Datasheet

UCC284–5, UCC284–12, UCC284–ADJ, UCC384–5, UCC384–12, UCC384–ADJ
LOW-DROPOUT 0.5-A NEGATIVE LINEAR REGULATOR
SLUS234D – JANUARY 2000 – REVISED FEBRUARY 2002
5
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
pin descriptions
GND: This is the low noise ground reference input. All voltages are measured with respect to the GND pin.
SD/CT: This is the shutdown pin and also the short-circuit timing pin. Pulling this pin more positive than –0.7 V
puts the circuit in a low-current shutdown mode. Placing a timing capacitor between this pin and GND sets the
short-circuit charging time, t
ON
during an overcurrent condition. During an overcurrent condition, the output
pulses at approximately a 2.5% duty cycle.
NOTE:The CT capacitor must be connected between this pin and GND, not VIN, to assure that the
SD/CT pin is not pulled significantly negative during power-up. This pin should not be externally
driven more negative than –5 V or the device will be damaged.
VIN: This is the negative input supply. Bypass this pin to GND with at least 1 µF of low ESR or ESL capacitance.
VOUT: Regulated negative-output voltage. A single 4.7-µF capacitor should be connected between this pin and
GND. Smaller value capacitors can be used for light loads, but this degrades the load-step performance of the
regulator.
VOUTS: This is the feedback pin for sensing the output of the regulator. For the UCC384-5 and UCC384-12
versions, VOUTS can be connected directly to VOUT. If the load is placed at a considerable distance from the
regulator, the VOUTS lead can be used as a Kelvin connection to minimize errors due to lead resistance.
Connecting VOUTS at the load moves the resistance of the VOUT wire into the control loop of the regulator,
thereby effectively canceling the IR drop associated with the load path.
APPLICATION INFORMATION
overview
The UCCx84-x family of negative low-dropout linear (LDO) regulators provides a regulated-output voltage for
applications with up to 0.5 A of load current. The regulators feature a low-dropout voltage and short-circuit
protection, making their use ideal for demanding applications requiring fault protection.
programming the output voltage on the UCC384
The UCC384-5 and UCC384-12 have output voltages that are fixed at –5 V and –12 V respectively. Connecting
VOUTS to VOUT gives the proper output voltage with respect to ground.
The UCC384-ADJ can be programmed for any output voltage between –1.25 V and –15 V. This is easily
accomplished with the addition of an external resistor divider connected between GND and VOUT with VOUTS
connected to the center tap of the divider. For an output of –1.25 V, no resistors are needed and VOUTS is
connected directly to VOUT. The regulator-input voltage cannot be more positive than the UVLO threshold, or
approximately –3 V. Thus, low dropout cannot be achieved when programming the output voltage more positive
than approximately –3.3 V. A typical application circuit is shown in Figure 1.