M
Dual 180° Out-of-Phase Buck Controllers with
Sequencing/Prebias Startup and POR
6
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Pin Description
PIN
NAME
FUNCTION
1
COMP2
Compensation Pin for Regulator 2 (REG2). Compensate REG2
’
s control loop by connecting a series resistor
(R
COMP2
) and capacitor (C
COMP2A
) to GND in parallel with a second compensation capacitor (C
COMP2B
) as
shown in Figure 1.
2
FB2
Feedback Input for Regulator 2 (REG2). Connect FB2 to a resistive divider between REG2
’
s output and GND to
adjust the output voltage between 1V and 18V. To set the output voltage below 1V, connect FB2 to a resistive
voltage-divider from REF to REG2
’
s output. See the
Setting the Output Voltage
section.
3
ILIM2
Current-Limit Adjustment for Regulator 2 (REG2). The PGND
–
LX2 current-limit threshold defaults to 100mV if
ILIM2 is connected to V
L
. Connect a resistor (R
ILIM2
) from ILIM2 to GND to adjust the REG2
’
s current-limit
threshold (V
ITH2
) from 50mV (R
ILIM2
= 100k
) to 300mV (R
ILIM2
= 600k
). See the
Setting the Valley Current
Limit
section.
4
OSC
Oscillator Frequency Set Input. Connect a resistor from OSC to GND (R
OSC
) to set the switching frequency from
100kHz (R
OSC
= 60k
) to 600kHz (R
OSC
= 10k
). The controller still requires R
OSC
when an external clock is
connected to SYNC. When using an external clock, select R
OSC
as described above, and set the external clock
frequency to twice the desired switching frequency.
5
6
7
V+
REF
GND
Input Supply Voltage. 4.5V to 23V.
2V Reference Output. Bypass to GND with a 0.22μF or greater ceramic capacitor.
Analog Ground
8
CKO
Clock Output. Clock output for external 2- or 4-phase synchronization (see
the
Clock Synchronization (SYNC,
CKO)
section).
9
SYNC
Synchronization Input or Clock Output Selection Input. SYNC has three operating modes. Connect SYNC to a
200kHz to 1200kHz clock for external synchronization. Connect SYNC to GND for 2-phase operation as a master
controller. Connect SYNC to V
L
for 4-phase operation as a master controller (see the
Clock Synchronization
(SYNC, CKO)
section).
10
ILIM1
Current-Limit Adjustment for Regulator 1 (REG1). The PGND
–
LX1 current-limit threshold defaults to 100mV if
ILIM1 is connected to V
L
. Connect a resistor (R
ILIM1
) from ILIM1 to GND to adjust REG1
’
s current-limit threshold
(V
ITH1
) from 50mV (R
ILIM1
= 100k
) to 300mV (R
ILIM1
= 600k
). See the
Setting the Valley Current Limit
section.
11
FB1
Feedback Input for Regulator 1 (REG1). Connect FB1 to a resistive divider between REG1
’
s output and GND to
adjust the output voltage between 1V and 18V. To set the output voltage below 1V, connect FB1 to a resistive
voltage-divider from REF and REG1
’
s output. See the
Setting the Output Voltage
section.
12
COMP1
Compensation Pin for Regulator 1 (REG1). Compensate REG1
’
s control loop by connecting a series resistor
(R
COMP1
) and capacitor (C
COMP1A
) to GND in parallel with a second compensation capacitor (C
COMP1B
) as
shown in Figure 1.
RST
Open-Drain Reset Output (MAX1858A/MAX1876A Only).
RST
is low when either output voltage is more than 10%
below its regulation point. After soft-start is completed and both outputs exceed 90% of their nominal output
voltage (V
FB
_ > 0.9V),
RST
becomes high impedance after a 140ms delay and remains high impedance as long
as both outputs maintain regulation. Connect a resistor between
RST
and the logic supply for logic-level
voltages.
13
N.C.
Connect to GND or leave unconnected for the MAX1875A.