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> APP 4065
Keywords:
control loop, LDMOS, FET, bias, base station, power amplifier, RF
APPLICATION NOTE 4065
Implementing a MAX1385-Based Control Loop in
C/C++
Jun 21, 2007
Abstract: Maxim's MAX1385 evaluation kit (EV kit) software includes a Windows® graphical user interface
(GUI) program; however, the time cost of updating this display interferes with the control loop. This application
note shows a more optimal control-loop program, using a console menu system instead of a GUI.
When used with the MAX1385EVKIT+ demo board, the control loop achieves a regulation accuracy of ±2%.
This accuracy is limited by the gate driver output step size and the FET transconductance. Drain-current
regulation step size is determined by the MAX1385's gate-voltage increment multiplied by the FET's effective
transconductance. Because the MAX1385EVKIT uses an IRFZ44N MOSFET to close the loop for
demonstration purposes, the regulation may not be the same as it would be when used with an LDMOS FET.
Required Hardware
Maxim MAX1385EVKIT+
Maxim CMAXQUSB+ (includes USB A-B cable)
Windows 2000/XP PC with USB port
5VDC at 100mA power supply
10VDC at 1000mA power supply
DMM for measuring drain current
DMM for measuring drain voltage
DMM for measuring PGAOUT amplified current-sense voltage
Optional: oscilloscope for monitoring GATE1 voltage and PGAOUT1 drain current
Setup
Download and unzip the necessary
executable and source code files
(ZIP, 736kB).
Assemble the hardware according to
Figure 1.
Plug the CMAXQUSB header P3 into the MAX1385EVKIT connector J1.
Connect the MAX1385EVKIT's DRAIN1 and DRAIN2 pins to the current meter (-).
Connect the current meter (+) to the power supply (+).
Connect the MAX1385EVKIT's SOURCE1 and SOURCE2 pins to the power supply (-).
Connect the voltage meter (+) to the MAX1385EVKIT's DRAIN1 pin.
Connect the voltage meter (-) to the MAX1385EVKIT's SOURCE1 pin.
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Connect the MAX1385EVKIT's AVDD pin to the DVDD pin (or, optionally, connect to an external 5V DC
supply).
More Detailed Image
(PDF, 387kB)
Figure 1. MAX1385EVKIT hardware configuration.
Procedure
Set the CMAXQUSB's
VDD Select
jumper to the 5V position.
Connect the CMAXQUSB to the PC's USB port. If this is the first time a CMAXQUSB has been attached to
the PC, the plug-and-play wizard will appear. Guide the GUI to the installed location of the device driver, in
MAX1385_Appnote_src.zip\src\USB_driver.
Start the DEMO1385.EXE program. A console will appear on the screen. Enter the following series of
commands at the console:
Command
Action
Connects to the CMAXQUSB module. Verify that the software reports: Board connected.
Got board banner: Maxim CMAXQUSB V01.04.32 >
C
Searching for MAX1385...
Found MAX1385 at 0x4e
Note: when using MAX1385EVKIT with CMAXQUSB,
connect 5V DVDD supply to AVDD.
Test menu/verify power-up values
Test menu/servo mode/input register/FIFO register
Test menu/servo mode/ADC command/trigger channel 2 (current CS1)
Test menu/servo mode/target value 0x0020
Test menu/servo mode/convergence step positive 1
Test menu/servo mode/hysteresis one step
Test menu/servo mode/maximum loop duration set to 60 seconds
Test menu/servo mode/run
Test menu/write register/FineCalThru1 register, value 0x0300
TVP
T S I FF
TSA2
T S T 0020
TSC1
TSH1
T S M 60000
TSR
T W FCT1 0300
T S O FCT1 0300 Test menu/servo mode/output register/FineCalThru1 register, initial value 0x0300
Monitor the regulation by watching the DMM.
The voltage on PGAOUT1 regulates between 20.8mV and 21.7mV, which is a variation of 0.45mV (2%)
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around an average of 21.25mV.
