HUMMER SERIES
40 OR 70 WATT
PIN CONNECTIONS
E
XTERNAL
C
APACITOR
S
ELECTION
H
OLD
U
P
M
ODULE
CAUTION: Do not connect the HUMMER module’s input return pin
to the Cext return. This connection will short the module’s current
limit sense resistor resulting in excessive currents that can also
damage the DC/DC converter.
The external capacitor supplies the energy for the DC/DC
converter’s operation during power failure. Interpoint recommends
CLR-79 or CLR-81 wet slug tantalum capacitors because of their
high CV properties and extended temperature operation. An alter-
native choice is a high quality grade aluminum electrolytic. To
ensure maximum system stability, the capacitors should have a
minimum ESR of 0.25 ohms, a minimum capacitance of 330 uF, and
a maximum capacitance of 1 F.
The capacitance needed and derating required will depend on the
system requirements, the load, and the efficiency of the converter
being supplied power. The amount of capacitance for a given hold-
up time is determined by the formula
I
NHIBIT
F
UNCTION
The HUMMER module’s inhibit pin disables the internal boost
converter when the Inhibit pin is pulled low. This is accomplished by
an external connection to the Vin Return pin or Vout Return pin. The
inhibit open circuit voltage is is 10 V and the short circuit current is
15 mA. It is open-collector TTL or CMOS compatible. The pin is
diode-isolated and can be reverse biased to include the input poten-
tial. Power Fail and Capacitor Charged flags are operable when the
unit is inhibited.
C=
2P∆t
n
(
V12
–
V22
)
FLAG FUNCTIONS
where
:
P
OWER
F
AIL
F
LAG
The Power Fail Flag output is implemented by a comparator moni-
toring the input voltage. (The comparator is also used to inhibit
HUMMER module’s operation; note however, that the flag is func-
tional when the unit is inhibited.) The input voltage threshold is
nominally 14.5 V to indicate that sufficient voltage is present for
operation. The comparator output drives an internal MOSFET buffer
which connects to the external Power Fail pin. The buffer is of an
open drain configuration and requires an external pull-up resistor
and voltage for indication. The maximum recommended pull-up
voltage is 36 V. The maximum short circuit should not exceed 10mA.
The buffer is protected by a shunt zener diode connected between
the drain and the Cext Return. In normal operation, the input voltage
exceeds the 14 V threshold and the output is high (open drain).
When the input voltage is below 12 V the output is low, and the
MOSFET conducts to the Return.
C is required capacitance (in Farads).
P is power to the load (output of converter) to be held up (in watts)
n is the efficiency of the converter at rated load (in %)
∆t
is required hold-up time (in seconds)
V1is charged capacitor voltage (in volts)
V2is low-line voltage of DC/DC converter (in volts)
For a 50 msec hold-up of 30 W output from a converter with a effi-
ciency of 80% and a 16 VDC low line and a 40 V capacitor charge:
C=
(2) • (30) • (0.050)
3
= 2790 µF
;
C=
(0.80) • (40
2
– 16
2
)
1075.2
C
APACITOR
C
HARGED
F
LAG
A Capacitor Charged Flag is implemented by a comparator moni-
toring the HUMMER module’s +Cext terminal. The capacitor voltage
threshold is 36 V, at which point the external capacitor is charged to
80% of its maximum value. When the capacitor discharges, the flag
resets at 20 VDC indicating that approximately 10% of the charge
remains. The comparator output drives a MOSFET buffer amplifier,
and the buffer output connects to the Cap Charged pin. The buffer
is of an open drain configuration and requires a pull-up resistor and
voltage for indication. The maximum recommended pull-up voltage
is 36 V. The maximum short circuit current should not exceed 10
mA. During normal operation, the input is 40 V, exceeding the
threshold, and the output is high (open circuit). When the capacitor
voltage is below 20 V, the output is low, and the MOSFET conducts
to the Return. The HUMMER module must be supplied with a
minimum of 8 VDC for biasing internal circuits to obtain correct
output states.
Note: The output power delivered by the HUMMER module to
deliver 30 W to the load with an 80% efficient converter is 37.5
watts. The HUM-40 is rated to deliver a maximum of 40 watts to
the input of the converter. Interpoint data sheets for individual
converters supply an efficiency curve vs. line and load for each
converter model. In calculations, assume the efficiency rating for
the nominal (usually 28 V) line condition.
Note: If the Capacitor Charged pin is connected to the converter’s
inhibit pin as shown in Figure 3, use 20 V as the low line figure in
the formula.
D
IODE
S
ELECTION AND
C
ONNECTION
An external diode is required for system operation as shown in
Figure 3, with the diode anode connected to the HUMMER module’s
VCS pin and the DC/DC converter’s +V in pin. This diode supplies
input voltage to the converter when the internal voltage control
switch (VCS) is open. The diode should be selected with a minimum
current rating of 5 A and a voltage breakdown rating of 50 V or
greater (similar to Motorola MDR1060 or equivalent).
6
HUM 268621 Rev B
All technical information is believed to be accurate, but no responsibility is
assumed for errors or omissions. Interpoint reserves the right to make changes in
products or specifications without notice. HUMMER is a trademark of Interpoint.
Copyright © 1994 - 2003 Interpoint Corporatation. All rights reserved.
®
CRANE [ Crane Aerospace & Electronics. ]
