R1191 Datasheet, PDF (7/33 Pages) RICOH electronics devices division – Supply Current Typ. 50uA (Fast Mode)

R1191x
TECHNICAL NOTES
When using these ICs, consider the following points:
• Phase Compensation
In these ICs, phase compensation is made for securing stable operation even if the load current is varied. For
this purpose, use a capacitor C2 with good frequency characteristics and ESR (Equivalent Series Resistance).
(Note: If additional ceramic capacitors are connected with parallel to the output pin with an output capacitor for
phase compensation, the operation might be unstable. Because of this, test these ICs with as same external
components as ones to be used on the PCB.)
• PCB Layout
Make VDD and GND lines sufficient. If their impedance is high, noise pickup or unstable operation may result.
Connect a capacitor C1 with a capacitance value as much as 2.2μF or more between VDD and GND pin, and as
close as possible to the pins.
Set external components, especially the capacitor C2, as close as possible to the ICs, and make wiring as
short as possible.
• Thermal Shutdown Function
There is the built-in thermal-shutdown function in R1191x series. It discontinues operation of the IC when the
junction temperature becomes over 150°C (Typ.) and IC re-operates when the junction temperature under
130°C (Typ.). If the temperature increasing keeps the IC repeats ON and OFF operating. The output becomes
the pulse condition.
• Chip Enable (CE) Circuit and High-speed/ Low Supply Current Switching (ECO) Circuit
To maintain the stability of the output voltage, please do not use the intermediate electric potentials (the
voltage values between VCEH and VCEL) for the CE pin and the ECO pin. The use of the intermediate electric
potentials increases the supply current and causes the unstable output voltage.
• Auto-discharge Function
R1191xxxxD has adopted Auto-discharge function, which decreases the output voltage quickly to 0V by
turning on the transistor between VOUT pin and GND pin when switching “Active” to “Standby” and releases the
electrical charges accumulated in the external capacitor.
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