MAX16816 Maxim Integrated Products, MAX16816 Datasheet - Page 17

• Manufacturer Part Number: MAX16816
• Description: Programmable Switch-Mode LED Driver
• Manufacturer: Maxim Integrated Products

an analog control signal is applied to DIM, the
MAX16816 compares the DC input to an internally gen-
erated 200Hz ramp to pulse-width modulate the LED
current (f
linearly adjustable from 0 to 100% (0.2V < V
Use the following formula to calculate voltage, V
necessary for a given output current duty cycle, D:
where V
Connect DIM to REF through a resistive voltage-divider
to apply a DC DIM control signal (Figure 2). Use the
required dimming input voltage, V
above and select appropriate resistor values using the
following equation:
where V
15kΩ ≤ R
A minimum 20µs pulse width is necessary for proper
operation during dimming.
The MAX16816 is capable of stand-alone operation, of
synchronizing to an external clock, and of driving exter-
nal devices in SYNC mode. For stand-alone operation,
set the EEPROM Oscillator Enable/Disable (RTOF) bit
to ‘1’ to use the fixed internal 125kHz oscillator or set
RTOF to ‘0’ and program the switching frequency by
connecting a single external resistor, R
RTSYNC and ground. Select a switching frequency,
f
using the following formula:
where the switching frequency is in kHz and R
Figure 2. Creating DIM Input Signal from REF
SW
, between 125kHz and 500kHz and calculate R
Oscillator, Clock, and Synchronization
DIM
REF
DIM
3
+ R
is the voltage applied to DIM in volts.
R
R
R
= 200Hz). The output current duty cycle is
3
4
is the 3V reference output voltage and
4
4
= R
V
≤ 150kΩ.
DIM
R
______________________________________________________________________________________
T
3
Programmable Switch-Mode LED Driver
x V
=
= (D x 2.6) + 0.2V
DIM
REF
DIM
with Analog-Controlled PWM Dimming
500kHz
f
SW
MAX16816
/ (V
AGND
REF
×
2 k
- V
5 Ω
DIM
DIM
)
, calculated
DIM
T
T
, between
is in kΩ.
< 2.8V).
DIM
T
,
To synchronize the MAX16816 with an external clock
signal ranging from 125kHz to 500kHz, set the RTOF bit
to ‘0’ and connect the clock signal to the RTSYNC
input. The MAX16816 synchronizes to the clock signal
after the detection of 5 successive clock edges at
RTSYNC.
A buffered clock output, CLKOUT, can drive the
RTSYNC input of an external PWM controller for multi-
channel applications. CLKOUT can drive capacitive
loads up to 500pF.
If the PWM switching frequency is set to 125kHz, the
RTSYNC oscillator can be temporarily disabled by setting
the EEPROM RTOF bit to ‘1’. In this case, the internal
125kHz frequency-fixed oscillator drives the PWM. See the
EEPROM and Programming section for more information
on setting the Oscillator Enable/Disable bit in the EEPROM.
The MAX16816 is capable of multichannel operation
and is configurable as a master or slave in a Master-
Slave configuration, or in a Peer-to-Peer configuration.
Connect CLKOUT to the SYNC input of an external
device to use the MAX16816 as a master clock signal.
Connect an external clock signal to RTSYNC to config-
ure the MAX16816 as a slave. To setup two MAX16816
devices in a daisy-chain configuration, drive the
RTSYNC input of one MAX16816 with the CLKOUT
buffer of another (Figure 3).
R
switching. The differential voltage across R
compared to the 200mV voltage-trip limit of the current-
limit comparator, ILIM. Set the current limit 20% higher
than the peak switch current at the rated output power
and minimum voltage. Use the following equation to
calculate R
Figure 3. Master-Slave/Peer-Peer Clock Configuration
SENSE
R
T
sets the peak current through the inductor for
RTSYNC
SENSE
R
SENSE
MASTER/PEER
MAX16816
ILIM and HICCUP Comparator
:
= V
CLKOUT
Multichannel Configuration
SENSE
/ (1.2 x I
RTSYNC
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MAX16816
SLAVE/PEER
PEAK
CLKOUT
)
SENSE
17
is