TK65020 데이터 시트보기 (PDF) - Toko America Inc
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TK65020 Datasheet PDF : 14 Pages
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ADVANCED INFORMATION
TK65020
SINGLE-CELL APPLICATION
The TK65020 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 2.5 V. The device operates at a fixed
nominal clock frequency of 83 kHz.
In its simplest form, a boost power converter using the
TK65020 requires only three external components: an
inductor, a diode, and a capacitor.
and Noise Considerations” section) can be determined if
needed or desired.
The TK65020 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
The analysis is easier to follow when referencing the
simple boost circuit below.
VIN
GND
SW
NC
GND
VOUT
+
VOUT
di/dt = VIN/ L
IPEAK
di/dt = - (VOUT + Vf - VIN)/ L
FIGURE 1: SIMPLE BOOST CONVERTER
t (on)
t (off)
t (deadtime)
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 TK65020 monitors the voltage of the output capacitor
and has a 2.5 V threshold at which the converter switching
becomes deactivated. So the output capacitor charges up
to 2.5 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 TK65020 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 filtering component values (consult the “Ripple
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.
January 1999 TOKO, Inc.
Page 5
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