DHAB S/134 - Driver Reference (C Implementation)

LEM Automotive Current Transducer, Open Loop Hall Effect
Document version: 15 February 2016 / v2

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1. Overview

Dual-channel Hall-effect current transducer. Each channel produces a ratiometric analog voltage output proportional to the primary current. No digital interface - the driver must read ADC values and convert them to amperes.

Channel	Range	Sensitivity	Use case
CH1	±50 A	40 mV/A	High-accuracy low current
CH2	±200 A	10 mV/A	Wide-range high current

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2. Electrical Characteristics

Power Supply

Parameter	Min	Typ	Max	Unit
Supply voltage (Uc)	4.75	5.0	5.25	V
Current consumption (Ic)	-	15	20	mA
Max output current (Iout)	-1	-	1	mA
Load resistance (RL)	10	-	-	kΩ
Capacitive load (CL)	1	-	100	nF

Output Clamping Voltages (both channels, @ Uc = 5 V)

Limit	Min	Typ	Max	Unit
V_sz low	0.2	0.25	0.3	V
V_sz high	4.7	4.75	4.8	V

Driver note: Any raw ADC reading at or near these clamp levels indicates saturation / over-range - flag accordingly.

Output Internal Resistance

Min	Max	Unit
1	10	Ω

Frequency Bandwidth

Value	Condition
278 Hz	@ −3 dB

Timing

Parameter	Max	Unit
Power-up time	1	ms
Setting time after overload (ts)	10	ms

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3. Conversion Formula

The output voltage is fully ratiometric - both offset and sensitivity scale with Uc:

Ip = (5/Uc) × (Vout − Vo) × (1/G)

Where:

• Ip - Primary current to compute [A]
• Uc - Actual supply voltage [V]
• Vout - Measured output voltage [V]
• Vo - Offset voltage = Uc / 2 at Ip = 0 [V]
• G - Sensitivity [V/A]

Channel-specific constants

Symbol	CH1	CH2	Unit
G	0.040	0.010	V/A
Vo	Uc/2	Uc/2	V
Ipm	±50	±200	A

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4. C Implementation

#include <stdint.h>
#include <stdbool.h>

/* ── Compile-time constants ────────────────────────────────── */
#define DHAB_UC_NOMINAL_V       5.0f   /* Nominal supply [V]           */
#define DHAB_G_CH1_V_PER_A      0.040f /* Channel 1 sensitivity [V/A]  */
#define DHAB_G_CH2_V_PER_A      0.010f /* Channel 2 sensitivity [V/A]  */
#define DHAB_CLAMP_LOW_V        0.30f  /* Output clamp low  [V]        */
#define DHAB_CLAMP_HIGH_V       4.70f  /* Output clamp high [V]        */
#define DHAB_IRANGE_CH1_A       50.0f  /* CH1 measuring range [A]      */
#define DHAB_IRANGE_CH2_A       200.0f /* CH2 measuring range [A]      */

/* ── Return type ────────────────────────────────────────────── */
typedef struct {
    float   current_A;    /* Computed primary current [A]        */
    bool    saturated;    /* true if output is clamped / invalid */
    bool    out_of_range; /* true if |current_A| > channel range */
} dhab_result_t;

/* ── Core conversion ────────────────────────────────────────── */
/**
 * @brief Convert a measured output voltage to primary current.
 *
 * @param vout_V   ADC-measured output voltage [V]
 * @param uc_V     Actual supply voltage [V] (measure if possible; use 5.0 if not)
 * @param g_V_per_A Channel sensitivity: DHAB_G_CH1_V_PER_A or DHAB_G_CH2_V_PER_A
 * @param range_A  Full measuring range: DHAB_IRANGE_CH1_A or DHAB_IRANGE_CH2_A
 * @return dhab_result_t
 */
static inline dhab_result_t dhab_convert(float vout_V,
                                          float uc_V,
                                          float g_V_per_A,
                                          float range_A)
{
    dhab_result_t r = {0};

    /* Saturation detection */
    r.saturated = (vout_V <= DHAB_CLAMP_LOW_V) || (vout_V >= DHAB_CLAMP_HIGH_V);

