Step-up DC/DC Controller

EC9215

Page 12 of 15

5J15N-Rev.F001

Function Description

Setting Oscillating Frequency

The oscillator circuit generates a triangular saw tooth wave with a peak of 0.9V and through

0.16V using the timing capacitor (CT) and the timing resistor (RT ) that are connected to OSC pin.

This oscillator can provide oscillating frequency up to 1MHz

Setting Output Voltage

The output voltage is set using the INV pin and a resistor divider connected to the output is

shown in the Typical Operating Circuit. The internal reference voltage is 0.5V with 2% variation,

so the ratio of the feedback resistors sets the output voltage according to the following

equation:

To avoid the thermal noise from feedback resistor, the resistance R2 is smaller than 100kW and

1% variation is recommended.

Error Amplifier

The

error amplifier detects

the

output

voltage

of

the switching regulator and outputs the

PWM control signal. The voltage gain is fixed, and connecting a phase compensation resistor

and capacitor to the FB pin (pin 8) provides stable phase compensation for the system.

PWM Comparator

The voltage comparator has one inverting and three non-inverting inputs. The comparator is a

voltage/pulse width converter that controls the ON time of the output pulse depending on the

input voltage. The output level is high (H) when the saw-tooth wave is lower than the error

amplifier output voltage, soft‐ start setting voltage, and idle period setting voltage