Rainbow-electronics MAX6948B Manual de usuario descargar pdf (Pagina 12)

High-Efficiency PWM LED Driver with Boost

Converter and Five Constant-Current GPIO Ports

MAX6948B

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

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)

Table 5. Boost-Converter Output PWM (LSB) Register Format (0x21)

Table 6. Boost-Converter Status Register Format (0x22)

X = Don’t care.

D7 Bit 9 — Boost-converter output PWM bit 9 (MSB) 0

D6 Bit 8 — Boost-converter output PWM bit 8 0

D5 Bit 7 — Boost-converter output PWM bit 7 0

D4 Bit 6 — Boost-converter output PWM bit 6 0

D3 Bit 5 — Boost-converter output PWM bit 5 0

D2 Bit 4 — Boost-converter output PWM bit 4 0

D1 Bit 3 — Boost-converter output PWM bit 3 0

D0 Bit 2 — Boost-converter output PWM bit 2 0

D7–D2 Reserved 000000 — 000000

D1 Bit 1 — Boost-converter output PWM bit 1 0

D0 Bit 0 — Boost-converter output PWM bit 0 (LSB) 0

D7, D6, D5 Reserved 000 — 000

D4 Schottky open

0 Schottky diode present

Read only

1 Schottky diode open

D3 Current limit

0 Normal output current

Read only

1 Converter output current exceeded the current limit

D2 Thermal shutdown

0 Normal operation

Read only

Device temperature has exceeded thermal

shutdown threshold

D1 Overvoltage

0 Normal operation

Read only

1 V

OUT

exceeded overvoltage limit

D0 Boost standby

Boost converter operating according to PWM

1 Boost converter in standby mode

1 2 ... 7 8 9 10 11 12 13 14 15 16 17 ... 27 28

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