AS7620B-BQFT-500 - AMS AG - Product.Network

AS7620

500mA Hysteretic High Voltage Step-Down Converter

with Dual Power Monitor

Data Sheet

www.austriamicrosystems.com Revision 1.12 1 - 16

1 General Description

The AS7620 is an easy-to-use, high-efficiency, high-

voltage, hysteretic step-down DC-DC converter,

operating in asynchronou s mode. Its low-power

architecture extends hold-up time in battery-backed and

critical applications where maximum up-time over a wide

input supply voltage range is needed, while still

providing for high efficiencies of up to 90% during pea k

current demands.

Although the AS7620 is optimized for 24V applications

found in industrial and medical systems, its ability to

support 100% Duty Cycle makes the AS7620 ideal for

applications demanding maximum up-time and soft

power fail behavior. In combination with low idle current

of only 30µA, on-demand switching reduces operating

current at low load currents.

By selecting an appropriate inductor value, operating

current can be lowered and switching frequencies tuned

to certain load conditions.

A pin-strapped current limit input minimizes inductor

peak current and thus inductor size and cost for any

given application.

The device further includes output short-circuit

protection and thermal shutdown. In shutdown mode,

only 1µA (typ) of current is consumed.

Figure 1. Block Diagram

2 Key Features

! Low quiescent current for efficient partial load

operation

! Wide Supply Voltage Range, 3.6V to 32V

! 100% Duty Cycle extends operating range

! Pin-programmable cycle-by-cycle current limit

! Integrated PMOS el i m i nates bootstra p capacitor

! Resistor-programmable Early Power Fail Warning

Input

! Power-Good Flag

! Thermal Shutdown

! Fixed 3.3V and adjustable output (1.2V to VIN)

! Small 4x4mm 12-Lead MLPQ Enhanced Power

Package

! Specified from -40ºC to +125ºC junction and 85ºC

maximum ambient temperatures

3 Applications

The AS7620 is suitable for Industrial 24VDC

applications like PLCs, robotics; Home Security and

Building Control applications; Solid-state utility meters;

Signage and LED column power; and Sensor interfaces.

ILIM

VIN

SHDN

VEPF

LDO

Temp Level

Shifter

Soft-Start ISENSE

VREF

Hysteretic

Controller

AS7620

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AS7620

Data Sheet - P i n As s i g n m e nt s

4 Pin Assignments

Figure 2. Pin Assignments (Top View)

Pin Descriptions

Table 1. Pin Descriptions

Pin Name Pin Number Description

VIN 1High Voltage Power Supply Input

GND 2 Must be connected to GND

LX 3 Power Output to Induct or

GND 4 Must be connected to GND

FB 5 Feedback input

ILIM 6 Current Limit input

SHDN 7Shutdown input, active low

GND 8 Must be connected to GND

GND 9 Must be connected to GND

PF 10 Early Power Fail output, open drain, active LOW

VEPF 11 Comparator voltage input for early power fail warning

PG 12 Power Good, open drain, active HIGH output, monitors feedback voltage

PGND Pad Exposed pad. Connect to GND plane to help thermal dissipation

456

VIN

GND

ILIM

VEPF

GND

SHDN

AS7620

PGND

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AS7620

Data Sheet - A b s o lu t e M a x im u m R a ti n g s

5 Absolute Maximum Ratings

Stresses beyond those list ed in Table 2 may cause permanent damage to the device. These are stress ratings only,

and functional operation of the device at these or any other conditions beyond those indicated in Electrical

Characteristics on page 4 is not implied. Exposure to absolute maximum rating conditions for extended periods may

affect device reliability.

Table 2. Absolute Maximum Ratings

Parameter Min Max Units Comments

VIN -0.3 40 V

LX -0.3 VIN+0.3 V

FB, SHDN -0.3 VIN+0.3

or 5.5 V Whichever is lower

All other pins except LX, FB an d SHDN -0.3 3.6 V

Latch-Up -30 +30 mA Norm: JEDEC 781

1. Voltage on pin 7 (SHDN) limited to +5.5V

Package Power Dissipation 1 W θJA = 32ºC/W for a 4-layer board, 4 vias,

TAMB = +70ºC

Operating Temperature Range -40 +125 ºC Junction temperature

Electrostatic Discharge -1000 +1000 V Norm: HBM MIL-Std. 883E 3015.7 methods

Humidity (Non-Condensing) 5 90 %R.H.

