Datasheet

MAX17501 60V, 500mA, Ultra-Small, High-Efciency,
Synchronous Step-Down DC-DC Converter
www.maximintegrated.com
Maxim Integrated │ 13
Detailed Description
The MAX17501 synchronous step-down regulator oper-
ates from 4.5V to 60V and delivers up to 500mA load
current. Output voltage regulation accuracy meets ±1.7%
over temperature.
The device uses a peak-current-mode control scheme.
An internal transconductance error amplifier generates an
integrated error voltage. The error voltage sets the duty
cycle using a PWM comparator, a high-side current-sense
amplifier, and a slope-compensation generator. At each
rising edge of the clock, the high-side p-channel MOSFET
turns on and remains on until either the appropriate or
maximum duty cycle is reached, or the peak current limit
is detected.
During the high-side MOSFET’s on-time, the inductor
current ramps up. During the second half of the switching
cycle, the high-side MOSFET turns off and the low-side
n-channel MOSFET turns on and remains on until either
the next rising edge of the clock arrives or sink current
limit is detected. The inductor releases the stored energy
as its current ramps down, and provides current to the
output (the internal low R
DSON
pMOS/nMOS switches
ensure high efficiency at full load).
This device also integrates enable/undervoltage lockout
(EN/UVLO), adjustable soft-start time (SS), and open-
drain reset output (RESET) functionality.
PFM Operation
TheA andBversionsof theMAX17501 featurea PFM
scheme to improve light load efficiency. At light loads,
once the part enters PFM mode, the inductor current is
forced to a fixed peak of 125mA (typical) every clock cycle
until the output rises to 103.3% of nominal voltage. Once
output reaches 103.3% of nominal voltage, both high-
side and low-side FETs are turned off and the part enters
hibernate operation until the load discharges output to
101.3% of nominal voltage. Most of the internal blocks
are turned off in hibernate operation to save quiescent
current. Such an operation reduces the effective switch-
ing frequency of the converter at light loads, resulting in
reduced switching losses and improved light load effi-
ciency. The part naturally exits PFM mode when the load
current exceeds 62.5mA (typical).
Linear Regulator (V
CC
)
An internal linear regulator (V
CC
) provides a 5V nominal
supply to power the internal blocks and the low-side
MOSFET driver. The output of the V
CC
linear regulator
should be bypassed with a 1μF ceramic capacitor to
GND.Thedeviceemploysanundervoltage-lockoutcircuit
that disables the internal linear regulator when V
CC
falls
below 3.7V (typical). The internal V
CC
linear regulator can
source up to 40mA (typical) to supply the device and to
power the low-side gate driver.
Operating Input Voltage Range
The maximum operating input voltage is determined by
the minimum controllable on-time and the minimum oper-
ating input voltage is determined by the maximum duty
cycle and circuit voltage drops. The minimum and maxi-
mum operating input voltages for a given output voltage
should be calculated as:
OUT OUT(MAX) DCR
IN(MIN)
MAX
OUT(MAX)
V (I (R 0.47))
V
D
(I 0.73)
+ ×+
=
+×
=
×
OUT
IN(MAX)
SW (MAX) ON(MIN)
V
V
ft
where V
OUT
is the steady-state output voltage, I
OUT(MAX)
isthemaximumloadcurrent,R
DCR
is the DC resistance
of the inductor, f
SW(MAX)
is the switching frequency (max-
imum) and t
ON(MIN)
is the worst-case minimum switch
on-time (120ns). The following table lists the f
SW(MAX)
and D
MAX
values to be used for calculation for different
versions of the MAX17501:
Overcurrent Protection/HICCUP Mode
The device is provided with a robust overcurrent-pro-
tection scheme that protects the device under overload
and output short-circuit conditions. A cycle-by-cycle peak
current limit turns off the high-side MOSFET whenever
the high-side switch current exceeds an internal limit of
760mA (typ). A runaway current limit on the high-side
switch current at 780mA (typ) protects the device under
high input voltage, short-circuit conditions when there is
insufficient output voltage available to restore the inductor
current that built up during the on period of the step-down
converter. One occurrence of the runaway current limit
triggers a hiccup mode. In addition, if due to a fault condi-
tion, output voltage drops to 71.14% (typ) of its nominal
value any time after soft-start is complete, hiccup mode
is triggered.
PART VERSION f
SW (MAX)
(kHz) D
MAX
MAX17501A/B/E/F/G 640 0.92
MAX17501H 320 0.965