MCP18480 datasheet(39/64 Pages) MICROCHIP

39 / 64 page

 2003 Microchip Technology Inc.

DS20091B-page 39

MCP18480

4.0

APPLICATIONS INFORMATION

The MCP18480 can be programmed to have the PWR-

GOOD signal be either active-high or active-low via the

ISET pin and the connection of the external RISET resis-

tor (see Section 6.8.8, “Bias Block”). If the RISET resis-

tor is connected between ISET and VNEG, the

PWRGOOD output pin is an active-high signal. If the

RISET resistor is connected between ISET and VREFIN,

the PWRGOOD output pin is an active-low signal.

For systems using an active-low-enabled DC/DC con-

verter module, the MCP18480 should be programmed

for a high-active PWRGOOD output. Tying the RISET

resistor to the VNEG pin configures the PWRGOOD to

be an active-high signal. The active-high PWRGOOD

switches on the external NPN and the collector of the

external NPN (labeled as GOODPWR) is pulled to

VNEG, enabling a low-active GOODPWR and resulting

in enabling the DC/DC module.

For active-high DC/DC converter modules, the

MCP18480 should be programmed for a low active

PWRGOOD output. Connecting RISET to the VREFIN

pin will enable an active-low PWRGOOD output. Refer

to Figure 4-1 and Figure 4-2 for schematics.

Figure 4-1 shows a typical telecom application circuit

where the DC/DC module is active-high. Figure 4-2

shows a typical telecom application circuit where the

DC/DC module is active-low. The polarity of the

MCP18480’s PWRGOOD pin (active-high or active-

low) is dependant on the state of the ISET pin.

FIGURE 4-1:

Typical Operating Circuit for Telecom Applications with Active-High power Module -

foldback current limit enabled.

RUV1

ROV2

RUV2

CUVD

RISET

Ctimer

RDISCH

RUVHYS

RPOS

CBYP2

RSENSE

RDRAIN1

RDRAIN2

RFB1

RFB2

CGD

RGD

RG1

CG1

QPG2

QPG3

RPG2

RPG6

CBYPL

RBYPL

VNEG

RPG1

RPG5

Ω

2µF

10nF

1.74 M

Ω

453 k

Ω

280 k

Ω

59 k

Ω

30.9 k

Ω

800 nF

124 k

Ω

680 nF

1.6 M

Ω

0.01

Ω

7.5 k

Ω

110 k

Ω

MPSA43

100 nF 10Ω 3.3 nF

18 k

Ω

680

Ω

36 k

Ω

36 k

Ω

1500

Ω

100 µF

51 k

Ω

2N5400

NTE261

124 k

Ω

115 k

Ω

1.74 M

Ω

1.6 M

Ω

NTE2388

24.9 k

Ω

5V RPG3

RPG4

QPG1

RESTART

ENABLE

PWRGOOD

VPOS

OVTH

UVTH

UVHYS

UVD

VREFIN

VREFOUT

ISET

TIMER

OVO

DRAINTH

VFB

GATE

SENSE

VNEG

RDISCH

DC/DC

Converter

Module

VIN+

VIN-

VOUT+

VOUT-

ON/OFF

100 V

78V

Fuse 10A

GND

Transorb

CBYP1

ROV1

GOODPWR

MCP18480

SRS

SEN

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