Storage Temperature -55 125 ºC

Junction Temperature 150 ºC

Package body temperature 260 ºC

Norm: IPC/JEDEC J-STD-020C.

The reflow peak soldering temperature (body

temperature) specified is in accordance with

IPC/JEDEC J-STD-020C “Moisture/Reflow

Sensitivity Classification for Non-Hermetic

Solid State Surface Mount Devices”.

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AS7620

Data Sheet - E l e c tr i c a l Ch a r a c t e ri s t i c s

6 Electrical Characteristics

TJ = -40 to +125ºC, VOUT=3.3V, LX=10µH, CX=100µF (unless otherwise specified). Typ. values at VIN= +24V and

TAMB= +25ºC.

Table 3. Electrical Characteristics

Symbol Parameter Conditions Min Typ Max Units

VIN Input Voltage Range 3.6 24 32 V

VCC VEPF, ILIM -0.3 3.6 V

VST Start-up Voltage 3.3 V

VOUT Output Voltage

AS7620-A 1.19 VIN V

AS7620-B Initial, at 25ºC amb. 3.267 3.300 3.333 V

Over line, load and temperature 3.218 3.383

VFB Feedback voltage AS7620-A Initial, at 25ºC amb. 1.178 1.190 1.202 V

Over line and temperature 1.166 1.214 V

AS7620-B 3.218 3.300 3.383

VHYS Controller

Hysteresis AS7620-A At FB node 81530

AS7620-B 22 42 82

VEPF Early Power Fail Threshold at VEPF 1.19 V

VPG Power Good Threshold of VFB at FB pin 91 93 95 %

Line Regulation VIN=8V to 24V, RL=200Ω0.1 % / V

Load Regulation 10% to 90% load change 0.9 %

IFB Input Bias

Current AS7620-A FB pin 200 nA

AS7620-B 3 5 µA

IOUT Output Current ILIM/2 mA

ILIM Switch Current Limit ILIM=0V1

1. LX=100µH, CX=10µF, Initial accuracy only. For temperature variation, please refer to performance graphs.

192 240 288

ILIM=VOUT2

2. VOUT from 1.5V to 3.6V

576 720 864

ILIM=open 800 1000 1200

P-Channel on resistance 0.4 0.8 Ω

Maximum Duty Cycle At VIN=3.6V 100 %

tON Minimum On-Time Current limit is not attained to turn

off the switch before the minimum

on-time expired 81012µs

tOFF Minimum Off-Time 0.22 0.42 0.62 µs

IQQuiescent Current Non-switching 30 45 µA

IOUT=500µA 37 µA

ISHDN Shutdown Current 15µA

VLO Shutdown Threshold SHDN 1 V

IIBN Logic Input Bi as Current SHDN 1 µA

TSHDN Shutdown Temperature 150 175 ºC

TSHDN Hysteresis 10 ºC

TJOperating Temperature junction -40 125 ºC

TAMB ambient -40 85 ºC

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AS7620

Data Sheet - Ty p i c al O p e r a ti n g C h ar a c t e r is t i c s

7 Typical Operating Characteristics

Figure 3. Efficiency vs Output Current, VOUT=4.5V Figure 4. PMOS Rdson vs. Temperature

Figure 5. GND Current vs. IOUT @ TAMB Figure 6. GND Current vs. Temperature @ IOUT=0A

Figure 7. Current Limit Threshold vs VIN Figure 8. Average Switching Frequency vs VIN

100

200

300

400

500

600

700

800

900

1000

-40 -20 0 20 40 60 80 100 120

Temp (C)

Rdson ( m ohm ) .

100

1 10 100 1000

Iout (mA)

Ef ficiency (%)

VIN=32V

VIN=12V

VIN=24V

VIN=5V

28.0

30.0

32.0

34.0

36.0

38.0

40.0

42.0

-40-20020 40 6080100120

Temp ( C)

IGND (u A )

100

1000

10000

1.0 10.0 100.0 1000.0

I out (mA)

IGND (uA)

VIN=32V

VIN=24V

VIN=12V

VIN=5V

VIN=32V

VIN=24V

VIN=5V

VIN=12V

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

5 1015202530

Vin (V)

CL (mA)

ILIM GND

ILIM VOUT

ILIM FLOATING

100

1000

10000

100000

1000000

5 7 9 1113151719212325272931

Vin (V)

Fsw (Hz)

