ADP3208C ON Semiconductor, ADP3208C Datasheet - Page 27

• Manufacturer Part Number: ADP3208C
• Description: 7-bit,programmable,dual- Phase,mobile,cpu,synchronous Buck Controller
• Manufacturer: ON Semiconductor

Pulling TTSNS to less than 1 V disables the overvoltage
protection function. In this configuration, VRTT should be tied
to ground.
REVERSE VOLTAGE PROTECTION
Very large reverse current in inductors can cause negative V
voltage, which is harmful to the CPU and other output
components. The ADP3208C provides a reverse voltage
protection (RVP) function without additional system cost. The
V
CSREF pin voltage drops to less than −300 mV, the ADP3208C
triggers the RVP function by disabling all PWM outputs and
driving DRVL1 and DRVL2 low, thus turning off all MOSFETs.
The reverse inductor currents can be quickly reset to 0 by
discharging the built-up energy in the inductor into the input
dc voltage source via the forward-biased body diode of the
high-side MOSFETs. The RVP function is terminated when the
CSREF pin voltage returns to greater than −100 mV.
Sometimes the crowbar feature inadvertently causes output
reverse voltage because turning on the low-side MOSFETs
results in a very large reverse inductor current. To prevent
damage to the CPU caused from negative voltage, the
ADP3208C maintains its RVP monitoring function even after
OVP latch-off. During OVP latch-off, if the CSREF pin voltage
drops to less than −300 mV, the low-side MOSFETs is turned
off. DRVL outputs are allowed to turn back on when the CSREF
voltage recovers to greater than −100 mV.
Figure 37 shows a typical Over Voltage Protection test. FB pin is
shorted to ground causing the control to command a large duty
cycle. The output voltage climbs up. When the output voltage
is climbs 200 mV above the DAC voltage, the PWRGD signal
de-asserts. When the output voltage climbs to 1.7V, Over
Voltage Protection is enabled. In Over Voltage Protection, the
phase 1 and phase 2 low side drive turns on the low side power
MOSFETs. The low side MOSFETs pull the output voltage low
through the power inductor. When the output voltage falls
below -300 mV, Reverse Voltage Protection is enabled. In
Reverse Voltage Protection, all power MOSFETs are turned off.
This protects the CPU from seeing a large negative voltage.
CORE
voltage is monitored through the CSREF pin. When the
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CORE
OUTPUT ENABLE AND UVLO
For the ADP3208C to begin switching, the VCC supply voltage
to the controller must be greater than the V
the EN pin must be driven high. If the VCC voltage is less than
the V
ADP3208C shuts off. In shutdown mode, the controller holds
the PWM outputs low, shorts the capacitors of the SS and
PGDELAY pins to ground, and drives the DRVH and DRVL
outputs low.
The user must adhere to proper power-supply sequencing during
startup and shutdown of the ADP3208C. All input pins must be
at ground prior to removing or applying VCC, and all output
pins should be left in high impedance state while VCC is off.
THERMAL THROTTLING CONTROL
The ADP3208C includes a thermal monitoring circuit to detect
whether the temperature of the VR has exceeded a user-defined
thermal throttling threshold. The thermal monitoring circuit
requires an external resistor divider connected between the
VCC pin and GND. The divider consists of an NTC thermistor
and a resistor. To generate a voltage that is proportional to
temperature, the midpoint of the divider is connected to the
TTSNS pin. An internal comparator circuit compares the
TTSNS voltage to half the VCC threshold and outputs a logic
level signal at the VRTT output when the temperature trips the
user-set alarm threshold. The VRTT output is designed to drive
an external transistor that in turn provides the high current,
open-drain VRTT signal required by the IMVP-6+ specification.
The internal VRTT comparator has a hysteresis of approximately
100 mV to prevent high frequency oscillation of VRTT when
the temperature approaches the set alarm point.
CURRENT MONITOR FUNCTION
The ADP3208C has an output current monitor. The IMON pin
sources a current proportional to the inductor current. A
resistor from IMON pin to FBRTN sets the gain. A 0.1 μF is
Figure 37. Over Voltage Protection and Reverse Voltage Protection
CCUVLO
threshold or the EN pin is a logic low, the
PWRGD
OUTPUT VOLTAGE
LOW SIDE GATE
LOW SIDE GATE
PHASE 2
PHASE 1
ADP3208C
CCOK
threshold and