MAX783CSLASHD datasheet(20/28 Pages) MAXIM

20 / 28 page

Triple-Output Power-Supply Controller

for Notebook Computers

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___________EV Kit Standard Features

o Battery Range: 5.5V to 20V*

o Load Capability: 5V at 3A*

3.3V at 3A*

12V at 120mA or

15V at 200mA

o 3.3V and 5V Keep-Alive Linear Regulator Outputs

o Dual PCMCIA VPP Outputs

o Oscillator Sync Input

For wider input voltage range or higher load current,

see the Design Procedure.

_________________EV Kit Description

The MAX783 evaluation kit (EV kit) is a preassembled

and tested demonstration board that embodies the

standard application circuit, with some extra pull-up

and pull-down resistors needed to set default logic sig-

nal levels. The board comes configured to accept bat-

tery voltages between 5.5V and 20V, but it can be

reconfigured for voltages between 5.5V and 30V. The

maximum voltage for safe operation (20V) is deter-

mined by the breakdown voltage rating of the external

MOSFETs and input filter capacitor (C1 and C2) volt-

age ratings; if these are replaced with high-voltage

devices, the board can tolerate 30V input without dam-

age (36V absolute max).

Load current capability of the standard board is 3A at

each main output (5V and 3.3V) and 60mA at each 12V

VPP output. Load current capability can also be config-

ured by selecting appropriate external components

and sense resistor values, with practical load capability

up to 7A at each main output and 500mA on the 15V

flyback output (see the

Design Procedure for reconfig-

uring both load and input voltage capability). All func-

tions are controlled by two on-board dipswitches,

which can be overridden by external CMOS/TTL logic

signals if desired (provided the dipswitches are set to

off first).

See Table 3 for the EV kit components. These compo-

nents correspond exactly to Figure 1's Standard

Application Circuit, with the addition of the following

chip resistors (which are required only to set default

logic and supply levels). The comparator outputs both

swing 0V to 5V unless R14 is removed and R12 is

installed, in which case their output swing is 0V to 15V.

R3-R11 1M

Ω 5% resistors (logic pull-down, usually not

needed and not installed in normal applications)

R12

Open-circuit (no resistor installed)

R13

100k

Ω 5% chip resistor (SYNC pull-down,

usually shorted out)

R14

560

Ω 5% resistor (pull-up for comparator sup-

ply, usually shorted out or left open)

___________EV Kit Quick Reference

Connect a stiff (30W or better) bench power supply to the

+VIN and GND pads found on the edge of the board.

Turn up the input voltage to somewhere between 5V and

20V. Set switches SW2A, SW2B, and SW2C on (if they

are not already on), taking the device out of shutdown

and turning on the main switching regulators. Set switch

SW2D off so that the oscillator is set to 200kHz, which is

the appropriate frequency for the 6V-20V input range.

The main outputs are now regulating and ready for heavy

loads. For best output accuracy and noise characteris-

tics, loads should be returned separately to the GND

pad corresponding to and adjacent to each output

(+3OUT and +5OUT). Normal full-load regulation

error is typically -2.5% while keeping the outputs with-

in tolerance. If the measured error is higher, there may

be drops in the wiring or ground. Ensure the voltmeter

is sensing directly at the output and ground pads.

To observe normal PWM switching action, place a 1A

load on either output and observe the corresponding

switching node (device LX_ pin) while varying the input

voltage. Without a load, the switching waveforms are

intermittent and difficult to trigger on and it may appear

that the board isn’t working (except for the presence of

output voltage).

To exercise the VPP controls, first ensure the 3.3V

switch-mode supply is ON. The loosely regulated fly-

back voltage (13V to 19V) will be present at the edge

pad marked “+15OUT”. Turn on each VPP output by

setting the appropriate code on SW1, where ON = HIGH

(see Table 1).

The 5V linear regulator output is always present, even in

shutdown mode, and can be measured at the VL pad. If

the battery is connected and VL is not at 5V or close to it,

something is wrong (excess VL load, possibly). The preci-

sion 3.3V linear regulator (REF) is activated by taking the

device out of shutdown mode (by turning SW2C on).

Turning on the SW2D sets the oscillator to 300kHz, but

the external component values should be changed first

(see the

Design Procedure). The oscillator can be syn-

chronized to an external clock signal by driving the

SYNC pad with a 240kHz to 350kHz pulse train of 5V

amplitude while SW2D is off.

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Evaluation Kit Information

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