Technical Reference Note (APC08)
Method 2: External DC Source
(continued)
Vo Adjustment to Higher Voltages
Example:
Module version: APC08G03-9 (3V to 6Vin, 2.5Vo).
Requiring to adjust the output voltage from Vo = 2.5V to 3.3V
Vo = 3.3V, V
r
= 0.87V, R
1
= 3.09kΩ, R
2
= 1.69kΩ (from Table 1). Based on Equation (3), Vt = -1.84V.
If application of negative voltage is not desired, the limiting resistor
Rt
can either be changed to a lower value (Rt
= 1kΩ,
such
that Vt = 0.60V per Equation 3), or use Method 1.
Power Good Signal Operation (Option (-9MA)):
PG pin provides an output signal indicating the Vout is
operational (TTL logic signal). It can sink current up to a
max of 5mA and can have a maximum external pull-up
voltage of 6V. Please see recommended setup shown on
Figure 6.
For multiple module configurations, the PG pin/signal
can be used to drive the Enable signal of the other
module for simple sequencing scheme.
Figure 6. PGood setup.
Active Current Share Operation (Option (-9MA)):
Active Current share pin is compatible with APC08 modules only. Connecting this pin directly with the same Pin from another
module guarantees current sharing to within 40% to 60% Iout. Note that this pin is not compatible with competitive modules
that employ active current sharing.
To attain efficient current sharing between like modules, the following points are recommended:
a) The modules to be shared should be located as close as possible into the host card.
b) The copper tracks that connect Vo and GND should at least be 0.60" in width with at least 2 oz. Cu.
c) Due to tolerances of turn-on time characteristics, the initial load current of two APC08 units connected in current sharing
configuration should be less than the OCP point of one module. This is to ensure that the first unit that reaches Vo set-point
is capable of supplying the load current. This also eliminates the possibility of false triggering the OCP protection. The load
current can then be ramped up to the desired loading condition (typical 13A max combined for 2 modules in parallel) after
both outputs have stabilized.
d) Due to mismatches on the output voltage setpoints of the two converters in parallel, it is recommended to maintain a
minimum load current (typical 1.5A) on the output.
MODEL: APC08 SERIES
OCTOBER 4, 2004 - REVISION 03
SHEET 11 OF 23
ASTEC [ Astec America, Inc ]
