MC34163 ON Semiconductor, MC34163 Datasheet - Page 9

• Manufacturer Part Number: MC34163
• Description: (MC33163 / MC33163) Step-Up/Down/Inverting Switching Regulators
• Manufacturer: ON Semiconductor

a fractional ohm resistor, R
switch transistor Q
monitored by the Current Sense comparator. If the voltage
drop exceeds 250 mV with respect to V
will set the latch and terminate output switch conduction on
a
configuration ensures that the Output Switch has only a
single on−time during a given oscillator cycle. The
calculation for a value of R
threshold is tightly controlled over temperature and has a
typical input bias current of 1.0 mA. The propagation delay
from the comparator input to the Output Switch is typically
200 ns. The parasitic inductance associated with R
circuit layout should be minimized. This will prevent
unwanted voltage spikes that may falsely trip the Current
Limit comparator.
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
efficiency, 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 2.5 A
and is designed to switch a maximum of 40 V collector to
emitter, with up to 3.4 A peak collector current. The
minimum value for R
applications, as in Figures 21 and 25, 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
The switch current is converted to a voltage by inserting
Figures 12 and 13 show that the Current Sense comparator
Internal thermal shutdown circuitry is provided to protect
To aid in system design flexibility and conversion
When configured for step−down or voltage−inverting
cycle−by−cycle
R SC(min) + 0.25 V
R SC +
2
. The voltage drop across R
SC
basis.
is:
SC
3.4 A
SC
I pk (Switch)
, in series with V
0.25 V
is:
This
+ 0.0735 W
CC
Comparator/Latch
, the comparator
CC
and output
MC34163, MC33163
SC
and the
http://onsemi.com
SC
is
9
additional device heating and reduced conversion
efficiency.
collector current will be in the range 10 mA over
temperature. A 1N5822 or equivalent Schottky barrier
rectifier is recommended to fulfill these requirements.
saturation voltage in step−down and voltage−inverting
converter applications. This input is connected through a
series resistor and capacitor to the switch emitter and is used
to raise the internal 2.0 mA bias current source above V
An internal zener limits the bootstrap input voltage to V
+7.0 V. The capacitor’s equivalent series resistance must
limit the zener current to less than 100 mA. 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.
a supply voltage range of 2.5 V to 40 V. When operating
below 3.0 V, the Bootstrap Input should be connected to
V
1.7 V at room temperature is possible.
Package
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 17 and 18 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.
and flexibility of this circuit architecture. Three main
converter topologies are demonstrated with actual test data
shown below each of the circuit diagrams.
CC
Figure 10 shows that by clamping the emitter to 0.5 V, the
A bootstrap input is provided to reduce the output switch
Parametric operation of the MC34163 is guaranteed over
The MC34163 is contained in a heatsinkable 16−lead
The following converter applications show the simplicity
. Figure 16 shows that functional operation down to
C B(min) + I Dt
DV
APPLICATIONS
+ 4.0 mA t on
4.0 V
+ 0.001 t on
CC
CC
.