MAX16930 Datasheet, PDF (16/29 Pages) Maxim Integrated Products – 2MHz, 36V, Dual Buck with Preboost and 20μA Quiescent Current

MAX16930/MAX16931
2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
Preboost
The MAX16930/MAX16931 include an asynchronous
current-mode preboost with adjustable output. This pre-
boost can be used independently, but is ideally suited
for applications that need to stay fully functional during
input voltage dropouts typical for automotive cold-crank
or start-stop.
The preboost is turned on by bringing EN3 high.
EN3 can be used for power-supply sequencing and
implementing a boost timeout to prevent overheating the
components used for the boost converter.
While the boost circuit is essential to maintain func-
tionality during undervoltage events, it reduces system
efficiency. During normal operation, the boost diode dis-
sipates power and the resistive dividers at INS and FB3
sink significant amounts of quiescent current.
Increasing the Efficiency of the
Boost Circuit (TERM)
The MAX16930/MAX16931 provide a feature to improve
the efficiency of the boost circuit when it is not active:
• TERM provides a switch to GND for the INS and FB3
voltage-dividers. This switch opens during standby
mode and shutdown mode to reduce the quiescent
current by 240µA, assuming that resistors used in the
voltage-divider network are in the range of 100kI.
Preboost n-Channel
MOSFET Driver (DL3)
DL3 drives the gate of an external n-channel MOSFET.
The driver is powered by the 5V (typ) internal regulator
(BIAS) or the external bypass supply (EVTVCC). DL3
asserts low during standby mode.
Switching Frequency
in Boost Controller
The preboost switching frequency (f_BOOST) is derived
from the buck controllers switching frequency (f_SW) by set-
ting FOSC. See the Electrical Characteristics table. On the
MAX16930, f_BOOST can be set equal to f_SW by connecting
FBSTSEL to ground or to 1/5fsu by connecting FBSTSEL
to BIAS. The gate driver of the preboost turns on simul-
taneously with the high-side driver of buck 1. FSELBST
should be connected to ground on the MAX16931.
Current Limit in Boost Controller
A current-sense resistor (R_CS), connected CS3P and
CS3N, sets the current limit of the boost converter. The
CS input has a voltage trip level (V_CS) of 120mV (typ).
The low 120mV current-limit threshold reduces the power
dissipation in the current-sense resistor. Use a current-
sense filter to reduce capacitive coupling during turn
on. See the Shunt Resistor Selection in Boost Converter
section.
Thermal-Overload, Overcurrent, and
Overvoltage and Undervoltage Behavior
Thermal-Overload Protection
Thermal-overload protection limits total power dissipation
in the devices. When the junction temperature exceeds
+170NC, an internal thermal sensor shuts down the
devices, allowing them to cool. The thermal sensor turns
on the devices again after the junction temperature cools
by 20NC.
Overcurrent Protection
If the inductor current on the MAX16930 and MAX16931
exceed the maximum current limit programmed at
CS_ and OUT_, the respective driver turns off. In an
overcurrent mode, this results in shorter and shorter high-
side pulses.
A hard short results in a minimum on-time pulse every
clock cycle.
Choose the components so they can withstand the short-
circuit current if required.
Overvoltage Protection
The devices limit the output voltage of the buck convert-
ers by turning off the high-side gate driver at approxi-
mately 115% of the regulated output voltage. The output
voltage needs to come back in regulation before the
high-side gate driver starts switching again.
Maxim Integrated
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