MAX1729 View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX1729

ECB and LCD Display Bias Supply with Accurate Output Voltage and Temperature Compensation

Maxim Integrated 

ECB and LCD Display Bias Supply with Accurate

Output Voltage and Temperature Compensation

Pin Description

PIN NAME

FUNCTION

1

IN

Supply Input. Bypass with 0.1µF capacitor to ground. Connect to supply side of inductor (L1).

2

TC

Temperature-Sensor Output. Bypass to GND with a 1000pF capacitor.

3

REF

Reference Voltage Output. Bypass to GND with a 0.1µF capacitor.

4

COMP

Compensation Pin. In internal feedback mode (Figure 2), bypass with a 1µF capacitor. In external feedback

mode, COMP is a buffered inverse version of CTLIN (Figure 3).

5

FB

Feedback and Mode Control Input. Connect to GND for internal feedback mode operation.

6

CTLIN Control Input. Drive low for more than 1.2ms to put the device into shutdown.

7

OUT Bypass to GND with a 1.0µF capacitor.

8

PS

Output of boost converter and input to LDO. Bypass to GND with a 0.068µF capacitor.

9

LX

Drain of the internal MOSFET Switch

10

GND Ground

Detailed Description

The MAX1729 is designed to provide bias voltage for

ECB or LCD displays. It is composed of a step-up

DC-DC converter followed by a linear regulator

(Figure 1), a combination that provides step-up/step-

down voltage conversion while minimizing output rip-

ple. The device allows you to adjust a display’s color or

contrast by dynamically adjusting the MAX1729’s out-

put voltage using a PWM control signal. In internal

feedback mode, the output voltage is adjustable

between +2.5V and +16V. In external feedback mode,

the output voltage is adjustable, and its range is set by

a resistor network that is programmed to match the out-

put voltage range of LCD/ECB displays needing a max-

imum output up to +18V.

Boost Converter

The MAX1729’s DC-DC boost converter is implemented

with an on-chip N-channel MOSFET, a diode, and an

error comparator. The IC’s unique PFM control system

varies the on-time and off-time of the switch based on the

boost converter’s input and output voltage values, as fol-

lows:

tON =

K

VIN

tOFF ≥

K

VPS − VIN

where K is typically 8V-µs. This timing maintains discon-

tinuous conduction and sets the peak inductor current

(IPEAK) to:

IPEAK

=

K

L

where L is the inductance of L1 (Figures 2, 3, and 4).

When the error comparator detects that the drop across

the linear regulator (VPS - VOUT) is less than approximate-

ly 0.6V, the internal switch is turned on (tON initiates) and

current through the inductor ramps to IPEAK. At the end of

tON, the switch is turned off for at least tOFF, allowing the

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