MAX15039_11 Datasheet, PDF(16/19 Page) Maxim Integrated Products – 6A, 2MHz Step-Down Regulator with Integrated Switches Open-Drain, Power-Good Output

English

English German Russian Spanish Italian Polish Chinese Japanese Korean French Portuguese	Language :

MAX15039_11 Datasheet, PDF (16/19 Pages) Maxim Integrated Products – 6A, 2MHz Step-Down Regulator with Integrated Switches Open-Drain, Power-Good Output

◁

6A, 2MHz Step-Down Regulator

with Integrated Switches

R2 = CO x ESR

Set the third compensation pole at 1/2 of the switching

frequency. Calculate C2 as follows:

C2 =

Ï Ã R1 Ã fS

The above equations provide application compensation

when the zero-cross frequency is significantly higher than

the double-pole frequency. When the zero-cross frequen-

cy is near the double-pole frequency, the actual zero-

cross frequency is higher than the calculated frequency.

In this case, lowering the value of R1 reduces the zero-

cross frequency. Also, set the third pole of the type III

compensation close to the switching frequency if the

zero-cross frequency is above 200kHz to boost the phase

margin. The recommended range for R3 is 2kÎ© to 10kÎ©.

Note that the loop compensation remains unchanged if

only R4âs resistance is altered to set different outputs.

MODE Selection

The MAX15039 features a mode selection input

(MODE) that users can select a functional mode for the

device (see Table 2).

Forced-PWM Mode

Connect MODE to GND to select forced-PWM mode. In

forced-PWM mode, the MAX15039 operates at a con-

stant switching frequency (set by the resistor at FREQ

terminal) with no pulse skipping. PWM operation starts

after a brief settling time when EN goes high. The low-

side switch turns on first, charging the bootstrap

capacitor to provide the gate-drive voltage for the high-

side switch. The low-side switch turns off either at the

end of the clock period or once the low-side switch

sinks 1.35A current (typ), whichever occurs first. If the

low-side switch is turned off before the end of the clock

period, the high-side switch is turned on for the remain-

ing part of the time interval until the inductor current

reaches 0.9A, or the end of clock cycle is encountered.

Starting from the first PWM activity, the sink current

threshold is increased through an internal 4-step DAC

to reach the current limit of 11A after 128 clock periods.

This is done to help a smooth recovery of the regulated

voltage even in case of accidental prebiased output in

spite of the initial forced-PWM mode selection.

Table 2. Mode Selection

MODE CONNECTION

OPERATION MODE

GND

Forced PWM

Unconnected or

VDD/2

Forced PWM. Soft-start up into a

prebiased output (monotonic startup).

VDD

Skip Mode. Soft-start into a prebiased

output (monotonic startup).

COMPENSATION

TRANSFER

FUNCTION

DOUBLE POLE

OPEN-LOOP

GAIN

THIRD

POLE

GAIN (dB)

POWER-STAGE

TRANSFER

FUNCTION

SECOND

POLE

FIRST AND SECOND ZEROS

Figure 4. Type III Compensation Illustration

Soft-Starting Into a Prebiased Output

Mode (Monotonic Startup)

When MODE is left unconnected or biased to VDD/2, the

MAX15039 soft-starts into a prebiased output without dis-

charging the output capacitor. This type of operation is

also termed monotonic startup. See the Starting Into

Prebiased Output waveforms in the Typical Operating

Characteristics section for an example.

In monotonic startup mode, both low-side and high-

side switches remain off to avoid discharging the prebi-

ased output. PWM operation starts when the FB voltage

crosses the SS voltage. As in forced-PWM mode, the

PWM activity starts with the low-side switch turning on

first to build the bootstrap capacitor charge.

16 ______________________________________________________________________________________

▷