PGA281
SBOS664A –MARCH 2013–REVISED JUNE 2013
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POWER SUPPLY
The PGA281 requires three supply voltages: the high-voltage analog supply, the low-voltage output amplifier
supply, and the digital I/O supply. This architecture allows an optimal interface (level-shift) to the different supply
domains.
The high-voltage analog supplies, VSP and VSN, power the high-voltage input stage section. The substrate of
the device is connected to VSN; therefore, it must be connected to the most negative potential.
The low-voltage analog output supplies, VSOP and VSON, operate within the high-voltage supply boundaries
with two minimal limitations:
1. The usable range for VSON is from a minimum 5 V below VSP to as low as VSN. This 5 V provides the
headroom for the output supply voltage of +2.7 V to +5 V. Even with less than a 5-V supply, this voltage
difference is required for proper operation.
2. The common-mode control input, VOCM, requires a voltage at least 2 V less than VSP in order to support
internal rail-to-rail performance.
These limitations are applicable when using a minimum supply or an extremely asymmetrical high-voltage
supply. In most practical cases, VSON is connected to the ground of the system 3-V or 5-V supply.
VSOP can be turned on first or can be higher than VSP without harm, but operation fails if VSP and VSN are not
present.
Observe the maximum voltage applied between VSOP and VSON because there is no internal protection.
Positive digital supply DVDD and digital ground VSON can also be set within the boundaries of VSP and VSN.
However, DVDD must be 1 V less than VSP. DVDD can be turned on without the analog supply being present
and is operational. Observe the maximum supply voltage because there is no internal protection. VSOP can be
connected with DVDD if desired.
The negative digital supply is connected to the VSON pin. Take care if using split supplies on the VSOP and
VSON pin because the logic low and high thresholds are determined by DVDD and VSON. In normal operation,
VSON is connected to the system ground.
VSN is connected to the substrate; therefore, the voltage at VSON must not turn on the substrate diode to VSN.
Use external Schottky diodes from VSON to VSN to prevent this condition.
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