L5985TR STMicroelectronics, L5985TR Datasheet - Page 19

• Manufacturer Part Number: L5985TR
• Description: IC REG SW 2A STEP DOWN 8-VFQFPN
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L5985TR

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 18 V
• Current - Output: 2A
• Frequency - Switching: 250kHz ~ 1MHz
• Voltage - Input: 2.9 ~ 18 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-VFQFN, 8-VFQFPN
• Power - Output: 1.5W
• Output Voltage: 3 V
• Output Current: 2 A
• Input Voltage: 2.9 V to 18 V
• Switching Frequency: 220 KHz to 275 KHz
• Operating Temperature Range: - 40 C to + 150 C
• Mounting Style: SMD/SMT
• Duty Cycle (max): 100 %
• For Use With: 497-6387 - BOARD EVAL FOR L5985
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-6861-2; L5985TR

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