isppac-powr1208 Lattice Semiconductor Corp., isppac-powr1208 Datasheet - Page 18

• Manufacturer Part Number: isppac-powr1208
• Description: In-system Programmable Power Supply Sequencing Controller And Monitor
• Manufacturer: Lattice Semiconductor Corp.

Lattice Semiconductor
Figure 1-8. MOSFET Gate Charge vs. Gate-Source Voltage
Using this method, it becomes straightforward to estimate the gate rise time for a given charging current. As an
example a MOSFET’s source voltage (V
(V
and down the plot of Figure 1-8, a V
equal to the product of current (I) and time (t
expressed as:
For this example, let us assume a charging current of 10.9µA. Gate charging time is given by:
Validation of this result can be seen in the scope plot shown in Figure 1-9. The top set of traces shows gate rise
times for various (5.5µA to 50.3µA) gate drive currents. The trace labeled 10.9µA shows a 0-10V rise time of just
over 3 milliseconds, which agrees to within 25% of our predicted value, well within the limits of device-to-device
variation.
G
) will be 10V in this condition. The device’s gate-to-source voltage (V
GS
t
CHARGE-TIME
0
9
6
3
S
0
of 6.7V corresponds to ~40 nC of gate charge (Q
) will be 3.3V when the device is fully switched on, while the gate voltage
CHARGE-TIME
t
Q
CHARGE-TIME
G
, Total Gate Charge (nC)
20
=
i
=
1-18
10.9 x 10
40 x 10
dQ
dt
) when current is constant, gate charging time can be
40
=
-9
Q
-6
I
C
G
A
= 3.7 x 1
60
GS
ispPAC-POWR1208 Data Sheet
) will therefore be 6.7V. Reading across
G
). Because charge is
(1)
(2)
(3)