L9305 datasheet(20/107 Pages) STMICROELECTRONICS

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6.1.1

Current set point programming

The targeted average current set point is independently programmable for each channel through the dedicated

SPI register (Channel_x.Current_Set_Point) and it is 13-bit wide. The current resolution is programmable in two

resolution steps through the HILOAD bit (D[8] in Channel_x.Configuration1) which will also set the maximum

regulated current. Below is a brief summary for using HILOAD to select current range and resolution.

•

HILOAD = 0 → Normal current mode - Single bit resolution = 0.25 [mA] - Max Avg. Current 1.5 [A].

TargetAverageCurrent=Setpoint12:0*0.25mA

•

HILOAD = 1 → High current mode - Single bit resolution = 0.33 [mA] - Max Avg. Current 2.0 [A].

TargetAverageCurrent=Setpoint12:0*0.33mA

The maximum guaranteed ripple current for the device’s specified accuracy is 0.5 [A] peak to peak for HILOAD=0

and 0.66 [A] peak to peak for HILOAD=1, so that the max load current for correct current control is

•

1500 mA + 250 mA = 1750 mA for HILOAD = 0

•

2000 mA + 330 mA = 2330 mA for HILOAD = 1

If the channel is enabled and programmed with 0x0000h current set point, the power output is forced with duty

cycle 0 (recirculation path fully on) and the current measurement is disabled; set point codes higher than 0x1770h

are reserved for calibration and offset compensation purposes: in case such codes are selected, the accuracy is

not guaranteed.

When CHx.SETPOINT=0000 and channel x is controlled Hardware mode (CONFIGURATION1.D[2]=0), then

current measurement is disabled and AVGCUR always returns all ‘0’, even if channel x is driven full-on.

6.1.2

PWM switching period programming

The PWM switching period is programmable as shown in the next table, through the dedicated 11-bit field in the

SPI register Channel_x.Control Configuration (CTRLCFG):

Table 11. PWM period and Frequency Programming

PWM code [10:0]

Period [µs]

Frequency

[Hz]

Status

hex

dec

0x000

20000

Short period/High frequency range

PWM Period = 50 µs + PWM Code D[10:0] * 5 µs

0x001

18180

…

0x009

10520

0x00A

100

10000

PWM Period = PWM Code D[10:0] * 10 µs

Normal Period/Frequency range.

0x00B

110

9090

…

0x681

1665

16650

60.06

0x682

1666

16660

60.02

0x683

1667

16670

60.02

Values clamped to maximum period of 16.67 ms

…

16670

60.02

0x7FF

2047

16670

60.02

6.1.3

Current control loop configuration

Hardware current control feedback Frequency Mode is user programmable for either variable or fixed frequency

operation through register Channelx_CTRLCFG, bit D[11].

In fixed frequency current control configuration, the programmed PWM period is exactly the actuated period. The

control algorithm and a Proportional-Integral (PI) processing circuit with ramp-compare control the duty cycle.

In variable frequency current control configuration, the programmed PWM period is the target set point for the

inner frequency control loop. The control algorithm and a zero crossing integrator control both PWM period and

duty cycle. The actual PWM period may differ from the target PWM period, especially during transients.

L9305

Current control drivers

DS12774 - Rev 10

page 20/107

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