ISOTMP35RDFPR datasheet(15/44 Pages) TI2

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7.3.2.2 Driving Capacitive Loads

The ISOTMP35R output stage drives capacitive loads commonly encountered in practical systems, including

ADC inputs, PCB interconnects, and external filtering networks. Without additional series isolation resistance,

the device supports capacitive loads up to 2.2nF while maintaining a phase margin of at least 45°. This condition

enables direct interfacing with many ADC inputs and short PCB traces without requiring external buffering.

In applications with larger capacitive loads, a series isolation resistor (RISO) improves loop stability. The resistor

isolates the output stage from the load capacitance and reduces the phase shift introduced by the load,

preventing oscillation or excessive peaking. Figure 7-2 shows the simulated phase margin as a function of

load capacitance and RISO.

Load Capacitance (F)

100

120

10p

100p

10n

100n



100





100



200



300



400



500



600



700



800



900



1000



Figure 7-2. Simulated Phase Margin vs Capacitive Load for Different RISO Values

When RISO is greater than or equal to 300Ω, the device maintains a phase margin greater than or equal to 45°

across the full capacitive load range, enabling stable operation independent of load capacitance. This behavior

simplifies system design by removing the need to tightly control load capacitance in applications with long PCB

traces, cables, or large input filtering capacitors. Figure 7-3 illustrates a typical implementation using RISO to

isolate the output from a large capacitive load.

VOUT

VDD

Thermal Diodes

–

CLOAD

VDD

(3.1V to 34V)

CBYPASS

ISOTMP35R

RISO

GND

ADC

RFILTER

CFILTER

GND

To High

Capacitive Load

Figure 7-3. Driving Capacitive Loads Using Series Isolation Resistor (RISO)

Table 7-1 provides recommended RISO values for typical capacitive load ranges. The values are derived from

the phase margin behavior shown in Figure 7-2 and provide practical design guidance for maintaining stable

operation.

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ISOTMP35R

SNIS244A – SEPTEMBER 2025 – REVISED MAY 2026

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