ISL8270MEVAL1Z datasheet(17/56 Pages) RENESAS

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ISL8270M

FN8635 Rev.4.00

Page 17 of 56

Aug 17, 2017

Switching Frequency and PLL

The device’s switching frequency is set from 296kHz to 1067kHz

using the pin-strap method as shown in Table 5, or by using a

PMBus command FREQUENCY_SWITCH. The ISL8270M

incorporates an internal Phase-Locked Loop (PLL) to clock the

internal circuitry. The PLL can be driven by an external clock source

connected to the SYNC pin. When using the internal oscillator, the

SYNC pin can be configured as a clock source as a external sync to

other modules. Refer to “SYNC_CONFIG (E9h)” on page 46 for more

information. A standard 1% resistor is required if using pin-strap.

Loop Compensation

The module is internally compensated using the PMBus

command ASCR_CONFIG. The ISL8270M uses the ChargeMode

control algorithm that responds to output current changes within

a single PWM switching cycle, achieving a smaller total output

voltage variation with less output capacitance than traditional

PWM controllers.

Input Undervoltage Lockout (UVLO)

The Input Undervoltage Lockout (UVLO) prevents the ISL8270M

from operating when the input falls below a preset threshold,

indicating the input supply is out of its specified range. The UVLO

threshold (VUVLO) can be set between 4.18V and 16V using the

pin-strap method as shown in Table 6, or by using the PMBus

command VIN_UV_FAULT_LIMIT. A standard 1% resistor is

required if using pin-strap.

Fault response to an input undervoltage fault can be programmed

with the PMBus command VIN_UV_FAULT_RESPONSE.

SMBus Module Address Selection

Each module must have its own unique serial address to

distinguish between other devices on the bus. The module

address is set by connecting a resistor between the SA pin and

SGND. Table 7 lists the available module addresses. A standard

1% resistor is required.

TABLE 5. SWITCHING FREQUENCY RESISTOR SETTINGS

fSW

(kHz)

RSET

(kΩ)

296

14.7, or connect to SGND

320

16.2

364

17.8

400

19.6

421

21.5

471

23.7

533

26.1, or OPEN

571

28.7

615

31.6

727

34.8

800

38.3

842

42.2

889

46.4

1067

51.1, or connect to V25

TABLE 6. UVLO RESISTOR SETTINGS

UVLO

(V)

RUVLO

(kΩ)

4.5

OPEN

10.8

Connect to V25

4.18

26.1

4.59

28.7

5.06

31.6

5.57

34.8

6.13

38.3

6.75

42.2

7.42

46.4

8.18

51.1

8.99

56.2

9.90

61.9

10.90

68.1

12.00

13.20

82.5

14.54

90.9

16.00

100

TABLE 7. SMBus ADDRESS RESISTOR SELECTION

RSA

(kΩ)

SMBus

ADDRESS

19h

1Ah

12.1

1Bh

13.3

1Ch

14.7

1Dh

16.2

1Eh

17.8

1Fh

19.6

20h

21.5

21h

23.7

22h

26.1

23h

28.7

24h

31.6

25h

34.8, or connect to SGND

26h

38.3

27h

42.2, or open

28h

46.4

29h

51.1

2Ah

56.2

2Bh

61.9

2Ch

68.1

2Dh

2Eh

TABLE 6. UVLO RESISTOR SETTINGS (Continued)

UVLO

(V)

RUVLO

(kΩ)

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