IOUT=500µA

IOUT=5mA

IOUT=50mA

IOUT=500mA

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AS7620

Data Sheet - Ty p i c al O p e r a ti n g C h ar a c t e r is t i c s

Figure 9. Average Switching Frequency vs IOUT

(ILIM=open) Figure 10. Shutdown Current vs. Temperature

Figure 11. Line Regulation @ IOUT=10mA Figure 12. Line Regulation @ IOUT=500mA

Figure 13. Load Regulation Figure 14. Line Regulation VOUT=5V @ 10mA

30000

60000

90000

120000

150000

180000

210000

240000

270000

300000

330000

0 100 200 300 400 500

Iout (mA )

Fsw (Hz)

VIN=5V

VIN=12V

VIN=24V

VIN=32V

0.8

0.9

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

-40 -20 0 20 40 60 80 100 120

Temp (C)

ISHDN ( uA

)

VIN=5V

VIN=12V

VIN=24V

VIN=32V

-10% 10%

-0.800%

-0.600%

-0.400%

-0.200%

0.000%

0.200%

0.400%

0.600%

0.800%

Vout Variation (%)

Vin Vari ation (%)

-10% 10%

-0.400%

-0.300%

-0.200%

-0.100%

0.000%

0.100%

0.200%

0.300%

0.400%

Vout Variation (%)

Vin Vari ation (%)

-1.000%

-0.800%

-0.600%

-0.400%

-0.200%

0.000%

0.200%

0.400%

0.600%

0.800%

1.000%

0.1 1 10 100 1000

Iout (mA)

Vout Vari ati on %

VOUT

VIN

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AS7620

Data Sheet - Ty p i c al O p e r a ti n g C h ar a c t e r is t i c s

Figure 15. Line Regulation VOUT=5V @ 10mA Figure 16. Load Regulation VOUT=5V 10mA→500mA

Note: All measurements taken at VIN=24V, VOUT=3.3V, and TAMB=25ºC using the typical application circuit specified

in Figure 17, unless otherwise specified.

VOUT

VIN

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AS7620

Data Sheet - D e ta i l e d D es c r i p t io n

8 Detailed Description

Figure 17. System Diagram of AS7620-A with Early Power Fail Warning

Shut Down

The device can be shut down by providing a voltage low er than 1V at the SHDN pin (7). In this condition, the

consumption is only 1µA (typ.). The AS7 620 is providing an internally regulated pull-up circuit. No external pull-up

resistor shall be used, which could otherwise damage the shutdown input. Connect the SHDN input directly to an open

drain port only.

Soft Start

The device implements a soft start by limiting the inrush current into the output choke. Initially, the internal PMOS is

turned on until the current reaches the programmed current limit (see Current Limit on page 9) and then is immediately

turned off. It will be turned on again when the current approaches 0A. In this time frame, the FB voltage (VFB) will be

lower than the reference and so the duty cycle will be driven by the current limit only.

Regulation

Both AS7620-A and AS7620-B are based on a hysteretic control method. Moreover, the switch current is monitored to

make the converter always work in discontinuous current mode (DCM). The advantages of this type of control system

can be summarized as following:

! High efficiency even at light load

! Intrinsically stable

! Simplicity

! Readiness during the load transient

The internal PMOS is switched on when the VFB is lower than VREF-VHYST/2 and the current is 0A (DCM). The on time

will be terminated if the VFB is over VREF+VHYST/2 or if the current limit (CL) is triggered. In practice, consideri ng the

most common application conditions (L=10µH ÷ 100µH; C=10µF - 100µF) and setting the CL threshold according to

the load, the on time is normally terminated by the CL intervention and the outpu t voltage ripple will stay within 1.25%

of the output voltage (typ.) or VHYST * VOUT / VREF.

Table 4. AS7620 Output Voltage Options

AS7620 AS7620A-BQFT AS7620B-BQFT

VOUT ADJ. 3.3V

2.2µF

100µF

10µH VOUT

3.6V to 32V

VIN

ILIM

COUT

R7R6

CIN

AS7620-A

VEPF

VHYS

VIN

SHDN

3.3V

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AS7620

Data Sheet - D e ta i l e d D es c r i p t io n

VOUT Selection

The AS7620-B features a 3.3V fixed output voltage. The AS7620-A provides an adjustable output from 1.2V (VREF) up

to virtually VIN (see 100% Duty Cycle Operation on page 11). To select the desired VOUT, the related resisto r divider

has to be tuned according to the following formula:

(EQ 1)

Where:

Rh is the high side resistor of the output divider

Rl is the resistor of the output divider

Note: It is suggested to select resistors in the range of hundreds of kΩ in order to limit the current consumption.

