MICRF004/RF044

Micrel

MICRF004

10

February 9, 2000

SEL0, SEL1, SWEN, and SHUT Pins

to Internal

Circuits

VDDBB

VSSBB

SEL0,

SEL1,

SWEN

Q2

Q3

Q1

VSSBB

SHUT

Q4

Figure 6a. SEL0, SEL1, SWEN

to Internal

Circuits

VDDBB

VSSBB

SHUT

Q2

Q3

Q1

VSSBB

Figure 6b. SHUT

Control input circuitry is shown in Figures 6a and 6b. The

standard input is a logic inverter constructed with minimum

geometry MOSFETs (Q2, Q3). P-channel MOSFET Q1 is a

large channel length device which functions essentially as a

“weak” pullup to VDDBB. Typical pullup current is 5

µA,

leading to an impedance to the VDDBB supply of typically

1M

Ω.