energy is transferred directly from the input supply to the output through the inductor. The maximum duration of the "on" state is inversely proportional to the difference between the input voltage (V IN) and the output voltage (VOUT). The transition from the "on" state to the "off" state can be initiated by one of two different means. As mentioned above, the maximum duration of the "on" state is inversely proportional to the difference between the input voltage (V IN) and the output voltage (VOUT). If the duration of the "on" cycle exceeds this maximum, the controller immediately switches to the "off" state independent of other factors. Understanding that when the converter is in a dropout condition (V IN ≈ VOUT), the maximum “on” time is infinite and the “on” state is constantly applied. By limiting the duration of the "on" cycle, the peak inductor current is also being limited. The second method for initiating the "off" cycle is triggered when the duration of the "on" cycle exceeds a minimum on-time duration and the output voltage (V OUT) exceeds the regulation threshold. Therefore, the actual duration of the "on" cycle will vary between a minimum on-time (T ON(MIN)) and a maximum on-time (T ON(MAX)) depending upon the load current. At very light loads the on-time duration will be at a minimum; at very heavy loads the on-time will be at a maximum. This ability to vary the duration of the on cycle is a proprietary control scheme which can produce a ten-fold reduction in ripple when compared to competing devices. The transition from the "off" state to the "null" state occurs after sufficient time has been allowed for the inductor current to return to zero. The actual duration of the "off" VIN VOUT C D L SW1 + FIGURE 1: SIMPLE "BUCK" CONVERTER |
Similar Part No. - TK65423M |
|
Similar Description - TK65423M |
|
|
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 |