MP6004 datasheet(17/23 Pages) MPS

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MP6004—PRIMARY-SIDE REGULATED FLYBACK/BUCK 80V DCDC CONVERTER

MP6004 Rev. 1.0

www.MonolithicPower.com

4/14/2015

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

APPLICATION INFORMATION

EN Control Setting

MP6004 turns on when EN goes high, and it

turns off when EN goes low. EN is pulled low

internally by an approximate 0.9 MΩ resistor.

In flyback mode, the maximum on time is

limited at about 8 μs. The secondary-side

rectifier diode conduction time should be longer

than 3 μs for FB1 feedback sampling. If VIN

decreases and the inductor current cannot

ramp the IPK to setting value within the

maximum on time, the diode conduction time

decreases to less than 3 μs, causing FB1

feedback sample failure. The MP6004 treats

this failure as a VOUT drop and generates more

pulses, causing VOUT to overshoot. In this

condition, EN can be used to program VIN

UVLO and shuts down the part before VIN drops

(triggering the maximum on time). Since the EN

high-level voltage is 3.9 V and the low-level

voltage is 1.3 V, it is hard to program the VIN

UVLO with a small hysteresis. In this condition,

one resistor divider and one Zener diode is

recommended (see Figure 4).

Figure 4—VIN UVLO setting with EN control

For example, the MP6004 should be turned on

before VIN rises to 36 V and shut down before

VIN drops to 20 V. One 20 V Zener diode (D4)

and a resistor divider (R5 = 100 kΩ/R6 = 49.9

kΩ) can be selected to program the VIN UVLO.

The programmed VIN rising threshold can be

calculated with Equation (8):

IN_R

100k

49.9k

20V

3.9V

31.7V

49.9k

Ω+

(8)

The programmed VIN falling threshold is

calculated with Equation (9):

IN_F

100k

49.9k

20V

1.3V

23.9V

49.9k

Ω+

(9)

In buck mode, FB2 feedback is not affected by

the rectifier diode conduction time, but the

Zener

diode

and

resistor

divider

are

recommended to set the appropriate VIN UVLO.

There is an internal Zener diode on EN, which

clamps the EN voltage to prevent runaway. The

maximum pull-up current for the internal Zener

clamp (assuming 6.5 V) should be less than 0.5

mA. If EN is driven with an external signal, use

a signal voltage less than 6.5 V or connect EN

to the signal through a pull-up resistor that

ensures the maximum pull-up current is less

than 0.5 mA. If using a resistor divider (see

Figure 4) and VIN-VZENER is higher than 6.5 V,

the minimum resistance for the pull-up resistor

R5 should be calculated with Equation (10):

ZENER

6.5V

0.5mA

−−

−<

(10)

VCC Power Supply Setting

The VCC voltage is charged through the internal

LDO by VIN. Normally, VCC is regulated at 5.4 V,

typically. A capacitor no less than 1 µF is

recommended for decoupling between VCC and

GND.

In flyback mode, VCC can be powered from the

transformer auxiliary winding to save the high-

voltage LDO power loss.

Figure 5—Supply VCC from auxiliary winding

The auxiliary winding supply voltage can be

calculated with Equation (11):

OUT

D1F

D3F

V(V

V ) V

=×

−

(11)

Where NA and NS are the turns of the auxiliary

winding and the output winding, VD1F is the

output rectifier diode voltage drop, and VD3F is

the D3 voltage drop in Figure 5.

VCC voltage is clamped at about 6.2 V by one

internal Zener diode. The clamp current

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