UCC1890

UCC2890

UCC3890

provides inherent short circuit protection. However,

to ensure output voltage startup when the output is

frequency.

=

– 0.4V

reduction of off time. The frequency of operation in-

value.

3. In this region, a transconductance amplifier reduces

input to the transconductance amplifier is the pin FB.

(In this mode the pin CS should be shorted to VDD.)

= 1.25V or to be connected to

late at nominal

=

1.25V

falls to zero and the circuit returns to the minimum

The range of switching frequencies is established by

Frequency

=

1

TON

TON

=

CT

• 3.4V

TOFF

=

(region 2)

The above equations assume VDD = 9, the voltage

at TON = 11V, the voltage at TOFF = 0.4V.

OPERATION (CURRENT OUTPUT)

Figure 2 shows a typical current mode application. In

current mode, operation is the same as in voltage

mode, except that in region 3 the transconductance am-

plifier is controlled by the current sense amplifier which

cuit then regulates the current in the shunt to the nomi-

nal value

=

100mV

The circuit shown in this schematic would be suitable

for an application which trickle charges a battery at a

low current, (e.g. C/10), and has a battery load which

draws a high current, (e.g. C), when turned on. In that

100mV

=

C

10

Figure 2. Typical Current Mode Application

UDG-96055

APPLICATION INFORMATION (cont.)

4