Texas Instruments ISO35T Small EVM ISO35TEVM-434 ISO35TEVM-434 Scheda Tecnica
Codici prodotto
ISO35TEVM-434
V
S
OSC
FF
4.7
F
m
Common Variations
Figure 2. Simplified Transformer Driver
A pair of Schottky diodes and a bulk capacitor build a full-wave rectifier providing the input voltage for the
TPS76333 linear voltage regulator.
TPS76333 linear voltage regulator.
This low-dropout (LDO) voltage regulator offers the benefits of low dropout voltage, low-power operation,
and miniaturized packaging. The regulator features low dropout voltages and quiescent currents compared
to conventional LDO regulators. Offered in a 5-terminal, small-outline, integrated-circuit SOT-23 package,
the TPS76333 is ideal for cost-sensitive designs and for applications where board space is at a premium.
and miniaturized packaging. The regulator features low dropout voltages and quiescent currents compared
to conventional LDO regulators. Offered in a 5-terminal, small-outline, integrated-circuit SOT-23 package,
the TPS76333 is ideal for cost-sensitive designs and for applications where board space is at a premium.
A combination of new circuit design and process innovation has enabled the usual PNP pass transistor to
be replaced by a PMOS pass element. Because the PMOS pass element behaves as a low-value resistor,
the dropout voltage is very low (typically 300 mV at 150 mA of load current) and is directly proportional to
the load current. Because the PMOS pass element is a voltage-driven device, the quiescent current is
very low (140
be replaced by a PMOS pass element. Because the PMOS pass element behaves as a low-value resistor,
the dropout voltage is very low (typically 300 mV at 150 mA of load current) and is directly proportional to
the load current. Because the PMOS pass element is a voltage-driven device, the quiescent current is
very low (140
µ
A maximum) and is stable over the entire range of output load current (0 mA to 150 mA).
The TPS76333 also features a logic-enabled sleep mode to shut down the regulator, reducing quiescent
current to 1
current to 1
µ
A maximum at T
J
= 25
°
C. The TPS76333 output provides a regulated 3.3-V power supply to
the ISO35T bus-side circuitry (V
CC2
) as shown in
Although not required, a 0.047-
µ
F or larger ceramic bypass input capacitor, connected between IN and
GND and located close to the TPS763xx, is recommended to improve transient response and noise
rejection. A higher-value electrolytic input capacitor may be necessary if large, fast-rise-time load
transients are anticipated and the device is located several inches from the power source.
rejection. A higher-value electrolytic input capacitor may be necessary if large, fast-rise-time load
transients are anticipated and the device is located several inches from the power source.
Like all low-dropout regulators, the TPS76333 requires an output capacitor connected between OUT and
GND to stabilize the internal loop control. The minimum recommended capacitance value is 4.7
GND to stabilize the internal loop control. The minimum recommended capacitance value is 4.7
µ
F and
the equivalent series resistance (ESR) must be between 0.3
Ω
and 10
Ω
. Capacitor values of 4.7
µ
F or
larger are acceptable, provided the ESR is less than 10
Ω
. Solid tantalum electrolytic, aluminum
electrolytic, and multilayer ceramic capacitors are all suitable, provided they meet the requirements
described previously. Most of the commercially available 4.7-
described previously. Most of the commercially available 4.7-
µ
F surface-mount solid tantalum capacitors,
including devices from Sprague, Kemet, and Nichico, meet the ESR requirements stated previously.
3
Common Variations
Powering the ISO35T requires a 1CT : 1.5CT transformer (T1) to assure sufficient headroom for the
TPS76333 LDO to provide a regulated 3.3-V output. The external transformer used with the ISO35T must
have a center-tapped primary winding. The turns ratio of the transformer must provide the minimum
required output voltage at the maximum anticipated load current with the minimum input voltage.
TPS76333 LDO to provide a regulated 3.3-V output. The external transformer used with the ISO35T must
have a center-tapped primary winding. The turns ratio of the transformer must provide the minimum
required output voltage at the maximum anticipated load current with the minimum input voltage.
lists suitable transformers for the circuit in
Table 1. Recommended Isolation Transformers
Manufacturer
1:1.5 Transformer
Coilcraft
DA2303-AL
Murata
782485/55C
2
Isolated, Full-Duplex, 1-Mbps, 3.3-V to 3.3-V RS-485 Interface
SLUU470B
–
December 2010
–
Revised June 2011
Copyright
©
2010
–
2011, Texas Instruments Incorporated