IRF7807PBF Datasheet, PDF (4/8 Pages) International Rectifier – HEXFET® Chip-Set for DC-DC Converters

IRF7807/APbF
For the synchronous MOSFET Q2, R is an im-
ds(on)
portant characteristic; however, once again the impor-
tance of gate charge must not be overlooked since it
impacts three critical areas. Under light load the
MOSFET must still be turned on and off by the con-
trol IC so the gate drive losses become much more
significant. Secondly, the output charge Q and re-
oss
verse recovery charge Q_rr both generate losses that
are transfered to Q1 and increase the dissipation in
that device. Thirdly, gate charge will impact the
MOSFETs’ susceptibility to Cdv/dt turn on.
The drain of Q2 is connected to the switching node
of the converter and therefore sees transitions be-
tween ground and V . As Q1 turns on and off there is
in
a rate of change of drain voltage dV/dt which is ca-
pacitively coupled to the gate of Q2 and can induce
a voltage spike on the gate that is sufficient to turn
the MOSFET on, resulting in shoot-through current .
The ratio of Q_gd/Q_gs1 must be minimized to reduce the
potential for Cdv/dt turn on.
Spice model for IRF7807 can be downloaded in ma-
chine readable format at www.irf.com.
Figure 2: Q_oss Characteristic
Typical Mobile PC Application
The performance of these new devices has been tested
in circuit and correlates well with performance predic-
tions generated by the system models. An advantage
of this new technology platform is that the MOSFETs
it produces are suitable for both control FET and syn-
chronous FET applications. This has been demon-
strated with the 3.3V and 5V converters. (Fig 3 and
Fig 4). In these applications the same MOSFET IRF7807
was used for both the control FET (Q1) and the syn-
chronous FET (Q2). This provides a highly effective
cost/performance solution.
3.3V Supply : Q1=Q2=IRF7807
5V Supply : Q1=Q2=IRF7807
93
95
92
91
94
90
93
89
92
88
87
Vin = 10V
86
Vin = 14V
85
Vin = 24V
84
91
Vin = 10V
90
Vin = 14V
Vin=24V
89
1
1.5
2
2.5
3
3.5
4
4.5
5
1
1.5
2
2.5
3
3.5
4
4.5
5
Load Current (A)
Load Current (A)
Figure 3
4
Figure 4
www.irf.com