IC-TW28 Datasheet, PDF (73/80 Pages) IC-Haus GmbH – 10-BIT SIN/COS INTERPOLATOR

iC-TW28
R
LED
C
iC-TW28
R
LED
C
r ^{y Positive Polarity}
iC-TW28 ina LED_CFG.pol = 0
10-BIT SIN/COS Negative Polarity
LED_CFG.pol = 1
INTERPOLATOR
prelim WITH AUTO-CALIBRATION AND LINE DRIVER
Rev D2, Page 73/80
iC-TW28
LED
3.3V
R
C
Negative Polarity
LED_CFG.pol = 1
iC-TW28
LED
3.3V...5V
R
C
Positive Polarity
LED_CFG.pol = 0
Where V_f is the forward voltage drop of the LED and
I_max is the maximum forward current of the LED or
15 mA, whichever is less. This gives a filter cutoff one
decade below the PWM frequency. For example, with
the iC-SD85 infrared LED (V_f = 1.4 V and I_max = 20 mA),
R = 127 Ω and C > 120 nF for LED_CFG.freq = 3.
Figure 43: High Current/Voltage LED Connection
5V
Configure the3.3VLED output as push-pull by setting
LED_CFG.odrain = 0. Configure the LED polarity to
mat^iCc^-h^TWth²e⁸ specRific connection as shown.
LED
C
Select the desired LED PWM frequency using
LED__NC_egF_atG_ive._Pfr_oe_larq_ity (see LED_CFG.freq on page 39).
In gLeEDn_eCFrGa.pl,ol = 1use the highest PWM frequency
(97.6 kHz) to minimize filter capacitor size by select-
ing LED_CFG.freq = 3. Lower PWM frequencies may
be selected if interference is a problem.
Size the current-limiting resistor and filter capacitor us-
ing the following formulas:
R[kΩ] = ^{3.3 − Vf[volts]}
I_max[mA]
1
C[µF] > _{2(LED_CFG.freq+3) × R[kΩ]}
Once the current-limiting resistor has been chosen to
enforce the maximum LED current, LED_START can
be calculated to provide the desired nominal LED oper-
ating current as
LED_START = INT ^Inom · 256
I_max
For example, for a nominal LED current of 8 mA with
the iC-SD85,
8
LED_START = INT · 256 = 137
15
Note: As the iC-TW28 runs at 3.3 V, the LED output
may not be able to power a blue LED because V_f
may exceed 3 V. To operate the LED from 5 V, use an
external n-channel FET as shown in Figure 43 (right
side). This circuit also avoids an overvoltage at pin
LED (V(LED) < AVDD + 0.3 V is required).