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PDF TC120 Data sheet ( Hoja de datos )
| Número de pieza | TC120 | |
| Descripción | PWM/PFM Step-Down Combination Regulator/Controller | |
| Fabricantes | Microchip Technology | |
| Logotipo |  |
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TC120
PWM/PFM Step-Down Combination Regulator/Controller
Features
• Internal Switching Transistor Supports 600mA
Output Current
• External Switching Transistor Control for Output
Currents of 2A+
• 300kHz Oscillator Frequency Supports Small
Inductor Size
• Short Circuit Protection
• Built-In Undervoltage Lockout
• 95% Typical Efficiency
• Automatic Switchover to Current-Saving PFM
Mode at Low Output Loads
• Automatic Output Capacitor Discharge While in
Shutdown
• Programmable Soft-Start
• Power-Saving Shutdown Mode
• Small 8-Pin SOP Package
Applications
• Portable Test Equipment
• Local Logic Supplies
• Portable Audio Systems
• Portable Scanners
• Palmtops
• Electronic Organizers
Device Selection Table
Part
Number
Output
Voltage Package
(V)
Operating
Temp.
Range
TC120503EHA 5.0 8-Pin SOP -40°C to +85°C
TC120333EHA 3.3 8-Pin SOP -40°C to +85°C
TC120303EHA 3.0 8-Pin SOP -40°C to +85°C
Package Type
8-Pin SOP
VIN 1
EXTW 2
CPC 3
SHDN/SS 4
TC120
8 LX
7 EXT
6 GND
5 SENSE
General Description
TC120 is a 300kHz PFM/PWM step-down (Buck) DC/
DC regulator/controller combination for use in systems
operating from two or more cells, or in line-powered
applications. It uses PWM as the primary modulation
scheme, but automatically converts to PFM at low
output loads for greater efficiency. It requires only an
external inductor, Schottky diode, and two capacitors to
implement a step-down converter having a maximum
output current of 600mA (VIN = 5V, VOUT = 3.3V). An
external switching transistor (P-channel MOSFET) can
be added to increase output current capability to
support output loads of 2A or more.
The TC120 consumes only 55µA (max) of supply
current (VOUT = 3.3V) and can be placed in shutdown
mode by bringing the shutdown input (SHDN) low.
During shutdown, the regulator is disabled, supply
current is reduced to 2.5µA (max), and VOUT is
internally pulled to ground, discharging the output
capacitor. Normal operation resumes when SHDN is
brought high. Other features include a built-in under-
voltage lockout (UVLO), an externally programmable
soft start time, and output short circuit protection. The
TC120 operates from a maximum input voltage of 10V
and is available in a low-profile 8-Pin SOP package.
Functional Block Diagram
VIN
CIN
VIN LX
EXTW
EXT
TC120XX03
CPC
GND
L1
D1
VOUT
COUT
SHDN/SS
CSS
4.7nF
SENSE
© 2002 Microchip Technology Inc.
DS21365B-page 1
1 page  
3.0 DETAILED DESCRIPTION
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-
nents are a Schottky diode, inductor and an output
capacitor. Operating in this configuration, the TC120 is
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
resistance of the inductor.
FIGURE 3-1:
TEST CIRCUIT
VIN
+
–
47µF/10V
Tantalum
VIN LX
EXTW
EXT
TC120XX03
CPC
GND
L1
22µH
IN5817
VOUT
+
–
COUT
47µF/10V
Tantalum
SHDN/SS
CSS
4.7nF
SENSE
3.1 Inductor Selection
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 22µH
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
20mΩ). To minimize radiated noise, consider using a
toroid, pot core or shielded-bobbin inductor.
TC120
3.2 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.
3.3 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.) 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
47µF 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.
3.4 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 VINMAX.
3.5 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 3-2, an inverting charge pump is
formed, enabling the internal gate voltage to swing
from a negative voltage to +VIN. This increased drive
lowers the RDSON 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.
© 2002 Microchip Technology Inc.
DS21365B-page 5
5 Page 
TC120
Sales and Support
Data Sheets
Products supported by a preliminary Data Sheet may have an errata sheet describing minor operational differences and recom-
mended workarounds. To determine if an errata sheet exists for a particular device, please contact one of the following:
1. Your local Microchip sales office
2. The Microchip Corporate Literature Center U.S. FAX: (480) 792-7277
3. The Microchip Worldwide Site (www.microchip.com)
Please specify which device, revision of silicon and Data Sheet (include Literature #) you are using.
New Customer Notification System
Register on our web site (www.microchip.com/cn) to receive the most current information on our products.
2002 Microchip Technology Inc.
DS21365B-page 11
11 Page | ||
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| PDF Descargar | [ Datasheet TC120.PDF ] | |
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