View CS3865C_592052.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

CS3865C
CS3865C
High Performance Dual Channel Current Mode Controller with ENABLE
Description
The CS3865C is a high performance, fixed frequency, dual current mode controller. It is used in Off-Line and DC to DC converter applications and require a minimum number of external components. This integrated circuit features a unique oscillator for precise duty cycle limit and frequency control, a temperature compensated reference, two high gain error amplifiers, two current sensing comparators, and two high current totem pole outputs ideally suited for driving power MOSFETs. One of the outputs VOUT2 is switchable via the ENABLE 2 pin. Also included are protective features consisting of input and reference undervoltage lockouts each with hysteresis, cycle-by-cycle current limiting, and a latch for single pulse metering of each output. The CS3865C has a 14V start voltage and is pin compatible with the MC34065H.
Features
s Oscillator has Precise Duty Cycle Limit and Frequency Control s 500kHz Current Mode Operation s Automatic Feed Forward Compensation s Separate Latching PWMs for Cycle-By-Cycle Current Limiting s Internally Trimmed Reference with Undervoltage Lockout s Switchable Second Output s Two High Current Totem Pole Outputs s Input Undervoltage Lockout with Hysteresis s Low Start-Up and Operating Current
Block Diagram
VCC
VREF
5.0V Ref
VCC Undervoltage Lockout
VREF Undervoltage Lockout
SYNC CT RT Latching PWM 1 Oscillator
VOUT1
Package Options
Sense1
+
VFB1
16L PDIP & SO Wide
SYNC 1 CT RT
2 3 16 15 14 13 12 11 10 9
-
Error Amp 1 COMP1 ENABLE2 Latching PWM 2 VOUT2
VCC VREF ENABLE2 VFB2 COMP2 Sense2 VOUT2 Pwr Gnd
VFB1 4
VFB2
+ -
Error Amp 2 COMP2
Sense2
COMP1
5
Sense1 6 VOUT1 7 Gnd 8
Gnd
Pwr Gnd
Cherry Semiconductor Corporation 2000 South County Trail, East Greenwich, RI 02818 Tel: (401)885-3600 Fax: (401)885-5786 Email: info@cherry-semi.com Web Site: www.cherry-semi.com
Rev. 12/16/96
1
A
(R)
Company
CS3865C
Absolute Maximum Ratings Total Power Supply and Zener Current .........................................................................................................................50mA Output Current, Source or Sink (Note 1)...........................................................................................................................1.0A Output Energy (capacitive load per cycle) .......................................................................................................................5.0J Current Sense, Enable and Voltage ......................................................................................................................-0.3 to +5.5V Feedback Inputs High State (Voltage)..........................................................................................................................................5.5V Low State (Reverse Current) ......................................................................................................................-5.0mA Error Amp Output Sink Current......................................................................................................................................10mA Storage Temperature Range ................................................................................................................................-65 to +150C Operating Junction Temperature...................................................................................................................................+150C Operating Ambient Temperature.............................................................................................................................0 to +70C Lead Temperature Soldering Wave Solder (through hole styles only) .................................................................................10 sec. max, 260C peak Reflow (SMD styles only) ..................................................................................60 sec. max above 183C, 230C peak
Electrical Characteristics: VCC = 15V, RT = 8.2k, CT = 3.3nF, for typical values TA=25C, for min/max values TA is the operating
ambient temperature range that applies [Note 3]. TEST CONDITIONS MIN PARAMETER TYP MAX UNIT