Source Code Walk-Through
The source code was developed with the free dev-cpp IDE, which uses the GNU gcc-3.4.2 C++ compiler.
Listing 1
shows a simplified version of the C++ code performed inside the regulation loop. Output statements
and error handling have been removed for clarity.
Listing 1. Simplified C++ code.
Menu System
The complete source code implements the console menu system seen in
Listing 2,
which connects to the
CMAXQUSB module.
Listing 2. Console menu system.
============================================================
CmodComm test program main menu when not connected
A) adjust timing parameters
L) CmodLog... functions
C) connect
D) Debug Messages
X) exit
---------------------------------------------
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C
Board connected.
Got board banner: Maxim CMAXQUSB V01.04.32 >
Searching for MAX1385...
Found MAX1385 at 0x4e
Note: when using MAX1385EVKIT with CMAXQUSB,
connect 5V DVDD supply to AVDD.
============================================================
CmodComm test program main menu after successful connect
T) Test the device
8) CmodP8Bus... functions
A) adjust timing parameters
L) CmodLog... functions
P) CmodPin... functions
S) CmodSpi... functions
M) CmodSMBus... functions
$) CmodCommStringWrite list of hex codes
R) CmodBoardReset
D) Disconnect
============================================================
T Test menu
T ?
Hunt for active devices
T R
Read register
T W
Write register
T S
Servo loop
T VP
Verify Power-On Register Values
T VM reg mask
Verify Register Memory Persistence, All Combinations ...
T VW reg mask
Verify Register Memory Persistence, Walking-One's test ...
============================================================
Write register:
T W AD
Write ADCCON
T W AH
Write ALMHCFG
T W AS
Write ALMSCFG
T W FI1
Write FINE1
T W FI2
Write FINE2
T W FC1
Write FINECAL1
T W FC2
Write FINECAL2
T W FCT1
Write FINECALTHRU1
T W FCT2
Write FINECALTHRU2
T W FT1
Write FINETHRU1
T W FT2
Write FINETHRU2
T W HC
Write HCFG
T W HT1
Write THRUHI1
T W HT2
Write THRUHI2
T W HW1
Write HIWIPE1
T W HW2
Write HIWIPE2
T W IH1
Write IH1
T W IH2
Write IH2
T W IL1
Write IL1
T W IL2
Write IL2
T W LD
Write LDAC
T W LT1
Write THRULO1
T W LT2
Write THRULO2
T W LW1
Write LOWIPE1
T W LW2
Write LOWIPE2
T W P
Write PGACAL
T W SC
Write SCLR
T W SS
Write SSHUT
T W TH1
Write TH1
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T
T
T
T
W
W
W
W
TH2
TL1
TL2
X /hexRegAddr/
Write
Write
Write
Write
TH2
TL1
TL2
any register by its hexadecimal address
============================================================
Read register:
T R AH
Read ALMHCFG
T R AS
Read ALMSCFG
T R FF
Read FIFO
T R FI1
Read FINE1
T R FI2
Read FINE2
T R FL
Read FLAG
T R HC
Read HCFG
T R HW1
Read HIWIPE1
T R HW2
Read HIWIPE2
T R IH1
Read IH1
T R IH2
Read IH2
T R IL1
Read IL1
T R IL2
Read IL2
T R LW1
Read LOWIPE1
T R LW2
Read LOWIPE2
T R TH1
Read TH1
T R TH2
Read TH2
T R TL1
Read TL1
T R TL2
Read TL2
T R X /hexRegAddr/
Read any register by its hexadecimal address
============================================================
T S Test Servo menu
T S O FCT1 0300 output register [wr_FINECALTHRU1, initial value 0x0300]
T S I FF
input register [rd_FIFO]
T S A 2
ADC input channel [ bit 2 = 0x0004 = ADCCON_CURRENT_CS1 ]
T S T 0020
target value [0x0020]
T S C 1
ConvergeStep [1]
T S H 1
hysteresis [1]
T S M 60000
max_loop_duration_msec [60000]
T S R
servo loop run
============================================================
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