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AS1302

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

8 Detailed Description

Functional Description

The AS1302 is a high efficiency and low noise switched capacitor DC-DC converter that is capable of boost operation.

It is equipped with two built-in coupled H-bridge type switch configurations. Based on the value of the output voltage

the system automatically initiates mode-switching to achieve the highest possible efficiency. The regulation of the

output voltage is achieved by a regulation loop, which modulates the current drive capability of the power transistors so

that the amount of charge transferred from the input to the output at each clock cycle is controlled and is equal to the

charge needed by the load.

Regulation Loop

The AS1302 operates at a constant frequency. For the regulation loop power transistors, a resistor divider and an error

amplifier are used to keep the output voltage within the allowed limits. The error amplifier takes the feedback and

reference signals as inputs and generates the error voltage signal. The error voltage controls a driver that triggers the

gate voltage of the power transistor which modulates the current drive capability of the power amplifier. The modulated

transistor controls the charge transferred from the input to the output and therefore the regulation of the output is

realized. This regulation concept which is based on adjusting the amount of charge transferred, delivers the smallest

voltage ripple possible.

Figure 32. AS1302 - Functional Block Diagram

Light/Heavy Load Monitor

To detetect the output current in the 2:3 and in the 1:2 mode, a current sense is used. The device switches to a lower

switching frequency (49kHz typ), due to a detected light-load condition. With this frequency an excellent light-load

efficiency is achieved and no audible noise is generated. If the load is increasing (typically more than 3mA), the device

operates at 1.2MHz.

+

VBATT

CBAT

VOUT

COUT

C1+

C1-

C2+

C2-

EN

CFLY1

CFLY2

Double-H Bridge

Topology

Vmode

Vctrl

Ref

POR

Temp

State Machine

&

Control Logic

Mode

Select

GND

CLK

AS1302

On

Off

Bias

it

() t

d

∫

Soft-

start