s Reference Section Reference Output Voltage, VREF Line Regulation Load Regulation Total Output Variation over Line, Load and Temperature Output Short Circuit Current s Oscillator and PWM Sections Total Frequency Variation over Line and Temperature Frequency Change with Voltage Duty Cycle at each Output Sync Input Current 11VVCC15V, TlowTAThigh 11VVCC15V Maximum High State VIN=2.4V Low State VIN=0.8V 46.0 46.5 49.0 0.2 49.5 170 80 51.5 1.0 52.0 250 160 kHz % % A IOUT=1.0mA, TJ=25C 11VVCC15V 1.0mAIOUT10mA 4.85 30 100 4.9 5.0 2.0 3.0 5.1 20.0 25.0 5.15 V mV mV V mA
s Error Amplifiers Voltage Feedback Input Input Bias Current Open-Loop Voltage Gain Unity Gain Bandwidth Output Current Output Voltage Swing VOUT=2.5V VFB=5.0V VOUT=2.0 to 4.0V TJ=25C (note 6) Source VOUT=3.0V, VFB=2.3V Sink VOUT=1.2V, VFB=2.7V High State, RL=15k to ground, VFB=2.3V Low State, RL=15k to VREF, VFB = 2.7V 2 65 0.7 60 -0.45 2.00 5.0 2.42 2.50 -0.1 100 1.0 90 -1.00 12.00 6.2 0.8 1.1 2.58 -1.0 V A dB MHz dB mA mA V
Power Supply Rejection Ratio VCC=11V to 15V
CS3865C
Electrical Characteristics: VCC = 15V, RT = 8.2k, CT = 3.3nF, for typical values TA=25C, for min/max values TA is the operating
ambient temperature range that applies [Note 3]. TEST CONDITIONS MIN PARAMETER TYP MAX UNIT
s Current Sense Section Current Sense Input Voltage Gain Maximum Current Sense Input Threshold Input Bias Current Propagation Delay s Output 2 Enable Pin Enable Pin Voltage High State Low State Low State Input Current s Drive Outputs Output Voltage Low State High State Output Voltage with UVLO Activated Output Voltage Rise Time Output Voltage Fall Time ISINK=20mA ISINK=200mA ISOURCE=20mA ISOURCE=200mA VCC=6.0V, ISINK=1.0mA CL=1.0nF (Note 6) CL=1.0nF (Note 6) 0.1 1.6 13.5 13.4 0.1 28 25 0.4 2.5 V V V V V ns ns Output 2 enabled Output 2 disabled VIL= 0V 3.5 0.0 100 250 VREF 1.5 400 V V A Current Sense Input to Output (Note 6) (Notes 4 and 5) (Note 4) 2.75 430 3.00 480 -2.0 150 3.25 530 -10.0 300 V/V mV A ns
13.0 12.0
1.1 150 150
s Undervoltage Lockout Section Start-Up Threshold Minimum Operating Voltage After Turn-On Hysteresis s Total Device Start-Up Current Operating Current VCC=12V (Note 7) 15.5 0.6 20 17.0 1.0 25 19.0 mA mA V CS3865C 13 9.0 14 10.0 4 15 11.0 V V V
Power Supply Zener Voltage ICC=30mA
Note 1: Maximum package power dissipation limits must be observed. Note 3: Adjust VCC above the Start-Up threshold before setting to 15V. Note 4: This parameter is measured at latch trip point with VFB =0V. Note 5: Comparator gain is defined as: V Compensation AV = V Current Sense
Note 6: These parameters are guaranteed by design but not 100% tested in production. Note 7: Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible: Tlow=0C ; Thigh=+70C
3
CS3865C
Package Pin Description
PACKAGE PIN # PIN SYMBOL FUNCTION
16 L PDIP & SO Wide 1 SYNC A positive going pulse applied to this input will synchronize the oscillator. A DC voltage within the range of 2.4V to 5.5V will inhibit the oscillator. Timing capacitor CT connects pin to ground setting oscillator frequency. Resistor RT connects to ground setting the charge current for CT. Its value must be between 4.0k and 16k. The inverting input of error amplifier 1. Normally it is connected to the switching power supply output. The output of error amplifier 1, for loop compensation. Output 1 pulse by pulse current limit. Drives the power switch at output 1. Logic ground Power ground. Power device return is connected to this pin. Drives the power switch at output 2. Output 2 pulse by pulse current limit. Output of error amplifier 2, for loop compensation. Inverting input of error amplifier 2. Normally it is connected to the switching power supply output. Output 2 disable. A logic low at this pin disables VOUT2. 5.0V reference output. It can source current in excess of 30mA. The positive supply of the IC. Typical Performance Characteristics Timing Resistor vs. Oscillator Frequency
16 MAXIMUM DUTY CYCLE (%) RT TIMING RESISTOR (K)
100p
1.0n
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
CT RT VFB1 COMP1 Sense1 VOUT1 Gnd Pwr Gnd VOUT2 Sense2 COMP2 VFB2 ENABLE2 VREF VCC
Max. Output Duty Cycle vs. Oscillator Frequency
50 48 46 44 42 40 38 10k VCC = 15V RT = 4.0k to 16k CL = 15pF TA = 25C 30k 50k 100k 300k 500k 1.0M OUT 1 OUT 2
14
2.2n
220
330
F
F
500
pF
3.3
pF
