Datasheet UCC1810, UCC2810, UCC3810 Datasheet (UNITRODE)

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Dual Channel Synchronized Current Mode PWM

UCC1810 UCC2810 UCC3810

FEATURES

• Single Oscillator Synchronizes Two PWMs

• 150

• 2mA Operating Supply Current

• Operation to 1MHz

• Internal Soft Start

• Full-Cycle Fault Restart

• Internal Leading Edge Blanking of the

• 1 Amp Totem Pole Outputs

• 75ns Typical Response from Current

• 1.5% Tolerance Voltage Reference

A Startup Supply Current

Current Sense Signal

Sense to Output

BLOCK DIAGRAM

DESCRIPTION

The UCC3810 is a high-speed BiCMOS integrated circuit which implements two synchronized pulse width modulators for use in off-line and DC-to-DC power supplies.

The UCC3810 provides perfect synchronization between two PWMs by using the same oscillator. The oscillator’s sawtooth waveform can be used for slope compensation if required.

Using a toggle flip flop to alternate between modulators, the UCC3810 ensures that one PWM will not slave, interfere, or otherwise affect the other PWM. This toggle flip flop also ensures that each PWM will be limited to 50% maximum duty cycle, insuring adequate off-time to reset magnetic elements.

This IC contains many of the same elements of the UC3842 current mode controller family, combined with the enhancements of the UCC3802. This minimizes power supply parts count. Enhancements include leading edge blanking of the current sense signals, full cycle fault restart, CMOS output drivers, and outputs which remain low even when the supply voltage is removed.

02/99

UDG-92062-1

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ABSOLUTE MAXIMUM RATINGS

VCCVoltage (Note 3). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11V

VCCCurrent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20mA

OUT1, OUT2 Current, Peak, 5% Duty Cycle. . . . . . . . . . . .±1A

OUT1, OUT2 Energy (Capacitive Load) . . . . . . . . . . . . . . 20µJ

Analog Inputs (FB1, FB2, CS1, CS2, SYNC). . . . –0.3V to 6.3V

Operating Junction Temperature. . . . . . . . . . . . . . . . . . +150°C

Storage Temperature Range . . . . . . . . . . . . . –65°C to +150°C

Lead Temperature (Soldering, 10 seconds) . . . . . . . . . . 300°C

UCC1810 UCC2810 UCC3810

CONNECTION DIAGRAM

DIL-16, SOIC-16 (TOP VIEW) J or N Package, DW Package

Note 1: All voltages are with respect to GND. All currents are

positive into the specified terminals.

Note 2: Consult Unitrode Integrated Circuits Product & Appli-

cations Handbook for information regarding thermal specifications and limitations of packages.

Note 3: In normal operation, V

is powered through a current

limiting resistor. Absolute maximum of 11V applies when driven from a low impedance such that the V

current does not exceed 20mA.

ELECTRICAL CHARACTERISTICS:

UCC1810; –40°C≤T

85°C for UCC2810; 0°C≤T

≤

Unless otherwise stated, these specifications apply for –55°C≤T

70°C for UCC3810; V

≤

= 10V (Note 4); RT= 150k; CT= 120pF;

125°C for

≤

No Load; TA= TJ. All parameters are the same for both channels.

PARAMETER TEST CONDITIONS MIN TYP MAX UNITS

Reference Section

Output Voltage T Load Regulation 0mA < I Line Regulation UVLO Stop Threshold Voltage +0.5V < VCC< Shunt

= 25°C 4.925 5.000 5.075 V

< 5mA 5 25 mV

REF

12 mV

Voltage

Output Voltage Full temperature range, 0mA < I

< 5mA 4.85 5.00 5.10 V

REF

Output Noise Voltage 10Hz < f < 10kHz, TJ= +25°C (Note 10) 235 µV Long Term Stability TA= +125°C, 1000 Hours (Note 10) 5 mV Output Short Circuit Current –8 –25 mA

Oscillator Section

Oscillator Frequency R

= 30k, CT= 120pF (Note 5) 840 940 1040 kHz

Oscillator Frequency RT= 150k, CT= 120pF (Note 5) 200 220 240 kHz Temperature Stability (Note 10) 2.5 % Peak Voltage 2.5 V Valley Voltage 0.05 V Peak-to-Peak Amplitude 2.25 2.45 2.65 V SYNC Threshold 0.80 1.65 2.2 V SYNC Input Current SYNC = 5V 30 µA

