TS19701A

CC/CV Primary-Side PWM Controller

4/9

Version: A12

Function Description

TS19701A is a cost effective PWM power switch optimized for off-line low power AC/DC applications including

battery chargers and adapters. It operates in primary side sensing and regulation, thus opto-coupler and TL431 are

not required. Proprietary built-in CV and CC control can achieve high precision CC/CV control meeting most

adapter and charger application requirements.

Startup Current and Start up Control

Startup current of TS19701A is designed to be very low so that VDD could be charged up above UVLO threshold

and starts up quickly. A large value startup resistor can therefore be used to minimize the power loss in application.

Operating Current

The Operating current of TS19701A is as low as 2.0mA. Good efficiency is achieved with the low operating current

together with ‘Muti-mode’ control features.

Soft Start

TS19701A features an internal soft start to minimize the component electrical over-stress during power on startup.

As soon as VDD reaches UVLO (OFF), the control algorithm will ramp peak current voltage threshold gradually

from nearly zero to normal setting of 0.91V. Every restart is a soft start.

CC/CV Operation

TS19701A is designed to produce good CC/CV control characteristic as shown in the Fig. 1. In charger

applications, a discharged battery charging starts in the CC portion of the curve until it is nearly full charged and

smoothly switches to operate in CV portion of the curve. In an AC/DC adapter, the normal operation occurs only on

the CV portion of the curve. The CC portion provides output current limiting. In CV operation, the output voltage is

regulated through the primary side control. In CC operation mode, TS19701A will regulate the output current

constant regardless of the output voltage drop.

Principle of Operation

To support TS19701A proprietary CC/CV control, system needs to be designed in DCM mode for flyback system

(Refer to Typical Application Diagram on page1). In the DCM flyback converter, the output voltage can be sensed

via the auxiliary winding. During MOSFET turn-on time, the load current is supplied from the output filter capacitor

Co. The current in the primary winding ramps up. When MOSFET turns off, the primary current transfers to the

secondary at the amplitude of

The auxiliary voltage reflects the output voltage as shown in fig.2 and it is given by

Where ∆V indicates the drop voltage of the output Diode.