Vicor Micro Family of DC-DC Converter - Manual (Page 54)

Design Guide & Applications Manual
For Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies
Maxi, Mini, Micro Design Guide Rev 4.9 vicorpower.com
Page 53 of 88
Apps. Eng. 800 927.9474 800 735.6200
11. Filter Input Attenuator Module (FIAM) Family
+S
+OUT
SC
–S
–OUT –IN
PR
PC
+IN
Note: The FIAM is shown in the on state. To disable,
open the connection between ON/OFF and –Out.
External Reverse
Polarity Protection
FIAM
–IN
EMI
GND
NC
+IN +OUT
NC
NC
ON
OFF
–OUT
Mini, Maxi, Micro
DC-DC Converter
F1
0.2 µF
Input C1
4,700 pF
4,700 pF
0.01 µF
0.01 µF
Figure 11–1 — Typical application (FIAM)
+OUT
-OUT -IN
+IN
EMI
Filter
Charge Pump /
Control
ON/OFF
EMI GND
Transient
Suppression
Q1
Q2
Figure 11–2 — Block diagram (FIAM)
Description:
The FIAM family of front-end modules (Figure 11–1)
provides EMI filtering, transient protection, and inrush
current limiting in DC-DC applications. The FIAM enables
designers using Vicor Maxi, Mini, and Micro DC-DC con-
verters, and in select cases VI Chip
® based devices, to
meet the transient immunity and EMI requirements of the
standards referenced in the respective model datasheet.
Theory of Operation:
Refer to the simplified FIAM block diagram Figure 11-2.
Internally, the FIAM employs a transient suppressor directly
across the input. A passive EMI filter that is tuned to
attenuate both common-mode and differential-mode
conducted emissions follow this.
When the FIAM ON/OFF control pin is tied to - OUT the
device is set to "ON" and will provide an output upon
application of input voltage.
When power is applied, the charge pump / control circuit
drives the gate of the MOSFET in series with the positive
rail (Q1). The charge pump limits the time rate of change
of the gate bias voltage, which results in a controlled
voltage ramp-up - this limits the rate at which the external
output capacitor is charged, thereby limiting the system
inrush current.
During normal operation Q1 is fully enhanced - essentially
a closed switch.
Surge protection is accomplished by robbing gate charge
of the Q1 by the bottom MOSFET Q2. During this
condition, the source terminal of the Q1 follows the gate,
offset by the gate threshold voltage. A transient surge
event at the input, or drain terminal of the Q1 is therefore
attenuated and absorbed by Q1 while in the source
follower mode. As a result, the transient surge is not
propagated to the output of the FIAM.
Removing the ON/OFF connection shuts down the charge
pump and turns off Q1.