33883 datasheet(14/21 Pages) FREESCALE

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Analog Integrated Circuit Device Data



Freescale Semiconductor

33883

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

LOW-DROP LINEAR REGULATOR

The low-drop linear regulator is supplied by VCC2. If VCC2

exceeds 15.0 V, the output is limited to 14.5 V (typical).

The low-drop linear regulator provides the 5.0 V for the

logic section of the driver, the Vgs_ls buffered at LR_OUT, and

the +14.5 V for the charge pump, which generates the

CP_OUT The low-drop linear regulator provides 4.0 mA

average current per driver stage.

In case of the full bridge, that means approximately

16 mA — 8.0 mA for the high side and 8.0 mA for the low

side.

Note: The average current required to switch a gate with

a frequency of 100 kHz is:

ICP = Qg * fPWM = 80 nC * 100 kHz = 8.0 mA

In a full-bridge application only one high side and one low

side switches on or off at the same time.

CHARGE PUMP

The charge pump generates the high-side driver supply

voltage (CP_OUT), buffered at CCP_OUT. Figure 8 shows the

charge pump basic circuit without load.

Figure 8. Charge Pump Basic Circuit

When the oscillator is in low state [(1) in Figure 8], CCP is

charged through D2 until its voltage reaches VCC - VD2. When

the oscillator is in high state (2), CCP is discharged though D1

in CCP_OUT, and final voltage of the charge pump, VCP_OUT,

is Vcc + VLR_OUT - 2VD. The frequency of the 33883 oscillator

is about 330 kHz.

EXTERNAL CAPACITORS CHOICE

External capacitors on the charge pump and on the linear

regulator are necessary to supply high peak current

absorbed during switching.

Figure 9 represents a simplified circuitry of the high-side

gate driver. Transistors Tosc1 and Tosc2 are the oscillator-

switching MOSFETs. When Tosc1 is on, the oscillator is at

low level. When Tosc2 is on, the oscillator is at high level. The

capacitor CCP_OUT provides peak current to the high-side

MOSFET through HSS during turn-on (3).

Figure 9. High-Side Gate Driver

Osc.

Vbat

VCP_OUT

Ccp_out

VLR_OUT

Ccp

(1)

(2)

VLR_OUT

OSC.

CCP

VCC

CP_OUT

CCP_OUT

Ccp_out

VLR-OUT

Ccp

Vcc

CP_out

SRC_HS

MOSFET

Tosc1

Tosc2

GATE_HS

pins

(3)

High-Side

MOSFET

Low-Side

MOSFET

SRC_HS

GATE_HS

VCC

CCP

CP_OUT

VLR_OUT

Tosc2

Tosc1

HSS

LSS

Pins

CCP_OUT

33883 Datasheet(PDF) 14 Page - Freescale Semiconductor, Inc

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