MAX1965TEEP Maxim Integrated, MAX1965TEEP Datasheet - Page 25

• Manufacturer Part Number: MAX1965TEEP
• Description: Current & Power Monitors & Regulators
• Manufacturer: Maxim Integrated

shown in Figure 8, a series RC snubber circuit at the
diode increases the damping factor, allowing the ring-
ing to settle quickly. Applications with multiple trans-
former windings require only one snubber circuit on the
highest output voltage.
The diode’s parasitic capacitance can be estimated
using the diode’s reverse voltage rating (V
capability (I
approximation is:
For the EC10QS10 Nihon diode used in Figure 8, the
capacitance is roughly 15pF. The output snubber only
needs to dampen the ringing, so the initial turn-on spike
that occurs during the blanking period is still present. A
100pF capacitor works well in most applications.
Larger capacitance values require more charge, there-
by increasing the power dissipation.
The snubber’s time constant (t
than the 60ns blanking time. A typical RC time constant
of approximately 30ns was chosen for Figure 8:
Under no-load conditions, leakage currents from the
pass transistors supply the output capacitor, even
when the transistor is off. Generally, this is not a prob-
lem since the feedback resistors’ current drain the
excess charge. However, charge may build up on the
output capacitor over temperature, making V
above its set point. Care must be taken to ensure that
the feedback resistors’ current exceeds the pass tran-
sistor’s leakage current over the entire temperature
range.
Careful PC board layout is critical to achieve low
switching losses and clean, stable operation. The
switching power stage requires particular attention.
Follow these guidelines for good PC board layout:
1) Place the power components first, with ground ter-
Minimum Load Requirements (Linear Regulators)
minals adjacent (NL source, C
ble, make all these connections on the top layer
with wide, copper-filled areas. Keep these high-cur-
rent paths short, especially at ground terminals.
O
R
), and recovery time (t
Applications Information
SNUB
______________________________________________________________________________________
PC Board Layout Guidelines
C
DIODE
=
C
t
Tracking/Sequencing Triple/Quintuple
SNUB
SNUB
=
I
0
V
RRM
SNUB
×
=
t
C
RR
30
SNUB
IN
) must be smaller
ns
, C
OUT
RR
RRM
). A rough
). If possi-
), current
LDO
rise
Power-Supply Controllers
2) Mount the MAX1964/MAX1965 adjacent to the
3) Group the gate-drive components (BST diode and
4) All analog grounding must be done to a separate
5) Ensure all feedback connections are short and
6) When trade-offs in trace lengths must be made, it’s
7) Route high-speed switching nodes away from sen-
The linear regulator controllers can be configured to
regulate high output voltages by adding a cascode
transistor to buffer the base-drive output. For example,
to generate an output voltage between 30V and 60V,
add a 2N5550 high-voltage NPN transistor as shown in
Figure 9A where VBIAS is a DC voltage between 3V
and 20V that can source at least 1mA. R
the cascode transistor by decreasing the voltage
across the transistor when the pass transistor saturates.
Similarly, to regulate a negative output voltage between
-20V and -120V, add a 2N5401 high-voltage PNP tran-
sistor as shown in Figure 9B.
switching MOSFETs in order to keep IN-LX current-
sense lines, LX-GND current-limit sense lines, and
the driver lines (DL and DH) short and wide. The
current-sense amplifier inputs are connected
between IN and LX, so these pins must be connect-
ed as close as possible to the high-side MOSFET.
The current-limit comparator inputs are connected
between LX and GND, but accuracy is not as
important, so give priority to the high-side MOSFET
connections. The IN, LX, and GND connections to
the MOSFETs must be made using Kelvin sense
connections to guarantee current-sense and cur-
rent-limit accuracy.
capacitor, IN bypass capacitor) together near the
MAX1964/MAX1965.
solid copper ground plane, which connects to the
MAX1964/MAX1965 at the GND pin. This includes
the VL bypass capacitor, feedback resistors, com-
pensation components (R
adjustable current-limit threshold resistors connect-
ed to ILIM.
direct. Place the feedback resistors as close to the
MAX1964/MAX1965 as possible.
preferable to allow the inductor charging path to be
made longer than the discharge path. For example,
it is better to allow some extra distance between the
input capacitors and the high-side MOSFET than to
allow distance between the inductor and low-side
MOSFET.
sitive analog areas (B_, FB_, COMP, ILIM).
Regulating High Voltage
COMP
, C
DROP
COMP
protects
), and
25