MIC24053 Datasheet, PDF(19/32 Page) Micrel Semiconductor – 12V, 9A High-Efficiency Buck Regulator

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MIC24053 Datasheet, PDF (19/32 Pages) Micrel Semiconductor – 12V, 9A High-Efficiency Buck Regulator

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case of a hard short. The load current-limit threshold

has a foldback characteristic related to the feedback

voltage as shown in Figure 4-3.

0.0

0.2

0.4

0.6

0.8

1.0

FEEDBACK VOLTAGE (V)

FIGURE 4-3:

MIC24053 Current-Limit

Foldback Characteristic.

4.6 Power Good (PG)

The Power Good (PG) pin is an open-drain output that

indicates logic high when the output is nominally 92%

of its steady-state voltage. A pull-up resistor of more

than 10 kÎ© should be connected from PG to VDD.

4.7 MOSFET Gate Drive

The Package Type shows a bootstrap circuit consisting

of D1 (a Schottky diode is recommended) and CBST.

This circuit supplies energy to the high-side drive

circuit. Capacitor CBST is charged, while the low-side

MOSFET is on, and the voltage on the SW pin is

approximately 0V. When the high-side MOSFET driver

is turned on, energy from CBST is used to turn the

MOSFET on. As the high-side MOSFET turns on, the

voltage on the SW pin increases to approximately VIN.

Diode D1 is reverse biased and CBST floats high while

continuing to keep the high-side MOSFET on. The bias

current of the high-side driver is less than 10 mA, so a

0.1 Î¼F to 1 Î¼F capacitor is sufficient to hold the gate

voltage with minimal droop for the power stroke

(high-side switching) cycle; that is, ÎBST = 10 mA x

1.67 Î¼s/0.1 Î¼F = 167 mV. When the low-side MOSFET

is turned back on, CBST is recharged through D1. A

small resistor (RG), which is in series with CBST, can be

used to slow down the turn-on time of the high-side

N-channel MOSFET.

The drive voltage is derived from the VDD supply

voltage. The nominal low-side gate drive voltage is VDD

and the nominal high-side gate drive voltage is

approximately VDD â VDIODE, where VDIODE is the

voltage drop across D1. An approximate 30 ns delay

between the high-side and low-side driver transitions is

used to prevent current from simultaneously flowing

unimpeded through both MOSFETs.

ï£ 2015 Microchip Technology Inc.

MIC24053

DS20005668A-page 19

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