MP1493 – 3A, 4.2V-16V INPUT, FAST TRANSIENT SYNCHRONOUS STEP-DOWN CONVERTER

MP1493 Rev. 1.15

www.MonolithicPower.com

11

12/9/2013

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As can be seen from equation 7, if there is

instability in PWM mode, we can reduce either

R4 or C4. If C4 can not be reduced further due to

limitation from equation 4, then we can only

reduce R4. For a stable PWM operation, the

SW

ON

-3

ESR

OUT

slope1

OUT

OUT

SW

on

TT

+-R

C

Io 10

0.7 π

2

-V

V

+

2L C

T -T

×

×

≥

××

(8)

Io is the load current.

ripple is almost the same whether the external

ramp is used or not. Figure 7 shows the

simplified circuit of the skip mode when both the

HS-FET and LS-FET are off.

Figure 7—Simplified Circuit in skip Mode

mode can be determined as follow:

()

REF

SLOPE2

12

OUT

V

V

(R

R // Ro) C

−

=

+×

(9)

Where Ro is the equivalent load resistor.

is lower than that is in the PWM mode, so it is

reasonable that the jitter in the skip mode is

larger. If one wants a system with less jitter

during ultra light load condition, the values of the

will decrease the ultra light load efficiency.

Soft Start/Stop

MP1493 employs soft start/stop (SS) mechanism

to ensure smooth output du ring power up and

power shut-down. When the EN pin becomes

high, an internal SS voltage ramps up slowly.

The SS voltage takes over the REF voltage to

the PWM comparator. The output voltage

smoothly ramps up with the SS voltage. Once SS

voltage reaches the same level of the REF

voltage, it keeps ramping up, while REF takes

over the PWM comparator. At this point, the soft

start finishes, it enters steady state operation.

The SS time is about 1ms.

When the EN pin becomes low, the internal SS

voltage is discharged through an internal current

source. Once the SS voltage reaches REF

voltage, it takes over the PWM comparator. The

output voltage will decrease smoothly with SS

voltage until zero level. s

Over-Current Protection (OCP) and Short-

Circuit Protection (SCP)

MP1493 has cycle-by cycle over-current limit

control. The inductor current is monitored during

the ON state. And it has two optional OCP/SCP

protection modes: latch-off mode and hiccup

mode.

For MP1493DS, the HS-FET turns off when the

inductor current exceeds the current limit and the

OCP timer—set at 50μs—starts. The OCP

triggers if the inductor current reaches or

exceeds the current limit every cycle in those

50μs. The MP1493DS short-circuit protection

(SCP) occurs when dead shorts occur—when the

inductor current exceeds the current limit and the

will trigger the OCP.

For MP1493DS-A, enters hiccup mode, that

periodically restarts the part when the inductor

current peak value exceeds the current limit and

Typically, the UV threshold is 50% below the

REF voltage. In OCP/SCP, MP1493DS-A will

disable the output voltage power, discharge

internal soft-start cap, and then automatically try

to soft-start again. If the over-current circuit

condition still holds after soft-start ends, it

repeats this operation cycle until the over-current

circuit condition disappears, and output rises

back to regulation level.

Over/Under-voltage Protection (OVP/UVP)

MP1493 monitors the output voltage through a

resistor divided feedback (FB) voltage to detect

over and under voltage on the output. When the

FB voltage is higher than 125% of the REF

voltage, it’ll trigger OVP. Once it triggers OVP,

the LS-FET is always on, while the HS-FET is off.

It needs power cycle to power up again. When