MAX17075(2008) View Datasheet(PDF) - Maxim Integrated

Part Name

Description

MFG CO.

MAX17075
(Rev.:2008)

Boost Regulator with Integrated Charge Pumps, Switch Control, and High-Current Op Amp

Maxim Integrated 

Boost Regulator with Integrated Charge Pumps,

Switch Control, and High-Current Op Amp

Short-Circuit Current Limit and Input Clamp

The operational amplifier limits short-circuit current to

approximately ±500mA if the output is directly shorted

to SUP or to BGND. If the short-circuit condition per-

sists, the junction temperature of the IC rises until it

reaches the thermal-shutdown threshold (+160°C typ).

Once the junction temperature reaches the thermal-

shutdown threshold, an internal thermal sensor immedi-

ately sets the thermal fault latch, shutting off all the IC’s

outputs. The device remains inactive until the input volt-

age is cycled. The operational amplifier has 4V input

clamp structures in series with a 500Ω resistance and a

diode (Figure 6).

Driving Pure Capacitive Load

The operational amplifier is typically used to drive the

LCD backplane (VCOM) or the gamma-correction

divider string. The LCD backplane consists of a distrib-

uted series capacitance and resistance, a load that can

be easily driven by the operational amplifier. However,

if the operational amplifier is used in an application with

a pure capacitive load, steps must be taken to ensure

stable operation. As the operational amplifier’s capaci-

tive load increases, the amplifier’s bandwidth decreas-

es and gain peaking increases. A 5Ω to 50Ω small

resistor placed between OUT and the capacitive load

reduces peaking, but also reduces the gain. An alterna-

tive method of reducing peaking is to place a series RC

network (snubber) in parallel with the capacitive load.

The RC network does not continuously load the output

or reduce the gain. Typical values of the resistor are

between 100Ω and 200Ω, and the typical value of the

capacitor is 10nF.

High-Voltage Switch Control

The MAX17075’s high-voltage switch control block

(Figure 7) consists of two high-voltage p-channel

MOSFETs: Q1, between SRC and COM; and Q2,

between COM and DRN. At power-up and only at

power up, before the switch control is enabled (a 1.5kΩ

pulldown is present on COM). At switch-off, COM is

high impedance.

The switch control input (CTL) is not activated until all

four of the following conditions are satisfied: the input

voltage exceeds UVLO, the soft-start routine of all the

regulators is complete, there is no fault condition

detected, and VDEL exceeds its turn-on threshold.

Once activated and if CTL is logic-high, Q1 turns on

and Q2 turns off, connecting COM to SRC. When CTL

is logic-low, Q1 turns off and Q2 turns on, connecting

COM to DRN.

SUP

POS

±4V

500Ω

NEG

OUT

MAX17075

VCC

5μA

DEL

Q3

VREF

MAX17075

SWITCH CONTROL

FAULT

REF_OK

2.25V

SRC

Q1

COM

Q2 1.5kΩ

BGND

CTL

OP AMP INPUT CLAMP STRUCTURE

Figure 6. Op Amp Input Clamp Structure

Figure 7. Switch Control

16 ______________________________________________________________________________________

DRN

Q4

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