L7981 STMicroelectronics, L7981 Datasheet - Page 21

• Manufacturer Part Number: L7981
• Description: Switching Converters, Regulators & Controllers 3A Step-Down Reg 3A DC 4.5-28V 250Khz
• Manufacturer: STMicroelectronics

Specifications of L7981

• Output Voltage: 0.6 V to 3 V
• Output Current: 3 A
• Input Voltage: 4.5 V to 28 V
• Switching Frequency: 250 KHz
• Operating Temperature Range: - 55 C to + 150 C
• Mounting Style: SMD/SMT
• Duty Cycle (max): 100 %
• Package / Case: QFPN-8
• Low Dropout Operation: 100% duty cycle
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

L7981
Equation 20
Figure 10. Type III compensation network
In
and the open loop gain (G
Figure 11. Open loop gain: module Bode diagram
The guidelines for positioning the poles and the zeroes and for calculating the component
values can be summarized as follow:
1.
2.
Figure 11
Choose a value for R
Choose a gain (R
the Bode diagram of the PWM and LC filter transfer function (G
f
P0
4
/R
=
0
1
1
LOOP
) in order to have the required bandwidth (BW), that means:
,
, usually between 1 kΩ and 5 kΩ.
Doc ID 15182 Rev 3
f
(f) = G
P1
=
----------------------------- -
2π R
PW0
⋅
1
3
· G
⋅
C
LC
3
,
(f) · G
f
P2
TYPEIII
=
------------------------------------------- -
2π R
⋅
(f)) are drawn.
4
1
⋅
------------------- -
C
C
Application informations
4
4
+
⋅
C
C
5
5
PW0
· G
LC
(f))
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