
MC33169
7
MOTOROLA ANALOG IC DEVICE DATA
Figure 8. Output Voltage versus Load Current
Figure 9. VTx Control Voltage versus Gate
Drive Output Voltage
VTx, POWER CONTROL INPUT VOLTAGE (V)
–4.03
–4.025
–4.02
–4.015
–4.01
–4.035
–4.04
0
V
O
0.5
1.0
1.5
LOAD CURRENT (mA)
2.0
2.5
3.0
3.5
4.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0
0
0.5
1.0
1.5
2.0
2.5
3.0
85
°
C
25
°
C
–25
°
C
0
°
C
OPERATING DESCRIPTION
The MC33169 is a power amplifier support IC that is
designed to properly switch “on” or “off” a MESFET Power
Amplifier either manually or by microprocessor. Controlling
the power drain of the RF Amplifier extends operating battery
life in many portable systems.
Outputs
The IC is designed to provide a –4.0 V or –2.5 V bias to
the gate of the RF Ampllifier MESFET devices prior to
application of a positive battery voltage to the drain. The
negative output voltage can provide up to 5.0 mA of current.
The positive voltage control requires an external
N–Channel logic level MOSFET, connected as a source
follower. The Gate Drive Output, Pin 8, can source or sink
3.0 mA to the external MOSFET. The low drive current slows
the MOSFET switching speed, thereby minimizing voltage
glitches on the VCC line which could cause disturbances to
other circuitry.
Inputs
A Sense Input, Pin 10, protects the Power Amplifier load
by monitoring the level of the negative output voltage. If the
negative voltage magnitude falls below a preset level, 3.2 V
typical for the –4.0 V version or 2.3 V for the –2.5 V version,
an undervoltage lockout circuit disables the external
MOSFET gate drive.
The Tx Power Control Input controls the N–Channel
external switching MOSFET in source follower mode, which
allows linear control of the RF Output voltage level.
The Idle mode input is CMOS compatible, allowing the RF
Amplifier to be placed in a standby mode, drawing less than
1.0
μ
A from the power source.