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AS7620

Datasheet - D e t a i l e d D e s c r i p t i o n

8 Detailed Description

Figure 17. System Diagram of AS7620-A with Early Power Fail Warning

Shut Down

The device can be shut down by providing a voltage lower than 1V at the SHDN pin (7). In this condition, the

consumption is only 1µA (typ.). The AS7620 is providing an internally regulated pull-up circuit. No external pull-up

resistor shall be used, which could otherwise damage the shutdown input. Connect the SHDN input directly to an open

drain port only.

Soft Start

The device implements a soft start by limiting the inrush current into the output choke. Initially, the internal PMOS is

turned on until the current reaches the programmed current limit (see Current Limit on page 9) and then is immediately

lower than the reference and so the duty cycle will be driven by the current limit only.

Regulation

Both AS7620-A and AS7620-B are based on a hysteretic control method. Moreover, the switch current is monitored to

make the converter always work in discontinuous current mode (DCM). The advantages of this type of control system

can be summarized as following:

!

High efficiency even at light load

!

Intrinsically stable

!

Simplicity

!

Readiness during the load transient

most common application conditions (L=10µH ÷ 100µH; C=10µF - 100µF) and setting the CL threshold according to

the load, the on time is normally terminated by the CL intervention and the output voltage ripple will stay within 1.25%

Table 4. AS7620 Output Voltage Options

AS7620

AS7620A-BQFT

AS7620B-BQFT

ADJ.

3.3V

2.2µF

100µF

10µH

3.6V to 32V

FB

PF

PG

AS7620-A

SHDN

3.3V