MAX16816 Datasheet, PDF (17/33 Pages) Maxim Integrated Products – Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming

Programmable Switch-Mode LED Driver
with Analog-Controlled PWM Dimming
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_DIM = 200Hz). The output current duty cycle is
linearly adjustable from 0 to 100% (0.2V < V_DIM < 2.8V).
Use the following formula to calculate voltage, V_DIM,
necessary for a given output current duty cycle, D:
V_DIM = (D x 2.6) + 0.2V
where V_DIM is the voltage applied to DIM in volts.
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_DIM, calculated
above and select appropriate resistor values using the
following equation:
R₄ = R₃ x V_DIM / (V_REF - V_DIM)
where V_REF is the 3V reference output voltage and
15kΩ ≤ R₃ + R₄ ≤ 150kΩ.
A minimum 20µs pulse width is necessary for proper
operation during dimming.
Oscillator, Clock, and Synchronization
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_T, between
RTSYNC and ground. Select a switching frequency,
f_SW, between 125kHz and 500kHz and calculate R_T
using the following formula:
R_T
=
500kHz
f_SW
× 25kΩ
where the switching frequency is in kHz and R_T is in kΩ.
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.
Multichannel Configuration
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).
ILIM and HICCUP Comparator
R_SENSE sets the peak current through the inductor for
switching. The differential voltage across R_SENSE is
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_SENSE:
R_SENSE = V_SENSE / (1.2 x I_PEAK)
REF
R₃
MAX16816
DIM
AGND
R₄
MASTER/PEER
MAX16816
RTSYNC CLKOUT
R_T
SLAVE/PEER
MAX16816
RTSYNC CLKOUT
Figure 2. Creating DIM Input Signal from REF
Figure 3. Master-Slave/Peer-Peer Clock Configuration
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