EVAL5985 STMicroelectronics, EVAL5985 Datasheet - Page 19

• Manufacturer Part Number: EVAL5985
• Description: BOARD EVAL FOR L5985
• Manufacturer: STMicroelectronics
• Type: DC/DC Switching Converters, Regulators & Controllersr

Specifications of EVAL5985

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 3.3V
• Current - Output: 2A
• Voltage - Input: 3.3 ~ 18V
• Regulator Topology: Buck
• Frequency - Switching: 500kHz
• Board Type: Fully Populated
• Utilized Ic / Part: L5985
• Input Voltage: 2.9 V to 18 V
• Output Voltage: 0.6 V to 16 V
• Product: Power Management Modules
• Silicon Manufacturer: ST Micro
• Silicon Core Number: L5985
• Kit Application Type: Power Management - Voltage Regulator
• Application Sub Type: Step Down Switching Regulator
• Kit Contents: Board
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• For Use With/related Products: L5985
• Other names: 497-6387; EVAL5985

L5985
5.4.1
Type III compensation network
The methodology to stabilize the loop consists of placing two zeros to compensate the effect
of the LC double pole, so increasing phase margin; then to place one pole in the origin to
minimize the dc error on regulated output voltage; finally to place other poles far away the
zero dB frequency.
If the equivalent series resistance (ESR) of the output capacitor introduces a zero with a
frequency higher than the desired bandwidth (that is: 2π * ESR * C
compensation network is needed. Multi layer ceramic capacitors (MLCC) have very low ESR
(< 1 mΩ), with very high frequency zero, so type III network is adopted to compensate the
loop.
In
(f
Equation 16
Equation 17
Figure 10. Type III compensation network
In
and the open loop gain (G
Z1
Figure 10
Figure 11
, f
Z2
) and three poles (f
the type III compensation network is shown. This network introduces two zeros
the Bode diagram of the PWM and LC filter transfer function (G
f
P0
=
f
Z1
0
LOOP
P0
,
=
, f
----------------------------------------------- -
2π C
Doc ID 13006 Rev 5
P1
f
(f) = G
P1
⋅
, f
=
P2
3
⋅
----------------------------- -
2π R
). They expression are:
1
(
PW0
R
⋅
1
1
+
3
· G
R
⋅
C
3
)
LC
3
,
,
(f) · G
f
Z2
f
P2
=
TYPEIII
=
----------------------------- -
2π R
------------------------------------------- -
2π R
⋅
⋅
(f)) are drawn.
1
4
4
⋅
1
⋅
C
------------------- -
C
C
4
4
4
Application information
OUT
+
⋅
C
C
5
5
< 1/BW), the type III
PW0
· G
LC
(f))
19/37