Datasheet
SLUS215B − OCTOBER 1998 − REVISED FEBRUARY 2004
8
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
voltage programming and shutdown feature for adjustable version
A typical application circuit based on the UCC383 adjustable version is shown in Figure 5. The output voltage
is externally programmed through a resistive divider at the ADJ pin.
Figure 4
Temperature (5C)
V
IN
− V
OUT
(V)
0.2
0.3
0.4
0.5
0.6
−40 10 60
V
OUT
= 3.3 V
V
OUT
= 5 V
TYPICAL DROPOUT VOLTAGE
vs.
CASE TEMPERATURE WITH A 3-A LOAD
V
OUT
+ 1.25
ǒ
1 )
R2
R1
Ǔ
Volts
The maximum programmed output voltage is constrained by the 9-V absolute rating of the IC (this includes the
charge pump voltage) and its ability to enhance the N-channel MOSFET. Unless the load current is below the
3-A rating of the device, output voltages above 7 V are not recommended. The minimum output voltage can
be programmed down to 1.25 V. However, the input voltage must always be greater than the UVLO of the part.
The adjustable version includes a shutdown feature, limiting quiescent current to 40 µA typical. The UCC383
is shut down by pulling the CT pin to below 0.25 V. As shown in Figure 5, a small logic level MOSFET or BJT
transistor in parallel with the timing capacitor can be driven with a digital signal, putting the device in shutdown.
If the CT pin is not pulled low, the IC internally pulls up the pin enabling the regulator. The CT pin should not
be forced high, as this interferes with the short-circuit-protection feature. Selection of the timing capacitor is
explained in Short-Circuit-Protection.
The adjustable version can be used in applications requiring remote voltage sensing (i.e. monitoring a voltage
other than or not directly tied to the VOUT pin). This is possible since the inverting input of the error-voltage
amplifier (see Block Diagram) is brought out to the ADJ pin.
(4)