MICRF004/RF044
SEL0, SEL1, SWEN, and SHUT Pins
VDDBB
Q1
VSSBB
SHUT
Q4
Q2
to Internal
Circuits
SEL0,
SEL1,
Q3
SWEN
VSSBB
Figure 6a. SEL0, SEL1, SWEN
VDDBB
Q1
VSSBB
SHUT
Q2
to Internal
Circuits
Q3
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 5µA,
leading to an impedance to the VDDBB supply of typically
1MΩ.
Micrel
MICRF004
10
February 9, 2000