L5981 STMicroelectronics, L5981 Datasheet - Page 22

• Manufacturer Part Number: L5981
• Description: IC REG SW STEP DOWN 1A 8-VFQFPN
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L5981

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 18 V
• Current - Output: 1A
• 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: 1 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 %
• Low Dropout Operation: 100 % duty cycle
• For Use With: 497-6385 - BOARD EVAL FOR L5981
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Application information
5.4.2
22/37
Type II compensation network
If the equivalent series resistance (ESR) of the output capacitor introduces a zero with a
frequency lower than the desired bandwidth (that is: 2π * ESR * COUT > 1 / BW), this zero
helps stabilize the loop. Electrolytic capacitors show not negligible ESR (> 30 mΩ), so with
this kind of output capacitor the type II network combined with the zero of the ESR allows
stabilizing the loop.
In
Figure 13. Type II compensation network
The singularity of the network are:
In
and the open loop gain (G
Figure 13
Figure 14
the type II network is shown.
the Bode diagram of the PWM and LC filter transfer function (G
f
Z1
=
----------------------------- -
2π R
LOOP
⋅
1
Doc ID 13004 Rev 6
4
(f) = G
⋅
C
4
,
PW0
f
P0
· G
=
LC
0
,
(f) · G
f
P1
TYPEII
=
------------------------------------------- -
2π R
⋅
(f)) are drawn.
4
⋅
1
------------------- -
C
C
4
4
+
⋅
C
C
5
5
PW0
· G
LC
L5981
(f))