12
10 CT= nF
pF
F
5.0 nF
nF
10 8.0
VCC= 6.0 15V 4.0 10k TA=25C 30k 50k 100k 300k 500k 1.0M f OSC OSCILLATOR FREQUENCY (Hz)
f OSC OSCILLATOR FREQUENCY (Hz)
Error Amp Open-Loop Gain & Phase vs. Frequency
AVOL, OPEN-LOOP VOLTAGE GAIN (dB) 100 80 60 40 20 0 -20 10k GAIN VCC = 15V VO = 1.5V TO 2.5V RL = 100k TA = 25C PHASE 0 30 60 90 120 150 180 10M Phase Margin (DEGREES) Vth, CURRENT SENSE INPUT THRESHHOLD (V) 0.6
Current Sense Input Threshold vs. Error Amp Output Voltage
VCC = 15V 0.5 0.4 0.3 0.2 0.1 0 0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 ERROR AMP OUTPUT VOLTAGE (V) TA = 125C TA = 25C TA = -55C
100k
1.0k
10k
100k
1.0M
f, FREQUENCY (Hz)
4
CS3865C
Typical Performance Characteristics: continued Reference Voltage Change vs. Source Current
0 VCC = 15V VREF, REFERENCE Voltage (mV) -4.0 -8.0 -12 -16 -20 -24 0 20 40 60 80 100 I ref, REFERENCE SOURCE CURRENT (mA) 120 TA = 125C TA = 25C
Reference Short Circuit Current vs. Temperature
ISC, REFERENCE SHORT CIRCUIT CURRENT (mA) 120
TA = -55C
100
80
60 -55
-25
0
25
50
75
100
125
TA, AMBIENT TEMPERATURE (C)
Output Saturation Voltage vs. Load Current
0
VCC SOURCE SATURATION (LOAD TO GROUND) VCC=15V 80S PULSED LOAD 120Hz RATE TA=25C
Supply Current vs. Supply Voltage CS3865C
32 ICC, SUPPLY CURRENT (mA)
RT=8.2k CT=3.3nF VFB 1.2=0V CURRENT SENSE 1.2=0V TA=25C
Vsat, OUTPUT SATURATION VOLTAGE (V)
-1.0 -2.0
24
TA= -55C
16
2.0 1.0 0 0
TA= -55C TA=25C GND
8.0
SINK SATURATION (LOAD TO VCC)
0 800 0 4.0 8.0 12 16 20 VCC, SUPPLY VOLTAGE (V)
200 400 600 OUTPUT LOAD CURRENT (mA)
Operating Description The CS3865C is a high performance, fixed frequency, dual channel current mode PWM controller specifically designed for off-line and DC to DC converter applications. It offers the designer a cost effective solution with minimal external components where independent regulation of two power converters is required. Each channel contains a high gain error amplifier, current sensing comparator, pulse width modulator latch, and totem pole output driver. The oscillator, reference, and undervoltage lockout circuits are common to both channels. Oscillator The oscillator uses precise frequency and duty cycle control. The frequency is programmed by the values RT and CT. Capacitor, CT, is charged and discharged by an equal magnitude internal current source and sink, generating a symmetrical 50 percent duty cycle waveform at CT. The oscillator peak and valley thresholds are 3.5V and 1.6V respectively. The source/sink current magnitude is controlled by resistor RT. For proper operation over temperature range, its value should be between 4.0k and 16k. As CT charges and discharges, an internal blanking pulse is generated that alternately drives the inputs of the upper and lower NOR gates high. This, in conjunction with a precise amount of delay time introduced into each channel, produces well defined non-overlapping output duty cycles. The second output, VOUT2 is enabled while CT is 5 charging, and the primary is enabled during the discharge. Even at 500kHz, each output is capable of approximately 44% duty cycle, making this controller suitable for high frequency power conversion applications. In many noise sensitive applications, it may be necessary to synchronize the converter with an external system clock. This can be accomplished by applying an external clock signal. For reliable synchronization, the oscillator frequency should be set about 10% slower than the clock frequency. The rising edge of the clock signal applied to SYNC, terminates CT`s charging and VOUT2`s conduction. By tailoring the clock waveform symmetry, accurate duty cycle clamping of either output can be achieved. Error Amplifier Each channel contains a fully-compensated error amplifier. The output and inverting input nodes are accessible. The amplifier features a typical dc voltage gain of 100 dB, and a unity gain bandwidth of 1.0 MHz with 71 degrees of phase margin. The non-inverting input is internally biased at 2.5V. The converter output voltage is typically divided down and monitored by the inverting input through a resistor divider. The maximum input bias current is -1.0A which will cause an output voltage error that is equal to the product of the input bias current and the equivalent input divider resistance.
