Since the TPS7H1111 output voltage is
equal to the SS_SET voltage (minus any offset error), it is also possible to
configure the TPS7H1111 by providing a voltage on SS_SET. As shown in Figure 8-2, a voltage source, VSET, is fed to SS_SET. A DAC can be used as the
voltage source to enable a configurable voltage control.
A few unique considerations should be
taken into account when using this method:
- When a voltage source is
provided on SS_SET, instead of relying on the ultra-low noise reference
current, the noise of VSET is passed to the output through the
unity gain error amplifier. It may be advisable to use an RC filter between
VSET and SS_SET as shown to minimize noise.
- Since the TPS7H1111 output
voltage directly follows SS_SET, there will be no soft-start during startup.
It is recommended to control the VSET voltage slew rate to ensure
desired soft-start time. An RC filter between VSET and the SS_SET
may help with this slew rate control.
- The SS_SET pin will output a
nominal 100 μA during operation and 2.1 mA during "soft-start" (when
VFB_PG < VFB_PG(rising)). In order to handle
this current, a shunt resistor may be required.