L6910 STMicroelectronics, L6910 Datasheet - Page 22

• 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
10 APPLICATION IDEA 2: POSITIVE BUCK-BOOST REGULATOR 3V TO 13.2V
In some applications the input voltage changes in a very wide range while the output must be regulated to a
fixed value. In this case a Buck-Boost topology can be required in order to keep the output voltage in regulation.
The schematic below shows how to implement a Buck-Boost regulating 5V at the output from both 3.3V and 5V
and 12V input buses.
In a Buck-Boost topology the current is delivered to the output during the OFF phase only. So, for a given current
limit, the maximum output current depends strongly on the duty cycle. Assuming a 100% efficiency and neglect-
ing the current ripple across the inductor, the relationship betweent the current limit and the maximum output
current is the following:
Where I
The worst case is with D
The worst case is with V
Obviously, since the efficiency is lower than 100% and the ripple is usually not negligible, the maximum output
current is always lower than the value calculated in the above formula
Figure 30. Positive buck-boost regulator 3V to 13.2V input / 5V 2.5A Output Circuit
22/29
VIN (3.3V-5V-12V BUSES)
VCC (12V BUS)
GNDCC
GNDCC
GNDIN
GNDIN
INPUT / 5V 2.5A OUTPUT
LIM
is the current limit and D is the duty cycle of the application.
C8
C6
G1
INMIN
MAX
R7
C7
C7
. Since, in a Buck-Boost application, D is given by the following formula:
.
C5
EAREF
D1
VCC
GND
OSC
SS
7
4
2
8
15
12
5
L6910/A
C9
BOOT
U1
C10
R1
I
OMAX
3
R5
R6
D
OCSET
6
C3
11
10
14
13
=
=
9
1
---------------------- -
V
I
LIM
C4
VREF
PGND
IN
UGATE
PHASE
LGATE
PGOOD
V
+
O
V
1 D
O
–
C12
Q1
Q2
Q2
R4
R3
D2
C11
L1
Q3
C1- C2
Q4
C13- 14
C13
- 14
R2
VOUT ( 5V 2.5A )
GNDOUT