MIC23156 datasheet(18/32 Pages) MICROCHIP

18 / 32 page

MIC23156

DS20005919A-page 18

 2017 Microchip Technology Inc.

5.7

HyperLight Load Mode

The MIC23156 uses a minimum on and off-time propri-

etary control loop. When the output voltage falls below

the regulation threshold, the error comparator begins a

switching cycle that turns the PMOS on and keeps it on

for the duration of the minimum on-time; this increases

the output voltage. If the output voltage is over the

regulation threshold, then the error comparator turns

the PMOS off for a minimum off-time until the output

drops below the threshold. The NMOS acts as an ideal

rectifier that conducts when the PMOS is off. Using a

NMOS switch instead of a diode allows for a lower

voltage drop across the switching device when it is on.

The synchronous switching combination between the

PMOS and the NMOS allows the control loop to work

in Discontinuous mode for light load operations. In Dis-

continuous mode, the MIC23156 works in HyperLight

Load to regulate the output. As the output current

increases, the off-time decreases, thus providing more

energy to the output. This switching scheme improves

the efficiency of MIC23156 during light load currents by

only switching when it is needed. As the load current

increases, the MIC23156 goes into Continuous

Conduction Mode (CCM) and switches at a frequency

centered at 3 MHz. The equation to calculate the load

when the MIC23156 goes into Continuous Conduction

Mode may be approximated by Equation 5-5:

EQUATION 5-5:

CALCULATING LOAD

WHEN IN CONTINUOUS

CONDUCTION MODE

As shown in Equation 5-5, the load at which the

MIC23156 transitions from HyperLight Load mode to

PWM mode is a function of the Input Voltage (VIN), Out-

put Voltage (VOUT), Duty Cycle (D), Inductance (L) and

frequency (f). As shown in Figure 5-3, as the output

current increases, the switching frequency also

increases until the MIC23156 goes from HyperLight

Load mode to PWM mode, at approximately 200 mA.

The MIC23156 will switch at a relatively constant

frequency, around 3 MHz, once the output current is

over 200 mA.

FIGURE 5-3:

SW Frequency vs. Output

Current.

5.8

Output Voltage Setting

The MIC23156 features dynamic voltage scaling and

setting hardware that allow the output voltage of the

buck regulator to be changed on-the-fly, in increments

of 10 mV. The output voltage is set according to one of

two registers that behave identically: BUCK_OUT1

when VSEL = 0 and BUCK_OUT2 when VSEL = 1. If the

BUCK_OUT value is changed while the VSEL is selected

and the regulator is enabled, then the output voltage will

immediately change to the new value using Dynamic

Voltage Scaling (DVS). Equation 5-6 describes the

relationship between the register value and the output

voltage:

EQUATION 5-6:

OUTPUT VOLTAGE

RELATIONSHIP

Note that the maximum output voltage is 2.4V, corre-

sponding to a register setting of 170 (0b10101010,

0xAA). An example of this calculation is demonstrated

in Section 5.13 “Calculating DAC Voltage Code”.









ILOAD >

(VIN – VOUT) D

 f

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

100

1000

10000

OUTPUT CURRENT (mA)

VOUT = 1.8V

COUT = 2.2 µF

2.2 µH

1.0 µH

Switching Frequency vs.

Output Current

VOUT = 0.7 + (0.01  REGBUCK_OUT)

MIC23156 Datasheet(PDF) 18 Page - Microchip Technology

MIC23156 Datasheet(HTML) 18 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Datasheet Download

Link URL