0.5A Step-Down Switching Regulator
TC2574
PIN DESCRIPTION
Pin No.
8-Pin PDIP
5
Pin No
16-Pin SOIC
12
Symbol
V
IN
Description
This pin is the positive input supply for the TC2574 step–down switching
regulator. In order to minimize voltage transients and to supply the switching
currents needed by the regulator, a suitable input bypass capacitor must be
present (C
IN
in Figure 1).
This is the emitter of the internal switch. The saturation voltage V
SAT
of this
output switch is typically 1.0V. It should be kept in mind that the PCB area
connected to this pin should be kept to a minimum in order to minimize
coupling to sensitive circuitry.
Circuit signal ground pin. See the information about the printed circuit board
layout.
Circuit power ground pin. See the information about the printed circuit board
layout.
This pin senses regulated output voltage to complete the feedback loop. The
signal is divided by the internal resistor divider network R2, R1 and applied to
the non–inverting input of the internal error amplifier.In the adjustable version
of the TC2574 switching regulator, this pin is the direct input of the error
amplifier and the resistor network R2, R1 is connected externally to allow
programming of the output voltage.
It allows the switching regulator circuit to be shut down using logic level
signals, thus dropping the total input supply current to approximately 80µA.
The input threshold voltage is typically 1.5V. Applying a voltage above this
value (up to +V
IN
) shuts the regulator off. If the voltage applied to this pin is
ower than 1.5 V or if this pin is left open, the regulator will be in the “on”
condition.
7
14
Output
2
4
1
4
6
3
SIG Gnd
PWR GND
FB
3
5
ON/OFF
REPRESENTATIVE BLOCK DIAGRAM AND TYPICAL APPLICATION
Unregulated
DC Input
CIN
+VIN
+
5
TC2574
1
3.1V Internal
Regulator
ON/OFF
ON/OFF
3
Output
Voltage Versions
Fixed gain
Error Amplifier
Current
Limit
Comparator
R2 (Ω)
Feedback
R1
+
–
Driver
3.3V
5.0V
12V
1.7k
3.1k
8.84k
+
R2
1.0k
–
Freq.
Shift
18kHz
1.235V
Band-Gap
Reference
+
–
Latch
For Adjustable version
R1 = open, R2 = 0Ω
Output
1.0 Amp
Switch
7
PWR GND
4
D1
L1
VOUT
SIG GND
2
52kHz
Oscillator
Reset
Thermal
Shutdown
+
COUT
Load
TC2574-1 1/6/00
4
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