CS3865C
Operating Description continued The error amp is compensated externally thru the VFB and COMP pins. Its output voltage is offset by two diode drops (1.4V) and divided by three before it connects to the inverting input of the current sense comparator. This guarantees that both outputs are disabled when the error amplifier output is at its lowest state which occurs when the power supply is operating at light or no-load conditions, or at the beginning of a soft-start interval. The minimum allowable error amplifier feedback resistance is limited by the amplifier's source current capability (0.5 mA) and the output voltage (VOH) required to reach the current sense comparator 0.5V clamp level with the error amplifier inverting input at ground. This condition happens during initial system start up or when the sensed output is shorted: 3 x 0.5V + 1.4V = 5800 RF(min) 0.5mA Current Sense Comparator and PWM Latch The CS3865C operates as a current mode controller. Output switch conduction is initiated by the oscillator and terminated when the peak inductor current reaches the threshold level established by the error amplifier output. Thus the error signal controls the peak inductor current on a cycle-by-cycle basis. The current sense comparator-PWM Latch combination ensures that only a single pulse appears at the drive output (VOUT) during any given oscillator cycle. The current is converted to a voltage by connecting a sense resistor RSense in series with the source of output switch Q1 and ground. This voltage is monitored through the Sense1,2 pins and compared to a voltage derived from the error amp output. The peak current under normal operating conditions is controlled by the voltage at COMP where: Ipk = V(COMP) - 1.4V 3RSense Abnormal operating conditions occur when the power supply output is overloaded or if output voltage is too high. Under these conditions, the current sense comparator threshold will be internally clamped to 0.5V. Therefore the maximum peak switch current is: 0.5V Ipk(max) = RSense Erratic operation due to noise pickup can result if there is an excessive reduction of the Ipk (max) clamp voltage. A narrow spike on the leading edge of the current waveform can usually be observed and may cause the power supply to exhibit an instability when the output is lightly loaded. The addition of an RC filter on the current sense input reduces this spike to an acceptable level. Undervoltage Lockout Two undervoltage lockout comparators have been incorporated to guarantee that the IC is fully functional before the output stages are enabled. Power supply terminal (VCC) and the reference output (VREF) are monitored by separate comparator. Each has built-in hysteresis to prevent erratic output behavior as their respective thresholds are crossed. The upper and lower thresholds of the VCC comparator are 14V and 10V respectively. The VREF comparator disables the drive outputs until the internal circuitry is functional. This comparator has upper and lower thresholds of 3.6V and 3.4V. A 17V zener is connected as a shunt regulator from VCC to ground to protect the IC and power MOSFET gate from excessive voltage. The guaranteed minimum operating voltage after turn-on is 11V. Outputs and Power Ground Each channel contains a single totem-pole output stage that is specifically designed for direct drive of power MOSFET's. The outputs have up to 1.0A peak current capability and have a typical rise and fall time of 28 ns with a 1.0nF load. Internal circuitry has been added to keep the outputs in active pull-down mode whenever an undervoltage lockout is active, eliminating the need for an external pull-down resistor. Although the outputs are optimized for MOSFET's, they can easily supply the negative base current required by bipolar NPN transistors for enhanced turn-off. Since the outputs do not contain internal current limits an external series resistor will be required to prevent the peak output current from exceeding the 1.0A maximum rating. The sink saturation (VOL) is less than 0.4V at 100mA. A separate ground pin, Pwr Gnd, is provided. Properly implemented, will significantly reduce the level of switching transient noise imposed on the control circuitry. This becomes important when the Ipk(max) clamp level is reduced. ENABLE2 This input is used to switch VOUT2. VOUT1 is used to control circuitry that runs continuously, e.g. volatile memory, the system clock, or a remote controlled receiver. VOUT2 output can control the high power circuitry that is turned off when not needed. Voltage Reference The 5.0V bandgap reference is trimmed to 2.0% tolerance. The reference has short circuit protection and is capable of sourcing 30mA for powering any additional external circuitry.
