
1
TC120
PWM/PFM STEP-DOWN COMBINATION
REGULATOR/CONTROLLER
TC120-1 7/27/99
PWM/PFM STEP-DOWN COMBINATION REGULATOR/CONTROLLER
FEATURES
s
Internal Switching Transistor Supports 600 mA
Output Current
s
External Switching Transistor Control for Output
Currents of 2A+
s
300 KHz Oscillator Frequency Supports Small
Inductor Size
s
Short Circuit Protection
s
Built-In Undervoltage Lockout
s
High (95%, Typ) Efficiency
s
Automatic Switchover to Current-Saving PFM
Mode at Low Output Loads
s
Automatic Output Capacitor Discharge While in
Shutdown
s
Programmable Soft-Start Time
s
Power-Saving Shutdown Mode
s
Small 8-Pin SOP Package
TYPICAL APPLICATIONS
s
Portable Test Equipment
s
Local Logic Supplies
s
Portable Audio Systems
s
Portable Scanners
s
Palmtops
s
Electronic Organizers
GENERAL DESCRIPTION
TC120 is a 300 KHz PFM/PWM step-down (Buck) DC/
DC regulator/controller combination for use in systems
operating from two or more cells, or in line-powered applica-
tions. 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 con-
verter having a maximum output current of 600 mA (VIN =5V,
VOUT = 3.3V). An external switching transistor (P-channel
MOSFET) can be added to increase output current capabil-
ity to support output loads of 2A or more.
The TC120 consumes only 39
A (max) of supply
current (VOUT = 3.3V) and can be placed in shutdown mode
by bringing the shutdown input (SHDN) low. During shut-
down, the regulator is disabled, supply current is reduced to
2.5
A(max), and VOUT is internally pulled to ground, dis-
charging the output capacitor. Normal operation resumes
when SHDN is brought high. Other features include a built-
in undervoltage lockout (UVLO), an externally program-
mable 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.
TYPICAL APPLICATION
TelCom Semiconductor reserves the right to make changes in the circuitry and specifications of its devices.
PIN CONFIGURATION
ORDERING INFORMATION
Part No.
Output
Package
Temperature
Voltage (V)
Range
TC120303EHA
3.0
8-Pin SOP – 40
°C to +85°C
TC120333EHA
3.3
8-Pin SOP – 40
°C to +85°C
TC120503EHA
5.0
8-Pin SOP – 40
°C to +85°C
TC120303
VIN
EXTW
CPC
SHDN/SS
LX
EXT
GND
SENSE
47
F/16V
Tantalum
CSS
4.7 nF
IN5817
L1
22
H
VOUT = 3V
VIN = 5V
COUT
47
F/10V
Tantalum
5V to 3.0V, 500 mA Step-Down Converter
1
2
3
4
8
7
6
5
TC120
8-Pin SOP
EXTW
CPC
SHDN/SS
VIN
GND
EXT
SENSE
LX