isppac-powr1208 Lattice Semiconductor Corp., isppac-powr1208 Datasheet - Page 17

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

Lattice Semiconductor
ispPAC-POWR1208 Data Sheet
Note that if the clock module is configured as “slave” (i.e. the CLK is an input), the actual time-out of the four timers
is determined by the external clock frequency.
Output Configuration Modes
The output pins for the ispPAC-POWR1208 device are programmable for different functional modes. The four out-
puts HVOUT1-HVOUT4, can be used as FET gate drivers or be programmed as open-drain digital outputs.
Figure 1-7 explains the details of the gate driver mode.
Figure 1-7. Basic Function Diagram for an Output in Gate Driver Mode
I
V
Source
PP
(0.5-50uA)
(8-12V)
Output to
IC Pin
≈ 8kΩ
Digital In
From Sequence
Controller
Figure 1-7 shows an output programmed for gate driver mode. In this mode the output is a current source that is
programmable between 0.5µA to 50µA. The maximum voltage that the output level at the pin will rise is also pro-
grammable. The levels required depend on the gate-to-source threshold of the FET and the supply voltage. The
maximum level needs to be sufficient to turn the gate-to-source threshold on and accommodate for the voltage of
the board also, since the source pin of the FET is tied to the supply of the target board. When the HVOUT pin is
sourcing current, charging a FET gate, the current is programmable between 0.5µA and 50µA. When the driver is
turned to the off state, the driver will sink current. through the 8kΩ resistor.
Predicting MOSFET Turn-on Time
Because the ispPAC-POWR1208’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.
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