33883 Datasheet, PDF (14/21 Pages) Freescale Semiconductor, Inc – H-Bridge Gate Driver IC

FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
LOW-DROP LINEAR REGULATOR
The low-drop linear regulator is supplied by V_CC2. If V_CC2
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 V_{gs_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:
I_CP = Q_g * f_PWM = 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 C_{CP_OUT}. Figure 8 shows the
charge pump basic circuit without load.
V_{VLLRR__OOUTUT}
O_Os_Sc_C._{. C1}
(2)
C_Cc_Cp _P
(1)
D^D1¹
A_C2
D^D2²
C^VP^CP_^_O^OUU^T T
C^C_C^c_P^p_{_}^__O^o_U^u_T^t
VV_Cb_Cat
Figure 8. Charge Pump Basic Circuit
When the oscillator is in low state [(1) in Figure 8], C_CP is
charged through D2 until its voltage reaches V_CC - V_D2. When
the oscillator is in high state (2), C_CP is discharged though D1
in C_{CP_OUT,} and final voltage of the charge pump, V_{CP_OUT},
is V_cc + V_{LR_OUT} - 2V_D. 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 C_{CP_OUT} provides peak current to the high-side
MOSFET through HSS during turn-on (3).
V_LV_{RL_R-OOUUTT}
TTooscc22
CCcp_CP
C^CP^P_^_O^ouU^t T
D_D1₁
Cc_Cp_P__{_}o_Ou_Ut _T
C^C1 C^C2
DD22
TTooscc11
VV_Cc_Cc
H^TS¹ S
L_TS₂S
(3)
GATE_HS
GATE_HS
RRg g
SR^SC^R_^CH^_S^HS
HS
Hi^Mgh^O-^SS^FEid^Te
MOSFET
LS
L_Mo_Ow_S-_FS_Ei_Tde
MOSFET
pTienrsminals
Figure 9. High-Side Gate Driver
33883
14
Analog Integrated Circuit Device Data
Freescale Semiconductor