MAX11014BGTM+ Maxim Integrated, MAX11014BGTM+ Datasheet - Page 18

• Manufacturer Part Number: MAX11014BGTM+
• Description: Special Purpose Amplifiers Auto RF MESFET Amp Drain-Current Cntrlr
• Manufacturer: Maxim Integrated
• Series: MAX11014, MAX11015r

Specifications of MAX11014BGTM+

• Rohs: yes
• Common Mode Rejection Ratio (min): 90 dB
• Operating Supply Voltage: 0.5 V to 11 V
• Supply Current: 2.8 mA
• Maximum Power Dissipation: 2162.2 mW
• Maximum Operating Temperature: + 105 C
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Package / Case: TQFN-48
• Available Set Gain: 13.98 dB

Once the control loop has been set, the MAX11014
automatically maintains the drain-current value. Figure
5 details the amplifiers that bias the channel 1 and
channel 2 control loops.
The dual current-sense amplifiers amplify the voltage
between RCS_+ and RCS_- by four and add an offset
voltage (+12mV nominally). These current-sense ampli-
fiers amplify sense voltages between 0 and 625mV
when V
Amplifiers section.
The current-sense amplifier output injects a scaled-down
replica of the MESFET drain current at the summing
node to complete the internal analog feedback loop. The
summing node drives the gate-drive amplifier through a
100kΩ series resistor. The gate-drive amplifier is config-
ured as an integrator by the external capacitor connect-
ed between GATE1/GATE2 and FILT2/FILT4. The
gate-drive amplifier includes automatic offset cancella-
tion between 0 and 24mV to null the 12mV offset from the
current-sense amplifier. See the Register Descriptions
and PGACAL (Write) sections.
The MAX11014’s analog control loop setpoint is
described by the following equation:
where:
V
(channel 2) when the THRUDAC1/THRUDAC2 register
code is set to 000h.
V
V
sense resistor.
Connect a capacitor from FILT2 to GATE1 to form an
integrator (setting the control-loop dominant pole) with
the channel 1 internal 100kΩ resistor. Connect a
capacitor from FILT4 to GATE2 to form an integrator
(setting the control-loop dominant pole) with the chan-
nel 2 internal 100kΩ resistor. The gate-drive amplifier’s
output drives the MESFET gates. See the Gate-Drive
Amplifiers section.
The channel 1 DAC voltage is output to FILT1 through a
series 580kΩ resistor. The channel 2 DAC voltage is
output to FILT3 through a series 580kΩ resistor.
Connect a capacitor from FILT1 to AGND and FILT3 to
AGND to set the filter’s time constant for the respective
channel.
Automatic RF MESFET Amplifier
Drain-Current Controllers
18
FILT
FILT
RCS_+
V
______________________________________________________________________________________
(CODE = 000h) = V
RCS
= V
- V
REFDAC
FILT1
_
+
RCS_-
−
V
(channel 1) and V
RCS
= the voltage drop across the current-
= +2.5V. See the Current-Sense
_
−
=
V
FILT
FILT1
(
CODE
(channel 1) and V
FILT3
=
4
(channel 2).
000
h
)
−
V
FILT
FILT3
The MAX11015 is designed to be used with a Class AB
amplifier configuration to independently measure the
drain current and set the GATE_ output voltages through
the serial interface. After sensing the drain current with
no RF signal applied, set the DAC code to obtain the
desired GATE_ voltage. Figure 6 details the amplifiers
that bias the channel 1 and channel 2 control.
The MAX11015 internal 12-bit DAC voltage is applied to
the gate-drive amplifier, which has a preset gain of
-2. See the Gate-Drive Amplifiers section. Setting the
DAC code between FFFh and 000h typically produces
a GATE_ voltage between 0 and (-2 x V
the HCFG (Read/Write) section for details on adjusting
the GATE_ maximum voltage.
The channel 1 DAC voltage is output to FILT1 through a
series 580kΩ resistor. The channel 2 DAC voltage is
output to FILT3 through a series 580kΩ resistor.
Connect a capacitor from FILT1 to AGND and FILT3 to
AGND to set the filter’s time constant for the respective
channel. Connect FILT2 and FILT4 to AGND
(MAX11015 only).
The dual current-sense amplifiers amplify the voltage
between RCS_+ and RCS_- by four and add an offset
voltage (+12mV nominally). The current-sense ampli-
fiers amplify sense voltages between 0 and 625mV
when V
Amplifiers section.
The dual current-sense amplifiers amplify the voltage
between RCS_+ and RCS_- and add an offset voltage.
Connect a resistor between RCS_+ and RCS_- to sense
the MESFET drain current. The current-sense amplifiers
scale the sense voltage by four. These amplifiers also
reject the drain supply voltage that appears as a DC
common-mode level on the current signal.
The gate-drive amplifier includes automatic offset can-
cellation between 0 and 24mV to null the 12mV offset
from the current-sense amplifier. See the PGACAL
(Write) section.
The gate-drive amplifiers control the MESFET gate bias
settings. The MAX11014’s channel 1 and channel 2
DAC voltages are routed through a summing node and
into the gate-drive amplifiers. The MAX11015’s channel
1 and channel 2 DAC voltages are routed directly to the
gate-drive amplifiers, which have a preset gain of -2.
See the 12-Bit DAC section for details on setting the
DAC codes.
REFDAC
= +2.5V. See the Current-Sense
MAX11015 Class AB Control
Current-Sense Amplifiers
Gate-Drive Amplifiers
REFDAC
). See