MAX17010 데이터 시트보기 (PDF) - Maxim Integrated

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MAX17010

Internal-Switch Boost Regulator with Integrated High-Voltage Level Shifter and Op Amp

Maxim Integrated 

Internal-Switch Boost Regulator with Integrated

High-Voltage Level Shifter and Op Amp

The high-voltage, level-shifting scan drivers are

designed to drive the TFT panels with row-drivers inte-

grated on the panel glass. Its eight outputs swing from

+30V (max) to -6.3V (min) and can swiftly drive capaci-

tive loads. The typical propagation delays are 40ns,

with fast 16ns rise-and-fall times. The buffers can oper-

ate at frequencies up to 50kHz.

Thermal-Overload Protection

The thermal-overload protection prevents excessive

power dissipation from overheating the device. When

the junction temperature exceeds TJ = +160°C, a ther-

mal sensor immediately activates the fault protection,

which shuts down all outputs except VL, allowing the

device to cool down. Once the device cools down by

approximately 15°C, cycle the input voltage (below the

UVLO-falling threshold) to clear the fault latch and

reactivate the device.

The thermal-overload protection protects the controller in

the event of fault conditions. For continuous operation,

do not exceed the absolute maximum junction tempera-

ture rating of TJ = +150°C.

Design Procedure

Main Step-Up Regulator

Inductor Selection

The minimum inductance value, peak current rating, and

series resistance are factors to consider when selecting

the inductor. These factors influence the converter’s effi-

ciency, maximum output-load capability, transient

response time, and output-voltage ripple. Physical size

and cost are also important factors to be considered.

The maximum output current, input voltage, output volt-

age, and switching frequency determine the inductor

value. Very high inductance values minimize the current

ripple and therefore reduce the peak current, which

decreases core losses in the inductor and I2R losses in

the entire power path. However, large inductor values

also require more energy storage and more turns of wire,

which increase physical size and can increase I2R losses

in the inductor. Low inductance values decrease the

physical size but increase the current ripple and peak

current. Finding the best inductor involves choosing the

best compromise between circuit efficiency, inductor

size, and cost.

The equations used here include a constant (LIR),

which is the ratio of the inductor peak-to-peak ripple

current to the average DC inductor current at the full-

load current. The best trade-off between inductor size

and circuit efficiency for step-up regulators generally

has an LIR between 0.3 and 0.5. However, depending

on the AC characteristics of the inductor core material

and ratio of inductor resistance to other power-path

resistances, the best LIR can shift up or down. If the

inductor resistance is relatively high, more ripple can

be accepted to reduce the number of turns required

and increase the wire diameter. If the inductor resis-

tance is relatively low, increasing inductance to lower

the peak current can decrease losses throughout the

power path. If extremely thin high-resistance inductors

are used, as is common for LCD panel applications, the

best LIR can increase to between 0.5 and 1.0.

Once a physical inductor is chosen, higher and lower

values of the inductor should be evaluated for efficiency

improvements in typical operating regions.

Calculate the approximate inductor value using the typi-

cal input voltage (VIN), the maximum output current

(IMAIN(MAX)), the expected efficiency (ηTYP) taken from

an appropriate curve in the Typical Operating

Characteristics, and an estimate of LIR based on the

above discussion:

L

=

⎛

⎝⎜

VIN

VMAIN

⎞

⎠⎟

2

⎛

⎝⎜

VMAIN −

IMAIN(MAX)

VIN

× fOSC

⎞

⎠⎟

⎛

⎝⎜

ηTYP

LIR

⎞

⎠⎟

Choose an available inductor value from an appropriate

inductor family. Calculate the maximum DC input cur-

rent at the minimum input voltage VIN(MIN) using con-

servation of energy and the expected efficiency at that

operating point (ηMIN) taken from an appropriate curve

in the Typical Operating Characteristics:

IIN(DC,MAX)

=

IMAIN(MAX) × VMAIN

VIN(MIN) × ηMIN

Calculate the ripple current at that operating point and

the peak current required for the inductor:

( ) IRIPPLE

=

VIN(MIN) × VMAIN

L × VMAIN ×

− VIN(MIN)

fOSC

IPEAK

=

IIN(DC,MAX)

+

IRIPPLE

2

The inductor’s saturation current rating and the

MAX17010’s LX current limit (ILIM) should exceed IPEAK

and the inductor’s DC current rating should exceed

IIN(DC,MAX). For good efficiency, choose an inductor

with less than 0.1Ω series resistance.

Considering the Typical Operating Circuit, the maximum

load current (IMAIN(MAX)) is 300mA, with an 8.5V output

and a typical input voltage of 3V. Choosing an LIR of 0.45

and estimating efficiency of 85% at this operating point:

L

=

⎛

⎝⎜

3V

8.5V

⎞

⎠⎟

2⎛

⎝⎜

8.5V − 3V

0.3A ×1.2MHz

⎞⎛

⎠⎟ ⎝⎜

0.85 ⎞

0.5 ⎠⎟

≈

3.6μH

14 ______________________________________________________________________________________

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