MAX15031 Datasheet, PDF (10/16 Pages) Maxim Integrated Products – 80V, 300mW Boost Converter and Current Monitor for APD Bias Applications

80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
FB
CNTRL
SGND
CN
CP
IN
Functional Diagram
V_REF
V_REF
PWR
OUTPUT ERROR AND CURRENT
COMPARATOR
-A
MUX
+A
-C
SWITCH
+C
SOFT-
PEAK CURRENT-LIMIT _CONTROL
COMPARATOR
LOGIC
START
REFERENCE
COMPARATOR
80V
DMOS
SWITCH
CURRENT
SENSE
CHARGE
PUMP
(DOUBLER)
MAX15031
CLK
UVLO
THERMAL
SHUTDOWN
V_REF
BIAS AND
REFERENCE
1x
CURRENT
MONITOR
CURRENT-
LIMIT
ADJUSTMENT
10x
CURRENT
LIMIT
OSCILLATOR
400kHz
LX
PGND
CLAMP
MOUT
RLIM
APD
ILIM
SHDN
BIAS
Detailed Description
The MAX15031 constant-frequency, current-mode, PWM
boost converter is intended for low-voltage systems that
require a locally generated high voltage. This device can
generate a low-noise, high output voltage required for
PIN and varactor diode biasing and LCD displays. The
MAX15031 operates either from +2.7V to +5.5V or from
+5.5V to +11V. For 2.7V to 5.5V operation, an internal
charge pump with an external 10nF ceramic capacitor is
used. For 5.5V to 11V operation, connect CP to IN and
leave CN unconnected.
The MAX15031 operates in discontinuous mode in
order to reduce the switching noise caused by reverse-
voltage recovery charge of the rectifier diode. Other
continuous mode boost converters generate large volt-
age spikes at the output when the LX switch turns on
because there is a conduction path between the out-
put, diode, and switch to ground during the time need-
ed for the diode to turn off and reverse its bias voltage.
To reduce the output noise even further, the LX switch
turns off by taking 10ns typically to transition from ON
to OFF. As a consequence, the positive slew rate of the
LX node is reduced and the current from the inductor
does not “force” the output voltage as hard as would
be the case if the LX switch were to turn off faster.
The constant-frequency (400kHz) PWM architecture
generates an output voltage ripple that is easy to filter.
An 80V vertical DMOS device used as the internal
power switch is ideal for boost converters with output
voltages up to 76V. The MAX15031 can also be used in
other topologies where the PWM switch is grounded,
like SEPIC and flyback converters.
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