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MAX6948B
High-Efficiency PWM LED Driver with Boost
Converter and Five Constant-Current GPIO Ports
Boost Converter
Boost-Converter Output PWM
The MAX6948B boost converter has 10-bit PWM opera-
tion using an internal 125kHz clock. This yields a PWM
period of 1024/125k = 8.192ms. PWM operation allows
the user to adjust the LED intensity and lower the average
current by enabling and disabling the boost converter at
a selectable rate. This rate is set using the boost-con-
verter output PWM registers (Tables 4, 5). The duty cycle
ranges from 0/1024 (no intensity or off) to 1023/1024 (full
intensity). Eight of the 10 bits, which include the MSB, are
in a single register (0x20) to allow a single I 2 C write to
set the majority of the intensity level and minimize visible
flicker during intensity changes. The LSB register (0x21)
allows for very fine adjustments in LED intensity.
Boost-Converter Status Register
The MAX6948B checks the boost converter and indi-
cates its status in the boost-converter status register
(Table 6). Faults indicated in this register include ther-
mal shutdown, overvoltage, and current limit. The boost
converter goes into standby mode whenever the boost
standby bit (D0) = 1.
Table 4. Boost-Converter Output PWM (MSB) Register Format (0x20)
REGISTER BIT
D7
D6
D5
D4
D3
D2
D1
D0
DESCRIPTION
Bit 9
Bit 8
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
VALUE
—
—
—
—
—
—
—
—
FUNCTION
Boost-converter output PWM bit 9 (MSB)
Boost-converter output PWM bit 8
Boost-converter output PWM bit 7
Boost-converter output PWM bit 6
Boost-converter output PWM bit 5
Boost-converter output PWM bit 4
Boost-converter output PWM bit 3
Boost-converter output PWM bit 2
DEFAULT VALUE
0
0
0
0
0
0
0
0
X = Don’t care.
Table 5. Boost-Converter Output PWM (LSB) Register Format (0x21)
REGISTER BIT
D7–D2
D1
D0
DESCRIPTION
Reserved
Bit 1
Bit 0
VALUE
000000
—
—
FUNCTION
—
Boost-converter output PWM bit 1
Boost-converter output PWM bit 0 (LSB)
DEFAULT VALUE
000000
0
0
Table 6. Boost-Converter Status Register Format (0x22)
REGISTER BIT
D7, D6, D5
D4
D3
DESCRIPTION
Reserved
Schottky open
Current limit
VALUE
000
0
1
0
1
FUNCTION
—
Schottky diode present
Schottky diode open
Normal output current
Converter output current exceeded the current limit
DEFAULT VALUE
000
Read only
Read only
0
Normal operation
D2
D1
D0
Thermal shutdown
Overvoltage
Boost standby
1
0
1
0
Device temperature has exceeded thermal
shutdown threshold
Normal operation
V OUT exceeded overvoltage limit
Boost converter operating according to PWM
register and configuration register
Read only
Read only
1
12
1
Boost converter in standby mode
Maxim Integrated
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