ADVANCED INFORMATION
TK654xx
NOISE CONSIDERATIONS (CONT.)
COIL
The coil magnetic field can also be a source of noise. This noise is more characteristic of radiated Electromagnetic
Interference (EMI). This radiated noise can interfere with RF communications systems if care is not taken by the system
designer. A shielded coil can improve this source of EMI.
SNUBBER
When the inductor current flowing through the output diode decays to zero, the parasitic capacitance at the switch pin
(pin 3) resulting from the internal switch and external diode has energy which rings back into the inductor. This high
frequency ringing is an undesirable source of radiated noise. Fortunately, due to the low amount of energy in this ringing,
a simple RC snubber as shown in Figure 5 easily eliminates it. In low noise applications the RC snubber is recommended,
although an efficiency penalty of approzimately 2% will result.
LBO
OUT
SW
LBI
V
GND
V
IN
V = 5 V
IN
V
= 3 V
OUT
L
1
100 µH
C
D
220
PF
1
1
22 µF
LL 103
1 K
FIGURE 5: OPTIONAL SNUBBER
Page 16
September 1999 TOKO, Inc.
TOKO [ TOKO, INC ]
