ADP3430 datasheet(22/26 Pages) ONSEMI

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ADP3430

http://onsemi.com

Figure 11. VR Thermal Monitor Circuit

TTSNS

VRHOT

ADP3430

OPTIONAL

TEMPERATURE

ADJUST

RESISTOR

0.1mF

PLACE THERMISTOR

NEAR CLOSEST PHASE

RTTSENSE

A voltage is generated from this current through the

thermistor and sensed inside the IC. When the voltage

reaches 0.81 V, the VRHOT gets set. This corresponds to

RTTSENSE values of 6.58 kW for VRHOT.

These values correspond to a thermistor temperature of

~100

°C and ~110°C when using the same type of 100 kW

NTC thermistor used in the current sense amplifier.

An additional fixed resistor in parallel with the thermistor

allows tuning of the trip point temperatures to match the

hottest temperature in the VR, when the thermistor itself is

directly sensing a proportionately lower temperature.

Setting this resistor value is best accomplished with a

variable resistor during thermal validation and then fixing

this value for the final design.

Additionally, a 0.1

mF capacitor should be used for

filtering noise.

Shunt Resistor Design

The ADP3430 uses a shunt to generate 5.0 V from the

12 V supply range. A trade off can be made between the

power dissipated in the shunt resistor and the UVLO

threshold. Figure 12 shows the typical resistor value needed

to realize certain UVLO voltages. It also gives the maximum

power dissipated in the shunt resistor for these UVLO

voltages.

Figure 12. Typical Shunt Resistor Value and Power Dissipation for Different UVLO Voltage

VIN (UVLO)

150

250

350

450

550

7.0

8.0

9.0

10.0

11.0

200

300

400

500

RSHUNT

7.5

8.5

9.5

10.5

0.10

0.20

0.30

0.40

0.50

0.15

0.25

0.35

0.45

PSHUNT

The maximum power dissipated is calculated using

Equation 35.

PMAX +

VIN(MAX) * VCC(MIN)

RSHUNT

(eq. 35)

where:

VIN(MAX) is the maximum voltage from the 12 V input

supply (if the 12 V input supply is 12 V

± 5%,

VIN(MAX) = 12.6 V; if the 12 V input supply is 12 V ± 10%,

VIN(MAX) = 13.2 V). VCC(MIN) is the minimum VCC voltage

of the ADP3430. This is specified as 4.75 V. RSHUNT is the

shunt resistor value.

The CECC standard specification for power rating in

surface mount resistors is: 0603 = 0.1 W, 0805 = 0.125 W,

1206 = 0.25 W.

Tuning the ADP3430

1. Build a circuit based on the compensation values

computed from the design spreadsheet.

2. Hook up the dc load to the circuit, turn it on, and

verify its operation. Also, check for jitter at no

load and full load.

DC Load Line Setting

3. Measure the output voltage at no load (VNL).

Verify that it is within tolerance.

4. Measure the output voltage at full load cold

(VFLCOLD). Let the board sit for ~10 minutes at

full load, and then measure the output (VFLHOT).

If there is a change of more than a few mV, adjust

RCS1 and RCS2 using Equation 36 and

Equation 38.

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