A5974ADTR STMicroelectronics, A5974ADTR Datasheet - Page 22

• Manufacturer Part Number: A5974ADTR
• Description: IC REG SW STEP-DOWN 2A 8SOIC
• Manufacturer: STMicroelectronics
• Series: -r
• Type: Step-Down (Buck), PWMr

Specifications of A5974ADTR

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.235 V ~ 35 V
• Current - Output: 2A
• Frequency - Switching: 500kHz
• Voltage - Input: 4 V ~ 36 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width) Exposed Pad
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 497-11423-2

Closing the loop
7.3
22/49
PWM comparator
The PWM gain is given by the following formula:
Equation 12
where V
minimum value. A voltage feed-forward is implemented to ensure a constant GPWM. This is
obtained by generating a sawtooth waveform directly proportional to the input voltage V
Equation 13
where K is equal to 0.038. Therefore the PWM gain is also equal to:
Equation 14
This means that even if the input voltage changes, the error amplifier does not change its
value to keep the loop in regulation, therefore ensuring a better line regulation and line
transient response.
In summary, the open loop gain can be expressed as:
Equation 15
Example:
The gain and phase bode diagrams are plotted respectively in
Considering R
If L = 12 µH, C
Finally R
OSCMAX
F
F
F
F
F
F
P1
P2
Z1
PLC
ZESR
0
= 44 kHz
1
= 1.6 kHz
= 9 Hz
= 220 kHz
= 2.5 kHz
= 5.6 kΩ and R
= 20 kHz
is the maximum value of a sawtooth waveform and V
C
OUT
= 4.7 kΩ, C
G s ( )
= 330 µF and ESR = 25 mΩ, the poles and zeroes of A
G
=
PWM
V
Doc ID 018762 Rev 1
2
OSCMAX
G
= 3.3 kΩ.
C
PWM
G
s ( )
= 22 nF and C
PWM
⎛
⎝
=
s ( )
–
s ( )
-------------------------------------------------------------
(
V
V
⋅
OSCMAX
OSCMIN
------------------- - A
R
=
1
R
--- -
K
+
1
2
R
=
2
V
P
⋅
const
–
cc
=
= 150 pF, the poles and zeroes of A
V
K V
O
OSCMIN
s ( ) A
⋅
CC
⋅
LC
)
⎞ s ( )
⎠
Figure 11
OSCMIN
and
Figure
is the
LC
A5974AD
become:
12.
0
CC
are:
.