Fairchild RC7352 service manual

RC7352

Parametric Measurement Unit

www.fairchildsemi.com

Features

• Force voltage/measure current and force current measure voltage functions

• Forced voltage range (-5V to +15V)

• Four programmable measured current ranges: Range A = ±20mA max Range B = ±200mA max Range C = ±1.0mA max Range D = ±40mA max

• High resolution current force/measure ±0.05% = 2 bits

• Internal control circuitry for selecting ranges

• High accuracy: 12 bit linearity and 0.5% gain error

• High current range D current limit protection set externally by the value of resistor R

DIL

• Measurement output voltage can be disabled

• Forced current ranges: Range A = ±20mA max Range B = ±200mA max Range C = ±1.0mA max Range D = ±40mA max

• Measured voltage range: -5V to +15V

Block Diagram

• High resolution voltage measurement (±0.05%) and accuracy: (±10mV max. offset) and 0.5% gain error

• Internal current limit for ranges (A, B, & C)

Applications

• ATE pin electronics measurements

• Instrumentation, meters

• Programmable voltage or current supply

Description

The RC7352 is a “Per Pin” Parametric Measurement Unit (PMU) that can force voltage and measure current or force current and measure voltage. The RC7352 forces voltages from +15V to -5V when +V currents up to ±40mA. All logic inputs for the RC7352 are TTL compatible, while the open collector logic outputs are TTL/CMOS compatible.

Setting the SI/V (Select I/V) pin low puts the RC7352 in the force voltage and measure current mode. The resulting output voltage at the DUT matches the input applied to the

is 20V and –VS is -10V, or

VIN

CAP

CAP_I

I/VIN

RADJ

CAP_V

V/I FORCE

V/I MEAS.

6 CA

+ –

–

– +

–

25 CB

WINDOW

COMPARATOR

26 I/V MN

4 I/V MX

15 I/V M

– + –

7 I/VOUT

+ –

–

5 VHS

I SENSE

27 VLS

20 VFB

I: FI/MV V: FV/MI

13 SI/V

+ –

LOGIC

BIAS

12 RS1

28 +VS (20V)

4:1 MUX

–

A = 4

–

21 VDIS

14 RS2

–

– +

–

– +

–

– +

RANGE A

IN EN

RANGEA.SCH

RANGE B 19

IN EN

RANGEB.SCH RANGE C 22

IN EN

RANGEC.SCH RANGE D 24

IN EN

RANGED.SCH

8 GND

OUT

RDIL

-VS (-10V)

RDIL

3 VEE (-10V)

65-7352-01

Rev. 1.1.2

RC7352 PRODUCT SPECIFICATION

I/VIN pin (please refer to block diagram). The I/VM pin provides a voltage proportional to the DUT current. V(I/VM) = (4 x R x I(DUT)), where R is the external range resistor (0.05% tolerance) and I(DUT) is the current supplied to the load. The resistors in the application circuit were chosen using this formula R range = (2V/Imax), for Range A this is RA = 2/20 mA or 100K.

When SI/V is high the RC7352 will force current and measure voltage. The range select pins RS1 and RS2 control the maximum output current (see Table 1), while magnitude of the forced current is given by the expresion

I(DUT) = V(I/VIN)/(4 x R) where R is the range resistor. In the FI/MV mode the v oltage

at the I/VM pin equals the device voltage. The I/VM pin can be connected to an A/D convertor to monitor the current or voltage at the load device.

The RC7352 also has a window comparator that can provide upper or lower limit fail information. I/Vmx and I/Vmn are voltage inputs for the upper and lower limits respectively. You must use the formulas listed above to calculate current limits for each range while voltage limits are 1:1. Their corresponding outputs, VHF (V high fail) and VLF (V low fail) can be used individually or “Wire ORed” to obtain a

composite signal. Additionally the VDIS pin can be set high to disable the window comparator and its I/O lines. Although this reduces overall power consumption, it also disables the I/VM output.

Table 1. Maximum Output Current on Pin Select

SI/V RS2 RS1 Mode

0 0 0 FV/MI Range A, Imax = ±20 mA 0 0 1 FV/MI Range B, Imax = ±200 mA 0 1 1 FV/MI Range C, Imax = ±1.0 mA 0 1 0 FV/MI Range D, Imax = ±40 mA 1 0 0 FI/MV Range A, Imax = ±20 mA 1 0 1 FI/MV Range B, Imax = ±200 mA 1 1 1 FI/MV Range C, Imax = ±1.0 mA 1 1 0 FI/MV Range D, Imax = ±40 mA

Notes:

1. FV/MI = Force Voltage Measure Current.

2. FI/MV = Force Current Measure Voltage.

3. +V

–5 ³ V

OUT

³ –VS+5

Pin Assignments

OUT

GND

RADJ

CAP_I

VEER

I/V

4 3 2 1 28 27 26

5 6

7 8 9

10 11

RC7352

13 14 15 16 17 18

SI/V

DIL

+VSVLFI/V

–V

I/VM

I/V

DIS

65-7352-02

CAP_V

PRODUCT SPECIFICATION RC7352

Pin Description

Pin Name Pin Number Pin Description

-V

GND 8 This pin should be connected to the printed circuit board’s ground plane. I/V

28 +VS should be bypassed to ground with a 10.0 mF tantalium capacitor placed as

close to the pin as possible.

