Datasheet

MAX16932/MAX16933
2.2MHz, 36V, Dual Buck
with 20µA Quiescent Current
14Maxim Integrated
between the PGOOD1 pin and any other external
components. All other pins are compliant with no
additional external components.
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 in the MAX16932/MAX16933
exceeds the maximum current limit programmed at CS_
and OUT_, the respective driver turns off. In an overcur-
rent 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 with-
stand 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.
Design Procedure
Buck Converter Design Procedure
Effective Input Voltage Range in Buck Converters
Although the MAX16932/MAX16933 can operate from
input supplies up to 36V (42V transients) and regulate
down to 1V, the minimum voltage conversion ratio (V
OUT
/
V
IN
) might be limited by the minimum controllable on-
time. For proper fixed-frequency PWM operation and
optimal efficiency, buck 1 and buck 2 should operate in
continuous conduction during normal operating condi-
tions. For continuous conduction, set the voltage conver-
sion ratio as follows:
>
OUT
ON(MIN) SW
IN
V
t × f
V
where t
ON(MIN)
is 50ns (typ) and f
SW
is the switching fre-
quency in Hz. If the desired voltage conversion does not
meet the above condition, pulse skipping occurs to
decrease the effective duty cycle. Decrease the switching
frequency if constant switching frequency is required. The
same is true for the maximum voltage conversion ratio.
The maximum voltage conversion ratio is limited by the
maximum duty cycle (95%).
<
−
OUT
IN DROP
V
0.95
VV
where V
DROP
= I
OUT
(R
ON,HS
+ R
DCR
) is the sum of the
parasitic voltage drops in the high-side path and f
SW
is
the programmed switching frequency. During low drop
operation, the devices reduce f
SW
to 25% (max) of the
programmed frequency. In practice, the above condition
should be met with adequate margin for good load-tran-
sient response.
Setting the Output Voltage
in Buck Converters
Connect FB1 and FB2 to BIAS to enable the fixed buck
controller output voltages (5V and 3.3V) set by a preset
internal resistive voltage-divider connected between
the output (OUT_) and AGND. To externally adjust the
output voltage between 1V and 10V, connect a resis-
tive divider from the output (OUT_) to FB_ to AGND
(see the Typical Operating Circuit). Calculate R
FB_1
and R
FB_2
with the following equation:


= −






OUT_
FB_1 FB_2
FB_
V
RR 1
V
where V
FB_
= 1V (typ) (see the Electrical Characteristics
table).
DC output accuracy specifications in the Electrical
Characteristics table refer to the error comparator’s
threshold, V
FB_
= 1V (typ). When the inductor conducts
continuously, the devices regulate the peak of the output
ripple, so the actual DC output voltage is lower than the
slope-compensated trip level by 50% of the output ripple
voltage.
In discontinuous conduction mode (skip or STDBY active
and I
OUT
< I
LOAD(SKIP)
), the devices regulate the valley
of the output ripple, so the output voltage has a DC regu-
lation level higher than the error-comparator threshold.
Inductor Selection in Buck Converters
Three key inductor parameters must be specified for
operation with the MAX16932/MAX16933: inductance