722BG Datasheet, PDF (6/10 Pages) Burr-Brown (TI) – DUAL ISOLATED DC/DC CONVERTER

INSTALLATION AND
OPERATING INSTRUCTIONS
Typical application connections for the 722 are shown in
Figures 1 and 2. Primary power (V_IN) is applied at the P+ and
V– terminals. The common or ground for V_IN may be con-
nected to either P+ or V–; the only requirement is that P+ and
V+ must be positive with respects to V–.
Power for the internal oscillator and switch drivers is derived
from the primary power by a voltage dropping resistor, R₁.
The value of R₁ as a function of V_IN is shown in the Typical
Characteristics section. Alternately, voltage for the V+ termi-
nal can be obtained from a separate source. V+ should be
+5V to +7.5V positive with respect to V–. If a separate source
is used, the V+ input must be applied before the P+ input in
order to avoid possible damage to the unit. P+ and V+ must
remain positive with respect to V– at all times (including
transients). If necessary, diode clamps should be attached
across these inputs.
The E pin enables the converter when connected to V+ and
disables it when connected to V–.
An external capacitor, C (0.47µF ceramic), is used to reduce
input ripple. It should be connected as close to the P+ and V–
pins as practical. Input leads to these terminals should also
be kept as short as possible. External shielding may be
appropriate in applications where RFI at the 900kHz nominal
oscillator frequency is a problem because the 722 is not
internally shielded.
Each output is filtered with an internal 0.22µF capacitor.
Output ripple voltage can be reduced below the specified
value by adding external capacitors up to 10µF between
each output and its common.
DISCUSSION
OUTPUT CURRENT RATINGS
At rated output voltage accuracy, the 722 is capable of
providing 64mA divided among its four outputs⁽¹⁾. A minimum
average output current of 3mA is recommended at each
output to maintain voltage accuracy.
Output channels⁽²⁾ can be connected in series or parallel for
higher output voltage or current.
ISOLATION CONFIGURATIONS
The fact that the two outputs of the 722 are isolated from the
input and from each other allows both two-port and three-port
isolation connections.
Figure 1 shows TI’s 3650 optically coupled isolation amplifier
connected in three-port configuration. One of the 722 chan-
nels provides power to the 3650 input. The other channel
supplies power to the 3650 output. The amplifier input and
output are isolated from each other and the system power
supply common. In this configuration, the 722 channel-to-
channel isolation specification applies to the amplifier input-
to-output voltage.
O/P Com
I/P Com
+V_O1 P+
C₁
C
–V_O1 V+
+V_O2 E
C₂
–V_O2 V–
722
FIGURE 1. Three-Port Isolation.
+15V
R₁
V_IN
Com
Power
Supply
Common
NOTES: (1) “Output” denotes a single output terminal (+V or –V) and its
associated common. (2) “Channel” denotes a pair of outputs (+V and –V) and
their associated common.
6
722
www.ti.com
SBVS016A