ZL2103ALAF datasheet(20/28 Pages) RENESAS

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ZL2103

FN6966 Rev 5.00

Page 20 of 28

May 3, 2011

In the ZL2103, the compensation zeros are set by configuring the

FC pin or via the I2C/SMBus interface once the user has

calculated the required settings. This method eliminates the

inaccuracies due to the component tolerances associated with

using external resistors and capacitors required with traditional

analog controllers.

The loop compensation coefficients can also be set via the

I2C/SMBus interface. Please refer to Application Note AN2033

for further details. Also refer to Application Note AN2035 for

further technical details on setting loop compensation.

Driver Dead-time Control

The ZL2103 utilizes a predetermined fixed dead-time applied

between the gate drive signals for the top and bottom MOSFETs.

In a synchronous buck converter, the MOSFET drive circuitry must

be operated such that the top and bottom MOSFETs are never in

the conducting state at the same time. This is because

potentially damaging currents flow in the circuit if both MOSFETs

are on simultaneously for periods of time exceeding a few

nanoseconds. Conversely, long periods of time in which both

MOSFETs are off reduces overall circuit efficiency by allowing

current to flow in their parasitic body diodes.

Therefore, it is advantageous to minimize the dead-time to

provide peak optimal efficiency without compromising system

reliability. The ZL2103 has optimized the dead-time for the

integrated MOSFETs to maximizing efficiency.

Power Management Functional

Description

Input Undervoltage Lockout

The input undervoltage lockout (UVLO) prevents the ZL2103 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 to either 4.5V or 10.8V using the SS

pin according to Table 6.

The UVLO voltage can also be set to any value between 2.85V

and 16V via the I2C/SMBus interface.

Once an input undervoltage fault condition occurs, the device

can respond in a number of ways as follows:

1. Continue operating without interruption.

2. Continue operating for a given delay period, followed by

shutdown if the fault still exists. The device will remain in

shutdown until instructed to restart.

3. Initiate an immediate shutdown until the fault has been

cleared. The user can select a specific number of retry

attempts.

The default response from a UVLO fault is an immediate shutdown

of the device. Please refer to Application Note AN2033 for details on

how to configure the UVLO threshold or to select specific UVLO fault

response options via the I2C/SMBus interface.

Output Overvoltage Protection

The ZL2103 offers an internal output overvoltage protection

circuit that can be used to protect sensitive load circuitry from

being subjected to a voltage higher than its prescribed limits. A

hardware comparator is used to compare the actual output

voltage (seen at the VSEN pin) to a threshold set to 15% higher

than the target output voltage (the default setting). If the VSEN

voltage exceeds this threshold, the PG pin will de-assert and the

device can then respond in a number of ways as follows:

1. Initiate an immediate shutdown until the fault has been

cleared. The user can select a specific number of retry

attempts.

2. Turn off the high-side MOSFET and turn on the low-side

MOSFET. The low-side MOSFET remains on until the device

attempts a restart.

The default response from an overvoltage fault is to immediately

shut down. For continuous overvoltage protection when operating

from an external clock, the only allowed response is an

immediate shutdown. Please refer to Application Note AN2033

TABLE 12. RESISTOR SETTING FOR LOOP COMPENSATION

G(dB)

Qfsw/fn

(k)

0.150

115.000

Open or 11

0.150

115.000

Low or 10

0.150

69.147

13.3

0.150

41.577

14.7

0.300

115.000

16.2

0.300

69.147

17.8

0.300

41.577

19.6

0.300

25.000

21.5

0.600

69.147

23.7

0.600

41.577

26.1

0.600

25.000

28.7

0.150

115.000

High or 12.1

0.150

69.147

31.6

0.150

41.577

34.8

0.300

115.000

38.3

0.300

69.147

42.2

0.300

41.577

46.4

0.300

25.000

51.1

0.600

69.147

56.2

0.600

41.577

61.9

0.600

25.000

68.1

0.150

115.000

75.0

0.150

69.147

82.5

0.150

41.577

90.9

0.300

115.000

100.0

0.300

69.147

110.0

0.300

41.577

121.0

0.300

25.000

133.0

0.600

69.147

147.0

0.600

41.577

162.0

0.600

25.000

178.0

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