Installation - 3
35
LOAD
OUTPUT 1/OUTPUT 2
CONNECTOR
+
_
-S - + +S
TWIST LEADS
WIRE RESISTANCE
LENGTH
MUST BE
UNDER 20
INCHES
TWIST PAIR
FIXTURE
CONNECTIONS
Figure 3-4. Remote Sense Connections with Test Fixture
Load Regulation and Voltage Drop in the Remote Sense Leads
The sense leads are part of the dc source’s feedback path and must be kept at a low resistance to maintain
optimal performance. One way to accomplish this is to use larger diameter wires for the sense leads (see
Table 3-2).
If this is impractical, you can account for the voltage regulation and readback error that will occur when
using higher resistance remote sense leads. The voltage load regulation and readback error can be
calculated using the following formula:
∆V = VLD+(RS+
RS+ + 251 )+ VLD- (RS-
RS- + 184 )
where: VLD+ and VLD- are the voltage drops in the + and − load leads.
RS+ and RS- are the resistances of the + and − sense leads.
Minimizing the load lead resistance reduces voltage drops VLD+ and VLD-. ∆V can be further minimized
by decreasing the resistance of the sense leads (RS+ and RS-) as much as possible.
Maintaining Stability while Remote Sensing
The remote sense bandwidth and slew rate of standard dc power sources are adequate for compensating
for load lead voltage drop for slow to moderate rates of load changes. However, the high pulsed current
draw of digital cellular phones presents a challenge to standard dc power sources operating in remote
sense mode. Their bandwidth and slew rate are not adequate for dealing with the 0.05 to 0.2 amp/µs slew
rates imposed by these devices. A large voltage transient occurs at the load, due to the inability of the dc
source to keep up with the rate of load change.
The dc source effectively compensates for load lead voltage drops resulting from very high slew rate load
current transitions. This keeps the remotely sensed output voltage at a relatively constant level. For 0.05
amp/µs to 0.2 amp/µs slew rate loading in typical test applications, the transient voltage is reduced more
than an order of magnitude over that of other standard dc sources.