MAX15014 datasheet(17/25 Pages) MAXIM

17 / 25 page

LDO Regulator

The LDO regulator operates over an input voltage from

5V to 40V, and can be enabled independently of the

DC-DC converter section. Its quiescent current is as

low as 47μA with a load current of 100μA. All devices

feature a preset output voltage of 5V (MAX1501_A) or

3.3V (MAX1501_B). Alternatively, the output voltage can

be adjusted using an external resistive-divider network

connected between LDO_OUT, SET_LDO, and SGND.

See Figure 5.

RESET Output

The RESET output is typically connected to the reset

input of a microprocessor (μP). A μP’s reset input starts

or restarts the μP in a known state. The MAX15014–

MAX15017 supervisory circuits provide the reset logic to

prevent code-execution errors during power-up, power-

down, and brownout conditions. RESET changes from

high to low whenever the monitored voltage drops below

the RESET threshold voltage. Once the monitored volt-

age exceeds its respective RESET threshold voltage(s),

RESET remains low for the RESET timeout period, then

goes high. The RESET timeout period is adjustable with

an external capacitor (CCT) connected to CT.

Thermal-Shutdown Protection

The MAX15014–MAX15017 feature thermal-shutdown

protection that limits the total power dissipation in the

device and protects it in the event of an extended

thermal-fault condition. When the die temperature exceeds

+160°C, an internal thermal sensor shuts down the part,

turning off the DC-DC converter and the LDO regulator,

and allowing the IC to cool. After the die temperature falls

by 20°C, the part restarts with a soft-start sequence.

Applications Information

Setting the Output Voltage

Connect a resistive divider (R3 and R4, see Figures

6 and 7) from OUT to FB to SGND to set the output

voltage. Choose R3 and R4 so that DC errors due to the FB

input bias current do not affect the output-voltage setting

precision. For the most common output-voltage

settings (3.3V or 5V), R3 values in the 10kΩ range are

adequate. Select R3 first and calculate R4 using the

following equation:

OUT





−









where VFB = 1.235V.

Inductor Selection

Three key inductor parameters must be speci-

fied for operation with the MAX15014–MAX15017:

inductance value (L), peak inductor current (IPEAK), and

inductor saturation current (ISAT). The minimum required

inductance is a function of operating frequency, input-

to-output voltage differential, and the peak-to-peak

inductor current (ΔIP-P). Higher ΔIP-P allows for a lower

inductor value, while a lower ΔIP-P requires a higher

inductor value. A lower inductor value minimizes size and

cost and improves large-signal and transient response,

but reduces efficiency due to higher peak currents and

higher peak-to-peak output-voltage ripple for the same

output capacitor. On the other hand, higher inductance

increases efficiency by reducing the ΔIP-P. Resistive

losses due to extra wire turns can exceed the ben-

efit gained from lower ΔIP-P levels, especially when the

inductance is increased without also allowing for larger

inductor dimensions. A good compromise is to choose

ΔIP-P equal to 40% of the full load current. Calculate the

inductor using the following equation:

OUT IN

OUT

P P

)

I −

−

×∆

VIN and VOUT are typical values so that efficiency is

optimum for typical conditions. The switching frequency

(fSW) is internally fixed at 135kHz (MAX15014/MAX15016)

or 500kHz (MAX15015/MAX15017) and can vary when

synchronized to an external clock (see the Oscillator/

Synchronization Input (SYNC) section). The ΔIP-P, which

reflects the peak-to-peak output ripple, is worst at the maxi-

mum input voltage. See the Output Capacitor Selection

section to verify that the worst-case output ripple is accept-

able. The inductor current (ISAT) is also important to avoid

current runaway during continuous output short circuit.

Select an inductor with an ISAT specification higher than

the maximum peak current limit of 2.6A.

Input Capacitor Selection

The discontinuous input current of the buck converter

causes large input ripple currents and therefore the input

capacitor must be carefully chosen to keep the input

voltage ripple within design requirements. The input volt-

age ripple is comprised of ΔVQ (caused by the capacitor

discharge) and ΔVESR (caused by the ESR of the input

capacitor). The total voltage ripple is the sum of ΔVQ and

ΔVESR. Calculate the input capacitance and ESR required

for a specified ripple using the following equations:

MAX15014–MAX15017

1A, 4.5V to 40V Input Buck Converters with

50mA Auxiliary LDO Regulators

www.maximintegrated.com

Maxim Integrated │ 17

MAX15014 bảng dữ liệu(PDF) 17 Page - Maxim Integrated Products

MAX15014 bảng dữ liệu(HTML) 17 Page - Maxim Integrated Products

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

bảng dữ liệu tải về

Link URL