L5987 STMicroelectronics, L5987 Datasheet - Page 23

• Manufacturer Part Number: L5987
• Description: IC REG STEPDOWN 3A 8VFQFPN
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L5987

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.6 V ~ 18 V
• Current - Output: 3A
• Frequency - Switching: 250kHz
• Voltage - Input: 2.9 V ~ 18 V
• Operating Temperature: -40°C ~ 150°C
• Mounting Type: Surface Mount
• Package / Case: 8-VFQFN, Exposed Pad
• Output Voltage: 0.6 V
• Output Current: 3 A
• Output Power: 1.5 W
• Input Voltage: 2.9 V to 18 V
• Switching Frequency: 250 KHz
• Mounting Style: SMD/SMT
• Duty Cycle (max): 100 %
• Low Dropout Operation: 100 % duty cycle
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

L5987
Equation 22
where K is the feed forward constant and 1/K is equals to 9.
3.
Equation 23
4.
Equation 24
5.
Equation 25
The suggested maximum system bandwidth is equals to the switching frequency divided by
3.5 (F
For example with V
the type III compensation network is:
In
71 kHz and the phase margin is 46°.
R
1
Figure 13
=
Calculate C
Calculate C
Set also the first pole at four times the system bandwidth and also the second zero at
the output filter double pole:
4.99kΩ
SW
/3.5), anyway lower than 100 kHz if the F
,
is shown the module and phase of the open loop gain. The bandwidth is about
R
4
5
2
by placing the zero at 50% of the output filter double pole frequency (f
by placing the second pole at four times the system bandwidth (BW):
=
OUT
1.1kΩ
= 3.3 V, V
R
,
3
R
=
3
Doc ID 14972 Rev 3
-------------------------- -
4 BW
----------------- 1
=
⋅
f
C
LC
220Ω
IN
5
R
1
= 12 V, I
=
–
R
------------------------------------------------------------- -
2π R
C
,
4
4
,
R
⋅
=
=
4
BW K
----------------- - R
4
=
O
-------------------------- -
π R
⋅
f
⋅
3.3kΩ
= 3 A, L = 10 μH, C
LC
C
⋅
C
C
4
1
4
4
⋅
3
⋅
4 BW
SW
⋅
=
f
LC
,
⋅
---------------------------------------- -
2π R
1
is set higher than 500 kHz.
C
⋅
3
–
=
3
1
1
3.3nF
⋅
4 BW
⋅
,
OUT
Application information
C
4
= 22 μF, ESR < 1 mΩ,
=
10nF
,
C
5
=
180pF
23/41
LC
):