LTC3816_15 Datasheet, PDF (30/44 Pages) Linear Technology – Single-Phase Wide VIN Range DC/DC Controller for Intel IMVP-6/IMVP-6.5 CPUs

LTC3816
APPLICATIONS INFORMATION
output voltage is ramped down, the controller continues
to hold the regulator output and PWRGD low until the
VR_ON pin toggles or the input supply resets.
During a VID transition, the power good comparators
are masked for 100µs. In deeper sleep mode (25µs after
DPRSLPVR pin transitions high), the power good com-
parators are disabled and PWRGD stays high unless the
switcher output voltage rises above its overvoltage fault
threshold OVF or the controller detects that the regulator
output voltage is 370mV lower than its nominal value.
The LTC3816 PWRGD pin can be configured for wire-OR
operation. Shorting PWRGD to ground externally triggers
a latchoff function. The regulator forces the output to a
zero voltage condition and stays in this state until either
the VR_ON pin or the input supply resets.
VRTT# and Thermal Shutdown
The LTC3816 includes a thermal monitoring circuit that
senses the potential at the RPTC pin. An internal 100µA
pull-up current source connects to an external nonlinear
PTC thermistor through this pin. At room temperature, the
low resistance PTC creates a low voltage at the RPTC pin.
At high temperatures, the PTC resistance increases expo-
nentially. If the resulting RPTC voltage is higher than 0.47V,
it trips the thermal monitor comparator, causing the open-
drain pin VRTT# to pull low signaling an overtemperature
1000
BG
BF
BE
100
BD
BC
BB
BA
10
AR
AS
event. The controller continues its normal operation with
no disruption to the output voltage. To reset this thermal
comparator, the voltage at the RPTC pin must drop below
0.1V. To accurately reflect the system temperature, the
nonlinear PTC thermistor should be mounted as close as
thermally possible to the hottest device, e.g., the inductor
or the MOSFET. To prevent the switching noise from af-
fecting the thermal sensing circuit, add a small capacitor
near the RPTC pin.
Figure 17 shows the Murata PTC PRF18 series typical re-
sistance-temperature characteristics. At room temperature,
all parts have about 470Ω nominal resistance. At higher
temperatures, the resistance increases exponentially. An
overtemperature event is detected by the LTC3816 when
the PTC thermistor ’s resistance exceeds 4.7k. By selecting
the appropriate thermistor from the series, this thermal
monitoring threshold can be set anywhere from 65°C to
145°C with 10°C resolution.
The LTC3816 includes a second thermal protection feature.
If the LTC3816 die temperature is higher than 150°C, the
controller pulls down the VRTT# pin. Under this condition
the CPU should initiate its thermal management opera-
tion. To untrip the VRTT# flag, the die temperature must
be dropped below 130°C. If the LTC3816 die temperature
exceeds 165°C, the driver is disabled and the controller is
latched in a thermal shutdown state until the power supply
is cycled or the VR_ON input toggles.
1
0
–20 0
20 40 60 80 100 120 140 160
TEMPERATURE (°C)
3816 F17
Figure 17. Murata Nonlinear PTC PRF18 Series Typical
Resistance-Temperature Characteristics. Extracted From
Murata PTC PRF18**471QB1RB Data Sheet
3816f
30