Rainbow Electronics MAX17036 User Manual
Page 31
MAX17030/MAX17036
1/2/3-Phase Quick-PWM
IMVP-6.5 VID Controllers
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31
Power-on reset (POR) occurs when V
CC
rises above
approximately 2V, resetting the fault latch and prepar-
ing the controller for operation. The V
CC
UVLO circuitry
inhibits switching until V
CC
rises above 4.25V. The con-
troller powers up the reference once the system
enables the controller, V
CC
is above 4.25V, and SHDN
driven high. With the reference in regulation, the con-
troller ramps the output voltage to the boot voltage
(1.1V) at 1/4 the slew rate set by R
TIME
:
where dV
TARGET
/dt = 12.5mV/µs x 71.5k
Ω/R
TIME
is the
slew rate. The soft-start circuitry does not use a variable
current limit, so full output current is available immedi-
ately. CLKEN is pulled low approximately 60µs after the
MAX17030/MAX17036 reach the boot voltage. At the
same time, the MAX17030/MAX17036 slew the output
to the voltage set at the VID inputs at the programmed
slew rate. PWRGD becomes high impedance approxi-
mately 5ms after CLKEN is pulled low. The MAX17030/
MAX17036 automatically operate in pulse-skipping
mode during soft-start, and use forced-PWM operation
during soft-shutdown, regardless of the DPRSLPVR and
PSI configuration.
If the V
CC
voltage drops below 4.25V, the controller
assumes that there is not enough supply voltage to make
valid decisions, and shuts down immediately. DH and DL
are forced low, and CSNI 10
Ω discharge FET is enabled.
Shutdown
When SHDN goes low, the MAX17030/MAX17036
enters low-power shutdown mode. PWRGD is pulled
low immediately, and the output voltage ramps down at
1/4 the slew rate set by R
TIME
:
where dV
TARGET
/dt = 12.5mV/µs x 71.5k
Ω/R
TIME
is the
slew rate. After the output voltage drops to 12.5mV, the
MAX17030/MAX17036 shut down completely—the dri-
vers are disabled (DL1 and DL2 driven low, PWM3 is
three-state, and DRSKP low), the reference turns off,
10
Ω CSNI discharge FET is turned on, and the supply
current drops below 1µA.
When an undervoltage fault condition activates the shut-
down sequence, the protection circuitry sets the fault
latch to prevent the controller from restarting. To clear
the fault latch and reactivate the controller, toggle SHDN
or cycle V
CC
power below 0.5V.
Current Monitor (IMON)
The MAX17030/MAX17036 include a unidirectional
transconductance amplifier that sources current pro-
portional to the positive current-sense voltage. The
IMON output current is defined by:
I
IMON
= G
m(IMON)
x
Σ(V
CSP
- V
CSN
)
where G
m(IMON)
= 1.6mS (typ) and the IMON current is
unidirectional (sources current out of IMON only) for
positive current-sense values. For negative current-
sense voltages, the IMON current is zero.
Connect an external resistor between IMON and GNDS
to create the desired IMON gain based on the following
equation:
R
IMON
= 0.9V/(I
MAX
x R
SENSE(MIN)
x G
m(IMON_MIN)
)
where I
MAX
is defined in the Current Monitor section of
the Intel IMVP-6.5 specification and based on discrete
increments (10A, 20A, 30A, 40A, etc.), R
SENSE(MIN)
is
the minimum effective value of the current-sense ele-
ment (sense resistor or inductor DCR) that is used to
provide the current-sense voltage, and G
m(IMON_MIN)
is the minimum transconductance amplifier gain as
defined in the
Electrical Characteristics
.
The IMON voltage is internally clamped to a maximum
of 1.1V (typ), preventing the IMON output from exceed-
ing the IMON voltage rating even under overload or
short-circuit conditions. When the controller is disabled,
IMON is pulled to ground.
The transconductance amplifier and voltage clamp are
internally compensated, so IMON cannot directly drive
large capacitance values. To filter the IMON signal, use
an RC filter as shown in Figure 1.
Temperature Comparator (
VRHOT)
The MAX17030/MAX17036 also feature an independent
comparator with an accurate threshold (V
HOT
) that
tracks the analog supply voltage (V
HOT
= 0.3V
CC
). This
makes the thermal trip threshold independent of the V
CC
supply voltage tolerance. Use a resistor- and thermistor-
divider between V
CC
and GND to generate a voltage-
regulator overtemperature monitor. Place the thermistor
as close to the MOSFETs and inductors as possible.
Fault Protection (Latched)
Output Overvoltage Protection
The overvoltage-protection (OVP) circuit is designed to
protect the CPU against a shorted high-side MOSFET
by drawing high current and blowing the battery fuse.
The MAX17030/MAX17036 continuously monitor the
output for an overvoltage fault. An OVP fault is detected
if the output voltage exceeds the set VID DAC voltage
by more than 300mV, or the fixed 1.5V (typ) threshold
t
V
dV
dt
TRAN SHDN
OUT
TARGET
(
)
=
(
)
4
t
V
dV
dt
TRAN START
BOOT
TARGET
(
)
=
(
)
4