MAX1965TEEP Maxim Integrated, MAX1965TEEP Datasheet - Page 24

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

where C
f
In systems where the step-down controller’s output is
not the highest voltage, a transformer may be used to
provide additional post-regulated, high-voltage outputs.
The transformer generates unregulated, high-voltage
supplies which power the positive and negative linear
regulators. These unregulated supply voltages are
dependent on the transformer’s turns ratio – number of
secondary turns (N
turns (N
vide supply voltages high enough to keep the pass
transistors from saturating. For positive output voltages,
connect the transformer as shown in Figure 6 where the
minimum turns ratio (N
by:
Tracking/Sequencing Triple/Quintuple
Power-Supply Controllers
24
Figure 7. Base-Drive Noise Reduction
POLE(CBE)
C
______________________________________________________________________________________
BE
N
P
POS
≤
IN(Q)
). So the transformer must be selected to pro-
2π
is the second pole required for stability.
≥
ƒ
POLE CBE
is the transistor’s input capacitance, and



V
LDO POS
1
(
S
) divided by the number of primary
(
POS
)



)
R I
V
+
= N
BE LOAD
OUT
V
SAT
R
S(POS)
BE T FE
Transformer Selection
+
V h
V
+
DIODE
/N
V h
a) POSITIVE OUTPUT VOLTAGE
b) NEGATIVE OUTPUT VOLTAGE (MAX1965 ONLY)
T FE
P
) is determined
MAX1964
MAX1965
MAX1965
-1






-
C
IN Q
( )
FB_
BF5
B_
B5
C
C
BE
BE
R1
R2
R4
R3
where V
under full load. For negative output voltages (MAX1965
only), connect the transformer as shown in Figure 6
where the minimum turns ratio (N
determined by:
Since power transfer occurs when the low-side MOS-
FET is on (DL = high), the transformer cannot support
heavy loads with high duty cycles.
The MAX1964/MAX1965 use current-mode control
schemes that sense the current across the high-side
MOSFET (N
turns on, the MAX1964/MAX1965 use a 60ns current-
sense blanking period to minimize noise sensitivity.
However, when the MOSFET turns on, the transformer’s
secondary inductance and the diode’s parasitic capac-
itance form a resonant circuit that causes ringing.
Reflected back through the transformer to the primary
side, these oscillations appear across the high-side
MOSFET may last longer than the blanking period. As
R
R
BE
BE
V
REF
N
SAT
NEG
C
Q
Q
LDO
PASS
H
PASS
is the pass transistor’s saturation voltage
). Immediately after the high-side MOSFET
≥
V




POS
C
C
V
BYP
BYP
LDO NEG
C
NEG
V
V
V
SUP
SUP
(
NEG
)
V
+
OUT
V
SAT
NEG
+
Snubber Design
V
DIODE
= N
S(NEG)




/N
P
) is