TS2581
PWM Controller
5/7
Version: A11
Application Information (Continue)
Output Capacitor Selection
The output capacitor is required to filter the output and provide regulator loop stability. The important capacitor
parameters are; the 100 KHz Equivalent Series Resistance (ESR), the RMS ripples current rating, voltage rating,
and capacitance value. For the output capacitor, the ESR value is the most important parameter. The ESR can be
calculated from the following formula.
ESR
L
RIPPLE
×∆=
= 0.6A x 80m
Ω
= 48mV
An aluminum electrolytic capacitor’s ESR value is related to the capacitance and its voltage rating. In most case,
higher voltage electrolytic capacitors have lower ESR values. Most of the time, capacitors with much higher voltage
ratings may be needed to provide the low ESR values required for low output ripple voltage. System stability is
depending on output capacitor’s ESR, Correct to choose output capacitor’s ESR is very important. It is
recommended to using a 220~470µF, the ESR values range is 40~130mΩ.
EN/CT
The pin is enable/shutdown and auto restart control functions. When system is normal operating, this pin is
enable/shutdown function. Pulling this pin below a threshold voltage of under 0.3V shuts the regulator off, and
pulling this pin from 0.5V to 1.5V turns the regulator on. However when V
OUT
is short (V
FB
<0.4V), the auto restart
function can be started that restart the regulator cycle by cycle. The cycle time is set by outside capacitor (C6).
Please refer the below waveform and formula, the t2 cycle is regulator off time and t1 cycle is current limit time. The
charge-current is 30uA and discharge-current is 1.3uA.
V
EN/CT
Time
t1
t2
Time
Iin (A)
0.5V
1.5V
0
Current Limit
Thermal Consideration
The SOP-8L package needs a heat sink under most conditions. The heat sink connect exposed pad of TS2581 to
obtain best effect. The size of the heat sink depends on the input voltage, the output voltage, the load current and
the ambient temperature.
