33883 Datasheet, PDF (15/21 Pages) Freescale Semiconductor, Inc – H-Bridge Gate Driver IC

FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
C_CP
C_CP choice depends on power MOSFET characteristics
and the working switching frequency. Figure 10 contains two
diagrams that depict the influence of C_CP value on V_{CP_OUT}
average voltage level. The diagrams represent two different
frequencies for two power MOSFETs, MTP60N06HD and
MPT36N06V.
21
20.5
20
19.5
19
18.5
18
5
25 45 65 85
CCc_Cp_P(n(Fn)F)
MTP60N06HD (Q_g=50nC)
MTP60N06HD (Q_g = 50 nC)
MTP60N06HD (Q_g = 50 nC)
21.5
21
220KkhHZz
1₁0₀0₀k_KH_hZz
20 kHz
100 kHz
20.5
20
19.5
19
18.5
5
25
45
65
85
C_{CCcpP (}(_nn_F)F)
MTP36N06V (Q_g = 40 nC)
Figure 10. V_{CP_OUT} Versus C_CP
The smaller the C_CP value is, the smaller the V_{CP_OUT}
value is. Moreover, for the same C_CP value, when the
switching frequency increases, the average V_{CP_OUT} level
decreases. For most of the applications, a typical value of
33 nF is recommended.
C_{CP_OUT}
Figure 11 depicts the simplified C_{CP_OUT} current and
voltage waveforms. f_PWM is the working switching frequency.
V_CV_{PC_pO_oUutT}
raAgeveVrCapg_oeut
V_{CP_OUT}
OOsscicllialltaortor
iinnhHigihgh
sStattaete _OisOiS_{nntastslctaoLei}c_wltoleialwl_ta_ortor
H^Hiⁱg^ghh^SS^idid^e e Turn On
turn on
∆∆VV_{CCcpP_ _ouOt UT}
I_{CIPCp__OouUt T}
ff==33303k0HkzHz
ff_PP_WWM_M
Peak
Peak C_Cu_urr_rre_enn_tt
Figure 11. Simplified C_{CP_OUT} Current and Voltage
Waveforms
As shown above, at high-side MOSFET turn-on V_{CP_OUT}
voltage decreases. This decrease can be calculated
according to the C_{CP_OUT} value as follows:
Q_g
∆V_{CP_OUT} = _{CCP_OUT}
Where Q_g is power MOSFET gate charge.
C_{LR_OUT}
C_{LR_OUT} provides peak current needed by the low-side
MOSFET turn-on. V_{LR_OUT} decrease is as follows:
Q_g
∆V_{LR_OUT} =
C_{LR_OUT}
TYPICAL VALUES OF CAPACITORS
In most working cases the following typical values are
recommended for a well-performing charge pump:
C_CP = 33 nF, C_{CP_OUT} = 470 nF, and C_{LR_OUT} = 470 nF
These values give a typical 100 mV voltage ripple on
V_{CP_OUT} and V_{LR_OUT} with Q_g = 50 nC.
Analog Integrated Circuit Device Data
Freescale Semiconductor
33883
15