Parameter

Formula

Value (for given example)

I

PK

V

193.75mA

I

1

(V

118.75mA

t

1

-R

14.61ns

t

2

[(V

[(V

(for a boost converter)

(for a buck converter)

17.5ns

t

3

2.3 • R

66ns

I

avg

[I

1.66mA

The total current being drawn from the linear regulator for a typical FC9911 circuit can be computed as follows (the values

provided are based on the continuous conduction mode boost design in the application note - AN-H55).

Current

Formula

Typical Value

Quiescent Current

1000µA

1000µA

Current sourced out of REF pin

(V

100µA

Current sourced out of RT pin

6

13.25µA

Current sourced out of SC pin

(1 / 2) • (2.5V / R

30.8µA

Current sourced out of CS pin

2.5V / R

SLOPE

61.6µA

Current drawn by FET GATE driver

I

AVG

1660µA

Total Current drawn from the linear

regulator

2.865mA

Note:

For a discontinuous mode converter, the currents sourced out of the SC and CS pin will be zero.

When the external FET is being turned on, current is being sourced out of the GATE and that current is being drawn from the

input. Thus, the average current drawn from V

the FET operation, the various values in the graph of Fig. 1 can be computed as follows:

FC9911

2012. 10. 31

8/13

Revision No : 0