Error Amplifier Section

FB Input Voltage COMP = 2.5V 2.44 2.50 2.56 V FB Input Bias Current ±1 µA Open Loop Voltage Gain 60 73 dB Unity Gain Bandwidth (Note 10) 2 MHz COMP Sink Current FB = 2.7V, COMP = 1V 0.3 1.4 3.5 mA COMP Source Current FB = 1.8V, COMP = 4V –0.2 –0.5 –0.8 mA Minimum Duty Cycle COMP = 0V 0 % COMP Soft Start Rise Time FB = 1.8V, Rise from 0.5V to REF–1.5V 5 ms

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UCC1810 UCC2810 UCC3810

ELECTRICAL CHARACTERISTICS:

UCC1810; –40°C≤T

85°C for UCC2810; 0°C≤T

≤

Unless otherwise stated, these specifications apply for –55°C≤T

70°C for UCC3810; VCC= 10V (Note 4); RT= 150k; CT= 120pF;

≤

125°C for

≤

No Load; TA= TJ. All parameters are the same for both channels.

PARAMETER TEST CONDITIONS MIN TYP MAX UNITS

Current Sense Section

Gain (Note 6) 1.20 1.55 1.80 V/V Maximum Input Signal COMP = 5V (Note 7) 0.9 1.0 1.1 V CS Input Bias Current

200 nA CS to OUT Propagation Delay CS steps from 0V to 1.2V, COMP = 2.5V 75 ns CS Blank Time (Note 8) 55 ns CS Overcurrent Threshold 1.35 1.55 1.85 V COMP to CS Offset CS = 0V 0.65 0.95 1.4 V

PWM Section

Maximum Duty Cycle R

T = 150k, CT = 120pF (Note 10) 45 49 50 %

Maximum Duty Cycle RT = 30k, CT = 120pF (Note 10) 40 45 48 % Minimum On Time CS =1.2V, COMP = 5V 130 ns

Output Section

OUT Low Level I

OUT = 20mA 0.12 0.42 V

IOUT = 200mA 0.48 1.10 V IOUT = 20mA, VCC = 0V 0.7 1.20 V

OUT High Level (VCC - OUT)

OUT Rise Time C

IOUT = –20mA 0.15 0.42 V IOUT = –200mA 1.20 2.30 V

OUT = 1nF 20 50 ns

OUT Fall Time COUT = 1nF 30 60 ns

Undervoltage Lockout Section

Start Threshold 9.9 11.3 13.2 V Stop Threshold 7.5 8.3 9.5 V Start to Stop Hysteresis 1.7 3.0 4.7 V ENABLE2 Input Bias Current ENABLE2 = 0V –20 –35 –55 µA ENABLE2 Input Threshold

0.80 1.53 2.00 V

Voltage

Overall Section

Startup Current V Operating Supply Current,

CC < Start Threshold Voltage 0.15 0.25 mA

VCC = 10V, FB = 2.75V 2.0 3.0 mA

Outputs Off Operating Supply Current,

CC = 10V, FB = 0V, CS = 0V, RT = 150k 3.2 5.1 mA

Outputs On Operating Supply Current,

CC = 10V, FB = 0V, CS = 0V, RT = 30k 8.5 14.5 mA

Outputs On

CC Internal Zener Voltage ICC = 10mA (Note 9) 11.0 12.9 14.0 V

V VCC Internal Zener Voltage Minus

0.4 1.2 V

Start Threshold Voltage

Note 4: Adjust VCCabove the start threshold before setting at 10V. Note 5: Oscillator frequency is twice the output frequency.

VCOMP

Note 6: Current Sense Gain A is defined by:

∆

=≤≤

VCS

∆

OSC

008.

≈

RT CT

VCS V

Note 7: Parameter measured at trip point of latch with FB = 0V. Note 8: CS Blank Time is measured as the difference between the minimum non-zero on-time and the CS to OUT delay. Note 9: Start Threshold Voltage and V

Internal Zener Voltage track each other.

Note 10: Guaranteed by design. Not 100% tested in production.

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PIN DESCRIPTIONS

COMP1, COMP2: The low impedance outputs of the er-

ror amplifiers. CS1, CS2: The current sense inputs to the PWM com-

parators. These inputs have leading edge blanking. For most applications, no input filtering is required. Leading edge blanking disconnects the CS inputs from all internal circuits for the first 55ns of each PWM cycle. When used with very slow diodes or in other applications where the current sense signal is unusually noisy, a small current sense RC filter may be required.

