L5985TR STMicroelectronics, L5985TR Datasheet - Page 24

• 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

Application information
24/37
Equation 22
Where f
Equation 23
and Vs is the saw-tooth amplitude. The voltage feed forward keeps the ratio Vs/Vin constant.
3.
Equation 24
4.
Equation 25
For example with V
ESR = 50 mΩ, the type II compensation network is:
Equation 26
In
37 kHz and the phase margin is 46°.
Figure 15
Calculate C
Then calculate C
(BW):
ESR
is the ESR zero:
is shown the module and phase of the open loop gain. The bandwidth is about
4
R
by placing the zero one decade below the output filter double pole:
1
OUT
=
3
1.1kΩ
in order to place the second pole at four times the system bandwidth
= 3.3 V, V
,
Doc ID 13006 Rev 5
R
R
C
2
IN
4
5
=
f
ESR
=
= 12 V, I
=
249Ω
C
⎛
⎝
------------------------------------------------------------- -
2π R
f
----------- -
4
ESR
f
=
LC
⋅
=
,
------------------------------------------- -
2π ESR C
⎞
⎠
------------------------------ -
2π R
4
O
2
R
⋅
⋅
⋅
= 2 A, L = 15 μH, C
4
C
⋅
----------- -
f
BW
ESR
C
=
10
4
4
1
4
⋅
10kΩ
4 BW
⋅
⋅
⋅
f
⋅
LC
-------- - R
V
V
OUT
IN
S
,
⋅
–
C
1
1
4
=
68nF
OUT
,
= 330 μF,
C
5
=
68pF
L5985