L5983TR STMicroelectronics, L5983TR Datasheet - Page 18

• Manufacturer Part Number: L5983TR
• Description: IC REG SW 1.5A STEPDOWN 8-VFQFPN
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L5983TR

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 18 V
• Current - Output: 1.5A
• 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
• For Use With: 497-6386 - BOARD EVAL FOR L5983
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-6860-2; L5983TR

Application information
5.4
18/43
Compensation network
The compensation network has to assure stability and good dynamic performance. The loop
of the L5983 is based on the voltage mode control. The error amplifier is a voltage
operational amplifier with high bandwidth. So, by selecting the compensation network the
E/A is considered as ideal, that is, its bandwidth is much larger than that of the system.
The transfer functions of the PWM modulator and the output LC filter are studied (see
Figure
(COMP pin) to the OUT pin, results:
Equation 10
where V
generates a sawtooth amplitude directly proportional to the input voltage, that is:
Equation 11
In this way the PWM modulator gain results constant and equal to:
Equation 12
The synchronization of the device with an external clock provided trough the SYNCH pin
can modify the PWM modulator gain (see
and how to keep it constant in spite of the external synchronization)
The transfer function on the LC filter is given by:
Equation 13
where:
Equation 14
9). The transfer function of the PWM modulator, from the error amplifier output
S
is the sawtooth amplitude. As seen in
f
LC
=
----------------------------------------------------------------------- -
2π
⋅
L C
G
⋅
LC
Doc ID 13005 Rev 7
s ( )
OUT
1
G
=
⋅
PW0
------------------------------------------------------------------------ -
1
1
+
G
V
+
S
PW0
----------------------------
2π Q f ⋅
=
-------------- -
R
Section 4.1
ESR
=
OUT
V
-------- -
V
1
⋅
IN
K V
s
s
+
=
⋅
,
------------------------- -
2π f
Section
=
V
-------- -
V
LC
IN
IN
s
--- -
K
1
⋅
f
s
+
zESR
zESR
=
⎛
⎝
to understand how this gain changes
------------------ -
2π f
9
4.1, the voltage feed forward
s
=
⋅
LC
------------------------------------------- -
2π ESR C
⎞
⎠
⋅
2
1
⋅
OUT
L5983