SP6127 Просмотр технического описания (PDF) - Signal Processing Technologies

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SP6127

High-Voltage, Step-Down Controller in TSOT6

Signal Processing Technologies 

______________________________________________________ GENERAL OVERVIEW

SP6127

Vout

CP1 2pF

CZ2 130pF

RZ2 200k

Vref =0.6V

Error Amplif ier

VF B

RZ

CZ

R1

200k, 1%

R2

Figure 1- RZ and CZ in conjunction with internal compensation components form a Type-

III compensation network

Loop Compensation Example 1- A converter

utilizing a SP6127 has a 3.3µH inductor and a

22µF/5mΩ ceramic capacitor. Determine

whether Type-III compensation is needed.

From equation (2) fESRZERO = 1.45MHz. From

f equation (3) DBPOLE = 18.4 kHz. Since the

condition specified in (1) is not met, Type-III

compensation must be used by adding

external components RZ and CZ. Using

equation (4) CZ is calculated to be 34pF (use

33pF). 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 the SP6127 has a 3.3µH inductor and

a 220µF, 82mΩ Aluminum Electrolytic

capacitor. Determine whether Type-III

compensation is needed.

From equation (2) fESRZERO = 8.8kHz. From

f equation (3) DBPOLE = 5.9kHz. Since the

condition specified in (1) is not met, Type-III

compensation needs to be used by adding

external components RZ and CZ. Using

equation (4) CZ is calculated 108pF (use 100

f f pF). Since ESRZERO / DBPOLE is approximately 2,

RZ must be set at 40kΩ.

Figure 2- Satisfactory frequency response of typical application circuit shown on page 1.

Crossover frequency fc is 100kHz with a corresponding phase margin of 60 degrees.

June 26, 2007

SP6127 TSOT-6 PFET Buck Controller

Page 5

 2007 Sipex Corporation

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