Output Voltage Adjust (Vadj
)
Input and Output Impedance
Output voltage, VO, can be adjusted by using an external resis-
tor or other external circuitry. If other circuitry is used, the
slew rate has to be limited to maximum 5 V/ms. To increase
VO a resistor should be connected between pin 8/9 and 11, and
to decrease VO a resistor should be connected between pin 8
and 9 (see fig. 3).
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 re-
sistance together with the capacitance acts as a lossless damping
filter. Suitable capacitor values are in the range 10–100 µF.
To increase output voltage:
Rounom=4.14×(1.28×Voi-Vod)/(Vod-Voi) kΩ
Vi is the initial output voltage when pin 8 and 9 are connected,
Vo is the desired output voltage.
Synchronization (Sync)
To decrease output voltage:
It is possible to synchronize the switching frequency to an ex-
ternal symmetrical clock signal. The input can be driven by an
TTL-compatible output and referenced to the input pin 11.
Iadj = 943×(1-(Vod/Voi)) µA
Vi is the initial output voltage when pin 8 and 9 are connected,
Vo is the desired output voltage.
Characteristics
min
typ
max
Unit
High level
2.2
1.2
0
6.5
2.2
0.4
1.5
688
V
*)
QJOꢀꢁꢂꢃ
Threshold level
1.7
V
Low level
V
Sink current
mA
kHz
1,'
Sync. frequency
*) Rise time <10ns
520
QJOꢀꢄꢅ
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 PO = n ×
power aOnd n the numOber of paralleled converters, to prevent
overloading any of the converters and thereby decreasing the
reliability performance.
@
ꢆ
Figure 2
0.9 × P max where P max is the maximum converter output
,
Current Limiting Protection (Ilim
)
The output power is limited at loads above the output current
limiting threshold (Ilim), specified as a minimum value.
Ordering Information
Capacitive Load
Version
Part No.
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 IO. Connect capacitors at the point of
load for best performance.
Surface mount
4128B SI
EN/LZT 146 089 R1A ©Ericsson Power Modules AB, March 2005
7
ERICSSON [ ERICSSON ]
