Datasheet

MAX17502 60V, 1A, Ultra-Small, High-Efciency,
Synchronous Step-Down DC-DC Converter
www.maximintegrated.com
Maxim Integrated │ 11
Detailed Description
The MAX17502 synchronous step-down regulator oper-
ates from 4.5V to 60V and delivers up to 1A 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.
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 MAX17502:
Overcurrent Protection/HICCUP Mode
The device is provided with a robust overcurrent-protec-
tion scheme that protects the device under overload and
output short-circuit conditions. A cycle-by-cycle peak cur-
rent limit turns off the high-side MOSFET whenever the
high-side switch current exceeds an internal limit of 1.65A
(typ). A runaway current limit on the high-side switch cur-
rent at 1.7A (typ) protects the device under high input volt-
age, short-circuit conditions when there is insufficient out-
put 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 condition, output
voltage drops to 71.14% (typ) of its nominal value any
time after soft-start is complete, hiccup mode is triggered.
In hiccup mode, the converter is protected by suspend-
ing switching for a hiccup timeout period of 32,768 clock
cycles. Once the hiccup timeout period expires, soft-start
is attempted again. This operation results in minimal
power dissipation under overload fault conditions.
RESET Output
The device includes a RESET comparator to monitor the
output voltage. The open-drain RESET output requires
an external pullup resistor. RESET can sink 2mA of cur-
rent while low. RESET goes high (high impedance) 1024
switching cycles after the regulator output increases
above 95.5% of the designated nominal regulated volt-
age. RESET goes low when the regulator output voltage
drops to below 92.5% of the nominal regulated voltage.
RESET also goes low during thermal shutdown. RESET
is valid when the device is enabled and V
IN
is above 4.5V.
PART VERSION f
SW (MAX)
(kHz) D
MAX
MAX17502E/F/G 640 0.92
MAX17502H 320 0.965