Analog Devices Linear ADI Power SCP-LT3094-EVALZ Demo Manual page 4

DEMO MANUAL SCP-LT3094-EVALZ
PGFB PIN CONFIGURATION
To achieve a very low 1/f corner, C4 may need to be sized
as high as 22µF , which dramatically increases the startup
time. To counter this, the set pin current is increased from
100µA to 2mA whenever PGFB voltage is less than 300mV.
If fast startup is not desired, set R5 to 0W.
If fast startup is desired, program enable divider R5 and
R6 such that PGFB is guaranteed to be above 300mV
when the set pin is at its desired voltage. A good rule of
thumb is to choose a transition voltage from 2mA to
100µA of set pin current roughly 10% lower than the de-
sired output voltage to account for resistor and reference
tolerance variation.
Use the following table to program the PGFB if fast startup
is desired, setting R6 to 10kΩ for the closest 1% resistor
value.
Table 4. PGFB Configuration
V (V) R5 (Ω)
OUT
0.8 14.0k
0.9 16.9k
1.0 20.0k
1.2 26.1k
1.5 34.8k
1.8 44.2k
2.0 53.6k
2.5 64.9k
3.0 80.6k
3.5 107k
4.0 110k
4.5 124k
5.0 140k
5.5 154k
6.0 169k
6.5 187k
7.0 200k
7.5 215k
8.0 232k
8.5 243k
9.0 261k
4
V (V) R5 (Ω)
OUT
9.5 274k
10.0 287k
10.5 301k
11.0 316k
11.5 332k
12.0 348k
12.5 365k
13.0 383k
13.5 392k
14.0 412k
14.5 422k
15.0 442k
15.5 453k
16.0 475k
16.5 487k
17.0 499k
17.5 511k
18.0 536k
18.5 549k
19.0 562k
19.5 576k
VOLTAGE INPUT-TO-OUTPUT CONTROL (VIOC)
CONFIGURATION
VIOC functionality allows the LT3094 to directly modulate
a preceding switching regulator feedback to maintain a
constant overhead voltage. For the LT3094, a 1.0V drop
provides a good balance between power loss and PSRR
figure of merit.
The VIOC pin is tied directly to pin 1 of the VIOC header,
and when using a compatible switching regulator, the
VIOC line must be connected by populating the series re-
sistor to drive the top of the feedback network. Refer to
the corresponding appendix page for details on calcula-
tion.
IMPORTANT: The LTC3094 cannot be used to drive buck
regulators if configured as inverting buck. Plugging the
SCP-LT3094-EVALZ into an inverting buck board will short
the regulator.
Rev. 0