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| 型号： | TC120503EHATR |
| 厂商： | Microchip Technology |
| 文件页数： | 5/14页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK 5V 0.6A 8SOP |
| 标准包装： | 1,000 |
| 类型： | 降压（降压） |
| 输出类型： | 固定 |
| 输出数： | 1 |
| 输出电压： | 5V |
| 输入电压： | 1.8 V ~ 10 V |
| 频率 - 开关： | 300kHz |
| 电流 - 输出： | 600mA |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.173"，4.40mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 8-SOP |
TC120
3.0
DETAILED DESCRIPTION
3.2
Input Bypass Capacitor
The TC120 can be operated as an integrated step-
down regulator (using the internal switching transistor);
or as a step-down regulator controller (using an
external switching transistor). When operating as an
integrated regulator, the only required external compo-
Using an input bypass capacitor reduces peak current
transients drawn from the input supply, and reduces the
switching noise generated by the regulator. The source
impedance of the input supply determines the size of
the capacitor that should be used.
nents are a Schottky diode, inductor and an output
capacitor. Operating in this configuration, the TC120 is
3.3
Output Capacitor
capable of supporting output load currents to a
maximum of 600mA with operating efficiencies above
85%. Efficiencies at high loads can be further improved
by using the on-board charge pump circuit to pull the
gate of the internal switching transistor below ground
for the lowest possible ON resistance. (For more infor-
mation, see Section 3.5 Improving High Load
Efficiency in Regulator Operating Mode ).
Higher output currents are achieved by operating the
TC120 with an external P-channel switching transistor
(controller mode). In this operating configuration, the
maximum output current is determined primarily by the
ON resistance of the P-channel switch and the series
The effective series resistance of the output capacitor
directly affects the amplitude of the output voltage
ripple. (The product of the peak inductor current and
the ESR determines output ripple amplitude.) There-
fore, a capacitor with the lowest possible ESR should
be selected. Smaller capacitors are acceptable for light
loads or in applications where ripple is not a concern. A
47 μ F Tantalum capacitor is recommended for most
applications. The Sprague 595D series of tantalum
capacitors are amongst the smallest of all low ESR
surface mount capacitors available. Table 3-1 lists
suggested components and suppliers.
resistance of the inductor.
3.4
Catch Diode
FIGURE 3-1:
TEST CIRCUIT
The high operating frequency of the TC120 requires a
high-speed diode. Schottky diodes such as the MA737
V IN
+
–
47 μ F/10V
Tantalum
V IN L X
EXTW EXT
TC120XX03
CPC GND
L1
22 μ H
IN5817
+
–
V OUT
C OUT
47 μ F/10V
Tantalum
or 1N5817 through 1N5823 (and the equivalent surface
mount versions) are recommended. Select a diode
whose average current rating is greater than the peak
inductor current; and whose voltage rating is higher
than V IN MAX .
C SS
4.7nF
SHDN/SS
SENSE
3.5
Improving High Load Efficiency in
Regulator Operating Mode
If the TC120 is operated at high output loads most (or
3.1
Inductor Selection
all) of the time, efficiency can be improved with the
addition of two components. Ordinarily, the voltage
Selecting the proper inductor value is a trade-off
between physical size and power conversion require-
ments. Lower value inductors cost less, but result in
higher ripple current and core losses. They are also
more prone to saturate since the coil current ramps
faster and could overshoot the desired peak value. This
not only reduces efficiency, but could also cause the
current rating of the external components to be
exceeded. Larger inductor values reduce both ripple
current and core losses, but are larger in physical size
and tend to increase the start-up time slightly. A 22 μ H
inductor is the best overall compromise and is recom-
mended for use with the TC120. For highest efficiency,
use inductors with a low DC resistance (less than
20m ? ). To minimize radiated noise, consider using a
toroid, pot core or shielded-bobbin inductor.
2002 Microchip Technology Inc.
swing on the gate of the internal P-channel transistor is
from ground to V IN . By adding a capacitor and diode as
shown in Figure 3-2, an inverting charge pump is
formed, enabling the internal gate voltage to swing
from a negative voltage to +V IN . This increased drive
lowers the R DS ON of the internal transistor, improving
efficiency at high output currents. Care must be taken
to ensure the voltage measured between V IN and CPC
does not exceed an absolute value of 10V. While this is
not a problem at values of V IN at (or below) 5V, higher
V IN values will require the addition of a clamping
mechanism (such as a Zener diode) to limit the voltage
as described. While this technique improves efficiency
at high output loads, it is at the expense of low load
efficiency because energy is expended charging and
discharging the charge pump capacitor. This technique
is therefore not recommended for applications that
operate the TC120 at low output currents for extended
time periods. If unused, CPC must be grounded.
DS21365B-page 5
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