Datasheet
Evaluates: MAX1739
MAX1739 Evaluation System/
Evaluation Kit
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Simple SMBus Commands
There are two methods for communicating with the
MAX1739: through the normal user-interface panel or
through the SMBus commands available from pressing
the MAXSMBUS button. A display pops up that allows
the SMBus protocols, such as Read Byte and Write
Byte, to be executed. To stop normal user-interface exe-
cution so that it does not override the manually set val-
ues, turn off the timer by unchecking the Automatic
Read checkbox.
The SMBus dialog boxes accept numeric data in binary,
decimal, or hexadecimal. Hexadecimal numbers should
be prefixed by $ or 0x. Binary numbers must be exactly
eight digits.
Detailed Description of Hardware
Jumper JU1
Jumper JU1 sets the MAX1739 to either ADC mode or
SMBus mode. There are two possible settings in ADC
mode: negative scale and positive scale. In negative
scale ADC mode, JU1 = 1-2, the brightness of the lamp
decreases as the voltage on the CTL/SCL pin increases.
In positive scale ADC mode, JU1 = 1-3, the brightness
of the lamp increases as the voltage on the CTL/SCL pin
increases. In SMBus mode, JU1 = 1-4, the SMBus inter-
face is enabled on the MAX1739. Refer to the
MAX1739/MAX1839 IC data sheet for more information.
Jumper JU2
Jumper JU2 connects the CRF/SDA pin to VL either
directly (position 1-2) or through a 10kΩ resistor (posi-
tion 2-3). This is a pullup resistor for the SMBus data sig-
nal.
In ADC mode, the CRF/SDA pin sets the reference input
voltage for the analog-to-digital converter (ADC).
Connecting this pin directly to V
L
sets the reference
input voltage to 5.3V. To use a voltage other than 5.3V,
leave JU2 open and apply an external voltage to the
CRF/SDA pad.
Jumper JU3
Jumper JU3 sets the voltage on the MINDAC pin. This
voltage sets the digital-to-analog converter’s (DAC’s)
minimum scale output voltage.
In the 1-2 position, MINDAC is connected to VL. In this
position, the lamp is completely off at the minimum
scale. Additionally, the DPWM chopping function is dis-
abled (refer to the MAX1739 IC data sheet).
In the 1-3 position, MINDAC is connected to REF
through a voltage-divider formed by R1 and R2. The
voltage on MINDAC is approximately 1V.
In the 1-4 position, MINDAC is connected directly to
REF. The voltage on MINDAC is 2V.
Jumper JU4
Jumper JU4, in the 1-2 position, enables the MAX1739
unless the SMBus suspend line (SH/SUS) pulls low.
In the 2-3 position, the MAX1739 is placed into shut-
down mode.
Jumper JU5
The jumper JU5 must be left open for SMBus operation
to prevent loading to the SMBus data signal.
For ADC mode, the shunt must be installed. This con-
nects the potentiometer R8 to the reference input volt-
age for the ADC (CRF/SDA).
Jumper JU6
When using this mode, jumper JU6 must be installed in the 1-2
position. This connects the R8 wiper to the CTL/SCL pin.
Adjusting R8 changes the voltage on this pin, which changes
the brightness of the lamp.
Jumper JU6, in the 2-3 position, connects CTL/SCL to VL
through a 10kΩ resistor. This position is for SMBus operation.
The resistor is a pullup resistor for the SMBus clock signal.
Table 2 lists the jumper settings.
Table 1. SH/SUS and SHMD Register Truth Table
SH /SUS SHMD2 SHMD1 SHMD0 OPERATING MODE
0 0 X 0 Operate
00X1
Shutdown
Status1 set
1 0 0 X Operate
101X
Shutdown
Status1 set
X1XX
Shutdown
Status1 set