L6910 STMicroelectronics, L6910 Datasheet - Page 8

• 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
Overcurrent protection is performed by the device comparing the drop across the high side MOS, due to the
R
upper MOS. Thus the overcurrent threshold (I
Where the typical value of I
R
overcurrent protection this relationship must be satisfied:
Where I is the inductance ripple current and I
In case of over current detectionthe soft start capacitor is discharged with constant current (10 A typ.) and when
the SS pin reaches 0.5V the soft start phase is restarted. During the soft start the over-current protection is al-
ways active and if such kind of event occurs, the device turns off both mosfets, and the SS capacitor is dis-
charged again (after reaching the upper threshold of about 4V). The system is now working in HICCUP mode,
as shown in figure 8. After removing the cause of the over-current, the device restart working normally without
power supplies turn off and on.
Figure 8. Hiccup Mode
4.6 Inductor Design
The inductance value is defined by a compromise between the transient response time, the efficiency, the cost
and the size. The inductor has to be calculated to sustain the output and the input voltage variation to maintain
the ripple current I
culated with this relationship:
Where f
the ripple current vs. the output voltage for different values of the inductor, with V
Increasing the value of the inductance reduces the ripple current but, at the same time, reduces the converter
response time to a load transient. If the compensation network is well designed, the device is able to open or
close the duty cycle up to 100% or down to 0%. The response time is now the time required by the inductor to
change its current from initial to final value. Since the inductor has not finished its charging time, the output cur-
rent is supplied by the output capacitors. Minimizing the response time can minimize the output capacitance
required.
8/29
DSON
dsON
, with the voltage across the external resistor (R
(also the variation with temperature) and the minimum value of I
SW
CH1 = SS; CH4 = Inductor current
is the switching frequency, V
L
between 20% and 30% of the maximum output current. The inductance value can be cal-
OCS
is 200 A. To calculate the R
I
IN
P
L
is the input voltage and V
=
I
I
OUTMAX
P
P
OUTMAX
) can be calculated with the following relationship:
V
----------------------------- -
=
IN
f
sw
R
-------------------------------- -
–
OCS
V
OCS
R
is the maximum output current.
+
OUT
I
dsON
L
---- -
2
Figure 9. Inductor Ripple Current vs. Vout
) connected between the OCSET pin and drain of the
I
I
OCS
=
V
-------------- -
OCS
V
I
OUT
PEAK
IN
9
8
7
6
5
4
3
2
1
0
value it must be considered the maximum
0 .5
OUT
is the output voltage. Figure 9 shows
OCS
. To avoid undesirable trigger of
Output V oltage [V ]
1.5
IN
= 5V and V
L=1.5 H, Vin=12V
2 .5
L=3 H, Vin=5V
IN
= 12V.
L=2 H,
Vin=12V
L=3 H,
Vin=12V
3 .5
L=1.5 H,
Vin=5V
L=2 H,
Vin=5V