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参数资料
| 型号： | TC120503EHART |
| 元件分类： | 稳压器 |
| 英文描述： | 0.7 A SWITCHING REGULATOR, 345 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封装： | SOP, 8 PIN |
| 文件页数： | 5/10页 |
| 文件大小： | 80K |
| 代理商： | TC120503EHART |
4
PWM/PFM STEP-DOWN COMBINATION
REGULATOR/CONTROLLER
TC120
TC120-1 7/27/99
external components to be exceeded. Larger inductor val-
ues reduce both ripple current and core losses, but are
larger in physical size and tend to increase the start-up time
slightly. A 22
H inductor is the best overall compromise and
is recommended for use with the TC120. For highest effi-
ciency, use inductors with a low DC resistance (less than 20
m
). To minimize radiated noise, consider using a toroid,
pot core or shielded-bobbin inductor.
Input Bypass Capacitor
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.
Output Capacitor
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.) Therefore, 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
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 1 lists
suggested component numbers and manufacturers.
Catch Diode
The high operating frequency of the TC120 requires a
high-speed diode. Schottky diodes such as the MA737 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 VIN(MAX).
Improving High Load Efficiency in Regulator
Operating Mode
If the TC120 is operated at high output loads most (or all)
of the time, efficiency can be improved with the addition of
two components. Ordinarily, the voltage swing on the gate
of the internal P-Channel transistor is from ground to VIN. By
adding a capacitor and diode as shown in Figure 3, an
inverting charge pump is formed, enabling the internal gate
voltage to swing from a negative voltage to +VIN. This
increased drive lowers the RDS(ON) of the internal transistor,
improving efficiency at high output currents. Care must be
taken to ensure the voltage measured between VIN and CPC
does not exceed an absolute value of 10V. While this is not
a problem at values of VIN at (or below) 5V, higher VIN 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.
Low Power Shutdown Mode/Soft Start Input
The SHDN/SS input acts as both the shutdown control
and the node for the external soft start capacitor, which is
charged by an internal 1
A current source. A value of 4700
pF (100 pF minimum) is recommended for the soft start
capacitor.
IMPORTANT: The soft start capacitor must be
connected between SHDN/SS and ground. Failure to do this
may cause large overshoot voltages and/or large inrush
currents resulting in possible instability. The TC120 enters
a low power shutdown mode when SHDN/SS is brought low.
While in shutdown, the oscillator is disabled and the output
discharge switch is turned on, discharging the output ca-
pacitor. Figure 4 shows the recommended interface circuits
to the SHDN/SS input. As shown, the SHDN/SS input should
be controlled using an open collector (or open drain) device,
such that the SHDN/SS input is grounded for shutdown
mode, and open-circuited for normal operation (Figure 5a).
If a CMOS device is used to control shutdown (Figure 5b),
the value of R1 and CSS should be chosen such that the
voltage on SHDN/SS rises from ground to 0.65V in 1.5 msec
(Figure 6). If shutdown is not used, CSS must still be
connected as shown in Figures 5c and 5d. SHDN/SS may
be pulled up with a resistor (Figure 5c) as long as the values
of RSS and CSS provide the approximate charging
characteristic on power up shown in Figure 6. CSS only may
also be connected as shown in Figure 5d with CSS chosen
at 4700 pF (minimum 100 pF).
Undervoltage Lockout (UVLO)
The TC120 is disabled whenever VIN is below the
undervoltage lockout threshold. This threshold is equal to
the guaranteed minimum operating voltage for the TC120
(i.e. 2.2V). When UVLO is active, the TC120 is completely
disabled.
Short Circuit Protection
Upon detection of an output short circuit condition, the
TC120 reduces the PWM duty cycle to a minimum value
using its internal protection timer. The sequence of events is
as follows: when an output voltage decrease to near zero is
detected (as the result of an overload), the internal (5 msec)
protection timer is started. If the output voltage has not
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| TC120503EHATR | 功能描述:开关变换器、稳压器与控制器 PWM/PFM Step-Down RoHS:否 制造商:Texas Instruments 输出电压:1.2 V to 10 V 输出电流:300 mA 输出功率: 输入电压:3 V to 17 V 开关频率:1 MHz 工作温度范围: 安装风格:SMD/SMT 封装 / 箱体:WSON-8 封装:Reel |
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| TC1210A | 制造商:Thomas & Betts 功能描述:Fittings Connector 4inch Steel |
| TC12-11CGKWA | 制造商:Kingbright Corporation 功能描述:DOT MATRIX 1.2" CMN CATHODE GREEN 制造商:Kingbright Corporation 功能描述:DOT MATRIX, 1.2" CMN CATHODE, GREEN 制造商:Kingbright Corporation 功能描述:DOT MATRIX, 1.2" CMN CATHODE, GREEN; Display Dots x Lines:5 x 7; LED Color:Green; Luminous Intensity:73mcd; LED Display Type:Dot Matrix; Peak Wavelength:574nm; Forward Voltage:2.1V; Display Size:22.9mm x 39mm ;RoHS Compliant: Yes |
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