    /* Ratiometric offset: Vo = Uc/2 */
    float vo_V = uc_V * 0.5f;

    /* Ip = (5/Uc) * (Vout - Vo) / G */
    r.current_A = (DHAB_UC_NOMINAL_V / uc_V) * (vout_V - vo_V) / g_V_per_A;

    /* Range check */
    float abs_i = (r.current_A < 0.0f) ? -r.current_A : r.current_A;
    r.out_of_range = (abs_i > range_A);

    return r;
}

/* ── Channel 1 helper (±50 A) ──────────────────────────────── */
static inline dhab_result_t dhab_read_ch1(float vout_V, float uc_V)
{
    return dhab_convert(vout_V, uc_V, DHAB_G_CH1_V_PER_A, DHAB_IRANGE_CH1_A);
}

/* ── Channel 2 helper (±200 A) ─────────────────────────────── */
static inline dhab_result_t dhab_read_ch2(float vout_V, float uc_V)
{
    return dhab_convert(vout_V, uc_V, DHAB_G_CH2_V_PER_A, DHAB_IRANGE_CH2_A);
}

ADC to Voltage (adapt for your platform)

/* Example: 12-bit ADC, 5 V reference */
#define ADC_RESOLUTION   4096u
#define ADC_VREF_V       5.0f

static inline float dhab_adc_to_voltage(uint16_t adc_raw)
{
    return ((float)adc_raw / (float)ADC_RESOLUTION) * ADC_VREF_V;
}

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5. Accuracy Reference

Channel 1 Accuracy (absolute, in Amperes)

Condition	−40 °C	−20 °C	0 °C	25 °C	65 °C	125 °C
@ 0 A	0.35	0.29	0.23	0.15	0.23	0.35
@ ±20 A	1.20	0.98	0.77	0.50	0.78	1.20
@ ±50 A	1.50	1.25	1.01	0.70	1.02	1.50

Best accuracy occurs near 25 °C. Worst at temperature extremes (−40 °C / 125 °C).

Sensitivity Error

Condition	Typical
@ 25 °C	±0.4 %
−10 °C < T < 65 °C	±1.0 %
−40 °C < T < 125 °C	±1.5 %

Offset Current (CH1)

Condition	Min	Max	Unit
@ 25 °C	−0.15	0.15	A
−10 °C to 65 °C	−0.23	0.23	A
−40 °C to 125 °C	−0.35	0.35	A

Linearity Error (both channels)

Condition	Typical
@ 25 °C, Uc = 5 V, full range	±0.5 %

Output Noise (both channels)

Parameter	Min	Max	Unit
V_no_pp (peak-peak noise)	−10	10	mV

Driver note: At CH1 sensitivity of 40 mV/A, 10 mV noise ≈ 0.25 A resolution floor. Apply a low-pass filter or oversample if higher resolution is needed.

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6. Operating Temperature

Mode	Range
High accuracy	−10 °C to +65 °C
Reduced accuracy	−40 °C to +125 °C

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7. Absolute Maximum Ratings (do not operate at these)

Parameter	Value	Unit
Max supply voltage	±14	V
Storage temperature	−40 to +125	°C
ESD (IEC 61000-4-2)	8	kV
Insulation voltage (AC, 50 Hz, 1 min)	2.5	kV
Max output current	±10	mA
Output short-circuit max duration	120	s

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8. Power-Up Sequence Notes

• Allow ≥ 1 ms after supply stable before sampling output.
• After an overcurrent / overload event, wait ≥ 10 ms (ts) before trusting readings.
• Ratiometric formula requires Uc to be measured or well-regulated; a 5 % Uc error causes a proportional current error.

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9. Recommended External Filtering (from datasheet schematic)

Net	Component	Value
Uc supply decoupling	C	100 nF
CH1 output filter	C	68 nF
CH2 output filter	C	68 nF
Primary current sense	C	47 nF

Place capacitors close to the sensor connector. Load resistance RL ≥ 10 kΩ on each output.