MAX15059 Datasheet, PDF (13/15 Pages) Maxim Integrated Products – 76V, 300mW Boost Converter and Current Monitor for APD Bias Applications

76V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
Diode Selection
The MAX15059’s high switching frequency demands a
high-speed rectifier. Schottky diodes are recommended
for most applications because of their fast recovery time
and low forward-voltage drop. Ensure that the diode’s
peak current rating is greater than the peak inductor cur-
rent. Also, the diode breakdown voltage must be greater
than VOUT.
Output Filter Capacitor Selection
For most applications, use a small output capacitor of
0.1FF or greater. To achieve low output ripple, a capaci-
tor with low ESR, low ESL, and high capacitance value
should be selected. If tantalum or electrolytic capacitors
are used to achieve high capacitance values, always
add a smaller ceramic capacitor in parallel to bypass the
high-frequency components of the diode current. The
higher ESR and ESL of electrolytic capacitors increase
the output ripple and peak-to-peak transient voltage.
Assuming the contribution from the ESR and capacitor
discharge equals 50% (proportions may vary), calculate
the output capacitance and ESR required for a specified
ripple using the following equations:
C _OUT[µF]
=
0.5
I_OUT
x ∆V_OUT

^t _S

−
I_LPEAK x L _OPTIMUM
(V_OUT − V_{IN_MIN})



ESR[mΩ] = ^{0.5 x ∆VOUT}
I_OUT
For very-low-output-ripple applications, the output of the
boost converter can be followed by an RC filter to further
reduce the ripple. Figure 2 shows a 100I, 0.1FF (RF CF)
filter used to reduce the switching output ripple to 1mVP-
P ^{with a 0.1mA load or 1mV}P-P ^{with a 4mA load. The}
output voltage regulation resistive divider must remain
connected to the diode/output capacitor node.
Use X7R ceramic capacitors for more stability over the
full temperature range.
VIN = 2.8V
TO 5.5V
L1
CIN
IN
CNTRL
D1
LX
RF
VOUT
SHDN
CIN
MAX15059
FB
R2
COUT
CF
R1
PGND
BIAS
SGND
Figure 2. Typical Operating Circuit with RC Filter
Input-Capacitor Selection
Bypass IN to PGND with a 1FF (min) ceramic capacitor.
Depending on the supply source impedance, higher val-
ues may be needed. Make sure that the input capacitors
are close enough to the IC to provide adequate decou-
pling at IN as well. If the layout cannot achieve this,
add another 0.1FF ceramic capacitor between IN and
PGND in the immediate vicinity of the IC. Bulk aluminum
electrolytic capacitors may be needed to avoid chatter-
ing at low-input voltage. In case of aluminum electrolytic
capacitors, calculate the capacitor value and ESR of the
input capacitor using the following equations:
C_IN[µF]
=
η
x
V_OUT
V_{IN_MIN}
x I_OUT
x 0.5 x
∆V_IN

^t S

−
I_LPEAK x L _OPTIMUM x V_OUT
V_{IN_MIN}(V_OUT − V_{IN_MIN})



ESR[mΩ] = ^{0.5 x ∆VIN x η x VIN_MIN}
V_OUT x I_OUT
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