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參數(shù)資料
| 型號： | TK65422M |
| 廠商： | TOKO Inc. |
| 英文描述： | STEP-DOWN CONVERTER WITH BATTERY MONITOR |
| 中文描述： | 降壓轉(zhuǎn)換器與電池監(jiān)視器 |
| 文件頁數(shù)： | 10/28頁 |
| 文件大?。?/td> | 762K |
| 代理商： | TK65422M |
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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 V
OUT
. 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 (V
OUT
).
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 (V
OUT
). 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
≈
V
OUT
), 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
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|---|---|
| TK65422MTL | STEP-DOWN CONVERTER WITH BATTERY MONITOR |
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| TK65423M | STEP-DOWN CONVERTER WITH BATTERY MONITOR |
| TK65423MTL | STEP-DOWN CONVERTER WITH BATTERY MONITOR |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| TK65422MTL | 制造商:TOKO 制造商全稱:TOKO, Inc 功能描述:STEP-DOWN CONVERTER WITH BATTERY MONITOR |
| TK65422MTL/422 | 制造商:TOKO 制造商全稱:TOKO, Inc 功能描述:STEP-DOWN CONVERTER WITH BATTERY MONITOR |
| TK65423 | 制造商:TOKO 制造商全稱:TOKO, Inc 功能描述:STEP-DOWN CONVERTER WITH BATTERY MONITOR |
| TK65423M | 制造商:TOKO 制造商全稱:TOKO, Inc 功能描述:STEP-DOWN CONVERTER WITH BATTERY MONITOR |
| TK65423MTL | 制造商:TOKO 制造商全稱:TOKO, Inc 功能描述:STEP-DOWN CONVERTER WITH BATTERY MONITOR |
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