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

GENERAL OVERVIEW
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.
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.
Nov07-08 RevG
SP6126: TSOT-6 PFET Buck Controller
5
 2008 Exar Corporation