16 –VS should be bypassed to ground with a 10.0 mF tantalium capacitor placed as

close to the pins as possible.

is the negative supply for range D. This pin should be bypassed with a 0.1 mF

ceramic capacitor to ground.

23 Input reference voltage for V

OUT

or I

. In the force voltage measure current mode

OUT

(FV/MI) V(I/V

) = V(I/VIN )

OUT

and V(I/VM) = 4 x I Where I

OUT

x R

OUT

is the device output current and R is the range resistor.

In the Force Current/Measure Voltage Mode

V I VIN¤()

------------------------= 4R´

)

OUT

. The current to the load is

OUT

serving as the voltage

OUT

I/V

OUT

V(I/VM) = V(I/V

7 The Load or Device under test is connected to I/V

supplied via the appropriate range resistor with I/V feedback point for the PMUs internal instrumentation amplifier.

SI/V 13 A TTL/CMOS signal applied to this pin selects either Force Voltage/Measure Current

or Force Current/Measure Voltage mode. A TTL/CMOS low level will select Force Voltage/Measure Current function. A TTL/CMOS high level selects Force Current/ Measure Voltage mode.

9 Resistor RA should be placed between RA and I/V

. RA tolerance should be

OUT

better than +0.05% to improve gain error. Maximum current for range A is shown in the equation below.

2V±

---------- -=

The ±2 volts represents the maximum voltage VA across RA. For Range A, IA should not exceed ±20 mA, i.e., RA should be higher than or equal to 100 kW. A metal film resistor should be used to reduce inherent resistor noise (schott and pop corn noise) and improve resolution. For maximum stability, a 300 pF capacitor should be connected across RA.

19 For Range B, IB should not exceed ±200 mA, i.e., RB should be higher than or equal

to 10 kW with ±0.05% tolerance. For maximum stability a 1,000 pF capacitor should be connected across RB.

22 For Range C, IC should not exceed ±1 mA, i.e., RC should be higher than or equal to

2 kW with ±0.05% tolerance.

24 For Range D, ID should not exceed ±40 mA, i.e., RD should be higher than or equal

to 50 W with ±0.05% tolerance.

D 1 Two diodes must be connected between D & R

, C

DIL

6, 25 A 30pF capacitor placed between these pins will improve stability.

2 Range D output for current limiting. An external resistor is connected between RDIL

and D to limit current to a value I

= 0.8V/RLM.

LIM

as shown in the block diagram.

RC7352 PRODUCT SPECIFICATION

Pin Description (continued)

Pin Name Pin Number Pin Description

RS1, 12 RS1 and RS2 are TTL or CMOS compatible. The truth table below shows the range

selection table.

I/VMX, I/V

DIS

I/VM 15 In the Force Voltage/Measure Current mode this output voltage is equal to four times

RADJ 10 The RADJ pin is provided to adjust the offset for the I

CAP_I CAP_V CA

14 RS1 RS2 Range Selected

LL A

L H B H H C H L D

The voltage applied to pin 4 sets the upper current or voltage limit for the measurement at pin 15 I/VM. To set the desired limit for current measurement a voltage equaling (4 x I

x R) must be applied on this pin. R is the external resistor of

the selected range (A, B, C, or D). For voltage measurement the voltage applied to this pin is the limit.

, High Fail, is an open collector output that requires a pull-up to the logic supply.

If the voltage at pin 15, I/VM, is greater than the threshold voltage at pin 4, I/VMX, VHF will become a logic low. The open collector structure makes wire-ORing of multiple PMU’s possible. Connect a 3,000 pF capacitor to GND to minimize oscillation at the cross-over point.

29 VLF mirror VHF for the lower threshold I/VMN. Connect a 3,000 pF capacitor to GND

to minimize oscillation at the cross over point.

21 When V

is tied to ground output I/VM, VHF and VLF are enabled. If V

DIS

is open VHF and VLF will require external pullups to maintain a logic high. And I/VM will be in a high impedance state.

the voltage across external resistor R of selected range A, B, C, or D through which the measured current is flowing ((I/V)M = 4.0 x IM x R). In the Force Current/ Measure Voltage mode this output is equal to the voltage at I/V out. This output can be disabled by applying a TTL HI on the V

20 VFB, voltage feedback, is the buffered output voltage, I/V

pin. (Pin 21)

DIS

. This pin should not

OUT

be loaded. Connect a 50K 1% resistor from VFB to CAP_V.

function. The best

SENSE

accuracy for V/IM is obtained when RADJ is shorted to analog ground. The point is terminated with a 100 W resistor in the block diagram.

11 18 17

CA is the common point for two 50 pF compensation capacitors that improve the stability of the PMU. These components are optional and can be omitted for some loads.

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