MP21600 datasheet(12/17 Pages) MPS

12 / 17 page

MP21600 – 0.6A, SYNCHRONOUS, STEP-DOWN CONVERTER WITH 11µA IQ

MP21600 Rev. 1.0

www.MonolithicPower.com

6/15/2017

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

HS_ driver

VREF

VFB

COT

Generator

IAAM

IL_ sense

FBCOMP

AAMCOMP

Figure 5: Simplified AAM Control Logic

AAM

b. Increase load in AAM

AAM

a. Light load in AAM

Figure 6: AAM Comparator Control TON

If the AAM comparator pulse is shorter than the

on-time generator, the operation mode follows

the diagram shown in Figure 7. Generally, this

can occur by using a very small inductance.

AAM

b. Increase load in on-timer

AAM

a. Light load in on-timer

Figure 7: On-Timer Control TON

In addition to the above on-timer method, the

AAM circuit has another 150ns of AAM blank

time in sleep mode. If the on-timer is less than

150ns, the high-side MOSFET (HS-FET) may

turn off after the on-timer generator pulse

without AAM control. In this condition, the

inductor current (IL) may not reach the AAM

threshold (see Figure 8). The on-time pulse in

sleep mode is around 40% larger than that the

on-time pulse in DCM or CCM.

AAM

150ns

Figure 8: AAM Blank Time in Sleep Mode

Figure 9 shows the AAM threshold decreasing

as TON increases gradually. For CCM, the

output current (Io) must be more than half of the

AAM threshold at least.

Figure 9: AAM Threshold Decreases with TON

Increase

The MP21600 has a ZCD to determine when

the inductor current starts reversing. When the

inductor current reaches the ZCD threshold, the

low-side switch turns off. AAM and the ZCD

circuit make the MP21600 work in DCM mode

at light load continuously, even if VOUT is close

to VIN.

Enable (EN)

When the input voltage is greater than the

under-voltage

lockout

threshold

(UVLO)

(typically 2V), the MP21600 can be enabled by

pulling EN higher than 1.2V. Leave EN floating

or pull EN down to ground to disable the

MP21600. There is an internal 1M

Ω resistor

from EN to ground. When the device is disabled,

the

part

enters

output

discharge

mode

automatically. The internal discharge MOSFET

provides a resistive discharge path for the

output capacitor.

Soft Start (SS)

The MP21600 has a built-in soft start that

ramps up the output voltage at a controlled slew

rate to avoid overshooting at start-up. The soft

start time is about 0.5ms, typically.

Current Limit

The MP21600 has a 1.3A high-side switch

current limit, typically. When the high-side

switch reaches its current limit, the MP21600

remains in hiccup mode until the current drops.

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