Datasheet

UDG-09215
t
PGD
t – Time
V
UV
V
OV
V
FB
V
PGOOD
Track
V
SS
V
SS, FLT, HI
V
SS, steady-state
V
DD
TPS40170
www.ti.com SLUS970A –MARCH 2011–REVISED NOVEMBER 2013
Power Good (PGOOD)
The TPS40170 provides an indication that the output voltage of the converter is within the specified limits of the
regulation as measured at the FB pin. The PGOOD pin is an open-drain signal and pulls low when any condition
exists that would indicate that the output of the supply might be out of regulation. These conditions include:
• V
VFB
is not within the PGOOD threshold limits.
• Soft-start is active, i.e., SS pin voltage is below V
SS,FLT,HIGH
limit.
• An undervoltage condition exists for the device.
• An overcurrent or short-circuit fault is detected.
• An over-temperature fault is detected.
Figure 34 shows a situation where no fault is detected during the startup, (the normal PGOOD situation). It
shows that PGOOD goes high t
PGD
(20 µs, typ.) after all the conditions (listed above) are met.
Figure 34. PGOOD Signal
When there is no power to the device, PGOOD is not able to pull close to GND if an auxiliary supply is used for
the power good indication. In this case, a built-in resistor connected from drain to gate on the PGOOD pull-down
device allows the PGOOD pin to operate like as a diode to GND.
PGND and AGND
NOTE
TPS40170 provides separate signal ground (AGND) and power ground (PGND) pins.
PGND is primarily used for gate driver ground return. AGND is an internal logic signal
ground return. These two ground signals are internally loosely connected by two anti-
parallel diodes. PGND and AGND must be electrically connected externally.
Bootstrap Capacitor
A bootstrap capacitor with a value between 0.1 µF and 0.22 µF must be placed between the BOOT pin and the
SW pin. It should be 10 times higher than MOSFET gate capacitance.
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