MAX1858A/MAX1875A/MAX1876A
Dual 180° Out-of-Phase Buck Controllers with
Sequencing/Prebias Startup and POR
6 _______________________________________________________________________________________
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
= 100kΩ) to 300mV (R
ILIM2
= 600kΩ). 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
= 60kΩ) to 600kHz (R
OSC
= 10kΩ). 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 V+ Input Supply Voltage. 4.5V to 23V.
6 REF 2V Reference Output. Bypass to GND with a 0.22µF or greater ceramic capacitor.
7 GND 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
= 100kΩ) to 300mV (R
ILIM1
= 600kΩ). 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.
