Figure 2
Input and Output Impedance
Both the source impedance of the power feeding and the load
impedance will interact with the impedance of the DC/DC
power module.
Due to the low energy storage capability of the power module,
it is very important to maintain a low characteristic impedance
at the input and output of the module i.e. a low ratio between
L and C.
Use an electrolytic capacitor across the input if the source
inductance is higher than 10
µH.
Their equivalent series
resistance together with the capacitance acts as a lossless
damping filter. Suitable capacitor values are in the range 10–
100
µF.
Synchronization (Sync)
It is possible to synchronize the switching frequency to an
external symmetrical clock signal. The input can be driven by
an TTL-compatible output and referenced to the input pin 17.
Characteristics
High level
Threshold level
*)
Low level
Sink current
Sync. frequency
*)
Output Voltage Adjust (V
adj
)
Output voltage, V
O
, can be adjusted by using an external
resistor or other external circuitry. If other circuitry is used,
the slew rate has to be limited to maximum 5 V/ms. If pins
8 and 9 are not connected together the output will decrease
to a low value. To increase V
O
a resistor should be connected
between pin 8/9 and 17, and to decrease V
O
a resistor should be
connected between pin 8 and 9 (see fig. 3).
To increase output voltage:
R
ounom
=4.3×(15.25-V
O
)/(V
O
-V
I
) kΩ
V
i
is the initial output voltage when pin 8 and 9 are connected,
V
O
is the desired output voltage.
To decrease output voltage:
R
odnom
=16.5×(V
I
-V
O
)/(V
O
-8.85) kΩ
V
i
is the initial output voltage when pin 8 and 9 are connected,
V
O
is the desired output voltage.
min
2.2
1.2
0
typ
max
6.5
Unit
V
V
V
mA
kHz
1.7
2.2
0.4
1.5
520
688
Rise time <10ns
Parallel Operation
Paralleling of several converters is easily accomplished by
direct connection of the output voltage terminal pins. The load
regulation characteristic is specifically designed for optimum
paralleling performance. Load sharing between converters will
be within ±10%. It is recommended not to exceed P
O
= n ×
0.9 × P
Omax
, where P
Omax
is the maximum converter output
power and n the number of paralleled converters, to prevent
overloading any of the converters and thereby decreasing the
reliability performance.
Ordering Information
Version
Surface mount
Part No.
4221A SI
Figure 3
Current Limiting Protection (I
lim
)
The output power is limited at loads above the output current
limiting threshold (I
lim
), specified as a minimum value.
Capacitive Load
The PKF series has no maximum limit for capacitive load
on the output. The power module may operate in current
limiting mode during start-up, affecting the ramp-up and the
start-up time. For optimum start performance we recommend
maximum 100
µF/A
of I
O
. Connect capacitors at the point of
load for best performance.
EN/LZT 146 040 R1A © Ericsson Power Modules AB, October 2003
7
ERICSSON [ ERICSSON ]
