Datasheet

MAX5066
Configurable, Single-/Dual-Output, Synchronous
Buck Controller for High-Current Applications
______________________________________________________________________________________ 11
Finally, a thermal-shutdown feature protects the device
during thermal faults and shuts down the MAX5066
when the die temperature exceeds +160°C.
Dual-Output/Dual-Phase Select (MODE)
The MAX5066 can operate as a dual-output indepen-
dently regulated buck converter, or as a dual-phase,
single-output buck converter. The MODE input selects
between the two operating modes. When MODE is
grounded (logic low), VEA1 and VEA2 connect to CEA1
and CEA2, respectively (see Figure 1) and the device
operates as a two-output DC-DC converter. When
MODE is connected to REG (logic high), VEA2 is dis-
connected and VEA1 is routed to both CEA1 and CEA2
and the device works as a dual-phase, single-output
buck regulator with each output 180° out of phase with
respect to each other.
Supply Voltage Connections (V
IN
/V
REG
)
The MAX5066 accepts a wide input voltage range at IN
of 5V to 28V. An internal linear regulator steps down V
IN
to 5.1V (typ) and provides power to the MAX5066. The
output of this regulator is available at REG. For V
IN
=
4.75V to 5.5V, connect IN and REG together externally.
REG can supply up to 65mA for external loads. Bypass
REG to AGND with a 4.7µF ceramic capacitor for high-
frequency noise rejection and stable operation.
REG supplies the current for both the MAX5066’s inter-
nal circuitry and for the MOSFET gate drivers (when
connected externally to V
DD
), and can source up to
65mA. Calculate the maximum bias current (I
BIAS
) for
the MAX5066:
where I
IN
is the quiescent supply current into IN (4mA,
typ), Q
GQ1
, Q
GQ2
, Q
GQ3
, Q
GQ4
are the total gate
charges of MOSFETs Q1 through Q4 at V
GS
= 5V (see
Figure 6), and f
SW
is the switching frequency of each
individual phase.
Low-Side MOSFET Driver Supply (V
DD
)
V
DD
is the power input for the low-side MOSFET dri-
vers. Connect the regulator output REG externally to
V
DD
through an R-C lowpass filter. Use a 1Ω resistor
and a parallel combination of 1µF and 0.1µF ceramic
capacitors to filter out the high peak currents of the
MOSFET drivers from the sensitive internal circuitry.
High-Side MOSFET Drive Supply (BST_)
BST1 and BST2 supply the power for the high-side
MOSFET drivers for output 1 and output 2, respectively.
Connect BST1 and BST2 to V
DD
through rectifier
diodes D1 and D2 (see Figure 6). Connect a 0.1µF
ceramic capacitor between BST_ and LX_.
Minimize the trace inductance from BST_ and V
DD
to
rectifier diodes, D1 and D2, and from BST_ and LX_ to
the boost capacitors, C8 and C9 (see Figure 6). This is
accomplished by using short, wide trace lengths.
Undervoltage Lockout (UVLO)/
Power-On Reset (POR)/Soft-Start
The MAX5066 includes an undervoltage lockout
(UVLO) with hysteresis, and a power-on reset circuit for
converter turn-on and monotonic rise of the output volt-
age. The UVLO threshold monitors V
REG
and is inter-
nally set between 4.0V and 4.5V with 200mV of
hysteresis. Hysteresis eliminates “chattering” during
startup. Most of the internal circuitry, including the
oscillator, turns on when V
REG
reaches 4.5V. The
MAX5066 draws up to 4mA (typ) of current before
V
REG
reaches the UVLO threshold.
The compensation network at the current-error ampli-
fiers (CLP1 and CLP2) provides an inherent soft-start of
the output voltage. It includes (R14 and C10) in parallel
with C11 at CLP1 and (R15 and C12) in parallel with
C13 at CLP2 (see Figure 6). The voltage at the current-
error amplifier output limits the maximum current avail-
able to charge the output capacitors. The capacitor at
CLP_ in conjunction with the finite output-drive current
of the current-error amplifier yields a finite rise time for
the output current and thus the output voltage.
Setting the Switching Frequency (f
SW
)
An internal oscillator generates the 180
o
out-of-phase
clock signals required for both PWM modulators. The
oscillator also generates the 2V
P-P
voltage ramps nec-
essary for the PWM comparators. The oscillator fre-
quency can be set from 200kHz to 2MHz by an external
resistor (R
T
) connected from RT/CLKIN to AGND (see
Figure 6). The equation below shows the relationship
between R
T
and the switching frequency:
where R
RT
is in ohms and f
SW(PER PHASE)
= f
OSC
/2.
Use RT/CLKIN as a clock input to synchronize the
MAX5066 to an external frequency (f
RT/CLKIN
). Applying
an external clock to RT/CLKIN allows each PWM section
to work at a frequency equal to f
RT/CLKIN
/2. An internal
comparator with a 1.6V threshold detects f
RT/CLKIN
. If
f
RT/CLKIN
is present, internal logic switches from the
internal oscillator clock, to the clock present at
RT/CLKIN.
f
R
Hz
OSC
RT
=
×25 10
10
.
I IfQQQQ
BIAS IN SW GQ GQ GQ GQ
=+×+++ ()
1234