PRELIMINARY TECHNICAL DATA

ADP1720

Rev. PrA | Page 7 of 9

THEORY OF OPERATION

Introduction

The ADP1720 is a high-voltage, micro-power, low dropout

linear regulator. Designed for robust operation, the ADP1720

includes current limiting and short-circuit protection, thermal

overload protection. With just 25µA of quiescent supply current

and a micro-power shutdown mode, this device is ideal for

applications that require low quiescent current. The small

thermally-enhanced MSOP package and 1µF ceramic output

capacitor provides a compact solution with low thermal

resistance for high power dissipation.

The ADP1720 is available in fixed output voltages of 3.3V and

5V, or its output voltage is adjustable over a range of 1.2V to

5V. The ADP1720 operates over the -40°C to 125°C ambient

temperature range.

Adjustable Output Voltage

The ADP1720 output voltage is adjustable over a 1.2V to 5.0

range. The output voltage is set by connecting a resistive

voltage divider from OUT to ADJ. The output voltage is

resistor from ADJ to GND. The maximum bias current into

ADJ is 100nA, so for less than 0.1% error due to the bias

current, use values less than 12k

Ω for R

Output Capacitor Selection

The ADP1720 is optimized for operation with small 1µF

ceramic capacitors. The ADP1720 maintains stability with

capacitance greater than 1

µF, 10uF maximum and over a wide

range of capacitor ESR values ( At least 1m

to 100m ).

Ceramic capacitors are manufactured with a variety of

dielectrics, each with different behavior over temperature and

applied voltage. When choosing your capacitor be sure to

choose a dielectric adequate to ensure the minimum

capacitance over the necessary temperature range.

Thermal Protection

The ADP1720 has an internal thermal shutdown function that

protects itself from thermal overloads. The thermal protection

circuitry activates and disables the output when the die

temperature exceeds 150°C. The thermal protection circuitry

has a typical hysteresis of 15°C. Once the die temperature

decreases beyond the hysteresis, the output is enabled again.

Current Limit

The ADP1720 uses internal current limiting to protect itself and

its load during overload and short-circuit conditions.

Shutdown

The ADP1720 enters a low power shutdown state by driving

EN to GND. In shutdown, the ADP1720 consumes less than

5

µA. For automatic startup connect EN to IN. Note that EN

withstands up to the +28V input voltage without damage.

Package and Power Dissipation

The ADP1720 use a thermally-enhanced MSOP package,

footprint.