Rainbow Electronics MAX17409 - Manual (Page 11)

MAX17409
1-Phase Quick-PWM GPU Controller
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Pin Description (continued)
PIN NAME FUNCTION
7 THRM
Comparator Input for Thermal Protection. THRM connects to the positive input of an internal
comparator. The comparator’s negative input connects to an internal resistive voltage-divider that
accurately sets the THRM threshold to 30% of the V
CC voltage. Connect the output of a resistor-
divider and thermistor-divider (between V CC and GND) to THRM with the values selected so the
voltage at THRM falls below 30% of V
CC
(1.5V when V
CC
= 5V) at the desired high temperature.
8 TON
Switching Frequency-Setting Input. An external resistor (R TON ) between the input power source and
TON sets the switching frequency (f SW = 1/t SW ) according to the following equation used to
determine the nominal switching period:
t SW = 16.3pF x (R TON + 6.5k )
TON enters a high impedance in shutdown to reduce the input quiescent current. If the TON current
is less than 10µA, the MAX17409 disables the controller, sets the TON OPEN fault latch, and pulls
DH and DL low.
9 PWRGD
Open-Drain Power-Good Output. The MAX17409 forces PWRGD low when SHDN is pulled low. After
the controller is properly powered up, PWRGD becomes a high-impedance output as long as the
feedback voltage is in regulation and the startup blanking time has expired.
PWRGD becomes active 5ms after the MAX17409 reaches the VID target. The MAX17409 pulls
PWRGD low when shutdown (
SHDN = GND) is pulled low, during startup, and during shutdown
transitions.
The PWRGD upper threshold is blanked during any downward output-voltage transition that occurs
when the MAX17409 is in skip mode (SKIP = V
CC ). PWRGD remains blanked until the transition-
related PWRGD blanking period expires and the controller detects the output is in regulation (error-
amplifier edge occurs).
Note: The pullup resistance on PWRGD causes additional shutdown current.
10 SHDN
Shutdown Control Input. Connect to V CC for normal operation. Connect to ground to put the
controller into the low-power 1µA (max) shutdown state. During startup, the controller ramps up the
output voltage with a 1.56mV/µs slew rate to the selected target voltage. During the shutdown
transition, the MAX17409 softly ramps down the output voltage with a 1.56mV/µs slew rate. Forcing
SHDN to 11V ~ 13V disables overvoltage protection, undervoltage protection, and thermal
shutdown, and clears the fault latches.
11–16 G0–G5
Low-Voltage (1.0V Logic) VID DAC Code Inputs. The G0–G5 inputs do not have internal pullups.
These 1.0V logic inputs are designed to interface directly with the µP. The output voltage is set by
the DAC code indicated by the logic-level voltages on G0–G5.
17 PGND Power Ground. Ground connection for the DL driver.
18 DL
Low-Side Gate-Driver Output. DL swings from V DD to PGND. DL is forced low in shutdown. DL is
also forced low when an output overvoltage fault is detected, overriding any negative current-limit
condition that might be present. DL is forced low in skip mode after detecting an inductor current
zero crossing.
19 V DD
Driver-Supply Voltage Input. V DD supplies power to the low-side gate driver (DL) and to the internal
BST switch used to refresh the BST capacitor. Connect V DD to the 4.5V to 5.5V system supply
voltage. Bypass V DD to PGND with a 1µF or greater ceramic capacitor.
20 BST
Boost Flying Capacitor Connection. BST provides the upper supply rail for the DH high-side gate
driver. An internal switch between V
DD and BST charges the flying capacitor while the low-side
MOSFET is on (DL pulled high and LX pulled to ground).
21 LX
Inductor Connection. LX serves as the lower supply rail for the DH high-side gate driver. The
MAX17409 also uses LX as the input to the zero-crossing comparator.