MAX16826 Datasheet, PDF (17/26 Pages) Maxim Integrated Products – Programmable, Four-String HB LED Driver with Output-Voltage Optimization and Fault Detection

Programmable, Four-String HB LED Driver with
Output-Voltage Optimization and Fault Detection
Overview of the Digital Section
Figure 3 shows the block diagram of the digital section in
the MAX16826. The I²C serial interface provides flexible
control of the IC and is in charge of writing/reading
to/from the register file unit. The ADC block is a 7-bit
5-channel SAR ADC. The eighth bit of the ADC data reg-
ister indicates an incomplete conversion or timeout has
occurred. This bit is set whenever the LED current fails to
come into regulation during the DIM PWM on-time. This
indicates there is either an LED open condition or the
CS_ on-time is less than 2µs.
A reason for this among other possibilities is an open
LED string condition. This eighth or MSB bit can be
tested to determine open string faults.
I²C Interface
The MAX16826 internal I²C serial interface provides
flexible control of the amplitude of the LED current in
each string and the switch-mode regulator output volt-
age. It is also able to read the current sink FET drain
voltages, as well as the switching regulator output volt-
age through OVP and thus enable some fault detection
and power dissipation minimization. By using an exter-
nal µC, the MAX16826 internal control and status regis-
ters are also accessed through the standard
bidirectional, 2-wire, I²C serial interface.
The I²C interface provides the following I/O functions
and programmability:
• Current sink FET drain and switching regulator out-
put-voltage measurement. The measurement for
each channel and the regulator output is stored in
its respective register and can be accessed
through the I²C interface. The SAR ADC measures
the drain voltage of each current sink FET sequen-
tially. This uses one 8-bit register for each channel
to store the measurement made by the 7-bit SAR
ADC and 1 bit to indicate a timeout during the ADC
conversion cycle.
• Adjustment of the switching regulator output. This is
used for adaptive voltage optimization to improve
overall efficiency. The switching regulator output is
downward adjustable by changing its reference
voltage. This uses a 7-bit register.
• Adjustment of the reference voltage of the current-
sink regulators. The reference voltage at the nonin-
verting input of each of the linear regulator drive
amplifiers can be changed to make adjustments in
the current of each LED string for a given sense
resistor. The output can be adjusted down from a
maximum of 316mV to 97mV in 1.72mV increments.
• Fault reporting. When a shorted string fault or an
overvoltage fault occurs, the fault is recorded.
• Standby mode. When a one is entered into the
standby register the IC goes into standby mode.
The 7-bit I²C address is 58h and the 8-bit I²C address
is B1h for a read operation and B0h for a write opera-
tion. Address the MAX16826 using the I²C interface to
read the state of the registers or to write to the registers.
Upon a read command, the MAX16826 transmits the
data in the register that the address register is pointing
to. This is done so that the user has the ability to confirm
the data written to a register before the output is
enabled. Use the fault register to diagnose any faults.
Serial Addressing
The I²C interface consists of a serial data line (SDA)
and a serial clock line (SCL) to achieve bidirectional
communication between the master and the slave. The
MAX16826 is a slave-only device, relying upon a mas-
ter to generate a clock signal. The master initiates data
transfer to and from the MAX16826 and generates SCL
to synchronize the data transfer (Figure 4).
SDA
t_LOW
t_SU,DAT
SCL
t_HD,STA
START CONDITION
t_HIGH
t_R
t_F
t_HD,DAT
t_SU,STA
t_HD,STA
REPEATED START CONDITION
t_BUF
t_SU,STO
STOP
START
CONDITION CONDITION
Figure 4. 2-Wire Serial Interface Timing Detail
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