L6910 STMicroelectronics, L6910 Datasheet - Page 10

• Manufacturer Part Number: L6910
• Description: IC PWM BUCK BST VM 16SOIC
• Manufacturer: STMicroelectronics

Specifications of L6910

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 230kHz
• Duty Cycle: 100%
• Voltage - Supply: 5 V ~ 12 V
• Buck: Yes
• Boost: Yes
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: -40°C ~ 150°C
• Package / Case: 16-SOIC (3.9mm Width)
• Frequency-max: 230kHz
• Output Voltage: 4 V
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: 497-3656-5; 497-4220-5; 497-4220-5

L6910 - L6910A
Figure 10. Compensation Network
The compensation network consists in the internal error amplifier and the impedance networks Z
C20) and Z
the highest 0dB crossing frequency to have fast response (but always lower than fsw/10) and the highest gain
in DC conditions to minimize the load regulation.
A stable control loop has a gain crossing with -20dB/decade slope and a phase margin greater than 45°. Include
worst-case component variations when determining phase margin.
To locate poles and zeroes of the compensation networks, the following suggestions may be used:
Modulator singularity frequencies:
Compensation network singularity frequency:
10/29
– Put the gain R5/R3 in order to obtain the desired converter bandwidth;
– Place
– Place
– Place
– Place
– Check the loop gain considering the error amplifier open loop gain.
FB
Z1
Z2
P1
P2
(R5, C18 and C19). The compensation network has to provide a closed loop transfer function with
before the output filter resonance
at the output filter resonance
at the output capacitor ESR zero
at one half of the switching frequency;
Z1
P1
LC
=
=
V
=
----------------------- -
R5 C19
---------------------------------------------- -
R5
OSC
-------------------------- -
L C
1
COMPARATOR
⎛
⎝
---------------------------- -
C18
C18 C19
1
PWM
OUT
1
+
V
COMP
C19
LC
R5
;
⎞
⎠
C18
ESR
LC
;
;
C19
+
-
EAREF
ESR
Z2
V
IN
=
=
C20
------------------------------------------ -
L
C
P2
R3
OUT
D03IN1512
-------------------------------- -
ESR C
ESR
R3
R4
=
+
R4
V
----------------------- -
R4 C20
1
1
OUT
OUT
1
C20
IN
(R3, R4 and