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: 2/20页
文件大小: 158K
代理商: TK65130MTL
Page 10
January 2001 TOKO, Inc.
TK651xxM
filtering component values (consult the “Ripple and Noise
Considerations” section) can be determined if needed or
desired.
The TK651xx runs with a fixed oscillator frequency, and it
regulates by applying or skipping pulses to the internal
power switch. This regulation method is called Pulse Burst
Modulation (PBM).
ANALYSIS OF SWITCHING CYCLE
Above is the input or inductor current waveform over a
switching cycle.
From an oscillator standpoint, the switching cycle consists
of only an on-time and an off-time. But from an inductor
current standpoint, the switching cycle breaks down into
three important sections: on-time, off-time, and deadtime.
The on-time of the switch and the inductor current are
synonymous. During the on-time, the inductor current
increases. During the off-time, the inductor current
decreases as it flows into the output. When the inductor
current reaches zero, that marks the end of the inductor
current off-time. For the rest of the cycle, the inductor
current remains at zero. Since no energy is being either
stored or delivered, that remaining time is called “deadtime.”
This mode of the inductor current decaying to zero every
cycle is called “discontinuous mode.” In summary, energy
is stored in the inductor during on-time, delivered to the
output during off-time, and remains at zero during deadtime.
The TK651xx is a boost converter control IC with the power
MOSFET switch built into the device. It operates from a
single battery cell and steps up the output voltage to a
regulated 2.7, 3.0 and 3.3 V. The device operates at a fixed
nominal clock frequency of 83 kHz.
In its simplest form, a boost power converter using the
TK651xx requires only three external components: an
inductor, a diode, and a capacitor.
The analysis is easier to follow when referencing the simple
boost circuit below.
THEORY OF OPERATION
The converter operates with one terminal of an inductor
connected to the DC input and the other terminal connected
to the switch pin of the IC. When the switch is turned on, the
inductor current ramps up. When the switch is turned off (or
“lets go” of the inductor), the voltage flies up as the inductor
seeks out a path for its current. A diode, also connected to
the switching node, provides a path of conduction for the
inductor current to the boost converter’s output capacitor.
The TK651xx monitors the voltage of the output capacitor
and has a 2.7, 3.0 and 3.3 V threshold at which the
converter switching becomes deactivated. So the output
capacitor charges up to 2.7, 3.0 and 3.3 V and regulates
there, provided that no more current is drawn from the
output than the inductor can provide. The primary task,
then, in designing a boost converter with the TK651xx
is to determine the inductor value (and its peak current
rating to prevent inductor core saturation problems)
which will provide the amount of current needed to
guarantee that the output voltage will be able to maintain
regulation up to a specified maximum load current.
Secondary necessary tasks also include choosing the
diode and the output capacitor. Then the snubber and
SINGLE-CELL APPLICATION
FIGURE 1: SIMPLE BOOST CONVERTER
VIN
GND
LOI
VOUT
SW
+
VOUT
I
PEAK
di/dt = - (V
OUT + Vf - VIN)/ L
t (off)
t (deadtime)
t (on)
di/dt = V
IN / L
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