May, 1997 TOKO, Inc.
Page 9
TK113xxB
DEFINITION AND EXPLANATION OF TECHNICAL TERMS (CONT.)
ON/OFF RESPONSE WITH CONTROL AND LOAD TRANSIENT RESPONSE
The turn on time depends upon the value of the output capacitor and the noise bypass capacitor. The turn on time will
increase with the value of either capacitor. The graph below shows the relationship between turn on time and load
capacitance. If the value of these capacitors is reduced, the load and line regulation will suffer and the noise voltage will
increase. If the value of these capacitors is increased, the turn on time will increase.
OUTPUT VOLTAGE RESPONSE
(OFF
→
ON)
-5
5
15
35
ILOAD = 10 mA, CNP = 1000 pF
25
45
1.0 μF
1.5 μF
0.47 μF
CL = 0.33
LOAD CURRENT STEP
200 mV/DIV
-5
5
15
TIME (μS)
35
ILOAD
A = 0 to 30, B = 5 to 35, C = 30 to 60 mA
25
45
B
C
A
CL = 0.33 μF
REDUCTION OF OUTPUT NOISE
Although the architecture of the Toko regulators is designed to minimize semiconductor noise, further reduction can be
achieved by the selection of external components. The obvious solution is to increase the size of the output capacitor.
A more effective solution would be to add a capacitor to the noise bypass terminal. The value of this capacitor should be
0.1
μ
f or higher (higher values provide greater noise reduction). Although stable operation is possible without the noise
bypass capacitor, this terminal has a high impedance and care should be taken to avoid a large circuit area on the printed
circuit board when the capacitor is not used. Please note that several parameters are affected by the value of the capacitors
and bench testing is recommended when deviating from standard values.
OUTPUT VOLTAGE RESPONSE
(OFF
→
ON)
0
ILOAD = 30 mA, CL = 2.2 μF
200
600
400
800
CN = 0.1 μF
CN = 0.1 μF