ISPPAC-POWR1208-01TN44I LATTICE SEMICONDUCTOR, ISPPAC-POWR1208-01TN44I Datasheet - Page 20

• Manufacturer Part Number: ISPPAC-POWR1208-01TN44I
• Description: ISP CONTROLLER, 1208, TQFP44, 5V
• Manufacturer: LATTICE SEMICONDUCTOR

Specifications of ISPPAC-POWR1208-01TN44I

• Input Voltage: 2.7V To 5.5V
• Digital Ic Case Style: TQFP
• No. Of Pins: 44
• Operating Temperature Range: -40°C To +85°C
• Svhc: No SVHC (15-Dec-2010)
• Operating Temperature Max: 85°C
• Operating Temperature: RoHS Compliant

Lattice Semiconductor
Predicting MOSFET Turn-on Time
Because the ispPAC-POWR1208P1’s MOSFET output drivers source a precise and well-defined output current, it
becomes possible to predict MOSFET gate rise times if one knows the value of the load capacitance presented by
the MOSFET being driven. The other method is by relating the total gate charge to the gate-to-source voltage.
Figure 9. 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 9, a V
to the product of current (I) and time (t
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 10. 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 gate voltage V
from 0V to 10V in slightly over 3 milliseconds, which agrees to within 25% of our predicted value, well within the lim-
its of device-to-device variation.
G
) will be 10V in this condition. The device’s gate-to-source voltage (V
GS
t
CHARGE-TIME
of 6.7V corresponds to ~40 nC of gate charge (Q
CHARGE-TIME
6.7
0
9
6
3
S
0
) will be 3.3V when the device is fully switched on, while the gate voltage
t
Q
CHARGE-TIME
G
=
, Total Gate Charge (nC)
20
) when current is constant, gate charging time can be expressed
10.9 x 10
i
40 x 10
=
20
dQ
dt
40
-9
=
-6
C
A
Q
I
G
= 3.7 x 10
60
ispPAC-POWR1208P1 Data Sheet
GS
) will therefore be 6.7V. Reading across
-3
s
G
). Because charge is equal
G
rising
(1)
(2)
(3)