TPS54162-Q1_15 Datasheet, PDF (22/42 Pages) Texas Instruments – 1-A 60-V STEP-DOWN DC/DC CONVERTER WITH LOW QUIESCENT CURRENT

TPS54162-Q1
SLVSA32C – OCTOBER 2009 – REVISED MAY 2010
Loop Control Frequency Compensation
www.ti.com
Figure 28. Type 3 Compensation
Type 3 Compensation
Type 3 compensation has been used in the feedback loop to improve the stability of the convertor and regulation
in the output in response to the changes in input voltage or load conditions. This becomes important because the
ceramic capacitors used to filter the output have a low Equivalent Series Resistance (ESR). Type 3
compensation is implemented by connecting external resistors and capacitors to the COMP pin (output of the
error amplifier, pin 15) of the device as shown in Figure 28.
The crossover frequency should be less than 1/5th to 1/10th of the switching frequency, and should be greater
than five times the double pole frequency of the LC filter.
f_c < f_sw × (0.1 to 0.2)
(14)
(14)
Where,
f_sw = switching frequency
The modulator break frequencies as a function of the output LC filter are derived from Equation 15 and
Equation 16. The LC output filter gives a double pole that has a –180° phase shift.
f= ¹
LC _2pÖLC
(15)
Where,
L = output inductor
C = output capacitor (C4 in functional block diagram)
The ESR of the output capacitor C gives a "ZERO" that has a 90° phase shift.
f=
1
ESR _{2pC × ESR}
(16)
Where,
ESR = Equivalent series resistance of a capacitor at a specified frequency
The regulated output voltage, V_Reg is given by Equation 17.
V = V _Reg
ref
1 + ^R4
R5
(17)
V_Reg
(18)
22
Submit Documentation Feedback
Copyright © 2009–2010, Texas Instruments Incorporated
Product Folder Link(s): TPS54162-Q1