A8296SESTR-T Allegro Microsystems Inc, A8296SESTR-T Datasheet - Page 9

• Manufacturer Part Number: A8296SESTR-T
• Description: IC REG LNB SGL SUPPLY 16-QFN
• Manufacturer: Allegro Microsystems Inc

Specifications of A8296SESTR-T

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

A8296
In-Rush Current
At start-up or during an LNB reconfiguration event, a transient
surge current above the normal DC operating level can be pro-
vided by the A8296. This current increase can be as high as the
set output current, for as long as required, up to a maximum of
48 ms.
Tone Generation
A 22 kHz tone is generated internally, and can be controlled on
and off via the TONECTRL pin as shown in figure 2. Note this
tone can be generated under no-load conditions, and does not
require the use of an external DiSEqC filter.
Figure 2. Internal tone, gated by TONECTRL pin
Figure 3. Boost inductor characteristic for the A8296.
TONECTRL
(LNB Ref)
Tone
Single LNB Supply and Control Voltage Regulator
LNB (V)
Component Selection
Boost Inductor
The A8296 is designed to operate with a boost inductor value
of 33 μH ±50%. The error amplifier loop compensation, current
sense gain, and PWM slope compensation were chosen for this
value of inductor. The boost inductor must be able to support the
peak currents required to maintain the maximum LNB output
current without saturating. Figure 3 can be used to determine the
peak current in the inductor given the LNB load current. The
“typical” curve uses V
f = 352 kHz, while the “maximum” curve assumes V
V
Boost Electrolytic Capacitor
The A8296 is designed to operate with a low-ESR electrolytic
boost capacitor of 100 μF ±25% . The ESR of the boost capacitor
must be less than 100 mΩ or the boost converter will be unstable.
General purpose electrolytic capacitors that do not specify an
ESR should be avoided. Allegro recommends an electrolytic
capacitor that is rated to support at least 35 V and has an rms
current rating to support the maximum LNB load. Figure 4 can
be used to determine the necessary rms current rating of the boost
capacitor given the LNB load current. The “typical” curve uses
Figure 4. Boost electrolytic capacitor characteristic for the A8296.
OUT
= 20 V, L = 26 μH, and f = 282 kHz.
IN
= 12 V, V
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
OUT
= 19 V, L = 33 μH, and
IN
= 9 V,
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