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參數(shù)資料
| 型號(hào)： | TC33163EOETR |
| 元件分類(lèi)： | 穩(wěn)壓器 |
| 英文描述： | 3.4 A SWITCHING CONTROLLER, 55 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | SOIC-16 |
| 文件頁(yè)數(shù)： | 14/17頁(yè) |
| 文件大小： | 225K |
| 代理商： | TC33163EOETR |
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TC33163
6
TC33163-1 5/16/00
Power Switching Regulators
A bootstrap input is provided to reduce the output switch
saturation voltage in step-down and voltage-inverting con-
verter applications. This input is connected through a series
resistor and capacitor to the switch emitter and is used to
raise the internal 2.0mA bias current source above VCC.
An internal zener limits the bootstrap input voltage to VCC
+ 7.0V. The capacitor’s equivalent series resistance must
limit the zener current to less than 100mA. An additional
series resistor may be required when using tantalum or
other low ESR capacitors. The equation below is used to
calculate a minimum value bootstrap capacitor based on a
minimum zener voltage and an upper limit current source.
Parametric operation of the TC33163 is guaranteed
over a supply voltage range of 2.5V to 40V. When operating
below 3.0V, the Bootstrap Input should be connected to
VCC. Figure 25 shows that functional operation down to
1.7V at room temperature is possible.
Package
The TC33163 is contained in a heatsinkable 16-lead
plastic dual-in-line package in which the die is mounted on
a special heat tab copper alloy lead frame. This tab consists
of the four center ground pins that are specifically designed
to improve thermal conduction from the die to the circuit
board. Figures 26 and 27 show a simple and effective
method of utilizing the printed circuit board medium as a
heat dissipater by soldering these pins to an adequate area
of copper foil. This permits the use of standard layout and
mounting practices while having the ability to halve the
junction-to-air thermal resistance. These examples are for a
symmetrical layout on a single-sided board with two ounce
per square foot of copper.
APPLICATIONS
The following converter applications show the simplicity
and flexibility of this circuit architecture. Three main con-
verter topologies are demonstrated with actual test data
shown of the circuit diagrams on the following page.
The switch current is converted to a voltage by inserting
a fractional ohm resistor, RSC , in series with VCC and output
switch transistor Q2. The voltage drop across RSC is moni-
tored by the Current Sense comparator. If the voltage drop
exceeds 250mV with respect to VCC , the comparator will set
the latch and terminate output switch conduction on a cycle-
by-cycle basis. This Comparator/Latch configuration en-
sures that the Output Switch has only a single on-time during
a given oscillator cycle. The calculation for a value of RSC is:
Figures 21 and 22 show that the Current Sense com-
parator threshold is tightly controlled over temperature and
has a typical input bias current of 1.0
A. The propagation
delay from the comparator input to the Output Switch is
typically 200nsec. The parasitic inductance associated with
RSC and the circuit layout should be minimized. This will
prevent unwanted voltage spikes that may falsely trip the
Current Limit comparator.
Internal thermal shutdown circuitry is provided to protect
the IC in the event that the maximum junction temperature
is exceeded. When activated, typically at 170
°C, the Latch
is forced into the “Set” state, disabling the Output Switch.
This feature is provided to prevent catastrophic failures from
accidental device overheating. It is not intended to be used
as a replacement for proper heatsinking.
Driver and Output Switch
To aid in system design flexibility and conversion effi-
ciency, the driver current source and collector, and output
switch collector and emitter are pinned out separately. This
allows the designer the option of driving the output switch
into saturation with a selected force gain or driving it near
saturation when connected as a Darlington. The output
switch has a typical current gain of 70 at 2.5A and is
designed to switch a maximum of 40V collector to emitter,
with up to 3.4A peak collector current. The minimum value
for RSC is:
When configured for step-down or voltage-inverting
applications, as in Figures 3 and 7, the inductor will forward
bias the output rectifier when the switch turns off. Rectifiers
with a high forward voltage drop or long turn-on delay time
should not be used. If the emitter is allowed to go sufficiently
negative, collector current will flow, causing additional de-
vice heating and reduced conversion efficiency.
Figure 19 shows that by clamping the emitter to 0.5V,
the collector current will be in the range 10
A over tempera-
ture. A 1N5822 or equivalent Schottky barrier rectifier is
recommended to fulfill these requirements.
RSC =
IPK (SWITCH)
0.25V
RSC(MIN) =
3.4A
0.25V = 0.0735
CB(MIN) = 1 V
t
= 4.0mA
4.0V
tON
= 0.001tON
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