ADP1621ARMZ-R7 Analog Devices Inc, ADP1621ARMZ-R7 Datasheet - Page 28

• Manufacturer Part Number: ADP1621ARMZ-R7
• Description: IC CTRLR DC/DC PWM STEPUP 10MSOP
• Manufacturer: Analog Devices Inc
• Type: Step-Up (Boost)r

Specifications of ADP1621ARMZ-R7

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Current - Output: 1A
• Frequency - Switching: 100kHz ~ 1.5MHz
• Voltage - Input: 2.9 ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Primary Input Voltage: 5.5V
• No. Of Outputs: 1
• Output Current: 1A
• No. Of Pins: 10
• Operating Temperature Range: -40°C To +125°C
• Msl: MSL 1 - Unlimited
• Frequency Max: 1.5MHz
• Termination Type: SMD
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: ADP1621-EVALZ - BOARD EVALUATION FOR ADP1621
• Voltage - Output: -
• Power - Output: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant
• Other names: ADP1621ARMZ-R7; ADP1621ARMZ-R7TR

ADP1621
LED DRIVER APPLICATION CIRCUITS
The ADP1621 can be used as an LED driver. Two LED application
circuits are shown in Figure 41 and Figure 42, where each circuit
is driving 20 white LEDs in series. Each white LED has a typical
current of 150 mA at a typical forward voltage of 4.0 V, with a
maximum voltage of 4.5 V over the temperature range of −40°C
to +125°C.
Two methods for dimming the brightness of the LEDs are
shown in Figure 41 and Figure 42. In Figure 41, a PWM signal
is fed to the SDSN pin to turn the ADP1621 controller on and
off. As a result, the LED current is turned on and off, and the
average LED current is dependent on the PWM duty cycle. The
advantage of this method is that no current flows through the
LEDs during the PWM off cycle. In addition, when the ADP1621 is
on, the forward current through the LEDs is constant, which
guarantees constant color emission across the entire dimming
range. Because the soft start period is fixed at 2048 oscillator
cycles, the PWM frequency range is limited.
As shown in Figure 41, because the natural switching frequency
chosen is 400 kHz, the useful PWM frequency range is 90 Hz to
195 Hz. However, when driving fewer LEDs, the ADP1621 can
be set to run at a faster frequency, increasing the maximum PWM
frequency. The PWM duty cycle can be between 5% and 95%. A
higher PWM duty cycle produces a higher average LED current.
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Another method for driving the LEDs is shown in Figure 42,
where the PWM signal is filtered by an RC low-pass filter and is
fed to the FB node. The effective FB voltage at the bottom of the
LED string is modulated in an analog manner by the PWM
duty cycle. Thus, the average current through the LEDs is
modulated accordingly. Unlike the case depicted in Figure 41, a
higher duty cycle produces a lower average LED current using
the filtered PWM scheme in Figure 42. The advantage of this
circuit is that the PWM frequency can be in the range between
90 Hz and 100 kHz, and the duty cycle can be between 5% and
95%. The disadvantage of this method is that the forward
current through the LEDs is directly modified to control the
brightness of the LEDs. Because the wavelength of the light
emitted from an LED is a weak function of its forward current,
perfect color purity across the entire dimming range cannot be
guaranteed.
If PCB space is a constraint, smaller inductors can be selected
for the circuits shown in Figure 41 and Figure 42. For example,
a 4.7 μH inductor can be used, and a 200 kHz switching fre-
quency can be selected. However, with this small inductor, the
system operates in DCM, which is slightly less efficient than
operating in CCM.