EDGE818 Просмотр технического описания (PDF) - Semtech Corporation
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EDGE818 Datasheet PDF : 15 Pages
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Edge818
TEST AND MEASUREMENT PRODUCTS
Application Information (continued)
Driving a Resistive Load
In addition to the VCC and VEE power supply levels, the
“driver high” (VH) and “driver low” (VL) levels used in an
application also have an effect on the total power
dissipation of the device illustrated using Figure 6.
External "Driver High" Buffer
Simplified
Edge818
Output
Stage
VH
Rds(H)
H
L
DOUT IL
RT
Therefore, the per-channel power dissipation due to the
Edge818 driving and resistive load is:
P = [IL(H) x Rds(H) x D + IL(L)] x [Rds(L) x (1–D)]
where
P
= The total power dissipated by the Edge818
as a result of the resistive load, RL [W]
IL(H) = The amount of current required by RL
during a logic “high” state [A]
Rds(H) = The output impedance of the Edge818
driver when driving a logic “high” state [Ω]
D = The normalized amount of time that logic
“high” is driven (Duty Cycle)
IL(L) = The amount of current required by RL
during a logic “low” state [A]
Rds(L) = The output impedance of the Edge818
driver when driving a logic “low” state [Ω]
Rds(L)
VT
VL
External "Driver Low" Buffer
Figure 6. Simplified Functional Schematic of Edge818
Output Stage and External Buffers
The CMOS switches of the Edge818’s output stage have
on-resistance values (depicted by Rds(H) and Rds(L) in
Figure 6) that vary as a function of VH and VL voltage
levels. The amount of current required by the load
impedance, RT, is also a function of the VH and VL voltage
levels as follows:
Switch in Figure 6 is in position “H”:
IL(H) =
VH – VT
Rds(H) + RT
Switch in Figure 6 is in position “L”:
IL(L) =
VL – VT
Rds(L) + RT
2004 Semtech Corp. / Rev. 5, 8/18/04
9
www .semtech.com
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