MAX1875-MAX1876 查看數據表（PDF） - Maxim Integrated

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MAX1875-MAX1876

Dual 180° Out-of-Phase PWM Step-Down Controllers with POR

Maxim Integrated 

Dual 180° Out-of-Phase PWM Step-

Down Controllers with POR

Pin Description (continued)

PIN

NAME

FUNCTION

14

DH1

High-Side Gate Driver Output for Regulator 1 (REG1). DH1 swings from LX1 to BST1.

15

LX1

External Inductor Connection for Regulator 1 (REG1). Connect LX1 to the switched side of the

inductor. LX1 serves as the lower supply rail for the DH1 high-side gate driver.

16

BST1

Boost Flying-Capacitor Connection for Regulator 1 (REG1). Connect BST1 to an external ceramic

capacitor and diode according to Figure 1.

17

DL1

Low-Side Gate-Driver Output for Regulator 1 (REG1). DL1 swings from PGND to VL.

18

PGND Power Ground

19

VL

Internal 5V Linear-Regulator Output. Supplies the regulators and powers the low-side gate drivers

and external boost circuitry for the high-side gate drivers.

20

DL2

Low-Side Gate-Driver Output for Regulator 2 (REG2). DL2 swings from PGND to VL.

21

BST2

Boost Flying-Capacitor Connection for Regulator 2 (REG2). Connect BST2 to an external ceramic

capacitor and diode according to Figure 1.

22

LX2

External Inductor Connection for Regulator 2 (REG2). Connect LX2 to the switched side of the

inductor. LX2 serves as the lower supply rail for the DH2 high-side gate driver.

23

DH2

High-Side Gate-Driver Output for Regulator 2 (REG2). DH2 swings from LX2 to BST2.

24

EN

Active-High Enable Input. A logic low shuts down both controllers. Connect to VL for always-on

operation.

Detailed Description

DC-DC PWM Controller

The MAX1875/MAX1876 step-down converters use a

PWM voltage-mode control scheme (Figure 2) for each

out-of-phase controller. The controller generates the

clock signal by dividing down the internal oscillator or

SYNC input when driven by an external clock, so each

controller’s switching frequency equals half the oscillator

frequency (fSW = fOSC/2). An internal transconductance

error amplifier produces an integrated error voltage at

the COMP pin, providing high DC accuracy. The voltage

at COMP sets the duty cycle using a PWM comparator

and a ramp generator. At each rising edge of the clock,

REG1’s high-side N-channel MOSFET turns on and

remains on until either the appropriate duty cycle or until

the maximum duty cycle is reached. REG2 operates out-

of-phase, so the second high-side MOSFET turns on at

each falling edge of the clock. During each high-side

MOSFET’s on-time, the associated inductor current

ramps up.

During the second-half of the switching cycle, the high-

side MOSFET turns off and the low-side N-channel

MOSFET turns on. Now the inductor releases the stored

energy as its current ramps down, providing current to

the output. Under overload conditions, when the induc-

tor current exceeds the selected valley current-limit (see

the Current-Limit Circuit (ILIM_) section), the high-side

MOSFET does not turn on at the appropriate clock edge

and the low-side MOSFET remains on to let the inductor

current ramp down.

Synchronized Out-of-Phase Operation

The two independent regulators in the MAX1875/

MAX1876 operate 180° out-of-phase to reduce input fil-

tering requirements, reduce electromagnetic interference

(EMI), and improve efficiency. This effectively lowers

component cost and saves board space, making the

MAX1875/MAX1876 ideal for cost-sensitive applications.

Dual-switching regulators typically operate both

controllers in-phase, and turn on both high-side

MOSFETs at the same time. The input capacitor must

then support the instantaneous current requirements of

both controllers simultaneously, resulting in increased

ripple voltage and current when compared to a single

switching regulator. The higher RMS ripple current

lowers efficiency due to power loss associated with the

input capacitor’s effective series resistance (ESR). This

typically requires more low-ESR input capacitors in

parallel to minimize input voltage ripple and ESR-related

losses, or to meet the necessary ripple-current rating.

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