Current Limit

The current is sensed during the on time of the internal PMOS. Three different current limit thresholds can be selected

by the ILIM pin:

1. 240mA (typ.) ILIM shorted to GND

2. 720mA (typ.) ILIM shorted to VOUT (from 1.5V to 3.6V)

3. 1000mA (typ.) ILIM floating

This threshold is intended as peak current limit. If the current reaches the threshold durin g the on time, the PMOS is

turned off and it will be turned on again only when the current approaches 0A and the feedback voltage is equal or

lower than VREF. The maximum output current is ILIM/2.

Switching Frequency

The switching frequency (fsw) changes according to the application conditions and, in particular , to the output current in

order to optimize the efficiency in any load condition. Anyway, it is always possible to estimate the fsw during the design

process. As described in the Regulation (refer to page 8) – the converter always works in DCM and, normally, the peak

current into the inductor is the CL threshold (ILIM). The average of the inductor current must be equal to th e output

current. The following formula provid es the relationship between inductor current and output cu rrent:

IOUT = (EQ 2)

Consequently, the fsw can be expres sed as following:

(EQ 3)

Figure 18. Chart Illustrating the Fsw vs. IOUT in a S tandard Application (VIN=24V, VOUT=3.3V, L=10µH, ILIM=1A)

VOUT VREF 1Rh

-------

⎝⎠

⎛⎞

•=

Tsw

----------1

---ILIM2L•VIN

•

VIN VOUT

–()VOUT

•

--------------------------------------------------

••

Fsw 2IOUT

•VIN VOUT

–()VOUT

••

ILIM2L•VIN

•

----------------------------------------------------------------------------

Fsw vs. I out

100

150

200

250

300

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

Iout (A)

F sw (KHz)

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AS7620

Data Sheet - D e ta i l e d D es c r i p t io n

Power Fail / Power Good

AS7620A-B monitors input and output voltage by VEPF (pin 11) and VFB (pin 5) respectively. Two dedicated flags PF

(pin 10) and PG (pin 12) are provided outside to inform about early input power fail (active low) and output within

regulation. Figure 19 illustrates the typical connection for VEPF. During start up, PF is initially low . By selecting R3, R4,

R5 and R6, it is possible to set the desired input voltage threshold above which the input power is considered stable.

Once VIN (VDDH in Figure 19) reaches Vinth, PF is released and so an additional voltage contribution from VDD is

added at the VPF pin, realizing in fact a hysteresis to eliminate PF oscillation due to power supply noise.

Figure 19. Open-Drain Output Stage for Comparator

Table 5 provides the resistors values covering al l the standard input BUS. The resis to rs val ues are 1% comm ercial

values. It is mandatory to use the correct resistors values to guarantee the respect of maximum absolute voltages at

EPF and PF pin. VDD has been consider ed 3.3V. Otherwise EPF pin should be shorted to GND and PF left floating.

Terminology:

VRST: Reset voltage for the EPF. It is 90% of the Input BUS voltage.

VTRIP: Trip voltage for the EPF. It is 80% of the Input BUS voltage.

Thermal Protection

The internal junction temperature is continuo usly monitored. If it reaches 150ºC (min), the PMOS is turned off. The

device can switch again if the temperature is decreased by at least 10ºC. If the over-temperature persists, the device

will be shut down again resulting in a hiccup mode for the output power.

Table 5. EPF Network Selection with Different Input BUS

VIN (V) VRST (V) VTRIP (V) R3 (KΩ)R4 (KΩ)R5 (KΩ)R6 (KΩ)

5 4.5 4 365 143 1740 1370

6 5.4 4.8 464 143 1870 1430

9 8.1 7.2 768 140 2050 1580

12 10.8 9.6 1070 140 2100 1650

15 13.5 12 1370 140 2150 1690

20 18 16 1870 140 2210 1740

24 21.6 19.2 2260 140 2260 1740

28 25.3 22.5 2670 140 2260 1740

VDDH

3.6…32V

VDD

1.2…3.6

Power Fail

RON

VREF

INV

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AS7620

Data Sheet - A p p l ic a t i o n In f o r m a ti o n

9 Application Information

Input Capacitors

An input capacitor is required to sustain the peak current requested by the turning on of the internal PMOS. When

used, the capacitor helps to reduce the noise and saves the input battery life. The input capacitor has to withstand the

input RMS current, which can be calculated by the following formula:

(EQ 4)

While designing for wide input/output voltage range, the worst case of Irms=1/2*IOUT must be considered. Suggested

capacitors are low ESR OSCON, polymer, aluminum or MLCCs. Tantalum types are not recommended fo r their

weakness in withstanding big inrush currents.

