VNF1248F datasheet(30/79 Pages) STMICROELECTRONICS

30 / 79 page

Capacitive charging mode–CCM

Digital logic implements a PWM-based control of high-side driver to allow charging a capacitive load through the

off-chip power MOSFET driven by the device.

Load charging is split in two phases:

•

Start charging: in this phase the load is charged with a slower PWM period, to check for possible short

circuit on output; a maximum number of PWM pulses is allowed to reach a minimum VOUT value, otherwise

CCM is aborted

•

Standard charging: in this phase the load is charged with a nominal PWM period until VDS reaches an

internally defined threshold (100 mV), or timeout limit is reached

Burst mode control is configured by the following programmable parameters:

•

PWM period (CR#5 - CCM_PWM_T): PWM period (Ton + Toff) set during standard charging phase

•

PWM Ton time (CR#5 - CCM_PWM_TON): PWM interval time with high-side driver turned on

•

PWM Ton Multiplying Factor (CR#3 - CCM_PWM_TON_MF): to multiply by 1/2/4/8 Ton time defined by

CCM_PWM_TON setting, for duty cycle configuration

•

PWM start period (CR#5 - CCM_PWM_SC_T): PWM period (Ton + Toff) set during starting phase (short

circuit check)

•

PWM start pulses max number (CR#5 - CCM_PWM_SC_T_NB): Max number of PWM pulses during

starting phase (short circuit check)

•

CCM timeout (CR#5 – CCM_PWM_TIMEOUT): Maximum time allowed to charging phase

•

VOUT threshold (CR#3 – CCM_VOUT_THR): VOUT limit to overcome to switch form starting phase to

standard charging phase

According to parameter settings, PWM frequency and duty cycle allowed ranges are:

•

PWM standard frequency = 1/CCM_PWM_T → [250 Hz : 20 kHz]

•

PWM standard duty cycle = CCM_PWM_TON_MF*CCM_PWM_TON/CCM_PWM_T

–

CCM_PWM_T = 50 μs (min.) → CCM_PWM_TON_MF x [2 : 100]%

–

CCM_PWM_T = 4 ms (max.) → CCM_PWM_TON_MF x [0.025 : 1.25]%

•

PWM start frequency = 1/CCM_PWM_SC_T → [250 Hz : 500 Hz]

•

PWM start duty cycle = CCM_PWM_TON_MF*CCM_PWM_TON/CCM_PWM_SC_T

–

CCM_PWM_SC_T = 2 ms (min.) → CCM_PWM_TON_MF x [0.05: 2.5]%

–

CCM_PWM_SC_T = 4 ms (max.) → CCM_PWM_TON_MF x [0.025 : 1.25]%

Burst mode control can be activated in two different ways.

•

Control registers: two trigger bits (CR#1 - CCM_CTRL_ON, CCM_CTRL_OFF) are available to,

respectively, turn-on or turn-off CCM burst mode when the device is in unlocked/locked state

•

DIN input: specific toggling sequence on this pin (at least 4 rising edges within tDIN_TOGGLE_TOUT) allows to

turn-on CCM burst mode when the device is in fail-safe state; DIN must be kept high during CCM, as DIN

is driven low load charging is stopped and the device exits from CCM burst mode

CCM operation status is accessible through a specific field in SR#1 register (CCM_STATUS), encoding the

following information:

•

IDLE: CCM operation not started

•

RUN: CCM operation started, running

•

CHARGED: CCM operation completed successfully (VDS fixed threshold reached)

•

CHARGE INCOMPLETE: CCM operation aborted (timeout or short-circuit condition) or stopped (CCM

switched off while running)

VNF1248F

Capacitive charging mode–CCM

DS14109 - Rev 7

page 30/79

VNF1248F Datasheet(PDF) 30 Page - STMicroelectronics

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