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.
It is most important to have the ratio between L and C as low as
possible, i.e. a low characteristic impedance, both at the input and
output, as the power modules have a low energy storage capability.
Use an electrolytic capacitor across the input if the source induct-
ance is higher than 10 mH. Their equivalent series resistance to-
gether with the capacitance acts as a lossless damping filter. Suita-
ble capacitor values are in the range 10–100 mF.
Synchronization (Sync)
Figure 2
It is possible to synchronize the switching frequency to an exter-
nal symmetrical clock signal. The input can be driven by an TTL-
compatible output and referenced to the input pin 17.
Output Voltage Adjust (Vadj
)
Output voltage, VO, 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 VO a resistor should be connected between pin 8/9 and 17,
and to decrease VO a resistor should be connected between pin 8
and 9 (see fig. 3).
Characteristics
min
typ
max
unit
High level
2.2
1.2
0
6.5
2.2
0.4
1.5
688
V
V
Threshold level*)
Low level
1.7
V
Sink current
Sync. frequency
mA
kHz
To increase output voltage:
520
Rounom=4.20×(6.35-VO)/(VO-VI) kW
*)
Rise time <10ns
VI is the initial output voltage when pin 8 and 9 are connected,
VO is the desired output voltage.
Parallel Operation
Paralleling of several converters is easily accomplished by direct
connection of the output voltage terminal pins. The load regula-
tion characteristic is specifically designed for optimum paralleling
performance. Load sharing between converters will be within
To decrease output voltage:
Rodnom=18×(VI-VO)/(VO-2.7) kW
VI is the initial output voltage when pin 8 and 9 are connected,
VO is the desired output voltage.
10%. It is recommended not to exceed P = n × 0.9 × P max
,
O
O
where POmax 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.
Order Info
Version
Part No.
Surface mount
PKF 4211A SI
Through hole
PKF 4211A PI
Figure 3
Current Limiting Protection (Ilim
)
The output power is limited at loads above the output current
limiting threshold (Ilim), specified as a minimum value.
Capacitive Load
Information given in this data sheet is believed to be accurate and reliable. No respon-
sibility is assumed for the consequences of its use nor for any infringement of patents
or other rights of third parties which may result from its use.
No license is granted by implication or otherwise under any patent or patent rights of
Ericsson Microelectronics. These products are sold only according to Ericsson
Microelectronics’ general conditions of sale, unless otherwise confirmed in writing.
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 mF/A of
IO. Connect capacitors at the point of load for best performance.
Specifications subject to change without notice.
EN/LZT 146 79 R1A ©Ericsson Microelectronics AB, June 2001
7
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