MP2316 Rev. 1.11

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13

4/11/2017

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maximum frequency can be calculated by the

following equations, choose the lower value of

them as the maximum frequency:

6

SW-max

IN

on-min

OUT

10

F(KHz)

V(V)

T(ns)

V(V)





(4)

6

IN

OUT

SW-max

off-min

IN

(V (V)-V (V)) 10

F(KHz)

T(ns) V (V)







(5)

Where Ton-min typical value is 90ns and Toff-

min typical value is 150ns.For example, VIN=12V,

Vout=1.2V, the maximum frequency we can set

is about 1.1MHz. MP2316 is optimized to operate

at high switching frequency with high efficiency.

High switching frequency makes it possible to

use small-sized LC filter components to save

system PCB space.

Forced PWM Operation

Whenever V

below V

is turned ON

V

IN

T

V

RAMP

V

EAO

I

OUT

V

SW

HS-FET

Driver

LS-FET

Driver

I

L

Figure 4—Force PWM Operation

When the MP2316 works in Forced PWM, the

MP2316 enters continuous-conduction mode

(CCM) where the HS-FET and LS-FET repeat

the on/off operation, even if the inductor current

goes to zero or negative value. The switching

the timing diagram during this operation.

Light-Load Operation

When the MP2316 works in auto PFM/PWM

mode and during light-load operation—the

MP2316 automatically reduces the switching

frequency to maintain high efficiency, and the

inductor current drops near zero. When the

inductor current reaches zero, the LS-FET driver

goes into tri-state (high Z). Hence, the output

capacitors discharge slowly to GND through LS-

FET, R1, and R2. This operation greatly

improves device efficiency when the output

current is low.

Figure 5—Light Load Operation

Light-load operation is also called skip mode

because the HS-FET does not turn on as

frequently as during heavy-load conditions. The

frequency at which the HS-FET turns on is a

function of the output current—as the output

current increases, the time period that the current

modulator regulates becomes shorter, and the

HS-FET turns on more frequently. The switching

frequency increases in turn. The output current

reaches the critical level when the current

modulator time is zero, and can be determined

using the following equation:

IN

OUT

OUT

OUT

SW

IN

(V

V

) V

I

2L F

V





 

(6)

The device reverts to PWM mode once the

output current exceeds the critical level. After that,

the switching frequency stays fairly constant over

the output current range.

Application When Input Voltage is Close to

Output Voltage.

MP2316 extends the on time when output

voltage loses regulation when input voltage is

close to output voltage. The switching frequency

drops correspondingly in order to achieve larger

duty cycle to keep output regulated. If the Vin is

very close to Vout, Ton extension circuit will force

MP2316 working in PWM mode with higher than

expected frequency. Increasing Vin to certain

level, part will exit this mode. Refer to Figure 6,

MP2316 can work at auto PFM/PWM mode when

Vin is above the curve. If auto PFM/PWM mode

is required at input voltage below the curve, use

Enable startup instead of input voltage startup.