L6722TR STMicroelectronics, L6722TR Datasheet - Page 14

• Manufacturer Part Number: L6722TR
• Description: IC BUCK ADJ 2A TRPL 36VFQFPN
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L6722TR

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 3
• Voltage - Output: Adj to 0.8V
• Current - Output: 2A
• Frequency - Switching: 100kHz
• Voltage - Input: 12V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 36-VFQFN, 36-VFQFPN
• Power - Output: 3.5W
• Operating Temperature Range: - 40 C to + 125 C
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-5904-2

5 Driver section
5
5.1
Figure 5.
14/34
4000
3500
3000
2500
2000
1500
1000
500
0
50
Driver section
The integrated high-current drivers allow using different types of power MOS (also multiple
MOS to reduce the equivalent RdsON), maintaining fast switching transition.
The drivers for the high-side mosfets use BOOTx pins for supply and PHASEx pins for return.
The drivers for the low-side mosfets use the VCC pin for supply and PGND pin for return.
The controller embodies a anti-shoot-through and adaptive dead-time control to minimize low
side body diode conduction time maintaining good efficiency saving the use of Schottky diodes:
when the high-side mosfet turns off, the voltage on its source begins to fall; when the voltage
reaches 2V, the low-side mosfet gate drive is suddenly applied. When the low-side mosfet turns
off, the voltage at LGATEx pin is sensed. When it drops below 1V, the high-side mosfet gate
drive is suddenly applied. If the current flowing in the inductor is negative, the source of high-
side mosfet will never drop. To allow the low-side mosfet to turn-on even in this case, a
watchdog controller is enabled: if the source of the high-side mosfet doesn't drop, the low side
mosfet is switched on so allowing the negative current of the inductor to recirculate. This
mechanism allows the system to regulate even if the current is negative.
Power conversion input is flexible: 5V, 12V bus or any bus that allows the conversion (See
Section
Power dissipation
L6722 embeds high current mosfet drivers for both high side and low side mosfets: it is then
important to consider the power that the device is going to dissipate in driving them in order to
avoid overcoming the maximum junction operative temperature. In addition, since the device
has an exposed pad to better dissipate the power, the thermal resistance between junction and
ambient consequent to the layout is also important: thermal pad need to be soldered to the
PCB ground plane through several VIAs in order to facilitate the heat dissipation.
Two main terms contribute in the device power dissipation: bias power and drivers' power.
●
HS=1xSTS12NH3LL; LS=1xSTS25NH3LL
HS=1xSTS12NH3LL; LS=2xSTS25NH3LL
HS=1xSTD55NH2LL; LS=1xSTD95NH02L
HS=2xSTD55NH2LL; LS=2xSTD95NH02L
100
Dissipated power
Device Power (P
pins and it is simply quantifiable as follow (assuming to supply HS and LS drivers with the
same VCC of the device):
150
Switching frequency [kHz] per phase
7.3) can be chosen freely.
L6722; Rgate=0; Rmosfet=0
200
250
300
DC
350
) depends on the static consumption of the device through the supply
400
P
450
DC
500
=
V
550
CC
⋅
4000
3500
3000
2500
2000
1500
1000
(
500
I
0
CC
50
+
HS=1xSTS12NH3LL; LS=1xSTS25NH3LL
HS=1xSTS12NH3LL; LS=2xSTS25NH3LL
HS=1xSTD55NH22L; LS=1xSTD95NH02L
HS=2xSTD55NH22L; LS=2xSTD95NH02L
100
3
⋅
150
I
BOOTx
L6722; Rhs=2.2; Rls=3.3; Rmosfet=1
Switching Frequency per phase [kHz]
200
)
250
300
350
400
450
500
L6722
550