ISL72991RH Datasheet, PDF (2/3 Pages) Intersil Corporation – Radiation Hardened Negative Low Dropout Adjustable Voltage Regulator

ISL72991RH
Application Information
Typical User Application:
VIN
VIN
VOUT
VOUT
ILIM
SD
ISL72991RH
GND
ADJ
FIGURE 1. TYPICAL APPLICATION SCHEMATIC
Output Voltage Programming
The output voltage of the regulator can be programmed with
two external resistors and is described by the following
equation: V_OUT = V_REF x (1+R2/R1) - (I_ADJ x R2).
Output Current Limit Programming
The output current limit threshold of the regulator can be
programmed with a single external resistor connected from
I_LIM to ground. The current flowing into the I_LIM pin is
described by the following equation: I_LIM = 1V/(R_CL + 2400).
The graph below shows the relationship between I_LIM and
the output current limit threshold, I_{OUT_LIM}.
Capacitor Selection
An input capacitor is required if the regulator is located more
than 6 inches from power supply filter capacitors. A 10µF
solid tantalum capacitor is recommended.
An output capacitor of at least 10µF must be used to insure
stability of the regulator. Additional capacitance may be
added as required to improve the dynamic response of the
regulator. Solid tantalum and/or ceramic capacitors are
recommended.
Loop Compensation
The output capacitor and ESR comprise a zero in the loop
transfer function that must be compensated with a pole to
insure loop stability in accordance with the following
equation: C_C x R2 = C_OUT x ESR. The compensating
capacitor should be a low ESR ceramic type.
Layout Guidelines
The stability of the regulator is sensitive to layout. It is
strongly recommended that a continuous copper ground
plane (1 ounce or greater) be used. In addition, component
lead lengths and interconnects should be minimized, but
should not exceed 1/2 inch. Finally, the return lead of the
compensation capacitor (C_C) should be connected as close
as possible to the GND pin of the IC.
I_LIM (A)
FIGURE 2. I_{OUT_LIM} vs I_LIM
2