CT: The timing capacitor of the oscillator. Recommended values of C nect the timing capacitor directly across C

ENABLE2: A logic input which disables PWM 2 when low. This input has no effect on PWM 1. This input is internally pulled high. In most applications it can be left floating. In unusually noisy applications, the input should be bypassed with a 1nF ceramic capacitor. This input has TTL compatible thresholds.

FB1, FB2: The high impedance inverting inputs of the error amplifiers.

GND: To separate noise from the critical control circuits, this part has two different ground connections: GND and PWRGND. GND and PWRGND must be electrically connected together. However, use care to avoid coupling noise into GND.

OUT1, OUT2: The high current push-pull outputs of the PWM are intended to drive power MOSFET gates through a small resistor. This resistor acts as both a current limiting resistor and as a damping impedance to minimize ringing and overshoot.

are between 100pF and 1nF. Con-

and GND.

UCC1810 UCC2810 UCC3810

PWRGND: To separate noise from the critical control

circuits, this part has two different ground connections: GND and PWRGND. GND and PWRGND must be electrically connected together.

REF: The output of the 5V reference. Bypass REF to GND with a ceramic capacitor≥0.01µF for best performance.

RT: The oscillator charging current is set by the value of the resistor connected from R lated to 1V, but the actual charging current is 10V/R Recommended values of RT are between 10k and 470k. For a given frequency, higher timing resistors give higher maximum duty cycle and slightly lower overall power consumption. Supply current decreases with increased R

T by the relationship:

ICC

∆

For more information, see the detailed oscillator block diagram.

SYNC: This logic input can be used to synchronize the oscillator to a free running oscillator in another part. This pin is edge triggered with TTL thresholds, and requires at least a 10ns wide pulse. If unused, this pin can be grounded, open circuited, or connected to REF.

VCC: The power input to the IC. This pin supplies current to all functions including the high current output stages and the precision reference. Therefore, it is critical that V

be directly bypassed to PWRGND with an

0.1µF ceramic capacitor.

T to GND. This pin is regu-

APPLICATION INFORMATION

Leading Edge Blanking and Current Sense

Figure 1. shows how an external power stage is connected to the UCC3810. The gate of an external power N-channel MOSFET is connected to OUT through a small current limiting resistor. For most applications, a 10Ω resistor is adequate to limit peak current and also practical at damping resonances between the gate driver and the MOSFET input reactance. Long gate lead length increases gate capacitance and mandates a higher series gate resistor to damp the RLC tank formed by the lead, the MOSFET input reactance, and the UCC3810 driver output resistance.

The UCC3810 features internal leading edge blanking of the current sense signal on both current sense inputs. The blank time starts when OUT rises and continues for 55ns. During that 55ns period, the signal on CS is ignored. For most PWM applications, this means that the CS input can be connected to the current sense resistor as shown above. However, high speed grounding practices and short lead lengths are still required for good performance.

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APPLICATION INFORMATION (cont.)

Figure 1. Detailed block diagram.

UCC1810 UCC2810 UCC3810

Oscillator

The UCC3810 oscillator generates a sawtooth wave at CT. The sawtooth rise time is set by the resistor from RT to GND. Since RT is biased at 1V, the current in RT is 1V/RT. The actual charging current is 10 times higher. The fall time is set by an internal transistor on-resistance of approximately 100Ω. During the fall time, all outputs are off and the maximum duty cycle is reduced below 50%. Larger timing capacitors increase the discharge time and reduce frequency. However, the percentage

maximum duty cycle is only a function of the timing resistor RT and the internal 100Ωdischarge resistance.

Error Amp Output Stage

The UCC3810 error amplifiers are operational amplifiers with low output resistance and high input resistance. The output stage of one error amplifier is shown above. This output stage allows the error amplifier output to swing close to GND and as high as one diode drop below 5V with little loss in amplifier performance.

Figure 2. Oscillator. Figure 3. Error amp output stage.

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TYPICAL CHARACTERISTICS

UCC1810 UCC2810 UCC3810

Figure 4. Error amp and gain phase response.

Figure 5. Oscillator frequency vs. temperature.

Figure 7. Oscillator frequency vs. RTand C

Figure 8. Maximum duty cycle vs R

Figure 6. ICCvs. oscillator frequency.

Figure 9. Maximum duty cycle vs. frequency.

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APPLICATION INFORMATION (cont.)

UCC1810 UCC2810 UCC3810

Figure 10. Typical application.

UDG-94022

UNITRODE CORPORATION 7 CONTINENTALBLVD. • MERRIMACK, NH 03054 TEL. (603) 424-2410 FAX (603) 424-3460

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