MAX1864 Maxim, MAX1864 Datasheet - Page 11

• Manufacturer Part Number: MAX1864
• Description: xDSL/Cable Modem Triple/Quintuple Output Power Supplies
• Manufacturer: Maxim

the voltage across the load. Under overload conditions,
when the inductor current exceeds the selected cur-
rent-limit (see Current Limit), the high-side MOSFET is
not turned on at the rising edge of the clock and the
low-side MOSFET remains on to let the inductor current
ramp down.
The MAX1864/MAX1865 operate in a forced-PWM
mode, so even under light loads the controller main-
tains a constant switching frequency to minimize cross-
regulation errors in applications that use a transformer.
The low-side gate-drive waveform is the complement of
the high-side gate-drive waveform, which causes the
inductor current to reverse under light loads.
Figure 1. Standard MAX1864 Application Circuit
xDSL/Cable Modem Triple/Quintuple Output
______________________________________________________________________________________
1µF
1µF
C2
C1
C
8.2nF
100kΩ
COMP
R
R
47kΩ
COMP
POK
IN
VL
ILIM
POK
FB
COMP
MAX1864
D1
CENTRAL CMPSH-3
GND
OUT
FB2
BST
FB3
DH
B2
LX
DL
B3
10Ω
R
C
0.1µF
R
10Ω
DL
BST
DH
30kΩ
10kΩ
R3
10kΩ
10kΩ
R4
R1
R2
4700pF
220Ω
2200pF
C
R
R
220Ω
C
BE3
BE3
BE2
BE2
N
N
H
L
Q2
Q1
1
T1
C
470µF
The MAX1864/MAX1865s’ current-sense circuit ampli-
fies (A
the high-side MOSFET’s on-resistance (R
I
the internal slope compensation signal are summed
together (V
inverting input. The PWM comparator turns-off the high-
side MOSFET when V
back voltage (V
further than 5mm from the controller, and connect IN
and LX to the MOSFET using Kelvin sense connections
to guarantee current-sense accuracy and improve
stability.
IN
INPUT
9V TO 18V
INDUCTOR
C7
10µF
C4
10µF
C6
10µF
C3
10µF
V
V
OUT3
OUT2
100mA
V
300mA
V
= 5.0V
= 5) the current-sense voltage generated by
= 2.5V
D2
NIHON EP05Q03L
OUT
C
470µF
C5
470µF
OUT
1A
). This amplified current-sense signal and
= 3.3V
SUM
T1
COMP)
) and fed into the PWM comparator’s
NL, NH: INTERNATIONAL RECTIFIER
Power Supplies
Q1: TIP30
Q2: 2N3905
IRF7303
SUM
. Place the high-side MOSFET no
exceeds the integrated feed-
Current-Sense Amplifier
DS(ON)
11
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