6

HUMMER SERIES

40 OR 70 WATT

®

PIN CONNECTIONS

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

C=

2P∆t

where

:

2

–

V2

2

)

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

1075.2

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.

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).

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 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.

FLAG FUNCTIONS

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.

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.

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.