HA16114P/PJ/FP/FPJ, HA16120FP/FPJ
Guide to the Functional Description
The description covers the topics indicated below.
Oscillator
1. frequency
(f
OSC
) control and
synchronization
GND*
1
1
2
3
4
5
6
7
8
(Top view)
16
15
14
13
12
11
10
9
Vref
ADJ
DB
ON/
OFF
TM
CL(−)
V
IN
OUT
SYNC
R
T
C
T
IN(−)
Vref adjustment,
undervoltage
5. lockout, and
overcurrent
protection
6. ON/
OFF
pin
usage
DC/DC output
2. voltage setting
and error
amplifier usage
3.
Dead-band and
soft-start settings
E/O
IN(+)
Intermittent
7. mode timing
during
overcurrent
Output stage and
4. power MOS FET
driving method
P.GND*
1
8.
Setting of
current limit
Note: 1. P.GND is a high-current (±1 A maximum peak) ground pin connected to the totem-pole output circuit.
GND is a low-current ground pin connected to the Vref voltage reference. Both pins must be grounded.
1. Sawtooth Oscillator (Triangle Wave)
1.1 Operation and Frequency Control
The sawtooth wave is a voltage waveform from which the PWM pulses are created (See figure 1). The
sawtooth oscillator operates as follows. A constant current I
O
determined by an external timing resistor R
T
is fed continuously to an external timing capacitor C
T
. When the C
T
pin voltage exceeds a comparator
threshold voltage V
TH
, the comparator output opens a switching transistor, allowing a 3I
O
discharge current
to flow from C
T
. When the C
T
pin voltage drops below a threshold voltage V
TL
, the comparator output
closes the switching transistor, stopping the 3I
O
discharge. Repetition of these operations generates a
sawtooth wave.
The value of I
O
is 1.1 V/R
T
Ω.
The I
O
current mirror has a limited current capacity, so R
T
should be at least
5 kΩ (I
O
≤
220
µA).
Internal resistances R
A
, R
B
, and R
C
set the peak and valley voltages V
TH
and V
TL
of the sawtooth waveform at
approximately 1.6 V and 1.0 V.
Rev.2.0, Sep.18.2003, page 6 of 37
RENESAS [ RENESAS TECHNOLOGY CORP ]
