SP6126 Datasheet, PDF (5/14 Pages) Sipex Corporation – High-Voltage, Step Down Controller in TSOT6

Loop Compensation Example 1- A converter
utilizing a SP6126 has a 6.8uH inductor and
a 22uF/5mΩ ceramic capacitor. Determine
whether Type-III compensation is needed.
From equation (2) f_ESRZERO = 1.45MHz. From
equation (3) f_DBPOLE = 13 kHz. Since the
condition specified in (1) is not met, Type-III
compensation has to be used by adding
external components RZ and CZ. Using
equation (4) CZ is calculated 61.2pF (use 62
pF). Following the guideline given in table 1,
a 2kΩ RZ should be used.
The steps followed in example 1 were used
to compensate the typical application circuit
shown on page 1. Satisfactory frequency
response of the circuit, seen in figure 2,
validates the above procedure.
GENERAL OVERVIEW
Loop Compensation Example 2- A converter
utilizing a SP6126 has a 6.8uH inductor and
a 150uF, 82mΩ Aluminum Electrolytic
capacitor. Determine whether Type-III
compensation is needed.
From equation (2) f_ESRZERO = 13kHz. From
equation (3) f_DBPOLE = 5 kHz. Since the
condition specified in (1) is not met, Type-III
compensation has to be used by adding
external components RZ and CZ. Using
equation (4) CZ is calculated 160pF (use
150 pF). Since f_ESRZERO ÷ f_DBPOLE is
approximately 3, RZ has to be set at 30kΩ.
Figure 2- Satisfactory frequency response of typical application circuit shown on page
1. Crossover frequency fc is 80kHz with a corresponding phase margin of 65 degrees.
Mar 29-07 RevD
SP6126: TSOT-6 PFET Buck Controller
5
 2007 Sipex Corporation