Datasheet

MAX16952
Maxim Integrated | 12www.maximintegrated.com
36V, 2.2MHz Step-Down Controller
with Low Operating Current
Detailed Description
The MAX16952 is a current-mode, synchronous PWM
buck controller designed to drive logic-level MOSFETs.
The device tolerates a wide input voltage range from
3.5V to 42V and generates an adjustable 1V to 10V or
fixed 5V output voltage. This device can operate in
dropout mode, making it ideal for automotive and
industrial applications with undervoltage transients.
The internal switching frequency is adjustable from
1MHz to 2.2MHz with an external resistor and can be
synchronized to an external clock. The high switching
frequency reduces output ripple and allows the use of
small external components. The device operates in
both fixed-frequency PWM mode and a low quiescent
current skip mode. While working in skip mode, the
operating current is as low as 50μA.
The device features an enable logic input to disable the
device and reduce its shutdown current to 10μA.
Protection features include cycle-by-cycle current limit,
overvoltage detection, and thermal shutdown. The
device also features integrated soft-start and a power-
good monitor to help with power sequencing.
Supply Voltage Range (SUP)
The supply voltage range (V
SUP
) of the MAX16952 is com-
patible to the typical automotive battery voltage range
from 3.5V to 36V and can tolerate up to 42V transients.
Slow Ramp-Up of the Input Voltage
If the input voltage (V
SUP
) ramps up slowly, the device
operates in dropout mode until V
SUP
is greater than the
regulated output voltage. The dropout mode is detected
by monitoring high-side FET on for eight clock cycles.
Once dropout mode is detected, the controller issues a
forced low-side pulse at the rising edge of switching
clock to refresh the BST capacitor. This maintains the
proper BST voltage to turn on the high-side MOSFET
when the device is in dropout mode.
System Enable (EN) and Soft-Start
An enable control input (EN) activates the MAX16952
from its low-power shutdown mode. EN is compatible
with inputs from automotive battery level down to
3.5V. The high-voltage compatibility allows EN to be
connected to SUP, KEY/KL30, or the inhibit pin (INH)
of a CAN transceiver.
A logic-high at EN turns on the internal regulator. Once
V
BIAS
is above the internal lockout level, V
UVL
= 3.1V (typ),
the controller starts up with a 5ms fixed soft-start time.
Once regulation is reached, PGOOD goes high
impedance.
A logic-low at EN shuts down the device. During shut-
down, the internal linear regulator and gate drivers turn
off. Shutdown is the lowest power state and reduces
the quiescent current to 10μA (typ).
To protect the low-side MOSFET during shutdown, the
step-down regulator cannot be enabled until the output
voltage drops below 1.25V. An internal 30Ω pulldown
switch helps discharge the output. If the EN pin is tog-
gled low then high, the switching regulator shuts down
and remains off until the output voltage decays to
1.25V. At this point, the MAX16952 turns on using the
soft-start sequence.
Fixed 5V Linear Regulator (BIAS)
The MAX16952 has an internal 5V linear regulator to
provide its own 5V bias from a high-voltage input supply
at SUP. This bias supply powers the gate drivers for the
external n-channel MOSFETs and provides the power
required for the analog controller, reference, and logic
blocks. The bias rail needs to be stabilized by a 2.2μF or
greater capacitance at BIAS, and can provide up to
45mA (typ) total current.
Oscillator Frequency and
External Synchronization
The MAX16952 provides an internal oscillator
adjustable from 1MHz to 2.2MHz. To set the switching
frequency, connect a resistor from FOSC to SGND. See
the Setting the Switching Frequency section.
The MAX16952 can also be synchronized to an external
clock by connecting the external clock signal to
FSYNC. For proper frequency synchronization,
FSYNC’s input frequency must be at least 10% higher
than the programmed internal oscillator frequency. A
rising clock edge on FSYNC is interpreted as a syn-
chronization input. If the FSYNC signal is lost, the inter-
nal oscillator takes control of the switching rate,
returning to the switching frequency set by the resistor
connected to FOSC. This maintains output regulation
even with intermittent FSYNC signals. The maximum
synchronizable frequency is 2.4MHz.
When FSYNC is connected to SGND, the device oper-
ates in skip mode. When FSYNC is connected to BIAS
or driven by an external clock, the MAX16952 operates
in skip mode during soft-start and transitions to fixed-
frequency PWM mode after soft-start is over.