6
CS3865C
Operating Description: continued Design Considerations High frequency circuit layout techniques are imperative to prevent pulse-width jitter. This is usually caused by excessive noise pick-up imposed on the current sense and voltage feed-back inputs. Noise immunity can be improved by lowering circuit impedances at these points. The printed circuit board layout should contain a ground plane with low current signal and high current switch and output grounds returning on separate paths back to the input filter capacitor. Ceramic bypass capacitors (0.1F) connected directly to VCC and VREF may be required to improve noise filtering. They provide a low impedance path for filtering the high frequency noise. All high current loops should be kept as short as possible using heavy copper runs. The error amp compensation circuitry and the converter output voltage-divider should be located close to the IC and as far as possible from the power switch and other noise generating components.
Timing Diagram
SYNC CT Latch 1 "Set" Input COMP1 Sense1 Latch 1 "Reset" Input VOUT1
ENABLE2 0V Latch 2 "Set" Input COMP2 Sense2 Latch 2 "Reset" Input VOUT2
Applications Diagram
Dual Boost Regulator
VCC CF1 + 5.0V CF2 VREF 2.5V R Sync VOUT1 RFB1 RFB2 VFB1 COMP1 ENABLE2 VOUT2 RFB3 RFB4 VFB2 COMP2 + Error Amp 2 RT + Oscillator Q1 PWM Latch 1 S Q R VOUT1 RSense1 Sense1 Q2 Current Sense Comparator 1 2R + 1.0mA R 0.5V PWM Latch 2 S RQ R VOUT2 L2 D2 + VOUT2 COUT2 R Internal Bias + 3.4V 20k + Reference Regulator
+ -
VIN
VCC + UVLO -
+ -
17V 14V L1 D1 VOUT1 COUT1
VREF UVLO
CT
Current Sense 2R Comparator 1 + + Error 1.0mA R + 0.5V Amp 1 250A +
Sense2
RSense2
Gnd
Pwr Gnd
7
CS3865C
Package Specification
PACKAGE DIMENSIONS IN mm (INCHES) PACKAGE THERMAL DATA
D Lead Count 16L PDIP 16L SO Metric Max Min 19.69 18.67 10.50 10.10 English Max Min .775 .735 .413 .398
Thermal Data RJC RJA typ typ
16 Lead PDIP 42 80
16 Lead SO 23 105
C/W C/W
Surface Mount Wide Body (DW); 300 mil wide
7.60 (.299) 7.40 (.291)
10.65 (.419) 10.00 (.394)
0.51 (.020) 0.33 (.013)
1.27 (.050) BSC
2.49 (.098) 2.24 (.088)
2.65 (.104) 2.35 (.093)
1.27 (.050) 0.40 (.016)
REF: JEDEC MS-013
0.32 (.013) 0.23 (.009) D 0.30 (.012) 0.10 (.004)
Plastic DIP (N); 300 mil wide
7.11 (.280) 6.10 (.240)
8.26 (.325) 7.62 (.300) 3.68 (.145) 2.92 (.115)
1.77 (.070) 1.14 (.045)
2.54 (.100) BSC
.356 (.014) .203 (.008)
0.39 (.015) MIN. .558 (.022) .356 (.014) Some 8 and 16 lead packages may have 1/2 lead at the end of the package. All specs are the same.
REF: JEDEC MS-001
D
Ordering Information
Part Number CS3865CGN16 CS3865CGDW16 CS3865CGDWR16
Rev. 12/16/96
Description 16L PDIP 16L SO Wide 16L SO Wide (tape & reel) 8
Cherry Semiconductor Corporation reserves the right to make changes to the specifications without notice. Please contact Cherry Semiconductor Corporation for the latest available information.
(c) 1999 Cherry Semiconductor Corporation

▲Up To Search▲

Price & Availability of CS3865C

	To Download CS3865C Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .