LT8410 Ver la hoja de datos (PDF) - Linear Technology

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componentes Descripción

Fabricante

LT8410

Ultralow Power Boost Converter with Output Disconnect

Linear Technology 

LT8410/LT8410-1

APPLICATIONS INFORMATION

or 0805 size capacitor will be adequate. A 0.1μF to 1μF

capacitor placed on the CAP node is recommended to filter

the inductor current while a 0.1μF to 1μF capacitor placed

on the VOUT node will give excellent transient response

and stability. To make the VREF pin less sensitive to noise,

putting a capacitor on the VREF pin is recommended, but not

required. A 47nF to 220nF 0402 capacitor will be sufficient.

Table 2 shows a list of several capacitor manufacturers.

Consult the manufacturers for more detailed information

and for their entire selection of related parts.

Table 2. Recommended Ceramic Capacitor Manufactures

MANUFACTURER

PHONE

WEBSITE

Taiyo Yuden

(408) 573-4150 www.t-yuden.com

Murata

(814) 237-1431 www.murata.com

AVX

(843) 448-9411 www.avxcorp.com

Kemet

(408)986-0424 www.kemet.com

TDK

(847) 803-6100 www.tdk.com

Setting Output Voltage

The output voltage is set by the FBP pin voltage, and VOUT

is equal to 31.85 • VFBP when the output is regulated,

shown in Figure 1. Since the VREF pin provides a good

reference (1.235V), the FBP voltage can be easily set by

a resistor divider from the VREF pin to ground. The series

resistance of this resistor divider should be kept larger than

200KΩ to prevent loading down the VREF pin. The FBP pin

can also be biased directly by an external reference. For

over voltage protection, the output voltage is limited to

40V. Therefore, if VFBP is higher than 1.235V, the output

voltage will stay at 40V.

50

40

30

20

10

0

0

0.5

1

1.5

2

FBP VOLTAGE (V)

8410-1 F01

Figure 1. FBP to VOUT Transfer Curve

Connecting the Load to the CAP Node

The efficiency of the converter can be improved by connecting

the load to the CAP pin instead of the VOUT pin.

The power loss in the PMOS disconnect circuit is then

made negligible. No quiescent current will be consumed

in the internal feedback resistor divider string during

shutdown since the PMOS transistor will be open and the

internal feedback resistor divider is connected at the VOUT

pin. The disadvantage of this method is that the CAP node

cannot go to ground during shutdown, but will be limited

to around a diode drop below VCC. Loads connected to the

part should only sink current. Never force external power

supplies onto the CAP or VOUT pins.

Maximum Output Load Current

The maximum output current of a particular LT8410 series

circuit is a function of several circuit variables. The following

method can be helpful in predicting the maximum load

current for a given circuit:

Step 1. Calculate the peak inductor current:

IPK

= ILIMIT

+

VIN

• 150 • 10–6

L

mA

where ILIMIT is 25mA and 8mA for LT8410 and LT8410-1

respectively. L is the inductance value in Henrys and VIN

is the input voltage to the boost circuit.

Step 2. Calculate the inductor ripple current:

( ) IRIPPLE =

VOUT + 1 – VIN

• 200 • 10–6

mA

L

where VOUT is the desired output voltage. If the inductor

ripple current is less than the peak current, then the circuit

will only operate in discontinuous conduction mode. The

inductor value should be increased so that IRIPPLE < IPK.

An application circuit can be designed to operate only in

discontinuous mode, but the output current capability

will be reduced.

Step 3. Calculate the average input current:

IIN(AVG) = IPK

–

IRIPPLE mA

2

84101f

9

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