Output Inductor

The inductor together with the output capacitor represents the output filter. Using the AS7620, the inductor is charged

and completely discharged at every switching cycle being that the converter is forced to work in DCM. Values from

10µH to 100µH are suitable to work with AS7620 and its selection should consider the followin g statements:

! Bigger inductor implies lower fsw

! Bigger inductor implies lower bandwidth

The inductor must be rated to withstand the peak current (ILIM) and the RMS current

Output Capacitor

The output capacitor together with the inductor represents the output filter . The bigger the capacitance is, the lower will

be the output ripple. Usually, low ESR MLCCs are preferred as they are inexpensive and small in size. Any value from

10µF is suitable, considering the load transient specifications of the application as well.

Free Wheeling Diode

The inductor current is forced through the diode during the off-times. The average current flowing through it is

The reverse voltage must be higher than the input voltage and safely it is common to consider 30% more. Normally, a

schottky diode is preferred because of its low forward voltage.

Stability

Even though the hysteretic voltage mode is intrinsically stable, an excessive noise at the FB could cause instability . For

this reason care must be taken drawing the layout, reducing the noise and shie lding the FB path from it. The main

noise generator is the switching node, which is commu tated from GND to VIN by the internal PMOS and the free

wheeling diode and through which a pulse current flows. It is wise to add a MLCC capacitor as close as possible to the

VIN pin of the device and provide a wide/short path between the LX pin and the external components (inductor and

diode). It is preferable to draw the FB path as far as possible from the LX node and, perhaps, shielding it with a GND

track. Another recommendation is to use low ESL output capacitors, thus avoiding electrolytic parts. A big ESL adds a

square wave contribution on the FB that can make the device work improperly.

100% Duty Cycle Operation

Thanks to the PMOS structure of the internal switch, the device can actually work at 100% duty cycle. This feature is

very helpful during the load transient, because the maximum power can be transferred to the output in order to recover

as fastest. The device will try to work at 100% duty whenever the FB voltage is lower than the upper window’s

threshold. Moreover, in this condition, the safety is always guaranteed by the current limit.

Irms IOUT VOUT VIN VOUT

–()•

VIN

--------------------------------------------------•=

Irms IOUT2IL2

Δ3

-----------

---fsw ILIM2L•

VOUT

------------------------

••

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AS7620

Data Sheet - A p p l ic a t i o n In f o r m a ti o n

Demo Board

A demonstration board is available to test the device functionalities and perfo r mance in a standard application. For

further information, please refer to the AS7620EB datasheet.

Figure 20. Demo Board Photograph

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AS7620

Data Sheet - P a c k age Drawings and Markings

10 Package Drawings and Markings

The device is available in a 12-Lead MLPQ package.

Figure 21. 4x4mm MLPQ Package Drawings

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AS7620

Data Sheet - P a c k age Drawings and Markings

Table 6. 4x4mm MLPQ Package Dimensions

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AS7620

Data Sheet - O r d e ri n g I n fo r m a t i o n

11 Ordering Information

The devices are available as the standard products shown in Table 7.

All devices are RoHS compliant and free of halogene substances.

Table 7. Ordering Information

Model Description Delivery Form Package

AS7620A-BQFT 500mA hysteretic buck converter,

adjustable output Tape and Reel, 6000 pcs 12-Lead MLPQ, 4x4mm

AS7620A-BQFT-500 500mA hysteretic buck converter,

adjustable output Tape and Reel, 500 pcs 12-Lead MLPQ, 4x4mm

AS7620B-BQFT 500mA hysteretic buck converter, 3.3V

output Tape and Reel, 6000 pcs 12-Lead MLPQ, 4x4mm

AS7620B-BQFT-500 500mA hysteretic buck converter, 3.3V

output Tape and Reel, 500 pcs 12-Lead MLPQ, 4x4mm

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AS7620

Data Sheet

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austriamicrosystems AG reserves the right to change specific ations and prices at any time and without notice.

Therefore, prior to designing this product into a system, it is necessary to check with austriamicrosystems AG for

current information. This product is intended for use in normal commercial applications. Applic ations requiring

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