EHA-PA1AN1-R02-L1 datasheet(4/4 Pages) VIMARLOW

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EHA-PA1AN1-R02-L1

DOC # 102-0388 REV 3 - PAGE 4 OF 4

APPLICATION NOTES

VOUT and VSTORE Capacitor

For pulsed load applications, the VOUT capacitor should be

sized to provide the necessary current when the load is

pulsed on. The capacitor value required will be dictated by

the load current, the duration of the load pulse, and the

amount of voltage drop the circuit can tolerate. The capacitor

must be rated for the voltage selected for VOUT by VS1 and

VS2.



 









Load

Pulse

out

OUT

ImA t

∆ VOUT is the maximum allowable voltage drop on VOUT. Note

that there must be enough energy available from the input

voltage source for VOUT to recharge the capacitor during the

interval between load pulses. Reducing the duty cycle of the

load pulse will allow operation with less input energy.

The VSTORE capacitor may be a very large value (thousands

of microfarads or even Farads), to provide holdup at times

when the input power may be lost. Note that this capacitor

mat charge to 5.25V (regardless of the settings for VOUT), so

ensure that the holdup capacitor has a working voltage rating

of at least 5.5V at the temperature for which it will be used.

The VSTORE capacitor can be sized using the following:



5.25

LDO

Burst

Store

OUT

t f T















where 6μA is the quiescent current of the LTC3108, IQ is the

load on VOUT in between bursts, ILDO is the load on the LDO

between bursts, IBURST is the total load during the burst, t is

the duration of the burst, f is the frequency of the burst,

TSTORE is the storage time required, and VOUT is the output

voltage required. Note that for a programmed output voltage

of 5V, the VSTORE capacitor cannot provide any beneficial

storage time. Storage capacitors requiring voltage balancing

are not recommended due to the current draw of the

balancing resistor.

In many pulsed load applications, the duration, magnitude

and frequency of the load current bursts are known and fixed.

In these cases the charge current required from the LTC3108

to support average load must be calculated, by the following:

Burst

CHG



where IQ is the sleep current on VOUT required by the external

circuitry in between bursts (including cap leakage), IBURST is

the total load current during the burst, t is the time duration

of the burst and T is the period of the transmit burst rate

(essentially the time between bursts).

SET-UP TIPS

To assess your thermal interface between the EHA-PA1AN1-

R02-L1 and your heat source and estimate your expected

maximum current, follow these procedures to measure your

short circuit current:

Connect a 200Ω resistor in series between pins 1 and

Connect a voltmeter across the 200Ω resistor.

Bring the hot side of the assembly to the desired

temperature by raising the source temperature and

monitoring the hot side thermistor via pins 9 and 10

on the wire harness.

Note that pins 9 and 10

measure the hot side of the TEG and not the source

temperature.

There could be several degrees

difference between TSOURCE and THOT, so Marlow

recommends mounting a thermocouple to the source

to independently monitor TSOURCE. If the discrepancy

is greater than 5°C, there may be thermal interface

mounting

issues

and

Marlow

recommends

remounting the EHA-PA1AN1-R02-L1.

Allow the assembly temperature to stabilize and

measure the voltage drop across the resistor.

Convert the voltage to a current using I=V/R.

Check that the short circuit current matches closely

with the performance curve plot on page 1.

To evaluate operation under electrical load conditions use the

following procedure:

Connect the load/battery/capacitor/resistor between

pins 1 and 2 (See image below).

Connect a voltmeter across the load.

If possible, connect a small resistor or current shunt

series

between

and

the

load/battery/capacitor/resistor between pins 1 and 2.

Use this shunt to calculate current out of VOUT.

Bring the hot side of the assembly to the desired

temperature by raising the source temperature and

monitoring the hot side thermistor via pins 9 and 10

on the wire harness.

Measure

the

voltage

drop

across

the

load

device/resistor and the current from the shunt. Use

voltage and current to calculate power.

Check the calculated power against the performance

curve plot on page 1.

The EHA-PA1AN1-R02-L1 is now ready for further evaluation

in your application. If you have any questions on this test

procedure or how to test the unit in your application, please

contact a Marlow application engineer for further assistance.

For more information, please refer to the Contact Us section

of this datasheet.

Converter

VSTORE

VLDO

VOUT

PGD

GND

µP

SENSORS

RF LINK

TEG

220µF

2.2µF

CUSTOMER

ADDITION

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